Longitudinal variation in the stress–strain properties of wool fibers

In order to obtain information on possible end-to-end differences in the physical properties of wool caused by weathering of the more exposed portions, a comparison has been made of the stress–strain characteristics of the tip and root halves of fibers taken from the midback region of sheep reared outdoors over a 6-month summer to winter period. The results were further compared with the tip and root halves of fibers taken from animals reared indoors under conditions of essentially continuous darkness. When 11 features of the stress–strain curves were compared, it was found that for the outdoor wools the tip halves had lower initial moduli, higher yield strains, and lower yield moduli than the root halves. In contrast, the dark grown wools showed no end-to-end differences. The greater ease of extension of the tip halves of outdoor wools may be attributed to light-induced diminution in the levels of crosslinking within the keratin structure. The results show that normal environmental influences caused end-to-end differences and that longitudinal variations in physical properties may be a typical characteristic of all field grown wools at the time of harvesting.