In-Situ Grafted Ethylene Propylene Diene Monomer (EPDM) Rubber Multiblock Copolymers as Compatibilizers for Polyethylene (PE) and Isotactic Polypropylene (iPP) Blends

Abstract

Addressing the mounting issue of plastic waste, particularly the recycling of polyethylene (PE) and isotactic polypropylene (iPP), requires inventive and economically viable solutions. Employing compatibilizers for physical recycling is one of the most promising ways. This study utilizes reversible free radical reaction to facilitate the grafting reaction of ethylene propylene diene monomer (EPDM) between PE (or iPP) at the interface. Only 1wt.%-3wt.% EPDM is required for reactive blending, resulting in the formation of a graft multi-block copolymer that significantly improves the compatibility between PE and PP. This improvement notably enhances the mechanical properties, especially the elongation at break, which can reach up to 700%. Even after three processing cycles, the elongation at break of samples can still reach approximately 400%. The mechanism for reactive compatibilization has been supported by various characterization techniques, including tensile, rheology, peeling, and transmission electron microscope (TEM) tests. The mechanical properties of the samples were diminished when EPDM was replaced by the synthesized copolymer of ethylene and ethylidene norbornene (CEENB) and vinyl-terminated polyethylene (VPE). This observation confirms that EPDM located at the PE/iPP interface significantly contributes to the formation of grafted multi-block copolymers. Notably, the grafting reaction causes a negligible shift in the molecular weight peak, indicating minimal degradation and cross-linking of the polymers. The reversible free radical reaction involving sulfur and tetramethyl thiuramyl monosulfide (TMTM) reagents plays an important role in reducing side reactions.