Long-Chain-Branched Polypropylene with an Ester Group as an Effective Compatibilizer To Improve the Performance of PP/PET Blends

To address the compatibility challenges between polypropylene (PP) and poly(ethylene terephthalate) (PET), a long-chain-branched polypropylene compatibilizer featuring ester groups (LCB-PP-E) was synthesized from PP and pentaerythritol triacrylate (PETA), facilitated by the initiator dicumyl peroxide. The structure of LCB-PP-E was characterized by using infrared spectroscopy, rheology, and melt flow index analysis, while potential reaction mechanisms were discussed. The morphology of the blend was examined by scanning electron microscopy and Raman spectroscopy. The effects of LCB-PP-E on the thermodynamic and crystallization behavior of PP/PET blends were studied by dynamic mechanical analysis, differential scanning calorimetry, and polarizing microscopy. LCB-PP-E sampled at the reaction peak point exhibited a longer branched PP chain compared to that of LCB-PP-E obtained at the balance torque, facilitating better entanglement with PP macromolecules. Furthermore, the ester groups on LCB-PP-E engaged in transesterification reactions with the ester groups on the PET chains. The combined effects of these interactions effectively reduced the interfacial tension between the two phases, resulting in a decreased size of the dispersed PET phase and a more uniform distribution. Additionally, the introduction of LCB-PP-E significantly narrowed the crystallization and glass transition temperature difference between the phases. The enhanced compatibility led to an increase in elongation at break, demonstrating a transition of the blend from a brittle material to a ductile material. This compatibilization system shows substantial potential for high-quality applications in PP/PET recycled plastics.