Design of a versatile lignin-based synergistic anti-aging reagent for natural rubber composites

This research designed a versatile lignin-derived synergistic anti-aging reagent for natural rubber (NR) composites. Soda lignin (SL) was modified via Mannich reaction producing tryptophan-grafted lignin (TL). The molecular structure of TL was confirmed through FTIR, XPS, 2D-HSQC and elemental analysis. Thermal analysis showed an elevated glass transition temperature (186 degrees C) for TL, indicating enhanced molecular rigidity. NR composites with varying amounts of SL and TL were analyzed for vulcanization characteristics, mechanical properties and anti-aging performance. The NR-TL series exhibited a substantial increase in the vulcanization torque and hardness compared to the NR-SL series, reflecting a superior stiffening effect of TL. The NR-TL series demonstrated remarkable anti-aging performance, with NR-TL10.0 (containing 10.0 phr of TL) achieving improvements of 63.7% in tensile strength (after thermal-aging) and 86.4% in the anti-aging coefficient compared to the NR-SL counterpart. These enhancements are attributed to improved dispersion of TL and enhanced radical scavenging efficiency. The anti-aging mechanism of TL was clarified, pointing to an intramolecular synergism with a favorable radical transfer route from aminyl to phenoxy radical. This work presents a facile approach to prepare a novel lignin-based multifunctional reagent with excellent anti-aging effectiveness, significant mechanical reinforcement, and high vulcanization efficiency for rubber materials.