FAILURE AND DEFORMATION STUDIES OF SYNDIOTACTIC POLYSTYRENE

Syndiotactic polystyrene (sPS) is a chemically resistant, high-heat, s emicrystalline polymer which is currently under development by The Dow Chemical Co. The research reported herein was undertaken to determine the critical fracture strength, i.e., the critical stress intensity f actor, K-1C, and the fracture energy, Glc, of sPS. The studies were ai med at developing a basic understanding of the failure mechanism and t oughness of sPS. This work included investigations of the effect of mo lecular weight, as well as flow-induced anisotropy. Scanning electron microscopy (SEM) was used to aid in the determination of the failure m echanism. During failure testing, it was observed that sPS fails with a slow, controlled crack growth and ruptures with an almost nondetecta ble amount of yielding, as based on a tensile dilatometry investigatio n and a plane strain, biaxial yield experiment. The proposed failure m echanism, based on the scanning electron micrographs, is one of constr ained crazing, followed by void coalescence with the spherulite nuclea tors acting as stress concentrators in the system. The damage appears to be greatly confined, with little initial cold-drawing of the spheru lites. Addition of a nucleator reduces the K-1C values somewhat, as ad ded nucleation sites proliferate the sites for stress concentration ac ross the sample. (C) 1997 John Wiley & Sons, Inc.