Read a chapter pdf 2.31 MB

Transcription

1
Mechanical Properties of Polymers
1.1 Introduction
In the past, results of standard tests such as tensile strength, Izod impact strength and
softening point have been given major emphasis in the technical literature on plastics.
More recently, however, with the increasing use of plastics in more critical applications,
there has been a growing awareness of the need to supplement such information with
data obtained from tests more closely simulating operational conditions.
For many applications, the choice of material used depends upon a balance of stiffness,
toughness, processability and price. For a particular application, a compromise
between these features will usually be necessary. For example, it is generally true
that, within a given family of grades of a particular polymer, the rigidity increases as
impact strength decreases. Again, processing requirements may place an upper or a
lower limit on the molecular weight (MW) of the polymer that can be used, and this
will frequently influence the mechanical properties quite markedly. Single test values
of a given property are a less reliable guide to operational behaviour with plastics
than with metals. This is because for plastics the great mass of empirical experience
and tradition of effective design which has been built up over centuries in the field of
metals is not yet available. Furthermore, no single value can be placed on the stiffness
or the toughness of a plastic because:
• Stiffness will vary with time, stress and temperature.
• Toughness is influenced by the design and size of the component, the design of
the mould, processing conditions and the temperature of use.
• Stiffness and toughness can be affected by environmental effects such as thermal
and oxidative ageing, ultraviolet (UV) ageing and chemical attack (including the
special case of environmental stress corrosion).
In addition, a change in a specific polymer parameter may affect processability and
basic physical properties. Both of these factors can interact in governing the behaviour
of a fabricated article. Comprehensive experimental data are therefore necessary to
understand effectively the behaviour of plastic materials, and to give a realistic and
reliable guide to the selection of material and grade.
1
Physical Testing of Plastics
In many applications, plastics are replacing traditional materials. Hence, there is
often a natural tendency to apply to plastics tests similar to those that have been
found suitable for gauging the performance of the traditional material. Dangers
can obviously arise if plastics are selected on the basis of these tests without clearly
recognising that the correlation between values of laboratory performance and field
performance may be quite different for the two classes of materials.
It is therefore important to realise that standard tests are not devised to give direct
prediction of end-use performance. In general, the reverse is the case. That is, if a
particular grade of a particular polymer is found to perform satisfactorily in a given
end use, it can then be characterised with reasonable accuracy by standard tests, and
the latter tests then used to ensure the maintenance of the required end-use quality.
Availability of instrumentation for mechanical testing is discussed in Appendix 1.
Typical mechanical properties of a range of polymers are listed in Table 1.1.
Table 1.1 Mechanical properties of polymers
Polymer
Low-density
polyethylene (LDPE)
High-density
polyethylene (HDPE)
Crosslinked
polyethylene (PE)
Polypropylene (PP)
Ethylene-propylene
Polymethyl pentene
Styrene-butadiene
Styrene-ethylenebutylene-styrene
High-impact
polystyrene (PS)
PS, general purpose
2
Flexural
Notched
Tensile
modulus/ Elongation Strain
Izod impact Surface
strength (modulus of at break at yield
strength
hardness
(MPa)
elasticity)
(%)
(%)
(kJ/m)
(GPa)
Carbon/hydrogen-containing polymers
10
0.25
400
19
1.064
SD 48
32
1.25
150
15
0.15
SD 68
18
0.5
350
N/Y
1.064
SD 58
26
26
28
28
2
0.6
1.5
1.6
80
500
15
50
N/Y
N/Y
6
N/Y
0.05
0.15
0.04
0.08
RR 85
RR75
RR 70
SD 75
6
0.02
800
N/Y
1.064
SA 45
42
2.1
2.5
1.8
0.1
RM 30
34
3
1.6
RM 80
Oxygen-containing polymers
Epoxies, general
purpose
Acetal
(polyoxymethylene)
Polyesters (bisphenol),
polyester laminate
(glass filled)
Polyester (electrical
grade)
Polybutylene phthalate
Polyethylene
terephthalate (PET)
Polyether ether ketone
(PEEK)
Diallyliosphthalate
Diallyl phthalate
Alkyd resin glass fibre,
reinforced
Polyarylates
Polycarbonate (PC)
Polyphenylene oxide
Phenol-formaldehyde
Styrene-maleic
anhydride
Cellulose acetate
Cellulose propionate
Cellulose acetate
butyrate acrylics
Ethylene vinyl acetate
Polyamide (PA) 6
PA 4,6
PA 11
PA 6,9
PA 12
PA 6,6
PA 6, 12
Nylon/acrylonitrilebutadiene-styrene (ABS)
alloy
PA-imide
Polyimide
Polyetherimide
600
80
1.3
N/A
0.5
RM 113
50
27
20
8
0.10
RM 109
280
16
1,5
N/A
1.064
RM 125
40
9
2
N/A
0.4
RM 125
52
2.1
250
4
0.06
RM 70
55
2.3
300
3.5
0,02
RM 30
92
3.7
50
4.3
0,083
RM 99
82
70
11.3
10.6
0.9
0.9
N/A
N/A
0.37
0.41
RM 112
RM 112
72
8.6
0.8
N/A
0.24
RM 125
68
50
65
45
2.2
2.1
2.5
6.5
50
200
60
1.2
8.8
3.5
4.5
N/A
0.29
0.05
0.16
0.024
RR 125
RM 70
RR 119
RM 114
52
3
1.8
2
0.03
RL 105
30
35
1.7
1.76
60
60
4
4
0.26
0.13
RR 71
RR 94
70
2.9
2.5
N/A
0.02
RM 92
0.02
750
N/A
Nitrogen-containing polymers
1
60
4.5
1
30
11
0.9
320
20
1.4
15
10
1.4
200
6
1.2
60
4.5
1.4
300
7
1.064
SA 85
0.25
0.1
0.05
0.06
0.06
0.11
0.04
SD 75
SD 85
RR 105
SD 78
RR 105
RR 90
RR 105
17
40
100
52
50
50
59
51
47
2.14
270
6
0.85
RR 99
185
72
105
4.58
2.45
3.3
12
8
60
8
4
8
0.13
0.08
0.1
RM 109
RM 100
RM 109
3
Polyurethane (PU)
thermoplastic elastomer
Ether ester amide
elastomer
Urea formaldehyde
Styrene acrylonitrile
ABS
Acrylate-styreneacrylonitrile
Polytetrafluroethylene
Poyvinylfluoride
Polyvinylidene fluoride
Perfluoroalkoxyethylene
Ethylene tetrafluoro
ethylene
Ethylene chlorotrifluoro
ethylene
Fluorinated ethylene
propylene
24
0.003
700
N/Y
1.064
SA 70
57
10
0.6
N/A
0.02
RM 115
72
34
3.6
2.1
2.4
6
3.5
2
0.02
0.18
RM 80
RR 96
35
2,.5
10
3.3
0.1
RR 106
0.16
0.18
0.12
1.064
RM 69
SD 80
SD 90
SD 60
Fluorine-containing polymers
0.70
400
70
1.4
150
30
5.5
6
N/A
0.7
300
85
25
40
100
29
28
1.4
150
15
1.064
RR 50
30
1.7
200
5
1.064
RR 93
14
0.6
150
6
1.064
RR 45
Chlorine-containing polymers
Chlorinated poly(vinyl
chloride) PVC
Unplasticised PVC
(UPVC)
Plasticised PVC
58
3.1
30
5
0.06
SA 70
51
3
60
3.5
0.08
RR 110
0.007-0.03
280-95
N/Y
1.05+
SA 85
Sulfur-containing polymers
Polyphenylene sulfide
91
13.8
0.6
N/A
0.6
RR121
Polysulfone
70
2.65
80
5.5
0.07
RM69
Polyethersulfone
84
2.6
60
6.6
0.084
RM 85
Silicon-containing polymers
Silicones
28
3.5
2
N/A
0.02
RM 80
*These are typical room-temperature values of Notched Izod impact strength. A material that
does not break in the Izod test is given a value of 1.06 + kJ/m; the + indicates that it has a
higher impact energy than the test can generate.
N/A = if material is brittle and does not exhibit yield point
N/Y = if material is ductile and does not exhibit yield point
RM = Rockwell M 123 hardness (hard)
RR = Rockwell R 112 hardness
SA 65 = Shore A 65 hardness (soft)
SD 75 = Shore D75 hardness
Source: Author’s own files
4
14-20
Each of those measurements will now be discussed in further detail.
1.2 Tensile Strength
This is the room temperature tensile strength at yield for ductile materials and at
break for brittle materials. An excellent rating indicates high tensile strength, and
a very poor rating indicates low tensile strength. The values given in Table 1.1 are
typical room-temperature values taken at break for brittle materials and at yield for
ductile materials.
1.2.1 Electronic Dynamometer Testing of Tensile Properties
ATS FAAR supplies the Series TC200 computer-governed dynamometer, which can
carry out tensile, compression, and flexural tests on a variety of material. All details
of the tests are managed, including computing the final results and presenting them in
alphanumerical or graphical form. Moreover, the use of a personal computer (PC) for
the management of dynamometers gives the extra advantage of storing (at will) the
results of the tests in an electronic data file which can be utilised to obtain organised
print-outs, historical series, and go-no-go checks. Full automation of all operations
(including computations) increases the precision, reproducibility, and speed of analysis
due to the elimination of otherwise unavoidable human errors.
Tests that can be carried out by this dynamometer include those listed below and
those shown in Table 1.2:
• Tensile strength (tensile modulus) tests with or without preloading, according to
specifications of ASTM D638-03 [1], DIN EN ISO, 527-1 [2] and DIN EN ISO
527-2 [3].
• Compression and compressive strength tests according to specifications ASTM
D695-02a [4] and DIN EN ISO 179-1 [5].
• Flexural and flexural strength tests according to specifications ASTM D790-03
[6], ASTM D732 [7] and DIN EN ISO 178 [8].
5
Table 1.2 Mechanical properties of polymers using the Dyanometer test
Method
ATS FAAR
Measurement Test suitable for meeting the
Apparatus
units
following standards
code number
Tensile impact
16.10050
kJ/m2
DIN EN ISO 8256 [9]
strength
Tensile strength
16.00121
N/mm2
ASTM D638-03 [1]
(tensile modulus)
16.00122
Psi
DIN EN ISO 527-1 [2]
2
16.00126
kg/cm
16.00127
Compression
16.00121
N/mm2
ASTM D695-02a [4]
strength and
16.00122
Psi
DIN EN ISO 604 [23]
compressive stress
16.00126
N/mm2
16.00127
Flexural strength
16.00121
N/mm2
ASTM D790-03 [6]
(Dyanometer)
16.00122
Psi
ASTM D732 [7]
16.00126
kg/cm2
DIN EN ISO 178 [8]
16.00127
ASTM = American Society for Testing and Materials
DIN EN ISO = Deutsches Institut für Normung Europa Norm International
Standards Organization
The TC 100 instrument can also undertake cycles between preset limits, creep and
relaxation studies, peeling experiments, and measurement of friction co-efficient and
puncture resistance of films.
Typical tensile strength data are quoted in Table 1.1.
Polymers of excellent tensile strength (i.e., >100 MPa) include: epoxies, polyester
laminates, polyamide (PA) 4/6, PA-imide, polyetherimide, polyvinylidene fluoride.
Polymers with very good impact strength (i.e., 60-100 MPa) include: acetals,
polybutylene terephthalete, polyethylene terephthalate (PET), polyallylphthalate,
polyetherketone, polycarbonate (PC), polyphenylene, styrene-maleic acid, copolymer,
acrylics, PA 11, PA 6/9, PA 12, polyimide 6/6 PA 6/12, polyimide: urea-formaldehyde,
styrene-acrylonitrile copolymer, chlorinated polyvinyl chloride (PVC), polyphenylene
sulfide, polysulfone, silicones, and alkyd resins.
6
600
280
70
100
100
Polyesters
(bisphenol polyester
laminate) glass filled
Polyester, sheet
moulding
compound
PA 4,6
Polyvinylidene
fluoride (20%
carbon fibrereinforced)
5.5
1
11
16
80
6
30
2.5
1.5
13
Tensile Flexural Elongation
strength modulus at break
(MPa)
(GPa)
(%)
Epoxies, general
purpose
Polymer
N/A
11
N/A
N/A
Not
applicable
(N/A)
Strain
at yield
(%)
0.12
0.1
0.8
1.06 +
0.5
Notched
Izod
(kJ/m)
Tensile strength, flexural
modulus, HDT, detergent
resistance, hydrolytic
stability
Reasonable HDT, good
chemical resistance
High flexural modulus,
heat distortion temperature
(HDT), resistance to UV
and gamma irradiation,
toughness
Impact strength and cheap
when compared with
epoxies
modulus, detergent
resistance, resistance to
gamma radiation, heat
distortion temperature
(HDT), wear properties, low
resin shrinkage during cure
Excellent or good
performance in the
following
Elongation at break,
expensive, gamma
irradiation resistance,
dielectric properties,
surface finish, toughness
Moisture absorption
More expensive than
polyesters. Dielectric
constant, dielectric
strength, flame spread,
hydrolytic stability,
elongation stability,
HDT
Heat resistance, solvent
resistance, elongational
at break
Poor surface finish,
high cost, elongation
at break and volume
resistivity
Poor performance in
the following
Table 1.3 Identification of polymers with outstanding tensile strength and flexural modulus
7
8
68
Polyacrylates
70
Polysulfone
2.2
2.65
10.6
70
Diallyl phthalate
13.8
11.3
91
Polyphenylene
sulfide (glass fibrereinforced)
3.3
Diallyl iso-phthalate 82
(long glass fibrereinforced)
105
Polyetherimide
50
80
0.9
0.9
0.6
60
15
5.5
N/A
N/A
8
1.06 +
0.07
0.41
0.37
0.031
0.10
Impact strength, heat
resistance and UV resistance
High temperature
performance, electrical
properties, hydrolytic
resistance, tensile strength,
dimensional stability
modulus, notched Izod,
detergent resistance, HDT,
tracking resistance, UV
radiation
modulus, notched Izod,
detergent resistance, HDT,
tracking resistance, UV
radiation
Flexural strength, flexural
modulus
Tensile strength, cost,
oxygen index, detergent
resistance, gamma
irradiation and UV
resistance
Stress cracking with
hydrocarbons, needs
350 °C processing
temperature.
Surface finish
Volume resistance,
dielectric strength,
dissipation factor,
flammability, hydrolytic
stability, high cost,
elongation at break
Volume resistance,
dielectric strength,
dissipation factor,
flammability, hydrolytic
stability, high cost,
elongation at break
Electrical properties,
notched Izod
Stress cracking with
chlorinated solvents,
notched impact
strength, high cost,
tracking, resistance,
flexural modulus,
toughness
In Table 1.3 are listed those polymers of high impact tensile strength and also those
which have a high flexural modulus. This shows that a high tensile strength is no
guarantee of a high flexural modulus.
In selecting a polymer for a particular end-use application, it is frequently necessary
to compromise on polymer properties. Thus, while epoxy resins have excellent tensile
strength and flexible modulus as well as detergent resistance, they have low resistance
to gamma radiation, poor heat distortion performance, and a poor wear properties.
They are also expensive and have a poor volume sensitivity and surface finish.
Son and co-workers [11] showed that the addition of a thermothropic liquid crystalline
aromatic polyester produces an improvement in the tensile strength and modulus of
blends with polyether ketone while simultaneously producing a significant decrease
in elongation at break.
Tasdemir and Yildirim [12] showed that rigid plastics such as polystyrene (PS), PVC,
polymethyl methacrylate, polypropylene (PP), Nylons and PC, epoxies, unsaturated
polyester resins, and PA can be toughened and their impact properties improved by
incorporation in the formulation of 5-20% of a rubbery elasomer such as acrylonitrilebutadiene-styrene (ABS) terpolymer.
1.3 Flexural Modulus (Modulus of Elasticity)
This is the short-term modulus of materials at specified temperatures. Ratings for
flexural modulus have been assigned at 20 ºC and are usually determined at ~1%
strain. An ‘excellent’ rating indicates a high flexural modulus; a ‘very poor’ rating
indicates a low flexural modulus. A ‘not applicable’ status indicate that the material
has a modulus of limited practical use.
1.3.1 Torsion Test
AST FARR supplies a torsion test instrument for the measurement of the apparent
modulus of elasticity versus temperature of plastics and elastomers (Table 1.4 and
Appendix) following specifications ASTM D1043 [14], DIN 53477 [15], ISO 498
[22] and BS 2782 [13].
9
Method
Modulus
elasticity
versus
temperature
(torsion test)
Modulus
of elasticity
or flexural
modulus
(bend test)
Table 1.4 Modulus of elasticity of polymers
ATS FAAR
Measurement
Test suitable for meeting the
Apparatus
units
following standards
code
number
10.22000
GPa
ASTM D1043 [14]
DIN 53477 [15]
10.22001
ISO 458 [16]
BS 2782 [13]
10.29000
kN/mm2
psi
kg/cm2
ASTM D1896 [17]
ASTM D3419 [18]
ASTM D3641 [19]
ASTM D4703 [20]
ASTM D5227 [21]
DIN EN ISO 178 [8]
DIN EN ISO 604 [26]
This apparatus consists of an assembly of interdependent units. It is compact and
very easy to operate. It features an accurate torque applications system with a broad
angular measurement range.
The temperature is electronically controlled and the fully automatic system of presetting heating periods and torque is electronic. The apparatus is equipped with a
set of weights allowing a wide range of torques to be applied to specimens having
difference dimensions. The distance between the clamps can be varied in the range
20-100 mm.
It is thus possible to measure accurately the apparent modulus of elasticity of specimens
obtained from a wide range of materials. The modulus is, in this case, defined as
‘apparent’ because it is obtained by measuring the angular torsion of the specimens
under test.
In its regular version, the apparatus can conduct tests in the temperature range -100
ºC to +100 ºC. A special version, however, allows one to run tests between 100 ºC
and +300 ºC. The torque application system is assembled on ball bearings of very
10
reduced dimensions and utilises the same ‘pivot’ contrivance used in watch making.
As a consequence, all radial frictions are reduced to zero and the main pulley can be
rotated even if applying torques <0.0005 N/m. The initial zero point can be adjusted
so as to allow tests to be undertaken even on specimens having planar deformation
between +5º and -5º. Cooling is obtained by solid carbon dioxide or by liquid nitrogen
so as to achieve maximum operational flexibility.
1.3.2 Hand Test
ATS FAAR also supply hand test apparatus for the measurement of the modulus of
elasticity (flexural modulus) according to specifications ASTM D1869 [17], ASTM
D3419 [18], ASTM D3641 [19], ASTM D4703 [20], D ASTM 5227 [21], DIN EN
ISO 178, [8] DIN EN ISO 527-1 [2], DIN EN ISO 527-2 [3] and DIN ISO 604 [23]
(see Table 1.4).
Table 1.4 Modulus of elasticity of polymers
Method
ATS FAAR
Measurement
Test suitable for meeting
Apparatus code
units
the following standards
number
Modulus
10.22000
GPa
ASTM D1043 [14]
elasticity versus
10.22001
DIN 53477 [15]
temperature
ISO 458 [16]
(torsion test)
BS 2782 [13]
Modulus
10.29000
kN/mm2
ASTM D1896 [17]
of elasticity
psi
ASTM D3419 [18]
or flexural
kg/cm2
ASTM D3641 [19]
modulus (bend
ASTM D4703 [20]
test)
ASTM D5227 [21]
DIN EN ISO 178 [8]
DIN EN ISO 604 [26]
Janick and Krolikowski [24] investigated the effect of charpy notched impact strength
on the flexural modulus of PE and PET. Polymers with good flexible modulus (between
11
6 GPa and 80 GPa) include polydiallyephthalate (11.3 GPa), phenol-formaldehyde
(6.5 GPa), alkyd resins (8.6 GPa) and polyphenylene sulfide (13.8 GPa) as well as
glass-filled polyesterlaminate (16 GPa) epoxy resins (80 GPa), silica-filled epoxies
(15 GPa) and acetals containing 30% carbon fibre (17.2 GPa).
1.4 Elongation at Break
Elongation at break is the strain at which a polymer breaks when tested in tension at
a controlled temperature (i.e., the tensile elongation at specimen break).
An increasing number of applications are being developed for thermoplastics in which
a fabricated article is subjected to a prolonged continuous stress. Typical examples
are pipes, crates, cold water tanks, and engine cooling fans. Under such conditions
of constant stress, materials exhibit (to varying extents) continuous deformation with
increasing time. This phenomenon is termed ‘creep’.
A wide variety of materials will, under appropriate conditions of stress and
temperature, exhibit a characteristic type of creep behaviour (Figure 1.1).
D
C
Strain
B
A
0
Time
Figure 1.1 Creep behaviour of PE. Source: Author’s own files
12
The general form of this creep curve can be described as follows. Upon application
of the load, an instantaneous elastic deformation occurs (O-A). This is followed
by an increase in deformation with time as represented by the portion of the curve
A-D. This is the generally accepted classic creep curve, and is usually considered to
be divided into three parts:
• A-B: The primary stage in which creep rate decreases linearly with time.
• B-C: The secondary stage where the change in dimensions with time is constant
(i.e., a constant creep rate).
• C-D: The tertiary stage where the creep rate increases again until rupture occurs.
With thermoplastics, the secondary stage is often only a point of inflection, and the
final tertiary stage is usually accompanied by crazing or cracking of the specimen
or, at higher stresses, by the onset of necking (i.e., marked local reduction in crosssectional area). In assessing the practical suitability of plastics, we are interested in
the earlier portions of the curve, prior to the onset of the tertiary stage, as well as in
the rupture behaviour.
As the values of the stress, temperature, and time of loading vary with differing
applications, the type of information extracted from these basic creep data will also
vary with the application. There are several alternative methods (some of which are
discussed later in this book) of expressing this derived information, but whichever
form is used (whether tabular of graphical), it is unlikely to cover all eventualities.
It is thus considered of most value to give the actual creep curves and to discuss by
means of examples the methods by which particular data can be extracted from these
basic creep curves.
Typical creep curves for PE and PP at 23 ºC are shown in Figures 1.2 and 1.3. Lin
and co-workers [25] discussed the accuracy of creep phenomena in reinforced PA
and PC composites. The phenomenon of increasing dynamic creep and temperature
under tension-tension fatigue loading are compared between semi-crystalline and
amorphous composites.
13
6
Total strain (%)
5
4
3
6.2 MPa
2
4.8 MPa
3.4 MPa
1
2.1 MPa
0
0.1
1
10
Time (hours)
1000
Figure 1.2 Creep of high-density polyethylene (HDPE) at 23 ºC. Source: Author’s
own files
6
15.9 MPa
Total strain (%)
5
13.8 MPa
4
11.7 MPa
3
9.7 MPa
2
7.6 MPa
5.5 MPa
1
3.4 MPa
0
0.1
10
100
1000
Time (hours)
Figure 1.3 Creep of PP homopolymer at 23 ºC. Source: Author’s own files
14
1
To minimise as far as possible the influence of processing variables, studies have
been carried out using tensile creep tests on carefully prepared compression moulded
specimens. With injection moulded articles, creep properties will also be subject to
variation with the amount and direction of residual flow orientation. However, with
crystalline polymers such as the polyolefins, creep effects will also be influenced
by variations in density caused by a combination of flow orientation, compressive
packaging and cooling effects. Stresses will generally be complex and often involve
compressive and flexural components. However, articles should be designed to limit the
strains occurring to quite low levels, where a reasonable correlation can be expected
between tensile, compressive and flexural creep data.
1.4.1 Basic Creep Data
In general, the first step in building up a comprehensive picture of creep behaviour
is to obtain creep curves (elongation versus time) at a series of stress levels, each at a
series of test temperatures. It is common practice to plot strain on a linear scale against
time on a logarithmic scale. Each curve should preferably cover several decades on the
logarithmic time scale so that subsequent extrapolations will have a firm foundation.
Wong and co workers [26] combined a commercially available research-grade
dynamic mechanical analyser with a Fourier transform infrared (FTIR) spectrometer
for the simultaneous mechanical analysis and dynamic IR spectral measurement of
films of a polyester urethane elastomer under large amplitude creep deformation.
Differential orientation of various segments of the molecule was observed during
the creep and recovery process. Permanent damage to the elastomer observed after
a large displacement was attributed to the irreversible destruction of its microscopic
network structure.
Table 1.5 lists polymers with outstanding percentage elongation at break. High
elongation at break is not necessarily accompanied by high tensile strength. Also
listed in Table 1.5 are the particularly good and particularly poor performance
characteristics which accompany high elongation at break.
Janick and Krolikowski [24] studied the effect of properties such as elongation at
break, tensile strength, flexural strength, elastic modulus and fleural modulus on
the elongation at break performance of PET–low-density polyethylene (LDPE) and
PET-PP blends.
15
16
10
6
55
17
24
Styreneethylenebutylenestyrene
Polyethylene
terephthalate
Ethylenevinyl acetate
(25% vinyla
acetate)
Polyurethane
(thermoplastic
elastomer)
0.003
0.02
2.3
0.02
0.25
700
750
300
800
400
NY
NY
3.5
No
yield
(NY)
19
1.06 +
1.06 +
0.02
1.06 +
1.06 +
Tensile Flexural Elongation Strain Notched
strength modulus at break at yield
Izod
(MPa)
(GPa)
(%)
(%)
(kJ/m)
Low-density
polyethylene
Polymer
Abrasion resistance, tensile
strength, flame spread,
flexural modulus
Tensile strength, stiffness,
flammable, UV resistance,
environmental stress cracking
Poor performance
Tensile strength, chemical
resistance, dissipation factor,
flammability, heat distortion
temperature, flexural
modulus
low temperature
modulus
characteristics, detergent
resistance, fatigue
index, strain at yield,
toughness
cost, strain at yield,
toughness
Limited hydrolysis resistance,
stiffness, detergent
high mould shrinkage
resistance, electrical
properties, elongation at
break
low-temperature
properties, electrical
properties, toughness
chemical resistance,
electrical properties,
cost, toughness
Excellent or very good
performance
Table 1.5 Identification of polymers with outstanding elongation at break
51
52
50
Polyamide
6,12
Polyamide
11
Polyamide
6,9
50
Polyamide
12
1.4
0.9
1.4
1.4
-
320
300
200
-
20
7
6
-
0.05
0.04
0.06
Low heat distortion
temperature, dissipation
factor, flammability, flexural
modulus
High cost, strength and heat
resistance
-
-
Cost, impact strength
impact strength, heat
resistance, fatigue index,
toughness
Low water absorption,
detergent resistance,
elongation at break,
low water absorption,
toughness, dielectric
strength
17
Lyons [27] obtained creep rupture data and tensile behaviour for glass-filled PA and
polyphthalamide at 23-150 ºC.
A polyphthamide with 33% glass reinforcement exhibited a good combination of
creep resistance, strength and ductility.
1.5 Strain at Yield
This is an indication of the degree of strain that a material can accept without
yielding. The values given are typical room-temperature values. If a material is brittle
and does not exhibit a yield point, then the value given in Table 1.1 is termed ‘NA’.
If the material is ductile and does not exhibit a yield point, then the value is given
as ‘NY’ in Table 1.1. An excellent rating indicates a ductile material with no yield
