DRAFT July 2009

DRAFT
July 2009
DRAFT
July 2009
Content
Page
7.1
Introduction
1
7.2
Fibre Blend
7.2.1
General Principle
7.2.2
Type of Fibre Blends
1
1
2
7.2.3
Advantage of Fibre Blends
4
Yarn
7.3.1
Yarn Spinning
6
6
7.3.2
7.3.3
7.3.4
7.3.5
7.3.6
Fibre Spinning
Classification of Yarns
Novelty Yarns
Yarn Numbering Systems
Yarn Twisting
7.3
7.4
7.5
12
15
16
19
21
Fabric Construction
7.4.1
Fabric and Types
7.4.2
Woven Fabrics
23
23
25
7.4.3
7.4.4
7.4.5
32
38
39
Knit Fabrics
Non-woven Fabrics
Fabric Properties
Fabric Colouration
7.5.1
Colour Basics
7.5.2
Brief History of Dyes
7.5.3
Classification of Dyes
50
50
51
51
7.5.4
7.5.5
7.5.6
Dyeing
Dyeing Methods
Dyeing Machinery
56
57
59
7.5.7
7.5.8
7.5.9
7.5.10
Printing
Printing Methods
Printing Equipments
Fastness
62
63
64
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7.6
7.7
7.8
July 2009
Finishing
7.6.1
Pre-Treatments
68
68
7.6.2
69
After-Treatments
Fabric Quality
7.7.1
Strength
75
75
7.7.2
7.7.3
7.7.4
7.7.5
Pilling Resistance
Dimensional Stability
Colourfastness
Flammability
78
78
79
81
7.7.6
7.7.7
7.7.8
Toxicity
Rules and Regulations
Trademarks
83
84
88
Latest Development and Environmental Issues
7.8.1
Functional Textiles
7.8.2
Smart Fabrics
7.8.3
Plasma Technology
7.8.4
Environmental Protection
90
90
92
94
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7.1
July 2009
Introduction
Clothing (衣), then food (食), habitat (住) and transportation (行) are the four elements
that are necessary to daily living. Fabrics which are made from a variety of fibres are
the materials for making clothing and textile products. Each type of fibre or fabric has
its own properties and can be made into a variety of end products with different
functions Different ways to spin the fibre or to weave the yarn into fabric can change
the properties and affect the appearance, colour, hand feel, style of the products. These
properties should also be considered when designing fashion, developing textile
materials and constructing garments in order to select or create the most suitable
textile materials in meeting the needs of the wearers. Nowadays, the textile industry is
able to produce functional textiles with extra functions such as UV protection and
antibacterial.
7.2
Fibre Blend
Fibre blending is a common method to produce new textile materials by combining
properties of individual fibre components together. There are many fibre blends
available in the market. Some examples are cotton – polyester, nylon – spandex, wool –
rayon, etc. They serve a wide range of properties to suit different applications.
7.2.1 General Principle
Blending is the mixing of two or more components together to form a new material. It
can be done in several ways. Fibres can be blended in the fibre or yarn stages. The
blending of staple fibre and staple fibre requires homogeneously mixing two together
before yarn spinning. For the blending of filament fibre and staple fibre, filament is
required to chop into short segments before blending. Another method is to spin staple
fibre onto a filament core. The outcome of this would be that the core spun yarn
maintains the strength of filament fibre but the appearance of the staple fibre. The
blending of two synthetic fibres can form bi-component fibre. Fibre blends can also be
done by weaving and knitting different yarns into a single fabric. The fabric produced will
have properties of the two or more different textile fibres.
There are many combinations of blended materials. Some examples are natural –
natural and natural – synthetic fibres. There are also many ways of blending. Some
examples are staple – staple, core spun and bi-constituents. The properties of fibre
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blends can be determined by the selection of component fibres and the fine tuning of
blending ratio. Fibre blend composition is an important information for International
trade. Many countries such as USA and Europe have imposed tariffs on different textile
materials. It is rare to have fibre blend with 50% / 50% composition as there are no
restrictions on the major components present in blended fabrics that would affect the
tariff involved.
7.2.2 Types of Fibre Blends
Blending can be classified into different categories based on the textile fibre
composition or way of blending used. The following are some common combinations of
different fibre types:
A
B
C
Blending nature
Type
Examples
Natural– Natural
Cellulosic – Cellulosic
Cotton – Ramie
Protein – Protein
Wool – Cashmere
Cellulosic Regenerated
Cotton - Rayon
Protein - Regenerated
Wool – Rayon
Cellulosic - Synthetic
Cotton – Polyester,
Cotton – Spandex
Protein - Synthetic
Wool – Polyester,
Wool – Acrylic
Natural – Regenerated
Natural – Synthetic
D
Synthetic –
Regenerated
―
Polyester – Rayon
E
Synthetic – Synthetic
―
Nylon - Spandex
Apart from composition, classification of blended fabrics can be based on the way the
fibres are blended.
Blending Nature
Type
Examples
A
Staple - Staple
Yarn
Cotton - Ramie
B
Core spun (Staple –
Filament Blends)
Yarn
Cotton – Polyester Core
Yarn
C
Bi-Constituent or
Synthetic Filament
Acrylic – Acrylic
Tri-Constituent
D
Blended Fabric
Filament
Fabric
Polyester Warp / Cotton
Weft
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Blending of various textile fibres gives new textile materials different merits.
(A) Cotton – Ramie Blends
This is an example of blending of two natural cellulosic fibres. The first advantage is cost
reduction as cotton is cheaper than ramie. Second advantage is that ramie is stronger
than cotton. Hence, the blended fabric has a better strength. Thirdly, Ramie is more
water absorbent and dries quicker than cotton. This enhances the water absorption
power and dry rate of the blended fabric. Fourthly, cotton can render the blend softer as
ramie is a kind of stiffer and brittle fibre. The new fabric feels more comfortable. The
degree of enhanced properties depends on the blending composition.
(B) Cotton – Polyester Blends
This is a popular fibre blend for all kinds of applications such as clothing, furniture,
bedding items, etc. There are several types of blending. They are namely, T/C, CVC and
CVS. T/C blend refers to polyester – cotton blend. “T” standard for a famous brand of
polyester called Terylene produced by ICI. Polyester is the major component and
polyester fibre content is higher than that of cotton in the finished blended fabric.
Common ratios are 65/35, 80/20, etc. This kind of blended fabric demonstrates
polyester properties such as wrinkle free, low shrinkage and it is compromised with
better water absorption.
CVC stands for Chief Value Cotton in which cotton is the major component and such
type of blended fabric demonstrates the advantages of cotton. CVS stands for Chief
Value Synthetic with polyester is the major component and such type of blended fabric
demonstrates the advantages of polyster.
(C) Wool – Polyester Blends
The major disadvantages of wool product are shrinkage and felting. The blending of
polyester and wool makes the fabric resistant to shrinkage and felting. As polyester is
low in moisture content, this will maintain wool’s quick dry property. Polyester is also
easy to clean and this perfectly fits with wool’s soil resistant property. The blended fabric
is commonly used for making suits and trousers.
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(D) Nylon – Spandex Blends
This kind of blended fabric is a common fabric used for swimwear and sportswear as
nylon provides good abrasion resistance and high strength. The incorporation of
spandex renders the fabric highly stretchable. All these properties are basic
requirements for fabrics used for swimwear and sportswear.
(E) Bi-Constituent Fibres
Man-made fibres can be blended together in the fibre spinning stage. Two different
materials can be extruded together to form a single fibre. Two component materials are
permanently joined together and cannot be separated. Fibre content analysis of such
type of fibre is usually through the chemical approach.
Figure 7.1 Several types of bi-constituent or tri-component fibres with different textile
materials A, B and C are fused together to form a single fibre
7.2.3 Advantages of Fibre Blending
Chemical synthesis is the major approach employed to create new materials. However,
such process is time consuming and costly. This may also requires technological
advancement, which is very likely to further increase the cost. The blending of different
textile fibres in yarn or different yarns in fabric is a well known economic method to
produce new textile materials. The development time can be kept to a minimum as all
the technologies required are already well developed. This is why blending is a cheaper
process. When fibres are blended, the weakness of one type of fibre may be
complemented by the strength of the other. The following is the summary of the
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advantages of fibre blending.
Low cost
Quick development time
Advantages of different fibre components can be combined and manifested
Enhancement of particular advantages of a fibre component
Minimise, reduce or compromise of demerits of a fibre component
Give a chance to fine tune various properties to suit different applications by
changing fibre composition
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7.3 Yarn
Yarn is a thread-like material with continuous length made from textile fibres being
twisted together. The process is called yarn spinning. Staple fibre itself has limited
length (ranging from an inch to few inches). Yarn spinning can produce threads with
continuous length for fabric manufacturing. Filament fibres need fewer twisting to form
stable threads. Man-made textile materials are thermoplastics and fibre extrusion (or
fibre spinning) is required for the production of filament fibres. The thickness of the yarn
and the number of twist will affect the thickness, weight, way of handling and end use
of the fabric.
7.3.1 Yarn Spinning
The conversion of fibres into yarns is called yarn spinning. The principle of yarn spinning
is twisting fibres together for coherence. There are two common processes for yarn
production, viz ring and open end spinning.
(A) Preparation of Fibres for Yarn Spinning
Takes cotton as an example, Figure 7.2 illustrates the flow of the use of cotton from
harvesting to shipment in the form of cotton fibre. Cotton seeds are harvested from
plants and dried to reduce moisture. The dried seeds are then cleaned. Leaves, stems
and other useless parts are removed. The next process is called ginning, which involves
the use of machine to separate fibres from the seeds. Separated fibres are called lint.
Cotton lint is then packed into standard package called bale. Bales are arranged into
specific dimensions and weights. The bales are then graded depending on the fineness,
staple length and colour of cotton lint. Graded cotton is then priced and shipped out.
Remaining seeds are used for oil extraction.
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Figure 7.2 Flowchart illustrating processes from harvesting cotton to shipping out for
yarn spinning
Figure 7.3 Saw ginning machine is used to separate cotton seeds from lint
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Figure 7.4 Universal density bales of cotton lint
Upon spinners receiving the bales, they will open the bales and further clean the lint.
The lint is then being put through the following processes before yarn spinning.
(i)
Carding
Each carding machine is set with hundreds of fine wires that separate the fibres and pull
them into somewhat parallel form. A thin web of fibre is formed and passes through a
funnel-shaped device that produces a ropelike strand of parallel fibres. Blending takes
place by joining laps of fibres.
(ii)
Combing
When a smoother, finer yarn is required, fibres are subject to a further paralleling
method. A comb-like device arranges fibres into parallel form with short fibres falling out
of the strand.
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Carded yarn
Combed yarn
Figure 7.5 Carded and combed yarn
(iii) Drawing Out
After carding or combing, the fibre mass is referred to as the sliver. Several slivers are
combined into one before the process of drawing out. The combined silver passes
through a series of rollers rotating at different rates of speed. The process elongates the
combined sliver into a single more uniform strand that is given a small amount of twist
and fed into large cans. Carded slivers are drawn twice after carding. Combed slivers
are drawn once before combing and twice more after combing.
(iv) Twisting
The slivers are fed through a machine called the roving frame where the strands of
fibres are further elongated and given additional twist. These strands are called the
roving.
(B) General Types of Yarn Spinning
(i)
Ring Spinning
The roving is fed from the spool through rollers (drafting zone) where one roller turns
slow and the next roller turns fast. This arrangement elongates the roving. It then
passes through the eyelet, moving down and through the traveler. The traveler moves
freely around the stationary ring at 4,000 to 12,000 rpm. The spindle turns the bobbin at
a much faster speed (~25,000 rpm). Rotation of the bobbin and the movement of the
traveler twist and wind the yarn in one operation.
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Figure 7.6 Ring spinning
(ii)
Open-end Spinning (Rotor Spinning)
The sliver is fed into the spinner by air jet. It is then delivered to a rotary beater that
separates the fibres into a thin stream that is then carried into the rotor by a current of air
through a duct and is deposited in a V-shaped groove along the sides of the rotor. As the
rotor turns, twists are produced and the yarn is formed. The formed yarn is an one end
yarn and is then packed tightly in rolls. The twisting of yarn is determined by the ratio of
rotor speed and the linear speed of yarn transfer.
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Figure 7.7 Open-end spinning
Open–end spinning produces twisting on the yarn surface and a more uniform yarn than
ring spinning. The yarn produced with this technique is less strong, more extensible,
bulkier, more abrasion resistant and absorbent. The technique brings to the yarn two
advantages. It is fed by sliver instead of roving in ring spinning. This simplifies the
process step and saves cost. It can also be modified to remove any remaining trash,
thereby improving the quality of the yarn.
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Figure 7.8 Comparison of ring spun and open-end yarn. Ring spun yarn has twisting
throughout whole piece of yarn. Open-end yarn has twisting only on the outer surface
and fibres in the centre are parallel to the yarn axis. Ring spun yarn is finer and stronger
than open-end yarn.
7.3.2 Fibre Spinning
Fibre spinning is a similar process to yarn spinning but it refers to the formation of fibre
from polymeric substances. It is a manufacturing process of synthetic fibre. There are
three types of fibre spinning process, viz dry, melt and wet spinning. The fibres
produced are in filament form and can be further processed to staple form for better
imitation of natural fibres.
