35—the Ageing of Wool. Part I: Ageing at Various Temperatures

Experiments are described in which the stress-relaxation and recovery behaviour is investigated for Lincoln-wool fibres in bending as a function of the ageing time at temperatures of 20, 40, and 60°C. It is found that, at any temperature, the effect of increasing the ageing time by one decade is to shift the stress-relaxation curve by one decade to longer stress-relaxation times. Furthermore, the three sets of curves corresponding to the three temperatures are proportional to one another, although a marked decrease in stiffness occurs with increasing temperature. The recovery curves, which are independent of temperature, are successfully predicted from the stress-relaxation-moduli data by using the equations of generalized linear viscoelasticity.