The optical birefringence of injection-moulded polystyrene and polyethylene

Abstract

Injection-moulded plaques of polystyrene and of two types of high-density polyethylene have been produced under different moulding conditions. Microscopic examination coupled with birefringence measurements on polystyrene and polyethylene show that the plaques contain a flow-induced molecularly ordered structure together with, in the case of polyethylene, a thin (∼4µm) disordered surface layer. Thermal annealing of the polystyrene birefringence and “frozen-in” strain distribution have been measured and interpreted in terms of phenyl group reorientation and molecular rearrangement, respectively.