Impact of Molecular Structure on the Ability of Commercial Polyolefins to Compatibilize High-Density Polyethylene/Isotactic Polypropylene Blends

Recycling of polyolefins is a growing concern as these materials make up approximately 50% of plastic waste. We report research that elucidates the relationship between the sequence distribution of commercially available ethylene-propylene random copolymers and an ethylene/1-olefin copolymer to their effectiveness as a compatibilizer of high-density polyethylene (HDPE)/isotactic polypropylene (iPP) blends. The compatibilization of both HDPE-rich and iPP-rich blends is examined to determine the impact of matrix composition on the ability of these compatibilizers to enhance mechanical properties of the phase separated blend. Overall, the results show that increasing the concentration of the semicrystalline ethylene content and ethylene-ethylene-ethylene triad components in the copolymer compatibilizer improved the tensile toughness of both blends. The toughness of the HDPE-rich blend was improved up to a factor of 20, while the toughness of the iPP-rich blend merely doubled in the presence of 5 wt% compatibilizer loading. These findings indicate that the compatibilization of these blends with random copolymers is entanglement-dependent; however, the presence of semicrystalline segments can greatly increase the compatibilizer efficiency. Additionally, ethylene-1-olefin copolymers appear to improve the toughness of the compatibilized blends the most  in the HDPE-rich blends, whereas the ethylene-propylene rubbers are the most effective compatibilizer in the iPP-rich blends.