Warm hydrostatic extrusion of polyethylene

Hydrostatic extrusion of high density polyethylene at an extrusion ratio of 15:1 was investigated in the temperature range between 100 and 134°C. A thin‐walled tube was extruded having a tensile strength of 370 MPa and a tensile modulus of 10 GPa. The extrusion rate was limited by severe extrudate distortion which occurs at a limiting shear stress under stick‐slip conditions. Even during steady extrusion wall slip was evident. At a constant extrusion speed, the extrusion pressure was found to be very sensitive to the extrusion temperature. An increase from 120 to 125°C reduced the extrusion pressure by half. Various thermal pretreatments of the starting billets were found to have little effect on the extrusion behavior and physical properties of the extrudate.