Wool fibre tenacity and its relationship to staple strength

Abstract

Wool fibre tenacity and its relationship to staple strength was studied in a pen-feeding trial of 40 New Zealand Romney ewes. A method for estimating fibre tenacity is described based on normalizing fibre breaking load by cross-sectional area measured on fibre fracture-surfaces. The validity of this protocol was demonstrated by showing that (i) fibre diameter measured at the point of rupture was not significantly (P > 0.05) changed by breaking, and (ii) that the tenacity estimate was not significantly (P > 0.05) correlated with cross-sectional area variation along fibres, and (iii) showed lower fibre-to-fibre variation than other accepted measures of intrinsic material strength. The majority (83.5%) of the 1200 fibres broken in this study cleaved in smooth-planed fractures normal to the long axis of the fibre, the remaining fibres demonstrated axial-splitting following rupture. Tenacity did not differ significantly between the two break-types (P > 0.05). Tenacity demonstrated small negative correlations (P < 0.05) with fibre cross-sectional area and ellipticity. No change in tenacity (P > 0.05) occurred within fine, slow-growing 'wool-break' regions and tenacity did not vary significantly (P < 0.05) between body sites on sheep. Tenacity showed no significant variation (P > 0.05) with differential winter feeding, but significant variations (P < 0.01) of wool tenacity occurred between sheep. The sheepto-sheep differences in tenacity showed significant relationships with two indices of staple strength, work (P < 0.01) and peak-force (P < 0.01). Variability in fibre tenacity between sheep and its relationship to staple strength may provide some explanation of the origin of 'tender' and 'sound' wools.