Injection moldings of Syndiotactic Polystyrene: effect of processing conditions on morphology

摘要

Syndiotactic Polystyrene, sPS, is a relatively newly developed material, which is gaining an increasing success from an industrial point of view, due to a range of interesting features, including an outstanding dimensional stability, a considerable resistance to water and a high melting temperature. In this work, a sPS (Dow, Questra QA101) was injection molded in a simple rectangular cavity and the effect of holding pressure and mold temperature was explored. Morphology distribution in molded samples was analyzed by several techniques, including optical microscopy, IR spectroscopy, X-Rays diffraction. Results show a distribution along thickness direction of transparent layers (which both IR and X-Rays revealed to be amorphous) and white, opaque layers (crystalline). Molding tests were analyzed by a software code developed at University of Salerno. Simulations pointed out the effect of thermomechanical history on material crystallization kinetics. In particular, the effects of pressure and flow fields on final morphology were clearly revealed by the analysis of software results. In particular, material crystallization kinetics resulted to be inhibited by high pressures and enhanced by strong flow fields. An independent material characterization, based on solidifications under high pressure and different cooling rates, confirmed that the effect of an increasing pressure during cooling is toward a reduction of final crystallinity degree.