and high elongation to break. ‘Not applicable’ indicates a brittle material with low
elongation to break.
Materials rated ‘very good’ to ‘very poor’ include all those exhibiting yield, ranked
according to their strain at yield, as well as ductile materials with lower elongation
to break than those rated as ‘excellent’, and brittle materials with higher elongation
to break than those rated as ‘not applicable’. In general, ductile materials range from
‘excellent’ to ‘very poor’ by descending elongation to break, and brittle materials
from ‘poor’ to ‘not applicable’ by descending elongation to break.
1.5.1 Isochronous Stress-strain Curves
Where it is necessary to compare several different materials, basic creep curves alone
are not completely satisfactory. This is particularly so if the stress levels used are
not the same for each material. If the stress endurance time relevant to a particular
application can be agreed, a much simpler comparison of materials for a specific
application can be made by means of isochronous stress-strain curves.
As an example, let us consider a milk crate in which we can assume that the moulding
will not be continuously loaded for times >100 hours. From the basic creep curves, the
strain values at the 100 hours point for various stresses can be readily determined. For
each material, a stress-strain curve can now be drawn corresponding to the selected
loading time of 100 hours. Now let us suppose that for this application it is further
stipulated that after 100 hours of continuous loading the strain shall be ≤1%. The
stress that can be sustained without violating the strain-endurance stipulation can then
be conveniently read off for each material from the isochronous stress-strain curves,
thereby indicating with reasonable confidence the stress than can be used for design
18
purposes for each of the materials considered. Examples of these interpolations are
demonstrated in Figure 1.4.
1000
7 MPa
3
5.3 MPa
2
3.5 MPa
1
Stress (psi)
Total strain (%)
4
750
500
250
1.8 MPa
0
0.1
1
10
102
Time (hours)
103
0
0
1
2
3
4
Total strain (%)
Figure 1.4 Isochronous stress-strain curve of PE. Source: Author’s own files
Hay and co-workers [28] developed an approximate method for the theoretical
treatment of pressure and viscous heating effects on the flow of a power-law fluid
through a slit die. The flow was assumed to remain one-dimensional and the
accuracy of this approximation was checked via finite element simulations of the
complete momentum and energy equations. For pressures typically achieved in the
laboratory, it was seen that the one-dimensional approximation compared well with
the simulations. The model therefore offered a method of including pressure and
viscous heating effect in the analysis of experiments, and was used to rationalise
experimentally pressure profiles obtained for the flow of polymer melts through a slit
die. Data for the flow of a LDPE and a PS melt slit die showed that these two effects
were significant under normal laboratory conditions. The shear stress-strain rate
curves would thus be affected to the point of being inaccurate at high shear rates. In
addition, it was found that the typical technique to correct for a pressure-dependent
viscosity was also inaccurate, being affected by the viscous heating and heat transfer
from the melt to the die.
Thermomechanical analysis is an ideal technique for analysing fibres because the
measured parameters - dimension change, temperature and stress - are major variables
that affect fibre processing. Figure 1.5 shows the thermal stress analysis curves for
19
a polyolefin fibre as received and after cold drawing. In this experiment, fibres are
subjected to initial strain (1% of initial length), and the force required to maintain
that fibre length is monitored. As the fibre tries to shrink, more force must be exerted
to maintain a constant length. The result is direct measurement of the shrink force of
the fibre. Shrink force reflects the orientation frozen into the fibre during processing,
which is primarily related to the amorphous portions of the fibre. Techniques that track
fibre crystallinity, therefore, are not as sensitive a measure of processing conditions
as thermomechanical analysis. In this case, the onset of the peak of the shrink force
indicates the draw temperature, whereas the magnitude of the peak is related to the
draw ratio of the fibre. It has been shown that the area under the shrink force curve
(from the onset to maxima) can be correlated to properties such as elongation at
break and knot strength. Other portions of the thermomechanical analysis thermal
stress plot can yield additional information. For example, the initial decreasing slope
is related to the expansion properties of the fibre, and the appearance of secondary
force peaks can be used to determine values such as heat set temperature in Nylon.
As received
0.6
Cold drawn
0.2
20
40
60
Force (N)
0.4
0.0
80 100 120 140 160 180 200
Temperature (°C)
Figure 1.5 Application of thermomechanical analysis to thermal stress analysis of
polyolefin films (as received and cold drawn). Source: Author’s own files
20
1.5.2 Stress-time Curves
With thermoplastic materials, above a certain stress, the stress-strain curve shows a
marked departure from linearity (i.e., above such values further increases in stress lead
to disproportionately greater increases in elongation). By study of the isochronous
stress-strain curves of a material it is possible to decide upon a certain strain that
should not be exceeded in a given application. The stress required to produce this
critical strain will vary with the time of application of the load, so that the longer
the time of application, the lower will be the permissible stress.
From isochronous stress-strain curves relating to endurance times of, for example,
1, 10, 100, and 1,000 hours, the magnitude of stress to give the critical strain at
each duration of loading can be readily deduced. This procedure can be repeated for
different selected levels of strain. In general, the more critical the application and the
longer the time factor involved, the lower will be the maximum permissible strain.
For the polyolefin family of materials, the upper limit of critical strain will always be
governed by the onset of brittle-type rupture (e.g., hair cracking at elongations that
are low compared with those expected from the short-term ductility of the material).
With thermoplastics of intermediate modules (e.g., HDPE, PP) the stress-strain curves
depart slightly from linearity at quite low strains. Thus, if accurate results are to be
obtained from standard formulae, it is sometimes necessary to limit the critical strain
and the corresponding design stress to low values. One commonly selected criterion
with high-modulus thermoplastics (e.g., polyacetal) is to base the design stress and the
design modulus on that point on the stress-strain curve at which the secant modulus
falls to 85% of the initial tangent modulus. This procedure is illustrated in Figure 1.6
It would be wrong, however, in many applications to limit the critical strain to a low
value if the ductility of the material is to be fully utilised. Extreme examples are those
such as pipes where rupture behaviour is the controlling factor.
The above type of data can be conveniently summarised by the presentation of stresstime curves corresponding to different levels of permissible strain. Such curves enable
the time-dependency of different materials to be conveniently compared. If possible,
rupture data should also be included on such plots so that at longer times an adequate
safety margin over the rupture is always maintained.
As with normal creep curves, the time scale will normally be logarithmic. For
extrapolation purposes, however, a linear relationship can be obtained by also using
a logarithmic scale for the stress axis. In fact, if rupture data are to be included, a
double logarithmic plot is preferred.
21
C
Stress
B
AB = 85
AC
100
O
A
Strain
Figures 1.6 Stress-time curve. Source: Author’s own files
1.5.3 Stress-temperature Curves
The methods discussed so far have been concerned with the presentation of combined
creep data obtained at a single temperature. Thus, a further method is required to
indicate the influence of temperature.
One convenient method is to combine the information available from isochronous
stress-strain curves or stress-time curves obtained on the same materials at different
temperatures. For example, suppose the performance criterion for a particular
application is that the total strain should be ≤2% in 1,000 hours. Using the 1,000
hours isochronous stress-strain curve for each temperature and erecting an ordinate at
the 2% point on the strain axis, the individual working stresses for each temperature
can be obtained. Alternatively, by erecting an ordinate at the 1,000 hours point on
the stress-time curve for 2% strain for each temperature investigated, the individual
working stress can be similarly obtained. From these interpolated results, the stresstemperature curve can be drawn.
By similar procedures stress-temperature plots for other specific ‘time-permissible
strain’ combinations can be obtained.
22
1.5.4 Extrapolation Techniques
Normal creep curves in which percentage total strain (or total strain) on a linear scale
is plotted against time on a logarithmic scale show increasing curvature with time,
particularly at higher stress levels. Due to this curvature it is not possible to extrapolate
curves to longer times with certainty. If, however, a double-logarithmic plot is used
for a series of stresses at a given temperature, a family of parallel straight lines is
obtained. These can then be extrapolated quite easily. With PE and PP, the slope of
such curves remains constant or tends to decrease at very long times. Furthermore,
an increase in temperature also leads to a slight reduction in the slope of the family of
curves for a given material. A straightforward linear extrapolation of the log (strain)/
log (time) creep curves may thus involve an additional safety factor.
As mentioned above, stress-curves on a double-logarithmic scale are also linear and
can be easily extrapolated. In both cases, however, over-extrapolation should be
avoided (i.e., one decade and preferably not more than two).
1.5.5 Basic Parameters
Within a given family of materials of the same basic polymer, further condensation
of data can be achieved if the principal polymer parameters influencing creep can be
separated. For example, with PE, density and the melt index (MI) would be obvious
possibilities.
If such factors can be found then all the results can be combined in suitable trend
curves and the results for any intermediate grade interpolated. If good correlations
are obtained, the reliability in the individual results is automatically increased and
one can feel confident of predicting the creep behaviour of any material within a
particular family.
1.5.6 Recovery in Stress Phenomena
In some applications, the load, instead of being constantly applied, will be applied
only intermittently for limited periods. In the period between consecutive loadings
the part will thus have an opportunity to recover. The extent to which this occurs will
depend upon the ratio of the loaded time to the unloaded time. The recovery will be
approximately exponential. Thus, to achieve virtually complete recovery, the time
without load must be substantially longer than the time under load. The residual strain
for a fixed ratio of loaded to unloaded time will also depend upon the magnitude of
the strain experienced at the time of removal of the load.
23
With intermittent loading for relatively long time periods, higher permissible stresses
will be possible than with continuous loading. With repeated loading over short time
periods, however, fatigue effects could considerably reduce the value of the permissible
stress for a long total endurance.
1.5.7 Stress Relaxation
In many applications such as those involving an interference fit (e.g., pipe couplings,
closures), we are concerned more with the decrease in stress with time at constant
strain (stress relaxation) rather than with the increase in strain with time under
constant stress (creep).
To a first approximation, such data can be obtained from the basic family of creep
curves by sectioning through them at the relevant strain value parallel to the time
axis. That is, similar procedures are used as for obtaining stress-time curves.
1.5.8 Rupture Data
In applications in which strains up to the order of a few percent do not interfere with
the serviceability of the component, the controlling factor as far as permissible stress
is concerned will probably be the rupture behaviour of the material. The rupture
curve forms the limiting envelope of any family of creep curves. Care must therefore
be exercised in extrapolating creep data to ensure that for long-term applications a
suitable safety factor is always allowed over the corresponding extrapolated rupture
stress. In general, with thermoplastics, an increase in MW leads to improved rupture
resistance, which is not necessarily reflected by an improvement in creep resistance
and in fact may be associated with a decrease in creep resistance. An increase in
MW will also, in general, be associated with a decrease in processability, which will
tend to give higher residual stresses in fabricated articles which can in turn influence
rupture properties. In designing injection moulded articles, particular care should
be taken to ensure that the principal stresses experienced by the article in service
are (wherever possible) parallel to the direction of flow of material in the mould.
Avoidance of stress concentration effects, by appropriate design, will tend to minimise
the interference of rupture phenomena and allow greater freedom to design on the
basis of the creep modulus.
Certain environments reduce rupture performance with particular materials (e.g., PE
in contact with detergents) and allowance must be made for this, where necessary,
by the incorporation of an additional safety factor to the rupture stress. In general,
24
the resistance to rupture will be greater if the stress is applied in compression than
in tension.
Differing stress levels have been used for HDPE and LDPE for the reasons previously
discussed, so an easier comparison between grades can be made by the use of
isochronous stress-strain curves. These are shown in Figures 1.7-1.10 for times of
1, 10, 100, 1,000 hours, respectively.
6.2
5.5
65-045
58-045
50-075
4.8
Stress (MPa)
4.1
3.4
30-005
25-040
2.8
2.1
18-070
1.4
Actual Densities - g/ml
0.7
0
0
1
2
3
4
65-045
58-045
50-075
0.9630
0.9565 }High Density
0.9505
30-005
25-040
18-070
0.9270
0.9220 }Low Density
0.9160
5
6
7
8
Total strain at 1 hour (%)
Figure 1.7 Isochronous stress-strain curves of various grades of LDPE and HDPE
at 23 ºC (1 hour data). Source: Author’s own files
25
The data have been further combined in Figure 1.7, which demonstrates the marked
(but systematic) influence of density on the creep behaviour of PE. The curves in
Figure 1.11 are relevant to a total strain of 1%, but similar plots for other permissible
strains can be readily derived from the isochronous stress-strain curves. The linear
relationship between creep and density for PE at room temperature, irrespective of
the melt index over the range investigated (i.e., 0.2 to 5.5), has enabled the stress-time
curve of Figure 1.12 to be interpolated for the complete range of PE and for a range
of PP (Figure 1.13). In this case, the data have been based on a permissible strain of
2% but, as previously explained, data for other permissible strains can be similarly
interpolated from the creep curves. The effect of temperature on the creep properties
of PE is summarised in Figure 1.14.
6.2
5.5
65-045
58-045
50-075
4.8
Stress (MPa)
4.1
3.4
30-005
25-040
2.8
2.1
18-070
1.4
0.7
0
0
1
2
3
4
65-045
58-045
50-075
0.9630
0.9505
30-005
25-040
18-070
0.9270
0.9220 }Low Density
0.9160
5
6
7
8
at 23 ºC (10 hours data). Source: Author’s own files
26
6.2
65-045
58-045
50-075
5.5
4.8
Stress (MPa)
4.1
3.4
30-005
25-040
2.8
18-070
2.1
1.4
0.7
0
0
1
2
3
4
65-045
58-045
50-075
0.9630
0.9505
30-005
25-040
18-070
0.9270
0.9220 }Low Density
0.9160
5
6
7
8
at 23 ºC (100 hours data). Source: Author’s own files
27
6.2
5.5
65-045
58-045
50-075
4.8
4.1
Stress (MPa)
30-005
25-040
3.4
2.8
18-070
2.1
1.4
0.7
0
0
1
2
3
4
65-045
58-045
50-075
0.9630
0.9505
30-005
25-040
18-070
0.9270
0.9220 }Low Density
0.9160
5
6
7
8
at 23 ºC (1,000 hours data). Source: Author’s own files
28
1 hours
4.8
4.1
Stress to give 1 % total strain (MPa)
10 hours
3.4
100 hours
1000 hours
2.8
2.1
1.4
0.7
0.920
0.930
0.940
0.950
0.960
0.970
Actual density of polyethylenes (g/ml)
Figure 1.11 Effect of density on creep of PE at 23 ºC. Source: Author’s own files
29
8.3
0.965
0.960
0.955
Stress for 2% total strain (MPa)
6.9
0.950
5.5
0.940
4.1
0.930
2.8
0.925
0.920
1.4
0
0
10
100
1,000
10,000
Time (hours)
Figure 1.12 Interpolated stress-time curves of PE of various densities (2% total
strain). Source: Author’s own files
00
00
GM 61
KM 61
00
DE 61
KMT 61
00
GMT 61
00
00
0
0
10
100
1,000
10,000
Time (hours)
Figure 1.13 Interpolated stress-time curves of various grades of PP at 23 ºC (2%
total strain). KMT 61 and GMT 61= PP copolymers. KM 61, GM 61 and DE 61
= PP homopolymer. Source: Author’s own files
30
5.5
Stress to give 2% total strain in 1000 hours (MPa)
4.8
0.960
4.1
0.950
3.4
0.940
2.8
0.930
2.1
0.920
1.4
0.7
0
20
30
40
50
60
70
80
Temperature (ºC)
Figure 1.14 Interpolated stress-temperature curves of PE of different densities (2%
total strain at 1,000 hours). Source: Author’s own files
31
For PE, the principal factor controlling creep is density but the principal factor
influencing rupture behaviour is the melt index. Thus, for a given density, for long-term
applications, the higher the melt index the lower will be the maximum permissible
strain. This is particularly important at elevated temperatures.
The effect of temperature on the creep of PP is also conveniently summarised in
Figures 1.15 and 1.16. Although these curves refer specifically to 0.5% and 2% total
strain in 1,000 hours, similar interpolations have shown that to a first approximation
the fall off in stress with temperature is similar for other strain-time combinations.
In contrast to PE, an excellent correlation has been found between the creep and
melt index of PP. An increase in the melt index is associated with an increase in creep
resistance. This has been found for homopolymers and copolymers, and is illustrated
in Figure 1.17. For similar melt indices the inferior creep resistance of the copolymers
is also indicated, this difference being more marked for grades of lower melt index.
1.5.9 Long-term Strain-time Data
To illustrate the linearity of double-logarithmic plots of percentage total strain against
time, Figure 1.18 shows a typical family of curves at a range of stress levels for a
HDPE and Figure 1.19 shows that for a PP copolymer. From the uniform pattern
of behaviour, the linear extrapolation of the curves at lower stresses to longer times
appears well justified. As emphasised above, with the higher-melt-index materials at
higher temperatures, over-extrapolation is dangerous because of the possible onset
of rupture at comparatively low strains.
Figures 1.20 and 1.25 shows creep curves, isochronous stress-strain curves and
stress-time curves for a typical ABS terpolymer and a typical unplasticised polyvinyl
chloride (UPVC).
32
Stress to give 0.5% total strain in 1000 hours (MPa)
3.4
KM 61
2.8
GM 61
2.1
DE 61
KMT 61
1.4
GMT 61
0.7
0
20
30
40
50
60
70
80
Temperature (ºC)
Figure 1.15 Interpolated stress-temperature curves for various grades of PP (0.5%
total strain at 1,000 hours). DE 61 = PP copolymers. Source: Author’s own files
33
9.7
8.3
KM 61
GM 61
Stress to give 0.5% total strain in 1000 hours (MPa)
6.9
5.5
DE 61
KMT 61
4.1
GMT 61
2.8
1.4
0
20
30
40
50
60
70
80
Temperature (ºC)
Figure 1.16 Interpolated stress-temperature curves for various grades of PP (2%
total strain at 1,000 hours). DE 61 = PP homopolymers. Source: Author’s own files
34
18.5
1 hour
13.8
10 hours
1 hour
100 hours
11.0
x
8.3
100 hours
x
1000 hours
x
5.5
1000 hours
10 hours
x
Homopolymers
x Copolymers
2.8
0
0
10
100
1,000
Melt index (g/10 min)
Figure 1.17 Effect of melt index on creep of PP at 23 ºC. Source: Author’s own
files
Density 0.96 gm/ml
Melt index 0.3 gm/10 min (190 °C 2.16 kg)
6.2 MPa
4.8 MPa
3.4 MPa
1
0.1
0.1
1
10
100
1,000
10,000
10 years
2.1 MPa
1 year
Total strain (%)
10
100,000
Time (hours)
Figure 1.18 Long-term creep of HDPE at 23 ºC. Source: Author’s own files
35
36
0.1
0.1
1
10
10
Time (hours)
100
13.8 MPa
1000
3.4 MPa
5.5 MPa
7.6 MPa
9.7 MPa
11.7 MPa
10,000
1 year
Figure 1.19 Long-term creep of high-density PP copolymer at 23 ºC. Source: Author’s own files
1
19.5 MPa
Total strain (%)
6
5
27.6 MPa
Total strain (%)
4
3
2
20.7 MPa
1
13.8 MPa
6.9 MPa
0.1
1
10
100
1000
Time (hours)
Figure 1.20 Creep of typical ABS terpolymer (normal impact grade) at 23 ºC.
0
0
Stress to produce a given strain (MPa)
3% strain
0
2% strain
0
1% strain
0
0.5% strain
0
0
1
10
100
1000
10,000
Time (hours)
Figure 1.21 Interpolated stress-time curves for a typical ABS terpolymer (normal
impact grade) at 23 ºC. Source: Author’s own files
37
6
5
Total strain (%)
4
3
34.5 MPa
2
25.9 MPa
1
17.2 MPa
8.6 MPa
0
0.1
1
10
100
1000
Time (hours)
Figure 1.22 Creep of typical UPVC pipe formulation at 23 ºC. Source: Author’s
own files
41.4
34.5
Stress to produce a given strain (MPa)
3% strain
27.6
2% strain
20.7
1% strain
13.8
0.5% strain
6.9
0
0
10
100
1000
10,000
Time (hours)
Figure 1.23 Interpolated stress-time curves for a typical UPVC pipe formulation at
23 ºC.
Author’s own files
34.5Source:
MPa
38
Figure 1.24 Injection moulded dish used in measurement of falling weight strength.
Figures 1.25 Injection moulded ruler used in the study of weld effects (length, 37.5
cm). Source: Author’s own files
Stress-strain data have been reported for several polymers, including ultra-high MW
PE [29-30] syndiotactic PP [31] PA 6 [32], PP [33], PA 6,6 [34] and LDPE aluminium
foil laminates [35].
39
1.6 Impact Strength Characteristics of Polymers
Of the many properties of a plastic that influence its choice for a particular article or
application, the ability to resist the inevitable sharp blows and drops met in day-today use is one of the most important. The prime object of impact testing should be
to give a reliable guide to practical impact performance. However, the performance
requirements and the design and size of articles can be vary considerably. The method
of fabrication can also vary and, because all these factors can influence impact
performance, a reasonably wide range of data are required if most of these eventualities
are to be covered and materials and grades compared sensibly.
Available instrumentation is listed in Table 1.6.
Table 1.6 Impact resistance (Izod Charpy) and notched impact resistance
ATS FAAR
Number
Units
Suitable test
Izod Charpy impact test
Pendulum impact strength
(Izod and Charpy) and notched
impact strength
16.10000
16.10500
16.10600
ft.lb/in
kJ/m2
Nm/m
ASTM D26-56 [36]
DIN EN ISO 179 [37]
ISO 179-1 [5]
ISO 180 [38]
BS 2782 [13]
UNI EN ISO 180 [39]
Falling dart impact test (Fall-o-Scope ATS FAAR)
Impact resistance (free falling
dart)
ASTM D5420 [40]
ASTM D5628 [41]
DIN EN ISO 6603 [42]
Guided universal impact test (Fall-o-Scope ATS FAAR)
Impact resistance at low
temperature (cable)
1.6.1 Notched Izod Impact Strength
Of all the types of mechanical test data normally presented for grade characterisation
and quality-control purposes, the standard notched Izod test is probably the most
40
vigorously criticised on the grounds that it may give quite misleading indications
regarding impact behaviour in service. In most cases, however, the criticism should
be levelled at too wide an interpretation of the results, particularly the tendency to
overlook the highly important influence of the differences between the standard and
operational conditions in terms of dimensions, notch effects, and processing strains.
For example, in the Izod test, the specimens are of comparatively thick section (e.g.,
6.25 × 1.25 × 1.25 cm, or 6.25 × 1.25 × 0.625 cm) and are consequently substantially
unoriented. Even with injection moulded specimens (where some orientation does
exist), specimens are usually tested in their strongest direction (with the crack
propagating at a right angle to the orientation direction), which generally leads to high
values. Furthermore, specimens are notched with the specific intention of locating the
point of fracture and ensuring that as wide a range of materials as possible fracture
in a brittle manner in the test. It is thus reasonably safe to infer that, if a material
breaks in a ductile manner at the high impact energies involved in the Izod test it
will, in nearly all circumstances involving thick sections, behave in a ductile manner
in practice. Because of the severe nature of the test, it would be wrong, however, to
assume that because a material gives a brittle-type fracture in this test it will necessarily
fail in a brittle manner at low impact energies in service.
In cases in which high residual orientation is present, additional weakening can result
from the easier propagation of cracks in the direction parallel to the orientation.
A low Izod value does give a warning that care should be exercised in design to avoid
sharp corners or similar points of stress concentration. It does not by itself, however,
necessarily indicate high notch sensitivity.
1.6.2 Falling Weight Impact Test
The normal day-to-day abuse experienced by an article is more closely simulated by
the falling weight impact type test (see BS 2782) [13]. It is also much easier to vary the
type and thickness of specimens in this test. Furthermore, any directional weakness
existing in the plane of the specimens is easily detected.
ATS FAAR supplies the Fall-o-Scope Universal apparatus for free-falling dart impact
resistance tests (Table 1.6). The apparatus can be set to obtain the rate of energy
absorption during the impact. The apparatus can be used to conduct tests to different
specifications with computerised operation in the range 70-200 ºC.
One would normally expect the impact energy required for failure to increase with
