Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers

The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges associated with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepared using a grafting-through strategy by copolymerization of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (M-n = 6-28 kg/mol), graft numbers, and graft spacings were prepared. These graft copolymers were melt-blended with high-density polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 w/w), and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt % loading, with higher tensile strength observed for larger block numbers and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.