Compatibilization of PP/HDPE Blends with PE--PP Graft Copolymers.

The compatibilization of polyethylene (PE) and isotactic polypropylene (PP) blends is of particular interest due to the challenges associated with recycling these plastics from mixed waste streams. Polyethylene--PP copolymers (PE--PP) were prepared using a grafting-through strategy by copolymerization of ethylene with allyl-terminated PP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths ( = 6-28 kg/mol), graft numbers, and graft spacings were prepared. These graft copolymers were melt-blended with high-density polyethylene (HDPE) and PP (PP/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 PP.