Arriving at ultralow wear using cellulose/two-material composites

The development of environmentally friendly solid lubricants with exceptional wear resistance is imperative to address the escalating environmental concerns and performance limitations of conventional lubricants in demanding tribological applications. This study systematically investigated the wear resistance of hydroxypropyl methylcellulose (HPMC)/tungsten disulfide (WS₂)/graphene composites under normal applied loads (2 and 4 N) and varying solid lubricant contents (stoichiometric ratios of 0.2 referred to as CWG-0.2 and 10 referred to as CWG-10). Quantitative tribological tests revealed that the wear rate of HPMC composites exhibited distinct load dependence at fixed lubricant concentrations. Notably, CWG-0.2 and CWG-10 composites achieved an ultra-low wear rate below 10^-10 mm³, representing an approximately 95% reduction compared to pristine HPMC (10^-8 mm³). Surface characterization demonstrated that localized carbon phase clusters and interconnected carbon skeleton chains governed the ultra-low wear transition. Prolonged sliding (>10 000 cycles) induced the formation of a 10-50 nm-thick transfer film comprising WS₂ nanoflakes and a hybrid amorphous phase (C-O-W-S), as confirmed by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The exceptional performance, quantified through rigorous parametric analysis, positions HPMC composites as sustainable solid lubricants for precision machinery, aerospace bearings, and biodegradable micro-electromechanical systems requiring eco-friendly superlubricity.