Structural Studies of Hydrostatically Extruded Polypropylene

Abstract

A study was made on the X-ray long period and melting behavior of isotactic polypropylene extrudates with smooth surfaces. The extrusion was effected hydrostatically in the range of extrusion ratio Re from 2.0 to 6.5 at temperatures of 90—150°C. It was found that the long period of the extrudates increased with increasing temperature and also at higher extrusion ratios. The crystalline and amorphous layer thicknesses of the products extruded with Re=5.2 and 6.5 at 150°C were studied by nitric acid etching followed by a GPC measurement. We found that the extrudate for Re=6.5 had a larger average crystal thickness with narrower crystal size distribution than the extrudate for Re=5.2, but the ratio in thickness of amorphous to crystalline layers was almost the same for the two extrudates. Thickening of crystalline and amorphous layers at high extrusion ratios suggest that heat is generated in the sample near the die during hydrostatic extrusion and influences strongly the fine structure of the extrudates at high extrusion ratio and high temperature.