Polyethylene (PE) Vitrimer by Cross-linking Two Mass-produced Ethylene-based Polymers through One-step Reactive Blending

Abstract

Cross-linked polyethylene (XLPE) possesses excellent performance, making it an ideal choice for diverse applications. Yet traditional XLPE is hard to reprocess and recycle due to its three-dimensional cross-linked networks, causing serious environmental issues. Vitrimers, which combine the advantages of thermoplastics and thermosets, offer promising solutions for reuse of post-consumed XLPE. Although significant advances have been achieved, the preparation of polyethylene (PE) vitrimers in scalable, cost-effective, and efficient manners still remains a huge challenge. Here, we propose an industry-inspired strategy to obtain cost-effective PE vitrimers by directly cross-linking two mass-produced commodity ethylene-based polymers. Through a one-step reactive blending approach, trimethoxysilane-grafted polyethylene (TMS-PE) and ethylene vinyl acetate copolymer (EVA) were cross-linked via efficient transesterification between carboxylates and silicates, generating PE vitrimers with dynamic silicate (Si‒O‒C) cross-linkages. During the reactive blending process, considerable increases in torque were observed due to increases in viscosities after crosslinking, providing a solid proof for the successful preparation of targeted PE vitrimers. The transesterification was validated via the consumption of ester groups in EVA as revealed by FTIR analysis. The successful construction of robust cross-linked PE networks was further systematically analyzed by gel fraction testing and dynamic mechanical analysis (DMA). The thermomechanical and tensile properties of resultant vitrimers could be readily fine-tuned by simply adjusting the feed ratios. Compared to the pristine EVA, the tensile strength and Young’s modulus of the vitrimers nearly doubled and increased by eight times, respectively. The tensile strength, Young’s modulus, and elongation at break of PE vitrimers were well maintained after two reprocessing cycles, demonstrating their excellent recyclability. In summary, this work provides a practical solution for the preparation of low-cost and high-performance PE vitrimers, paving the way to the widespread and up-scaled use of recyclable XLPE.