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

ABSTRACT 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.