Anisotropic degradation of polymeric composites: From neat resin to composite

The degradation of polymer matrix composites was investigated through weight loss measurements. A methodology originally developed based on the shrinking core model was extended to account for matrix orientation, lay‐up sequence, and differences in neat resin and composite degradation. This methodology was derived based on mass transfer and kinetic considerations taking into account the inherent anisotropy and heterogeneity of polymer composites. The model systems used were a bismaleimide (X5260) and a condensation polyimide (Avimid N). Bismaleimide composites were aged at 250, 260, and 270°C in air, whereas both neat resin and composite Avimid N samples were aged at 371°C. Based on the experimentally observed time exponents, the degradation was modeled as diffusion and reaction controlled. The weight losses of both unidirectional and quasi‐isotropic samples were successfully predicted. In addition, correlation between the degradation of neat resin and composite samples was established for the Avimid N system. Finally, this methodology can be used in scaling up weight loss data, providing an important tool in evaluating materials for long‐term use at elevated temperatures.