In Situ Compatibilization of Isotactic Polypropylene and High-Density Polyethylene by a Melt Cobranching Reaction

Abstract

Incompatible polypropylene (PP) and polyethylene (PE) are di cult to separate in mixed recycling streams such as waste plastic packaging, which makes these polyole n mixtures unsuitable for highquality 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 modi ed blends were largely improved, and e cient 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 modi ed blend was clearly decreased, and the interfacial thickness increased. Compared with the pure iPP/HDPE blend, the initial crystallization temperature of iPP in the modi ed 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 signi cantly improved.

Structures of the co‐branching reactive products of isotactic polypropylene with high‐density polyethylene and the effect on the in situ compatibilization of mixed recycled materials

“…In the process of in situ generating the copolymer of isotactic polypropylene and high‐density polyethylene (iPP‐co‐HDPE) with a long‐chain co‐branched structure via a melt blending method, the hydrogen atoms on the HDPE molecular chain methylene group and on the PP molecular chain tertiary carbon atoms are easily seized by primary radicals to form macromolecular radicals. Meanwhile the carbon–carbon double bonds of the polyfunctional acrylate monomer (M) are opened and combine with the macromolecular radicals to form a branched structure centered on polyfunctional chain segments 30 . The in situ co‐branching product was verified by 1 H NMR (Figure 5b,c).…”

“…Meanwhile the carbon-carbon double bonds of the polyfunctional acrylate monomer (M) are opened and combine with the macromolecular radicals to form a branched structure centered on polyfunctional chain segments. 30 The in situ co-branching product was verified by 1 H NMR (Figure 5b,c). Prior to the 1 H NMR characterization of modified iPP/HDPE 50/50 blends, the modified samples were purified to remove impurities such as unreacted TMPTA.…”

“…Currently, due to their excellent compatibilization effects, the preparation of controllable long chain segment copolymers and their structure-property relationships are becoming a hot research topic in regards to the high-quality recycling of polyolefin mixed waste plastics. 16,[24][25][26][27][28][29] In our previous study, 30 trimethylolpropane triacrylate (TMPTA), 2,5-dimethyl-92,5-di(tert-butylperoxy) hexane (DHBP), and zinc dimethyldithiocarbamate (ZDMC) were used to economically and conveniently generate the long chain co-branched copolymers in situ for compatibilization of HDPE and IPP blends. Consequently, superior compatibility and mechanical properties of the HDPE/PP blends were obtained.…”

Ternary Blends of Polypropylene Copolymer, Polyethylene and Thermoplastic Polyurethane for Fused Deposition Modeling Three-Dimensional Printing Technology: Preparation, Printing and Properties

“…After being cooled to 110 °C and held still for 20 min, PPR crystals were markedly found in the binary blend; however, the structure of PPR spherulites appeared small, incomplete, and needle-like. This phenomenon was absolutely attributed to the mutual restriction of crystallization of the two polymer components . At a prolonged isothermal holding time (60 min), the continuous growth of PPR spherulites was evidently noted.…”

“…This phenomenon was absolutely attributed to the mutual restriction of crystallization of the two polymer components. 39 At a prolonged isothermal holding time (60 min), the continuous growth of PPR spherulites was evidently noted. It was difficult to differentiate the HDPE crystals from the relatively larger PPR spherulites.…”