Solid‐state coextrusion of high‐density polyethylene. I. Effects of geometric factors

Abstract

AbstractThe solid (crystalline) state coextrusion of two high‐density polyethylenes (HDPE) having weight‐average molecular weights (Mw) of 59,000 and 200,000 have been studied as a function of the geometrical arrangement and the volume fraction of the components. The extrusion rate increased nonlinearly with the volume fraction of the low‐Mw, component. The rate was faster when the low‐Mw, component was the core rather than the sheath in the initial cylindrical concentric billet. Thus the slow extrusion rate of high‐Mw HDPE alone was increased up to ten times by coextrusion with a small fraction of the low‐Mw, HDPE component in its center. Generally, the deformation flow profile changed gradually from a parabolic to a W‐shaped pattern as the volume fraction of the high‐Mw, component increased. However, the geometric arrangement of the two different Mw components also had a pronounced effect on the deformation. The deformation patterns showed that upon coextrusion the low‐ and high‐Mw HDPE's were extruded at the same rate and extrusion draw ratio. The geometrical arrangement had no substantial effects on the tensile modulus and strength of the extrudates; i.e., they increased linearly with volume fraction of the high‐Mw HDPE.