Stress relaxation in nylon and terylene: Influence of strain, temperature, and humidity

Stress relaxation data are presented for nylon 66 and Terylene yarns held at constant extensions from ½% to 15% for dry, 65% R.H. and wet conditions all at 25°C. and in the dry condition at 25, 50, and 75°C. A single composite relaxation curve fitted the data for Terylene at all strains at 25°C. A theory of stress relaxation gives a good fit for the experimental results of dry nylon at all temperatures between 25°C. and 75°C. In moist nylon, there are two relaxation processes superimposed on each other, one due to thermal agitation and the other due to absorption of extra moisture as the fiber is stretched. It is shown that the relaxation caused by the extra moisture absorbed is consistent with the change in moisture regain with strain at constant humidity calculated thermodynamically.