Rheology and tribology of nanocellulose-based biodegradable greases: Wear and friction protection mechanisms of cellulose microfibrils

Dispersions of microfibrillated cellulose (MFC) in triethyl citrate have been considered as biodegradable lubricants containing 1–7 % MFC. Due to the presence of microfibril entanglements, these dispersions exhibit shear-thinning and shear-thickening behaviors, as well as viscoelastic properties of gels, which makes them typical greases. Moreover, the dispersions maintain their ability to flow at temperatures as low as −50 °C, being potentially applicable as low-temperature lubricants. Microfibrils reduce friction and wear of steel surfaces in two ways. Microfibrils in low concentrations fill irregularities of friction surfaces and decrease their wear, while microfibrils in high concentrations create a smooth chromium-enriched tribological film on the wear surfaces and largely reduce their friction.