Effect of inclusions and blending on the mechanical performance of recycled multilayer PP/PET/SiOx films

Extending the useful life of materials through recycling has proven to be a n efficient means of reducing natural resource use and limiting the product ion of waste. In the case of polymer-based materials, in general, and of pa ckaging materials, in particular, material recovery is complicated by the p resence of incompatible polymers, as well as a priori undesirable contamina nts such as inorganic inclusions. This article investigated the recycling o f multilayer packaging material systems, based on polypropylene and silicon oxide-coated poly(ethylene terephthalate). In particular, the effect of a compatibilization of the blend using maleic anhydride-grafted polypropylene on the mechanical properties of the recycled material was examined. Withou t a compatibilizer, and at low compatibilizer concentrations, the blend exh ibits a coarse morphology and is brittle. At a concentration of 5% wt of th e compatibilizer, a fine morphology is obtained, and the blend shows excell ent ductility. Beyond this concentration, a brittle interphase forms betwee n the blend constituents, with a corresponding decrease in ductility. These results were confirmed by a study of strain-induced crystallization in the blend. Furthermore, the size of the SiOx inclusions, resulting from the fr agmentation of the oxide coating during reprocessing, had no detectable inf luence on the mechanical properties of the recycled blend, providing that t heir concentration is lower than 2 x 10(-3). This study showed that a contr ol of both the microstructure and interface properties considerably improve s the mechanical properties of the recycled material, leading to high added -value applications. (C) 2000 John Wiley & Sons, Inc.