The Non‐Monotonic Effect of Water on Lignin Dispersion in Natural Rubber

ABSTRACT Lignin, a byproduct of the paper and pulp industry, has emerged as an abundant, renewable, and promising sustainable alternative to conventional petroleum‐based fillers in tire formulations. Yet, its application in the real‐world is limited by poor dispersion in nonpolar rubber matrices due to hydrogen bonding and by high polarity from the presence of hydroxyl groups. This study investigates the influence of water on the dispersion behavior, interfacial interactions, and mechanical response of lignin–natural rubber composites. A nonlinear dependence of lignin agglomeration on water content was observed, with optimal dispersion at ~5%–10% of water. It is hypothesized that, although a controlled amount of water disrupts lignin–lignin interactions via competitive hydrogen bonding, excessive water causes lignin re‐agglomeration due to capillary bridging and water‐mediated interactions. Water, in the optimum quantity, reduces interparticle cohesion and facilitates improved dispersion. It enhances the filler–rubber contact, reducing the Payne effect by ~35%. Modulus@300% strain and tensile strength are improved by 17% and 25%, respectively. FTIR, FE‐SEM, HR‐TEM, and AFM analysis support this mechanism. The findings emphasize water as a key processing parameter and provide a realistic pathway to overcome lignin dispersion challenges, supporting its efficient utilization in a sustainable tire.