Objective Lignin is a naturally occurring polymer with moderate polarity, and its compatibility with the 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 has 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 the lignin macromolecule, resulting in the preparation of isoprene/acylated lignin copolymer material (ALI). Subsequently, the structural changes of the modified lignin, the dispersion properties of ALI in the rubber matrix, and the mechanical properties of the natural rubber composites were tested and analyzed.

Result The hydroxyl content of the 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 the rubber matrix. When the ALI content was 5 g, the tensile strength of the composite material reached 20.61 MPa, which is similar to that of the carbon black-filled sample. The elongation at break reached 581.20%, which was an increase of 42.40% compared to the carbon black-filled sample. This demonstrated that the modified lignin material had good dispersion in the filler-rubber network, leading to reinforcement of the rubber matrix.

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