(A) Dry Spinning
Dry spinning is based on the dissolution of polymer by volatile solvents. The polymer
solution then passes through the filter for removing un-dissolved substances and
extrudes through spinnerette. The extruded fibres then pass through a stream of hot air
for evaporation of the solvent (drying) and solidifying.
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Figure 7.9 Dry spinning
(B) Melt Spinning
Melt spinning is a technique that involves molten polymers. Melted polymers pass
through a heated filter for removing solid trash. They are then extruded through the
spinnerette. Afterwards, they pass through a stream of cool air. Extruded fibres solidify
upon cooling.
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Figure 7.10 Melt spinning
(C) Wet Spinning
This process is based on the modification of polymer. Modified polymers are soluble in a
particular solvent. The polymer solution is then being extruded through the spinnerette,
a technique similar to that involved in the dry spinning process. The extruded fibres then
pass through a coagulating bath that converts the modified polymers back to insoluble
form.
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Figure 7.11 Wet spinning
7.3.3 Classification of Yarns
Based on fibre length, yarn can be classified as staple and filament. Staples refer to
short fibres ranging from less than an inch to a few inches. Most of the natural fibres are
staples. Filaments refer to long fibres with continuous length. Most of the man-made
fibres are filaments. To imitate natural fibres, man-made filament fibres may be chopped
into shorter lengths. The only natural filament is silk. The length of filament fibres
extracted from silk cocoons is around a mile long. Yarn made from staple fibres needs
twisting to hold fibres together to form a single thread. Yarn made from filaments does
not need much twisting to hold filaments together. The twisting done in this way is not
easily seen.
Figure 7.12 Staple and filament yarn
Furthermore, yarn can be classified into single and ply depending on the number of
strands composing the yarn. Ply yarn is nomenclature with the number of strands in
front of “ply yarn”. For example, a double strand yarn is called “two ply yarn”.
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Figure 7.13 Z-twist ply yarn
7.3.4 Novelty Yarns (Fancy Yarns)
Yarn can also be texturised to give special effects. Such kind of yarn is called novelty
yarn or fancy yarn. Novelty yarns (also called fancy yarns) are yarns with an interesting
texture or other unusual features that distinguish them from ordinary yarns. Typically,
these yarns involve at least one or two strands of regular yarns twisted together with
something else to make an interesting texture and they are frequently made from
synthetics such as nylon but can also be composed of natural fibres.
Very often, novelty yarns involve frequent colour change. Most often these will be
obtained through the print process in which a fibre will be dyed in different colours
through the dyeing process. Sometimes different colours and effects can be obtained
by spinning yarns with different colours together. A series of colours or shades can be
dyed in a part of the yarn. As the yarn is long enough, the dyeing sequence will be
repeated for many times to enable a self-striping feature when knitted into fabric. If a
proper number of stitches is cast, then stripes will appear as the yarn is knitted into a
garment. Sock yarn companies have evidently taken a great interest in self-striping yarn.
Such kind of yarn has a wide array of different effects that can be obtained by knitting
the yarn in the round over the number of stitches normally cast for a sock.
(A) Bouclé
It appears as a length of loops of similar size and can range from tiny circlets to large
curls.
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(B) Eyelash Yarn
It appears as a thread base with several long strands spaced at even intervals that jut
out at an angle from the main strand. The long strands or hair can be metallic,
opalescent, matte or a combination of different types. The strands that jet out can be
curly or straight and can sometimes be in two different lengths.
(C) Flammé
It is generally a loose or untwisted core wrapped by at least one other strand. The extra
element can be a metallic thread or a much-thicker or much-narrower strand of yarn. It
can also be yarn that varies between thick and thin.
(D) Ladder Yarn (Train Tracks Yarn)
It is constructed like ladders with a horizontal stripe of material suspended between two
thinner threads, alternating with gaps.
(E) Ribbon Yarn (tape yarn)
It is made of ribbon but generally not the kind of ribbon used in sewing and millinery.
They are in fact ribbons made especially for knitting or crocheting with some in a tubular
form, some woven flat and some similar in appearance to bias tape. Ribbon yarn can be
composed of many materials ranging from synthetics to silk, and to plant fibres.
(F) Slub Yarn
This a 2-ply yarn with a textured and lumpy surface. The yarn is made up of a smooth
ply and one that is spun unevenly, which creates 'slubs' or lumps.
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(1) Bouclé
(2) Eyelash
(3) Flammé
(4) Ladder
(5) Ribbon
(6) Slub yarns
Figure 7.14 Various types of novelty yarns
(G) Composite Twist Core-spun Yarn
This is a new type of yarn claimed to be no torque. The yarn has a hard core covers with
dual spun. The dual spun layers are in opposite twist to counter balance torque.
Figure 7.15 Composite twist core spun yarn
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7.3.5 Yarn Numbering Systems
The fineness of yarn (yarn size) is an important parameter to determine the quality of
fabric properties. The way of describing yarn fineness is called yarn number. The finer
the yarn, the thinner and softer the fabric will become and the clothes will fit better.
Traditionally, there are many yarn number systems for different types of materials.
However, these methods can generally be categorized into two main types, the direct
and indirect systems. Most importantly, yarn size is defined by its length and mass.
(A) Direct Systems
“Direct” means the greater the yarn size, the greater the yarn number. It is based on the
mass of the yarn segment per unit length. Common systems are denier and tex. Denier
count (Td or D) is defined as weigh (in gram) of yarn per 9000 m of yarn segment. Tex
count (tex) is defined as weigh (in gram) per 1000 m of yarn segment.
Examples:
Yarns
Weigh per 1 m
(G)
Length per 1 g
(m)
20 D yarn
0.002
450
20 tex yarn
0.02
50
Figure 7.16
A yarn size of 20 tex yarn
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(B) Indirect Systems
“Indirect” means the greater the yarn size, the smaller the yarn number. It is based on
the length of the yarn segment per unit mass. Cotton count (‘s) is a typical example.
Cotton count is defined as the number of hanks of cotton yarn per 1 lb. traditionally,
cotton yarn is traded in hanks and the length is 840 yards.
Examples:
Yarns
Size
Length
per
1
lb Weigh per 1 yard
(yard)
(lb)
20 s’ cotton
yarn
Thinner yarn
16800
0.00006
10 s’ cotton
yarn
Thicker yarn
8400
0.0001
Figure 7.17 Yarns of size 20 s’ cotton count
In terms of SI unit, international metric count (Nm) is similar to cotton count and is
defined as number of km of yarn per 1 kg. The figure below lists out the various
conversions of different yarn number systems.
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Yarn Type Conversion
Equation
Cotton to Denier
5315 / Cotton Count
Denier to Cotton
5315 ÷ Denier
Cotton to Metric
Cotton Count x 1.69
Metric to Cotton
Metric Count x 1.69
Denier to Metric
9000 ÷ Denier
Metric to Denier
9000 ÷ Metric Count
Cotton to Tex
590.5 ÷ Cotton Count
Tex to Cotton
590.5 ÷ Tex Count
Tex to Metric
1000 ÷ Tex Count
Metric to Tex
1000 ÷ Metric Count
Tex to Denier
Tex Count x 9
Denier to Tex
Denier ÷ 9
Denier to Decitex
Denier ÷ 0.9
Metric to Decitex
10,000 ÷ Metric Count
Cotton to Decitex
5905 ÷ Cotton Count
Figure 7.18 Various conversion factors for different yarn number systems
7.3.6 Yarn Twisting
Twisting is to hold fibres together in yarn. The more the twisting, the greater holding
force imposed between fibres. As a result, a more compact yarn is produced (stiffer and
finer) which is usually used as the warp yarn of woven fabric. On the contrary, the less
the twisting, the softer the yarn will be. Also greater twisting gives greater yarn strength
but also a greater tendency for fabric skewness. It is a parameter that determines the
properties of fabrics. Twisting can be described by its direction and number of twisting
per inch (TPI). Yarn twisting direction is classified as Z and S direction.
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Figure 7.19 Various yarn directions (S and Z) and twist per inch
Although more twisting gives a stronger yarn, softness and absorbency will decrease.
Fabrics made from high TPI yarns give a harsh hand feel and less efficient to keep warm.
Furthermore, TPI cannot be increased continuously as over twisting will break the yarn.
TPI needs to be balanced between strength and softness.
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7.4
July 2009
Fabric Construction
Fibre is the raw material in the textile industry. Yarn is produced from fibre. Yarns are
then used for constructing fabrics. Fabrics are then applied for various kinds of final
textile products such as garment, bedding items, bag, etc.
Figure 7.20 Different stages of textile production
7.4.1 Fabric and Types
Fabrics, which are also called piece goods, are basically constructed from yarns. The
two processes used to convert yarns into fabrics are weaving and knitting. Fabrics
produced from weaving are called woven fabric. Fabrics produced from knitting are
called knit fabric. Besides, there is a third type of fabric that is produced directly from
fibre without weaving and knitting. It is called non-woven fabric. The production cost of
non-woven fabric is comparatively lower than that of woven and knit fabric. This kind of
fabric is popularly used in one time use garment, reusable shopping bags, particle filter,
etc. Fibres used to produce non-woven fabrics are held together by mechanical,
adhesive or heat fusion.
Fabrics are usually traded in rolls. Some common terms for various parts of a fabric are
as follows:
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Figure 7.21 Various terms of fabric
(A) Face and Back
Each piece of fabric has its face and back, which may differ from each other. Face is
usually the side with better appearance and more brilliantly coloured. Some fabrics
types such as plain weave, rib, interlock, etc have identical sides and their face and
back cannot always be distinguished.
(B) Length and Width
The long direction of fabric, which is the direction of machine producing the fabric, is
called warpwise, lengthwise or machine direction in woven fabrics. Yarns that run along
this direction are called warp or ends. The short direction of fabric is called weftwise,
widthwise or cross-machine direction in woven fabrics. Yarns that run along this
direction are called weft, filling or pick. For knit fabrics, the long direction is called wale
or machine direction while the short direction is called course or cross-machine
direction.
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(C) Fabric Edge
The edge of fabrics is called selvedge, which usually has a different structure from the
centre portion of the fabric. It is usually used for heat setting. Also, finishing or printing
may not apply to selvedge.
7.4.2 Woven Fabric
Woven fabric is the kind of fabric formed from interweaving two sets of yarns at a right
angle. Warp (or ends) yarns are parallel to the machine (lengthwise) direction. Weft
(filling or picks) yarns are horizontal to the cross machine (widthwise) direction.
(A) Weaving
It is a process in which warp yarns and weft yarns are interlaced to form fabrics. The
equipment for weaving is called weaving looms or simply weaving machine. Warp yarns
are winded on a very big roll called the warp beam. Weft yarns are winded on a spindle
shape apparatus called the shuttle. In the weaving process, warp yarns are separated
into two groups and fed to two comb-like frames (harness) which can be raised and
lowered alternately. This will produce an opening in the warp ends called shed. Weft
yarn is passed through the shed and packed closely by a reed. The warp frames raise
and lower alternately to complete a weaving action. A piece of fabric is produced by
repeating the same action. The up and down patterns of warp beams determine the
fabric construction.
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Figure 7.22 Side view of a weaving machine. The filling yarn insertion is perpendicular
to the page
Fill Insertion
Traditionally, filling yarn insertion is done by hand. Shuttle is thrown through the shed
from left to right and right to left alternatively. It is for sure that modern weaving
machines can do this in a more efficient and faster way. There are four main kinds of fill
insertion.
(1)
Shuttle
A modern from of shuttle machine that transfers shuttle mechanically. Usually, this is
done by spring loaded projection.
(2)
Projectile
This is a shuttleless loom that replaces shuttle with a bullet-shape projectile to carry the
filling yarns.
(3)
Rapier
It is a thin metallic shaft with a yarn gripping device. It includes a single or double rapier
that carries filling through the shed.
(4)
Water/Air Jet
This is a very fast weaving machine that employs either a jet of water or air to carry the
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filling yarn through the shed.
(B) Types of Woven Fabric and their Properties
Different arrangements of up/down pattern of warp and weft yarns produce a wide
variety of woven fabrics. According to the surface characteristics, there are woven
fabrics with plain surface and woven fabrics with raised surface. There are three types
of plain surface woven fabric. They are plain weaves, twills and, satins and sateens.
Pile fabrics are woven fabric with raised surface as there are short fibres on the
surface.
(i)
Plain Weave
Fabric with yarn either warp or weft passes over only one yarn. Many kinds of plain
weave fabric, e.g. canvas, poplin, chiffon, chambray, gingham, crepe, etc.
Figure 7.23 Plain weave
Poplin
Poplin is plain weave fabrics with high dense warp and low dense weft yarns. The count
of weft yarn is usually half of the warp. This produces crosswise rib characteristics on
the fabric.
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Figure 7.24 Poplin
Chambray
A plain weave fabric mainly made of cotton or rayon with similar warp and weft density
(~80 per inch). It is constructed with dyed warp beams and white weft yarns. The fabric
is commonly applied to the production of child’s garments.
