Rheological Behaviour of PP/PET and Modified PP/PET Blends. II. Dynamic Viscoelastic Properties

Abstract

The increasing amount of post-consumer waste leads to a search for effective recycling methods. Compatibilisation of immiscible blends of polypropylene (PP) and polyethylene terephthalate (PET) represents one such novel approach that allows recycling of significant scrap materials without any need for separation steps. The intention of this paper is to investigate the dynamic viscoelastic properties of unmodified and modified PP/PET blends. To study the effect of the matrix, three polypropylenes differing in flow properties were chosen. The compatibilisation was carried out by both one- or two-step reactive in situ techniques. In the former case, the addition of 1 wt.% of maleic anhydride, and in the latter, polypropylene supplied already modified by the producer were employed. The measurements were performed by using a rotational cone and plate rheometer at temperatures of 265 °C and 245 °C. Since PET is not melted at the lower temperature, completely different behaviour is observed in the two cases. The rheological functions generally decrease with PET content at 265 °C (conventional blend behaviour), while they increase at 245 °C, in a manner reminiscent particle-filled systems (including the yield behaviour). The positive effect of compatibilisation can be deduced not only from the results of the morphological study (dispersed phase size reduction, strengthened interfacial adhesion), but also through increased values of the viscous and elastic characteristics, which suggests enhanced interactions between the blend components. Comparing steady shear and dynamic viscoelastic properties, the extent of deformation applied during both types of measurements leading to different material responses should be considered.