Fibre Science Lecture Note (Chapter One)
1.1. Introduction to Textile fibres
Definition:-
1.Fiber:-
It is a fine strand of tissue of plant, animal or any synthetic material drawn out in to very slender filament subsequently out in to required length.
All fires are not Textile fiber.
2.Textile Fiber:-
Material of natural or artificial origin which can be converted in to yarn or. fabric for clothing : also fordomestic and industrial purpose
Textile fibres are the basic structural units of textile materials.
Requirements of fibers to be textile fibers:-
1.Length:-
A fiber to be a Textile fiber its length should be atleast hundred times its diameter, and this lengthshould not less than 12 mm desirable to be >20mm.Comparably width or diameter of material will determineits fineness .
2.Strength:-
During processing of textile fibers, fiber materialswill passes different processing stages (spinning,weaving, and chemical finishing).A fiber to be processable in different processing stages should have minimal
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strength. Final fabric strength also depends onstrength of fibre.
3.Flexibility:-
Flexibility is the ability of a material to be bentrepeatedly without break. It is an essential propertyof natural fibres. For man-made fibers we can applydifferent mechanisms.
4.Cheapness 5. Abundance
1.2. Classifications of Fibres
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Natural Fibers
1.Cotton fiber:-
Earliest use estimated between 3,000 BC & 5,000 BC.
Worn by Egyptians earlier than 2,500 BC.
Eli Whitney's invention of the cotton gin in 1793 revolutionized the processing of cotton.
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The development of the power loom in 1884 brought significant improvements and variations to cotton fabrics.
Major producers: United States, Soviet States, China and India. Lesser producers include Pakistan, Brazil, Turkey, Egypt, Mexico Iran and Sudan.
2.Wool:-
Earliest use estimated between 3,000 BC, and it was used by people of the Late Stone Age,
There are 40 different breeds of sheep, which produce approximately 200 types of wool of varying grades.
Major producers include: Australia, New Zealand, Soviet States, China, South Africa, and Argentina.
3.Silk:-
Believed discovered by a Chinese princess.
Silk is made from two continuous filaments cemented together and used to form the cocoon of the silkworm.
Silk culture began about 1725 BC, sponsored by the wife of China's emperor.
Secrets of cultivation and fabric manufacturing wereclosely guarded by the Chinese for about 3,000 years.
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There is a story that two monks smuggled seeds of the mulberry tree and silkworm eggs out of China by hiding them in their walking sticks.
India learned of silk culture when a Chinese princess married an Indian prince.
The major producer and exporter of silk is Japan.
Man-Made Fibres’
Natural fibres do have certain disadvantages: Cotton and
linen wrinkled easily silk had to be handled very
delicately Wool shrank and do not moth resistant. So
efforts began to find out more efficient fibers and then
rayon cames.
a. Rayon(artificial silk):- It is the first man-made fibre,
The first commercial production of rayon fibre in the United States was in 1910 by the American Viscose Company.
By using two different chemicals and manufacturing techniques, two basic types of rayon were developed.They were viscose rayon and cuprammonium rayon.
Today, only viscose rayon is being produced in the U.S.
b. Acetate:-
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The first commercial production of acetate fibre in the United States was in 1924 by the Celanese Corporation.
c. Nylon:-
Is the first synthetic fibre(its starting polymer ispetrochemical)
The first commercial production of nylon in theUnited States was in 1939 by the E. I. DuPont deNemours & Company, Inc. It is the second most usedman-made fibre in this country, behind polyester.
d. Acrylic:-
Have wool like appearance
The first commercial production of acrylic fibre in the United States was in 1950 by E. I. DuPont de Nemours & Company, Inc.
e. Polyester:-
Produced through condensation polymerization of ethylene glycol with terephthalic acid.
Is now the most used fibre and followed by nylon
The first commercial production of polyester fibre in the United States was in 1953 by E. I. DuPont de Nemours & Company, Inc. Polyester is the most used man-made fibre in the U.S.