specimen thickness, but the rate of increase will not be the same for all materials. In
addition, the effect of the fabricating process cannot be over-emphasised. I mentioned
41
above that residual orientation can lead to marked weakening and susceptibility to
cracking parallel to the orientation direction. Such residual orientation is extremely
likely to be brought about in the injection moulding process, where a hot plastic melt
is forced at a high shear rate into a narrow, relatively cold cavity. Naturally, the more
viscous the melt and the longer and narrower the flow path, the greater the degree
of residual orientation expected. Within a given family of grades the melt viscosity,
besides being influenced by temperature and shear rates, will also be affected by
polymer parameters such as MW and MW distribution. Thus, it cannot be assumed
that the magnitude of this drop in impact strength will be the same for differing
materials or for differing grades of the same material. For a satisfactory comparison
it is, therefore, essential to know that variation in impact strength with thickness of
unoriented compression moulded samples and injection moulded samples moulded
over a range of conditions.
In some investigations, a flat, circular, centre-grated, 15 cm diameter moulded dish
as (Figure 1.24) has been used. The dish is mounted in the falling weight impact
tester in its inverted position and located so that the striker hits the base 1.875 cm
from the centre because the area near the sprue is one of the recognised weak spots
of injection moulding. By means of inserts in the mould, the thickness of the base
of the moulding can be varied. For each material a family of curves is obtained for
variation of impact strength with thickness of compression moulded sheets moulded
under standard conditions, and of injection moulded dishes produced at a series of
temperatures. An estimate of the weakening effects of residual orientation and of
the tolerance that can be allowed on injection moulding conditions for satisfactory
impact performance is thus obtained.
A further factor that can adversely affect impact performance is often encountered
in injection moulding. Whether a single gate or multiple gates are used, it is usually
inevitable due to a non-uniform flow pattern during the mould-filling operation that
separate flow fronts meet to form a weld line. The strength at the weld line will vary
with the material, the injection moulding conditions, and the length and thickness of
the flow path, and can be considerably weaker that adjacent parts of the moulding.
Weld effects have been studied by means of a flat 37.5 × 3.125 cm ruler mould as
shown in Figure 1.25 which can be gated at one or both ends. The thickness of the
specimens can be varied by means of inserts. In this way, a series of comparisons
can be made between the falling weight impact strength of welded and non-welded
specimens at the same distance from the gate for varying path length to cavity thickness
ratios and differing moulding conditions.
Besides the average level at which failures occur in the falling weight impact test, the
type of failure can also be of importance in judging the relative impact performance
of a material in practice. There are generally three types of failure, as listed below:
42
• A ductile or tough failure in which the material yields and flows at the point of
impact, producing a hemispherical depression, which at sufficiently high impact
energies eventually tears through the complete thickness.
• A brittle failure in which the specimen shatters or cracks through its complete
thickness with no visible signs of any yielding having taken place prior to the
initiation of the fracture. (With specimens possessing a high degree of residual
orientation a single crack parallel to the orientation direction is obtained.)
• An intermediate or ‘bructile’ failure in which some yielding or cold flow of the
specimen occurs at the point of impact prior to the initiation and propagation of
a brittle-type crack (or cracks) through the complete thickness of the specimen.
These types of failure are shown in Figure 1.26.
An idea of the impact energy associated with these types of failure can be ascertained
by consideration of a typical load-deformation curve. This in general will be of the
form shown in Figure 1.27. From the definitions given above, a brittle-type failure
will occur on the initial, essentially linear part of the curve, prior to the yield point.
Figure 1.26 Examples of types of failure occurring in the falling weight impact
strength test. Source: Author’s own files
43
Brittle
Bructile
Load
Ductile
Yield Point
Deformation
Figure 1.27 Typical load-deformation curve. Source: Author’s own files
A bructile failure will occur on that part of the curve near to but following the yield
point. A ductile failure will be associated with high elongations on the final part of
the curve which follows the yield point. With the last type of failure, the deformation
at failure will be reasonably constant for a strike of given diameter. The area beneath
the curve up to failure gives a measure of the impact energy to cause failure. Hence, in
general, for a given thickness, tough-type failure is associated with high and reasonably
constant impact energy. Bructile failure is also associated with relatively high but
more variable energy. Brittle failures are generally associated with a low impact level.
If, in a given test, failures are all of the tough type, a reliable and reproducible measure
of the impact strength of the sample can be obtained. If, however, differing types of
failures are observed, a much wider variation in impact values can be obtained from
repeat tests.
44
However, the difference in energy level required to produce tough and brittle-type
failure varies for differing materials. In practice, the lowest level at which a failure
is likely to occur is as important as the estimated level at which 50% of the samples
are likely to fail, so it is necessary to have a measure of this variability. The 50%
failure level (F50) is the value usually reported in a falling weight impact test. This
can be obtained by repeating the falling weight test using the ‘probit’ rather than the
‘staircase’ procedure. In the former, sets of samples are tested at each of a series of
increasing energy levels between the limits at which, none or all the specimens in a
given set fail. If percentage failure is then plotted against impact energy on probability
paper, the slope of the curve gives an estimate of the variable and the likelihood of
occasional samples failing at low impact levels.
A final important factor that requires consideration for many applications is the
influence of temperature because some thermoplastics undergo a tough-brittle
transition, with a correspondingly marked drop in impact performance, just below
ambient temperature. Changes in notch sensitivity with temperature have been
ascertained by the use of notched bar tests (as described above) and change in
impact strength with temperature by the falling weight test and standard Izod test.
Comparatively thick compression- and/or injection moulded specimens have been
used in these investigations to ensure that the starting value of the impact strength at
room temperature is high and that change in this value is easily detected.
• Gardner Impact Test
Lavach [45] discussed the factors that affect results obtained by the Gardner impact
test. This test is used by plastics producers to approximate the mean failure energy
for many plastics. The test is inexpensive and easy to operate. The test equipment can
be placed close to the manufacturing equipment, permitting fast and nearly online
determination of the impact resistance of an article. The test is useful for finding the
mean failure energy for brittle thermoplastics such as acrylic and high-impact PS,
with standard deviations between 8% and 10%.
1.6.3 Notch Sensitivity
The sharpness of a notch is well known to have a strong influence on the impact
performance of notched specimens. The extent of this effect is found to vary
considerably from polymer to polymer. To investigate this point, impact values
obtained with the BS notch of 0.10 cm tip radius have been compared with those
obtained with other tip radii, namely 0.025 cm (the ASTM standard), 0.050 cm and
0.20 cm. The results for notch sensitivity are conveniently expressed by plotting the
impact value as a ratio of the BS value against the notch tip radius or alternatively
45
plotting the actual Izod value on a logarithmic scale against notch tip radius on a
linear scale. The steeper the slope of the curve, the greater the notch sensitivity of
the material and the more essential it is to remove sharp radii and points of stress
concentration in design if optimum performance is to be obtained.
If the limitations described above are remembered, the results of notched bar tests
give useful information. However, for realistic comparisons of materials, additional
impact data are required.
Reference was made above as to how a low Izod value gives a warning regarding
the care that should be exercised in design to remove points of stress concentration
if optimum impact behaviour is to be obtained with a component in practice. It was
also mentioned that a more reliable measure of notch sensitivity can be obtained by
carrying out tests using a series of notch radii rather than a single standard notch.
Figure 1.28 shows the relative notch sensitivities of some polyolefins and a few other
well-known thermoplastics. Polyolefins are of intermediate notch sensitivity, this being
more marked with the higher melt-index grades. Among the polyolefins, the low meltindex PP copolymer designated GMT 61 has the lowest notch sensitivity, whereas the
higher-melt-index PE and PP homopolymers (e.g., 65-045, KM 61) have the highest.
Figure 1.29 shows the variation in standard Izod impact strength (0.10 cm notch tip
radius) with temperature for the same range of materials. By far the most temperaturesensitive is the low melt-index PP copolymer. It is interesting to compare the sharp
fall-off in notched impact strength with this material between 23 ºC and 0 ºC with
the steady values obtained for falling weight impact strength for the same temperature
range (Figure 1.30). The removal of points of stress concentration is thus the most
vital factor governing the impact performance of this grade at temperature of 0 ºC
and below. Figure 1.31a shows in more detail the notched impact behaviour of PP
at room temperature. A semi-logarithmic plot has been used so that the overall level
and notch sensitivity can be determined. The marked influence of the melt index and
the superiority of the copolymers over the homopolymers are clearly demonstrated.
Figure 1.31b and c show similar data for 0 ºC and -20 ºC, respectively. With the
exception of the low melt index PP copolymer, notch sensitivities are similar to those
at room temperature, but the marked drop in overall level brought about by a decrease
in temperature is again clearly demonstrated.
46
200
Notch sensitivity
180
160
140
120
80
60
40
20
0.25
0.50
1.0
2.0
Notch tip radius (mm)
Figure 1.28 Typical notch sensitivities of some thermoplastics at 23 ºC. Source:
47
1068
HDPE (low MI) 60-004
BSI Izod impact strength (1 mm notch) (J/m notch)
801
534
HDPE (MI = 1.0)
ABS (high impact)
267
PP (GMT 61)
ABS (normal impact)
HDPE–65045
PP KMT 61
PP GM 61
0
–30
Toughened polystyrene
–20
–10
0
10
20
30
Temperature (°C)
Figure 1.29 Influence of temperature on Izod impact strength of various polymers.
HDPE low melt index and high melt index. Source: Author’s own files
48
748
641
GMT 61
Falling weight impact strength (1/m F50)
534
ABS (high impact)
427
65-045
KMT 61
ABS (normal impact)
320
214
107
KM 61
0
–30
–20
–10
0
10
20
30
Temperature (°C)
Figure 1.30 Effect of temperature on falling weight impact strength of 0.060 inch
compression moulded specimens of various polymers. Source: Author’s own files
49
1068
(a)
BS notch
ASTM notch
GMT 61
534
Izod impact strength (ft lb/inch notch)
267
KMT 61
GM 61
107
KM 61
53
PM 61
27
11
5
0.3
0.5
1.0
2.0
534
(b)
Izod impact strength (ft lb/inch notch)
267
BS notch
ASTM notch
GMT 61
KMT 61
107
53
GM 61
27
11
5
0.3
0.5
1.0
50
2.0
534
(c)
267
Izod impact strength (J/m notch)
ASTM notch
BS notch
GMT 61
107
KMT 61
53
GM 61
27
11
5
0.3
0.5
1.0
2.0
Figure 1.31 Variation of Izod impact strengths of various grades of PP with notch
tip radius at (a) 23 ºC; (b) 0 ºC; and (c) -20 ºC. PM 61 = PP homopolymer. Source:
Figures 1.32 and 1.33 show the combined data for room temperature and -20 ºC for
HDPE and for ABS terpolymer and toughened PS, respectively. Of particular note
is the very small effect of temperature on the impact level and notch sensitivity of
HDPE, although the effect of MW (or melt index) is again clearly demonstrated. This
indicates the suitability of HDPE for low-temperature applications.
One important practical example of the controlling influence of notch sensitivity in
governing impact behaviour is that of embossed surfaces. Table 1.7 gives the results
of falling weight impact tests in which a series of different textured finishes have been
investigated for a range of PP. The injection moulded disc specimens possessed one
texture and one plain, smooth surface. If the embossed surfaces were struck, high
impact values were obtained. However, if the smooth surface was struck (so that the
textured surface was placed in tension), very low impact values were obtained, with
the magnitude of the drop depending upon the depth and sharpness of the embossing.
51
The sharper the pattern, the lower the value obtained. In practice, it will generally be
the textured surface that is struck but, if the reverse applies, considerable care should
be exercised in the choice of the finish.
2670
MI = 0.4
1068
23 ºC
MI = 1.0
–20 ºC
534
MI = 2.0
23 ºC
267
–20 ºC
MI = 4.5
23 ºC
–20 ºC
107
23 ºC
–20 ºC
53
27
ASTM notch
BS notch
11
5
0.3
0.5
1.0
2.0
Figure 1.32 Variation of Izod impact strength of 0.96 HDPE with notch tip radius
at 23 ºC and -20 ºC. Source: Author’s own files
52
1.5
24.4
Embossed
11.7
Embossed
Smooth
0.5
Smooth
2.2
Embossed
20.3
0.8
12.5
0.4
4.5
0.4
Rough
finish
(Martin’s)
Smooth
grain (mould
decoration
incorporated)
0.4
Surface 2
13.6
0.9
1.9
0.4
1.9
0.4
Rough
finish
(Dornbush)
Surface 3
>24.4
4.6
21.7
0.5
3.8
0.5
Smooth
grain (mould
decoration
incorporated)
Surface 4
>24.4
1.9
10.7
0.4
2.0
0.4
Medium
finish
(Dornbush)
Surface 5
Falling weight impact strength at 23 oC – kJ/m2
Surface 1
Smooth
Surface
towards
striker
KMT 61
GM 61
PM 61
Polypropylene
grade
Table 1.7 Effect of embossing on falling weight impact strength at 23 oC
2.7
2.7
2.8
2.8
2.7
2.7
Specimen
thickness
(mm)
53
1068
534
ABS (high impact)
23 ºC
267
–20 ºC
23 ºC
107
ABS (normal impact)
–20 ºC
23 ºC
53
–20 ºC
27
BS notch
ASTM notch
11
5
0.3
0.5
1.0
2.0
Figure 1.33 Variation of Izod impact strength of ABS terpolymer and toughened PS
with notch tip radius and temperature. Source: Author’s own files
1.6.4 Falling Weight Impact Tests: Further Discussion
Figure 1.34 gives the variation in falling weight impact strength with thickness at 23 ºC
of a range of materials in substantially stress-free compression moulded samples.
54
However, in practice, fabricated articles are seldom stress-free (particularly injection
moulded articles). Residual orientation can result in a marked reduction in impact
strength. This is illustrated in Figures 1.35-1.41 covering high- and low melt-index
PP (Figures 1.35 and 1.38), PP copolymer (Figure 1.37) HDPE (Figure 1.38), normalimpact and high-impact ABS terpolymers (Figures 1.39 and 1.40) and toughened PS
(i.e., styrene-butadiene copolymer, Figure 1.41).
41
Falling weight impact strength (J (F50))
Unplasticised PVC sheet
27
Polypropylene copolymer (low MI)
Acrylonitrile butadiene styrene
terpolymer (high impact)
High density polyethylene
Polypropylene copolymer (high MI)
14
Acrylonitrile butadiene styrene
(normal impact)
Polypropylene homopolymer (low MI)
Polypropylene hornopolymer (high MI)
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Thickness (mm)
Figure 1.34 Effect of thickness on falling weight impact strength of some typical
thermoplastics at 23 ºC (compression moulded samples).
55
41
IM = Injection moulded
CM = Compression moulded
27
CM
IM 280 ºC
14
IM 200 ºC
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Thickness (mm)
Figure 1.35 Falling weight impact strength of high melt index PP copolymer at 23
ºC. Source: Author’s own files
56
41
CM = Compression moulded
CM
IM 240 ºC
27
IM 280 ºC
14
IM 200 ºC
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Thickness (mm)
Figure 1.36 Falling weight impact strength of low melt index PP copolymer at
23 ºC. Source: Author’s own files
57
14
CM
CM
CM = Compression Moulded
MI = 0.6
11
8
MI = 3.0 (nucleated)
5
All samples when
injection moulded
3
CM
MI = 3.0
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Thickness (mm)
Figure 1.37 Falling weight impact strength of PP copolymers (comparison of
moulded and injection moulded specimens at 23 ºC. Source: Author’s own files
27
CM
IM 280 ºC
14
IM 240 ºC
IM 200 ºC
0
0
0.5
1.0
1.5
2.0
2.5
3.0
Thickness (mm)
Figure 1.38 Falling weight impact strength of HDPE at 23 ºC.
58
3.5
41
IM 240 ºC
27
IM 260 ºC
14
CM
IM 220 ºC
0
0
0.5
1.0
2.0
1.5
2.5
3.0
3.5
Thickness (mm)
Figure 1.39 Falling weight impact strength of ABS terpolymer (normal impact
grade) at 23 ºC. Source: Author’s own files
41
27
IM 220 ºC
IM 260 ºC
IM 240 ºC
CM
14
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Thickness (mm)
Figure 1.40 Falling weight impact strength of ABS terpolymer (high impact grade)
at 23 ºC. Source: Author’s own files
59
5
CM
4
3
IM 260 ºC
IM 240 ºC
IM 220 ºC
2
1
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Thickness (thousandth of inch)
Figure 1.41 Falling weight impact strength of typical toughened PS at 23 ºC.
The change in impact strength with injection moulding temperature gives an indication
of the process adaptability of each material. With high-impact ABS terpolymers,
there is little difference in the level of falling weight impact strength over the range
of injection moulding temperatures. With all materials except PP homopolymers and
toughened PS, the impact strength of injection moulded samples produced at higher
temperatures is similar to that of the virtually non-oriented compression moulded
samples. With toughened PS, the impact strength of injection moulded samples is
markedly lower than that of compression moulded samples, although a slight effect
of injection moulding temperature has been observed.
The marked drop in impact strength that can result from weld lines is demonstrated
in Figure 1.42 for a PP copolymer. At lower thickness, where the flow path to cavity
60
thickness ratio is correspondingly higher, the impact strength measured at the weld
is very much lower than that measured with a similar non-welded specimen. The
positioning of gates to minimise weld effects is thus of vital importance in obtaining
optimum behaviour in an injection moulded article of a given design.
Figures 1.30 and 1.43 show the effect of temperature on the falling weight impact
strength for compression moulded and injection moulded specimens, respectively, of
a range of materials. The reduction in impact strength with decrease in temperature is
particularly marked with the injection moulded samples of the two otherwise higher
impact-resistant types: PP copolymers and ABS terpolymers. The superior impact
strength at low temperatures of injection moulded HDPE is clearly illustrated.
41
Melt temperature: ∆ 200 °C
240 °C
280 °C
Non-weld specimens
27
14
Compression moulded
Weld specimens
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Thickness (mm)
Figure 1.42 Effect of weld lines on the falling weight impact strength of PP
copolymer at 23 ºC. Source: Author’s own files
61
19
GMT 61
16
14
Typical ABS (high impact)
65-045
11
Typical ABS
(normal impact)
KMT 61
8
5
3
GM 61 KM 61
0
–30
–20
–10
0
10
20
30
Temperature (°C)
Figure 1.43 Effect of temperature on falling weight impact strength of 2.0 mm
thick injection moulded specimens of various polymers moulded at 240 ºC. 65045-HDPE. Source: Author’s own files
As mentioned above with regard to end-use performance, the minimum level at which
failures are likely to occur is of equal importance to the usually quoted F50 level. This
is particularly true if different types of failure are obtained in the falling weight impact
62
test. Such variations in the type of failure frequently occur as temperature is reduced
below ambient temperature. The probit method is then the preferred procedure of
evaluation of impact strength behaviour.
The additional information that can be obtained by this method is demonstrated in
Figures 1.44-1.46. For a low melt index HPDE (Figure 1.44) the probit is almost
horizontal at ambient temperature and at -20 ºC. For a typical high-impact ABS
terpolymer (Figure 1.45), the slopes of the curves are relatively steep compared with
HDPE unless the impact strength is very low. The probability of failure occurring at
low temperatures and at a low impact levels is thus higher with PP copolymers and
ABS than with HDPE. In fact, the results indicate that the impact strength of the
latter material at -20 ºC is slightly superior to that at 23 ºC.
22
19
Impact energy (J)
16
–20 °C
14
11
–20 °C tough
23 °C
8
5
Polyethylene
0.947 density
0.3 melt index
23 °C tough
3
0
0.01
0.1
0.5
2
0.05 0.2
1
10
5
30
20
50
40
70
60
90
80
98
95
99
99.8
99.99
99.9
Failiure (%)
Figure 1.44 Probit curves for a low melt-index HDPE (nominal thickness: 2.0 mm,
injection moulded at 270 ºC). Source: Author’s own files
63
22
19
16
Impact energy (J)
Tough/Bructile + 10 °C
14
Tough/Bructile/Brittle + 10 °C
11
23 °C tough
8
5
3
23 °C
10 °C
0 °C
–10 °C brittle
–20 °C brittle
0
0.01
0.1
0.5
2
0.05 0.2
1
10
5
30
20
50
40
70
60
90
80
98
95
99
99.8
99.99
99.9
Failiure (%)
Figure 1.45 Probit curves for a typical high-impact ABS terpolymer (nominal
thickness: 2.00 mm, injection moulded at 240 ºC). Source: Author’s own files
22
Bructile 0 °C
19
Impact energy (J)
16
Tough/Bructile 23 °C
14
Bructile + 10 °C
Bructile – 10 °C
11
8
5
Bructile – 20 °C
3
0
0.01
0.1
0.5
2
0.05 0.2
1
10
5
30
20
50
40
70
60
90
80
98
95
99
99.8
99.99
99.9
Failiure (%)
Figure 1.46 Probit curves for a PP copolymer (nominal thickness: 2.0 mm,
injection moulded at 240 °C). Source: Author’s own files
64
1.6.5 Effect of Molecular Parameters
The major influence of MW on the impact behaviour of polyolefins with regard to
notched Izod and falling weight impact tests is emphasised. With HDPE, MW is the
prime factor controlling impact behaviour, and density is a secondary factor. This is
clearly demonstrated in Figures 1.47 and 1.48, which show the results for commercial
HDPE. However, it is generally thought that for any given density there is a critical
melt index which increases as the density decreases. Above this value, a marked fall-off
in impact strength occurs. Furthermore, within a given family of grades, a decrease
in the melt index is usually accompanied by a slight reduction in density.
A comparison of the impact data with the creep data also confirms, particularly with
PP polymers, that an increase in impact strength is accompanied by a decrease in
creep resistance.
Falling weight impact strength (J(F50))
14
0.958
0.961
12
0.951
11
0.955
0.960
0.964
9
0.960
0.957
0.961
0.951
0.958
8
7
0.1
1
10
100
Melt index (g/10 min at 190 °C/2.16 kg)
Figure 1.47 Effect of the melt index on falling weight impact strength of various
HDPE at 23 ºC (1.5 mm compression moulded samples).
65
14
0.28
Falling weight impact strength (J(F50))
12
Nominal 0.3 melt index
0.28
1.1
11
3.2
2.3
Nominal 5.0 melt index
4.4
5.9
9
5.5
4.4
8
14.0
7
0.950
0.955
0.960
0.965
Density (g/ml)
Figure 1.48 Effect of density on falling weight impact strength of HDPE in various
melt indices at 23 ºC (1.5 mm compression moulded samples). Source: Author’s
own files
Janik and Krolikowski [24] investigated the effect of Charpy notched impact strength
and other mechanical properties (tensile strength, flexural strength, elastic modulus,
flexural modulus, melt viscosity, fracture) on the mechanical and rheological properties
of PE-PET blends.
Pick and Harkin-Jones [44, 45] and others investigated the relationship between
the impact performance of rotationally moulded PE products and their dynamic
mechanical properties.
Comparisons with regard to impact performance were made between metallocenecatalysed linear low-density polyethylene (LLDPE) and Ziegler-Natta LLDPE. The
transitions evident in dynamic mechanical thermal analysis (DMTA) results are related
66
to changes in impact performance with temperature. The beta transition is found to
fall in the transition region between high impact performance at low temperatures
and lower impact performance at ambient temperatures.
1.7 Shear Strength
Apparatus for the measurement of this property according to ASTM D732 [71] is
available from ATS FAAR (Table 1.8). Briatico-Vangosa and co-workers [33] discussed
the relationship between surface roughness and shear strength in ultra high MW PE.
Table 1.8 Instrumentation, compressive set and mould shrinkage
Method
ATS FAAR
Apparatus code
number
Compressive set to measure 10.65000 (stress)
permanent deformation
10.07000 (strain)
Mould shrinkage
injection
compression and postshrinkage
-
Units
%
Test suitable for
meeting the following
standards
ASTM D395 [46]
ISO 815 [48]
UNI 6121 [49]
DIN 53464 [50]
1.8 Elongation in Tension
Apparatus for the measurement of this property according to ASTM D32 [73] is
available from ATS FAAR (Table 1.8).
1.9 Deformation Under Load
The use of light-scattering and X-ray beams to measure polymer deformation has
been reported by Lee and co-workers [51] and Riekel and co-workers [52].
67
1.10 Compressive Set (Permanent Deformation)
The equipment described in the following section is supplied by ATS FAAR (Table 1.8).
Tests can be carried out under constant load Method A according to ASTM D395-03
[53]. The test is used to determine the capability of rubber compounds and elastomers
in general to maintain their elastic properties after prolonged action of compression
stresses. According to Method A of ASTM D395 [53], this stress is applied by a
constant load.
The tester incorporates a spring with a calibration curve and is accurately calibrated
to have a slope of 70 ± 3.5 kN/m at 1.8 kN force. Spring deflection is indicated by
