30—The Torsional Rigidity of Textile Fibres

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Abstract
The initial resistance to twisting, or torsional rigidity, of single fibres from thirty-four samples has been measured by the torsion pendulum method, with period of oscillation from 4 to 9 seconds and twist less than half a turn per cm. Using preliminary experiments on the influence of tension, damping and period of oscillation on the rigidity values as a basis, four sets of inertia bars were designed and used to cover the range of fineness and rigidity commonly met in textile fibres. The values of rigidity modulus at 65 per cent r.h. and 20°C range from 41 × 1010 dyn/cm2 for glass fibres to 0·05 × 1010 dyn/cm2 for polythene fibres. Relatively high moduli (2 to 3 × 1010 dyn/cm2) are possessed by kapok, cotton, calcium alginate fibre and silk; intermediate values (0·9 to 1·6 × 1010 dyn/cm2) are given by flax, ramie, viscose and cuprammonium rayon, wool, regenerated protein fibres, polyester fibres and those based on vinyl chloride, vinyl cyanide and vinyl alcohol; relatively low moduli (0·3 to 0·8 × 1010 dyn/cm2) are shown by cellulose acetate fibres, polyamide fibres, and polyvinylidene chloride-based fibre. The anisotropy as measured by the ratio of Young's modulus to rigidity modulus is discussed. The estimation of shape factors, that is, the ratio of the torsional rigidity of a fibre of a given cross-sectional shape to that of a similar fibre of circular cross-section, is dealt with in an appendix.

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