The effects of polyvinyl chloride hierarchical structure on processing and properties

Abstract

AbstractThe hierarchical structures in PVC are such that the larger structures formed during polymerization are broken down to smaller structures during processing. These smaller structures have properties dependent on their microstructure. While PVC's microstructure is mostly amorphous, it contains crystallites that act as physical crosslinks connected together by tie molecules. The microstructure is extended to a larger three dimensional structure by melting during processing followed by recrystallization upon cooling. The strength of this larger three dimensional structure is interpreted from the roughness of extrudate from a zero land length die. This visual method is more sensitive for detecting large three dimensional network structure than measuring capillary entrance pressures, especially for very weak three dimensional structures. Both higher processing temperatures and higher molecular weight PVCs contribute strength to this three dimensional structure which plays a large role in determining lzod impact and stress rupture. Plasticized PVC has a structure similar to rigid PVC as judged by the roughness characteristics of its extrudate. In this case, the plasticizer is soluble in the amorphous phase leaving the crystallites intact.