Effects of N‐(4‐Hydroxyphenyl)Maleimide Grafting and Rubber Epoxidation on the Morphology, Viscoelasticity, and Performance of Natural Rubber/Polypropylene Thermoplastic Vulcanizates

ABSTRACT Four thermoplastic vulcanizates (TPVs) with a 50/50 rubber/polypropylene (PP) weight ratio—natural rubber (NR)/PP, epoxidized natural rubber containing 25 mol% epoxide (ENR‐25)/PP, N‐(4‐hydroxyphenyl)maleimide‐grafted NR (NR‐ g ‐HPM)/PP, and HPM‐grafted ENR‐25 (ENR‐25‐ g ‐HPM)/PP—were prepared by dynamic vulcanization using phenolic‐modified PP (PhHRJ‐PP) as a compatibilizer. FTIR confirmed the presence of imide, aromatic, and phenolic functional groups derived from HPM. SEM showed that HPM grafting refined the morphology of the vulcanized rubber, decreasing the mean rubber‐domain size from 2.715 to 2.109 μm for the NR‐based TPVs and from 3.488 to 3.113 μm for the ENR‐25‐based TPVs. The NR‐ g ‐HPM/PP exhibited the best overall balance of mechanical properties. Compared with the unmodified NR/PP counterpart, its tensile strength increased from 11.35 to 13.25 MPa, elongation at break increased from 351.2% to 368.8%, and tension set decreased from 30% to 28%. In contrast, ENR‐25‐ g ‐HPM/PP exhibited the highest oil resistance and thermal stability, with only 3.70% swelling in engine oil and a first‐stage degradation temperature of 411.27°C, compared with 12.50% swelling and 388.80°C, respectively, for the NR/PP TPV. Thus, HPM‐grafted NR offers a more favorable balance of toughness and elastic recovery, while HPM‐grafted ENR‐25 is better suited for TPV applications that require enhanced oil resistance and thermal stability.