The Effects of Foaming and Annealing on Mechanical Properties and DSC Scans of Gas Saturated and Non-gas Saturated High Impact Polystyrene

Abstract

A series of high impact polystyrene (HIPS) specimens was prepared under different processing conditions to study the effects of CO₂ sorption and annealing conditions on thermal response and mechanical properties of gasified and/or foamed materials. The process variables included gas-saturation, non gas-saturation, foaming temperature and annealing temperature. In this study, samples were first saturated with CO₂, foamed if necessary then desorbed, and finally followed by sub-Tg annealing. The thermal response and mechanical properties followed the opposite trend of materials which were first sub-Tg annealed then exposed to CO₂ performed by previous workers. This suggests that gas sorption and annealing produce opposite effects. Gas sorption followed by annealing may annul a portion of the gas sorption effect, and vice versa. The glass transition temperature is an important factor that affects the trend of the results of mechanical properties in the foamed then annealed materials.