IMPRESSION CREEP OF ABS POLYMERS

The impression creep behaviour of acrylonitrile-butadiene-styrene (ABS) polymers with various butadiene contents was investigated under punching 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 thermally activated processes. The temperature within the testing range had little effect on the activation shear strain volume, which increased with increasing butadiene content. The slope between the activation enthalpy and temperature increased gradually when the temperatures were below 353 K and then became steeper when the temperature approached the glass transition temperature. The activation enthalpy reached a maximum of 1050 kJ mol(-1) at 380 K and then decreased upon further increase in temperature. Two parallel deformation mechanisms were proposed to explain this behaviour. One is a stress activation slip process which 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.