Comparative Analysis of Tribological Performance of Nano-Enhanced Hybrid Bio-Lubricant with Conventional Synthetic Oil

Abstract

The need to have environmentally friendly lubricants has triggered a lot of research on the development of biodegradable and renewable alternatives to petroleum-based oils. The intrinsic lubricity of vegetable oils like cottonseed oil (CSO) and palm oil (PO) is due to the polar ester structures in them; however, limitations in wear properties and load-carrying capacity restrict their direct application in industries. This experiment compares the tribological behavior of CSO, PO, and a hybrid CSO-PO mixture with nano-additives (MoS2, TiO2, and SiO2) at 1, 1.5 and 2 wt.% and compares these formulations with a commercial synthetic lubricant (SAE 20W50). Nano-enhanced bio-lubricants were made through the controlled dispersion method and evaluated with a four-ball tribotester under the ASTM D4172 conditions. Wear scar diameter (WSD) and coefficient of friction (COF) were the main performance indicators. The data show that the addition of nanoparticles significantly enhances tribological behavior, and 1.5 wt% is the most optimal loading. The hybrid CSO-PO + 1.5 wt% MoS2 had the lowest WSD (509 μm) and COF (0.061). Compared to the synthetic oil (WSD = 530 μm and 0.088), the optimized nano-bio lubricant had a 3.96% wear reduction and a 30.68% friction reduction. These results indicate that nano-enhanced hybrid vegetable oil formulations, particularly those containing MoS2, have the potential to provide better friction reduction and competitive wear resistance, and thus have a high potential as sustainable, high-performance alternatives to traditional synthetic lubricants.