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In Situ Compatibilization of Isotactic Polypropylene and High-Density Polyethylene by a Melt Cobranching Reaction
Summary
Researchers developed an in-situ co-branching reaction to compatibilize normally incompatible polypropylene and polyethylene blends during melt processing, enabling mixed plastic waste streams to be recycled into higher quality products. This approach could make it economically viable to recycle mixed polyolefin packaging waste that currently ends up in landfill or the environment.
Abstract Incompatible polypropylene (PP) and polyethylene (PE) are difficult to separate in mixed recycling streams such as waste plastic packaging, which makes these polyolefin mixtures unsuitable for high-quality products. In this work, based on the free radical branching reaction, a co-branching reaction of isotactic polypropylene (iPP) and high-density polyethylene (HDPE) blends was carried out in the presence of the peroxide, free radical regulator and multifunctional acrylate monomer, and a star-like long-chain branching (LCB) copolymer was acquired. The effect of in situ compatibilization on the structure and mechanical properties of iPP/HDPE was investigated, and the compatibilization mechanism was discussed. Results showed that the mechanical properties of the modified blends were largely improved, and efficient in-situ compatibilization of iPP and HDPE could be taken place in a wide process window. Moreover, the size of the dispersed phase in the modified blend was clearly decreased, and the interfacial thickness increased. Compared with the pure iPP/HDPE blend, the initial crystallization temperature of iPP in the modified iPP/HDPE blend was increased, and long branched chains of the LCB copolymer were physically entangled with the chemical identical homopolymers or even participate in the crystallization of iPP and HDPE. Thanks to the in situ compatibilization strategy, the compatibility of iPP/HDPE was significantly improved.