a vernier system with an accuracy of 0.05 mm applied directly to the moving plate.
The tester may be placed in an oven or in a cryogenic chamber to conduct tests in
the range of +70 ºC to 30 ºC as indicated by ASTM specifications.
Tests can be carried out under constant deflection Method B according to ASTM D395
[53], ISO 815 [48] and UNI 6121 [49]. This method applies a constant compression
stress to specimens having a diameter of 29 ± 0.5 mm or 13 ± 0.2 mm with a thickness
of 12.5 ± 0.5 mm or 6 ± 0.2 mm. After introduction of the specimens, the apparatus
is placed in a conditioning chamber for a preset time at a preset temperature. At the
end of the heating period, the final thickness of the specimen is measured.
1.11 Mould Shrinkage
Apparatus for the measurement of this property according to DIN 53464 [50] is
available from ATS FAAR (Table 1.8). Bertacchi and co-workers [54] reported on
computer-simulated mould shrinkage studies on talc-filled PP, glass-reinforced PA
and a PC/ABS blend.
1.12 Coefficient of Friction
This is an assessment of the coefficient of friction of materials in terms of dynamic
(sliding) friction against steel. Friction is influenced by temperature, surface
contamination and, most importantly, by the two material surfaces:
• An excellent rating indicates a low coefficient of friction.
• A very poor rating indicates a high coefficient of friction.
68
Miyata and Yamodka [55] used scanning probe microscopy (SPM) to determine the
micro-scale friction force of silicone-treated polymer film surfaces. Polyurethane (PU)
acrylates cured by an electron beam were used as polymer films. The micro-scale
friction force obtained by SPM was compared with macro-scale data, such as surface
free energy as determined by the Owens-Wendt method and the macro-scale friction
coefficient determined by the ASTM method. These comparisons showed a good linear
relationship between the surface free energy and friction force, which was insensitive
to the nature of polymer specimens or to silicone treatment methods. Good linearity
was also observed between the macro-scale and the micro-scale friction force. It was
concluded that SPM could be a powerful tool in this field of polymer science. Everar
and co-workers [56] reported coefficient of friction measurements for nitrile rubber.
Frictional properties of PA, polyacetals, PET/poly tetrafluoroethylene (PTFE) [33] as
well as polyesters and acrylics [353] have also been studied.
1.13 Fatigue Index
This is an assessment of the ability of materials to resist oscillating (or dynamic), load
or deflection-controlled deformation:
• An excellent rating indicates excellent resistance to fatigue loading.
• A very poor rating indicates poor resistance to fatigue loading.
ATS FAAR supply flexing machines (De Mattia) for the measurement of resistance
to dynamic fatigue to ASTM D430-95 [57] and ASTM D813-95 [58] (Table 1.9).
These test methods are utilised to test the resistance to dynamic fatigue of rubber-like
materials if subjected to repeated bending. The tests simulate the stresses in tension or
in compression of inflexion or in a combination of the three modes of load application
to which the materials will be subjected when in use.
The failure of tested specimens is indicated by cracking of the surface or, as prescribed
by ASTM D813 [58] specifications, by the dimensional increase of a nick made on
the specimen before starting the test. In the case of composite materials, the failure
can show up as separation of the different layers.
Lin and co-workers [59] also investigated the static tensile strength and fatigue
behaviour of long glass-fibre-reinforced semi-crystalline PA (Nylon 6,6) and
amorphous PC composites. The static tensile measurement at various temperatures and
tension-tension fatigue loading tests at various levels of stress amplitudes were studied.
The two-parameter Weibull distribution function and the pooled Weibull distribution
function was applied to obtain the statistical probability distribution of experimental
data of static tensile strength and fatigue life under different stress amplitude tests.
69
The increasing dynamic creep property and temperature under tension-tension
fatigue loading are compared between semi-crystalline and amorphous composites.
Results show that the static tensile strength of PA composites is higher than that of
PC composites, with lower fatigue life and more sensitivity to temperature. The slope
of S-N0 curves of long glass-fibre-reinforced semi-crystalline PA and amorphous PC
composites are almost identical.
Table 1.9 Instrumentation for measurement of dynamic fatigue
Method
ATS FAAR Apparatus
code number
Test suitable for meeting the
following standards
Resistance to dynamic
fatigue on bending
(De Mattia apparatus)
10.23000
10.23001
10.23003
ASTM D430 [57]
ASTM D813 [55]
Cold bend test (cables)
10.65053
ASTM D430 [57]
ASTM D813 [58]
1.14 Toughness
Toughness tests are traditionally carried out at 40 ºC (-40 ºF) or at 20 ºC (68 ºF).
This quantity is related to the notched Izod impact strength. It includes an assessment
of the overall fracture toughness of the polymer.
1.15 Abrasion Resistance or Wear
This is an assessment of the rate at which material is lost from the surface of the
specimen when abraded against a steel face. Wear rates are dependent upon numerous
factors, including contact pressure, relative velocity, temperature and initial surface
roughness. This rating considers the inherent ability of a material to resist wear:
• An excellent rating indicates excellent resistance to wear.
• A very poor rating indicates poor resistance to wear.
70
Table 1.10 Comparison of fatigue index, abrasion resistance and coefficient
of friction
Polymer
Type
Fatigue
Wear
Coefficient of
index
friction
LDPE
Crosslinked polyethylene
HDPE
Polypropylene
Polybutylene
Polymethyl pentene
Ethylene-propylene
copolymer
Styrene-ethylene-butylene
copolymer
High-impact polystyrene
Polystyrene
Epoxy resins
Acetal copolymer
Polyesters
Polybutylene terephthalate
Polyethylene terephthalate
Polyether ether ketone
Ethylene tetrafluoro ethylene
Polycarbonate
Polyphenylene oxide
Acrylonitrile-butadienestyrene terpolymer
Phenol-formaldehyde
Perfluoroalkoxy ethylene
Styrene-maleic anhydride
copolymer
Polymethylmethacrylate
Ethylene vinylacetate
copolymer
Polyamide 11
Polyamide 12
Polyamide 6,6
Polyamide 6,10
Polyamide 6
Polyamide 6,9
Polyamide 6, 12
Polyamide-imide
General
purpose (GP)
GP
GP
GP
GP
GP
GP
Very good
Poor
Very poor
Good
Very good
Excellent
Very good
Very good
Excellent
Good
Good
Good
Very good
Good
Good
Very poor
Good
Good
Very poor
Poor
Very poor
GP
Good
Good
Very poor
GP
GP
GP
GP
GP
GP
GP
GP
GP
GP
GP
30% glass
fibre-reinforced
GP
GP
GP
Poor
Good
Poor
Very good
Good
Good
Poor
Very good
Very good
Poor
Very poor
Poor
Very poor
Very poor
Good
Poor
Good
Good
Good
Poor
Poor
Very poor
Poor
Very poor
Very poor
Very poor
Very poor
Poor
Very poor
Good
Very poor
Poor
Good
Very poor
Poor
Very good
Poor
Good
Very poor
Very poor
Very poor
Poor
Very poor
GP
25% vinyl
acetate
GP
GP
GP
GP
GP
GP
GP
GP
Poor
Very good
Good
Poor
Very poor
Very poor
Very good
Very good
Very good
Very good
Very good
Very good
Very good
Poor
Good
Good
Good
Good
Good
Good
Good
Very good
Good
Good
Good
Good
Good
Good
Good
Poor
71
Polyimide
Polyetherimide
Polyurethane
Polyetherester amide
Urea formaldehyde
Styrene-acrylonitrile
copolymer
Acrylate-styrene-acrylonitrile
terpolymer
Polytetrafluoroethylene
Polyvinyl fluoride
Polyvinylidene fluoride
Perfluoroalkoxy ethylene
Ethylene chlorotrifluoroethylene
Fluorinated ethylene
propylene copolymer
Chlorinated PVC
Unplasticised PVC
Plasticised PVC
Polyphenylene sulfide
Polysulfone
Polyether sulfone
Silicones
GP
GP
GP
GP
Foam
High impact
Poor
Very poor
Excellent
Very good
Very poor
Very poor
Very good
Poor
Very good
Very good
Very poor
Very poor
Good
Poor
Very poor
Very poor
Very poor
Very poor
GP
Very poor
Very poor
Very poor
GP
GP
GP
20% glass
fibre-reinforced
Glass fibrereinforced
GP
Very good
Very good
Excellent
Good
Very good
Poor
Good
Poor
Excellent
Good
Very good
Good
Very good
Poor
Very good
Very good
Very poor
Poor
GP
GP
GP
Glass fibrereinforced
10% glass
fibre-reinforced
GP
GP
Very poor
Poor
Good
Poor
Poor
Poor
Poor
Good
Very poor
Very poor
Very poor
Poor
Poor
Good
Good
Very poor
Poor
Good
Very good
Good
Very good
Apparatus for the measurement of this property according to the DIN specification
is available from ATS FAAR (ATS FAAR apparatus code number 10.55000).
In Table 1.10 is recorded the fatigue index, abrasion resistance, and coefficient of
friction for a range of polymers. This information is useful if combined with the major
mechanical requirement of the polymer in reaching a decision on compromises that
need to be made when choosing a polymer that is suitable for a particular application.
Polymers which, for example, have a combination of a very good category for all
three characteristics include HDPE, various PA, PE, fluoroethylene and polyvinylidine
fluoride. Recent work on the measurement of mechanical properties of these properties
is reviewed in Table 1.11.
72
Table 1.11 Review of work on the determination of mechanical and thermal
properties of polymers
Polymer
Property discussed
Reference
Polylactic acid
Mechanical
[65]
Polyethylene
Mechanical
[66]
Polypropylene
Mechanical
[67, 68]
Ethylene-1-octene
Mechanical
[69]
Polypropylene
Mechanical and thermal
[70, 72, 77, 79]
Ethylene-vinyl acetate
[71]
High-density polyethylene
[72]
Polyimide-modified epoxy
[73]
High-impact polystyrene
[74]
Polypropylene wood composite
[75]
Polycarbonate
[76-79]
Polycarbonate diols
[80]
Poly(3-hydroxybutyrate-cohydroxyvalerate)
[81]
PVC-polymethylmethacrylate
blends
[82]
PVC-wood composites
[83]
Polyurethane
[84]
Epoxy resin
[95]
Polycarbonate-PVC blend
[86]
Polyethylene-ethylene vinyl
acetate mixtures
[87]
Polyethylene-lignin polyblends
[88]
Polystyrene
[89]
Polypropylene-low-density
polyethylene blends
[90]
Polyethylene
[91]
Bisphenol epoxy vinyl ester
[92]
Fibre-reinforced polypropylene
[93]
Fluorocarbon elastomer
[95]
Acrylic elastomer
[94]
Polymethylmethacrylate
[96]
Polyethylene-terephthalatepolybutylene terephthalate
blends
[97]
73
1.16 Effect of Reinforcing Agents and Fillers on Mechanical
Properties
Several typical reinforcing agents and filler have been used to improve or alter the
mechanical properties of polymers. These include glass fibre, glass beads, calcium
carbonate, minerals, mica, talc, clay, carbon fibres, carbon nanotubes, aluminium or
other metal powders, silica and silicones [80-94, 96].
1.16.1 Glass Fibres
1.16.1.1 Poly Tetrafluoroethylene
The incorporation of 25% of glass fibre increases the tensile strength from 25 MPa
to 180 MPa and the flexural modulus of PTFE from 0.07 GPa to 1.03 GPa while
reducing the elongation at break from 400% to 240%.
1.16.2 Polyethylene Terephthalate
Incorporation of 30% glass fibres increases the tensile strength of PET from 55 MPa
to 100 MPa and the flexural modulus from 2.3 GPa to 9.5 GPa while reducing the
elongation at break from 300% to 2.2%. Glass-filled PP has been the subject of several
studies involving tensile testing and the measurement of notched Izod impact strength.
Gupta and co-workers [97] observed a maximum improvement of the mechanical and
thermal properties in PP at 1% of a chemical coupling agent. However, deterioration
in impact strength and elongation at break occurred with increasing contents of glass
fibre in the polymer Type B in Table 1.12.
Other publications cover the effect of glass fibres on the mechanical and electronical
properties of epoxies [109, 110], the crystallinity of PA 6 [111] and the thermal
properties of PET [112].
74
Table 1.12 Effect of fillers on the mechanical properties of polymers
Polymer
Filler or nofiller (general
purpose)
Glass fibre
reinforcement
CaCO3
Mineral
Carbon
fibre
Aluminium
Silica
Silicone
lubricant
Type A improvement in tensile strength
PEEK
T = 92
F = 3.7
E = 50
I = 0.08
T = 151
F = 10.3
E = 2.2
I = 0.09
Polyamideimide
T = 18.5
F = 0.6
E = 12
I = 0.13
T = 195
F = 11.1
E=5
I = 0.10
PET
T = 55
F = 2.3
E = 300
I = 0.02
T = 100
F = 9.5
E = 2.2
I = 0.06
(30% glass)
PTFE
T = 25
F = 0.07
E = 400
I = 0.11
T = 180
F = 1.03
E = 240
(25% glass)
Nylon 6
T = 40
F=1
E=4
I = 0.25
T = 145
F = 1.6
E = 3.15
I = 0.6
PC
T = 65
F = 2.8
E = 110
T=
165
F = 13
E = 2.7
(30%
carbon
fibre)
Type B deterioration and impact strength
PI
T = 72
F = 2.46
E=8
I = 0.08
PP
T = 33
F = 1.5
E = 150
I = 0.07
T = 79
F = 132
E = 1.2
I = 0.24
(40% glass)
T = 2.6
F = 2.0
E = 80
I = 0.05
(20%
CaCO3)
75
Polyalkylphthalate
T = 70
F = 10.6
E = 0.9
I = 0.40
Epoxy
resins
T = 600
F = 80
E = 1.3
Acetal
T = 73
F = 2.6
E = 65
I = 0.06
T = 57
F = 9.5
E = 0.9
I = 0.35
(30%
mineral)
T = 68
F = 1.1
T = 58
F = 1.1
E = 0.8
T = 48
F = 9.5
E = 1.0
T=
72
F=
15
E=
1
T = 85
F=
17.2
E=1
I=
0.04
T = 55
F = 2.1
E = 50
I=
0.085
E: Elongation (%)
F: Flexural modulus (GPa),
I: Izod impact strength (kJ/m)
PC: Polycarbonate
PEEK: Polyether ether ketone
PET: Polyethylene terephthalate
PI: Polyimide
PP: Polypropylene
PTFE: Polytetrafluoroethylene
T: Tensile strength (MPa)
Some of these fillers or reinforcing agents (e.g., filler glass) improve the tensile strength
of the blend over that of the general glass-free polymer (Type A, Table 1.12). Glassfibre additions in general lead to an increase in the flexural modulus (or modulus of
elasticity) and a decrease in the elongation at break. In the case of other polymers
(Type B, Table 1.12), addition of fillers such as glass fibre and calcium carbonate
causes a distinct decrease in tensile strength (usually with an accompanying decrease
in flexural modulus, elongation and impact strength). Some particular examples of
these effects are discussed in more detail below.
The effects of fillers on mechanical properties are reviewed at Table 1.12.
1.16.2.1 Polyether Ether Ketone
As seen in Table 1.12, the incorporation of 50% glass fibre into polyether ether
ketone (PEEK) increases the tensile strength from 92 MPa to 151 MPa and increases
76
the flexural modulus from 3.7 to GPa 10.3 GPa while decreasing the elongation at
break from 50% to 2.2%.
1.16.2.2 Polyimide
In the case of polyimide, the incorporation of 40% glass fibre increases the flexural
modulus from 2.46 GPa to 132 GPa with hardly any effect on tensile strength. The
elongation at break falls from 8% to 1.2%.
1.16.2.3 Polyamide Imide
The incorporation of glass fibre increases the tensile strength of PA-imide from 18.5
MPa to 195 MPa (Table 1.2) and the flexural modulus from 0.6 GPa to 11.1 GPa
while the elongation at break falls from 12% to 5%.
The effect of glass beads on the mechanical properties of PP has been studied [114].
Various workers have studied the effect of glass fibres on the influence of various
factors such as melt temperature [351], weld line strength [352] and on annealing
[353] on glass-reinforced polymers.
1.16.3 Calcium Carbonate
Calcium carbonate has been used as a reinforcing agent for polyetherether ketone
[104], ABS terpolymer [85], PP [106], and PP-vinyl acetate (PPVA) copolymer [107].
Tang and co-workers [99] showed that the tensile modulus of the PPVA copolymer
increased with increase in filler weight fraction. The impact strength decreased rapidly
when the weight fraction of calcium carbonate fell below 10% and then decreased
gradually with increasing weight fraction of calcium carbonate.
1.16.4 Modified Clays
Various workers have investigated the mechanical and thermal properties of polymers
in which had been incorporated organically modified clays and Montmorillonites
(Table 1.13). In general, it was found that increasing the clay contents of a polymer
increased the storage and loss modulus as well as Young’s modulus and reduced
crystallinity. The glass transition temperature (Tg) increased and thermal stability
tended to improve.
77
Table 1.13 Influence of incorporation of organically modified clays and
montmorillonite nanocomposites in polymers
Polymer
Property investigated
Reference
A Montmorillonite
Polyurethane
Glass transition (Tg), particle
size, electrical
[334]
PVDF
Thermal
[335]
Polytrimethylene triphthalate
Heat stability, mechanical
[336]
Polyimide-amide
Rheological
[337]
Acrylonitrile-butadiene-styrene
Thermal
[338]
PE
Thermal
[339]
Polypropylene-ethylene-propylene diene
Mechanical and viscoelastic
[340]
Hydroxy benzoic acidhydroxynaphthoic acid copolymers
Thermal
[341]
LDPE
Rheological
[342]
Polyamide
Mechanical and rheological
[343]
Polystyrene nanocomposites
Thermal
[344]
B Organically modified clays
PLA
Rheological
[345]
PS
Rheological
[346, 347]
PE
Thermal
[278]
Ethylene-propylene diene elastomers
[279]
PP
[280]
PP
Viscoelastic
[281]
Maleic anhydride-based PP composites
Rheological
[282]
Epoxies
Thermomechanical
[283]
Nylon 12
Thermal and rheological
[284]
High-impact PS-PET nanocomposite
[285]
Fluroroelastomers
Thermal
[286]
LDPE = Low-density polyethylene
PE = Polyethylene
PLA = Polylactic acid
PP = Polypropylene
PS = Polystyrene
PVDF = Polyvinylidene fluoride
78
Clay-polyvinylidene fluoride composites have a significantly improved storage modulus
to the base polymer over the temperature range -100 ºC to 150 ºC [102]. Gupta and
co-workers [103] and Yan and co-workers [104] reported on the mechanical and
thermal behaviour of glass-fibre filled or glass bead-filled polyvinylidene-bentoniteclay nanocomposites, which were shown to have a significantly improved storage
modulus to the base polymers [95].
1.16.5 Polymer-silicon Nanocompsites
It has been found that the Tg of ABS, silica [145] and polymerthyl methacrylates silica
nanocomposites [146] increased with silica content. Also, the thermal properties
were enhanced. Thus, the degradation temperature at 10% weight loss was ~30 ºC
higher than that of pristine polymethyl methacrylate. Other properties that have been
studied include mechanical, viscoelastic, thermal and optical properties [136-144]
(Table 1.14).
Table 1.14 Properties of polymer-silica nanocomposites
Polymer
Property studied
Reference
Ethylene diamine and maleic
Mechanical
[147]
anhydride-grafted PP
Epoxies
[148]
PS
Viscoelastic
[149]
Polyacrylonitrile
Thermal
[150]
Poly(3,4 ethylene-dioxythiophene)
Optical
[151]
Phenylene-vinylene oligomers
Optical
[152]
PP
Crystallinity
[153]
PET
Crystallinity
[154]
1.16.6 Carbon Fibres
Various mechanical properties have been determined on carbon fibres epoxy
composites [155], as well as LDPE [156] and polyvinylidene fluoride [158].
79
Carbon fibre has been used in PC blends. For instance, 30% carbon fibre increased the
tensile strength of PC from 68 MPa to 165 MPa and increased the flexural modulus
from 2.8 GPa to 13 GPa while decreasing the elongation at break from 110% to
2.7%. Carbon fibre has also been used as a reinforcing agent in epoxy resins [106].
1.16.7 Carbon Nanotubes
As will be discussed in Chapter 3, the incorporation of carbon nanotubes into
polymers can have beneficial effects on electrical properties such as conductivity. The
measurement of mechanical properties of these polymers is reviewed in Table 1.15.
Table 1.15 Effect of carbon nanotubes on mechanical properties
Polymer
Property measured
Reference
Epoxy composites
Tensile and thermal
[159]
Epoxy matrices
[160]
Polyurethanes
[161]
Polyethylene composites Mechanical and rheological
[162]
Polyethylene glycol
Morphological and rheological
[163]
Polycaprolactone
Rheological
[164]
Nylon 10,10
[165]
PET
Crystallinity
[166]
PHB
Morphological and thermal
[167]
PC
Rheological
[168]
Polyetheramide and
Mechanical and electrical properties
[169]
epoxy resins
Epoxy resins
Mechanical and electrical
[170]
PEEK
Rheological and electrical
[171]
PI
Crystallinity
[172]
[173]
Polysilsesquioxane
Morphological and thermal
[174]
80
1.16.8 Miscellaneous Fillers/Reinforcing Agents
Natural materials that have been used to modify polymer properties include wood
sawdust [126, 127], coconut fibre [128] carbon fibres, [129], oat husks, cocao, shells
[130], sugarcane fibres, [131] and banana fibre [132]. Mohanty and co-workers [101]
observed a 70% increase in the flexural strength of polyorpylene to which had been
added 30% jute with a maleic anhydride-grafted PP coupling agent.
Other materials that have been incorporated into polymers to modify mechanical and
other properties include calcium sulfate in styrene-butadiene rubber [115]; barium
sulfate in PE [115] and PP; [116] talc in PP [117]; aluminium in epoxies [118];
kaolinile-muscovite in PVC-polybutyl acrylate [119]; aluminium in PE [120]; nickel
in epoxies [121]; copper in PE [122]; gold in PS [123]; caesium bromide in polyvinyl
alcohol [124]; nickel-cobalt-zinc ferrite in natural rubber [125]; and carbon black in
various polymers [133-134].
1.16.9 Test Methods for Fibre Reinforced Plastics
Sims [175] reviewed some UK contributions to the development of fibre-reinforced
plastics such as those used for glass reinforced plastic pressure vessels and pipes. He
also discussed the need for harmonising and validating the many variants of property
testing methods currently in use.
Sims [175] has pointed out that a redraft of ISO 527 tensile testing for plastics has
resulted in two complementary parts for composites: Part 4 based on ISO 3268 [176]
covers isotropic and orthotropic materials and Part 5 covers unidirectional materials
[175]. There is a need to harmonise these two methods into a new part 5. Inputs
were included from ISO, ASTM, CRAG and EN aerospace methods. The remaining
three parts are: Part 1 - general principles; Part 2 - plastics and moulding materials
(including short fibre-reinforced materials); and Part 3 - films. ISO DIS 527-5 has in
parallel been voted as a European Committee for Standardization (CEN) standard
(EN 527-5) and should, with part 4, replace EN61 [185] and possibly two Aerospace
EN standards [149-180].
Obtaining agreement between ISO, CEN General series, EN aerospace-carbon only,
ASTM and JIS in specimen sizes for unidirectional reinforced materials was a notable
first step towards harmonisation of the test methods, particularly because the 1.25
cm wide ASTM specimen [182] has been in extensive use for many years. The agreed
dimensions are 15 × 1 mm for 0º and 25 × 2 mm for 90º fibre direction specimens
[179]. After agreement on the specimen sizes (which is the same in all standards series
81
except EN Aerospace for glass-fibre systems [180]), several other aspects of the test
method were decided upon during drafting of the new standard.
A complete list of recommended mechanical test methods for fibre-reinforced plastics
has been reported [183-213].
1.17 Application of Dynamic Mechanical Analysis
1.17.1 Theory
Dynamic mechanical analysis (DMA) provides putative information on the viscoelastic
and rheological properties (modulus and damping) of materials. Viscoelasticity is the
characteristic behaviour of most materials in which a combination of elastic properties
(stress proportional to strain rate) are observed. DMA simultaneously measures the
elastic properties (modulus) and viscous properties (damping) of materials.
DMA measures changes in mechanical behaviour such as modulus and damping as a
function of temperature, time, frequency, stress, or combinations of these parameters.
The technique also measures the modulus (stiffness) and damping (energy dissipation)
properties of materials as they are deformed under periodic stress. Such measurements
provide quantitative and qualitative information about the performance of materials.
The technique can be used to evaluate elastomers, viscous thermoset liquids, composite
coatings and adhesives, and materials that exhibit time, frequency and temperature
effects or mechanical properties because of their viscoelastic behaviour.
Some of the viscoelastic and rheological properties of polymers that can be measured
by DMA are [223, 224, 354]:
• Modulus and strength (elastic properties)
• Viscosity (stress-strain rate)
• Damping characteristics
• Low- and high-temperature behaviour (stress-strain)
• Viscoelastic behaviour
• Compliance
• Stress relaxation and stress relaxation modulus
82
• Creep
• Gelation
• Projection of material behaviour
• Polymer lifetime prediction
Basically, this technique involves measurement of the mechanical response of a polymer
as it is deformed under periodic stress. It is used to characterise the viscoelastic and
rheological properties of polymers.
DMA is measurement of the mechanical response of a material as it is deformed
under periodic stress. Material properties of primary interest include modulus (E´),
loss modulus (E´´), tan δ (E´´/E´), compliance, viscosity, stress relaxation and creep.
These properties characterise the viscoelastic performance of a material.
DMA provides material scientists and engineers with the information necessary to
predict the performance of a material over a wide range of conditions. Test variables
include temperature, time, stress, strain and deformation frequency. Because of
the rapid growth in the use of engineering plastics and the need to monitor their
performance and consistency, DMA has become the fastest-growing thermal analysis
technique.
Recent advances in materials sciences have been the cause and effect of advances in
the technology of materials characterisation.
The theory of DMA has been understood for many years. However, because of the
complexity of measurement mechanics and the mathematics required to translate
theory into application, DMA did not become a practical tool until the late 1970s
when DuPont developed a device for reproducibly subjecting a sample to appropriate
mechanical and environmental conditions. The addition of computer hardware and
software capabilities several years later made DMA a viable tool for the industrial
scientist because it greatly reduced analysis times and labour-intensity of the technique.
DMA provides information on the viscoelastic properties of materials. Viscoelasticity
is the characteristic behaviour of most materials in which a combination of elastic
properties (stress proportional to strain) and viscous properties (stress proportional to
strain rate) are observed. DMA simultaneously measures elastic properties (modulus)
and viscous properties (damping) of a material. Such data are particularly useful
because of the growing trend towards the use of polymeric materials as replacements
for metal and structural applications.
83
The DuPont 9900 system controls the test temperature and collects, stores and analyses
