Micromorphology-tensile behavior relationship in injection molded general purpose polystyrene

Abstract

Study of micromorphology-tensile behavior relationship for general purpose polystyrene is carried out by using a single-stage reciprocating screw injection molding machine. The research investigated the effects of processing conditions i.e. varying injection speed from 2.5 in/s to 3.0 in/s on the development of structural hierarchy of GPPS, by using two different mold designs; a 2-cavity and a 4-cavity mold. From the tensile bars that were produced by using different injection speeds and mold designs, tensile properties were calculated. After comparing the tensile properties of close to sprue and away from sprue in 4-cavity mold there was no significant difference in any of the tensile properties. By comparing the two mold designs it was concluded that the specimens at an injection speed of 2.5 in/s from a 2-cavity mold are stronger compared to samples produced in an asymmetric 4-cavity mold at the same injection speed. Mackerel bands are observed in all specimens which are close to sprue in 4-cavity mold but these bands are observed only at injection speed 3.0 in/s for away from sprue and 2-cavity mold. This research concludes that by using a symmetric mold at slow injection speeds, the intensity of crazes can be decreased and thus improve the tensile properties.