MORPHOLOGY OF NASCENT ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE REACTOR POWDER - CHAIN-EXTENDED VERSUS CHAIN-FOLDED CRYSTALS

The morphology of nascent ultra-high molecular weight polyethylene (UHMW-PE) reactor powders was investigated, stimulated by new developments concerning the high degree of drawability of low-temperature compacted films of these powders. Usually these nascent reactor powders possess relatively high melting temperatures (138-143-degrees-C), generally attributed to the presence of (more or less) chain-extended crystals. This study however, shows that the commonly accepted relationship between a high melting temperature and the presence of chain-extended crystals cannot be generalized in the case of UHMW-PE powders. Based upon thermal analysis (differential scanning calorimetry), electron microscopy, wide-angle X-ray scattering and electron beam irradiation, it was concluded that the high melting temperatures could be related to a fast reorganization process during dynamic heating.