Rheological Evaluation and Life Cycle Assessment (LCA) of Lubricating Nanofluids Formulated with Multi-Walled Carbon Nanotubes

The addition of nanomaterials to lubricants represents a promising strategy for optimizing their performance under demanding operating conditions. This study evaluates the rheological behaviour and environmental impact of nanofluids based on 5W-30 and 20W-50 engine oils containing multi-walled carbon nanotubes (MWCNTs), aimed at determining their technical and environmental feasibility for industrial applications. The raw materials and dispersions were characterized by Transmission Electron Microscopy (TEM), Scanning Electron Miscroscopy (SEM) and Fourier-Transform Infrared Spectroscopy (FTIR). Rheological behaviour was analyzed using a Rheotest 6000 rheometer at different MWCNT concentrations (0.25 wt%, 0.50 wt%, and 0.75 wt%) across a thermal range of 20 °C to 160 °C. Additionally, a Life Cycle Assessment (LCA) was performed with a SimaPro software via the IPCC and ReCiPe methods. Rheological results revealed that the incorporation of MWCNTs alters the oil behaviour from Newtonian to pseudoplastic. Regarding environmental analysis, the IPCC method showed a slightly higher carbon footprint for the 20W-50 oil () compared to the 5W-30 oil (), demonstrating that the oil mass generates a significantly greater impact than the nanoparticles. Furthermore, the ReCiPe evaluation identified higher impacts on human health from global warming as well as human toxicity (carcinogenic and non-carcinogenic), confirming trends consistent with the 20-year IPCC model and ratifying the dominance of the base fluid in the overall environmental footprint. In conclusion, the developed nanofluids exhibit favorable rheological responses for advanced lubrication, featuring an environmental impact profile primarily governed by the selection of the base oil.