Secondary Properties

Textile Science and Care 3(2+1)

Lesson 03 : Properties Of Textile Fibres

Secondary Properties

Physical Properties:
Physical Shape:
The physical shape of the fibre is an important factor in determining many of its properties. It includes the surface contour (smooth, rough, serrated), the shape of the cross section and the width and length of the fibre. The shape of the cross section influences certain factors such as lustre, body and hand. The surface contour in turn influences cohesiveness, resiliency, loft and thickness. It contributes to resistance to abrasion, Pilling and comfort factors such as absorbency and warmth. The cross sectional shape can be changed for all artificial fibres unlike natural fibres as the fibres are moulded though spinnerets.

Density: Density is the mass of a unit volume of material. It is expressed as gms/cubic cm or pounds per cubic foot. The specific gravity of a fibre indicates the density relative to that of water at 4oC. All textile fibres are heavier than water except olefin fibres. Only these fibres float on water. Cotton, wool fibres are heavy and nylon is comparatively lighter. The lower the density the more the covering power. A pound of wool and a pound of nylon weigh the same but the fibres are more in nylon than in wool. High density results in heavy fabrics, low density results in light weight fabrics.

A light weight fibre helps a fabric to be warm without being heavy. Acrylic fibres being light comparatively are wool like in appearance and are used extensively instead of wool to produce light weight sweaters & blankets.

Lustre: Lustre is the amount of light reflected from a surface. It is more subdued than shine. Light rays are broken up into many short rays unlike the shine in which the light ray is reflected back wholly without any breaks. The lustre is due to smoothness, fibre length, flat or lobal shape. It determines the fibres natural brightness or dullness. The natural fibre silk has the high lustre and cotton is the dullest natural fibre. All man-made fibres are produced with lustre controlled. It is not always desirable to produce bright fabrics. So the lustre is controlled by the addition of pigments such as titanium dioxide in spinning solution. The lustre in natural and man-made fibres can also be improved by various finishing techniques. For example the lustre in cotton is improved by mercerization.

Absorbency: Generally textile fibres have certain amount of water as an integral part of the fibre. All most all textiles fibres are naturally hygroscopic (i.e they pick up moisture from air). But the amount of moisture the fibres absorb may differ. Absorbency in the ability to take in moisture and moisture regain is the percentage of moisture a bone-dry fibre will absorb from the air under the standard conditions of temperature and moisture. Fibres that absorb water easily are known as hydrophilic (water loving) fibres. Natural protein and vegetable fibres, rayon and acetate are hydrophilic fibres. Fibres that have difficulty in absorbing water are known as hydrophobic fibres.

Many synthetic fibres are hydrophobic in nature. The absorbency of glass fibre is ‘0’. The absorbency of a fibre is due to the hydroxyl groups present within the fibre and the amorphous molecular arrangement. The fibres having crystalline arrangement are generally hydrophobic.

Absorbency is an important factor in all textile fibres especially those which are used for apparels as it influences many other fabric properties such as comfort, warmth, water repellency, static build up, dyeability, shrinkage, wrinkle resistance etc. It is easy to wash a hydrophobic fabric as it does not absorb stains and it dries quickly.

Among the textile fibres the natural protein fibres silk and wool are the most absorbant of all fibres. Next comes the natural and man-made cellulosic fibres.

The absorbency of a textile fabric is controlled by the type of yarn and fabric construction and also by finishing. For example: in cotton, the absorbency is increased by kier boiling, mercerization and napping. Pile construction increases the area of absorption.

Elasticity: Elasticity is defined as the ability of fibres to return back to original shape after being stretched. Elastic recovery is the ability of fibres to return from strain and is expressed in percentage. If a fibre returns to original length after stretching to a specified length, it is said to have 100% elastic recovery.

Elasticity is required in fabrics when subjected to stretch during wear. This property is influenced by the side chains & cross linkages between the molecules. If strong bonds are present in between chains of molecules, the fibre tends to return to its original length. If the bonds are not strong it can’t recover to its original length but takes up the new shape. Thus creases appear on the material. Some fibres show immediate elastic recovery, and some fibres may show delayed elastic recovery. For example, the creases on a silk material disappear if hung overnight. Wool, silk, viscose and nylon are having good elasticity. Cotton and acetates have poor elastic recovery. Polyester has moderate elongation but has good elastic recovery. It is apparent that both the elongation and elastic recovery are considered together in evaluating fibres, yarns and fabrics.

