A Comparative Study of the Reinforcing Behavior of Lignin in Polar and Non‐Polar Rubbers

Abstract Bio‐based resources as reinforcing agents for elastomers is an important area of research. In this study, different types of lignin were employed as reinforcing fillers for different synthetic elastomers. Polychloroprene (CR), a polar rubber, and solution styrene butadiene rubber (SSBR), a non‐polar rubber, were used as matrix materials. Results showed that elastomers filled with Kraft lignin exhibited better mechanical performance than those filled with lignosulfonate. Without chemical modification, Kraft lignin effectively reinforced polar polychloroprene rubber, increasing its tensile strength by 3.5 times, modulus by 2 times, and elongation at the break by 2 times. However, for non‐polar SSBR, the use of lignin surface modifiers such as alkyl isocyanates improved the dispersion and reinforcing efficiency of Kraft lignin. Particularly, in this SSBR system the elongation at break values crossed 900%, which is very high for synthetic rubber like SSBR. A noticeable improvement in lignin dispersion was observed by field emission scanning electron microscopy when in situ surface modification of the lignin was done with alkyl isocyanates. To understand the reinforcing effect of Kraft lignin, various mechanical, dynamic mechanical, and physical tests were conducted with the rubber composites.