Surface Quenching Induced Microstructure Transformations in Extrusion Foaming of Porous Sheets

Abstract

Abstract In this article, a new technology is described to manufacture open cell thermoplastic foamed sheets with the aid of surface-quenching phenomenon during an extrusion process. As the gas laden polymer extrudate exits the slit die, its surface is rapidly quenched which results in freezing of cells on the surface, while the cells at the core continue to grow and leads to development of open-cellular microstructure at the core. Influence of chill roll temperature was found to be extremely significant in developing porous morphological attributes. Subsequently, synergistic effect of physical blowing agent (N2) content and chill roll temperature was examined for their expansion ratio and foam thickness. Fascinatingly, with reduced chill roll temperatures open-cell microstructure and high expansion ratio was obtained although its thickness was observed to decrease. Further, influence of chill roll rotating speed on foam microstructure and expansion ratio was studied. Lower chill roll rotational speed resulted in development of open-cellular microstructure; while at higher speeds, closed cell morphology was obtained. The results coherently demonstrate that by controlling the chill roll temperatures; open-cellular microstructure can be developed in sheet extrusion foaming process.