From the perspective of cells as dispersed phase in foam injection molding: Cell deformation of PP/PTFE foams

Abstract

The objective of the present work was to study deformation of cells of polypropylene/polytetrafluoroethylene (PP/PTFE) composite foams prepared via foam injection molding (FIM) with supercritical nitrogen (N2) as foaming agent. Different contents of N2 and various contents of PTFE were applied as variables to study the cell deformation in the flow direction. Scanning electronic microscope (SEM) was used to study the cell structure. It is found that the increase in both contents of N2 and PTFE were favourable for deformation of the cells. With the increase in both the contents of N2 and PTFE, the cell density increased, the cell size in short axis decreased, and the change in cell size in long axis depended on the cell structure being upon deformation or not. The deformation of the cells was signified by an abrupt increase of cell size in long axis and the ratio of cell size in long axis to short axis being larger than one. It is then found that the cell deformation in this study occurred unexpectedly with the increase in cell density. This is attributed to the fact that the increase in either N2 or PTFE content increases both the cell density and the tendency of cell deformation. This study has brought a new perspective to study the cell deformation in FIM via regarding cells as dispersed phase, and will provide experimental support for preparation of foams with oriented cells in the future.