Molecular engineering of lignin to develop effective anti-thermo-oxidative agents for natural rubber

Developing high-performance lignin-based anti-thermo-oxidative agents offers a promising pathway for both the valorization of lignin and the sustainability of rubber materials. To enhance the thermo-oxidation resistance of natural rubber (NR), this study tailored lignin's structure via facile molecular engineering approaches, producing p-aminodiphenylamine-grafted lignin (PL) and (2-dodecen-1-yl)succinic anhydride (DDSA)/p-aminodiphenylamine co-grafted lignin (DPL) with high grafting yields. Their structures were verified by FTIR, 2D-HSQC and elemental analysis. The introduction of p-aminodiphenylamine significantly improved the thermal stability of lignin, while the incorporation of DDSA markedly enhanced its hydrophobicity and reduced its glass transition temperature. In NR composites, both PL and DPL impart a high vulcanization efficiency and a rubber reinforcing effect. Notably, the NR/DPL sample after thermo-oxidative aging exhibits an improvement of 138.5% in tensile strength and 44.2% in elongation at break compared to the NR/L benchmark, and shows the highest anti-aging coefficient (0.52) outperforming NR/L by threefold. DSC, FTIR and TG-MS were applied to illustrate the thermo-oxidative behavior of the NR samples. This work provides a molecular engineering strategy for shaping lignin into an effective bio-based anti-thermo-oxidative agent.