Foaming of an Immiscible Blend System Using Organic Liquids as Blowing Agents

Abstract

Foaming of blend systems is a promising approach to develop cellular materials with a set of desired properties. However, foaming of blend systems is not only a chance but also a challenge, as different polymers have to be foamed at the same foaming conditions. The best conditions during foaming are individual to each polymer and influence the obtained cellular structure. In immiscible polymer blends like poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) the differences in glass-transition temperature (Tg) and viscosity are vast and can inhibit the foaming of the blend system. In order to minimize the above-mentioned difference in Tg and viscosity, one approach is to choose a blowing agent, which shows a selective solubility in one polymer phase, working as a selective plasticizer. The aim of the present study is to evaluate systematically the foaming behavior of immiscible PPE/SAN blend systems using ethanol and n-pentane as blowing agents. Mass uptake of ethanol and n-pentane in the PPE/SAN-blends as function of the blend composition is measured, offering a selective solubility of ethanol in SAN, while n-pentane shows a high affinity to PPE. The plasticizing effect on the blend phases PPE and SAN is theoretically estimated using the Chow-equation and the WLF-equation. After foaming the blowing agent saturated blend samples in an oil-bath at different temperatures, the density reduction and the cellular structures are analyzed and correlated to the blend morphology, the blowing agent solubility in the blend phase, the rheological properties and the glass transition temperature of the nonsaturated and saturated blend phases.