Structure and rheology of recycled PET modified by reactive extrusion

In this work pyromellitic dianhydride (PMDA) was used as a chain extender t o increase the molecular weight of polyethylene-terephthalate (PET) industr ial scraps with low intrinsic viscosity (IV = 0.48 dl/g), coming from a PET processing plant. The reaction was performed in a single step through reac tive extrusion. Different percentages of chain extender were used in order to investigate the effect of PMDA content on the molecular structure (avera ge molecular weight, molecular weight distribution, branching) of PET. Rheo logical and thermal characterizations were performed on treated PET extrude d samples. Ln particular, the increase in the dynamic viscosity at low freq uencies and the high pronounced shear thinning behavior observed in the PMD A-treated PET samples were correlated to the broadening of the M-w/M-n and to the long chain branching. These structural changes are also responsible for the decrease in the T-mc and Delta H-mc and the increase in the T-cc va lues increasing the PMDA content in the PET samples. The study was performe d also on bottle grade PET (IV = 0.74 dl/g) for comparison purpose. The res ults have pointed out that with an amount of PMDA included between 0.50 and 0.75% the chain extending reaction produces an increase of M-w, a broadeni ng of M-w/M-n and branching phenomena, that modify the PET scraps in order to make the recycled polymer suitable for film blowing and blow molding pro cesses. (C) 2000 Elsevier Science Ltd. All rights reserved.