Super toughness and reinforcement of recycled high-density polyethylene/ poly(ethylene terephthalate) composite achieved by oriented spherical crystal structure

The simultaneous toughening and reinforcement of immiscible blend system is one of the main obstacles to the additive-free physical recycling of polyethylene (PE)-based mixed waste. To address this challenge, a low-cost volume-pulsation injection molding (VPIM) method is introduced into physical recycling to construct oriented spherical crystal structure with radial skeleton that has never been reported before, achieving both super- toughness and reinforcement of multi-recycled HDPE/PET composite. Compared with those of virgin HDPE prepared by conventional injection molding (CIM), impact and yield strengths of multi-recycled HDPE/PET composite prepared by VPIM are increased by 3629 % and 48 %, respectively. According to phase, crystal, and impact-fractured surface morphologies, excellent mechanical properties of multi-recycled HDPE/PET composite under VPIM are attributed to the formation of rPET submicron-fibrils, satisfactory interfacial adhesion, and oriented spherical crystals with radial skeleton. The morphological analysis results are verified by DSC, DMA, 2DWAXD, and 2D-SAXS. The influence mechanism of VPIM is proposed to reveal that the construction of oriented spherical crystal structure with radial skeleton is derived from the radial growth of hybrid shish-kebabs with multiple shish. This study enriches the microstructure control of immiscible blend systems and paves a new avenue toward additive-free physical recycling of plastic waste.