TEXTILE CHEMISTRY – UNIT IPROPERTIES OF FIBRE

DR. S. VANITHA

ASSISTANT PROFESSOR

PG & RESEARCH - DEPARTMENT OF CHEMISTRY

GAC, CBE-18

CRYSTALLINITY

• Crystallinity defines the degree of long-range order in a material, and strongly affects its

properties

• The more crystalline a polymer, the more regularly aligned its chains

• Increasing the degree of crystallinity increases hardness and density

CRYSTALLINITY AND AMORPHOUSNESS OF A FIBRE

CRYSTALLINITY:

• Crystallinity refers to the degree of structural order in a fibre molecule

• In a crystal, the molecular chains are arranged in regular manner and periodic

AMORPHOUSNESS:

• Amorphous region of the fibre is defined as the region of the fibre where there is no longer the order of chain molecules

• The polymer chains are randomly placed in amorphous region

• As a result, there is more air space in the amorphous fibre

CHARACTERISTICS OF AMORPHOUS AND CRYSTALLINE FIBRES

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POLYMER SYSTEM OF SOME COMMON FIBRES

CRYSTALLINITY AND INTERMOLECULAR FORCES

• Intermolecular forces are essential for crystal formation

• In Nylon, one can see from the picture that the polaramide groups in the backbone chain of nylon 6,6 arestrongly attracted to each other

• They form strong intermolecular hydrogen bonds

• This strong binding holds the chains together, and asthe chains are symmetrical, they tend to form crystals

• This raises the melting point of the crystals whencompared to polymers without such strongintermolecular interactions

• Cotton fibre is relatively inelastic because of its crystalline polymer system, and for

this reason cotton textiles wrinkle and crease readily

• Wool is the weakest natural fibre while silk is the strongest natural fibre

• Nylon is the first synthetic fibre ,exceptionally strong and elastic and stronger than

polyester fibres’ with excellent toughness, abrasion resistance and easy to wash

characteristics and to dye in a wide range of colours

• Jute is the cheapest fibre and most important vegetable fibre crop in the world

next to cotton

TENSILE STRENGTH

• Tensile strength is the measure of the maximum resistance of longitudinal stress before it

breaks

• The different properties of each fibre depends upon the source and orientation of that

particular fibre

• There are different properties of fibre like absorbent nature, strength, chemical

resistance, crimp etc.,

• Among these tensile strength is an important parameter since the fibres are supposed to

exposed to tension and stress during subsequent stages of making yarn, fabric and then

clothing

• Even the functionality and wear and tear of particular clothing depends upon this vital

property

• To determine the tensile strength of any fibre, it is tied to a hook at one end and weighted

are slowly added to the other end until the fibre break

• Silk: Silk has good tensile strength, which allows it to withstand great pulling pressure. Silk

is the strongest natural fibre and has moderate abrasion resistance. Elongation at break: Silk

fibre is an elastic fibre and may be stretched from 1/7 to 1/5 of its original length before

breaking

• Cotton: Cotton is moderately strong fibre. It has a tenacity of 3-5 gm/den. the strength is

greatly affected by moisture; The wet strength of cotton is 20%, which is higher than dry

strength.

• Nylon: The high tensile strength of nylon makes it ideal for heavy fabrics used in home

decor. Tensile strength, ultimate 82.7 MPa (megapascals), Elongation at break is 50 %,

Tensile modulus 2.93 GPa.

• Wool: The tensile strength of wool in dry condition is 1 – 1.7 and 0.8 – 1.6 in wet condition.

Elongation at break, standard elongation is 25 – 35% and 25 – 50% in wet condition.

TEAR STRENGTH

• Tear resistance or tear strength is a measure of how well a material can

withstand the effects of tearing

• It is vital for textiles, bullet-proof jackets, worker jeans, tents, apparel, sacks

and industrial applications

• If the tear strength is high, the punctures in the fabrics do not propagate

easily

• The knitted fabric is less strong as compared to the woven fabric

• The GSM of the fabric indicates the tear strength

• Higher the GSM, higher is the tearing strength

• The strength of the yarn has a direct relation to the tearing strength of the

fabric

• Higher the yarn strength, higher is the tear strength

• Spun yarn has low tear strength as compared to filament yarn

ABRASION RESISTANCE

• Abrasion resistant fabric withstands surface wear from rubbing, extending

the life of a product and protecting the person who wears it

• There are two different test methods commonly used by the textile industry

to assess abrasion resistance: Wyzenbeek and Martindale

• Both of these test methods are limited to measuring flat abrasion resistance

of a textile, they do not consider edge abrasion or other types of surface

wear that may occur in actual applications

WHERE ARE ABRASION RESISTANT FABRICS USED?

• Weather- and Marine-related Industries

• Footwear

• Safety and Protective Gear

• Furniture

• Backpacks

• Hospital and Medical Equipment

LUSTRE

• Lustre refers to the degree of light that is reflected from the surface of a fibre

or the degree of gloss or sheen that the fibre possesses

• The inherent chemical and physical structure and shape of the fibre can

affect the relative lustre of the fibre

• With natural fibres, the lustre of the fibre is dependent on the morphological

form that nature gives the fibre, although the relative lustre can be changed

by chemical and/or physical treatment of the fibre in processes, such as

mercerization of cotton

• Man-made fibres can vary in lustre from bright to dull depending on the amount of

delustrant added to the fibre

• Delustrants such as titanium dioxide tend to scatter and absorb light, thereby

making the fibre appear duller

• The desirability of lustre for a given fibre application will vary and is often

dependent on the intended end use of the fibre in a fabric and on current fashion

trends

• Cotton and Silk fibres have a natural lustre which is due to the natural polish on the

surface and it's nearly circular cross sectional shape

THERMAL PROPERTIES

The property which is shown by a textile fibre when it is subjected to heating is called

thermal property.

Thermal properties are including:

1. Thermal conductivity

2. Heat of wetting or heat of absorption

3. Glass transition temperature

4. Melting temperature

5. Heat setting

6. Thermal expansion

Thermal conductivity:

• Thermal conductivity is the rate of heat transfer in degree along the body of a textile fibre by conduction. Higher the thermal conductivity indicates the fibre more conductive

• Thermal conductivity is measure by co-efficient of thermal conductivity

Heat of wetting:

• When a textile fibre absorb moisture or water it gives of some amount of heat which is called heat of wetting or heat of absorption

• Heat of absorption resulting from changes in moisture regain rather than the thermal conductivity

• If 1gm of dried textile fibre is completely wetted then heat in calory/gm is involved which is known as heat of wetting for that fibre

Glass transition temperature(Tg):

• The temperature up to which a fibre behaves hard as like glass and after which it behaves

soft as like rubber is called glass transition temperature and it is denoted by Tg

• The range of Tg is lies between -100˚C to 300˚C

Melting temperature:

• A temperature at which fibre melt completely is called melting temperature

• At melting temperature fibre loses its identity and convert it into a viscous liquid

• At melting temperature fibre also loses its strength and some molecular weight

Thermal expansion:

• Thermal expansion can be measured by co-efficient of thermal expansion and

which is defined as the fractional increase in length of a specimen to rise in

temperature by 1˚C

• Co-efficient of thermal expansion ═ length increased / initial length of specimen ═

∆L / L ═ L2-L1 / L1

Heat setting:

• Heat setting is the process of stabilizing the form of fibres, yarns, fabric or garment

by means of successive heating or cooling in dry and wet condition