Tribological and thermo-chemical performance of copper nanoparticle-enhanced mustard and soybean oil based bio-lubricants

The growing demand for eco-friendly lubrication has spurred interest in biodegradable, plant-based lubricants as alternatives to traditional oil-based products. In this study, copper nanoparticles (CuNPs) were incorporated into soybean and mustard oil-based bio-lubricants to evaluate their influence on friction, heat, and physical properties. The nanoparticles were dispersed in the base oils at different concentrations of 0.15%, 0.30%, 0.45%, 0.60%, and 0.90%. It was achieved by using a combination of magnetic stirring and ultrasonication, ensuring stable dispersion and uniform suspension. The tribological performance of the lubricants was evaluated using a pin-on-disc wear test. The key properties of the lubricants, such as thermal conductivity, flash and fire points, pH stability, acid value, and pour point, were systematically evaluated. Surface roughness parameters ( R a , R q , R z , and R t ) were evaluated to reveal tribofilm formation and underlying wear mechanisms. Research results revealed that adding CuNPs significantly improved lubricant performance, with the best performance found at 0.45 wt%. At this concentration, the mustard oil-based nano-lubricant showed superior performance, as evident by minimal wear loss (0.0025 g), higher thermal conductivity (0.1494 W/m·K), higher flash and fire points (330°C and 335°C), smooth surface roughness Ra = 0.282 µm), and improved low-temperature flow behavior (pour point of −12.8°C). In contrast, the soybean oil-based nano-lubricant exhibited slightly higher wear loss (0.0047 g), despite greater chemical stability, with smaller variations in pH and acid value. CuNP-enhanced mustard oil shows potential as an eco-friendly lubricant, warranting further investigation under industrial conditions.