Figure 7.25 Chambray fabric
(ii)
Twill
This a kind of woven fabric with the weft yarn passes over more than one warp yarn.
Such construction will produce different slanted patterns on the fabric surface. If the
pattern slants to right hand side, the fabric is called S twill. Fabric with pattern slants to
left hand side is called Z twill. Common examples are 2/1, 2/2, 3/1 twill, herringbone, etc.
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(A) 2/1 S-twill
(B) 2/2 Z-twill
Figure 7.26 Twill fabrics
Denim
This is a very popular type of twill fabric for making jeans, jackets, shirts, bags, etc. The
warp beam is dyed with indigo and weft yarns are usually not dyed. It is usually made of
cotton, rayon or cotton/polyester blends. The fabric is comfortable, very durable with a
wash look.
Figure 7.27 Denim fabric (Z twill)
(iii)
Satin and Sateen
Similar to twill, fabrics with a weft yarn pass over five to eight warp yarns are classified
as satin or sateen. As one yarn floats over so many yarns, the face will mainly show the
float yarns. For warp on the face, this kind of fabric is called satin. For weft on the face,
this kind of fabric is called sateen.
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(A) satin
(B) sateen
Figure 7.28 Satin and sateen fabric
(iv) Pile Fabrics
Pile fabrics are fabrics with short fibres (pile) on the surface. Usually, pile is produced
from cutting floating yarns on the surface of fabrics and having them brushed. Corduroy
and velvet are two popular examples.
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(A) corduroy
(B) velvet
Figure 7.29 Fabric construction of corduroy and velvet
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7.4.3 Knit Fabrics
Knit fabrics are fabrics produced by interlocking loops of yarn.
Figure 7.30 Single jersey
(A) Knitting
Unlike weaving, knitting is done based on a single yarn. Knit fabrics are composed of
continuous interlocking loops. The major part of the machine is (latched) needles which
have hooks with flipping latches. Those needles will move up and down according to a
rotating metal cam at the base. The flipping latch will open and close during the knitting
action cycle to grab new yarn segment through the yarn loop. A new yarn loop is called
a stitch. A knit fabric is formed from repeating these actions.
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Figure 7.31 Knitting action for constructing a weft knit fabric. Step 1: Needle in ground
position and it is closed and holding a yarn loop. Step 2: Needle moving up according to
the clearing cam and the yarn loop flip open the latch. Step 3: Needle continues to move
up and the open hook passes over a new yarn segment. Step 4: Needle hooks the new
yarn segment and moves downward. The old loop flips up the latch and closes the hook.
Step 5: Needle moves downward and draws the yarn through the old loop to form a new
loop. The process repeats.
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Figure 7.32
July 2009
Basic design of a latched needle. Various parts of the needle serve
different functions. The hook is for collecting yarn and drawing the yarn through the yarn
loop. The latch enables the hook to close and open. The roundout is for holding the loop.
The butt is to translate the needle motion according to the clearing cam.
There are two types of stitches depending on either the next stitch passes through the
previous loop from above or below. If the stitch passes from above, it is called a purl
stitch. If it goes below, it is called a knit stitch.
Figure 7.33 Purl and knit stitch
(B) Types of Knit Fabric and their Properties
According to the orientation of loops, there are two types of knit fabrics, viz weft and
warp knit. Traditionally, weft knit fabrics are used more for clothing. Warp knit fabrics are
for special applications.
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(i)
July 2009
Weft Knit
Weft knit is a fabric formed from parallel courses of yarn running horizontally. This
direction is called course. The loop is aligned parallel to the fabric axis and called wale.
Basically, the fabric can be produced from a single yarn. Most of the knit fabrics
commonly used are weft knit.
Single Jersey
This is the most common and simplest kind of weft knit fabric. The fabric is formed from
continuous knit stitches. The face and back of this kind of fabric are completely
different. Rows of “V” shape can be seen on the face side and on the back side are
rows of “half circle” shape.
(A) Face side (sketch)
(B) Back side (sketch)
(C) Face side (photo)
(D) Back side (photo)
Figure 7.34 Single jersey fabric
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Rib
Knit fabrics are constructed with alternate purl and knit stitches form the rib. The fabric
formed by one purl stitch alternates one knit stitch is called 1 x1 rib fabric. Similarly, the
fabric formed by two purl loops with one knit loop is called 2 x1 rib fabric. Rib fabrics
have twice the thickness of single jersey fabrics and they are more extensive along the
course direction.
(A) 1x1 rib
(B) 2x2 rib
Figure 7.35 Rib fabric
Interlock
This is a double knitted fabric with two identical layers that interlace together. Both
sides of the fabric are identical. It is a stable knit fabric with less shrinkage.
Figure 7.36 Interlock fabric.
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French Terry
Knit fabrics with extra yarn inserts that contain hanging loops form a raised surface.
Those fabrics are mainly applied to towel and infant clothing production as the loosely
twisted loop yarn renders the fabrics greater water absorbency and softness.
Figure 7.37 French terry fabric
(ii)
Warp Knit
Fabric formed from many yarns that run vertically. Loops interlock each other
horizontally. Warp knit is a technique commonly used to construct lace, mesh, elastic
knit, etc, for lingerie and swimwear.
Figure 7.38 Warp knit fabric
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Lace
An openwork fabric patterned with open holes in the work made by machine or by hand.
The formation of these holes is done via the removal of threads from a woven fabric but
many kinds of lace are made by the warp knit technique.
Figure 7.39 Lace fabric
(Source: http://www.asyoulikeitbridal.com)
7.4.4 Non-woven Fabrics
The cost for producing non-woven fabrics is usually cheaper than that of woven and knit
fabrics as no yarn is required in the production process. Non-woven fabrics are formed
directly through fibre compression. The interlocking of fibres can be done by mechanical
(friction), adhesive and heat fusing. Mechanical bonding is done by piercing the fibres
with saw-like needles which will roughen the surface of fibres as the friction between
fibres locks each other.
Figure 7.40 Non-woven fabric
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7.4.5 Fabric Properties
Different fabrics possess various kinds of properties. These properties can basically be
classified into different categories based on their physical characteristics, chemical
composition, etc.
(A) Physical Properties
Fabrics can be specified by several fundamental physical properties, viz fabric weight,
fabric count and yarn count.
(i)
General Fabric Specifications
Fabric weight is the measurement of the weight of fabric per unit area. It is an indication
of fabric density and it relates to other fabric properties such as strength, etc. Fabric
weight is an important specification that is usually included in buying contracts.
Traditionally, it will express as ounce per square yard (oz/yd2) or simply called ounce. It
is still commonly used for woven fabric specification. SI unit version is gram per square
meter (g/m2). This is commonly used in knit fabric.
Another property for fabric specification is fabric count. It is the number of yarns per unit
distance of fabric. The common practice is to express the number of yarn per one inch.
Woven fabric construction can be specified as number of warp yarn per inch and weft
per inch. For knit fabrics, it can be specified as the number of wale per inch and the
number of course per inch.
Yarn count is another specification for fabric that has been explained in the previous
section.
Different fabric constructions give different properties. Woven fabrics are generally
more dimensionally stable to laundering, more abrasion resistant, less extensible and
not elastic, except with spandex yarn. On the contrary, knit fabrics are a more delicate
construction; knit fabrics are better in terms of drape, more flexible, softer, with greater
extensibility and certain amount of elasticity. However, knit fabrics are less strong, less
abrasive resistant and less dimensionally stable to laundering.
(ii)
Abrasion Resistance
Abrasion resistance refers to the fabrics’ resistance to rubbing until defects appear.
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Common defects are yarn breakage, fabric rupture, removal of coating, removal of pile,
etc. This is one of the measures to test fabric durability. Products with higher abrasion
resistance are ensured to be more durable. Abrasion resistance is a complex property.
The performance of abrasion resistance depends on the material used, its smoothness,
yarn size, yarn twisting, fabric construction, fabric thickness, etc. Polyamide (or Nylon)
and polyester are well known as materials with good abrasion resistance. They are the
major fibres used for sportswear. High amount of rubbing is expected during their usage.
Furthermore, a high twisted yarn has a greater holding force between fibres and gives
better abrasion resistance.
(iii) Dimensional Stability
Dimensional stability refers to the dimensional change, change in length and width and
fabric skewness after repeating laundering. Fabrics made from interlacing or
interlocking of yarns are not rigid materials. They can extend or shrink upon usage and
processing. Generally, fabrics tend to shrink rather than grow. The main reason is that
tension set in textile processing such as spinning, weaving, colouration, etc may release
upon un-tension wet process, i.e. washing.
(iv) Shrinkage in Cellulosic Fabrics
The shape of cellulosic fibres is hold by weak hydrogen bonding. Hydrogen bonding
between molecular chains can be destroyed by water. Water will swell the fibre and
release the stress set in previous processing. As a result, fibres shrink. Upon drying,
water molecules evaporate and new inter-molecular chain hydrogen bondings form and
set the shape of fibres that have shrunk.
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Figure 7.41 Cellulosic shrinkage and wrinkle formation through the wet–dry state such
as laundering
(v)
Strength
Strength can be measured in many ways depend on the type of material being tested.
These ways include tensile, compression, shearing, etc. Commonly, textile material
strength can be measured in three ways.
Fabrics
Strength
Woven fabrics
Tensile strength
Tearing strength
Knit fabrics
Bursting strength
Tensile Strength
Tensile strength for textile materials is defined as the maximum pulling force (Fbreaking)
that a material can stand before rupture per width of specimen under tension. The
tensile strength of warp and weft are usually different. As warpwise direction is always
under tension in weaving and processing, warp requires a higher tensile strength than
weft yarn.
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Fbreaking
Tensile Strength = ——————————
Specimen
Tearing Strength
Tearing strength for textile materials is the force required to tear off a certain length of a
fabric sample. Similar to tensile strength, tearing strength of warp yarn is stronger than
that of weft yarn. Tearing strength parallel to weft is stronger than that of warp direction.
(A) Tearing along warp direction and .
weft yarns breaks the fabric.
(B) Tearing along weft direction and
warp yarns breaks the fabric
Figure 7.42 Tearing strength
Bursting Strength
Knit fabric strength is expressed by its bursting strength. It is similar to inflating a
balloon until it burst. With the help of highly elastic rubber membrane, knit can be
inflated to burst. The pressure required is called bursting strength.
(vi) Extensibility
Another important property for fabric is extensibility. This relates to garment fitting.
Fabric construction allows certain degree of extensibility. Generally speaking, knit
fabrics are more extensible than woven fabrics as the interlocking loops of knit fabrics
can extend under stress. Extensibility of a fabric also depends on the material used.
Synthetic fibres are mainly made of thermoplastic materials and these materials can be
extended more than natural cellulosic fibres. Regenerated cellulosic fibres can also be
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considered as a kind of plastic material and they give greater extension then natural
cellulosic fibres.
(vii) Elasticity
Elasticity is very similar to extensibility; however, elasticity refers to the retention of the
original dimension after the removal of stress or simply the fabric’s recovery ability. This
can also be called the memory of the material. Rubber is a well known elastic
substance. Textile fibres are inelastic, except spandex. Spandex or elastane fibre is
made from segmented polyurethane polymer. Besides, elasticity partly comes from the
material itself. It can partly come from fabric construction. The interlocking of loops in
knit fabrics renders the fabric greater elasticity. Woven fabric construction is generally
inelastic but elasticity can be imposed by incorporating elastic yarn in the production of
woven fabrics. In the market, it is not difficult to find elastic denim jeans that such
production principle is applied to it.
(viii) Thermal Insulation
This is one of the functions of textiles. Irrespective of the textile materials involved,
some specific fabric constructions are able to increase the fabrics’ ability to keep warm.
For example, raised fabrics can trap more air, which is a poor thermal conductor, to
allow more heat to be trapped within the clothing. Apart from that, a more compact
construction can prevent air flow and minimise heat loss by convection.
(ix) Air Permeability
This property refers to the restriction of air flow through the fabric, it is an opposite
property to the thermal insulation; however, good air permeability allows fabrics to
breathe. This means that sweat can evaporate and freely pass through clothing. This is
one of the measures used to evaluate clothing of their comfortability. It is an important
parameter for sportswear application.
(x)
Water Proofing
Without specific finishing done, most of the textile materials are not water proofing.
Water proofing is generally achieved by applying hydrophobic reagents on fabrics.
(xi) Water Absorbency
Most of the textile materials are able to absorb water and moisture. Wet textiles usually
demonstrate strength loss after being wet, except natural cellulosic fibres. Water
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absorbency is important in some applications such as towel, sportswear, underwear,
etc.
(xii) Comfortability
Whenever consumers select clothing, comfortability is a very important factor to them. It
is not a property that stands on its own. It most certainly relates to a number of physical
and chemical properties such as softness, smoothness, breathability, water absorbency,
absence of skin irritant, compatible pH level, etc. Some of the factors can be collectively
called hand feel. Comfortability is a subjective property and it varies from user to user.
(xiii) Heat Stability
Textile products may form wrinkles upon daily use and laundering, particularly cellulosic
materials. Ironing is usually applied to remove wrinkles. Heat stability is an important
factor that affects the ironing temperature that the fabrics can afford.
