Moisture uptake of a polycarbonate blend exposed to hygrothermal aging

As an extension of an earlier study on aging of a polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend, this paper has explored the roles of two competing phenomena, physical aging and moisture diffusion, during hygrothermal aging. Moisture absorption experiments at four different relative humidity conditions were compared with full immersion condition. Uptake curves show two different diffusion behaviour including Fickian moisture absorption and anomalous peak overshoot. The equilibrium moisture uptake in the polymer system, the coefficient of diffusion of moisture and the dual glass transitions were characterized. In general, the uptake behaviour could be explained using free volume expansion and contraction concepts that are associated with diffusion and structural recovery theories, respectively. However, using statistical methods, it was found that the relationship between the effects of aging temperature and relative humidity is both complex and interactive, with either diffusion or relaxation processes dominating depending on the extent of hygrothermal exposure.