Objective Lignin is a naturally occurring polymer with moderate polarity, and its compatibility with rubber matrix is insufficient. As a reinforcing filler in the rubber industry, it is difficult to achieve a direct reinforcement effect on rubber. To reduce the polarity of lignin and improve its compatibility with non-polar rubber, a new type of copolymer-modified lignin material had been developed.

Method Lignin was modified by acylation with acrylolyl chloride, and the acylated lignin was copolymerized with isoprene via free radical copolymerization. This process introduced long-chain alkyl side groups into lignin macromolecule, resulting in the preparation of isoprene/acylated lignin copolymer material (ALI). Subsequently, the structural changes of modified lignin, dispersion properties of ALI in rubber matrix, and the mechanical properties of natural rubber composites were tested and analyzed.

Result The hydroxyl content of modified lignin material decreased, and the contact angle increased from 66.13° to 80.16°, indicating a decrease in molecular polarity and an improved compatibility with rubber matrix. When the ALI content was 5 g, the tensile strength of composite material reached 20.61 MPa, which was similar to that of carbon black-filled sample. The elongation at break reached 581.20%, which was an increase of 42.40% compared with carbon black-filled sample. This demonstrated that the modified lignin material had good dispersion in filler-rubber network, leading to reinforcement of rubber matrix.

Conclusion The isoprene/acetylated lignin copolymer material prepared in this study successfully improves the compatibility between lignin and rubber matrix. The natural rubber composites exhibite good strength and toughness, achieving reinforcement of natural rubber.