the resulting data. Data analysis software for the DuPont 983/9900 DMA system
provides hardcopy reports of all measured and calculated viscoelastic properties,
including time/temperature superpositioning of the data for the creation of master
curves. A separate calibration programme automates the instrument calibration
routine and ensures highly accurate, reproducible results. In addition to measuring
the specific viscoelastic properties of interest, the four modes provide a more complete
characterisation of materials (including their structural and end-use performance
properties). The system can also be used to simulate and optimise processing
conditions, such as those used with thermoset resins.
The DuPont 983 DMA system can evaluate a wide variety of materials, ranging
from the very soft (e.g., elastomers, supported vicious liquids) to the very hard (e.g.,
reinforced composites, ceramics, metals). The clamping system can accommodate a
range of sample geometries, including rectangles, rods, films and supported liquids.
The DuPont 983 instrument produces quantitative information on the viscoelastic
and rheological properties of a material by measuring the mechanical response of a
sample as it is deformed under periodic stress.
1.17.2 Instrumentation (Appendix 1)
Seiko Instruments supplies the Exstar 6000 Series, DMM 6100 [225]. The instrument
can determine characteristics such as Tg damping intensity, heat resistance and creep
and stress relaxation of various materials. This allows the user to obtain complete
characterisation of a processed material. The instrument can also be used to evaluate
the compatibility, anisotropy, vibration absorbency, MW, degree of crystallinity and
degree of orientation of polymeric and elastomeric materials.
Recently introduced instruments from TA Instruments include the DMA Q800 analyser
[226, 227]. The instrument can be used for the testing of mechanical properties of a
broad range of viscoelastic materials at temperatures ranging from -150 ºC to 600 ºC.
The DMA Q800 system is claimed to provide unmatched performance in stress-strain
control and measurement. It uses a proprietary non-contact linear motor to provide
precise stress control and optical encoder technology for unmatched sensitivity and
resolution in strain deflection.
The Mettler-Toledo Incorporated SDTA 861 DMA analyser [235] can provide
measurements over wide frequency ranges (1 mHz to 1 kHz) and large dynamic
stiffness ranges. A schematic of the instrument is illustrated and examples represented
of test data for various rubbers obtained using this equipment. Other suppliers include
Rheometric Scientific and Thermocahn [229].
84
Arm-locking pins
Electromagnetic
driver
LVDT
LVDT adjustment screw
Flexure pivot
Sample arm
Slide lock
Sample
Mechanical slide
Vernier adjustment knob
Clamp
Control and sample
thermocouples
Figure 1.49 DMA Electromechanical System, linear variable differential
transformer. Source: Author’s own files
Figure 1.49 shows the mechanical components of the DuPont 983 DMA system. The
clamping mechanism for holding samples in a vertical configuration consists of two
parallel arms, each with its own flexure point, an electromagnetic driver to apply
stress to the sample, a linear variable differential transformer for measuring sample
strain, and a thermocouple for monitoring sample temperature. A sample is clamped
between the arms and the system is enclosed in a radiant heater and Dewar flask to
provide precise temperature control.
Easily interchanged clamp faces are designed to accommodate various geometries:
smooth and serrated faces for rectangular shapes and notched faces to hold cylinders
or tubing. A horizontal clamping system with smooth clam faces is available to hold
soft samples and supported liquids.
The sample is clamped between the ends of two parallel arms, which are mounted
on low-force flexure pivots, allowing motion in only the horizontal plane. The
distance between the arms is adjustable by means of a precision mechanical slide to
accommodate a wide range of sample lengths. An electromagnetic motor attached
to one arm drives the arm/sample system to a strain selected by the operator. As the
85
original sample system is displaced, the sample undergoes flexural deformation. A
linear variable differential transformer mounted on the driven arm measures the
response of the sample (strain and frequency) to the applied stress, and provides
feedback control to the motor.
The sample is positioned in a temperature-controlled chamber which contains a
radiant heater and a coolant distribution system. The radiant heater provides precise
and accurate control of sample temperature. The coolant distribution system uses
cold nitrogen gas for smooth, controlled sub-ambient operation and for quench
cooling at the start or end of a run. The radiant heater and the coolant accessory
are controlled automatically by the DuPont 983 system to ensure reproducible
temperature programming. An adjustable thermocouple, mounted close to the sample,
provides precise feedback information to the temperature controllers, as well as the
readout of sample temperature.
1.17.3 Fixed Frequency Mode
This mode is used for accurate determination of the frequency-dependence of materials
and prediction of end-use product performance. In the fixed frequency mode, applied
stress (i.e., force per unit area that tends to deform the body, usually expressed in
Pa (N/m)) forces the sample to undergo sinusoidal oscillation at a frequency and
amplitude (strain), i.e., deformation from a specified reference state, measured as the
ratio of the deformation to the total value of the dimension in which the strain occurs.
Strain is non-dimensional, but is frequently expressed in reference values (such as
percentage strain) selected by the operator. Energy dissipation in the sample causes
the sample strain to be out of phase with the applied stress (Figure 1.50a). That is,
the sample is viscoelastic, so the maximum strain does not occur at the same instant
as maximum stress. This phase shift or phase lag, defined as the phase angle (δ), is
measured and used with known sample geometry and driver energy to calculate the
viscoelastic properties of the sample.
The DuPont 983 analyser can be programmed to measure the viscoelastic
characteristics of a sample at up to 57 frequencies during a single test. In such
multiplexing experiments, an isothermal step method is used to hold the sample
temperature constant while the frequencies are scanned. The sample is allowed to
reach mechanical and thermal equilibrium at each frequency before data are collected.
After all the frequencies have been scanned, the sample is automatically stepped to
the next temperature and the frequency scan repeated. Multiplexing provides a more
complete rheological assessment than is possible with a single frequency.
86
1.17.3.1 Resonant Frequency Mode
This mode is used for detection of subtle transitions, which are essential for
understanding the molecular behaviour of materials and structure-property
relationships. Allowing a sample to oscillate at its natural resonance provides higher
damping sensitivity than at a fixed frequency, making possible detection of subtle
transitions in the material. Because of its high sensitivity, the resonance mode is
particularly useful in analysing polymer blends and filled polymers, such as reinforced
plastics and composites.
In the resonance mode, the DuPont 983 system operates on the mechanical principle of
forced resonant vibratory motion at fixed amplitude (strain), which is selected by the
operator. The arms and sample are displaced by the electromagnetic driver, subjecting
the sample to a fixed deformation and setting the system into resonant oscillation.
In free vibration mode, a sample will oscillate at its resonant frequency with decreasing
amplitude of oscillation (dashed line in Figure 1.50b). The resonance mode of the
DuPont 983 analyser differs from the free vibration mode in that the electromagnetic
driver puts energy into the system to maintain fixed amplitude (Figure 1.50b).
Phase angle (δ)
Fixed frequency
(a)
Stress (σ)
Stress
Strain
Strain (ε)
Time
87
(b)
Oscillation amplitude
Resonant frequency
Free vibration
983 DMA resonant mode
Time
Strain
recovery
t1
t2
t3
Time
88
t4
t5
Stress
Strain
Temperature
Temperature (°C)
Stress
t0
(c)
Stress relaxation
Strain
Temperature
Stress
Strain
Temperature (°C)
Creep
(d)
Strain
Stress
Strain
recovery
t0
t1
t2
t3
t4
t5
Time
Figure 1.50 Modes of operation in the DuPont 983 dynamic mechanical analyser.
The make-up energy, oscillation frequency and sample geometry are used by the
DMA software to calculate the desired viscoelastic properties.
1.17.3.2 Stress Relaxation Mode
Stress relaxation is defined as a long-term property measured by deforming a sample
at a constant displacement (strain) and monitoring decay over a period of time. Stress
is a very significant variable that can dramatically influence the properties of plastics
and composites.
Induced stress is always a factor in structural applications, and can result from
processing conditions, thermal history, phase transitions, surface degradation and
variations in the expansion coefficient of components in a composite. The modulus
of a material is not only temperature-dependent but also time-dependent, so the
stress relaxation behaviour of polymers and composites is of great importance to
the structural engineer. Stress relaxation is also important to the polymer chemist
developing new engineering plastics because relaxation times and moduli are affected
by polymer structures and transition temperatures. Therefore, it is essential that
89
polymeric materials that will be subjected to loading stress be characterised for stress
relaxation and creep behaviour.
Figure 1.51 shows the stress relaxation curves obtained for PC. The large drop in the
modulus of the material >130 ºC is caused by the increased mobility of the polymer
molecules as the Tg is approached.
The stress relaxation mode is used for measurement of ultra low-frequency relaxation in
polymers and composite structures (a primary indicator of the long-term performance
of materials). This mode of operation provides definitive information for prediction
of the long-term performance of materials by measuring the stress decay of a sample
as a function of time and temperature at an operator-selected displacement (strain).
Figure 1.50c is a schematic representation of the process of measuring stress relaxation
in a viscoelastic material. Using an isothermal step method, the sample is allowed to
equilibrate at each temperature in an unstressed state. The sample is then stressed
to the selected strain. The amount of driver energy (stress) required to maintain that
displacement is recorded as a function of time for a period selected by the operator.
After the measurements are recorded, the driver stress is removed and the sample is
allowed to recover in an unstressed state. This sample recovery (strain) can be recorded
as a function of time for a period selected by the operator. If the measurements at one
temperature are complete, the temperature is increased and the experiment repeated.
1.17.3.3 Creep Mode
Creep is defined as a long-term property measured by deforming a sample at a constant
stress and monitoring the flow (strain) over a period of time. Viscoelastic materials
flow or deform if subjected to loading (stress). In a creep experiment, a constant stress
is applied and the resulting deformation measured as a function of temperature and
time. Just as stress relaxation is an important property to structural engineers and
polymer scientists, so is creep behaviour.
The elastic modulus is a quantitative measure of the stiffness or rigidity of a material.
For example, for homogeneous isotropic substances in tension, the strain (ε) is related
to the applied stress (o′) by the equation E = o′/ε, where E is defined as the elastic
modulus. A similar definition of shear modulus (g) applies if the strain is shear.
For a PEEK laminate below the Tg, the laminate exhibits <2% creep, whereas above
the Tg creep increases to >10%.
90
16
14
(–) Percent creep
12
310 ºC
Mode: Creep
Size: 35.90 × 12.43
× 1.00 mm
10
270 290
170 190 210 230
250
150
8
6
130
4
2
110
90
0
0
200
400
600
800
1000
1200
1400
Time (min)
Figure 1.51 Stress relaxation modulus of PC. Source: Author’s own files
The thermal curve in Figure 1.52 shows the flexural storage modulus-and-loss
properties of a rigid pultruded oriented-fibre-reinforced vinyl ester composite. The
flexural modulus and Tg increase dramatically with post-curing, so the test can be used
to evaluate the degree of cure, as well as to identify the high-temperature mechanical
integrity of the composite.
The creep mode is used for the measurement of flow at constant stress to determine
the load-bearing stability of materials, which is a key to prediction of product
performance. The creep mode is used to measure sample creep (strain) as a function
of time and temperature at a selected stress. Using the isothermal step method,
the sample is allowed to equilibrate at each temperature in a relaxed state. After
equilibration, the sample is subjected to a constant stress (Figure 1.52). The resulting
sample deformation (strain) is recorded as a function of time for a period selected by
the operator. After the first set of measurements is made, the driver stress is removed
and the sample is allowed to recover in an unstressed state. Sample recovery (strain)
can be recorded as a function of time for any desired period. If the measurement at one
91
temperature is complete, the temperature is changed and the measurement repeated.
Creep studies are particularly valuable for determining the long-term flow properties
of a material and its ability to withstand loading and deformation influences.
50
50
40
40
1st temperature scan
(undercured as received)
30
2nd temperature scan
(post cured on 983 DMA
during 1st scan)
30
20
20
10
10
0
50
70
90
110
130
150
170
190
210
230
250
(– – –) E flexural storage modulus (GPa)
(– – –) E flexural storage modulus (GPa)
Amplitude (p–p) = 0.20 mm
0
Temperature (ºC)
Figure 1.52 Flexural storage modulus-and-loss properties of rigid extruded
oriented fibre reinforce vinyl ester composites. Source: Author’s own files
Whereas elastic modulus at a single temperature (as measured by a static-mode
instrument) is indicative of the properties and quality of metals, this is not necessarily
true of polymeric materials in which molecular relaxations dramatically influence
the temperature and time (reciprocal frequency) dependences of material properties.
DMA is the preferred tool for evaluation of the effects of the following variables on
the mechanical properties of materials:
• Temperature: Temperature scanning can determine if product performance will
remain within the specifications at end-use temperatures.
92
• Frequency (1/time) deformation: Frequency sweeps can be used to study the
frequency dependence of material properties.
• Load: Creep and stress relaxation measurements can determine the long-term
mechanical properties of materials and their ability to withstand loading and
deformation influences.
The DuPont 983 DMA is a versatile laboratory instrument for characterising the
viscoelastic and rheological behaviour of materials. Various applications of DMA are
reviewed in Sections 1.17.2.5-1.17.2.17. Various applications of DMA are reviewed
below.
1.17.3.4 Projection of Material Behaviour using Superpositioning
The effects of time and temperature on polymers can be predicted using timetemperature superpositioning principles. The latter are based upon the premise that
the process involved in molecular relaxation or rearrangements occur at greater rates
at higher temperatures. The time over which these processes occur can be reduced by
conducting the measurement at elevated temperatures and transposing the data to
lower temperatures. Thus, viscoelastic changes that occur relatively quickly at higher
temperatures can be made to appear as if they occurred at longer times simply by
shifting the data with respect to time.
Viscoelastic data can be collected by condcuting static measurements under isothermal
conditions (e.g., creep or stress relaxation) or by undertaking frequency multiplexing
experiments in which a material is analysed at a series of frequencies. By selecting
a reference curve and then shifting the other data with respect to time, a ‘master
curve’ can be generated. A master curve is of great value because it covers times or
frequencies outside the range readily accessible by experiment.
Figure 1.53a shows the DMA frequency multiplexing results for an epoxy/fibreglass
laminate. The plot shows the flexural storage modulus (E´) and the loss modulus
(E´´) as a function of temperature at various analysis frequencies. The loss modulus
peak temperatures show that the Tg moves to higher temperatures as the analysis
frequency increases. Through suitable calculations, the storage modulus data can
be used to generate a master curve (Figure 1.53b). The reference temperature of
this is 125 ºC and shows the effects of frequency on the modulus of the laminate
at this temperature. At very low frequencies (or long times), the material exhibits a
low modulus and would behave similarly to a rubber. At high frequencies (or short
times), the laminate behaves like an elastic solid and has a high modulus. This master
curve demonstrates that data collected over only two decades of frequency can be
transformed to cover more than nine decades.
93
10
1.4
(––––) Flexural storage modulus (GPa)
1.2
8
1.0
7
0.8
Mode: Fixed frequency
(0.1, 0.32, 1.0, 3.2, 8.0 Hz)
6
5
0.6
4
0.4
3
0.2
2
1
80
90
100
110
120
130
140
150
(– – –) Flexural storage modulus (GPa)
(a)
9
0.0
Temperature (°C)
10
(b)
9
8
Log [E (Pa)]
7
6
5
4
3
2
1
–6
–4
–2
0
2
4
6
Figure 1.53 Dynamic mechanical analysis (a) frequency multiplexing results for an
epoxy/fibreglass laminate; and (b) the master curve generated from fixed frequency
multiplexing data for epoxy fibreglass laminate. Source: Author’s own files
94
Example of the practical uses for superpositioning are:
• Gaskets: To measure flow (creep and stress relaxation) effects, which reduce seal
integrity over time.
• Force-fit of snap parts: To measure stress relaxation effects, which can lead to
joint failure.
• Structural beams: To measure modulus drop with time, which leads to increasing
beam deflection under load over time.
• Bolt plates: To measure the creep of the polymer, which reduces the stress applied
by the fastener.
• Hoses: To measure the creep of the polymer, which can lead to premature rupture
of the hose.
• Acoustics: To aid in the selection of materials that exhibit high damping properties
in specific frequency ranges.
• Elastomeric mounts: To assess the long-term creep resistance of mounts used for
vibration damping with engines, missiles and other heavy equipment.
• Structural parts: To measure high deformation frequencies, which cause shifting
of molecular transitions to high temperatures and can result in impact failure or
microcracking.
1.17.3.5 Prediction of Polymer Impact Resistance
Impact resistance is critical in the end uses of many commercial plastic products.
Measurement of impact properties, however, requires lengthy sample preparation
and is often irreproducible. For example, the ASTM drop weight (falling dart)
impact (DWI) method D5420 [40] and D5628 [41] requires an impact measurement
on as many as 30 samples. Each sample must be prepared by high-quality injection
moulding, followed by temperature conditioning at -29 ºC for 24 hours.
Low-temperature loss peak measured by DMA correlates with the ASTM DWI
values. DMA values are more precise than DWI measurements, so as few as four
determinations can be used to rank impact resistance. Sample preparation for DMA
is not lengthy and does not require sophisticated processing equipment because
surface effects are not critical and smaller samples are used. Figure 1.54 shows the
comparative DMA profiles for a series of impact-modified PP. The intensity of the
damping peak at -110 ºC correlates well with the DWI values at -29 ºC. Using these
95
types of data, a suitable calibration curve can be developed so that future formulations
can be rapidly screened by DMA.
1.17.3.6 Effect of Processing on Loss Modulus
PEEK is an important matrix material for thermoplastic composite applications. The
properties of PEEK laminate depend primarily on this morphology developed during
processing. Cooling rate, time in the melt, and sub-melt annealing are all critical
processing variables that can be simulated and the effects of changes immediately
evaluated by DMA. Figure 1.55 illustrates, for example, the effects of cooling rate
on loss modulus results. The peak maximum temperature, reflective of the Tg of the
matrix, increases significantly as the cooling rates is decreased. The magnitude of the
loss peak decreases and the peak width increases significantly as the cooling rate is
decreased. These changes in the loss modulus Tg peak can be explained in terms of
increased free volume as well as decreased level of crystallinity as the cooling rates
increase. A very fast cooling rate results in greater free volume in the amorphous
phase and imparts greater mobility to the polymeric backbone. A decrease in the
matrix crystalline content also results in greater mobility when passing through the Tg.
0.04
6
Tan δ
5
4
0.03
3
Impact resistance
DWI at –29 ºC
Curve J
1
2.4
2
7.2
3
17.2
4
27
5
60
6
>61
2
1
0.02
–130
–90
–50
–10
Temperature (°C)
Figure 1.54 Prediction of polymer impact resistance. Comparative dynamic
mechanical analysis profiles for a series of impact-modified PP.
96
Mode: Flxed frequency (1.0 Hz)
3.0
Flexural loss modulus (GPa)
A
A – “Quick cooled”
B – 20 ºC/min
C – 5 ºC/min
D – 2 ºC/min
E – Standard processing
2.5
B
2.0
C
D
1.5
E
1.0
0.5
120
130
140
150
160
170
180
190
200
210
Temperature (°C)
Figure 1.55 Effect of polymer processing on loss modulus by dynamic mechanical
analysis. Effect of cooling rate of PEEK composite loss modulus at the Tg.
1.17.3.7 Material Selection for Elevated-temperature Applications
The task of evaluating new materials and projecting their performance for specific
applications is a challenging one for engineers and designers. Often, materials are
supplied with short-term test information such as deflection temperature under load
(DTUL) (ASTM D648) [356], which is used to project long-term, high-temperature
performance. However, because of factors such as polymer structure, filler loading and
type, oxidative stability, part geometry and moulded-in stresses, the actual maximum
long-term use temperatures may be as much as 150 ºC below or above the DTUL.
DMA continuously monitors material modulus with temperature and hence provides
a better indication of long-term elevated-temperature performance.
Figure 1.56 illustrates the DMA modulus curves for three resins with nearly identical
DTUL: a PET, a polyethersulfone and an epoxy. The PET begins to lose modulus
97
rapidly at 60 ºC as the material enters the glass transition. The amorphous component
of the polymer achieves an increased degree of freedom and, at the end of the Tg,
the modulus of the material has declined by ~50% from room-temperature values.
Because of its crystalline component, the material then exhibits a region of relative
stability. The modulus again drops rapidly as the crystalline structure approaches the
melting point. Because the Tg in a semi-crystalline thermoplastic is 150 ºC below its
melting point, the actual modulus of a resin of this type at the DTUL is only 10-30%
of the room-temperature value. The DTUL of highly filled systems based on these
resins is more closely related to the melting point than to the significant structural
changes associated with the Tg.
18
Epoxy
16
14
[–––] E′ (GPa)
12
10
PES
8
PET
DTUL
218 °C
6
DTUL
224 °C
4
2
DTUL
218 °C
0
0
50
100
150
200
250
300
Temperature (°C)
Figure 1.56 Comparison of DTUL and DMA results. Source: Author’s own files
1.17.3.8 Storage Modulus
One of the values obtained in a DMA is the storage modulus which approximately
quantifies the flexural or tensile strength of a material. Figure 1.57 shows the
98
modulus of some common materials analysed over three decades of frequency using
the frequency scan mode. In this mode, the temperature is held constant and the
frequency at which the sample is oscillated is scanned from low to high, or from
high to low, frequencies.
In polymer materials exhibiting viscoelastic behaviour, the modulus and viscosity are
dependent upon the frequency of the DMA measurement. This frequency dependence
is quite different for materials with different degrees of molecular branching,
crosslinking, or MW distribution. The use of DMA in the frequency scan mode
of operation is particularly important in material analysis because these types of
molecular differences are very difficult to distinguish using any other thermal analysis
techniques. For example, a frequency scan can show clear differences between PE
samples having a difference in average MW of only a few percent.
The effect of frequency on materials and the corresponding rate dependence of
materials on it can supply additional information about the viscoelastic characteristics
of a polymer.
When frequency is being scanned, small differences in MW (and the distribution of
MW) can be detected by shifts in the viscosity and modulus curves.
Storage modulus data have been reported for PP-wood composites [234], basalt
fibre-reinforced PP [237], ethylene-propylene-diene terpolymer [238], polyvinyl
fluoride-clay nanocomposites [239] thermosetting resins [240] and water-based
adhesives [235, 236].
1.17.3.9 Frequency Dependence of Modulation and Elasticity
As shown in Figure 1.58, the frequency dependence of modulus and viscosity can be
measured at different temperatures through the Tg to predict long-term behaviour of
polymers. This information can be used to calculate how the polymer will perform
over long durations at various temperatures and mechanical stress.
99
1212
1011
Steel alloy
10
10
Modulus (Pa)
109
PTFE (25°C)
108
107
Chocolate (–5°C)
106
105
104
Uncured rubber
PDMS (20°C)
103
102
101
Frequency (Hz)
101
Figure 1.57 Examples of modulus range. Source: Author’s own files
1011
1011
PC Board 130°C
125°C
10
9
130°C
135°C
1010
145°C
108
109
107
10–2
10–1
100
101
Frequency (Hz)
