Characterization and analysis of waxes by differential thermal

Reprinted (rom
Reçu
le
'-
8
DEC.1969
•
PERGAMON
PRESS
OXFORD'NEW YORK LONDON PARIS
Ta1anta. 1967. Vol. 14. pp. 421 to 424. Pergamon
Press Lld.
Printed in Northern
lreland
CHARACTERIZATION AND ANALYSIS OF WAXES
BY DIFFERENTIAL THERMAL ANALYSIS
B. R.
CURRELL
Department of Chemistry, Northern Polytechnic, Holloway Road, London, N.7, U.K.
and
B. ROBINSON
Chiswick Products Ltd., P.O. Box 26, Burlington Lane,
Chiswick, London, W.4, U.K.
(Received 15 September 1966)
Summary- The characterization of waxes by differential thermal
analysis is described. An endothermic peak at 475-480° is characteristic of microcrystalline and polyethylene waxes, and measurement
of its area provides a method for the estimation of these waxes in
mixtures.
RECENT interest in the characterization
of paraffin and microcrystalline waxes and
in the analysis of mixtures of these waxes is typified by the papers by Ferris,l FOX,2
Templin3 and Ludwig.4 Lange and Jochinke5 have applied differential thermal
analysis (DTA) to a study of the melting and solidification of waxes (temperature
range 20-140°) and suggest that these curves may be used to characterize a wax and
in many cases to determine the components of a mixture. We have similarly applied
DTA but, in our case, in the range 20-600°.
From our studies of the melting curves we draw the same general conclusions as
Lange and Jochinke and suggest that, to a possibly limited extent, these curves may
be used to characterize a wax. The melting curves do not give unequivocal criteria
for distinguishing between microcrystalline
and polyethylene waxes and paraffin
waxes, but there is a tendency for most microcrystalline and polyethylene waxes to
be characterized by a single melting endotherm (Fig. 2), whereas the paraffin waxes
show at least two endotherms CFig. 1). Exceptions to this tendency are the Superla
165/170° and Jasber 180/185° waxes (e and h, Fig. 2) and the 140/145° ex Assam and
the 56/58° German Zeitz waxes (jandj, Fig. 1). The additional peaks in the paraffin
wax traces may be due to the crystalline transition orthorhombic -+ hexagonal which
Ludwig detected by infrared spectra.
DTA in the extended temperature range up to 600° does, however, provide a
ready means of distinguishing between microcrystalline and polyethylene waxes and
paraffin waxes. At the higher temperatures aIl the paraffin waxes showed broad
diffuse peaks which returned to baseline before 460°. ln contrast, a sharp peak at
475-480° is characteristic of all the microcrystalline and polyethylene waxes which we
have examined. This peak may be used to identify the presence of a microcrystalline
or polyethylene wax in a mixture and also to give a quantitative estimation of the
amount present; thus Table l shows the results obtained by measuring the area of
this peak and relating it to the amount of microwax C700 in an artificial mixture of
this microwax and the paraffin wax 135/140° exStanlow Refinery. The DTA trace
of the mixture containing 50,0 % of microwax is reproduced in Fig. 3.
421
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1
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Temperature,
1
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·C
1
200
1
300
1
400
1
SOO
1
1
o
œ
1
= ~ ~ =
1
1
1
1
1
0
Temperature,
Fm. l.-DTA
curves of paraffin waxes.
a, 135/140 ex Stanlow Refinery, sample 1; b, 135{140 ex Stanlow Refinery,
Sample 2; c, 140{145 ex Stanlow Refinery, sample 1; d, 140{145 ex Stanlow
Refinery, sample 2; e, 120{125 ex B.P. Trading Co;
140/145 ex Assam;
g, 135{140 ex Assam; h, 52{54 Russian; i, 52/54, German, Kopsen Webau;
j, 56/58 German, Zeitz.
f,
œ
1
= ~ ~ =
1
1
1
1
1
·C
Fm. 2.-DTA curves of micro and polyethylene waxes.
