Interfacial activity of hydrogenated polybutadiene block copolymers with HDPE and iPP

Blending poly(ethylene) and poly(propylene) is an attractive recycling strategy. However, phase separation and poor interfacial strength result in inferior mechanical integrity. Several EX and EXE diblock and triblock copolymers were blended at 1 to 5 wt.% in mixtures of commercial HDPE and iPP, where X denotes an iPP melt-miscible poly(ethylene-ran-ethylethylene) random copolymer and E represents hydrogenated 1,4-poly(butadiene). Micelle formation in the homopolymers, and morphology in HDPE/iPP blends, was probed using atomic force microscopy. Localization of high molecular weight EXE at domain interfaces resulted in exceptional blend ductility, while lower molecular weight EXE, and all EX diblocks, produced mechanically inferior plastics. The associated interfacial adhesion was measured directly using PE/EX/iPP and PE/EXE/iPP trilayer peel tests, and the results correlated closely with the blend tensile toughness. These findings support an interfacial strengthening mechanism that combines co-crystallization of HDPE and the E blocks, thereby anchoring the amorphous X blocks, which are topologically entrained with semicrystalline iPP.