Materials
Recommended Ironing Setting
Temperature
Cellulosic fibre
Hot
~200°C
Protein fibre
Warn
~150°C
Synthetic fibre
Cool
~110°C
Cellulosic fibres are very heat stable. They will char and do not melt at high temperature.
They can be used as a thermal insulated material such as thermal gloves. Animal fibres
are mainly protein fibres and their heat stability is of medium level. Similar to cellulosic
fibres, animal fibres will not melt but high heat may damage the fibres. Most of the
synthetic fibres such as polyester, nylon and acrylic are thermoplastics. They get
softened upon heating. This temperature that transforms the physical formation of
fabrics is called the glass transition temperature. It is important to note that synthetic
fibres do melt at certain high temperature. Specific types of synthetic fibres made of
highly crystalline polymers such as aramid or thermal setting materials such as
melamine are with high heat stability. They are usually used for the production of
firemen’s clothing.
(xiv) Static Electricity
Static electricity is the local accumulation of either positive or negative charges. Static
electricity is caused by the transfer of electrons from one object to another and during
rubbing. As charges are built up and accumulated, they may discharge to any
substances that are nearby. This is why there is sparking when clothe are taken off at
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night, particular in dry weather. Most of the textile materials are electrical insulators and
can build up charges readily when rubbing. Static electricity may create different
problems:
Skin irritation
Sticking dusts
Sparking
Damage electronic device
Figure 7.43 Static electricity
Measurement of Static Electricity
Static electricity is usually considered as the reverse of conductivity and it is defined as
the resistivity per unit length of material. The unit is m-1.
(B) Chemical Properties
(i)
Light Fading and Degradation
Light is electromagnetic radiations that can be classified into various types according to
their different wavelengths. Electromagnetic radiation spectrum contains low energy
radio waves, very high energy X-ray and cosmic ray. Sunlight (or daylight) is one of the
light sources that contains infrared, visible and ultraviolet radiations. Different types of
light interact with materials differently. Infrared radiation (IR) is related to heating effect.
Visible light is what naked human eye can see. Ultraviolet (UV) radiation is contains a
higher level of energy in terms of chemical bonding. It is well known that textile colour
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fades under light. UV is the main cause. UV can gradually degrade almost all colourants.
Apart from that, UV can also induce photo-degradation on finishing and textile materials.
In time, finishing and textile materials rupture and turn yellow.
(ii)
Photo-degradation
Photo-reactions are very complex sets of reactions mainly caused by free radicals
which cause the aging of materials.
(iii) Thermal Degradation
Heat can degrade textile materials through various kinds of chemical reactions that are
known as thermal degradations. Heat generally accelerates most of the chemical
reactions. For example, high temperature may degrade resin finishing and release
formaldehyde. This is one of the common problems that emerges during product
shipment. In the past, there were many overseas buyers complaining about the bad
smell that released from shipped products when opening up the carton boxes. Usually,
heat is not the only factor that contributes to this phenomenon. Moisture may support
and accelerate the degradation process.
(iv) pH Value
Acid or alkaline is commonly employed in textile processing. Different textile materials
demonstrate different effects. Cellulosic materials can damage or degrade under acidic
media but resistant to strong alkaline. Alkaline processes such as mercerization can
enhance tensile strength of cotton. On the contrary, alkaline can damage protein fibres
such as wool. So wool products are better handwashed with non-ionic detergent.
Residual acid or alkaline may induce skin irritation. Environmentally friendly garments
should have pH compatible to slightly acidic skin pH.
(v)
Bleaching
Bleaching is a process to make textiles white. Many natural fibres have their own
natural colour, which will hinder later colouration and subject to removal. The bleaching
mechanism destroys colour stains through either oxidation or reduction. Chemically,
these processes are called the redox reactions. Oxidation is a well known process in
which substances react with oxygen. Reduction can be simply referred as reactions
reversing the oxidised materials back to its original state. Generally, the textile industry
employs oxidative bleaching as the effect is more persistent. The main disadvantage of
reductive bleaching is that stains may form upon air oxidation.
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Commercially, there are two main types of bleaching agents, viz chlorine and
non-chlorine. Chlorine bleach is a strong bleaching agent that can oxidise most
colourants. High chlorine concentration can stripe colours from dyed textiles.
Non-chlorine bleaches are mild bleaching agents and colour safe. They only remove
colour stains and are popular bleaching agents for home laundering.
Redox Reactions
Redox reactions refer to the pairing of two chemical reactions, oxidation and reduction,
that take place simultaneously. One reactant is being oxidised and another reagent is
being reduced. Chemically speaking, this will be described with “oxidation number” of
an element or molecule. The oxidation number of the oxidised reagent is raised while
the reduced reagent is lowered. Specifically, redox reactions are based on the transfer
of electrons.
Figure 7.44
Redox reactions
(vi) Yellowing
White and denim fabrics are subject to yellowing which may be caused by various
chemicals such as acid, softener, polluted gases, antioxidant, etc or environmental
factors such as temperature, light, etc. Yellowing may be due to oxidative degradation
of textile materials or finishing, destruction of optical brightener, formation of yellowing
species, etc.
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(C) Flammability
Most of the textile materials can be burnt. Flammability is an important safety factor
that can be evaluated in different ways. They are:
Ease of ignition
Burn time
Burn rate
Burnt area
Burnt length
Different textile materials burn differently. Cellulosic materials burn most easily and
demonstrate afterglow. Afterglow is a very dangerous phenomenon which refers to the
recurrence of burning after the fire is extinguished. Animal hairs such as wool burn with
material charred. Animal hairs are flame resistant materials as flame removed fire will
extinguish. When synthetic fibres are being burnt, their component materials will melt
and drip. They are flame resistant and similar to animal hairs.
Apart from the material involved, fabric construction can also affect flammability of
fabrics. Plain surface fabrics are less vulnerable to burning than raised surface fabrics.
The reason is that raised surface is known to trap more air and have protruded parts for
easy ignition. With the similar reason, fabrics with loose construction may burn more
readily than fabrics with compact construction.
Essential Factors for Burning
There are three essential factors for burning to be present. They are fuel, oxygen and
ignition. Fuel is the substance that is flammable. Oxygen must be present to support
burning. Ignition is the temperature where substance will ignite (start burning). For
example, a match is a fuel. Simply a match will not burn until it rubs on a rough surface.
The rubbing action increases the surface temperature of the match through friction.
The match will not burn in the absent of air even with rubbing done repeatedly.
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Figure7.45
Essential factors for burning
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7.5 Colouration
7.5.1 Colour Basics
Red, blue, green, yellow, etc. are the usual ways to describe the colours of an item.
There are three basic elements for colour, viz light, object and observer, Without any
one of these elements, you cannot see the colour of any given object. The study of
colour is called colour physics. In order to describe colour more precisely, many colour
order systems such as RGB, CMYK, pantone, CIE Lab, etc have been developed for
different industries. The basic principle is to arrange different colours systemically in a
space called colour order space. CIE Lab is one of the common systems used in the
textile industry. CIE stands for La Commission Internationale de l'Eclairage (English:
International Commission on Illumination) which is an international authority on light,
illumination, colour and colour spaces.
Figure 7.46 Basic elements of colour
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CIE Lab Colour Space
The colour vision of human can be described by a set of primary colours called the
tristimulus values (XYZ). Colours can be systemically arranged with tristimulus values in
a three-dimensional space. This is one kind of colour order space. The major drawback
of XYZ colour space is nonlinearity and it is hard to apply. Based on the tristimulus
values, CIE has developed a linear colour space called Lab system. This space
arranges colours in accordance to their lightness (L), a and b (hue and intensity).
Figure 7.47 CIE Lab colour order space
7.5.2 Brief History of Dyes
The earliest record of people using dyestuffs is from China in 2600 B.C. Rome people in
715 B.C. had already established their set of wool dyeing technique. At 700 A.D.,
Chinese had documented their dyeing process that involved wax resist technique
(batik). In 1856, William Henry Perkin discovered the first synthetic dye stuff called
“Mauve”, which is a basic dye and it started the modern synthetic dye industry.
7.5.3 Classification of Dyes
Dyestuffs are water soluble coloured chemicals with affinity to fibres. Water insoluble
colourants are called pigment. Basically, dye molecules are composed of chromophore
and auxochrome. Chromophore is a chemical structure that is able to absorb certain
visible radiations and reflect the unabsorbed light energy. For example, a red dye
reflects red light and absorbs other radiations such as green, blue, etc.
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Dyes
Pigments
Soluble in its application medium,
usually water.
Insoluble in its application medium
With affinity (substantivity) to fibres
No affinity to fibres
Smaller particle size
Large particle size
Adhere to substrate by physical or
chemical linkage
Adhere to substrate by binder
Figure 6.48 Comparison between dyes and pigments
(A) Chromophore
Chromophores are chemical structures with alternate single and double carbon–carbon
bonding and the system is called the conjugated system. Commonly, structures are in
shapes such as aromatic ring, azo bond, etc. Electrons within the conjugated system
can transfer from carbon–carbon double bond to single bond. This shifting is called
electronic resonance and able to absorb visible light energy. Unabsorbed light energy is
reflected and this is the colour of the dye molecule.
Figure 7.49 Electronic resonance within a conjugated system
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(B) Auxochrome
Auxochromes are chemical structures that can assist chromophores to intensify the
colour, enabling dye water solubility and affinity. Colourants without auxochrome are
pigments. Common auxochrome structures are hydroxyl, carboxyl, sulfonic, amino
groups, etc.
(C) Interactions of Dyes and Textile Fibres
Dye has affinity to fibres. Affinity comes from dye molecules when they are having
specific interactions with certain structures of fibres. There are four types of interaction.
(i)
Van der Waal Forces
It is a weak attractive force depending on molecular mass. The greater the molecular
mass, the stronger the attraction force. Furthermore, the bigger the molecule, the bigger
the attraction force.
(ii)
Hydrogen Bonding
It is a specific bonding between the OH (hydroxyl) group. As oxygen atoms attract
electrons more strongly than hydrogen atoms, electrons in hydrogen–oxygen bonds will
shift to the oxygen side. Hence, the polar of the hydroxyl group with O is slightly
negative and H is slightly positive. Dyes and fibres with the hydroxyl group that
cellulosic fibres contain will attract each other. Such bonding is called the hydrogen
bonding.
(iii) Ionic Bonding
It is the attraction between the positive ions (cation) and the negative ions (anion).
Some of the chemical structures are able to ionise in water. For example, acid dye
ionizes to give hydrogen ions (H+) and anions (R-). Wool fibres contain amino (-NH2)
group that will form cations under acidic condition and it will attract dye anions.
(iv) Covalent Bonding
It refers to true bonding between the dye and the fibre. Dye with reactive group is able to
react with certain structures of a textile fibre. This can be considered as the strongest
bonding.
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Dye
–
Interactions
Fibre Example
Van
Waal Direct Dye
der
Forces
Hydrogen Bonding
Direct Dye
Ionic Bonding
Acid Dye
Covalent Bonding
Reactive Dye
Apart from these interactions, some dye molecules attach to the textile fibre based on
their own solubility. For example, vat dye can be reduced into soluble form during the
dyeing process and oxidised to become insoluble form after dyeing. This change in
solubility renders vat dye goods wet fastness. Disperse dye employs another principle.
It has differential solubility in aqueous medium and fibre phase. Disperse dyes are fairly
water soluble but highly soluble in fibre phase, so dye tends to stay in fibre rather than in
the aqueous dyebath. This can be considered as a solid solution.
(D) Dye and Toxicity
Congo Red is well known a carcinogenic dyestuff that has been banned long ago. It is a
kind of azo dye. The toxicity comes from the reduced amino products. The European
Union (EU) has already banned textile products that contain azo dyestuff with restricted
amines. EU has also complete restriction on textiles with sensitiwed and carcinogenic
dyes. They are disperse dyes. Dye toxicity is particular concerned in infant and children
products as they may put textiles into their mouths. Saliva resistance is an important test
in infant and children products.
Figure 7.50 Reaction scheme for the release of restricted amine from Congo Red
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Dyestuffs can be classified according to their chemical class or applications.
Figure7.51 Basic construction of a dye molecule
Although there are many dye classes, only a few types are popularly used. The
following table indicates the major colourfastness of popular various kinds of dyestuff.
Dye class
Reactive
dyes
Characteristic
A kind of dyestuff that is able
to react with fibres to form
Washing
fastness
Crocking Disadvantage
Very good Very good
Cannot attain
dark colours
chemical bonding; all round
fastness
Acid dyes
Major dyestuff for animal
(protein) and polyamide
Moderate
to poor
Excellent
Easy wash off
Disperse
dyes
Major dye for man-made
fibres
Good
Good
Some can cause
skin irritation
Direct dyes
Dye cellulose with big
molecular size
Poor
Good
Easy wash off
Vat dye
Water soluble only in dyeing
Excellent
Good
Careful dyeing is
stage
Sulfur Black
Used to dye for the black
colour
required
Poor to
good
Poor
Stain problem
from rubbing
Figure 7.52 General characteristics and fastness properties of some common dye
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(E) Colour Index
This is the technical reference published by the Society of Dyers and Colourists
(SDC) that collects details of all available commercial colourants, including both dyes
and pigments. Each colourant is assigned a name with the following name system:
[Application class] + [base colour] + [number]
C. I. name
Trivial name
Acid Red 66
Biebrich Scarlet
Basic Red 9
Sulphonated Pararosanilin
Acid Yellow 24
Martius Yellow
Direct Red 28
Congo Red
Solvent Red 23
Sudan III
Figure 7.53
Examples of the SDC colour index
7.5.4 Dyeing
Dyeing is a process where dye molecules migrate from aqueous phase to fibre phase.
