CHANGE OF MORPHOLOGY IN HIGH-MOLECULAR-WEIGHT POLYETHYLENE DURING DIEDRAWING

Deformed high molecular weight polyethylene (HMWPE) rod, produced by d ie drawing at 115-degrees-C, was cleaved longitudinally at liquid nitr ogen temperature and the cleaved surface was etched using a permangani c etching technique. A series of etched surfaces of HMWPE sections wit h different draw ratios (from 1 to 13) were analyzed employing scannin g electron microscopy (SEM). The change of crystalline structure in HM WPE during die drawing was observed. In undrawn HMWPE, the spherulites were made up of sheaflike lamellae and scattered within the amorphous phase. During die drawing in the first instance, the microscopically inhomogeneous deformation occurred and the spherulites aligned along t he drawing direction. At a draw ratio of about 7, local melting occurr ed, the spherulites disintegrated, and the sheaflike lamellae oriented , followed by strain-induced recrystallization and the growth of the l amellae. Finally, at a draw ratio of about 12, the plastic deformation of the lamellae occurred and microfibrils were formed.