Functionalized Lignin Enables Co-Cross-Linking of Natural Rubber and Simultaneous Carbon Black Dispersion

Lignosulfonate (LS), an abundant industrial byproduct featuring aromatic motifs, is actively investigated as a sustainable biomass-derived filler alternative to carbon black (CB) in natural rubber (NR). However, its inherent polarity presents significant challenges for achieving nanoscale compatibility within the nonpolar NR matrix. Herein, LS was modified with glycidyl methacrylate (GMA) to yield LSG, introducing polymerizable C═C bonds while reducing polarity. Density functional theory (DFT) calculations demonstrate a 25.8% increase in binding energy for the NR/LSG interface versus NR/LS. An aqueous solution of LSG was cocoagulated with natural rubber latex, facilitating the nanoscale dispersion of LSG in the NR matrix. Simultaneously, LSG underwent photoinitiated copolymerization with NR under UV irradiation, establishing an extensive covalent lignosulfonate/NR conetwork that was further strengthened during vulcanization, enabling multifaceted covalent cocrosslinking reinforcement of natural rubber. The resulting hybrid composite, incorporating both LSG and NR (NR@LSG), exhibited a tensile strength of 31.39 MPa. Representing a 32.1% increase compared to unfilled NR. LSG improved the dispersion of CB within the NR matrix. The particle size of NR@LSG@C is 33.3% smaller than that of NR@C. This strategy offers a sustainable approach for converting industrial lignin byproducts into high-performance rubber composite fillers, advancing the principles of the circular economy.