Eco-Friendly Fully Bio-Based Greases Fabricated From MTMS-Modified Phosphorylated Cellulose Nanofibrils and Castor Oil: Synergistic Structure-Performance Regulation and Tribological Properties

With increasing environmental awareness, developing renewable and biodegradable bio-based greases is a research priority. Herein, phosphorylated cellulose nanofibrils (PCNF) were selected as a bio-based thickener due to their renewability, excellent network-forming ability, and improved interfacial properties. However, the inherent hydrophilicity of PCNF limits its compatibility with non-polar vegetable oils. To overcome this, methyltrimethoxysilane (MTMS) was used for hydrophobic modification of PCNF, and fully bio-based greases were fabricated by combining modified PCNF (M-PCNF) with castor oil. The effects of MTMS silanization degree and M-PCNF content on the microstructure, physicochemical properties, rheology, and tribology of the greases were systematically investigated. Results show that increasing silanization degree enhances penetration, oil separation, and mechanical stability but reduces viscosity and structural strength. Increasing M-PCNF content improves thickening capacity, viscosity, structural strength, and rebuild rate. Notably, the friction coefficient of M-PCNF-based greases stabilizes at 0.04–0.06, lower than that of commercial lithium grease, demonstrating excellent friction-reducing stability. This work provides a feasible strategy for high-performance bio-based greases and offers insights into structure–property relationships relevant to cellulose-based thickener design for green lubrication.