The Craze Growth Response in Stress Relaxation Conditions for a Styrene-Acrylonitrile Copolymer during Physical Aging

Abstract

Craze growth in a styrene-acrylonitrile copolymer (SAN) wasstudied as a function of time after a quench (physical aging) at fourdifferent temperatures between 22 and 60°C. Thecraze growth experiments were performed in stress relaxation conditions.The craze length was found to grow linearly on a logarithmic loadingtime scale. A transition in the logarithmic growth rate was found tooccur on the logarithmic aging time scale. The transition was observedas a change in rate from high to approximately five times slower andoccurred over a relatively narrow range of aging times. The growth ratein the slow growth regime was relatively insensitive to temperature forall four temperatures studied. The transition was found to move toshorter aging times as temperature increases. Although the craze lengthbetween crazes in a sample could differ to a large extent, the growthrates themselves, were found to vary only within a±20% band.