THE EFFECT OF HIGH-PRESSURE ANNEALING ON THE MOLECULAR NETWORK IN POLYETHYLENE

The changes in the molecular network of several grades of polyethylene subjected to high pressure annealing are followed using a simple mode l which combines thermal expansion and mechanical measurements. It is found that annealing reduces the degree of molecular entanglement, par ticularly when performed well within the intermediate hexagonal phase. It is shown that this process can be used to improve the drawability and hence the ultimate physical properties of high molecular weight ma terial. In low molecular weight material it is necessary to retain a s ufficiently intact network which can orient the crystallites effective ly and which prevents the material from becoming friable. Copyright (C ) 1996 Elsevier Science Ltd.