Figure 1.58 Viscoelastic behaviour through the Tg of epoxy PC board.
100
Modulus (Pa)
Viscosity (Pa.s)
1010
1.17.3.10 Elastomer Low Temperature Properties
Flexibility is an important end-use property for elastomers. The Tg (which is the
point at which an elastomer (on cooling) goes from a flexible more rubber-like form
to a more rigid inflexible form) is a critical parameter in determining the suitability
of the elastomer for specific applications. Plots of flexural storage modulus (in GPa)
versus specimen temperature by DMA are very useful in evaluating the stiffness and
flexibility of polymeric materials.
1.17.3.11 Tensile Modulus
The tensile modulus of poly-p-phenylene [230], relaxation modulus in LDPE
[231], diglycidyl ether bisphenol A epoxy resins [232] and styrene-butadiene block
copolymers with doped polyaniline [233] has been determined by DMA.
1.17.3.12 Stress-strain Relationships
Choosing the best conditions of dynamic stress and strain is often difficult if creating
mechanical analysis methods for a series of samples. Sample behaviour will often
change if the stress or strain imposed on a sample is increased or decreased, so a
curve of stress versus strain is very valuable. The Newtonian or linear region for a
material can be measured with the stress scan mode of the DMA. This is the region
in which quantitative data can be obtained.
The stress scan (dynamic stress (10,000 Pa) versus strain (%)) of an unvulcanised
rubber material depicted the linear region of this material to be within 0.8-0.27%
strain and 2,000-4,200 Pa stress. Without this capability, this linear region of stress
and strain can only be approximated.
Stress-strain curves have been reported for PE [241], PC [241], PA [241], polybutylene
phthalate [250] and styrene-butadiene block copolymers [242].
A stress scan (i.e., dynamic stress (Pa) versus strain (5%) plots) will show the effect
of increasing stress on a polymer. There is usually an initial region in which the strain
is proportional to stress. Then, with increasing strain there can be deviations from
linearity due to various molecular effects. Calculations can determine proportional
limits, yield modulus, draw strength and ultimate modulus.
Kim and White [243] used DMA to study the stress relaxation behaviour of 3501-6
epoxy resin during cure.
101
Specimens were tested at several cure states to develop master curves of stress
relaxation behaviour during cure. Using the experimental data, the relaxation modulus
was then modelled in a thermorheologically complex manner. A exponential series
was used to describe the relaxation times. Shift functions used to obtain reduced
times were empirically derived based on curve fits to the data. The data showed
that the cure state had a significant effect on the stress relaxation of epoxy resin.
Furthermore, the relaxation behaviour above gelation was shown to be quite sensitive
to the degree of cure.
Venneman and co-workers [244] reported the results of a study of the elastomeric
properties of thermoplastic elastomers determined using temperature scanning
stress relaxation analysis and recoverable strain after hysteresis. The thermoplastic
elastomers tested were styrene-ethylene/butylene-styrene-based thermoplastic
elastomers blended with PP, polyphenylene ether (PPE) and PPE/PA 12.
1.17.3.13 Viscosity
Sepe [240] showed that DMA allows the modulus and viscosity of a polymeric
thermoset resin to be calculated, making it possible to follow crosslinking process
by continuously monitoring these properties as the sample is heated.
Various workers [245-248] have discussed the application of DMA to the study
of aspects of viscosity, elasticity and morphology. Bouton and Rheo [249] studied
viscosity effects in blends of PC with styrene-acrylonitrile and ABS terpolymer.
1.17.3.14 Miscellaneous Applications of Dynamic Mechanical Analysis
DMA has also been used to determine the mechanical and thermal properties of
LDPE and ethylene-propylene diene terpolymer containing jute filler, which had
improved flexural and impact properties to those of the base polymer [280]. Jeong
and co-workers [251] investigated the dynamic mechanical properties of a series of
polyhexamethylene terephthalate, poly (1,4-cyclohexylenedimethylene terephthalate)
and random copolymers thereof in the amorphous state as a function of temperature
and frequency. The effect of copolymer composition on dynamic mechanical properties
was examined and the dynamic mechanical properties interpreted in terms of the
cooperativity of segmental motions.
Costa and co-workers [252] characterised polimides using gel permeation
chromatography, differential scanning calorimetry (DSC), DMA optical microscopy
and small- and wide-angle X-ray scattering. Stability of liquid crystalline phases
102
was discussed with respect to the number of ethylene oxide units and enthalpies of
transition between crystalline and liquid crystalline phases as well as between liquid
crystalline and isotropic liquid phases. The technique has also been applied to the
study of thermal properties of epoxy-bis maleimide composites [253], the dynamic
mechanical and thermal properties of maleic anhydride-treated jute HDPE composites
[254], the curing behaviour and viscoelastic properties of epoxy-anhydride networks
[255] and the mechanical alpha- and gamma-relaxation process of short-chain PE
[256].
1.18 Rheology and Viscoelasticity
There are several rheological studies specific to particular polymers. These include
dynamic rheological measurements and capillary theometry of rubbers [257],
capillary rheometry of PP [258], degradation of PP [259], torsion rheometry of PE
[260], viscosity effects in blends of PC with styrene-acrylonitrile and ABS [249], peel
adhesion of rubber-based adhesives [261] and the effect of composition of melamineformaldehyde resins on rheological properties [262].
As discussed in Section 1.17, DMA offers an enhanced means of evaluating the
performance of polymeric systems at elevated temperatures. It provides a complete
profile of modulus versus temperature as well as measurement of mechanical damping.
Operating in the creep mode and coupled with the careful use of time-temperature
superpositioning, projections can be made regarding the long-term time-dependent
behaviour under constant load. This provides a much more realistic evaluation of the
short- and long-term capabilities of a resin system than the values of DTUL.
Rheology is concerned with the flow and deformation of matter. Viscoelastic properties
are more concerned with the flow and elasticity of matter.
Numerous references to rheology and viscoelasticity occur. Thus, 250 references have
been identified in the five-year period between 2004 and 2008.
In addition to various moduli (storage, loss, loss shear, plateau) the following
rheological properties of polymers can be determined by a range of techniques:
• Creep and stress relaxation
• Shear stress
• Stress relaxation behaviour
• Order-disorder transitions
103
• Shear rate dynamic viscosity
• Molecular entanglement
• Creep strain
• Tg
• Melt fracture
• Frequency dependence on dynamic moduli
• Clamping function of shear
Particular applications of the techniques in studies of the viscoelastic and rheological
properties of polymers are reviewed in Table 1.16.
Table 1.16 Measurement of rheological and viscoelastic properties of
polymers
Polymer
Property measured
Technique
Reference
LLDPE
Storage modulus (alpha Effects of β
[263]
relaxation)
irradiation
PS
Storage shear modulus DMTA
[264]
PBT and polyethylene
Stress relaxation
Instron tester
[274]
naphthalate
behaviour
Polyvinyl alcohol
Storage modulus
[265]
hydrogels and ferrogels
PEEK (fibre-reinforced) Specimens loaded in
DMA
[266]
flexure
Poly(styrene-butadiene- Order transition
Dynamic
[267]
isoprene)
mechanical
spectroscopy
PMMA and LDPE
Shear modulus and
Broadband
[268]
clamping
viscoelastic
spectroscopy
Polybutadienes
Zero shear rate
GPC, FTIR,
[269]
dynamic viscosity and
rheometry
Tg
104
Poly(phenylene
sulfide)-Fe3O4 magnetic
composite
Tg, steady state shear
deformation
DSC, DMA,
TGA
[270]
Ethylene-propylene
random copolymer
Plateau modulus and
entanglement
GPC, DSC,
oscillatory
rheometry
[271]
PP nanopolymer
Structure and
viscoelastic properties
X-ray
diffraction,
DMA, TGA
[272]
LLDPE
Creep strain stress
relaxation
DSC
[273]
Polyethylene oxidepolypropylene oxide
Steady-state shear and
oscillatory shear
-
[274]
Branched polystyrenes
Entanglements
Oscillatory
shear
measurement
[275, 276]
Tetrafluoroethylenehexafluoropropylene
copolymer
Zero shear rate
viscosity
Linear
rheological
properties
[277]
Poly(Nvinylpyrrolidone-codimethethylaminopropylmethacrylamide)
Radii of gyration
GPC, multiangle light
scattering
[278]
Polyvinyl acetate
Apparent viscosity,
viscous flow activation
energy
Viscometry
[279]
Lightly crosslinked
acrylic networks
Bulk rheological
properties, elastic
modulus, resistance
to interfacial crack
propagation
Dynamic
mechanical
spectroscopy
[280]
Polyethylacrylates
Zero rate shear,
viscosity dependence
Rheometric
measurements
[281]
Polyalkylether ketone
and polyaryl ether
ketone
Dynamic rheological
Viscosity
behaviour in oscillatory composition
shear mode
studies
[282]
105
PVDF
Shear rate
Apparent
viscosity,
activation
energy
[283]
PP modified by
ultrasonic waves
Structure of modified
PP
High-intensity [284]
ultrasonic wave
studies
Chlorinated
polyethylene/natural
rubber blends
Viscoelastic changes
and thermal
degradation
-
[284]
DMA = Dynamic mechanical analysis
DMTA = Dynamic mechanical thermal analysis
DSC = Dynamic scanning calorimetry
FTIR = Fourier-transform infrared spectroscopy
GPC = Gel permeation chromatography
LLDPE = Linear low-density polyethylene
PMMA = Polymethylmethacrylate
TGA = Thermogravimetric analysis
1.19 Physical Testing of Rubbers and Elastomers
A wide variety of physical tests are available for rubbers and elastomers (Table 1.17).
1.19.1 Measurement of Rheological Properties
Negretti Automation offers a range of rheological testing instruments for rubber
elastomers. Probably the top-of-the-market instrument is the THS rheometer. This
is a unique and versatile instrument offering a complete characterisation of flow
behaviour of a polymer in the unvulcanised state. Variable shear rates between 0.1/s
and 100/s are available using a die and rotor principle with a preheated chamber. A
typical curve obtained with this instrument is illustrated in Figure 1.59, which shows
the curve obtained in the measurement of rheological behaviour.
106
Table 1.17 Physical testing of rubbers and elastomers
Properties measured
Instrument
Testing
Supplier
to the
following
standards
Notes
Rheology
Measurement of
THS Rheometer
processability and
rheological behaviour
of raw (unvulcanised)
elastomers at variable
shear rates and
temperatures (viscosity and
elasticity)
BS EN ISO
9001 [287]
Negretti
Automation
Oscillating disc
rheometry. Full analysis of
vulcanisation curing
Rheo-Check 100C
BS
Barco
ASTM
Rheomicrocomputer ISO
package
Negretti
Automation
Oscillating die rheometer
Oscillating die
rheometer
BS
ASTM
ISO
Gibitre, Italy,
available from
Negretti
Automation
Mark III Mooney
viscometer
BS
ASTM
ISO
NFT
DIN
JIN
Negretti
Automation
Mark 8 Mooney
viscometer
BS
ASTM
ISO
NFT
DIN
JIN
Negretti
Automation
Viscometry
Viscosity measurement of
rubbers and elastomers
Weight-density-volume
variation
Balance check
and Rapid Direct
Reading density
check
Gibitre, Italy,
available from
Negretti
Automation
Hardness
IRHD Micro
durometer and
durometer support
Gibitre, Italy,
available from
Negretti
Automation
107
Brittleness point
Low temperature
brittleness check
ASTM
D1329 [288]
Gibitre, Italy,
available from
Negretti
Automation
and ATS
FAAR
Code
Nos.
10.2900
10.29005
10.12010
Ross flexing test
Measurement of
cut growth when
subject to repeat
bend flexing
ASTM
D1052 [289]
ATS FAAR
De Mattia type flexing test
De Mattia type
dynamic testing
machine
ASTM
DIN
Gibitre, Italy,
available from
Negretti
Automation
Mechanical properties
Yersley mechanical
oscillograph
ASTM D945
[290]
ATS FAAR
Resilience
Universal tensile testing
Mechanical stability of
natural and synthetic
lattices
Abrasion test
Peel adhesion test
Ozone degradation test
Ozone check
IRHD = International rubber hardness degrees
108
Gibitre, Italy,
available from
Negretti
Automation
and ATS
FAAR
Code no.
10.64002
Code no.
16.65100
B
Shear stress (kPa)
C
A
Time
Figure 1.59 Characterisation of polymer flow behaviour with a TMS rheometer
showing: (A) viscosity at very low shear rates, the stress measured is a function of
viscosity; (B) transient flow-step changes from low the high shear rates generate
a peak stress value which is a product of the thixotropic and structural features
of the sample; and (C) elasticity - high shear rates produce results that represent
elastic behaviour. Source: Author’s own files
The Rheocheck 100C is a classic oscillating disc rheometer offering a full analysis of
the vulcanisation curve with pre-set limits for quality-control purposes. It is available
from the standard cost-effective computer/printer/plotter package. The instrument
can be extended to include a Mooney viscometer.
The Barco Rheomicro computer package enables existing oscillating disc rheometers
to be converted to a powerful dynamic testing system.
The Gibitre oscillating die Rheocheck system available from Negretti Automation
is a moving die rheometer that enables the vulcanisation curve for any compound
to be produced rapidly at closely controlled temperatures. It is designed for rapid
computer-controlled quality checks in a production environment.
109
1.19.2 Viscosity and Elasticity
Depending upon temperature, shear rate and other flexural factors, the elements
of viscosity and elasticity impose a varying influence on processing behaviour.
A rheometer measures these in isolation in a single test, allowing prediction of
processing behaviour at an early stage. It also allows close control of raw polymers
of nominally identical specification from various sources, which often behave very
differently when processed.
Negretti Automation supplies the Negretti Mooney viscometer which meets the
requirements of all international standards. It is available with a digital control unit
and recorder to provide semi-automatic operation.
In this instrument, the viscosity of a material is derived by measuring the torque
required to rotate a disc squeezed between two samples of material at a defined
pressure. The diagram of the system (Figure 1.60) shows how the presence of the
sample around the shearing rotor causes a breaking reaction which can be measured
as a thrust against the calibrated U-beam. The net displacement of the U-beam (which
is proportional to the torque required to keep the rotor turning) is measured directly
on a gauge and can also be plotted on a chart recorder. The results are read or plotted
directly in Mooney units, which are universally used for viscosity measurement in
the rubber industry.
In accordance with the standards, the sample is preheated for a set time to a
temperature suitable for the test. For example, viscosity may be measured at 100 ºC,
whereas scorch tests normally use a higher temperature, typically 125 ºC.
In the mechanical layout of the viscometer (Figure 1.60), the rotor is driven by the
motor through the gear train and worm wheel. The axle carrying the ‘worm’ can
move laterally in the direction of the arrow. When the motor is started with the rotor
surrounded by a sample, rotation is resisted by the viscosity of the material. As a
result, the worm rotates against the worm wheel and tries to move in the direction
of the arrow. This movement is resisted by the U-beam and eventually the rotor is
forced to turn.
The deflection of the U-beam is related to the torque required to turn the rotor and
thus to the viscosity of the sample. The deflection can be read directly on the gauge,
which is calibrated in Mooney units. It can also control the linear deflection transducer
whose output drives a chart recorder.
Negretti Automation also supplies the Negretti Mark 8 Mooney viscomer which is a
computer-controlled instrument offering improved temperature control, repeatability,
hard copy of results, statistical memory and peripheral computer interface.
110
Rotation
Shearing
rotor
Worm and
worm wheel
Drivemotor
Resultant
thrust
Transducer
Calibrated
U-beam
Figure 1.60 Working details of a Negretti Mark 3 Mooney viscometer. Source:
1.19.3 Brittleness Point (Low-temperature Crystallisation)
Negretti Automation supplies the computer-controlled Gibitre low-temperature check
apparatus designed to test the low-temperature properties (-73 ºC, liquid carbon
dioxide), i.e., crystallisation effects and elastic recovery, of rubbers and elastomer
according to ASTM D1329 [288] by means of the temperature tests for rubber (TR)
test and brittleness point. ATS FAAR supplies an instrument for carrying out the
same measurements.
TR Test: After TR test positioning the test pieces in the relative mechanical system
using the special test piece extensions, they are then placed in the test chamber. The
chamber contains liquid cooled with carbon dioxide (-73 ºC) which is then gradually
111
heated to 20 ºC (2 ºC/min). The test assesses the temperature difference between the
two return values as a percentage.
After positioning the test pieces in a relative mechanical system, they are placed in the
test chamber. This contains liquid cooled with carbon dioxide (-73 ºC) to the required
temperature. A ‘ram’ comes into impact with the test pieces at a speed established
by the standards and this appears on the display. The test is repeated several times
using new test pieces to establish the brittleness temperature.
1.19.4 Flexing Test
The Ross flexing apparatus supplied by ATS FAAR measures, according to ASTM
D1052 [289], the cut growth of rubber or elastomer specimens when subjected to
repeated bend flexing. The machine allows the pierced flexed area of the specimen
to bend freely over a 10 mm-diameter rod at 90º with a frequency of 100 ± 5 or 50
± 5 cycles/min. The test is considered to have ended if the length of the cut (made
with a special nicking tool) has increased by 500%.
The test is widely used by all industries manufacturing rubber or elastomer goods
subjected (when in use) to repeated bending, such as shoes, tyres and conveyor belts.
Negretti Automation supplies the Gibitre De Mattia type dynamo tester which meets
the requirements of ASTM, BS and ISO standards. The equipment has been specially
designed by Gibitre to meet different requirements and can be used for other tests
besides the De Mattia type. Repeated flexing tests can be carried out on De Mattiatype pieces or other types.
1.19.5 Deformation
The Yerseley mechanical Oscillograph supplied by ATS FAAR measures, according
to ASTM D945 [290], the mechanical properties of rubber vulcanisations in the
small range of deformation that characterises many technical applications. These
properties include resilience, dynamic modulus, static modulus, kinetic energy, creep
and set under a given force.
1.19.6 Tensile Properties
Negretti Automation supplies universal testing machines with capacities up to 5 kN
(500 kg) and 10 kN (1,000 kg) complete with computer systems and printers.
112
1.19.7 Mechanical Stability of Natural and Synthetic Lattices
ATS FAAR supplies equipment for carrying out this test to ASTM specifications.
1.19.8 Abrasion Test
Negretti Automation supplies equipment to carry out abrasion tests on rubbers to
the DIN specification.
1.19.9 Peel Adhesion Test
Negretti Automation supplies equipment for carrying out 180º peel tests for adhesive
tapes and similar products to BS specifications.
1.19.10 Ozone Resistance Test
The Ozone Check supplied by Negretti Automation determines the resistance to
ozone of elsatomers used in the tyre industry.
1.20 Physical Testing of Polymer Powders
Methods for the testing of polymer powders have been reviewed by Chambers [291]
and Klaren [292], and are listed in Table 1.18. With the exception of particle-size
distribution and thermal analysis measurements (by DSC and differential thermal
analysis), none of these tests requires commercially produced equipment (i.e., they
are simple laboratory tests). Full ASTM test specifications for polymer powders are
described in ASTM D3451 [293]. Brief comments on the various tests on powders
included in Table 1.18 are given below.
113
Table 1.18 Test methods for polymer powders
Measurement
Standard test method(s)
Polymer powders
Particle-size distribution
ASTM D1921 [295]
BS ISO 13319 [296]
Storage stability
ASTM D609 [297]
DIN ISO 8130 [298]
Chemical and physical Stability
Ultraviolet and outdoor stability
Reactivity
ASTM D822-01 [299]
ASTM G155 [300]
ASTM D3451 [293]
DIN ISO 8130 [298]
Melt viscosity
ASTM D3451 [293]
Volatiles (stoving)
ASTM D3451 [293]
DIN ISO 8130 [298]
True density
DIN ISO 8130 [298]
ASTM D792 [301]
Bulk density
BS 2782 [13]
BS 2701 [302]
ASTM D1895 [303]
Powder flow
ASTM D1895 [303]
Test for cure
Electrical properties
Thermal analysis
By DSC and DTA
Tests on fused powder coatings
Defects
Glass
Whiteness
Film thickness
Hardness
ASTM D523-89 [304]
IN 53157 [305]
Adhesion
Flow deformation
ASTM D2794-93 [306]
Bend test
ASTM D522-93 [307]
Chemical resistance
Corrosion resistance
Glass transition
Melting
Cure
114
ASTM B117-64 [308]
1.20.1 Ultraviolet and Outdoor Resistance
Although the physical properties of a powder coating may be studied to predict
its probable behaviour in practice, there are occasions when UV and/or outdoor
resistance are required. There are two main procedures: artificial weathering and
natural weathering (Appendix 5).
1.20.2 Artificial Weathering
The Atlas Xenon Arc Weather-O-Meter is used to calculate artificial weathering
according to ASTM G155-04 a [300] and ASTM D822-01 [299]. The coated panel
is exposed to a cycle of 102 minutes of light, followed by 18 minutes of light together
with a water spray.
1.20.3 Natural Weathering
Various sites have been used for the evaluation of coatings e.g., Miami (FL, USA)
or Phoenix (AZ, USA). The site at Phoenix greatly differs from that at Miami with
respect to atmospheric conditions. Because of the elevation (2000 feet above sea
level) and the clear dry atmosphere (38% relative humidity as the annual average),
the percentage of UV in the solar radiation is higher in Phoenix than in the humid
climate at sea level in Miami. (Arizona has 4,000 sun hours per year compared with
the UK, which has with 1,000 sun hours.) The yearly average climate data of Arizona
and Florida are as follows:
• Arizona: Hours of sunlight: 3,993; cm of rain: 16; relative humidity: 38%; average
temperature: 21 ºC.
• Florida: Hours of sunlight: 2,271; cm of rain: 148; relative humidity: 58%; average
temperature: 24.5 ºC.
1.20.4 Reactivity
Thermosetting powders vary in their degree of reactivity, and some means of
quantifying this property is required. The basic method described in DIN ISO 8130
[298] and ASTM D3451 [293] involves melting the powder on a heating block at
160-200 ºC and stirring the molten material until gelation occurs.
There is undoubtedly some objectivity in this test, and slight differences in test method
could have a significant effect on the final result. Hence, elastomer repeatability is
115
reasonable, but there is considerable doubt as to how reproducible the method is
from one laboratory to another. Thus, the gelation test should be treated only as a
useful laboratory tool until sufficient evidence is available to justify inclusion in a
national standard.
1.20.5 Melt Viscosity
The fluidity of a material during the stoving process determines, to a large degree, the
smoothness of the final coating and the degree of edge coverage achieved. It may be
argued that the final appearance is the sole criterion for excellence, but some means
of quantitative measurement of melt viscosity is required for research work, and
is useful for quality control. A method is described in ASTM D3451 [294] which
employs a cone and plate viscometer. A simpler method is to use an inclined plane
whereby a pellet of the compressed powder is allowed to flow down on heated glass
plate set at a suitable angle. The total length of flow after a fixed time (usually 10
minutes) is related to the melt viscosity.
1.20.6 Loss on Stoving
Although stoving losses of coating powders are small when compared with
conventional finishes, some emission occurs, particularly with PU powders. Basically,
there are two methods of determination:
• Spraying onto a test plate and measuring mass loss after stoving.
• Placing powder on a tared dish and determining loss mass after heating in an
oven.
The first approach is favoured by the French (NFT 30-502) [310], whereas DIN ISO
8130-10 [298] and ASTM D3451-01 [293], describe dish methods. The dish method
has the advantage that it follows normal laboratory practice. The temperature of the
test and its duration can conveniently be the recommended cure schedule.
1.20.7 True Density
For powders of specific gravity above unity a pyknometer with water plus a wetting
agent may be used. DIN ISO 8130-7 [298], describes an air pyknometer which caters
for any powder (Appendix 5).
116
1.20.8 Bulk Density
Bulk density refers to the mass per unit volume of the powder (including air trapped
between the particles). Thus, this measurement enables the calculation to be made
of appropriate capacities for containers and hoppers. It is essential to ensure that the
sample is not compacted during the test, and this is normally achieved by pouring
the powder through a funnel into a measuring container. Methods are described in
BS 2782 [13] and ASTM D1895 [303]. A Rees-Hugill powder density flask is also
described in BS 2701 [302], (Appendix 5).
1.20.9 Powder Flow
The flow characteristics of a powder bear a complex relationship with the size,
distribution, shape and structure of particles. It is of particular significance in
connection with the ability of a powder to pass easily along feed lines to give the
necessary consistency of applications when using electrostatic spraying equipment.
The flow may be measured by determining the time for a prescribed volume of powder
to flow through a standard funnel, as described in ASTM D1895 [303] and DIN EN
ISO 813-10 [309].
This method has poor reproducibility in the case of thermosetting powders. This has
led to the development of an empirical technique by the Netherlands Organization
for Applied Scientific Research (TNO), which is described in the French standard
