Preparation of lignin-based filling antioxidant and its application in styrene-butadiene rubber

A novel filling antioxidant (Lig-g-RT) to improve the mechanical properties and antiaging performance of styrene-butadiene rubber (SBR) composites was prepared by grafting antioxidant intermediate p -aminodiphenylamine (RT) on the surface of lignin via the linkage of silane coupling agent. Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) measurements confirmed that RT was successfully grafted on the surface of lignin to produce the functionalized Lig-g-RT which shows a better thermal stability than lignin. Compared with SBR/lignin composite, the SBR/Lig-g-RT composite using latex co-precipitation method exhibits a much better filler dispersion, which contributes to the maintain of the physical mechanical properties of SBR vulcanizates. Moreover, the SBR/Lig-g-RT vulcanizate exhibits less chemical crosslink concentration and higher entanglement density than SBR/lignin vulcanizate according to the Mooney–Rivlin model analysis. In addition, the stabilizing effect of lignin/Lig-g-RT on the carbon-black filled SBR vulcanizates is comparable with that of commercial antioxidant N -1,3-dimethylbutyl- N ′-phenyl- p -phenylenediamine (4020), especially the SBR vulcanizate filled with 10 phr Lig-g-RT obtains the optimum thermo-oxidative aging properties. This functionalized Lig-g-RT not only provides an intramolecular synergistic antiaging effect for SBR vulcanizates and an improvement of filler dispersion, but greatly extends the comprehensive utilization of industrial lignin.