Study of thermal and mechanical properties of virgin and recycled poly(ethylene terephthalate) before and after injection molding

In this study, we compared the thermal properties (glass transition, melting point and crystallinity) and mechanical properties (Young’s modulus, elongation at break and impact strength) of post-consumer poly(ethylene terephthalate) (PET) bottles with those of the virgin resin. We studied two types of scraps of recycled PET: one arising from homogeneous deposits of bottles and the other of heterogeneous deposits soiled by contaminants such as PVC and adhesives. The presence of contaminants and residual moisture coming in the shape of scraps facilitate the crystallization of recycled PET compared to virgin PET and induces cleavages of chains during the melt processing. This leads to a reduction in intrinsic viscosity and consequently in molecular weight, and these decreases are more significant when the recycled resin is soiled. Virgin PET exhibited a ductile behavior (>200% of elongation at break),whereas post-consumer PET bottles exhibited a brittle one (<10% of elongation at break). This is a consequence of the difference in crystallinity, the presence of impurities in the recycled PET and the different thermal and mechanical history of the virgin and recycled materials.