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f. Triacetate:-
The first commercial production of triacetate fibre in the United States was in 1954 by the Celanese Corporation. Domestic Triacetate production was discontinued in 1985.
g. Spandex:-
It is an elastomeric man-made fibre (able to stretch at least 100% and snap back like natural rubber). Spandex is used in filament form.
The first commercial production of spandex fibre in the United States was in 1959 by E. I. DuPont de Nemours & Company, Inc
h. Polyolefin/ Polypropylene :-
The first commercial production of an olefin fibre manufactured in the U.S. was by Hercules Incorporated.
In 1966, polyolefin was the world's first and only Nobel-Prize winning fibre.
1.3 Fibre Structure and Properties
1.3.1 Fiber Morphology:-
Fiber morphology is the study of size, shape, and
structure of fiber. it includes macrostructure,
microstructure, submicroscopic structure, fine structure
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i. Macro Structure:
These are features of fiber that are discernible to the
eye. Properties include (length, color, and crimp).
Length: - based on length fibers can classified as Natural
(short staple fibers) Man-Made fibers(long filament and
filament tows)
Fig.1.1 comparison in length of natural and that of mam-made fibers
Color: - property of chemical make-up of fibre can also
distinguished fibers
Crimp:-is wave, bend, twist, coil, or curls along the
length of the fibre. Fibres’ do have different crimp
properties.
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Fig1.2 crimp structure of different fibers
ii. Microstructure:
These are features observable with a light microscope (cross-
sectional shape, diameter, and surface contour). Natural fibreshave characteristics that are identifiable by microscope. For
Manufactured fibres it is more difficult to identify b/c they
look alike under microscope .Manufactured fibres show
controlled cross sectional shape/diameter, while natural
fibres are not uniform.
Diameter is mesured in micrometer, denier or tex. Surface
contour refers to the outer surface of fibre along its length:
smooth, serrated, striated, rough, etc
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Fig1.3 Microscopic structures of different fibers
iii.Submicroscopic structure:-
Submicroscopic refers to features identified by electron
microscope.
Natural fibers : Outer cover, Inner area and Central core
Manmade fibers: Skin and Core
Fig1.4 features which are distinguishable by an electron microscope
iv.Fine structure:-
Refers description of arrangement of polymer molecules
within the fiber.
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When polymer mol. are closely packed, with a high degree
of short range and long range, they are CRYSTILINE in
form.
When polymer mol. are loosely packed, with a little or no
order in their arrangement, they are AMORPHOUS in form.
The arrangement of polymer mols. With respect to the
fiber axis is called ORIENTATION
Amorphous fibres are: -(weak, easily elongated, poorly
elastic, good moisture absorbency, dyeability, and
flexibility)
Oriented and crystalline fibres are :_(strong, stiff,
don’t stretch easily, recover from stretch quickly, non-
absorbent and are difficult to dye )
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Fig1.5. fiber crystallinity and orientation
FIBER CONSTRUCTION
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1.3.2. Fiber Properties
Fiber properties contribute to the properties of a fabric. For
example, strong fibers contribute to the durability of
fabrics; absorbent fibers are good for skin-contact apparel
and for towels and diapers; fibers that are self-extinguishing
are good for children's sleepwear and protective
clothing. To analyze a fabric in order to predict its
performance, start with the fiber. Knowledge of the fiber's
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properties will help to anticipate the fiber's contribution to
the performance of a fabric and the product made from it. Some
contributions of fibers are desirable and some are not. Fiber
properties are determined by the nature of the physical structure,
the chemical composition, and the molecular arrangement.
1. Physical StructureThe physical structure, or morphology, of fibers can be
identified by observing the fiber through a light, or
electron, microscope. In the text, photomicrographs taken by
electron microscopes at magnifications of 250-1,000 x will be
used to clarify details of the fiber's physical structure.
a. Length. Fibers are sold by the fiber producer as filament,
staple, or filament tow.
.Filaments:- are long continuous fiber strands of indefinite
length, measured in yards or meters. They may be either
monofilament (one fiber) or multifilament (a number of
filaments). Filaments may be smooth or bulked (crimped in
some way), as shown in Figure. Smooth filaments are used
to produce silk-like fabrics; bulked filaments are used in
more cotton-like or wool-like fabrics.
