Rheological characterisation of recycled poly(ethylene terephthalate) modified by reactive extrusion

Recycled poly(ethylene terephthalate) (R-PET) has poor melt strength and viscosity. Hence, the use of R-PET in blow moulding applications, where high melt strength is required, is limited. In this study reactive extrusion of post-consumer R-PET with a low molecular weight modifier: pyromellitic dianhydradide (PMDA) has been used as a way of improving the rheological properties of R-PET. Rheological characterisation of the reactive extruded R-PET (RER-PET) was performed by means of a parallel plate rheometer. The unmodified R-PET and virgin PET were also tested for comparison purposes. The RER-PET samples exhibited higher complex viscosity and higher storage modulus compared to unmodified R-PET sample. Increase in complex viscosity and storage modulus became more pronounced as the percentage of PMDA in R-PET was increased. At high PMDA concentrations, the modified Cole–Cole plots demonstrated a shift towards higher storage modulus values at a given loss modulus value. Viscoelastic properties observed were related to the molecular structure of modified samples. Rheology studies confirmed the increase in molecular weight of post consumer R-PET with an increase of PMDA concentration, and the formation of branching at concentration above 0.25 wt.% PMDA.