RECYCLING OF HIGH-DENSITY POLYETHYLENE CONTAINERS

The recycling of homogeneous high density polyethylene from containers for liquids gives rise to materials having mechanical properties that are strongly dependent on the reprocessing apparatus and the processi ng conditions. The thermomechanical degradation during processing give s rise to different modifications of the structure depending on the te mperature, residence time and applied stress. In general, it is possib le to say that if the reprocessing operations are carried out in appar atus with low residence time, the mechanical and rheological propertie s of the raw materials are only slightly influenced by the recycling o perations. Significant degradation phenomena and reduction of some mec hanical properties are observed on increasing the number of recycling steps in apparatus with large residence times. By adding antioxidant a gents the polymer maintains the initial properties even after several recycling cycles. The competition between formation of chain branching and chain scission can be considered to be responsible for this behav iour. (C) 1997 Elsevier Science Limited.