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  • 2.2.5-COTTON VALUE ADDITION-STRENGTH

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  • Strength

    Chapter 2 - Cotton value addition - The impact of cotton fibre properties on textile 

     
     
    The strength of individual cotton fibres is largely determined by the fineness of the fibres, whereas the tenacity (i.e. fineness or cross section corrected strength) of cotton is largely determined genetically. Cotton fibre strength, or more correctly cotton fibre tenacity, is generallymeasured on fibre bundles, as opposed to single fibres, at either zero-gauge or 1/8" (3.2 mm) gauge, with the latter increasingly beingmeasured and accepted worldwide as a better indicator of yarn and fabric strength than the former. High volume systems provide a reasonably accurate and reliable measure of cotton fibre strength. Although cottons with good strength usually give fewer problems and neps during processing than weaker cottons, cotton fibre tenacity per se does not play such an important role in processing, except probably in rotor spinning where it can improve spinning performance, particularly when spinning fine yarns. It is important to note, however, that in absolute terms (i.e. cN), finer and less mature cottons are weaker than coarser and more mature fibres, but when strength is expressed in terms of tenacity (cN/tex or gf/tex), i.e. corrected for fibre cross section or fineness, then this effect largely disappears. Finer, and therefore weaker, fibres will be more inclined to break during processing, but when converted into yarn of a constant linear density, will produce a stronger yarn because of the greater number of fibres in the yarn cross section. It is therefore always important to make a distinction between absolute fibre strength (i.e. uncorrected for cross section or fineness) and fibre tenacity (corrected for cross section or fineness). Even in terms of spinning performance, the effect of fibre strength is small, whereas fibre tenacity is virtually linearly related to yarn and fabric strength, all other factors being constant. Fibre tenacity is particularly important for rotor spinning. At optimum yarn twist, fibre tenacity has a greater effect on yarn tenacity than any other fibre property, strength utilization being typically 50%–60% for rotor yarns and 60%–70% for ring yarns, an increase in fibre strength of 1 cN/tex increasing yarn strength by some 0.5 cN/tex or more. A bundle tenacity above 30 cN/tex (HVI level) is generally desirable.