Unlocking the Potential of Lignin: Towards a Sustainable Solution for Tire Rubber Compound Reinforcement

This study tackles the persistent challenge of producing highly reinforced lignin-rubber composites, emphasizing the transformation of agro-industrial residues into value-added products. To address this challenge, we introduce a novel approach termed "in-situ surface modification utilizing a thermo-chemo-mechanical approach" which incorporates the utilization of biomass-derived kraft lignin and a thermally stable organofunctional surface modifier, specifically (3-aminopropyl) triethoxysilane. The resulting material exhibits unprecedented tensile strength (∼15 MPa) along with ∼300 % elongation at break, while typical gum rubber offers 1–2 MPa tensile strength. Additionally, for the other tensile properties like 100 %, and 200 % tensile modulus, the improvement is 7-fold (∼5.6 MPa) and 10-fold (∼11.3 MPa), respectively. Furthermore, this composite presents a higher degree of reinforcement than a passenger car radial (PCR) tire model compound (tensile strength ∼14.5 MPa, 100 % tensile modulus ∼2.2 MPa, and 200 % tensile modulus ∼5.6 MPa) comprised of silica and polysulfide-based coupling agent, with exactly a similar loading of filler. The dynamic mechanical and stress relaxation behavior of the composites are critically discussed concerning the dispersion of the lignin in the sSBR/BR rubber matrix. The morphological orientation and involved chemical interaction in the presence of a surface modifier are also studied in detail. Tear fatigue analysis using pure shear specimens indicates superior fracture toughness at a lower tearing energy regime compared to silica-filled PCR tire compounds. Overall, this study showcases the potential of lignin-reinforced elastomers, offering a promising route for sustainable engineering materials and commercial viability.