Influence of small amounts of polyvinylchloride on the recycling of polyethyleneterephthalate

Abstract

Polyethylene terephthalate (PET), and polyvinyl chloride (PVC), are commonly encountered in plastics stream coming from separate collections of plastic bottles. The presence of PVC in the recycled PET is very dangerous because of the chain scission provoked by the hydrogen chloride evolved from the macromolecules during degradation of PVC. Recycled PET must be free of PVC; contents of PVC as little as 100 ppm can induce degradation and discoloration of the polyester. PET, in its turn, is degraded when the processing is carried out in the presence of water. In previous work, however, the degradation of PET was eliminated and rather an increase of the molecular weight has been measured when the processing was carried out under nitrogen atmosphere. In this work PVC-contaminated PET has been processed under nitrogen flow and the results indicate that a competition between degradation and regradation occurs in these processing conditions and, if the PVC content is lower than 2000 ppm, not only no macroscopic change of the molecular weight is observed, but some increase is measured that increases on decreasing the PVC content. Moreover, the measure of the torque during processing and the good reproducibility of these tests allow us to detect the amount of PVC in recycled PET samples.