Dye molecules have a tendency to diffuse from aqueous medium towards textile fibres.
In the dyeing process, dye molecules are absorbed by the fibre and then they further
diffuse into the fibre interior. This is the dye absorption process. The dye finally will
attach to a particular location of the textile fibre called dye site. Different types of dye
have different dye sites on different fibres. The interaction between the textile fibre and
the dye determines the persistence of the final colour. This level of persistence is called
colourfastness. The process in which the dye is absorbed into the fibre is called
exhaustion. The total amount of dye exhausted includes both the amount of the
absorbed dye molecules and fixed dye molecules. It is what is referred as the shade or
how deep is the dyeing. The dye molecules being absorbed or fixed still have chance to
go back to the aqueous medium. This phenomenon is referred to as desorption. When
exhaustion rate is equal to desorption rate during the dyeing process, this state is called
equilibrium exhaustion. Further dyeing after this state will result in no change in shade
and the dyeing process is considered to be finished.
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Figure 7.54. Dyeing process
7.5.5 Dyeing Methods
Dyeing can be carried out in different stages of textile manufacturing. Colouration that is
applied to polymeric solution or melt before fibre extrusion is called dope dyeing.
Colouration that is applied to yarn stage are called cone dyeing and beam dyeing.
Dyeing in the fabric stage is the most common practice. It can be a batch or continuous
process. Besides, dyeing can be carried out in the product stage such as garment
dyeing. However, dyeing in the yarn stage or garment stage is not common practice.
Yarn dyeing may produce colour variation in fabrics. Another drawback is that the later
wet processing on fabrics may affect the final colour. Garment dyeing is a complex
process when trims such as lining and buttons are present. Various dyeing methods are
discussed as follows:-
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(A) Batik Dyeing
Batik dyeing is a traditional dyeing method and is a kind of resist dyeing process that is
used to produce patterned fabrics. Part of the fabric is coated with wax and dyed. Dye
can only penetrate fabric area without wax. The waxed area is left blank. After dyeing,
the wax is removed. The process can be repeated to obtain patterns with multiple
colours.
(B) Lap Dip
It is a small scale of dyeing usually performed in laboratory. This is normally a
preparatory stage of the dyeing recipe that matches as much as possible the colour
reference of customers.
(C) Dope Dyeing (Pigmentation)
Dope dyeing refers to the colouration of man-made fibres that takes place in polymer
either in the solution or melting (dope) state before fibre extrusion. This is not a dyeing
process. It is simply a process of mixing colourants into the dope. The colourants
employed are usually pigments. As colourants disperse in fibres, very good fastness
properties are shared. The drawbacks of such technique are the difficulties in colour
matching and possibilities of colour variation in fabrics.
(D) Cone Dyeing
Cone dyeing is a kind of yarn dyeing. Cones of yarn are placed in a perforated stand
which dye liquor can pass through. Dyeing evenness depends on the penetration of dye
liquor through the yarn cones. The rate if dye penetration is affected by the pressure of
the pump and the duration of dyeing time.
Similar to dope dyeing, difficulties in colour matching and colour variation in fabrics are
the drawbacks. Cone dyeing is commonly applied to yarn dye fabrics to produce stripe
or check pattern.
(E) Beam Dyeing
This is another yarn dyeing process. Warp yarns are winded on a big roller for dyeing
and the roller is called the warp beam. Beam dyeing shares the similar principles with
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cone dyes but the size of the beam used is much bigger than that of yarn cone. The
beam is placed on a perforated shaft and dye liquor is being pumped through the beam.
Denim and chambray are beam dyed fabrics with dyed warps and blank wefts.
(F) Batch Dyeing
Batch dyeing refers to the process of dyeing fabrics in a batch of a few tens of yards to a
few hundred yards. It is a common dyeing process done before the development of
continuous dyeing range. One of the disadvantages is the colour variation between
batches, so it is suitable for dyeing fabrics in small amount. Many small dye houses are
still using such method and the machinery used is simpler than that needed for
continuous dye range. It can also be used as a top dyeing process for modifying the
shade of fabrics to fit specific colour standard of customers.
(G) Continuous Dyeing
It is a complete dyeing process that may include fabric preparation, dyeing and
after-treatment. Contemporary automatic dyeing range may incorporate dye dispensing,
exhaustion, fixation, rinsing and drying together. This is a fast and large scale of
production involving fabrics that are in the size of a few thousands to over ten thousand
yards.
7.5.6 Dyeing Machinery
The basic design of dyeing equipments is a tough to hold dyeing solution and textile.
This is a dyebath. It should have facility for circulating either the dye solution or the
fabric to produce even dyeing. Heating facility is also important for dye exhaustion.
(A) Jig Dyeing Machine
With the jig dyeing machine, fabrics are being operated in an open width form. Fabrics
are being held in two rollers with only a part of the piece of fabric being dyed being
dipped in the dye bath. Fabrics are either being circulated or transferred repeatedly from
one roller to another roller for agitation.
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Figure 7.55 Jig dyeing machine
(B) Jet Dyeing Machine
The machine is a close system. The ends of fabrics are joined together to form a loop
and they are being circulated and moved around the dyeing chamber through a Venturi
jet. Given that the machine is a closed system, pressure can be applied to perform high
temperature dyeing.
Figure 7.56 Jet dyeing machine
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(C) Cone Dyeing Machine
All cone dye machines contain a platform with several perforated posts connected to a
pump. Dye liquor circulates through the posts to arrive at the dye chamber and then
back to the pump. Yarn cones are placed on the posts.
Figure 7.57 Cone dyeing machine
(D) Beam Dyeing Machine
The design principle of beam dyeing machines is similar to that of the cone dye
machines but in bigger size. Usually one dye chamber handles one warp beam. A
perforated shaft is connected to a pump that handles the circulation of dye liquor.
Figure 7.58 Beam dyeing machine
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(E) Continuous Dyeing Range
Each of this type of dyeing range usually contains a number of chambers for various
purposes. This type of machines is well equipped to complete the entire dyeing process
on its own, including the processes of dyeing, rinsing and drying. After dyeing, the range
can be connected to later after-treatment ranges. Advanced continuous dyeing range
are usually computerised and co-controlled by colour monitoring devices to ensure the
accuracy of the colours aimed. The running cost is usually higher than that of the
batchwise machine as the continuous dyeing range occupies more space, consumes
more water and electricity. Nonetheless, it is more efficient. The production cost per
yardage can be lower than that of batchwise dyeing. The following diagram illustrates
the arrangement of a continuous dyeing line.
Figure .59 Continuous dyeing range
7.5.7 Printing
This is a colouration process that produces patterns. Unlike dyeing, printing is a
localised colouration process. Print paste is employed to prevent lateral dye migration
and maintain the sharpness of patterns being produced. Paste is a concentrated dye
solution with thickening agents such as starch. Print fixation is usually done in high
temperature, for instance, by means of steaming, to ensure a quick dye fixation which
can prevent dye migration.
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7.5.8 Printing Methods
Textile industries nowadays employ major methods that concern the following aspects:
direct, resist, discharge and transfer.
(A) Direct Printing
A process of printing dyes directly on fabrics to create print patterns. This technique
creates coloured patterns on white fabrics.
(B) Resist Printing
Resist printing refers to the application of a resisting agent such as wax or colourants to
specific patterns to prevent the penetration of another dye. This technique produces
different coloured patterns on fabrics. The print paste used as a protection layer
contains a substance resistant to a second dye, which assist the development of colours
in specifically aimed areas of fabrics.
(C) Discharge Printing
Instead of dye, a discharging agent is printed on fabrics. The function of discharging
agents is to remove colours from fabrics. This technique creates blanks on dyed fabrics.
This technique can be combined with direct printing to produce fabrics with colour print
patterns on dyed fabrics.
(D) Transfer Printing
The printing is done on another media. For instance, paper. The printing is then
transferred to textile fabrics through ironing. Disperse dyes are usually employed as
they sublime during ironing and migrate to the fabrics. This technique produces very
fancy patterns.
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7.5.9 Printing Equipment
Screen printing is the major printing method being used nowadays. Print patterns are
transferred to nylon or metallic screens with pattern areas that are open and other areas
being blocked.
(A) Flatbed Screen Printing Machine
This method uses a screen spread over a frame. The portions of the design to be
printed are made of porous nylon fabric that allows the dyestuff to pass through the
screen. Print patterns with colour separations done are transferred on a series of flat
nylon screens. The areas that are not to be printed are covered or coated. Fabrics are
being fed intermittently for each individual colour printing. Dyestuff is poured into the
frame shell and is forced through the nylon by means of a squeegee moved back and
forth. Flatbed screen printing is versatile but expensive. Sometimes, a design pattern
may require as many as 40 - 50 silk screens with separate colours to be applied.
(B) Hot Press Machine
Steam or electrically heated press machines are used for heat transfer printing. The
machines are usually composed of two pressing flatbeds. These two flatbeds are either
heated both at the same time or just alone.
The rotary screens or rollers first print dyestuffs onto paper. The paper can then be kept
for use at any time. To print on fabric, the paper and fabric are put through hot rollers.
The dyestuffs sublimate into gas, which transfers from the paper base onto the fabric.
The advantages of this method are that it gives a clean, fine line on knitted fabric and
paper is inexpensive investment. However, this method can cause stiff hand feel of the
fabric and the dyestuff transfers only to the fabric surface without thorough penetration,
causing potential grin-through (fabric showing through) problems.
Heat-transfer printing has become more popular than before in recent years because of
the development in low-sublimation dyes and deeper-penetrating dyes as well as
relatively less waste water and fewer harmful discharges in dry dyeing. Dry printing is
considered as a more environmentally friendly dyeing method.
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(C) Roller Printing Machine
This is a kind of printing machine that is very efficient in producing stripe patterns. This
method requires separate roller engravings to be used for each colour in the pattern of
design.The patterns are engraved in a copper roller. Print paste then fills the engraved
area and transfers the patterns to the fabric.as it passes through the printing machine.
Figure 7.60 Roller printing machine
(D) Rotary Printing Machine
Rotary printing is a quicker version of screen printing and is continuous without breaks
between screens, Print patterns with colour separations done are transferred to a series
of metallic rotary screen which are porous in the areas to be printed. Fabrics are being
fed continuously. Dye is forced into the roller cylinder and through its porous screen as it
rolls over the fabric. The repetition frequency of print patterns is limited by the
circumference of the rotary screens.
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Figure 7.61 Rotary printing machine
(E) Digital Printer
This is a new development of the textile printing technology. This technique applies
digital printing to textiles. The process requires no print screens and the patterns are
stored electronically as a computer-aid design (CAD) file in computers. This printing
technique can produce very fancy and complicated patterns. It is even possible to
modify a print design according to the shape of garment pieces. Digital printing is a
flexible process that provides the opportunity for quick response to changes in colour or
design of customers. This method is increasingly used for sample development under
environment of short lead time and increasing demand for customisation.
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Figure 7.62 Structure of a printer head. Piezoceramic material changes shape
according to electronic signal and pressurises the pressure chamber and send out dye
droplets
7.5.10 Fastness
Fastness (or colourfastness) refers to the colour resistance of a product upon various
effects such as light, washing, etc. There are two aspects concerned, viz colour change
and colour staining. Colour change refers to the amount of colour loses when a material
is being exposed to various effects. It is a colour fading phenomenon as dye loss takes
place gradually. Colour staining refers to the migration of colours from a product to other
textile materials when in contact.
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7.6. Finishing
Finishing is an extensive term that refers to all kinds of pre-treatments and
after-treatments applied to textiles. Pre-treatments are referring to treatments prior to
dyeing which prepare fabrics for colouration. After-treatments are treatments applied to
fabrics after colouration, which enhance and add further properties to fabrics.
Figure 7.63 Pre-treatments and after-treatments
7.6.1 Pre-treatments
They are preparatory treatments to prepare fabrics for dyeing.
(A) Singeing
The process of burning off loose fibres on protruding fabric surfaces which may produce
“frosting” during colouration. During the process, fabrics are being passed through a row
of gas flame and then immediately through a quenching bath which may contain
desizing agent.
(B) Desizing
Size such as starch and PVA is commonly added to warp yarns during weaving to
strengthen the yarns and prevent yarn breakage. Below are the common desizing
methods.
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(C) Scouring
The process refers to the washing off of impurities in fabrics, also called kier boiling. For
cellulosic fibres, scouring refers to the treating of fabrics with strong alkaline such as
caustic soda or soda ash. The process removes most of the impurities such as natural
grease and wax and pectin which will hinder colouration and further finishing.
