Influence of processing parameters and composition on the effective compatibilization of polypropylene–poly(ethylene terephthalate) blends

The effects of the addition of different functionalized compatibilizers on toughness, morphology and rheological properties of a polypropylene (PP) – poly(ethylene terephthalate) (PET) (85–15 wt%) blend were studied. The three compatibilizers compared were: (Styrene Ethylene Butylene Styrene)-grafted-(glycidyl methacrylate); (Styrene Ethylene Butylene Styrene) – grafted – (maleic anhydryde); (polyolefin) – grafted – (glycidyl methacrylate), abbreviated to: SEBS-g-GMA, SEBS-g-MA and POE-g-GMA respectively. The effective grafting content was the same for all three compatibilizers. Before the comparison of the different compatibilizers was done, first the effects of three different processing temperatures and three different compatibilizer contents were investigated, based on the addition of SEBS-g-GMA. The compatibilization effect was significantly improved with an increase in processing temperature from 250 to 300 °C. The toughness was increased with almost a factor two and a decrease in the average domain size of the dispersed phase was observed. An increase in compatibilizer content from 0.25 to 2.5 wt% resulted in a finer dispersity as well as in a steep increase in toughness, which was noted to approach the brittle-to-ductile transition. The comparison of the three compatibilizers was subsequently done at the most promising processing temperature and content: 300 °C and 2.5 wt%. The results showed that the addition of SEBS-g-MA and POE-g-GMA had a less significant positive effect on the compatibilization compared to SEBS-g-GMA. The difference is attributed to a higher reactivity for GMA compared to MA and a higher possibility for migration towards the PP-PET interface for the SEBS chain compared to the POE chain.