Solid State Coextrusion of High Density Polyethylene. I. Effects of Geometric Factors.

摘要

The effects of geometry and volume fraction on the solid (crystalline) state coextrusion of two concentric different high density polyethylenes (HDPE) having weight average molecular weights (Mw) 59,000 and 200,000 have been studied. 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 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 the middle of the high Mw HDPE billet. Generally, the deformation flow profile changed gradually from a parabolic to a W shape pattern as the volume fraction of the high Mw component increased. However, the geometric arrangement of the two different Mw components in the initial billet had also a pronounced effect on 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. Geometry 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. (Author)