(D) Mercerisation (An optional finishing process)
Mercerisation is a process that applies caustic soda (NaOH) to fabrics to produce
silk-like appearance for cotton. Ribbon-like cotton fibres will swell and produce a
smooth shinny surface. In addition, treated cotton fibres will have greater strength and
better dye exhaustion.
(E) Bleaching
Bleaching is the process that removes natural colours present in textile fibres. The
process is important for producing white fabrics for later colouration. This is usually
done by oxidative type of bleaching. Hydrogen peroxide (H2O2), sodium hypochlorite
(NaClO) and sodium chlorite (NaClO2) are the common chemicals employed. The
advantage of oxidative bleaching is that the effects are permanent.
(F) Caustic Reduction
The surface of the polyester fibres is eroded away in a caustic bath which reduces the
weight of the fabrics and gives them a silk-like feel.
7.6.2 After-treatments
These treatments are used to add extra effects and finishes to fabrics. The process can
be mechanical or chemical in nature. The advancement in technology of
after-treatments is entering a new era with the application of nanotechnology in the
production process. Nanotechnology marks the beginning of the second industrial
revolution of the new millennium.
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Figure 7.64 Evolution of textile materials
(A) Mechanical Treatments
Mechanical treatments refer to all the treatments that are employed to modify textile
appearance mechanically.
(i)
Calendaring
Calendaring is a mechanical pressing process that uses heated metal calendars to
produce high luster fabrics. Fabric is passed between heavy rollers by applying heat
and pressure. The process produces different effects such as glaze, watermark or
moire. It is usually done on synthetic fabrics because the effects done cannot be kept
permanently on natural fibres.
(ii)
Embossing
A patterned calendaring process for producing raised or projected figures or designs in
relief on fabric surface.
(iii) Brushing (Raising or Napping)
A process employed to raise the fibres on the surface by rotating brushes. Short fibres
will loosen from the yarns upon brushing. It produces a soft, comfortable and raised
surface on fabrics. Brushing can be applied to either side or both sides of fabrics.
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(iv) Sanding and Peaching
Sanding is a process employed to treat fabric surface with abrasive sand. This can
produce a raised surface similar to suede on fabrics. When the size of sanding particle
reduces, a peach effect will be created on sanded fabric surface. This process is called
micro-sanding or peaching.
(v)
Shrinkage control (sanforizing process)
This process preshrinks cotton fabric so that it will not shrink during laundering
(vi) Pleating
Pleats refer to the folds in fabrics done by doubling the material upon itself and then
being pressed or stitched in place. Pleating is a pressing process usually done along
with heat to fix folding permanently.
(vii) Felting
It is the process of compacting masses of wool fibre under heat, moisture and
mechanical pressing to form mats as wool fibres possess scales on their surface and
they tend to entangle together under such situation. This process is carried out in fulling
mills.
(viii) Decatizing
This process uses heat and moisture to stabilise wool fabrics.
(ix) Heat setting
This process stabilises the fabric so that there will be no further changes in its
dimension or shape and thus improves the fabric's resilience. The effect is achieved by
heating thermoplastic (synthetic) fabrics to just below their melting point.
(x)
Laser Trimming
Traditionally, burn out effect requires the application of printing techniques that print
sulphuric acid paste on fabrics. Sulphuric acid will etch fabrics to form holes. With the
advancement of laser technology, laser trimming can produce any shapes of hole on
fabrics with accurate and sophisticated computer control.
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(B) Chemical Treatments
(i)
Shrinkage Resistance and Wrinkle Free
These properties are achieved on fabrics with the application of resin finish to fix the
fabric construction and prevent both shrinkage and wrinkle formation. Some of the
resins used are formaldehyde based, which may lead to formaldehyde related problems.
This is particular important for infant and children products. Wrinkle free finish also
increases tearing strength of products, in which case garment seams may need
enhancement.
(i)
Shrinkage Resistance and Wrinkle Free
These properties are achieved on fabrics with the application of resin finish to fix the
fabric construction and prevent both shrinkage and wrinkle formation. Some of the
resins used are formaldehyde based, which may lead to formaldehyde related problems.
This is particular important for infant and children products. Wrinkle free finish also
increases tearing strength of products, in which case garment seams may need
enhancement.
(ii)
Water Repellency and Resistance
Water repellency refers to the resistance of textile materials to wetting and water
penetration. Usually, this process is done based on hydrophobic agent or plastic coating
such as PVC, silicone, etc.
(iii) Soil Release (Stain Release)
Treatment of textile materials with waxy or hydrophobic agent can alter the surface
condition of textiles and produce a less sticky surface. Stain can be washed off easily
during laundering.
(iv) Easy Care
Easy care refers to the finishes that render textile products the durability to laundering, a
smooth appearance with no ironing is needed and a minimised shrinkage. Sometimes it
is called “durable press” or “wash-and-wear” finishes. This can be achieved by special
resin finish on cellulosic / thermoplastic fibre blends. Cellulosic part is permanently set
by heat setting the resin and thermoplastic fibre part.
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Flame Resistance
Flame resistance can be enhanced through the application of flame retardants, which
are chemicals that can reduce, minimise burning or self-extinguish. The major
drawbacks of flame resistance are its toxicity and durability. Some of the flame
retardants have been found toxic to human body and banned by the European Union.
(vi) Durable press (permanent press)
The application of resins to cotton or cellulosic fabrics for eliminating future ironing.
(vii) Antistatic Finishes
Antistatic finishes are particularly important in work clothes of the electronic and
petroleum industry. Antistatic finishes are done with the incorporation of conducting
substances on the fabric.
(viii) Antibacterial and Antifungal Finishes
Antibacterial and antifungal are finishes that resist bacterial or fungal growth on textile
materials. This can be achieved by incorporating germicides on fabrics to prevent odors
formed by bacterial decomposition of perspiration and mildew growth. A new technique
of applying a biocide called tributyl tin (TBT), which is commonly used in paint, for the
purpose has been put into practice. However, TBT is found to be highly toxic to human
and has been banned form being applied to textile products in European countries.
(ix) Moothproofing Finishes
This is a particular finish applied to wool products. Wool is susceptible to moth attack.
Mothproofing chemicals are incorporated with wool fibres to prevent moth and beetle
attack. These chemicals have a certain degree of resistance to laundering. Some of
these finishes are able to react with wool fibres to form linkage that enhances the
washing fastness of wool products.
(x)
Antipilling Finishes
Pilling resistance can be enhanced by reducing the surface friction of yarn surface.
Antipilling agents are polymers with low friction that can be coated on yarns to give a
smooth surface. An example of such antipilling agents is polyethylene.
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(xi) Nano Finishes
Nanotechnology refers to the manipulation substances in very small scale. Atomic size
is 1 x 10-10m and nanometre is 1 x 10-9m. Unlike traditional technology, nanotechnology
handles substances in molecular level. There are stain resistant garments available in
the market based on nano-finish. These products have good resistance to aqueous and
oily dirt.
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7.7 Fabric Quality
7.7.1 Strength
This is a factor for selecting suitable materials for specific applications. For example,
textiles used for casual wear and work wear are different. Work wear should use strong
materials as workers may carry heavy tools. On the contrary, strong materials are not
necessary to casual wear.
(A) Tensile Strength
This is a measurement of the maximum pulling a textile material can stand before it
breaks. The test is mainly done on woven fabrics. Tensile strength of textiles is defined
as the maximum breaking force per unit cross-section area. The common units are N/m
(m=metre) or lbf/in (in=inch). N stands for Newton, which is a SI (Systema International)
unit for force. lbf stands for pound-force and it is a non-SI unit for force. One Newton
equals to 0.225 pound-force. The test is conducted under tensile strength testers which
consist of two clamps. One is fixed and another is movable. The testers are equipped
with electronic load cells to record the force applied.
The greater the tensile strength means the stronger the material. Depending on
applications, different strengths are required. For example, bag requires a greater
strength rather than a shirt. Tensile strength depends on many factors. These factors
include materials, yarn twisting, fabric construction, finishing, etc.
Tensile Property
Tensile strength of textile materials is the breaking force per width of specimen. It is
important to note that this is only a simplified expression. For bulk materials such as
metal and plastic, tensile strength is defined as the breaking force per cross-sectional
area of the specimen.
Fbreaking
Tensile strength = ——————————
Width / Cross-section
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The following illustrates the difference between tensile strength for bulk materials and
textile fabrics. Furthermore, the unit for tensile strength of bulk materials is the
equivalent to pressure. N/m2, Pa (Pascal), lb/in2 (pound per square inch, psi) are the
common units used.
(A) bulk materials
(B) bulk fabrics
Figure 7.65 Tensile strength of various materials
Engineering studies tensile property of materials through tensile modulus (E) which is
defined as the ratio of stress and strain.
Stress
Tensile modulus (E) = ——————
Strain
Stress is defined as the ratio of tension over cross-sectional area. Strain is defined as
the ratio of original length of specimen to the strained length. When the increase of
stress is directly proportional to the increase of strain, a series of data concerning the
tensile modulus are collected which is called the elastic region. The modulus within this
region is called elastic modulus or Young’s modulus. If there is a continue increase in
stress but not in strain, the modulus will then go beyond the elastic region and finally
reach the yield point. When the materials are further stressed, they will reach the work
harden state where the materials will break. For textile materials, work harden is a state
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where polymer chains straighten and form better alignment, i.e. crystallinity increase,
therefore strength increases. As materials are further stressed, they will break. The
breakage stress is referred to as the tensile strength of materials.
Figure 7.66 Tensile modulus. (a) Tough substances such as steel (b) soft substances
such as textiles
As it is shown in the diagram, a tough material such as steel has a steep curve. Steel
behaves almost elastically before breakage. A soft material such as textile only has a
small elastic region. Furthermore, the curve is less steep than that of steel, which
means textiles can be stretched easily with small force when compared to steel.
(B) Tearing Strength
Tearing strength is another strength property for woven fabrics and it measures the
resistance of textiles in terms of tearing. Generally, the test is conducted with falling
pendulum testers (or Elmendorf testers). Test specimens are pre-cut a slit. Tearing is
done by the pendulums’ swinging motion. The tearing force or energy is recorded.
Tearing strength may drop dramatically after resin treatments such as wrinkle free finish.
The reason is that fabric constructions have been fixed and yarns cannot move to
counter balance the tearing force. Tearing strength is higher for loosely packed fabrics
as yarns can move to counter balance the tearing action.
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(C) Bursting Strength
Bursting strength measures the strength property of knit fabrics. It is the maximum
pressure required to burst a fabric. Pneumatic or hydraulic testers are employed for
such testing.
7.7.2 Pilling Resistance
Pilling refers to the entanglement of short fibre during textile material rubbing with other
surfaces and the subsequent spherical change of shape.
Figure 7.67 The development of pills
7.7.3 Dimensional Stability
Dimensional stability refers to the stability of various dimensions of textile materials
against home laundering process. For fabrics, such testing is based on the change in
length of the pairs of benchmarks put on the sample before and after washing. Both
lengthwise and widthwise dimensions are measured and changes are expressed in
percentage.
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(A) Shrinkage and Growth
Decrease in length between benchmarks after washing is shrinkage and increase in
length is growth. The amount of change depends on the textile material, fabric
construction and finish. Cellulosic materials always demonstrate shrinkage upon
washing. Shrinkage for woven fabrics is usually smaller when compared to knit fabrics.
Commercial requirements for growth are quite strict as they are related to the puckering
of products, which greatly affects their appearance.
(B) Skewness
Skeweness refers to the tilting appearance of fabrics after laundering. Skewness is also
called torque or spirality. Skewed fabrics affect the pattern marking process and waste
more fabric.
7.7.4 Colourfastness
Colourfastness means the resistance of colour of a product against various conditions
when using or during manufacturing. There are two effects, colour change and colour
staining. Colour change refers to the change in colour of the product before and after a
process. Basically, the change is fading. Which colour is getting less. Colour staining
refers to the migration of colour from product to neighborhood during a process.
(A) Light
Colourfastness to light refers to the resistance of colour when exposed to light, daylight,
store lighting in particular. Colour will fade under light when dyes or colourants are
destroyed. Normal daylight is a mixture of radiations of mainly infrared (IR), visible and
ultraviolet (UV). IR radiation is related to thermal energy. Visible radiation is the light
human eyes can detect. UV radiation has energy in the range of chemical bonding that
is able to break dye or colourant molecules.
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Figure 7.68 Colour fade away when dyed textiles are exposed to light
(B) Crocking
Crocking fastness measures the colour migration of products to adjacent materials
through rubbing.
(C) Washing
This particular fastness refers to the resistance of colour against various kinds of
washing including hand wash, machine wash, commercial laundering, etc. It is used to
develop garment care label. Colour change and staining are evaluated. Colour change
is an indication of the durability of colour against washing. Colour staining indicates the
migration of colour to other product including the colour migration caused by washing.
(D) Perspiration
The colour of textile products may be affected by sweat when in contact with skin. This
fastness measures the colour change and staining property of textile products under
contact of artificial human sweat. There are two types of sweat solution, viz acidic and
alkaline. Depending on the standard testing method, one type or both types of solution
are applied to products under controlled condition.
