In-situ surface grafting of lignin onto an epoxidized natural rubber matrix: A masterbatch filler for reinforcing rubber composites

To address the challenge of dispersing as well as reacting a filler with an incompatible natural rubber (NR) system and enhance material properties, this study explores melt grafting technique (e.g., in-situ reactions) to incorporate epoxidized-NR (ENR) into the lignin/NR system. The process involves melt-mixing (high temperature and shear forces) of ENR and lignin with dicumyl peroxide (DCP) acting as an initiator. The results illustrate the successful formation of covalent grafts between ENR and lignin through the opening of epoxy rings and shear-temperature-mediated etherification, facilitated by the peroxide initiator. Employing the ENR-lignin blend as a filler masterbatch, NR composites were developed, varying the lignin concentrations (0 to 50 phr) in the rubber. Remarkably, the NR composite formulation with 20 phr lignin exhibited significantly enhanced mechanical properties, which remained robust even after exposure to UV, humidity, and elevated temperature.