Extrusion of Polyethylene in Solid State under High Pressure

Abstract

Extrusion of high density polyethylene (PE) in solid state was carried out successfully with a cylinder-and-ram type device at the temperatures from 70°C up to 110°C, which corresponded with the temperatures of the region of viscoelastic crystalline dispersion. Large plastic deformation proceeded smoothly, and the cross sectional area of the extrudate was 1/16 of the original. The factor of 16 can not be realized by ordinary cold or hot drawing process of PE in solid state. Polymer crystals in the extrudate and also in the sample chips in the die hole were highly oriented. The crystal c-axis are in parallel with the extrusion in its direction. The degree of orientation was uniform in the cross section, suggesting that the movement of the solid polymer in the die hole was almost at the same velocity at the center of the hole as at the wall side.The dimensional stability of the extrudate against temperature change was remarkably high compared with the ordinary drawn PE. The extrudate did not shrink below 100°C, whereas the ordinary drawn sample highly shrank at 60°C. Another feature of the extrudates was its being highly transparent in appearance.