Length is an important parameter that determines the usefulness of a textile fibre. When a continuous yarn is to be made out of individual fibres, it should possess a considerable length with reference to its diameter, otherwise, it would not be possible to make a yam that would hold together the constituent fibres. This is referred to as the length to breadth ratio. The most useful fibres should have length to diameter/breadth ratios of more than 100: 1.
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Almost all textile fibres have the length to breadth ratio of more than 1000: 1.
Typical ratios for several natural fibres are as follows:
Length is the most important fibre property as far as ring spinning is concerned. As the fibre length increases the overlapping of fibres in the yarn increases. The increase in overlapping results into increased resistance to slippage. If the yarn is spun from long and short fibres, then yarn spun from long fibres has more strength.
Textile fibre length varies considerably within anyone sample. The variation is as high as 40% for cotton and about 50% for wool. Man-made staple fibres are more uniform.
As the drafting settings are done on the basis of longer fibres in the cotton, if there is a higher variation in fibre length, a significant number of fibres behave as short fibres (floating fibres) in drafting. As the length of these short fibres is much less than the setting between drafting rollers, these fibres become uncontrolled or floating fibres resulting in high irregularity in drafted strand. Higher irregularity in the drafting strand at various stages of drafting will give an irregular yarn having lower strength. The length uniformity thus affects the yarn irregularity and strength.
The strength indicates the resistance sustained by fibres, the yams or the fabrics to breakwhen force is applied to them.
The strength may be tensile strength, bending strength, bursting strength, etc. as per the direction of application of force. Fibre strength and elongation have a direct relationship with yarn strength and elongation another thing being constant. A stronger fibre result in stronger yarn and the same is true about fibre elongation.
The strength of any material is derived from the load it supports at the break and is thus a measure of its limiting load-bearing capacity. Normally strength of the textile fibre is measured in tension when the fibre is loaded along its long axis and is designated as “Tensile Strength”. The tensile strength of the textile fibre is measured as the maximum tensile stress in force per unit cross-sectional area or per unit linear density, at the time of rupture — called “Tenacity”, expressed in terms of grams per denier or grams per tex units.
Uniformity means the evenness of the individual fibres in its length and diameter.
A fibre possessing this property can produce reasonably even yarns. This is also important in connection with the strength of the resulting yarn. Uniform textile fibres should possess uniformity in their thickness and length.
Unfortunately, none of the principal natural fibres like cotton or wool has the same length and diameter of the fibre in the same lot. Fibres in any specified qualities, grades or lots vary considerably in length and diameter. On the other hand, manmade staple fibres are more uniform as they are cut to the exact length after being spun and drawn, and even the diameter can be controlled within close tolerance limits during its manufacture.
Spinnability includes several physical properties each having an effect on the ability of the fibres to be spun into yarn. Staple fibres must have to be capable of taking a twist or being twisted (Flexibility). They must have a certain degree of friction (Cohesion) against one another to stay in place when the pull is applied to the yarn. They must also be able to take on whole special finishes for lubrication during spinning or to provide additional surface resistance to abrasion.
The fibre should be sufficiently pliable; then only it can wrap around another fibre during spinning. If on the other hand, fibre is stiffer, then it is less adaptable for textile use, for example, glass and metallic fibres.
Cohesiveness is the property of clinging or sticking together in a mass.
Usually, rigid fibres have lower cohesiveness. It is generally assumed that a high degree of frictional resistance plays a part in the cohesiveness. It is the property of an individual fibre by virtue of which the fibres hold on to one another when the fibres are spun into yarn. This action is usually brought about by the high degree of frictional resistance offered by the surface of the fibres to separate one from the other.
The wool fibres, for example, have a saw-toothed surface, so that the projecting edges on its surface, called scales, easily catch on to one another when several such fibres are twisted together during spinning. On account of this, fibres offer resistance when an attempt is made to pull them apart.
Cotton fibres also possess irregular or rough surface. Further, due to the natural twist in the cotton fibre known as convolution, the fibres interlock themselves by friction when they are spun into yarns. The introduction of a crimp in synthetic fibre increases cohesion.
The fineness of a fibre is a relative measure of its thickness or diameter.
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Diameter measurement of textile fibres and yarns is not possible because of compressible nature and non-uniformity in diameter throughout its length therefore in textile fineness is expressed in terms of linear density.
If the fibre is finer there will be more number of fibres in the yarn cross section which will make more surface area available for inter-fibre friction and thus will provide more resistance to slippage. Due to this fact the yarns having the samecount, yarn spun from coarse and fine fibres, the yarn spun from finer fibres will have higher strength.
The fineness of cotton fibre is expressed in micrograms per inch i.e. micronaire. For wool fibre, fineness is given in microns and for manmade fibres, the fineness is given in denier or tex.
Resilience is the springing back or recovery of a fibre when it is released from a deformation.
The resistance to compression, flexing or torsion varies from fibre to fibre. Some fibres have a natural tendency to return to their original condition when any of the above-mentioned forces is applied, an important property where, for instance, recovery from creasing is required.
Wool is outstanding in this respect by virtue of its natural characteristics, but cellulosic fibres may be modified in such a manner so as to greatly improve these properties. This springiness of a fibre or its mass resilience is highly desirable for carpet wool. Because of resiliency fibre/yarn/fabrics hold their shape, drape gracefully and do not wrinkle.
Porosity can be defined as:
The ratio of the volume of air contained within the boundaries of the material to the total volume of a solid plus air or void, expressed as a percentage.
Porosity facilitates the absorption of moisture, liquid lubricants, dyes, oils and steam by the fibres so as to thoroughly permeate the fibre.
Porosity in fibre is important in wet processing. The natural and manmade fibres differ greatly in respect of porosity which in turn affects other properties of fibres and consequently the processing of fibres during textile manufacture. In general, natural fibres have higher porosity than synthetic fibres.
Natural lustre enhances the value of textile fibre, especially natural fibres. For example, the natural lustre of the silk gave it for a long time distinct advantage over the other textile fibres, and experiments were constantly made to improve the lustre of those fibres which were naturally dull.
Since the introduction of viscose, however, with its extremely high and almost metallic lustre, consumer taste has gone a little in the opposite direction, and many fabrics produced today are purposely delustred in order to give the desired matt finish. Therefore, it is evident that lustre, under certain conditions and for certain purposes, may enhance the value of a fibre. On the other hand, too much of brightness may be a source of aversion to the user and hence it has to be delustred to a required degree of lustre by the delustring process.
A textile fibre should withstand processing treatments and should not be easily susceptible tophysical, chemical and bacteriological attack, which may result in damage and decomposition.
The durability of clothing to average wear and tear depends somewhat more on the elasticity, flexibility and resistance of the fibre and fabric, rather than the absolute strength of either fibre or fabric. If a fabric possesses these three properties, its garment will absorb or counter more readily stresses and strains during wear. It will allow itself to be deformed with less resistance, thus reducing the chance of intermediate tearing or twisting. For these reasons wool garments owe much of their durability to the elasticity, resilience and flexibility of the fibre and fabric, even though wool is a weak fibre.
Strength combined with these properties provides excellent durability which is why nylon and polyester fibre fabrics seem to last forever. A raised fabric surface increases fabric resilience and provides longer resistance to abrasive surfaces, e.g. carpets, ribbed fabrics, etc.
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