Foaming Behaviour and Compressive Properties of Microcellular Nanostructured Polystyrene

Abstract

A batch foaming process has been employed to obtain microcellular materials from polystyrene plus a SBM copolymer (polystyrene-co-1,4-polybutadiene-co-poly(methyl methacrylate). In the first part of the process, raw materials were mixed and extruded in a proportion 90:10 to obtain the precursor materials, leading to a nanostructured assembly in which SBM self-organizes in the polystyrene matrix. In a second stage, foaming was carried out by means of supercritical CO₂ in a single step-process. Foamed samples were produced using a technique based on the saturation of the polymer under scCO₂, and final properties were controlled by varying the temperature. The swelling in scCO₂ was performed at 300 bar during 16 h, and subsequently releasing the gas with a fixed depressurization rate of 60 bar/min. Temperature was varied from 30 °C to 80 °C, leading to densities from 1.0 g/cm³ to 0.5 g/cm³ and cell sizes from 2 micron to 100 micron. In this part of the work, a comparison between foaming behaviour of neat PS and a nanostructured PS+SBM blend is reported, investigating the role of the nanostructured phase as nucleating agents for microcellular foaming. Finally, low rate compression tests were carried out, analyzing the dependence of mechanical parameters such as elastic modulus, yield stress and densification strain with density.