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Length: Textile fibres are available in different lengths. Filaments are long continuous fibres of indefinite length measured in yards or meters. Staple fibres are the short fibres and are measured in inches or centimeters and range in length from ¾ " to 18". All natural fibres except silk are staple fibres. Man-made and synthetic fibres are all filament fibres. They are made as filaments since their length can be controlled when the fibre forming solution escapes through the holes of a spinnerette . Sometimes filament fibres are also cut into staple length to produce certain desirable qualities. In order to cut the filaments into staple length, several thousands of filaments are taken in the form of a loose rope or strand, often made crimpy and are cut to produce staple fibres ranging in length from 1" to 5". The rope of fibres is also refered to as ‘Fibre tow’.
Fibrous materials must possess greater length than the diameter. This is referred as length to width ratio. A minimum ratio of 100:1 is considered essential. Majority of the fibres have greater length than the diameter.
Strength: Strength is the second primary property of all textile fibres. In order to be serviceable, all fibres must possess this quality. The strength must be adequate for processing or spinning into a yarn and further making into a fabric. Fibres may vary in strength and the strength within a fibre may not be uniform throughout. It depends upon mainly the molecular structure of fibres.
The strength of a fibre is defined as the ability to resist stress & is expressed in grams per denier. Denier is equal to the weight in grams of 9000 meters of filament. Fibre tenacity may vary from fibre to fibre. It may be as low as 1 gm/denier in acetate and as high as 8 gms/denier in glass. Strength can also be measured in pounds / sq.inch. This is referred as ‘tensile strength’. The strength of a fibre can never be confused with strength of yarn or fabric since it is possible to produce very strong and durable materials from weak fibres. The yarn or the fabric strength is controlled by many other factors which are discussed in the related chapters.
A strong fibre is durable, has a better tear strength and resists sagging and pilling. The tenacities of some selected fibres of consumers’ interest are given below.
FIBRE TENACITIES
Under Standard Conditions (700 F & 65% RH)
- Cotton - 4.0
- Silk - 4.5
- Wool - 1.5
- Rayon - 1.5 to 2.4
- Acetate - 1.2 to 1.5
- Nylon - 4.5 to 5.9 (High tenacity fibres– 5.9 to 9.2)
- Polyester - 4.4 to 7.8
- Glass - 7.0
Glass ranks first in tenacity than the other fibres. Next comes Nylon and Polyester. Some of these fibres loose or gain strength when wet. A good example for loss of strength during wet condition is Rayon and for gaining strength is cotton.
Flexibility or Pliability: It is also one of the important primary properties. Many natural fibres are available without this quality. So they are qualified for textile use. Certain degree of flexibility or pliability is necessary for a fibre to be used as a textile fibre. A textile fibre needs to be bendable. For example a glass rod cannot be bent without breaking, but a glass filament can be bent easily. This property is essential to create yarns and fabrics that can be creased, have the quality of drapability, ability to move with the body and should allow for the free movement and also be comfortable. A stiff fibre will make stiff fabrics, which cannot be used comfortably.
Cohesiveness or Spinnability: Cohesiveness is the ability of the fibres to stick together during spinning. The cohesiveness in fibres may be due to the longitudinal contour or the cross sectional shape that enable them to adhere together. The surface or the skin structure of the fibre may also influence cohesiveness. For example, wool fibre possesses scales on the outer skin of the fibre which help in interlocking fibres while spinning. If the surface or shape of a fibre do not contribute for cohesiveness, the same can be compensated by using filament yarns. As filaments are present throughout the length of the yarns, there is little necessity of having the ability to stick. So this cohesiveness is often conveniently replaced by spinning quality. Polyester is having the lowest cohesiveness but it can be made into staple yarns by using less percentage of cotton and later burning it through carbonising process.
Uniformity:In order to produce fine yarns, uniformity in the raw material is required. Fibres that are used to produce yarns need to be similar in length and width, in spinning quality and in flexibility. All man-made and synthetic fibres are uniform since they are made through artificial processing. But in case of natural fibres, it is not so. Fibres differ is many aspects, and so it is not possible to produce very fine materials in natural fibres unless some extra processing is done. The yarns composed of uniform
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