Molecular design of zwitterionic lignin gels for low-temperature wear protection in greases

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.