Lignin/Epoxidized Natural Rubber Compounds Based on Wet Mixing: Impact of Epoxidation Degree on the Interface of Compounds

Natural rubber (NR) possesses excellent comprehensive properties and plays an irreplaceable role in both national defense and people’s livelihood. In recent years, lignin, as a new development trend, has emerged as a reinforcing filler in natural rubber, partially replacing traditional carbon black, or serving as an antioxidant in rubber. However, lignin, a polar biomass filler, exhibits poor compatibility with non-polar natural rubber. To address the compatibility issue between the two, this paper adopts an in situ method, utilizing formic acid and hydrogen peroxide to modify natural rubber into two types of epoxidized natural rubber (ENR) with different degrees of epoxidation (E-25% and E-45%). Subsequently, through wet mixing, it is combined with a lignin aqueous solution (20 parts), and ethanol is used as a flocculant to prepare lignin/ENR composite rubber materials. Comprehensive characterization of the composite rubber materials reveals that after epoxidation modification, the interfacial compatibility between lignin and natural rubber has been significantly improved. Wet mixing also effectively enhances the dispersibility of lignin in the rubber matrix. Compared to natural rubber, the composite material with an epoxidation degree of 25% exhibits significantly superior mechanical properties and thermal stability. The tensile properties of the composite rubber increase from 29.4 MPa to 36.2 MPa, indicating the significant reinforcing effect of lignin. This study aims to investigate the effects of the epoxidation degree (25% and 45%) of epoxidized natural rubber (ENR) and the mixing method on the compatibility and reinforcement performance of composite rubber, providing a new method for preparing high-performance lignin/ENR composites.