Staple fibers: - are measured in inches or centimeters and range
in length from 2-46 cm (% of an inch to 18 inches). All
the natural fibers except silk are available only in
staple form. The man-made fibers are made into staple form
by cutting filament tow into short lengths.
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Filament tow: - consists of a loose rope or strand of several
thousand man-made fibers without a definite twist. Tow is
usually crimped after spinning
Fig 1.7 diagram of filament (bulk left, smooth right), staple, and filament tow
fibers
b. Diameter, Size, or Denier.
Fiber size plays a big part in determining the performance and
hand of a fabric (how it feels). Large fibers give crispness,
roughness, body, and stiffness. Large fibers also resist
crushing this is property that is important in carpets. Fine
fiber gives softness and pliability. Fabrics made with fine
fibers will drape more easily.
Natural fibers are subject to growth irregularities and are
not uniform in size or development. In natural fibers,
fineness is a major factor in determining quality. Fine
fibers are of better quality. Fineness is measured in
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micrometers (a micrometer is 1/1,000 millimeter or
1/25,400(inch).
Diameter Range (micrometers)
Cotton 16-20
Flax 12-16
Wool 10-50
Silk 11-12
Man-made fibers, diameter is controlled by the size of the
spinneret holes, by stretching or drawing during or after
spinning, or by controlling the rate of extrusion of the
spinning dope through the spinneret. Man-made fibers can
be made uniform in diameter or can be thick-and thin at
regular intervals throughout their length. The fineness of
man-made fibers is measured in denier. Denier is the weight in
grams of 9,000 meters of fiber or yarn. Tex is the weight in grams of 1,000
meters of fiber or yarn.
c. Cross-Sectional Shape:-
Shape is important in luster, bulk, body, texture, and hand or
feel of a fabric. These shapes may be round, dog-bone,
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triangular, lobal, bean-shaped, flat, or straw like. The
natural fibers derive their shape from (1) the way the
cellulose is built up during plant growth, (2) the shape of
the hair follicle and the formation of protein substances in
animals, or (3) the shape of the orifice through which the
silk fiber is extruded. The shape of man-made fibers is
controlled by the spinneret and the spinning method. The size,
shape, luster, length, and other properties
of man-made fibers can be varied by changes in the production
process.
d. Surface Contour.
Surface contour is defined as the surface of the fiber along
its length. Surface contour may be smooth, serrated, striated,
or rough. It is important to the luster, hand, texture, and
apparent soiling of the fabric. Figure 1.8 shows some of the
differences in the surface contours of different
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Fig 1.8 crossectional shapes and surface contour
e. Crimp Crimp may be found in textile materials as fiber crimp or
fabric crimp. Fiber crimp refers to the waves, bends, twists,
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coils, or curls along the length of the fiber. Fiber crimp
increases cohesiveness, resiliency, and resistance to
abrasion, stretch, bulk, and warmth. Crimp increases
absorbency and skin-contact comfort but reduces luster.
Inherent crimp occurs wool. Inherent crimp also exists in an
undeveloped state in bicomponent man-made fibers where it is
developed in the fabric or the completed garment (such as a
sweater) by using suitable solvents or heat treatment.
2. Chemical Composition And Molecular
ArrangementFibers are classified into groups by their chemical
composition. Fibers with similar chemical compositions are
placed in the same generic group. Fibers in one generic group
have different properties from fibers in another group. Fibers
are composed of millions of molecular chains. The length of
the chains, which varies just as the length of fibers varies,
depends on the number of molecules connected in a chain, and
it is described as degree of polymerization. Polymerization is the
process of joining small molecules-monomers-together to form a
long chain or a polymer. Long chains indicate a high degree of
polymerization and a high degree of fiber strength. Molecular
chains are not visible to the eye or through the optical
microscope. Molecular chains are sometimes described in terms
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of weight. The molecular weight is a factor in properties such
as fiber strength and extensibility. A fiber of longer chains
has a higher strength than a fiber of shorter chains of equal
weight; the fiber of longer chains is harder to pull apart
than the fiber of shorter chains.
