Anacardic Acid-Modified Fe₃O₄ Nanoparticles: Synthesis, Characterization, and Thermal and Tribological Performance in...

Magnetic iron oxide nanoparticles (Fe₃O₄) functionalized with anacardic acid (AAc), producing Fe₃O₄@AAc nanoparticles, were synthesized via chemical coprecipitation to improve the performance of biolubricants. The nanoparticles were characterized in terms of their structure, morphology, thermal properties, and magnetism. They exhibited a spherical morphology with an average diameter of 14.7 ± 4.2 nm, demonstrated good thermal stability, and contained approximately 12.4 wt % surface-bound AAc. Superparamagnetic behavior was preserved for the functionalized nanoparticles. To evaluate their effectiveness as performance-enhancing additives, Fe₃O₄@AAc nanoparticles were incorporated into a trimethylolpropane trioleate (TMPTO)-based biolubricant at concentrations of 0.05 and 0.15 wt %. Adding 0.05 wt % improved thermal resistance, and adding 0.15 wt % enhanced rheological stability, reducing both the coefficient of friction (COF) and wear. The nanoparticles lowered the activation energy for viscous flow and maintained Newtonian behavior up to 80 °C at 0.15 wt %. Tribological tests indicated that the 0.15 wt % formulation exhibited the lowest COF (0.036), a reduced wear scar diameter (WSD) (0.342 mm), and formation of a more stable protective tribofilm compared to pure biolubricant and reference mineral oil. These results confirm that anacardic acid functionalization promotes effective nanoparticle dispersion, with the magnetic nanoparticles acting as efficient additives that improve the thermal and tribological performance of the biolubricant.