Graphene vs. graphite as carbon-based additives in biolubricants: friction and anti-wear performance under high load conditions

Carbon-based additives such as graphite and graphene are increasingly used in advanced lubrication formulations due to their ability to reduce friction, enhance wear protection, and improve energy efficiency in mechanical systems.This study investigates the development of sustainable biolubricants enhanced with carbon-based additives, specifically micron-sized graphite powder (Gr, <10 μm) and graphene nanoplatelets (GNPs), at concentrations ranging from 0.05 to 0.1 wt%. The tribological performances of these formulations were systematically evaluated and compared. The most representative results show that 0.08 wt% GNPs reduced the coefficient of friction by up to 25 %, while graphite achieved up to 99.5 % reduction in wear volume under extreme pressure conditions. The results show that GNPs significantly reduced the coefficient of friction (COF) across different lubrication regimes, whereas graphite exhibited superior load-bearing capacity and enhanced wear protection. These findings demonstrate the potential of carbon-based additives to advance biolubricant performance and highlight the complementary, context-dependent advantages of graphite and graphene in lubricant design. • Bio-lubricants were developed using epoxidized soybean oil with dispersed graphite and graphene particles. • The effect of graphite and graphene addition on friction was investigated under a wide range of contact conditions. • Sliding tests under high contact pressure enabled the comparison of graphite and graphene in enhancing wear resistance. • Systematic analysis of surface morphology and wear debris helped identify the dominant wear mechanisms.