106—EFFECTS OF FIBRE DIAMETER AND CRIMP ON PROPERTIES OF WOOL FABRICS AND OTHER FIBRE ASSEMBLIES: PART II. PROPERTIES OF TOP, ROVING, YARN, AND FABRIC

The wools described in Part I were processed on the French-worsted system, and the yarns were woven into fabric. The specifications of the original experimental design1 were met reasonably well at the greasy-wool stage. As a result of fibre breakage during processing, however, crimp and length became confounded in terms of the original design. In the context of this study, this means that, effectively, only the consequences of variations in fibre diameter and crimp may be ascertained, with the effects of fibre length assumed to be negligible. The uncrimping behaviour of the 6 wools, as estimated from single-fibre load-extension curves, has been found to agree well with the level of crimp in the greasy-wool staples. The usual inverse relationship between uncrimping stress and Young's modulus obtains, and the stresses at 20% extension for the fibres from all 6 wools are statistically indistinguishable. The fibres from the high-crimp wools, however, exhibit lower breaking stresses, breaking extensions, and breaking energies. With top and roving, fibre crimp appears to be the most important factor in explaining the behaviour of the fibre assemblies. The largest elastic moduli and breaking stresses are shown by the three high-crimp wools; the lowest values for these properties are generally exhibited by the two low-crimp wools; and intermediate values by the one wool of intermediate crimp. The mechanical behaviour of yarn reflects the behaviour of the constituent fibres beyond the uncrimping region of the fibre load-extension curve. Crimp enters the picture indirectly, since fibres of higher crimp have lower elastic moduli and breaking stresses and extensions. Correspondingly, the yarns made from these fibres show the same lower mechanical properties. Both fibre diameter and crimp enter the picture when the bulk-compression properties of the yarns are considered, and the highest yarn specific volumes are generally associated with the two high-diameter, high-crimp wools. Diameter and crimp often appear to be of relatively equal importance in their relationship to fabric properties. The crease-recoveries (65% r.h.) of the six wools in fabric form are high and statistically indistinguishable from one another. Finished fabrics exhibit greater crease-recovery than R.T.D. (ready-to-dye) fabrics, and wetting-out lowers the crease-recovery. To a limited extent, extension-cycling tests carried out on the fabrics yield results in some accord with the crease-recovery tests in that the finished fabrics have greater elasticities, the largest elasticities being generally those of the three high-crimp wools, although the one wool of high diameter and low, crimp had large elasticity in the finished fabric. On the basis of earlier studies, it would be expected that this same wool would show the largest fabric flexural rigidity, and this has been found to be the case. Similarly, the smallest fabric flexural rigidity is exhibited by the one wool of low diameter and high crimp. The breaking properties of the fabrics are similar to those of the constituent yarns and fibres : the weaker fabrics are generally those prepared from the high-crimp wools.