NFT 30-500 [311].
The method consists of placing the powder in a standard fluidised bed with a plugged
orifice in the side of the chamber. The height of the powder during and after fluidisation
is measured. The powder is then refluidised and the plug removed for 30 seconds,
allowing powder to flow into a tared container. The powder is weighed and the flow
factor calculated as the product of this mass and the height difference. This is then
compared with flow factors previously obtained on a wide range of powders, the
flow characteristics of which are known. This enables a prediction of flow behaviour
to be obtained.
1.20.10 Test for Cure
Unlike coatings made from thermoplastic powders, which require only visual
inspection to see if the coating is satisfactory, thermosetting powder coatings require
additional examination to determine if the coating has achieved its full physical
properties. Simple mechanical tests may be used (as is the practice with conventional
117
paint finishes) but, particularly for epoxy powder coatings, it is not normal to use
chemical resistance as a criterion for suitability. A common method is to swab the
coating continuously for 30 seconds with a cotton wool pad soaked in methyl isobutyl
ketone. Any deterioration of the film (with the exception of a minor loss) may be
taken as in indication that the coating is insufficiently cured.
1.20.11 Electrical Properties
Application of the electrostatic technique to powders has drawn attention to the
need for powders to possess appropriate electrical characteristics if they are to hold
an electrical charge and be successfully processed. This has led to development of
special apparatus which in addition to measuring resistivity and powder charge also
acts as a diagnostic kit for the electrostatic spraying equipment. This apparatus was
developed by the Wolfson Unit at Southampton University (Southampton, UK) and
is manufactured by Industrial Development (Bangor) at University College, North
Wales (Bangor, Wales).
1.20.12 Thermal Analysis
The performance of powder coatings during fusion and subsequent cure may be
followed in detail by thermal analytical procedures such as differential thermal analysis
and DSC. These techniques offer an opportunity for the study of phase transitions
and cure behaviour under closely controlled conditions. DSC is a requirement in the
British Gas standard for epoxy powder-coated materials for the external coatings of
steel pipes (where it is used as a guide to ascertain optimum cure conditions).
1.20.13 Particle-size Distribution
Procedures based on several principles are used for the measurement of the particlesize distribution of polymer powders [312].
1.20.13.1 Methods Based on Electrical Sensing Zone (Coulter Principle)
Figure 1.61 shows, schematically, a simple form of apparatus. Particles, suspended
homogeneously at a low concentration in an electrolyte solution, are made to flow
through a small aperture (or orifice) in the wall of an electrical insulator, which is
commonly called an aperture (or orifice) tube – the aperture creates the sensing zone.
In addition, a current path is established between two immersed electrodes across
118
this aperture, setting a certain base impedance to the electrical detection circuitry. A
direct current is generally used. As each particle enters the aperture, it has effectively
displaced a volume of electrolyte solution equal to its own immersed volume. The
base impedance is therefore modulated by an amount proportional to the displaced
volume of the particle. This results in an electrical pulse of short duration being
created by each particle, the height of the pulse being essentially proportional to the
volume of the particle. The pulse may be measured, for example, as the change in
resistance, current, or voltage across the electrodes.
To vacuum
Tap
Pulse
amplifier
Main
amplifier
Electrodes
Threshold
Circuit
–
+
Stirred suspension
of particles in
electrolyte
Aperture
Manometer
contacts
Counter
driver
Horizontal
sweep
Oscilloscope
Digital
register
Mercury
manometer
Counter stop/start
Figure 1.61 Simple form of particle size analyser (schematic). Source: Author’s
own files
The passage of several particles produces a ‘train’ of pulses that can be observed on
an oscilloscope and analysed by counter and pulse height analyser circuits to produce
a number against particle volume (or equivalent spherical diameter) distribution. A
volume or mass (‘weight’) against size distribution can also be measured, calculated,
119
or computed. The ‘weight’ percentages are possible if all of the particles have uniform
density or have a known density distribution across their size range.
Simple models have only one counter and size level circuit (and so are called ‘singlechannel models’); more complex instruments can obtain number and/or mass (weight)
distributions automatically in up to 256 size channels within a few seconds. Counting
and sizing rates of up to some 10,000 particles per second are possible, with each
pulse height being measured to within 1% or 2%.
Most particulate materials are irregularly shaped, so the volumetric response is
invaluable because volume is the only single measurement that can be made of an
irregular particle to characterise its size. In biological applications, the size response is
usually left calibrated in volume units (femtolitres, or ‘cubic microns’), but industrially
it is conventional to report the equivalent spherical diameter calculated from it. This
volumetric method makes no assumptions about particle shape and indeed is not
greatly affected by particle shape except in extreme cases such as flaky materials such
as certain clays. To count the number of particles in a known volume of suspension,
such as for particular contamination studies or for a blood cell count, the sample
volume is accurately metered by means of a calibrated ‘monometer’. Figure 1.61
illustrates the original simple mercury siphon and metering system.
The shape of the aperture tube can vary according to application. For example, a very
narrow design, which can be inserted into glass ampoules as small as 1 ml capacity,
allows the particle contamination of injectable solutions to be measured.
Instrument designs have a range of extra features, including embedded microprocessors
and various data reduction handling and presentation methods, and manufacturers
should be contacted for details. The volumetric sizing resolution, speed of data
collection, statistical accuracy of counting, freedom from any optical response effects
and the reliability and simplicity of calibration make these devised unsurpassed for
providing particle counting and size-distribution analysis.
Coulter-type instrumentation available from Coulter Electronics Limited is listed in
Table 1.19 (multisiser and Model 2M) and Appendix 1.
1.20.13.2 Laser Particle Size Analysers
Light diffraction is one of the most widely used techniques for measuring the size of
particles in the range 0.1-1,000 µm. This popularity is partly due to the way precise
measurements can be made quickly and easily. It also stems from the flexibility of
120
the technique, particularly the way it can be adapted to measure samples presented
in various forms.
The method depends on analysing the diffraction patterns produced when particles of
different sizes are exposed to a collimated beam of light. The patterns are characteristic
of the particle size, so mathematical analysis can produce an accurate, reproducible
picture of size distribution.
Coulter Electronics Limited supplies a range of laser particle size distribution
apparatus (LS100 and LS130) (Table 1.19).
Christianson Scientific Equipment supplies the Fritsch Analysette 22 Laser Particle
Sizer, which operates over the particle size range 0.16–1250 µm. This is a universally
applicable instrument for determining particle-size distributions of all kinds of solids
which can be analysed in suspension in a measuring cell or dry feeding through a
solid particle feeder. In the Fritsch Analysette 22 system, laser diffraction apparatus
measuring the particle-size distribution is displayed on the monitor in various forms,
either as a frequency distribution or as a summary curve in tabular form. These can
be subsequently recorded on a plotter, stored on hard disc, or transferred to a central
computer via an interface. The time required for one measurement is ~2 minutes.
Table 1.20 lists some suppliers and working ranges of various particle-size distribution
methods.
Terray [313] examined laser diffraction as a method for the inline measurement of
particle size. Examples of the application of Insitec laser granulometers developed
by Malvern Instruments are described. These include their use for particle-size
measurement in the cryogenic grinding of plastics.
1.20.13.3 Photon Correlation Spectroscopy (Autocorrelation
Spectroscopy)
The Coulter N4 and its predecessor, the Nano-Sizer, use autocorrelation spectroscopy
of scattered light to determine the time-dependent fluctuations of the scattered light
which result from the Brownian motion of particles in suspension. The technique is
also known as photon correlation spectroscopy.
121
Table 1.19 Particle-size measurement instrumentation available from Coulter
Electronics Limited
Instrument
Type
Particle-size range
Analysis
time (s)
Measurement
30-90
Counting and
sizing
Coulter Multisiser
Coulter
0.4-1200 µm
(overall)
0.4-336 µm for
distributions to be
expressed as volume
(weight) against size
Model ZM (more basic
than the Multisiser)
Coulter
0.4-1200 µm
-
Counting and
sizing
Coulter LS series particle
size distribution analyser
Laser light
diffraction
0.1-810 µm
60
Particle sizing
LS130
LS100
Coulter series model N4
Photon
correlation
spectroscopy
(auto
correlation
spectroscopy)
0.003-3 µm
Model N45 measures
coefficients of particles by
laser light scattering and
converts them to size or
molecular weight
Model N4MD automated
laser based submicron
particle size analyser
Model N45D sub-micron
particle size analyser with
size distribution analysis
capability
-
-
0.003-3 µm
Sub-micro
particle
distribution
and molecular
weight
-
-
1.20.13.4 Sedimentation
The use of sedimentation, whereby the particle size is determined by the application
of Stokes’ law, is well established. The time taken for fine particles to complete the
sedimentation process is far too long for practical utility. However, the development
122
of the wide-scanning sedimentometer (whereby a suspension of particles that are
separated under gravity is scanned by a light beam which is attenuated accordingly)
has largely overcome this difficulty. A result may be obtained in 30 minutes by a
competent operator using hand calculation methods.
Table 1.20 Suppliers and working ranges of particle-size distribution
methods
Method
Particle size Equipment supplier
Model
range
Dry sieving
6-63 µm
Fritsch
Analysette 3 (20-25
mm)
Wet sieving
20-200 µm
Fritsch
Analysette 18
Microsieving
5-100 µm
Fritsch
Sedimentation in
0.5-500 µm Fritsch
Analysette 20
gravitational field
Laser diffraction
0.1-1100 µm Fritsch
Analysette 22
Electrical zone
0.4-1200 µm Coulter
Model ZM Coulter
sensing
Multisizer
Electron microscopy 0.5-100 µm Photocorrelation
0.5-5 µm
spectroscopy
Sedimentation in
0.5-10 µm
Fritsch
Analysette 21
centrifugal field
(Anderson Pipette
centrifuge)
Diffraction
1 µm-1 mm spectroscopy
Optical microscopy 0.5 µm-1
mm
Projection
0.05 µm-1
microscopy
mm
Image analysis
0.8-150 µm Joyce Leobl
Magiscan and
systems
down to 0.5 Instruments,
Magiscan P,
µm
Leitz, Karl Zeiss,
Autoscope P,
Cambridge
Videoplan II,
Instruments
Quantimet 520
123
1.20.13.5 Acoustic Spectroscopy
Particle-size measurement results obtained from the deconvolution of acoustic
attenuation over a broad frequency range is showing increasing potential in the
characterisation of emulsions and slurries at process concentrations over particle
sizes ranging from 0.01 µm to 1,000 µm [314]. The results of this study reveal
that the particle-size distribution in high and low-density contrast materials can be
accurately measured by acoustic spectroscopy. The technique is distinct from other
size-characterisation technologies in three ways: there are no optics involved because
the instrument can measure through opaque high-concentration suspensions; it
has an extremely wide dynamic range; and it is well suited for online applications
because it is a relatively robust instrument and dilution is not required. Trottier and
co-workers [317] discussed the applications of acoustic spectroscopy to particle-size
measurement for LDPE and HDPE.
1.20.13.6 Capillary Hydrodynamic Fractionation
Venkatesan and Silebi [315] used capillary hydrodynamic fractionation to monitor
an emulsion polymerisation of styrene monomer as a model system. A sample taken
from the reactor at different time intervals is injected into the capillary hydrodynamic
fractionation system to follow the evolution of the particle-size distribution of the
polymer particles formed in the emulsion polymerisation. After the colloidal particles
have been fractionated by capillary hydrodynamic fractionation, they pass through
a photo-diode array detector which measures the turbidity at several wavelengths
instantaneously, thereby enabling utilisation of turbidimetric methods to determine
particle-size distribution. The particle size instrument is not hindered by the presence
of monomer-swollen particles. The shrinkage effect due to monomer swelling is found
to be accurately reflected in particle-size measurements.
1.20.13.7 Small-angle Light Scattering
Boerschig and co-workers [316] mentioned that light scattering should prove useful
for the direct measurement of particle growth during flow-driven coalescence of PS/
polymethyl methacrylate blends.
1.21 Plastic Pipe Materials
Testing of polymer pipe materials is done to international standards. Impact resistance
(falling dart) is done to ASTM D2944 [367] and UNI EN ISO 748 [337]. Hydrostatic
124
pressure tests have been conducted on polyolefin pipe exposed to chlorinated water
[318-319] and failure mechanisms discussed.
The effect of welding [320] and long-term exposure to soil [321] of PE pipes has
been investigated.
Physical performance testing has also been carried out on rigid PVC [334] and isotatic
polybutene [335] as well as polyacrylate [337] pipes.
Sims [326] reviewed the international standardisation of test methods according to
BS4994 and BS 6464 for general-purpose pipes and pressure vessels.
1.22 Plastic Film
Additional tests for polymer films that have been mentioned in the literature are the
tear strength at ethylene-vinylacelate plasticiser [344], the coefficient of friction of
polyolefin plasticiser blown film [342] and oxygen absorption of food packaging
film [343].
Michaelie and co-workers [332] studied the gas barrier properties of PET films
coated with microwave-enhanced plasma, polymerised barrier layer polyacetylene
or polyhdifluoroethylene.
References
1.
ASTM D638-03, Standard Test Method for Testing Tensile Properties of
Plastics, 2003.
2.
DIN EN ISO 527-1, Plastics-Determination of Tensile Properties, Part 1:
General Principles, 1996.
3.
DIN ISO 527-2, Plastics-Determination of Tensile Properties, Part 2: Test
Conditions for Moulding and Extrusion Plastics, 1996.
4.
ASTM D695-02a, Standard Test Method for Compressive Properties of Rigid
Plastics, 2002.
5.
DIN EN ISO 179-1, Determination of Charpy Impact Properties, Part 1:
Non-Instrumental Impact Test, 2001.
125
6.
ASTM D790-03, Standard Test Methods for Flexural Properties of
Unreinforced and Reinforced Plastics and Electrical Insulating Materials,
2003.
7.
ASTM D732, Standard Test Method for Shear Strength of Plastics by Punch
Tool, 2002.
8.
DIN EN ISO 178, Plastics-Determination of Flexural Properties, 2003.
9.
DIN EN ISO 8256, Determination of Impact Strength, 2005
10. DIN EN ISO 604, Plastics-Determination of Compressive Properties, 2003
11. Y. Son, Y.S. Chun and R.A. Weiss, Polymer Engineering and Science, 2004,
44, 541.
12. M. Tasdemir and H. Yildirim, Journal of Applied Polymer Science, 2003, 83,
2967.
13. BS 2782-0, Method of Testing Plastics Part 0: Introduction, 1995.
14. ASTM D1043, Standard Test Method for Stiffness Properties of Plastics as a
Function of Temperature by Means of a Torsion Test, 2002.
15. DIN 53477, Testing of Plastics: Determination of Particle Size Distribution of
Moulding Materials by Dry Sieving Analysis, 1992.
16. ISO 458, Plastics – Determination of Stiffness on Torsion of Felxible
Materials – Part 1: General Method, 1985.
17. ASTM D1869-99, Standard Practice for Transfer Molding Test Specimens of
Thermosetting Compounds, 2004.
18. ASTM D3419, Standard Practice for In-Line Screw-Injection Molding Test
Specimens from Thermosetting Compounds, 2000.
19. ASTM D3641, Standard Practice for Injection Molding Test Specimens of
Thermoplastic Molding and Extrusion Materials, 2002.
20. ASTM D4703, Standard Practice for Compression Molding Thermoplastic
Materials into Test Specimens, Plaques, or Sheets, 2003.
21. ASTM D5227-01, Standard Test Method for Measurement of Hexane
Extractable Content of Polyolefins, 2001.
126
22. ISO 498, Natural Rubber Latex Concentrate – Preparation of Dry Films,
1992.
23. DIN ISO 604, Plastics Determination of Compressive Properties, 2003.
24. J. Janick and W. Krolikowski, Polymery, 2002, 47, 250.
25. S. H. Lin, C.C.M. Ma, N.H. Tai and I.H. Perng, Proceeding of Materials
Challenge, Diversification and the Future Symposium, Anaheim, CA, USA,
1995, 40, 2, 1046.
26. H. Wong, P.G. Thompson, J.R. Schoonover, S.R. Ambuchon and R.A.
Palmer, Polymer Macromolecules, 2001, 34, 7084.
27. J.J. Lyons, Polymer Testing, 1998, 17, 237.
28. G. Hay, P.E. Mackey, P.N. Awati and Y. Park, Journal of Rheology, 1999, 43,
1099.
29. C. Nakafuku and K. Nishimura, Journal of Applied Polymer Science, 2003,
87, 1962.
30. H-C. Wong, C.M. Sung and J. Hamilton, Journal of Material Science Letters,
1998, 7, 41.
31. T.C. Barany, E. Foldes, T. Czigany and J. Korgar-Kosis, Journal of Applied
Polymer Science, 2004, 91, 3462.
32. J.F. Mana and J.C.A. Viana, Polymer Testing, 2001, 20, 937.
33. F. Briatico-Vangosa, M.D. Rink, F. D’Oria and A. Verzelli, Polymer
Engineering and Science, 2000, 40, 1553.
34. A. Marcellon, A.R. Bunsell, R. Piques and P. Colomban, Journal of Materials
Science, 2003, 38, 2117.
35. S. Kao-Walter, J. Pahlstrom, T. Karlsson and A. Magnuson, Mechanics of
Composite Material, 2004, 40, 29.
36. ASTM D256-56, Standard Test Methods for Determination of Izod
Pendulum Impact Resistance of Plastics, 2005.
37. ISO 179-1 Plastics, Determination of Charpy Impact Properties, Part 1: NonInstrumental Impact Test, 2001.
127
38. ISO 180, Plastics: Determination of Izod Impact Strength, 2000.
39. UNI EN ISO 180, Plastics: Determination of Izod Impact Strength, 2001.
40. ASTM D5420, Standard Test Method for Impact Resistance for Flat Rigid
Plastic Specimen by Means of Striker Impacted by a Falling Weight (Gardner
Impact), 2004.
41. ASTM D5628, 96 e-I, Standard Method for Impact Resistance of Flat Rigid
Plastic Specimen by Means of a Falling Dart (Tup or Falling Mass), 2001.
42. DIN EN ISO 6603, Plastics: Determination of Puncture Impact Behaviour of
Rigid Plastics, 2000.
43. M. Lavach, Plastics Engineering, 1999, 55, 41.
44. L.T. Pick and E. Harkin-Jones, Polymer Engineering and Science, 2003, 43,
905.
45. Y. Kayano, H. Keskkula and D.R. Paul, Polymer, 1997, 38, 1885.
46. ASTM D395-03, Standard Test Method for Stiffness Properties of Plastic as a
Function of Temperature by Means of Torsion Test, 2003.
47. ISO 815, Rubber Vulcanised or Thermoplastic-Determination of
Compression Set at Ambient, Elevated or Low Temperature, 1993.
48. UNI ISO 815, Rubber, Vulcanised or Thermoplastic-Determination of
Compression Set at Ambient, Elevated or Low Temperatures, 2001.
49. UNI 6121, Elastomeri: Prodotti Finiti, Prodotti di Gomma Spugnosa aa
Lattice, Definizioni E Prove, 1967.
50. DIN 53464, Testing of Plastic. Determination of Shrinkage Properties of
Moulded Materials from Thermosetting Moulding Materials, 1962.
51. E.C. Lee, M.J. Solomon and S.J. Muller, Macromolecules, 1997, 30, 7313.
52. C. Riekel, M. Burghammer, M.C. Garcia, A. Gourier and S. Roth, Polymer
Preprints, 2002, 43, 215.
53. ASTM D395-03, Standard Test Method for Stiffness Properties of Plastics as
a Function of Temperature by Means of Torsion Test, 2003.
54. G. Beracchi, A. Pipino and G. Boero, Macplas, 2001, 26, 78.
128
55. T. Miyata and T. Yamaoka, Kobunshi Ronbunshu, 2002, 59, 415.
56. G. Evrard, A. Belgrine, F. Carpier, E. Valot and P. Dang, Revue Generale des
Caoutchouces et Plastiques, 1999, 777, 95.
57. ASTM D430-95, Standard Test Methods for Rubber Deterioration-Dynamic
Fatigue, 2000.
58. ASTM D813-95, Standard Test Method for Stiffness Properties of Plastics as
a Function of Temperature by Means of Torsion Test, 2000.
59. S.H. Lin, C.C.M. Ma, N.H. Tai and L.H. Pering in the Proceedings of the
SAMPE Conference - Materials Challenge-Diversification and the Future,
Anaheim, CA, USA, 1995, Volume 40, Book 2, p.1046.
60. A.M. Harris and F.C. Lee, Journal of Applied Polymer Science, 2008, 107,
2246.
61. A. Menzur, Journal of Applied Polymer Science, 2008, 108, 1574.
62. J. Jia, D. Raabe and W-M. Miao, Chinese Journal of Polymer Science, 2006,
24, 403.
63. T. Barany, E. Folden, T. Czigany and J. Karger-Kocsis, Journal of Applied
64. A. Flores, V.B.F. Mathot, G.H. Michler, R. Adhikari and F.J. Balta Calleja,
Polymer, 2006, 47, 5602.
65. S. Houshyai and R.A. Shanks, Journal of Applied Polymer Science, 2007,
105, 390.
66. T. Kuila, H. Archarya, S.K. Shrivastava and A.K. Bhowmick, Journal of
Applied Polymer Science, 2008, 108, 1329.
67. B.G. Girija and R.R.N. Sailaja, Journal of Applied Polymer Science, 2006,
101, 1109.
68. F-L. Jin and S-J. Park, Journal of Polymer Science, Part B: Polymer Physics
Edition, 2006, 44, 3348.
69. F. Parres, R. Balart, J. Lopez and D. Garcia, Journal of Materials Science,
2008, 43, 3203.
129
70. R. Bouza, A. Lasagabasta, M.J. Abad and L. Bareal, Journal of Applied
71. F. Rouabah, M. Fuis, A. Bourdenne, C. Picard, D. Dadach and H. Hodduoni,
Journal of Applied Polymer Science, 2008, 109, 1505.
72. S. Houshyar and R.A. Shonks, Macromolecular Material and Engineering,
2006, 291, 59.
73. F. Rouabah, M. Fois, L. Ibos, A. Bourdenne, D. Dadache, N. Haddaounis and
P Ausset, Journal of Applied Polymer Science, 2007, 106, 2710.
74. M.G. Ahangani and A. Fereidoon, Polymers, 2008, 153, 1.
75. A Eceiza, M. Martin, K. De la Caba, G. Kortaberria, N. Gabilondo, M.
Curcnera and I. Mondragon, Polymer Engineering and Science, 2008, 48,
297.
76. K.L. Pagnon, H.H. Chen, M.H. Innocentini-Mei and N.A. D’Souza,
Proceedings of the 66th SPE Annual Technical Conference, Milwauki WI,
USA, SPE, 2008, p.610.
77. R. Chakrabarti M. Das and D. Chakrabarti, Journal of Applied Polymer
Science, 2004, 93, 272.
78. S. Pop and K. Chaochanchaikul, Polymer International, 2004, 53, 1210.
79. C.V. Mythili, A.M. Retna and S. Gapalakrishanan, Journal of Applied
Science, 2005, 98, 284.
80. M. Funabashi, S. Hirose and H. Hatcheyame, Proceedings of Fourth
Asian- Australian Conference on Composite Materials (AAGM – 4), Sydney
Australia, Cambridge, Woodhead Publishing, Cambridge, UK, 2004, p.57.
81. A. Li, J. Chang, K. Wang, L. Lu, X. Yang and Y. Wang, Polymer
International, 2006, 55, 565.
82. A.J. Zattari, O. Bionchi, R.V.B. Oliveiri, L.B. Canto, C.A. Ferreiro and M.
Zeni, Process in Rubber, Plastics and Recycling Technology, 2006, 22, 69.
83. R.R.N. Sailaja, Polymer International, 2005, 54, 1589.
84. F.R. Kogler, T. Kich, H. Peterlick, S. Seidler and U. Schubert, Journal of
Polymer Science, Part B: Polymer Physics Edition, 2007, 45, 2215.
130
85. A.P. Gupta, U.K. Saroop and M. Verma, Polymer Plastics Technology and
Engineering, 2004, 43, 937.
86. D. Sheivastava, Journal of Applied Polymer Science, 2005, 96, 1691.
87. Ming-Zhang, C-Z. Wang, D-Z. Wu, Y-H. Yu and X-P. Yang, Polymer
Materials Science and Engineering, 2005, 21, 196.
88. S. Houshyar, R.A. Shanks and A. Hodzik, Journal of Applied Polymer
Science, 2005, 96, 2260.
89. E. Shrivakumar, K.N. Pandeu and S. Alam and C.K. Das, Polymer
International, 2005, 54, 1458.
90. Nohalen, L. Solar, I. Porcar, C.I. Vollo and G.M. Gomez, European Polymer
Journal, 2006, 42, 3093.
91. F. Rouhbah, K. Ayadi and N. Hoddaoui, International Journal of Polymeric
Materials, 2006, 55, 975.
92. M. Szostah, Molecular Crystals and Liquid Crystals, 2004, 416, 209.
93. I. Nigam, D. Nigam and G.N. Mathur, Polymer Plastics Technology and
94. Y.H. Nien and J. Chen, Journal of Applied Polymer Science, 2006, 100, 3727.
95. L. Priya and J.P. Jog, Journal of Polymer Science, Part B: Polymer Physics
Edition, 2003, 41, 31.
96. Q. Yuan, W. Jiang, L. An and L.K.Y. Li, Polymers for Advanced
Technologies, 2004, 15, 409.
97. A.P. Gupta, U.K. Saroop, G.S. Jha and M. Verma, Polymer Plastics,
Technology and Engineering, 2003, 42, 297.
98. B. Zhou, X. Ji, Y. Sheng, L. Wang and Z. Jiang, Burofears Polymer Journal,
2004, 40, 2357.
99. C.Y. Tang, L.C. Chan, J.Z. Liang, K.W.E. Cheng and T. Wong, Journal of
Reinforced Plastics and Composites, 2002, 21, 1337.
100.P.J.M. Von den Heuvrel, S. Goutianos, R.J. Young and T. Peijs, Composite
Science and Technology, 2004, 64, 645.
131
101.S. Mohonty, S.K. Nayak, S.K. Verma and S.S. Tripathyl, Journal of
Reinforced Plastics, and Composites, 2004, 23, 625.
102.L. Priya and J.P. Jog, Journal of Polymer Science, Part B: Polymer Physics
Edition, 2003, 41, 31.
103.A.P. Gupta, U.K. Saroop, G.S. Tha and M. Verma, Polymer Plastics,
Technology and Engineering, 2003, 42, 297.
104.Q. Yan, W. Jiang, L. An and R.K.Y. Li, Polymers for Advanced Technologies,
2004, 15, 409.
105.H. Xiaoming Xu, Y. Song, Q. Zheng and G. Ha, Journal of Applied Polymer
Science, 2007, 103, 2027.
106.W. Leong, Z.A.M. Ishak and A. Ariffin, Journal of Applied Science, 2004,
915, 3327.
107.O. Okzuk and H. Yildirim, Journal of Applied Polymer Science, 2005, 96,
1126.
108.J. Zhaoliang, Journal of Applied Polymer Science, 2007, 104, 1692.
109.F.H. Gojny, M.M.G. Wichman, B. Fiedler, W. Bauhofer and K. Schulte,
Composites: Part A, Applied Science and Manufacturing, 2005, 11, 1525.
110.Y. Nischitani, I. Sekiguchi, B. Hausnerova, N. Zolpazilova and T. Kitono,
Polymers and Polymer Composites, 2007, 15, 111.
111.E. Klata, S. Barysiak, K. Van De Velde, J. Garbarczyk and I. Krucinska, Fibres
and Textiles in Eastern Europe, 2004, 12, 64.
