Structure and rheology of recycled PET modified by reactive extrusion

In this work pyromellitic dianhydride (PMDA) was used as a chain extender to increase the molecular weight of polyethylene-terephthalate (PET) industrial 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 reactive extrusion. Different percentages of chain extender were used in order to investigate the effect of PMDA content on the molecular structure (average molecular weight, molecular weight distribution, branching) of PET. Rheological and thermal characterizations were performed on treated PET extruded samples. Ln particular, the increase in the dynamic viscosity at low frequencies and the high pronounced shear thinning behavior observed in the PMDA-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 values increasing the PMDA content in the PET samples. The study was performed also on bottle grade PET (IV = 0.74 dl/g) for comparison purpose. The results 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 broadening 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 processes. (C) 2000 Elsevier Science Ltd. All rights reserved.