Simultaneously achieving super toughness and reinforcement of immiscible high-density polyethylene/poly(ethylene terephthalate) composite via oriented spherical crystal structure

Simultaneous toughening and reinforcing of immiscible blend system is one of the main obstacles to mechanical recycling of polyethylene (PE)-based mixed waste. To address the challenge, this study proposed a low-cost processing strategy combining volume-pulsatile injection molding (VPIM) and thermal annealing to prepare microfibrillar composite, which constructs and optimizes oriented spherical crystal structure that has never been reported before. Under the synergistic effect of VPIM and annealing, both self-toughening and self-reinforcing of immiscible HDPE/PET composite are realized simply and cost-effectively. The impact strength, yield strength, and tensile modulus of VPIM-An samples are increased by 3220%, 32%, and 39.73%, respectively, compared with those of CIM samples. According to phase and crystal morphologies, PET submicron-fibrils, satisfactory interfacial adhesion, oriented spherical crystals with aligned thick lamellae inside, and interlinked microstructure are responsible for the remarkable enhancement in mechanical properties. These analysis results are supported by the evidence from DSC, DMA, impact-fractured surface morphology, 2D-WAXD, and 2D-SAXS. The synergistic effect mechanism of VPIM and annealing is proposed to uncover that oriented spherical crystal structure is composed of hybrid shish-kebabs with multiple shish and is endowed with interlinked characteristics. This paper enriches the structure control of immiscible polymer blends and paves a new avenue toward additive-free recycling of plastic waste.