Plastic Deformation of High Density Polyethylene in Solid State Extrusion

Abstract

An equation describing the process of solid state extrusion of high density polyethylene through a conical die with a taper of 20° was obtained by extending Sachs' equation to apply for polymeric materials which show considerable strain hardening. It was used to estimate the extruding pressure on the basis of the tensile data of the polymer. The agreement between observed and calculated values was satisfactory. Extruded polymers obtained at relatively low extrusion temperature, as low as 80°C, showed elastic after-effects, such as shrinkage at elevated temperatures. However, those extruded at relatively high temperatures, as high as 100°–120°C, showed extraordinary stability in their dimensions even at the temperatures as high as 120°C. Discussions on the basis of the slip line analysis were also made to interpret the discrepancies found between the calculated and observed results when the entrance angle of the die was increased.