IMPRESSION CREEP OF ABS POLYMERS

The impression creep behaviour of acrylonitrile-butadiene-styrene (ABS ) polymers with various butadiene contents was investigated under punc hing stresses of 10-120 MPa and at temperatures from 330 to 390 K (T-g = 376 K). It was found that the creep resistance of the ABS polymers decreased with increasing butadiene content. The impression velocities in the steady-state region were analysed using a theory involving the rmally activated processes. The temperature within the testing range h ad little effect on the activation shear strain volume, which increase d with increasing butadiene content. The slope between the activation enthalpy and temperature increased gradually when the temperatures wer e below 353 K and then became steeper when the temperature approached the glass transition temperature. The activation enthalpy reached a ma ximum of 1050 kJ mol(-1) at 380 K and then decreased upon further incr ease in temperature. Two parallel deformation mechanisms were proposed to explain this behaviour. One is a stress activation slip process wh ich dominates at temperatures below the glass transition temperature, and the other is a free volume assisted shear process which dominates at temperatures higher than the glass transition temperature.