Abrasion Resistance: It is the ability of fibres to withstand the rubbing or abrasion it gets in everyday use. All fabrics irrespective of the enduse are subjected to rubbing of some kind during wear. The fabric has to withstand rubbing, otherwise the fabric will show signs of damage and become unsightly. The resistance may be due to the tough outer layer and flexible molecular chains of the fibre. The size of the yarn also influences the abrasion resistance. Thick yarns resist abrasion than thin yarns. Yarn uniformity is also important as irregular yarns are abraded more easily than uniform yarns. Smooth fabrics with compact yarn arrangement are less susceptible to damage by abrasion than those with irregular surface in the low count.

Nylon has excellent resistance and acetate and glass have very poor abrasion resistance when compared to silk & wool. Cotton has better abrasion resistance. This is an important property, as it influences the durability and increases the resistance to splitting.

Hand: Hand is the way a fibre feels. It can be only detected by feeling it in between fingers. The hand varies due to the cross sectional shape, the length and diameter, the flexibility, the compressablity, resilience, surface contour of the fibres, surface friction and thermal characteristics of fibres .

The hand and drape of a fabric are inter dependent. The hand of a fabric may vary from very pliable to very stiff, from very soft to very hard, from very limpy to very springy, from rigid to high degree of stress, form very smooth to very rough, from slippery to harsh, from very cool to very hot and from wet to dry.

The hand of a yarn and fabric should not be confused with the hand of a fibre. It is possible to produce smooth yarns from rough fibres and vice versa.

Pilling: Ball like structures are often observed on polyester and nylon materials after few washes which make the material unsightly. Pilling is nothing but the balling up of fibre ends on the surface of fabrics. It is one of the disadvantages of staple fibre fabrics. In natural fibres the balls cut away from the fabric easily but synthetic fibres are so strong that they do not break away rapidly from the fabric. So the strength of fibres is a basic factor in the problem of pilling. Pills usually occur in areas that are abraded or subjected to abrasion during wear. Usually at the armpits of garments and back and lower edge of sarees, pilling can be seen. It can be made better by removing pills. But it is almost impossible to remove pilling from synthetics unless it is given singeing finish. In this the fabric passes through gas flames, so that the balls are burnt off. In order to inhibit the formation of pills on materials, they are given special finishes known as anti pilling finishes.

To prevent pilling close fabric construction is recommended. Tightly twisted yarns and longer staple fibres are helpful in preventing pilling. Fulling of wool, resin finishes on cotton are anti pilling finishes.

Loft and Resiliency: Loft is the ability of a fibre to spring back to original thickness after being compressed. Resiliency is the ability of a fibre to bounce back to shape following compression, bending or similar deformation. Wool and silk fabrics are more resilient. They can be deformed, crushed or wrinkled during wear but they come to shape upon hanging. Elastic recovery is an important factor while evaluating the resilience of a fibre. Usually good elastic recovery indicates good resiliency.

Static Electricity: This is the electricity produced by the friction of a fabric against itself or some other object. If a fabric is better conductor of electricity, it conducts away the electricity that is produced. But if the material is not a good conductor, the electricity produced cannot be conducted away, but it tends to pile up on the surface of the fabric. It the material comes in contact with a good conductor, a shock or transfer occurs. It may produce sparks, in gaseous atmosphere, it may give explosions. So it is a hazard in places where materials which are highly inflammable are present. So the use of synthetics is prohibited in operation theatres. Static electricity rapidly develops in cold and dry atmospheres. After wearing synthetics for few hours, it is better to wipe the garments with a wet towel. It carries away the electricity produced. Static electricity makes the fabric to cling to the body of the wearer. It attracts more dust and thus gives unsightly appearance. Fabrics cling to the machinery & thus cutting and stitching of garments is made difficult.

Antistatic finishes are given to fabrics in order to inhibit the piling up of static electricity on fabrics. But this is washed off after few washes.

Feltability: It is the ability of fibre to mat together. Using this property, it is possible to produce fabrics without the complicated processing of spinning and weaving. These are termed as non - woven felted materials. Some rug materials, carpet materials and apparels are produced by felting. The ability of wool to coil together, interlock & shrink when subjected to heat, moisture and pressure is responsible for felting of wool fibres. In fact the other fibres are also felted by using a suitable adhesive.

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Last modified: Wednesday, 9 May 2012, 6:48 AM