Molecular chains have different configurations in fibers. When
molecular chains are nearly parallel to the lengthwise axis of
the fiber, they are said to be oriented; when they are randomly
arranged or disordered, they are said to be amorphous. Crystalline
is the term used to describe fibers that have molecular chains
ordered relative to each other, and usually, but not
necessarily, parallel to the lengthwise axis of the fiber
(Figure 1.9). Different fibers vary in the proportion of
oriented, crystalline, and amorphous regions.
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Fig.1.9.polymer (a), amorphous area (b) crystalline area, but not oriented (c)
crystalline and oriented
The polymers in man-made fibers are in a random, unoriented
state when extruded from
the spinneret. Stretching, or drawing, increases their crystallinity
and orients them, reduces
their diameter, and packs their molecules together (Figure
1.10). Physical properties of the
fiber-such as strength, elongation, moisture absorption,
abrasion resistance, and receptivity absorption, abrasion
resistance, and receptivity of the fiber to dyes-are related
to the amount
of crystallinity and orientation.
Molecular chains are held to one another by cross links or by
intermolecular forces called hydrogen bonds and van der Waals forces.
The forces are similar to the attraction of a magnet
for a piece of iron. The closer the chains are together, the
stronger the bonds are. Hydrogen
bonding is the attraction of positive hydrogen atoms of one
chain for negative oxygen or nitrogen atoms of an adjacent
chain. Van der Waals forces are similar but weaker bonds. It
is in the crystalline area that hydrogen bonding and vander
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Waals forces occur. Cross links and intermolecular forces help
make crystalline polymers stronger than amorphous polymers.
Fig.1.10 Before and after drawing the fiber
1.4. Fundamental Characteristics of Textile
Fibers
Tensile Strength:Tensile strength is the breaking strength of any
material, which is commonly expressed as force per unit
crossectional area, e.g. as dynes per square cm: in these
terms tensile strength is described as the ability of
fibres’ to resist breakage under tension.
When a single fiber is being considered, the strength of
the fibre is commonly described as tenacity, which is
measure of specific stress at break i.e. breaking
Load/mass per unit length.
Tenacity is expressed in terms of grams per decitex or
centinewtons per tex(cN/tex).
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When a fiber is subjected to a force it will stretch to a
certain degree. This stretching is described as
elongation or extension, in terms of percentage of the
fibre’s original length.
It can be measured either as an elongation under a
certain load, or as the elongation reached when the fibre
breaks. Unless specified, the figure given the elongation
at break.
Elastic recovery: When a fiber is stretched by a small amount, it may
exhibit almost perfect elasticity. That is to say, it
will return to original length when it is released.
If, however, the fibre is subjected to a greater degree
of stretch, it may react in a much more complex way. Some
permanent deformation may take place, so that when it is
released the fibre will return to an elongated form.
This behaviour of a fibre ids denoted by describing its
recovery at certain elongations:
Thus, in the case of a fibre that returns completely to
its original length after say , a 2 % elongation, we can
say that the elastic recovery is 100%.
In the case of a fibre, which retains half its extra
length after release from an 8% elongation, we say that
it has a 50% elastic recovery at 8% elongation.
Stress-Strain diagramRedwan J. Page 24
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The tensile and elastic properties of a fibre are usually
summarized in stress-strain diagram. In this diagram, the
strain (i.e distortion in the fiber) is plotted against
the stress (i.e force) exerted on the fibre.
A stress-strain diagram gives a much more complete record
of the behavior of a fibre under tension than isolated
figures can. Typical stress-strain diagrams are providedfor many fibres.
A straight line on the stress strain diagram may indicate
that a fibre is truly elastic. The extension of the fibre
is proportional to the applied load. This is, however,
rarely achieved in practice.
As the load on a fibre increases beyond that needed to
causes a few percent extension, the deformation of fibre
is greater than that due to true elasticity. Superimposed
upon the elastic stretch there is some less permanent
deformation of the fibre, or plastic flow.
As the tension increases, the stress-strain curve
indicates how the fibre continues to deform up to the
point at which it eventually breaks.
