Fiber science

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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Fig1.6 typical models

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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).

ElongationRedwan J. Page 23


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


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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