Mechanochemical Methacrylation of Lignin for Biobased Reinforcing Filler in Rubber Compounds

The inclusion of biobased materials as fillers for rubber compounds is an emerging topic in the tire industry. This study investigates the use of kraft lignin, a byproduct of the paper industry, as an alternative reinforcing filler for rubber compounds. Methacrylation of lignin was achieved through mechanochemistry, resulting in an estimated functionalization degree of 22% for aliphatic and 17% for phenolic hydroxyl groups. The modified lignin was predispersed in natural rubber via coprecipitation with a natural rubber latex. The reinforcing effect of lignin was tested in model tread and sidewall compounds by using either a sulfur or peroxide vulcanization system. Dynamic mechanical tests revealed that methacrylated lignin enhances compatibilization, dispersion, and stiffness within the elastomeric matrix more effectively than unmodified lignin due to covalent bond formation during vulcanization. In peroxide-cured composites, functionalized lignin combined with silica exhibited a higher storage modulus and lower hysteresis compared to unmodified lignin, suggesting potential for designing fuel-efficient tires.