The stress-strain diagram therefore provides a much more
complete picture of the deformation caused in a fibre as
tension is applied to it.
1. The diagram includes tenacity and elongation at break.
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2. The area below stress-strain curve of a fibre provides a
measure of the energy needed to break the fibre and is
called work of rupture. It indicates the ability of the fibre
to withstand sudden shocks, and it is measured in grams
per decitex or centinewtons per tex.
3. Initial modulus is a measure of the fibre’s resistance to
small extensions. A high modulus means that the fibre has
a good resistance to stretching, and a low modulus means
that it requires little force to stretch it. Flexibility
and modulus are closely linked, a low modulus fibre
tending to be flexible and a high modulus fibre tending
to be brittle.
4. Average toughness is the ability of a fibre to endure large
permanent deformations without rupture. It is expressed
as grams per dtex or cNper tex.
The stress-strain behaviour of a fibre is of great important in practice, and
influences to a large gedree the behaviour of the fibre in textile manufacturer.
Moisture propertiesAll fibres tend to absorb moisture when in contact with
the atmosphere. The amount absorbed depend depends up on
the relative humidity of the air.
In practice, the moisture absorbing properties of a fibre
are described by a figure known as the regain. This is the
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weight of moisture present in a textile material expressed
as a percentage of its oven dry weight.
The percentage moisture content of a fibre is the weight
of moisture it contains, expressed as percentage of total
weight. This is measure of the amount of water held under
any particular set of circumstances.
Fibres vary greatly in the amount of moisture they will
absorb. A fibre which absorbs water readily is often more
suitable for use in certain types of clothing fabrics.
The ability of a fibre to absorb moisture will also affect
the processing and finishing of yarns and fabrics,
tensile, tensile, static accumulation and other
properties.
Thermal propertiesAll fibres are affected in one way or the other as they
are heated. The behaviour of fibres on heating is of real
importance, particularly within the range of temperatures
that are met in practical use.
Fabrics should e.g. withstand the temperatures used in
laundering and ironing without undue deterioration.
In the presence of air, most fibres will burn. The
readiness with which they catch fire and support
combustion is immense importance.
Electrical properties
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The dielectric strength of a fabric is important if the
material is to be used for insulation purposes in the
electrical industry. It also influences the degree to
which static electricity will accumulate on yarn or fabric
during processing or wear.
The electrical resistance of static electricity may be
described in terms of mass specific resistance, i.e. the
resistance of 1 gm specimen 1cm long.
Effect of sunlightAlmost every fibre is affected by the powerful radiations
of sun light.
Some will decompose and deteriorate fairly rapidly,
losing tensile strength and changing color. Others will
resist deterioration for ears, and particularly useful
for fabrics such as curtains, awnings and furnishings
which are constantly exposed to light.
Effects of organic solventsSolvents such as carbon tetrachloride and
trichloroethylene are commonly used for cleaning fabrics,
and the effect of these solvents on the fibre itself is
obviously important.
Effect of acids and alkalis
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Textiles are commonly subjected to acid solutions on one,
or another and the effects of different acids under
varying conditions are very important.
From the very earliest times alkaline agents have been
used for washing and scouring textiles. Soap itself forms
an alkaline solution in water.
Resistance to insects and microorganismsThe cellulose of plant fibres and the protein of animal
fibres are substance produced by living things. They are,
as might be anticipated, enjoyed by other living things
as food.
Cellulose is attacked by certain moulds and bacteria,
which decompose it and make use of the degradation
products as food.
Textiles stored in damp water houses are often affected
by mildews, which may discolour and weaken the fibres to
the point at which they become useless.
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Load-elongation or stress- strain diagram
Work of rupture and Initial mopdulus
& initial modulus of angle
tan
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Yield point and crimp
Comparison
At 65% r.h., 20 °C, 1 cm test length, 0.15mNtex–1
s–1
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Effects of Temperature:
When the temperature increases the tenacity and stiffness
of fibres is lower. The breaking extension is usually
higher.
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Comparison of fibres by their elastic recovery
Effect of Humidity on Elastic Recovery
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