a, Microwax C23; b, Microwax C700; c, Superwax Amber 1800; d, Starwax
Amber 180°; e, Superla 165{170;
Superla 165{170; g, Bareco Amber;
h, Jasber 180{185°; i, Polyethylene PA130; j, Polyethylene AC 629; k, Polyethylene AC6.
f,
Characterization
and analysis of waxes by differential thermal analysis
Exo
En'do
l
J
o
100
L--J300
200
J
J
400
500
·C
Temperoture,
curve of 1: 1 mixture of microwax C23 and paraffin wax 135{140 ex
Stanlow Refinery.
The shaded area gives a measure of the amount of microwax present (see Table 1).
Fm. 3.-DTA
TABLEL-TypICAL RESULTSOBTAINEDlN THE
ANALYSISOF MIXTURESOF MICROWAXC700
AND PARAFFINWAX 135{40 ex STANLOW
REFlNERY
Microwax found by
measuring the area of the,
peak at 475°, %
Microwax
present, %
71·9
50,0
67-3
47·2
19·2
51-6
15·6
53'9
"
o
w
1
o
L-J
100 200
1
300
1
400
1
500
1
0
Temperature,
1
1
1
1
100 200 300 400
1
500
·C
FIG. 4.-DT A curves of waxes.
a Hoechst Wax L; b, Hoechst Wax OM; c, Candelilla Wax; d, Beeswax; e, Carnauba
Flake.
423
424
B. R. CURRELLand B. ROBINSON
To provide a comparison the DTA traces of sorne other waxes are included (Fig.
4). These include the natural waxes Beeswax, Candelilla and Carnauba Plake and the
synthetic Hoechst waxes Land OMo
These resuIts are preliminary; a full evaluation of the limitations of this method
of analysing wax mixtures will be carried out when we have finished a programme of
work designed to define the limitations of DTA as a quantitative method; factors to
be taken into account will include variations in the size and thermal conductivity of
the samples, heating rate, crucible design and methods of packing.
EXPERIMENT
AL
The apparatus used was the American Instrument Co. DTA instrument. The sample (~100 mg)
and reference material (calcined alumina) were contained in inconel cups, the bases ofwhich rested on
chromel-alumel thermocouples; the cups were supported in an inconel block. Differentiai temperature
was plotted against block temperature on an Aminco X-Y recorder. Ail runs were carried out at a
heating rate of 8°/min.
To obtain maximum reproducibility in the quantitative experiments the same components, i.e.,
cups, block and furnace, were used throughout. The pair of cups used were chosen to be as nearly as
possible of the same weight.
Acknawledgements-We
wish to acknowledge the generosity of the American Instrument Co. in
providing the DT A equipment on loan, and also the experimental assistance given by Mr. P. Stevenson,
who carried out many of the runs.
Zusammenfassung-Die
Charakterisierung
von Wachsen durch
Differentialthermoanalyse
wird beschrieben. Ein endothermer Peak
bei 475-480° ist charakteristisch für mikrokristalline und Polyathylenwachse; Messung seiner Flache bietet eine Methode zur Bestimmung
dieser Wachse in Gemischen.
Résumé-On décrit la caractérisation de cires par analyse thermique
différentielle. Un pic endothermique à 475-480° est caractéristique de
cires microcristallines et polyéthyléniques et la mesure de son aire
fournit une méthode d'estimation de ces cires dans des mélanges.
REFERENCES
1.
2.
3.
4.
5.
S. W. Ferris, Tech. Assac., Paper Pulp lnd., Spec. Tech. Assac. Publ., 1963, 2, 1.
R. C. Fox, ibid. 1963,2,160.
P. R. Templin, ibid. 1963, 2, 51.
F. J. Ludwig, Anal. Chem., 1965, 37, 1737.
J. Lange and H. Jochinke, Fette Seifen Anstrichmittel, 1965, 67, 89.