Autoxidative transformation of green lubricants induced by bombax ceiba biodiesel and its tribo-thermal consequences

With the increasing demand for sustainable lubricants, Bombax ceiba biodiesel (BD) has become a promising additive for developing low-viscosity, eco-friendly biolubricants. In this study, modified biolubricant (MBL) formulations were created by blending the extracted raw Bombax ceiba biolubricants (BL) with different volumes of BD (5, 10, 15, and 20 mL). The chemical structures and compositions of BL, BD, and MBL were analyzed using ATR-IR, ¹H NMR, and GC–MS techniques. The tribological and heat transfer properties were assessed with a four-ball tribotester and KD2 Pro thermal property analyzer. Results showed that adding BD promoted molecular rearrangement within BL through autoxidation reactions, which caused a decline in tribo-thermal performance. Specifically, COF increased by 19.76 %, 46.40 %, 36.48 %, and 30.94 %, while thermal conductivity decreased by 0.62 %, 1.86 %, 1.86 %, and 3.10 % for MBL₁−MBL₄, respectively. Notably, blends containing more than 5 mL BD experienced excessive oxidative disintegration, which reduced key lubricating components and impaired tribological stability. Overall, Bombax ceiba biodiesel demonstrates potential as a sustainable additive for low-viscosity green lubricants, provided it is optimized within appropriate blending limits and benchmarked against commercial standards.