Structural Studies of Hydrostatic Extrudates of High Density Polyethylene

Abstract

A study was made on the superstructure of high density polyethylene extruded hydrostatically at high temperatures. It was found that the X-ray long period for the polyethylene extrudates decreased with increasing extrusion ratio (Re). The crystalline and amorphous layer thicknesses of the extrudates with Re=4.8 and 9.0 at 90°C were studied by nitric acid etching followed by GPC measurement. It was found that the average lamellar thickness of the crystalline core in the extrudate with Re=9.0 was slightly thicker than that with Re=4.8, while the long period for Re=9.0 was smaller than that for Re=4.8. This fact indicates that both the size of the crystal blocks and the thickness of the interlamellar amorphous layer in the microfibrils decrease remarkably with the extrusion ratio, while the lamellar thickness of the crystalline core in the microfibrils increases slightly. It may be concluded that amorphous chains in the original spherulitic structure are extruded substantially into the interfibrillar region and that these chains in the interfibrillar region form highly oriented bundles.