Tribological behaviour of novel chemically modified biopolymer-thickened lubricating greases investigated in a steel-steel rotating ball-on-three plates tribology cell

In this work, model renewable and biodegradable lubricating greases based on castor oil and chemically modified biopolymers (methylcellulose, chitin and cellulosic pulp) were tribologically characterized in a steel-steel ball-on-plates tribological cell coupled to a controlled-stress rheometer, and the results were compared to those provided by conventional lithium and calcium soap-based greases. Viscous flow, sliding velocity sweep and transient friction tests were carried out and resulting wear scars in the steel plates were evaluated by means of scanning electron microscopy (SEM). Different frictional responses were found depending on the thickener, especially at high temperature. Excepting for most severe conditions, wear is negligible when using chemically modified chitin and methylcellulose-based greases as lubricants.