Initiator-free melt grafting of maleic anhydride and styrene onto EPDM for transparent adhesive coatings in paper conservation

Ethylene–propylene–diene terpolymers (EPDM) exhibit good mechanical strength and aging resistance, making them suitable for protective coatings in paper-based heritage conservation. However, conventional initiator-assisted grafting methods often lead to discoloration, low grafting degree, and gelation, ultimately limiting their practical application. To address these issues, this study developed an initiator-free melt-grafting method to synthesize maleic anhydride (MAH)-grafted EPDM utilizing styrene (St) as a comonomer. Under heat and shear conditions, St facilitated the reaction between EPDM macroradicals and MAH, enabling efficient grafting without external chemical initiators. This approach achieved a grafting degree of 1.9%, while maintaining high optical transparency and resistance to yellowing, thus preserving the paper’s visual appearance. When applied as a coating, the modified EPDM significantly enhanced paper performance, increasing the tensile strength and folding endurance by 123% and 526%, respectively. Furthermore, the coated paper demonstrated improved stability under dry heat and hydrolytic aging conditions. These findings indicate that EPDM-g-(St-MAH) is an effective and durable material for long-term preservation of paper artifacts.