112.A. Pegoretti and A. Pencalti, Polymer Degradation and Stability, 2004, 86,
233.
113.L. Huang, Q. Yuan, W. Jiang, L. An and S.Y. Jiang, Journal of Applied
Polymers Science, 2004, 94, 1885.
114.S. Mishra and N.G. Shimpi, Journal of Polymer Science, 2007, 104, 2018.
115.F. Bianchi, A. Lazzeri, M. Pracella, A. Aguinu and G. Ligeri, Macromolecular
Symposium, 2004, 218, 191.
116.K. Wang, J. Wu and H. Zeng, Polymers and Polymer Composites, 2006, 14,
473.
132
117.D. Yun-Sheng, G. Hong-Wei and W. Seng-Shan, Polymer Materials Science
and Engineering, 2005, 21, 90.
118.E.S.A. Rachid, K. Ariffin, H. Akit and C.C. Kooi, Journal of Reinforced
Plastics and Composites, 2008, 27, 1573.
119.Z-H. Chen and K-C. Gung, Polymer Material Science and Engineering, 2007,
23, 203.
120.B. Mary, C. Dubois, P.J. Garreau and D. Brousgeay, Rheologica Acta, 2006,
45, 561.
121.J. Burghardt, N. Hansen, L. Hansen and G. Hansen in Proceedings of the
SAMPE ’06 Conference, Long Beach, CA, USA, 2006, Paper No.131.
122.A.S. Luyt, S.A. Molefi and H. Krump, Polymer Degradation and Stability,
2006, 91, 1629.
123.J. Liu, B. Cankurtaran, L. Weizorek, M.J. Ford and M. Cortie, Advanced
Functions Materials, 2006, 16, 1457.
124.N. Abdelaziz, Journal of Applied, Polymer Science, 2004, 94, 2178.
125.D. Puryanti, S.H. Amed, H.M. Abdullah and A.N.H. Yushaft, International
Journal of Polymeric Materials, 2007, 56, 327.
126.N. Sombatsompop, A. Kositchaiyong and W. Wimolala, Journal of Applied
127.B.L. Shah, S.E. Selke, M.B. Walters and P.A. Heiden, Polymer Composites,
2008, 29, 655.
128.C.Y. Lai, S.M. Sapuan, M. Ahmid, N. Yahya and K.Z.H.M. Dahlan, Polymer
Plastics Technology and Engineering, 2005, 44, 619.
129.E.M. Wouterson, F.C.Y. Boey, X. Hu and S-C. Wang, Polymer, 2007, 48,
3183.
130.E. Lezak, Z. Kulinski, R. Masirek, E. Piorkowgka and M. Pracella and K.
Gadzinowika, Macromolecular Bioscience, 2008, 8, 1190.
131.S.M. Luz, A.R. Goncalves, A.P. Del-Arco and D.M.C. Ferrao, Composite
Interfaces, 2008, 15, 841.
133
132.S. Joseph and S. J. Lumas, Journal of Applied Polymer Science, 2008, 109,
256.
133.H. Hu, J. Lin, Q. Zheng and X. Xu, Journal of Applied Polymer Science,
2006, 99, 3477.
134.S. Radhakrichnan, B.T.S. Ramanujam, A. Adhikara and S. Sivaram, Journal
of Power Sources, 2007, 163, 702.
135.K.I. Jung, S.W. Yoon, S.J. Sung and J.K. Park, Journal of Applied Polymer
Science, 2004, 94, 678.
136.H. Mirzazadeh, A.A. Katbab and S. Bazgir in the Proceedings of the 8th
IUPAC International Symposium on Polymers for Advances Technologies,
Budapest, Hungary, 2005, Paper No.41.
137.O. Kusmon, Z.A. Mohd Ishek, W.S. Chow and T. Tekeichi, European
Polymer Journal, 2008, 44, 1023.
138.E. Nazockdast, H. Nazockdost and F. Goharpey, Polymer Science and
139.H. Ardhyananta, H. Ismail and T. Takeichi, Journal of Reinforced Plastics
and Composites, 2002, 21, 822.
140.S. Hwan-Lee and J. Ryoun Youn, Polymer, 2007, 34, 1.
141.F. Kaya, M. Tanoglu and S. Okur, Journal of Applied Polymer Science, 2008,
109, 834.
142.C.Y. Lew, W.R. Murphy and G.M. McNally in the Proceedings of the Antec
62nd SPE Annual Conference, Chicago, IL, SPE, USA, 2004, p.304.
143.G. Sanchez-Olivares, A. Sanchez-Solis and O. Manerv, International Journal
of Polymeric Materials, 2008, 57, 417.
144.M.A. Kadei, M.Y. Lyn and C. Nah, Composites Science Technology, 2006,
66, 1431.
145.K. Zheng, L. Chen, Y. Li and P. Cui, Polymer Engineering and Science, 2004,
44, 1077.
146.Y-H. Hu, C-Y. Chen and C-C. Wong, Macromolecules, 2004, 37, 2411.
134
147.S.U. Ryadiansyah, H. Ismail and B. Azhari, Polymer Composites, 2008, 29,
1169.
148.V. Paseual, V. Sanchez and J.M. Martin-Martinez, Macromolecular Symposia,
2006, 233, 137.
149.C. Bartholom, E. Beyou, E. Bourgeat-Hamy, P. Cassagnau, P. Chanmonr, L.
David and N. Zydowicz, Polymer, 2005, 46, 9965.
150.O. Ruzimuradov, G. Rajan and J. Mark, Macromolecular Symposia, 2006,
245-256, 322.
151.J.C.S. Norton, M.G. Han, P. Jiang, G.H. Shim, Y. Ying, S. Greager and S.H.
Foulger, Chemistry of Materials, 2006, 18, 4570.
152.T.P. Ngnyen, S.H. Yang, J. Gomes and M.S. Wong, Synthetic Metals, 2005,
15, 269.
153.D.S. Chaudhary, M.C. Jalland and F. Cser, Polymers and Polymer
Composites, 2004, 12, 383.
154.D.W. Chae and B.C. Kim, Journal of Materials Science, 2007, 42, 1238.
155.J.L. Abot, A. Yasmin, A.J. Jacobson and I.M. Daniel, Composite Science and
Technology, 2004, 64, 263.
156.B. Hausner Nova, N. Zdrajilova, T. Kitano and P. Saha, Polymeri, 2006, 5,
33.
157.C-H. Chen and K-C. Lein, Polymers and Polymer Composites, 2006, 14,
155.
158.S. Vidhate, E. Ogunsona, J. Chung and N.A. D’Souza in the Proceedings of
the 66th SPE Annual Technical Conference, Milwaukee, WI, USA, 2008, p.74.
159.M.R. Loos, S.H. Pezzin, S.C. Amico, C.P. Bergmann and L.A.F. Coelho,
Journal of Materials Science, 2008, 18, 6064.
160.M.R. Loos, L.A.F. Coelho, S.H. Pezzin and S.C. Amico, Journal of Materials
Research, 2008, 11, 347.
161.H-C. Kuan, C-C.M. Ma, W-P. Chong, S-M. Yuen, H-H. Win and T-M. Lee,
Composites Science and Technology, 2005, 65, 1703.
135
162.K.Q. Xiao, L.C. Zhang and I. Zarudi, Composites Science and Technology,
2007, 67, 177.
163.Y.S. Song, Polymer Engineering and Science, 2006, 46, 1350.
164.D. Wu, L. Wu, Y. Sun and M. Zhang, Journal of Polymer Science, Part B:
Polymer Physics Edition, 2007, 45, 3137.
165.B. Wang, G. Sun and J. Liu, Polymer Engineering and Science, 2007, 47,
1610.
166.S. Tzavalas, D.E. Mouzakis, V. Drakonakis and V.E. Gregoriou, Journal of
Polymer Science, Part B: Polymer Physics Edition, 2008, 46, 668.
167.M. Lai, J. Li, J. Yang, J. Liu, X. Tong and H. Cheng, Polymer International,
2006, 53, 1479.
168.Y.T. Sung, M.S. Han, K.H. Song, J.W. Jung, H.S. Lee, C.K. Kum, J. Loo and
W.N. Kim, Polymer, 2006, 47, 4434.
169.T. Aoki, Y. Ono and T. Ogasawara in the Proceedings of the American
Society for Composites 21st Technical Conference, Dearborn, MI, USA, 2006,
Paper No.31.
170.S-M. Yuen, C-C. M Ma, C-Y. Chuang, Y-H. Hsiao, C.L. Chiang and A-D.
Yu, Composites Part A, 2008, 39, 119.
171.D.S. Bangarusam Path, V. Alstradt, H. Ruckdeseschel, J.K.W. Sandler and
M.S.P. Shaffer, Journal of Plastics Technology, 2008, 6, 19.
172.V.E. Yudin, V.M. Svetlidnya, A.N. Shumkaov, D.G. Letenko, A.Y. Feldman
and G. Marom, Micromolecular Rapid Communications, 2005, 26, 885.
173.S. Peeterbroveck, M. Alexandre, J.B. Nagy, N. Moreau, A. Destrec, F.
Monteverde, A. Pulmont, R.J. Jerome and P. Dubois, Macromolecular
Symposia, 2005, 22, 115.
174.S-M. Ynen, C-C. M Ma, C-C. Teng, H-H. Wu, H-C. Kuan and C-L. Chiang,
Journal of Polymer Science, Part B: Polymer Physics Edition, 2008, 46, 472.
175.G.D. Sims, International Standardisation of Coupon and Structural Element Test Methods, ECCM-Composite, Testing and Standardisation 2, Hamburg,
Germany, 1994.
136
176.ISO 3268, Plastics –GRP – Determination of Tensile Properties, 1978.
177.ISO/DIS 527 – Part 5, Plastics – Determination of Tensile Properties – Test
Conditions for Unidirectional Fibre-Reinforced Plastic Composites, 1994.
178.EN 61:1977, Glass Reinforced Plastics – Determination of Tensile Properties, 1977.
179.prEN 2561, Carbon-Thermosetting Resin Unidirectional Laminates – Tensile
Test Parallel to the Fibre Direction, 1989.
180.prEN 2747, Glass Reinforced Plastic – Tensile Test Parallel to the Fibre
Direction, 1990.
181.M. Hojo, Y Sawada and H. Miyairi, Effects of Tab Design and Gripping
Conditions on Tensile Properties of Unidirectional CFRP in Fibre and
Transverse Direction, ECCM-Composites: Testing and Standardisation,
Amsterdam, The Netherlands, 1992.
182.ASTM D3039, Test Method for Tensile Properties Fibre-Resin Composites,
1993.
183.G.D. Sims, Developments in Harmonisation of Standards for Polymer Matrix
Composites, EECM Composite Testing and Standardisation, Amsterdam, The
Netherlands, 1992.
184.G D Sims, Composites, 1991, 22, 4, 267.
185.BS 4994:1987, Design and Construction of Vessels and Tanks in Reinforced
Plastics, 1987.
186.BS 6464:1984, Specifications for Reinforced Plastics Pipes, Fittings and Joints
for Process Plant, 1984.
187.ISO 10119:1992, Carbon Fibres – Determination of Density, 1992.
188.ISO 10120:1991, Carbon Fibres – Determination of Linear Density, 1991.
189.ISO/DIS 10548, Carbon Fibres – Determination of Size content and Size
Amount, 2002.
190.ISO/DIS 10617, Carbon Fibres – Definition and Vocabulary, 2010.
191.ISO 10352, Fibre Reinforced Plastics – Moulding Compounds and Prepregs,
Determination of Mass per Unit Area, 1991.
137
192.prEN 2557, Carbon Fibre Preimpregnates – Test Method for the
Determination of Mass Per Unit Area, 1998.
193.EN 2339, Test Method for the Determination of Mass per Unit Area of
Woven Textile Glass – Fibre Fabric Preimpregnates, 1993.
194.P.T. Curtis, Crag Test methods for the Measurement of Engineering Properties
of Fibre Reinforced Plastics, 3rd Edition, RAE TR 88012, 1988.
195.G.D. Sims, Development of Standards for Advanced Polymer Matrix
Composites – A BPF/ACG Overview, NPL Report DMM(A)8, 1990.
196.G.D. Sims, Standards for Polymer Matrix Composites, Part I Assessment for
Crag Test Methods Data, NPL Report DMM(M)6, 1990.
197.G.D. Sims, Standards for Polymer Matrix Composites, Part II Assessment
and Comparison of Crag Test Methods, NPL Report DMM(M)7, 1990.
198.ISO 178, Plastics – Determination of Flexural Properties of Rigid Plastics,
1993.
199.ISO 8515, Textile Glass Reinforced Plastics: Determination of Comparison
Properties Parallel to the Laminate, 1991.
200.ISO 4585, Textile Glass Reinforced Plastics-Determination of Apparent
Interlaminar Shear Strength by Short Beam Test, 1989.
201.ASTM D3518, In-Plane Shear Stress-Strain Response of Unidirectional
Reinforced Plastics, 1991.
202.S. Kellas, J. Morton and K.E. Jackson, Damage and Failure Mechanisms in
Scaled Angle-Ply Laminates, ASTM STP 1156, 257-280, 1993.
203.prEN 6031, FRP – Determination of In-Plane Shear Properties (+ Tensile
Test, 1995.
204.ISO 5725, (BSI 5497, 1987), Precision of Test Methods, Part 1: Guide for
the Determination of Repeatability and Reproducibility for a Standard Test
Method by Inter-Laboratory Trial, 1986.
205.ISO CD 13586, Plastic-Determination of Energy Per Unit Area of Crack
(Gc) and the Critical Stress Intensity Factor (Kc), Linear Elastic Fracture
Mechanics Approach, 2000.
138
206.R. Khoshravan and C. Bathias, Delamination Tests of DCB and ENF
Composite Specimens in Mode I and Mode II, Annual Report of VAMAS
WG5, 1990.
207.W.R. Broughton and A. Vamas, Round-Robin Project on Polymer Composite
Delamination in Mode I and Mode II; Cyclic Loading, NPL Report
DMM(A)47, 1992.
208.G.D. Sims and A. Vamas, Round-Robin on Fatigue Test Methods for Polymer
Matrix Composites. Part I, Tensile and Flexural Tests of Unidirectional
Material, NPL Report DMM(A)180, 1989.
209.G.D. Sims, Interim VAMS Report on Part 1 of Polymer Composites Fatigue
Round-Robin.
210.ASTM D3044, Standard Test Method for Shear Modulus of Plywood, 1976.
211.G.D. Sims, W. Nimmo, F.A. Johnson and D.H. Ferriss, Analysis of PlateTwist Test for In-Plane Shear Modulus of Composite Materials, NPL Report
DMM(A)54, 1992.
212.S.W. Tsai and H.T. Hahn, Introduction to Composite Materials, Technomic
Publishing Company, Lancaster, PA, USA, 1980.
213.G.G. Sims, International Standardisation of Coupon and Structural Element
Test Methods, ECCM-Composites: Testing and Standardisation 2, Hamburg,
Germany, 1994.
214.ASTM D5379/D3579M – 1993, Standard Test Method for Shear Properties
of Composite Materials by the V-Notched Beam Method, 1993.
215.ISO 6603, Plastics – Determination of Multi-Axial Impact Behaviour of Rigid
Plastics, Part 1 – Falling Dart Method; Part 2 – Instrumented Puncture Test,
1989.
216.W.R. Broughton and G.D. Sims, An overview of Through-Thickness Test
Methods for Polymer Matrix Composites, NPL Report DMM(A)148, 1994.
217.G.D Sims and M.J. Lodeiro, An overview of Structural Element Test Methods
for Polymer Matrix Composites, NPL Report, 1994.
218.G.D. Sims, D.H. Ferriss and D. Payne, An Overview of Design Aids for
Structural Design of Polymer Matrix Composites, NPL Report, 1994.
139
219.G.D. Sims and W. Nimmo, A Review of Test Methods for Polymer Matrix
Composites at Non-Ambient Temperatures, NPL Report, 1994.
220.ISO/CD3 1172, Textile Glass Reinforced Plastic, Prepregs, Moulding
Compounds and Composites – Determination of Glass and Filler Content,
Method of Calcination, 1994.
221.ISO/CD2 11667, Fibre Reinforced Plastics - Moulding Compounds and
Prepregs - Determination of Fibre, Resin and Filler Content – Method by
Dissolution, 1994.
222.BS 18, Method for Tensile Testing of Metals (Including Aerospace Materials,
1987. [Withdrawn, replaced by BS EN 10002:1990]
223.C. Treny and B. Dupenray in the Proceedings of the 55th SPE ANTEC
Conference, Toronto, Canada, 1997, p.2805.
224.P.C. Haschke, Machine Design, 2001, 73, 61.
225.Exstae 6000, Series Dynamic Mechanical Spectrometers, Seiko, Instruments
226.H.T. Jones, SAMPE Journal, 2002, 38, 91.
227.H. Wong, D.G. Thompson, J.R. Schoonover, S.R. Ambushon and R.A.
Palmer, Macromolecules, 2001, 34, 7084.
228.J. Foreman, J.E.K. Schawe and M.W. Wagner inProceedings of the 162nd ACS
Rubber Division Conference, Pittsburgh, PA, USA, 2002, Paper No.13.
229.F. Gouin, Plastiques et Elastomeres Magazine, 2001, 53, 17.
230.D. Dean, M. Husband and M. Trimmer, Journal of Polymer Science, Polymer
Physics Edition, 1998, 36, 2971.
231.E. Kontou and G. Spathis, Journal of Applied Polymer Science, 2003, 88,
1942.
232.L. Heux, J.J. Halary, F. Laupretre and I. Monnerie, Polymer, 1997, 38, 767.
233.M.E. Leyva, B.G. Soares and D. Khastgir, Polymer, 2002, 43, 7505.
234.J. Son, D.J. Gardner, S. O’Neill and C. Metaxas, Journal of Applied Polymer
Science, 2003, 89, 1638.
140
235.D.W. Bamborough in the Proceedings of the Technomic Pressure Sensitive
Adhesive Technology Conference, Milan, Italy, 2001, Paper No.10.
236.D.W. Bamborough in the Proceedings of the Technomic Pressure Sensitive
Adhesives Conference, Basel, Switzerland, 1993, Section 111, p.2.
237.M. Botov, H. Betchev, D. Bikiaris and D. Panayiotou, Journal of Applied
238.D. Singh, V.P. Malhotra and J.L. Vats, Journal of Applied Polymer Science,
1999, 71, 1959.
239.L. Priya and J.P. Jog, Journel of Polymer Science, Polymer Physics Edition,
2003, 41, 31.
240.M. Sepe, Injection Moulding, 1999, 7, 52.
241.O. Schroder and E. Schmachtenberg in the Proceedings of the ANTEC 2001
Conference, Dallas, TX, USA, 2001, Paper No.405.
242.R.A. Palmer, P. Chen and M.H. Gilson in the Proceedings of the ACS
Polymeric Materials Science and Engineering Conference, Orlando, FL, USA,
Fall 1996, 75, p.43.
243.Y.K. Kim and S.R. White, Polymer Engineering and Science, 1996, 36, 2852.
244.W. Venneman, S. Barbe, K. Kummerlow, K.G. Cai, A.C.A. Reid, S. Srinivan
and S. de Vogel in the Proceedings of a Rapra Technology Conference - TPE
2004, Brussels, Belgium, 2004, p.141.
245.P. Maltese, Materie Plastiche ed Elastomeri, 1995, 4, 225.
246.China Plastic and Rubber Journal, 2002, 10-11, 68.
247.M. Exrin in the Proceedings of the 60th Annual Technical Conference ANTEC
2002, San Francisco, CA, USA, 2002, Session M40, Paper No.202.
248.J.L. Leblanc, Revue Generale des Caoutchoucs et Plastiques, 1995, 745, 41.
249.J. Bouton and S.A. Rheo, Plastiques et Elastomers, Magazine, 2000, 52, 34
250.G. Sarrkel and A. Choudhury, Journal of Applied Polymer Science, 2008,
108, 3442.
251.Y.G. Jeong, S.C. Lee and W.H. Jo, Macromolecular Research, 2006, 14, 416.
141
252.G. Costa, G.C. Eastwood, J.P.A. Fairclough, J. Paprotny, A.J. Ryan and P.
Stagnaro, Macromolecules, 2008, 41, 1034.
253.J. Seo, W. Jang and H. Han, Macromolecular Research, 2007, 15, 10.
254.S. Mohanty, S.K. Verma and S.K. Nayak, Composites Science and
Technology, 2006, 66, 538.
255.P. Musto, M. Abbate, G. Ragosta and G. Scarinzi, Polymer, 2007, 48, 3703.
256.I.S. Kolesov, R. Androsch and H.J. Radusch, Macromolecules, 2005, 38, 445.
257.F. Declerq in the Proceedings of the Technical Rubber Goods; Part of Our
Everyday Life Conference, Puchov, Slovakia, 1996, p.173.
258.M. Fujiyama, Y. Kitajima and H. Inata, Journal of Applied Polymer Science,
2002, 84, 2128.
259.B. Vergnes and F. Berzin, Macromolecular Symposia, 2000, 158, 77.
260.H. Kwag, D. Rana, K. Cho, J. Rhee, T. Woo, B.H. Lee and S. Choe, Polymer
Engineering and Science, 2000, 40, 1672.
261.A.B. Kummer in the Proceedings of the Pressure Sensitive Tape Council 23rd
Annual Technical Seminar: Pressure Sensitive Tapes for the New Millennium,
New Orleans, LA, USA, 2000, p.25.
262.M. Doyle and J. A.E. Manson in the Proceedings of the ANTEC 2000
Conference, Orlando, FL, USA, 2000, Paper No.169.
263.A.L.A Bobovich, Y, Unigovski, E.M. Gutman and E. Kolmakov in the
Proceedings of ANTEC 63rd Annual Conference, SPE, Boston, MA, USA,
2005.
264.M. Patel, Polymer Testing, 2004, 231, 107.
265.P.D.B. Jung, D. Bhattacharyya and A.J. Easteel, Journal of Material Science,
2005, 40, 4775.
266.R. Hernandez, A. Sarafian, D. Dopez and C. Myangos, Polymer, 2004, 45,
5543.
267.J.D.O. Mela and R.W. Radford, Journal of Composite Materials, 2004, 38,
1815.
142
268.W. Lifeng, E.W. Cochran, T.P. Lodge and F.S. Bates, Macromolecules, 2004,
37, 3360.
269.J. Capodagli and R. Lakes, Rheologica Acta, 2008, 47, 777.
270.O. Robles-Vadquez, A. Gonzales-Alvarez, J.E. Puig and O. Manero, Rubber
Chemistry and Technology, 2006, 79, 859.
271.D. Wu, L. Wu, F. Goa, M. Zhong and C. Yan, Polymer Engineering and
Science, 2008, 48, 966.
272.J. Ding, X. Ding, X. Riwei and Y. Ding Sheng, Journal of Macromolecular
Science, 2005, 1344, 308.
273.K.K. Kar, P. Paik and J.U. Otaigbe, in the Proceedings of 62nd SPE Annual
Conference - ANTEC 2004, Chicago, IL, USA, 2004, p.2495.
274.A.L. Bobovitch, Y. Linigovski, E.M. Gutman, E. Kolmakov and S.
Yyazovkin, Journal of Applied Polymer Science, 2007, 103, 3218.
275.J.P. Habas, E. Pavie, A. Happ and J. Perelasse, Rheologica Acta, 2008, 47,
765.
276.J. Hepperle, H. Muenstedt, P.K. Haug and C.D. Eisenbach, Rheologica Acta,
2005, 45, 151.
277.J. Hepperle and H. Muenstedt, Rheologica Acta, 2006, 45, 717.
278.J. Strange, S. Waechtex, H. Muenstedt and H. Kaspar, Macromolecules, 2007,
40, 2409.
279.J. Jachowicz, R. McMuller, C. Wu, L. Senak and D. Koelmel, Journal of
Applied Polymer Science, 2007, 105, 190.
280.F. Yang, X-H. Xiong, Q. Wang and L. Li, Polymer Materials Science and
281.A. Lindner, B. Lestriez, S. Mariot, C. Creton, T. Maevis, B. Luehmann and R.
Brummer, Journal of Adhesion, 2006, 82, 267.
282.L. Andreozzi, V. Castelvetro, M. Faetti, M. Giordano and F. Zulli,
Macromolecules, 2006, 39, 1880.
283.J. Chan, X. Liu and D. Yang, Journal of Applied Polymer Science, 2006,
102, 4040.
143
284.J-L. Zhang, L. Shen, W. Chun Li and Q. Zheng, Polymer of Materials Science
and Engineering, 2006, 22, 123.
285.K.Y. Kim, G.J. Nam, S.M. Lee and J.W. Lee, Journal of Applied Polymer
Science, 2006, 99, 2132.
286.P. Prasopnatre, P. Saroui and C. Sirisinha, Journal of Applied Polymer
Science, 2009, 111, 1051.
287.ISO 9001, Quality Management Systems – Requirements, 2001.
288.ASTM D1329, Standard Test Method for Evaluating Rubber Property –
Retraction at Lower Temperatures (TR Test), 2002.
289.ASTM D1052, Standard Test method for Measuring Rubber DeteriorationCut Growth using Ross Flexing Apparatus, 2005.
290.ASTM D945 – 92el, Standard Test Methods for Rubber Properties in
Compression or Shear (Mechanical Oscillograph), 2001.
291.R. H. Chambers, Polymers Paint and Colour Journal, 1979, 169, 1109.
292.K.H.J. Klaren, Journal of the Oil and Colour Chemists’ Association, 1977,
60, 205.
293.ASTM D3451-01, Standard Guide for Testing Coating Powders and Powder
Coatings, 2001.
294.ASTM D3451-0, Standard Guide for Testing Coating Powders and Powder
Materials, 2001.
295.ASTM D1921, Standard Test Methods for Particle Size of Plastic Materials,
2001.
296.BS ISO 13319, Determination of Particle Size Distribution – Electrical
Sensing Zone Method, 2000.
297.ASTM D609, Standard Practice for Preparation of Cold-Rolled Steel Panels
for Testing Paint, Varnish, Conversion Coatings and Related Coating
Products, 2000.
298.DIN ISO 8130-10, Coating Powders, 2005.
299.ASTM D822-01, Standard Test Method for Stiffness Properties of Plastics as
a Function of Temperature by Means of a Torsion Test, 2001.
144
300.ASTM G155-04a, Standard Practice for Operating Xenon Arc Light
Apparatus for Exposure of Non-Metallic Materials, 2004.
301.ASTM E308, Standard Practice for Computing the Colours of Objects by
Using the CIE System, 2008.
302.BS 2701, Specification for Rees-Hugill Powder Density Flask, 1965.
303.ASTM D1895-96, Standard Test Methods for Apparent Density, Bulk Factor,
and Pourability of Plastic Materials, 2003.
304.ASTM D523, Standard Test Method for Specular Gloss, 2008.
305.DIN 53157, Paints and Varnishes – Pendulum Damping Test, 2000.
306.ASTM D2794-93, Standard Test Method for Resistance of Organic Coatings
to the Effects of Rapid Deformation (Impact), 2004.
307.ASTM D522-93a, Standard Test Methods for Mandrel Bend Test of Attached
Organic Coatings, 2001.
308.ASTM B117-64, Standard Practice for Operating Salt Spray (Fog) Apparatus,
2003.
309.DIN EN ISO 8130-10, Coating Powders Part 10: Determination of
Deposition Efficiency, 2011.
310.NFT 30 – 5-2, Peinturs en Poudre Thermodurcissables Determination de le
Temperature and Acclomeration, 1977.
311.NFT 30 – 500, Peinturs en Poudre Thermodurcissables de l’aptitude a la
Projection, 1976.
312.ASTM D1921, Standard Test Method for Particle Size (Sieve Analysis) of
Plastic Materials, 2001.
313.M. Terray, Informations Chimie, 1998, 398, 121.
314.R. Trottier, J. Szalanski, C. Dobbs and A. Felix in the Proceedings of the ACS
Polymeric Materials Science and Engineering Conference, Orlando, FL, USA,
Fall 1996, 75, 58.
315.J. Venkatesan and C.A. Silebi in the Proceedings of the ACS Polymeric
Materials Science and Engineering Conference, Orlando, FL, USA, 1996,
Volume 75, p.99.
145
316.C. Boerschig, B. Fries, W. Gronski, C. Weis and C. Friedrich, Polymer, 2000,
41, 3029.
317.R. Trottier, J. Szalanski, C. Dobbs and A. Felix in the Proceedings of the ACS
Polymeric Materials Science and Engineering, Orlando, FL, 1996, Volume 75,
p.58.
318.M. Ifwarson and K. Aoyama in Proceedings of the Institute of Materials
Plastic Pipes X Conference, Goteborg, Sweden, 1982, p.731.
319.R. Vegas, Revista de Plastico, Modernos, 2002, 83, 589.
320.C. Bonter and E. Schmechtenberg, Kunststoffe Plast Europe, 2000, 90, 38.
321.D.V. Reddy and S. Ataoglu, Journal of Advances Materials, 2004, 36, 43.
322.S. Ghoch and D.K. Tully, Plastics Industry, 1982, 9, 12.
323.M.A. Gomez, G. Ellis and C. Marco, Revista de Plasticos Modernos, 2002,
83, 582.
324.Y. Germain, Polymer Engineering and Science, 1998, 38, 657.
325.UNI 7448, Tubi di PVC Rigido (Non Plastificato), Metodi di Prova, 1975.
326.G.D. Sims in the Proceedings of the BPF Conference - Designed for Life
Composites, London, UK, 1994, Publication No. 293/9, p.101.
327.ASTM D1709, Standard Test Methods for Impact Resistance of Plastic Film
by the Free-Falling Dart Method, 2004.
328.UNI EN ISO 7765-1, Plastics Film and Sheeting – Determination of Impact
Resistance by the Free-Falling Dart Method – Part 1: Staircase Methods,
2005.
329.R.M. Patel, P. Saavedra, J. de Groot, C. Hinton and R. Guerra in the
Proceedings of the TAPPI: Polymers, Lamination and Coatings Conference,
Toronto, Ontario, Canada, 1997, Book 1, p.239.
330.S.S. Wood and A.V. Pocius in the Proceedings of the Annual SPE Conference
- ANTEC 2000, Orlando, FL, USA, 2000, Paper No.33.
331.M.G. Cernak and W.L. Chiang in the Proceedings of the TAPPI Polymers,
Laminations and Coatings Conference, Toronto, Ontario, Canada, 1997,
Book 2, p.479.
146
332.W. Michaeli, S. Goehel and R. Dahlmann, Journal of Polymer Engineering,
2004, 24, 107.
333.R.M. Patel, P Saavedra, J. de Grat, C. Hinton and R. Guerra in the
Proceedings of the TAPPI Polymers, Laminates and Coatings Conference,
Toronto, Ontario, Canada, 1997, Book 1, p.239.
334.H-T. Lee and L-H. Lin, Macromolecules, 2006, 39, 6133.
335.Y.P. Wang, X. Goa, R.M. Wong, H.G. Liu, C. Yang and Y.B. Xiong, Reactive
and Functional Polymers, 2008, 687, 1170.
336.Z. Liu, K. Chen and D. Yan, Polymer Testing, 2004, 23, 323.
337.T. Mikolajczyk and M. Olejnik, Fillers and Textiles in Eastern Europe, 2007,
15, 26.
338.B. Pourabbas and H. Azimi, Journal of Composite Materials, 2008, 42, 2499.
339.K. Stoeffler, P.G. Lafleur and J. Denault, Polymer Engineering and Science,
2008, 48, 1449.
340.H. Mirzazadeh and A.A. Katbaly, Polymers for Advanced Technologies,
2006, 17, 975.
341.J. Bandyopadhyaly, S.S. Ray and M. Bousmina, Macromolecular Chemistry
and Physics, 2007, 208, 1979.
342.Y.C. Kim, S.J. Lee, J.C. Kim and H. Cho, Polymer Journal (Japan), 2005, 37,
206.
343.W.S. Chaw and Z.A. Mohd Ishak, Express Polymer Letters, 2007, 1, 77.
344.D-R. Yei, S-W. Kuo, H-K. Fe and F-C. Chang, Polymer, 2005, 46, 741.
345.D.Y. Wei, S. Innace, E. Di Maio and L. Nicolais, Journal of Polymer Science
– Polymer Physics Edition, 2005, 43, 689.
346.S. Tanoue, L.A. Utracki, A. Garcia Rejon, P. Sammut, I. Pesneau, M.R. Kamal
and I. Lyngaae-Jorgensen, Polymer Engineering and Science, 2004, 44, 1061.
347.K. Stoeffler, P.G. Lafleur and J. Renault in the Proceedings of the 64th SPE
Annual Conference – ANTEC 2006, Charlotte, NC, USA, 2006, p.263.
147
348.ASTM D693-03a, Stand and Test Methods for Deflection Temperature under
Load of Plastics.
349.L. Zsedai, G. Kalacska, K. Vercommen and K. Van Acber, International
Science and Technology, 2002, 29, T17.
350.P.M. Taylor and D.M. Pollet, Journal of Textile Institute, Part 1: Fibre Science
and Textile Technology, 2000, 91, 1.
351.E.A. Poppe, K. Leidig, K. Schirmer and L. Jayle, Revue General des
Caoutchoucs et Plastiques, 1997, 760, 41.
352.R. Selden, Polymer Engineering and Science, 1997, 37, 205.
353.M.Y. Keating, L.B. Malone and W.D. Saunders, Journal of Thermal Analysis
and Calorimetry, 2002, 69, 37.
354.S.C. Shik, Popular Plastics and Packaging, 2003, 48, 55.
355.ASTM D2944-71, Standard Test Method of Sampling Processed Peat
Materials, 1998.
356.ASTM D648, Standard Test Method for Deflection Temperature of Plastics
Under Flexural Load in the Edgewise Position, 2007.
148

Read a chapter pdf 2.31 MB

Transcription

Similar documents

ru-200 roofing underlayment - WaterBlock® Building Systems

Brochure - Gimatic

Swatchcard - National Office Furniture

Alro Plastics

Wind Turbine Lubricant Tests - Southwest Research Institute

EXTENDED LIFE ORANGE

MIL-SPEC RECYCLED - Solvents and Petroleum Service

Wholesale Adult Uniforms

nylatron® gsm pa6

Nerf Energy - TheChalkface.net