(E) Water
This colourfastness measures colour change and staining of textile products under
prolonged contact with water. It is particularly important for the development of the
drying instructions for colour blocks products with light and dark colours after laundering.
If there is colour staining observed, such product is recommended to dry promptly after
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laundering, otherwise self staining may take place.
(F) Bleaching
Bleaching is one of the processes in care. Colourfastness to bleaching measures the
colour resistance of textiles in respect of commercial bleaches. There are two main
types of commercial bleaches, viz chlorine and non-chlorine bleach. Chlorine bleach is
liquid bleach which reacts vigorously. Not all colours are safe for this bleach.
Non-chlorine bleaches are mild bleach and colour safe. They are available in both
powder and liquid form.
Commercial Bleaches
Commercial chlorine bleach is composed of hypochlorite, which is a strong bleaching
agent. High concentration of such solvent may strip colours. Chlorine bleach may react
vigorously with other reagents such as washing powder, other bleaching agents and
generate toxic gas, so it is not recommended to be used together with other reagents.
Commercial non-chlorine bleaches are mainly composed of two types of chemicals,
sodium perborate and hydrogen peroxide. They are mild bleaching agents which are
colour safe. They are usually applied together with other reagents. Sodium perborate
bleach is in powder form and hydrogen peroxide type bleach is a viscous liquid. All
commercial bleaches are oxidative chemical and decompose gradually upon storage.
They are recommended to be placed in dark and cold environment.
7.7.5 Flammability
Flammability is a safety requirement for textile clothing in USA. Textile clothing is
separated in two groups, which are general wearing apparel and children’s sleepwear.
Testing and requirements on these two groups of clothing are not the same.
(A) General Wearing Apparel
This group covers all sorts of commercial textile fabrics and wearing apparel except for
children’s sleepwear. The regulation exempts footwear, glove and hat. Those products
must pass a 45°C burning test. The test measures the time requires to burn a definite
size of fabric swatch. This time of burning is referred as the burn time. Based on the
burn time, products are classified into three classes, I, II and III. Class I is the best result.
The criteria for fulfilling Class I is that the burn time of a product should be longer than
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3.5 seconds for plain surface fabrics. Stricter requirements are imposed on raised
surface fabrics; the burn time of a given product should be more 7.0 seconds as this
kind of fabric burns more easily.
(B) Children’s Sleepwear
This is a particular item that special attention is required to be paid to in USA. Children’s
sleepwear refers to the garment worn for sleeping and in the size of 0 to 14. As children
may wear sleepwear and play around. Loose fitting sleepwear may catch fire easily
when there is open flame such as candle. Given that children are not able to strip off the
burning garment supposedly on their own, stricter burning test standards have been
imposed on such kind of product. Fabric samples are tested in vertical manner and the
test measures only the char length. Burning time or rate is not important in that item.
Textile materials used for children’s sleepwear must be able to self-extinguish. The
general requirement is that the average char length of five specimens cannot exist 7.0
inch. The following illustration shows the styles that the USA Consumer Products Safety
Commission (CPSC) may consider as children’s sleepwear.
Figure 7.69 Typical styles considered by CPSC as children’s sleepwear
(Source:
US Consumer Products Safety Commission)
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July 2009
Toxicity
(A) Formaldehyde
It is a common chemical that may be present in textile materials, particularly resin
treated materials such as wrinkle free finish. Common resins employed include
formaldehyde base resins such as urea-formaldehyde resin, melamine-formaldehyde,
etc. Formaldehyde has two problems, viz smell and health. Excessive presence of
formaldehyde on textiles will give a fishy smell. As the resin technology begun, the
chemistry of resin has not been very stable and was subject easily to degradation in
damp environment. Therefore, many shipped textile products in the past might have a
fishy smell. Nowadays, smell problem is not encountered very often given the change in
resin chemistry and very stable resins are available. In respect of health related issues,
formaldehyde may cause skin irritation and cancer when entering human body. This is
particularly important for infant and children’s garment as they usually put things into
their mouths.
Formaldehyde is soluble in water. The amount of formaldehyde present in textile
products is calculated by the amount of formaldehyde extracted by water from textile
products. The extracted formaldehyde is used to react with chemicals to make it
coloured. The coloured solution is then subject to spectrophotometric analysis to
quantify the formaldehyde amount present. The concentration of formaldehyde present
in textile materials is usually expressed in part per million (ppm). 1 ppm means 1 gram of
textile material containing 10-6 g (0.000001 g) of formaldehyde.
(B) Lead and Heavy Metals
Lead and heavy metals may present in paint coating and plastic materials as stabilizer
and catalyst. Lead is a well known heavy metal toxic to human. As lead level in the
blood builds up, it will poison and damage the central nervous system. Consumer
product safety regulations of USA restrict the total amount of lead permitted in paint and
coating of consumer products to be not greater than 600 ppm (0.06%). Besides, many
other heavy metals such as mercury, chromium, arsenic, etc are highly toxic, too. The
European Union has restrictions on the extractable level of eight different heavy metals
present in consumer products. These metals are mercury, lead, chromium, arsenic,
antimony, barium, cupper and selenium.
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(C) Azo Dyes
“Azo” is a chemical structure referring to a double bonded nitrogen bridge (–N=N–). This
is a common structure for dye molecules and may cleave to give out amines (-NH2).
Some of the amines are carcinogen (cancer inducing chemical) or suspected
carcinogen. The European Union has listed 20 restricted amines that no more than 30
ppm of any of these restricted amines is allowed to be present in textile materials.
7.7.7 Rules and Labeling
Many countries have law and regulations on textile products. There are two forms of
control imposed on the regulations, product safety and labeling of textile products.
Product safety involves flammability, mechanical and chemical hazards. The purpose of
labeling is to inform consumers of what materials a given textile product contains and its
basic caring method.
(A) Fibre labeling
Fibre labeling is a mandatory requirement for textile articles in major markets such as
USA, Europe, etc. It requires all the textile products to have labels that contain
information in respect of fibre content of products, manufacturer or importer
identification and country of origin at the point of sale. The disclosure of fibre content
needs to be in the form of generic names defined in correspondence to different
countries’ regulations. Fibre generic names accepted in USA are different than those of
Europe. The figure below compares some common fibre generic names used in USA
and Europe. The languages used for the labels are also monitored according to the
importing countries. For example, English should be used in USA. However, Canada
requires labels to be printed in both the language of English and French.
USA
Europe*
Cotton
Cotton
Wool
Wool
Silk
Silk
Rayon / Viscose
Viscose
Spandex / Elastane
Elastane
Nylon
Polyamide / Nylon
Figure 7.70 Comparison between fibre generic names using in USA and Europe
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Figure 7.71 Fibre label
(B) Care Labeling
Care labeling is another mandatory requirement for wearing apparel in USA. In Europe,
there is no particular care labeling regulation. However, there are product liability
directives to prevent consumer loss and these directives require wearing apparel to
have care label. Care labels provide consumer with care instruction information in
laundering the apparel. Care labels in USA can be in the form of pure text, symbols or
symbols with text. For European countries, care symbols based on ISO standards are
preferred. The following diagram shows the care symbols used in USA.
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Figure 7.72 USA care symbols based on ASTM standard. As a minimum, laundering
instructions include, in order, four symbols: washing, bleaching, drying and ironing. Dry
cleaning instructions include one symbol. Additional symbols or words or both may be
used to clarify the instructions.
(i)
Labeling in Hong Kong
Hong Kong SAR government did not have a particular rule and regulation for labeling
textile garments. According to consumer rights, it is required to have garment label to
indicate care and fibre content, Hong Kong accepts all worldwide labeling system, but
language should be in Chinese, English or both.
(ii)
Children Products
Children’s garments or products require additional safety considerations similar to toys.
There are two major aspects concern, mechanical and chemical hazard. In USA,
additional flammability regulation is required for children’s sleepwear.
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Mechanical Hazards
This type of hazard involves three sub-categories, viz small parts, sharp point and sharp
edge. Small parts are lethal and can cause potential choking hazards. Any products for
infants of the age of year three or below should not carry any small parts. Warning labels
are required for products having small parts for infants aged above year three. Sharp
points and sharp edges are potential to the piercing and cutting of the skin. All children’s
products are regulated to prevent such hazards from taking place.
Chemical Hazards
Another safety concern is toxicity. Harmful chemicals present on children’s products
may lead to serious health problems as children’s may put clothing items or accessories
in their mouths. This is a direct intake of harmful substances. Children’s products
usually are required to be toxic-free. One of the harmful chemicals is lead (Pb), which
can poison the central nervous system upon accumulation. USA has regulations in
controlling the total amount of lead present in coating in children’s products. Apart from
lead, European countries restrict seven more heavy metals in children’s products.
These metals are mercury (Hg), chromium (Cr), cadmium (Cd), arsenic (As), antimony
(Sb), barium (Ba) and selenium (Se).
Drawstrings
Drawstrings refer to strings that go through a channel to control the size of openings.
Drawstrings are particularly dangerous when they are present in the neck area of
children’s wear, which may cause strangulation hazards. Drawstrings present in the
waist area may also cause dragging hazards. Therefore, it is highly recommended to
remove or replace such design from children garments.
Figure 7.73 USA care symbols based on the ASTM standard
(Source: US Consumer Products Safety Commission)
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7.7.8 Trademark
(A) Woolmark
Woolmark is a globally reconginsed textile fibre brand and is the guarantee of fibre
content and quality specification. A unique quality endorsement will be given to
products that meet the standard and specifications determined by the Woolmark
Programme. Through the licensing of Woolmark, the products can be allowed to use
the related brand name: Woolmark, Woolmark Blend and Wool Blend. These brand
names are mainly used in the clothing, interior textile and home laundry sector.
(B) GORE-TEX
GORE-TEX is a technology in high-performance windproof, waterproof and breathable
clothing. GORE-TEX® fabrics are created by laminating GORE-TEX® membrane to
high-performance textiles. The membrane gives durable waterproofing properties with
breathability to the treated fabrics.
(A) GORE-TEX fabrics.
Figure 7.74 GORE-TEX (Source:
(B) GORE-TEX membrane
www.gore-tex.com)
(C) Lycra
LYCRA® is a brand name for spandex / elastane. Spandex can enhance the quality and
improve the appearance of clothing.. It is widely used in swimwear, underwear, jeans,
casual wear, tops, socks and hosiery.
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(D) Oeko-Tex 1000
A number of prominent textile testing institutions have already recognised the trend to
non-harmful fabrics in the 90s. They have jointly defined the standards that a textile
product has to fulfill in order to qualify as safe in every respect. They have also set out
guidelines that have documented these relevant requirements. Manufacturing plants
that have undergone the comprehensive examination and have achieved the
prescribed standard can attach the “Confidence in textiles – Eco-friendly factory
according to Oeko-Tex Standard 1000 label” to their production site. The former and still
valid Oeko-Tex Standard 100 provided the basis. Unfortunately, the Oeko-Tex Standard
1000 certificate is not yet widely known in the marketplace.
To obtain the label, the plants’ compliance with environmentally relevant legislation and
regulations must be verified. This is primarily a matter of analyzing exhaust air and
wastewater values as well as noise emissions. The dyestuffs and chemicals in use are
also required to be reviewed in terms of their compliance with Oeko-Tex Standard 1000
and in some cases replaced, which, for sure, in turn results in adjustments to
formulations and processes.
(A) Oeko-tex 100
(B) Woolmark
(C) Gore-tex
(D) Lycra
Figure 7.75 Trademarks
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7.8
July 2009
Latest Development and Environmental Issues
7.8.1 Functional Textiles
The very beginning functions of textile fabrics are for keeping warm and protecting the
body. Upon development, the additional functions such as water proof, wind blocking,
antibacterial, antistatic, etc are incorporated in fabrics.
(A) Moisture Management (Quick Dry)
This is an advanced development for textile material which can manage the moisture
together with air permeability. Traditional water proofing textile is simultaneously air
impermeable, which makes the wearers feel uncomfortable. Moisture managing textiles
usually have good wickability and low water absorbency. Another characteristic of this
kind of textile is its water vapor permeability.
Figure 7.76 Moisture management
(B) Stain Proof
Stain proof refers to a textile’s resistance to both aqueous and oily based stains. This
can be achieved with the advancement of fluoropolymer chemistry and nanotechnology.
Textile can be incorporated with a very thin (molecular layer) fluoropolymer layer which
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renders the fabric surface a very low surface tension to resist aqueous and oily based
stains.
(C) Wind Blocking
This is one of the thermal insulation requirements. Wind is the major contribution to
convection heat loss. Wind blocking finishes are able to prevent air flow through fabrics
under certain pressure.
(D) UV Protection
As there is a massive use of inflammable fluorocarbon gases as propellant in spray
products, the ozonosphere gets holes. Ozonosphere is a particular gas layer of
atmosphere that contains ozone that blocks and prevents harmful UV (ultra violet)
radiation from reaching the ground. High energy UV can produce damage in human
deoxyribose nucleic acid (DNA) and cause skin cancer. There is a need for developing
UV protective clothing. UV protection of garment can be indicated by the UV Protection
Factor (UPF), which measures the blocking ability of fabrics to UV. For example, a UPF
30 fabric allows 1/30 of the UV radiation pass through the fabric and blocks 96.7% of the
radiation. The maximum UPF rating is 50+, which means the fabric can block over 98%
of the UV radiation.
