Synthesis of Biomass‐Based Antioxidant and Its Application in Natural Rubber Latex Composites

ABSTRACT Natural rubber latex (NRL) is an essential rubber material. However, the unsaturated double bonds in natural rubber molecular chains render it highly susceptible to thermo‐oxidative aging. Current industrial antioxidants tend to migrate and precipitate in rubber matrices, thereby resulting in environmental pollution. In this study, a biomass‐based antioxidant AL‐g‐RT was successfully prepared by grafting 4‐aminodiphenylamine (RT) onto alkali lignin (AL) using 3‐glycidoxypropyltrimethoxysilane (KH560). The effects of AL‐g‐RT, as well as traditional antioxidants including pentaerythritol tetrakis[ β ‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionate] (1010) and N ‐isopropyl‐ N ′‐phenyl‐ p ‐phenylenediamine (4010NA), on the curing characteristics, mechanical properties, migration resistance and thermo‐oxidative aging resistance of NRL composites were systematically investigated. Fourier transform infrared spectroscopy (FTIR), water contact angle (WCA) and scanning electron microscopy (SEM) verified the successful synthesis of AL‐g‐RT. This modified product significantly reduced the hydrophilicity of AL, improves its interfacial compatibility with rubber matrices, and exhibits outstanding migration resistance. At a fixed dosage of 2 phr for all antioxidants, the AL‐g‐RT/NRL composite presents the highest crosslinking density and optimal mechanical properties. Compared with conventional small‐molecule antioxidant systems, it possesses superior retention ratios of crosslinking density and mechanical properties, together with a higher aging coefficient during long‐term thermo‐oxidative aging.