Study of PP/PS Interpolymer Foam Rod Extrusion; Surface and Cell Wall Quality

Abstract

PP/PS interpolymer foam was tested in the rod extrusion process while using chemical blowing agents (CBA) and carbon dioxide physical blowing agent (PBA), respectively. Foam density decreases as blowing agent level increases. After it dips to a minimum, the foam density curve goes up. Although both CBA and PBA show the similar density curve dipping, the nature and the magnitude of change seem quite different. Gas loss induced melt fracture and plasticizing effects seem plausible in describing the dip phenomenon. In addition, SEM was taken to investigate cell wall and strut morphology, in which cell wall porosity increases as carbon dioxide increases. Cell wall opening mechanism appeared to qualitatively correlate with the secondary nucleation in carbon dioxide foaming.