Evaluation of the relative significance of fibre diameter and fibre curvature when processing New Zealand Romcross type wool

Abstract

Research has shown a technical description of a blend for most woollen carpet applications can be met with objective measurements, namely mean fibre diameter, fibre length after carding, wool bulk, proportion of medullation, base colour and vegetable matter content. The compressional property of wool as reflected in bulk is strongly related to mean fibre diameter and mean fibre curvature. Both these measurements can now be measured simultaneously with recently developed electronic instrumentation. While the processing implications of changes in mean fibre diameter are well understood, the processing implications of changes in objectively measured mean fibre curvature have not been investigated in detail. A total of 360 New Zealand Romcross type fleeces shorn from yearling sheep, with an individual range in mean fibre diameter of 23.2–40.6 μm and an individual range in mean fibre curvature of 34–115°/mm were used. The individual fleeces were sorted to create five, similar-sized, wool-processing lines with the following specifications for mean fibre diameter and mean fibre curvature. Lot 1: low fibre diameter/high fibre curvature (30.2 μm, 72°/mm); Lot 2: high fibre diameter/high fibre curvature (33.5 μm, 70°/mm); Lot 3: medium fibre diameter/medium fibre curvature (32.1 μm, 64°/mm); Lot 4: low fibre diameter/low fibre curvature (31.1 μm, 58°/mm); and Lot 5: high fibre diameter/low fibre curvature (34.5 μm, 51°/mm). Each processing lot was scoured, combed to reduce the proportion of short fibre within each lot and spun into yarn on the semi-worsted system. Mean spindle speed at break (50 fibres in cross-section) and yarn breaking load were greatest for Lot 4 and lowest for Lot 2. Increasing fibre diameter and increasing fibre curvature resulted in less unevenness within the yarn and a decrease in neps. Coarse highly crimped fibre produced the bulkiest yarn while the finer straighter fibre produced the lowest bulk yarn. Potential wearability of knitted garments using yarn spun from each processing lot was assessed using standard knitted squares. Increasing fibre diameter and increasing fibre curvature resulted in greater relaxation shrinkage in length, while decreasing fibre diameter and increasing fibre curvature resulted in increased extensibility in width. Overall resistance to felting shrinkage increased as crimp and diameter increased. There was no difference in pilling between the processing lots. The presented results indicate that increasing fibre curvature in Romcross type sheep as may occur through selection or crossbreeding associated with improving lamb production, will have a beneficial effect on the performance of products made from their wool.