Beijing Institute of Technology

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.

• A high-performance, fire-retardant coating (DCNC/40PEN) is developed; • DCNC/40PEN can adhere to different substrates and self-heal at room temperature; • DCNC/40PEN features closed-loop recyclability and biodegradation; • Phosphorus-free DCNC/40PEN provides superior fire protection for various materials. Although widely applied in diverse industries, conventional fire-retardant coatings generally suffer from poor adhesion and fire protection. These coatings are typically phosphorus-containing and non-recyclable, making their waste prone to causing environmental issues, e.g., bioaccumulation and (micro)plastic pollution. Inspired by the multi-non-covalent adhesion mechanism of ticks, we designed a strongly adhesive and self-healing coating (DCNC/40PEN) with superior fire protection by incorporating hydrogen bonding, π-π stacking, and cation-π interactions. Incorporating these interactions into a dynamic covalent network further imparts closed-loop recyclability and biodegradability to the coating. DCNC/40PEN can adhere to diverse substrates and self-heal at room temperature due to the non-covalent and covalent interactions within its structure. DCNC/40PEN features closed-loop recyclability and biodegradation because of its dynamic covalent network. Owing to the catalytic and crosslinking carbonization of sulfonate and Schiff base groups, phosphorus-free DCNC/40PEN delivers exceptional fire protection for various materials, e.g., wood, polymer foams, and steel. At a coating thickness of 100 μm, DCNC/40PEN significantly increased the limiting oxygen index and vertical combustion (UL-94) rating of wood to 35.0% and V-0. The multifunctionality and sustainability of DCNC/40PEN enable it to outperform commercial and reported fire-retardant coatings and adhesives. This work presents an innovative design strategy for the next generation of sustainable, versatile fire-retardant coatings, accelerating “green” development.