Orientation and residual stress distributions in injection molded engineering plastics

A summary is presented of findings on the microstructure and the mechanical properties of the injection moldings of two engineering plastics i.e., a poly(phenylene ether) and a poly(ether imide). The initial impetus for selecting these two resins as the materials of study was the observation that injection moldings of unmodified poly(phenylene ether) had an affinity to develop cracks while those of poly(ether imide) did not. Both resins exhibited high birefringence and high compressive residual stress values at or close to the surface of their moldings. The stress optical coefficients of PEI were found to be greater both above and below the glass transition temperature than those of PPE. Thus, although the birefringence levels are close, the results suggested greater degrees of orientation for PPE specimens, collaborated by our earlier melt rheology and simulation studies with these two resins.