Stress relaxation of a polycarbonate blend after hygrothermal aging

This work has studied the competing effects of physical aging and moisture absorption on the relaxation behaviour of a polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) polymer blend after being subjected to both thermal and hygrothermal aging. Physical aging was simulated by thermal aging the blend at temperatures up to 80 C-a similar to which is below the glass transition temperatures of ABS and PC in the blend, respectively. Nine different combinations of relative humidity and temperature were investigated for hygrothermal aging. In both cases, two sets of aging times were applied: "short" term (a parts per thousand currency sign16 hour aging) and "long" term (@168 hour aging). The short term tests were used to generate momentary master curves by applying time/aging-time and time/moisture superposition principles. Using the Kohlrausch-Williams-Watts (KWW) expression, the model parameters determined from curve fitting master curves were used to predict longer term stress relaxation behaviour. The predictions, verified against experimental results, showed reasonable agreement for all hygothermal exposure conditions except for full immersion. Moreover, comparisons of KWW parameters for both short and long term tests suggested that physical aging processes dominate absorbed moisture effects in terms of influencing viscoelastic behaviour, especially when the aging temperature approaches 80 C-a similar to.