Thermo-Physical Performance and Dispersion Stability of Cellulose Nanocrystal (CNC) Bio-Nano additives in SAE40 Engine Oil

Abstract

The performance of conventional SAE 40 engine oil is limited by poor thermal conductivity and viscosity instability at elevated operating temperatures. This study investigates the feasibility of using sustainable cellulose nanocrystals (CNC) as a bio-based nano-additive to enhance the thermo-physical performance and dispersion stability of SAE 40 engine oil. CNC-based nanolubricants were prepared using a two-step dispersion method at volume concentrations ranging from 0.1% to 0.9%. Thermal conductivity, viscosity behaviour, viscosity index (VI), UV–Vis absorbance stability, and long-term sedimentation characteristics were systematically evaluated. The results indicate that thermal conductivity increased with CNC concentration, with the highest enhancement achieved at 0.9 vol%. In contrast, viscometric analysis revealed that a low CNC loading of 0.1 vol% produced the highest viscosity index of 155.32, representing an improvement of approximately 2.5% compared to base SAE 40 oil. UV–Vis and visual stability analyses confirmed that CNC dispersions remained stable for up to 60 days, with acceptable sedimentation behaviour observed at higher concentrations. Overall, the findings demonstrate a trade-off between thermal enhancement and viscosity stability, with 0.7 vol% CNC being optimal for thermal performance, while 0.1 vol% provides the most balanced overall lubricant performance. These results highlight the potential of CNC as a sustainable alternative nano-additive for environmentally responsible engine oil formulation.