Production and tribological evaluation of polypropylene nanocomposites with reduced graphene oxide (rGO) for using in water-lubricated bearings

In this work, polypropylene (PP) nanocomposites with microwaves reduced graphene oxide (rGO) were prepared and tribologically evaluated with a focus on their use in water-lubricated sliding bearings. The PP+rGO nanocomposites were produced at low concentrations of rGO (0.05-1 wt.%) and large-scale by twin-screw extrusion, and their mechanical and water wettability properties were evaluated by uniaxial tension, Shore D hardness and contact angle measurements, respectively. Tribological performance of the nanocomposites was assessed under dry, water lubricated and micro-abrasion conditions by accelerated wear and friction tests using a micro-abrasion tester. The elastic modulus, tensile strength and hardness of the nanocomposites were enhanced, while toughness and wettability decreased with increasing the rGO content. Separately, their friction coefficient and specific wear rates remained almost unchanged for dry testing, but were reduced with water lubrication. Reduction of friction coefficient and specific wear rates are attributed to decreased adhesion and slip of the water lubricating layer at the nanocomposites surfaces. In contrast, friction and wear of the nanocomposites increased with rGO content under micro-abrasion, which is ascribed to reduction of toughness by the addition of rGO. The results in this work suggest PP+rGO nanocomposites as potential alternative materials to produce water-lubricated bearings.