Submicron Scale Dispersion of Lignin Achieved by Green‐Solvent Casting Blending Enables Carbon Black Level Reinforcement in SBR Composites

Replacing fossil-derived carbon black (CB) with sustainable fillers is a major challenge in elastomer design. Here, we demonstrate that a green-solvent casting method using 2-methyltetrahydrofuran (2-MeTHF) enables submicron-scale dispersion (∼200 nm) of lignin within a styrene-butadiene rubber (SBR) matrix without chemical modification. Unlike conventional melt-mixed composites that contain micron-scale agglomerates, AFM-IR chemical mapping directly visualized homogeneous lignin domains and rubber phase that could not be separated by SEM, revealing a fine filler network responsible for mechanical reinforcement. Dynamic mechanical analysis showed that the 20 vol% lignin composite achieved a storage modulus and Payne effect comparable to those of SBR/CB composites, confirming the formation of a percolated filler network. Moreover, the reduction of tan δ at 60°C indicated lower hysteresis loss and the potential for improved rolling resistance. These findings established that processing-induced nanoscale dispersion, rather than chemical surface modification, governs the reinforcement efficiency of bio-based fillers. The present approach offers a simple, scalable, and environmentally benign route to valorize lignin as a functional reinforcing phase in high-performance and sustainable elastomers, paving the way for next-generation tire and flexible material applications.