Improvement of the mechanical properties of photo-oxidized films after recycling

Mechanical recycling of post-consumer plastics gives rise, in most cases, to secondary materials with mechanical properties worse than those of the reclaimed polymer. This is mostly due to the thermomechanical treatment undergone during the melt reprocessing operations. In this work, low density polyethylene films have been photo-oxidized in artificial accelerated ageing conditions and then the brittle films have been melt reprocessed. It is shown that the secondary material, after reprocessing, shows mechanical properties, in particular elongation at break, better than those of the photo-oxidized films. This behaviour has been attributed to the fact that the melt reprocessing has the effect of homogenizing the various defects resulting from photo-oxidation. These defects are present in different concentrations varying with the distance from the outer layers of the films as a result of oxygen starvation effects. Because the heterogeneity in the distribution of these various defects is mostly responsible for the failure of the samples, reprocessing causes an improvement of the ultimate properties of the recycled material. (C) 2001 Elsevier Science Ltd. All rights reserved.