Maintaining lubrication at low temperatures is a persistent challenge. Here, we present zwitterionic lignin gels synthesized through a volatile organic compounds (VOCs)-free, initiator-free thermal route, which achieves the polymer growth and network structure in gels by inhibiting radical polymerization of lignin. This molecular regulation yields gels with solid-like viscoelasticity, shear-thinning behavior, and rapid recovery. The optimized 10 wt. % lignin gel provides a stable friction coefficient (COF) of ~0.06 at 25°C, reduces wear by ~70% compared with 20 wt.% lignin gel, and at −20°C, outperforms two commercial greases with over 50% lower wear. It surpasses the commercial benchmarks, owing to its gradual viscosity–temperature response that sustains boundary-film formation. Dissipation monitoring (QCM-D) and X-ray Photoelectron Spectroscopy (XPS) analyses confirm strong interfacial adsorption and the formation of protective tribofilms. These results demonstrate that lignin molecular regulation enables sustainable zwitterionic gels with superior low-temperature anti-wear performance, offering a promising alternative to petroleum-based greases. • A solvent-free, initiator-free strategy is developed to synthesize zwitterionic lignin gels by exploiting lignin’s intrinsic radical-scavenging ability to regulate polymerization. • Lignin molecular regulation enables an optimized 10 wt% gel with a balanced viscoelastic network, shear-thinning flow, and rapid structural recovery. • Superior tribological performance is achieved, with the 10 wt% gel showing a stable COF (~0.06) and ~70% wear reduction compared with higher-lignin gels at 25 °C. • Outstanding low-temperature lubrication (−20 °C) surpasses two commercial greases, reducing wear by more than 50% owing to a gradual viscosity–temperature response. • QCM-D and XPS analyses reveal a robust tribofilm, formed by strong physical adsorption and tribochemical reactions, explaining the gel’s durable boundary lubrication. • Demonstrates a sustainable, lignin-based alternative to petroleum greases with excellent low-temperature wear protection.
Wu et al. (Sun,) studied this question.