Environmentally Friendly Lubricants: The Role of Biopolymers in Modern Tribology

Abstract

ABSTRACT Energy losses due to friction and wear are a major challenge for the energy efficiency and sustainability of mechanical systems, motivating the development of green tribology strategies. This review provides a critical and integrative analysis of biopolymers derived from renewable resources, including cellulose, chitin, alginate, and starch as constituents of lubricants and tribological coatings. Contrary to previous reviews, this work introduces a mechanistic classification that connects biopolymer chemical properties such as charge, hydrophilicity, and molar mass to main lubrication mechanisms, including interfacial adsorption, hydrated lubrication, viscoelastic dissipation, and biopolymer‐nanoparticle hybrid systems. A quantitative synthesis of the literature data shows that modified biopolymers and nanocomposites consistently achieve better tribological performance than their unmodified counterparts. Wear reductions exceeding 50% and 0.05 as a coefficient of friction are reported for systems based on chitosan, modified cellulose, and zwitterionic hydrogels reinforced with nanofillers under moderate to high loads. Chemical modification strategies and controlled nanoparticle incorporation have also been reported to improve thermo‐oxidative stability, depending on whether stability is assessed via viscosity retention, oxidation‐induction time, or chemical integrity during high‐temperature aging (typically in the ~120°C–150°C range). This review identifies the most promising biopolymer–modification–nanoparticle combinations, highlights the current limitations related to the heterogeneity of experimental parameters, and proposes guidelines for the rational design of high‐performance, sustainable biolubricants aimed at reducing the energy and environmental footprint of tribological systems.