Competition between degradation and chain extension during processing of reclaimed poly(ethylene terephthalate)

During processing of poly(ethylene terephthalate) (PET) hydrolytic chain scission, induced by the presence of small amounts of water, is the main cause of degradation. During repeated reprocessing chain scission can also occur because of the presence of other polymeric contaminants like PVC. In order to avoid or to limit hydrolytic chain cleavage adequate drying of PET before melt processing is necessary. Of course this practice is even more recommended when repeated processing steps are used, as for PET recycling. The behavior of recycling PET obtained from post-consumer water bottles when treated in a melt mixer under different conditions has been investigated in order to better understand the processing conditions that can reduce or avoid the hydrolytic chain scission. During processing both degradation (chain scission) and chain extension occur. When the processing is carried out under a nitrogen atmosphere the latter mechanism prevails leading to a polymer having larger molecular weight. (C) 1998 Elsevier Science Limited. All rights reserved.