Terrestrial UV Radiations
With the protection of the ozonosphere, high energy UV radiations cannot reach
terrestrial. There are two types of UV radiation that can reach the ground, UVA and UVB.
UVA radiation has a wavelength from 315 to 400 nm and UVB ranges from 280 to 315
nm. UVA causes premature skin aging. UVB causes sun burn and DNA damage, which
may lead to skin cancer.
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Chromophore
UVB filter
HO or
singlet O2
Chromophore
UVB filter
Figure 7.77 Interaction of UVB and DNA
(E) Germ Killing
Pure silver is well known for its germ killing property. With the introduction of
nanotechnology to the textile industry, nano-silver can be applied to textile materials to
provide such function.
(F) Skin Care and Fragrance
With the introduction of nanotechnology, textile materials can be able to release
fragrance, skin care chemical or even medicine gradually. Useful chemicals can be
trapped in a coating layer with micro-capsule. Rubbing and touch rupture the capsule
and release the chemical.
7.8.2 Smart Fabrics
With the incorporation of other technologies such as electronics, textile products
nowadays are equipped with extra new functions such as shape memory, television,
etc.
(A) Shape Memory Fabric
With the discovery of shape memory polymers (SMP), shape memory clothing is
feasible. Triggered by heat, shape memory polymers can retain previous shape. When
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these shape memory materials in garments are activated, the air gaps between
adjacent layers of clothing are increased in order to give better heat insulation. The
incorporation of shape memory materials into garments confers greater versatility in the
protection that the garment provides against extreme heat or cold.
(B) Garment Integrated with Electronic Devices
This is a combination of miniaturized electronic components and textile materials and
clothing. The product has an artificial intelligence but looks like an ordinary clothing
equipped with different functions, such as using conductive thread to embroider an
audible keypad on the jacket, integrating electronic products with clothing as ‘wearable
electronics”, using optical and electrical fibres that are woven to fabric to monitor the
health condition of wearer, sealing light-emitting diode (LED) on fabric to produce
patterns of light, etc.
(C) Temperature Sensitive Fabrics
The fundamental job of clothes is to keep us warm or cool, so it's no surprise that many
of the smart textiles that enters the market nowadays look to regulate body temperature.
Paraffin has been applied on fabrics. Paraffin changes its phase according to air
temperature. When the body is hot, paraffin liquefies and heat can pass out the garment.
As the body gets cold, paraffin solidifies and blocks heat loss from the garment. This
kind of fabric is called phase-change fabric.
(D) Touch Sensitive Fabrics
Consoles and hard plastic switches can be replaced by soft fabric controls. The controls
on the car dashboards may be an integral part of the interior upholstery and the laptop
could be part of a bag.
(E) Autoclean Fabrics
With the advancement of nanotechnology, many specific compounds can be applied to
textile materials. Incorporating minute size of titanium oxide (TiO2) in textiles can render
the textiles the auto-clean property. TiO2 is a good photo-oxidation catalyst which can
destroy stain and dirt under sunlight. Normally speaking, odor is formed on bacterial
action with perspiration. With such kind of garment, perspiration can be disintegrated
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under light and no smell is produced during the process.
(F) Medicinal Application
Many diseases require the use of medication in a long term and gradual period.
Microcapsule fabric can incorporate medicine in the capsule and have it released
gradually to wearers.
7.8.3 Plasma Technology
Plasma is basically a collection of ionic gases. Plasma can be generated through
heating of gases or electrical bombardment. Plasma is a reactive gas that only reacts on
superficial level of textile fibres. It can modify the fibre surface through either etching or
addition of polymer. This is a versatile technology which may increase the wetability of
fibres but at the same time increases water repellency. Advantages of plasma
treatments to conventional wet processes are water saving and that plasma treatments
do not affect the central structure of fibres.
Figure 7.78 Plasma treatments in textiles
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For example, the plasma treatment for antipilling of wool is a much safer treatment than
chlorination. Plasma treatment can etch away surface scales without damaging the
inner part of wool fibres.
What can Plasma do?
Plasma is a complex gas mixture with ions (cations and anions), electrons and free
radicals. Certain amount of electronically excited molecules may also be present.
Generally, plasma has three effects on textiles and they are shown as follows:Etching
This refers to the taking away of some substances from the surface of fabrics. This
will increase the surface roughness and wetability.
Surface chemical group modification
This refers to the change in surface chemical groups depending on the nature of
the plasma applied. The newly formed chemical groups can induce further surface
chemical reactions.
Plasma polymerisation or plasma that controls vapour deposition
This refers to the deposition of very thin films of polymers onto textile fibres. The
properties of deposited polymer change the surface properties such as water repellency
of textile materials.
Below are common types of plasma employed and their effects.
Plasma
Effect
Argon
Increase surface roughness
Oxygen
Modification of surface chemical groups – Increase
hydrophilicity
Fluorocarbon
Polymerisation – Increase hydrophobicity
Ammonia,
Carbon Dioxide
Modification of surface chemical groups
The following chart, summarises the effects of plasma on textile materials. Plasma is a
versatile technology that reduces water consumption, which suits the current trend of
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environmental protection. Furthermore, plasma only deals with surface (only a few
nanometers at stick) and will not affect the inner part of the fibre and retain the material
strength.
Figure 7.79 Effects of plasma on textiles
7.8.4 Environmental Protection
Textile production from the stage of fibre to garment and textile products creates a lot of
environmental impacts. Synthetic fibre production generates chemical wastes. Textile
processing such as bleaching, washing, dyeing, rinsing, etc uses up tremendous
amount of water and produce high volume of waste water. In addition, the industry
consumes large amount of petroleum for energy generation, synthetic fibre production,
colourant and auxiliary chemical production. Environmental protection is an
unavoidable aspect for the future development of the industry.
(A) Waste Water Treatment
Textile processing uses great amount of water, particularly in the dyeing and finishing
processes. Waste water is highly polluted with acid, base, starch and other chemicals.
Many countries have waste water discharge regulations that require the textile industry
to pre-treat waste before discharging it to the sewage system.
The measurement of the amount of pollutant present in waste water is indicated by the
amount of oxygen consumption for biological system or chemical.
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(i)
July 2009
Biological Oxygen Demand (BOD)
This measurement measures how fast biological organisms use up the oxygen in
polluted water. It is usually performed over a 5-day period at 20° Celsius. It is used in
water quality management and assessment.
(ii)
Chemical Oxygen Demand (COD)
This measurement measures the amount of organic compounds in water. Most of the
applications of COD determine the amount of organic pollutants found in surface water
such as lakes and rivers, making COD a useful measurement of water quality. It is
expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed
per litre of solution.
(iii) Activated Sludge
Many dyeing plants are installed with waste water treatment and employ activated
sludge treatment as the major water purification process. Activated sludge is a process
in which air or oxygen is forced into sewage liquor to develop a biological floc that
reduces the organic content of the sewage. The biological floc mainly contains bacteria
and protozoa fed on the dissolved organisms in the water. The purified water can be
drain down the sewage or recycle for further use.
(B) Biodegradable versus Recycling
Waste accumulation is one of the environmental concerns for many cities. Two major
approaches to reduce waste are “biodegradable” and “recycling”
Biodegradability refers to the degradability of materials by living organisms, mainly
bacteria, in the soil. Reclamation is one kind of waste treatment that applies the method
of waste biodegradation. Bacteria decompose waste to simpler forms and the degraded
substances may provide nutrient to the plantation on top. Non-biodegradable wastes
are stable in the soil for decades and the pace of their recycling circle is slow. They are
being accumulated on a daily basis and occupy enormous space. One way to reduce
waste is to have them produced biodegradable in the first place.
Recycling refers to the extract of materials from waste and re-use them for new products.
Many cities are practicing the classification of waste disposal which is a practice that
facilitates the gathering and handling of re-useable materials. It is obvious nowadays
that many daily products can be made from recycled materials such as tissue paper,
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writing pads, glass container, packaging material, etc. There are three common
recycling marks present in daily products.
Recycle mark for
Green Dot which
Recycle mark, which introduced by
battery which
needs special
treatment before
disposal.
used in the paper
industry. It means
the company has
contribution to
Society of Plastic Industry for
plastics (SPI), indicates the product
is made from recycled plastic. The
center digit indicates the types of
recycling.
recycled plastic and sometime the
plastic abbreviation will write below.
PE-HD stands for high density
polyethylene.
Figure 7.80 Various recycling marks on daily products
(i)
Biodegradability
Biodegradability reduces waste by breaking down materials through bacterial actions.
Advantages
-
Natural process
-
Breakdown products may re-entre nature as plant nutrients
Lower cost as soil contain many bacteria
Disadvantages
-
Slow process and take long time to complete
The process may release toxic substances and further harm the environment
-
Not all materials can be degraded completely. Plastic, glass and metal are
some examples of non-degradable materials.
Biodegradable products have limited shelf life
-
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(ii)
July 2009
Recycle
Recycle uses material repetitively, its advantages are:
Advantages
-
Reduce the need for new materials
Minimal waste
Functionally, recycled products may not be very different from new products
Disadvantages
-
Recycling requires energy and water
High cost given that advanced technology may be required
Education, regulation and government administration are required to practice
-
the classification of waste disposal
Recycled products usually are not attractive and they are usually in dark
-
colours as they are being recycled from coloured products
Not all materials are able to recycle. Thermosetting materials are an example of
non-recyclable material.
Biodegradation
Biodegradation is the process during which organic substances are broken down by
living organisms. The term is often used in relation to ecology, waste management,
environmental remediation (bioremediation) and plastic materials due to their long life
span. Organic materials can be degraded aerobically with oxygen or anaerobically
without oxygen. A term related to biodegradation is biomineralisation, which refers to
the process of organic matter being converted into minerals.
Biodegradable matters are generally organic materials such as plant and animal
matters and any other substances originating from living organisms. They can also be
artificial materials that are similar enough to plant and animal matters that can be put to
use by microorganisms. Some microorganisms have the astonishing, naturally
occurring and microbial catabolic capacity to degrade, transform or accumulate a huge
range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls
(PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, metals, etc.
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(C) Lyocell and Tencel®
Generally speaking, lyocell is a kind of rayon. Viscose is a popular rayon production
method. The process is based on toxic carbon disulfide (CS2) as the solvent. The
environmental impact of such process is the discharge of CS2 and xanthate (cellulose carbon disulfide solution). Lyocell is a green process that employs non-toxic amine
oxide as the solvent. Used amine oxides will be purified and recycled back to the
production system, which enables further reduction of chemical waste. Tencel® is the
trademark of lyocell which is produced by Lenzing Inc.
Figure 7.81 The lyocell process
(D) Organic Cotton
Conventional cotton plantation very much depends on chemicals. It takes up 10% of all
agricultural chemicals and 25% of the insecticides applied. According to certain studies,
a Tee-shirt made of cotton requires an average of 17 teaspoons of synthetic fertilisers
plus 3/4 teaspoons of active ingredients such as insecticides, pesticide and herbicides.
According to the information provided by the World Health Organization (WHO), around
20,000 deaths occur annually due to pesticide poisoning in developing countries.
Organic cotton refers to the cotton that is grown naturally without the usage of artificial
fertilisers, herbicides and pesticides. It is a kind of natural and clean cotton, which is
very suitable for infant and children’s products.
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(E) Bamboo Rayon
Viscose rayon is made by using wood pulps as raw material. Although wood pulps are
industrial waste of the wood industry, wood is still considered as a non-renewable
resource. Trees need many years to grow. Bamboo is an alternative source of cellulose
that in fact grows much faster than other plants. Making rayon out of bamboo reduces
the use of tree.
(F) Synthetic Fibres made from Resources other than Petroleum
Polylactic acid (PLA) fibre is a synthetic fibre made from fermented sugar extracted from
corn or sugar beet. Chemists have been able to successfully convert natural sugar
obtained from plants such as sugar cane and corn into ethanol, a substance that can be
used as fuel for automobiles. This is one of the substitutions of petroleum.
(G) Polyester Recycling
Given the negative environmental impact of the PVC material, the selection of
packaging material in the industry has been shifted to polyester. Polyethylene
terephthalate (PET) is the most commonly used polyester and it is also the polyester
fibre that we wear. PET has been being recycled from shot drink bottles and bubble
packaging materials for clothing. PET packaging material is cleaned and crashed before
the process of re-melting and being extruded to form new fibres. One of the major
limitations of PET recycling is its colour. The colour of PET can only be dark.
Figure 7.82 Recycling of polyester packaging materials
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(H) Water and Energy Saving
Same as any other industries or business operations, the textile industry is the course of
adopting many energy saving operations in the production process to reduce energy
consumption. Furthermore, the implementation of waterless production processes such
as plasma treatment reduces water consumption. Many organisations are operating
under worldwide environmental protection standards such as ISO 14000 to reduce
energy or water consumption, save resources and reduce and recycle waste.
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Not for Sale
The copyright of the materials in this booklet belongs to the Education Bureau. The
materials can be used by schools only for educational purpose. Written prior permission
of the Education Bureau must be sought for other commercial uses.
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