Recent progress in tribological and thermophysical behaviour of bio-based nanolubricant: a review

The United Nations adopted 17 Sustainable Development Goals (SDGs) in 2015 as a global framework to eradicate poverty, protect the planet, and promote sustainable development across social, economic, and environmental dimensions. Among these, "SDG 13: Climate Action" emphasizes the need for urgent efforts to mitigate climate change, reduce its impacts, and enhance education and early warning systems related to climate risks. In response to environmental concerns, including fossil fuel depletion, harmful emissions from hydrocarbon combustion, and the non-biodegradable nature of synthetic oils, there has been growing research into bio-based lubricants. These lubricants are gaining attention due to their (i) higher viscosity index, which provides effective lubrication at elevated temperatures and reduces mechanical wear, (ii) lower emissions of harmful greenhouse gases such as carbon dioxide, methane, ozone, nitrous oxide, and chlorofluorocarbons, and (iii) biodegradability, which minimizes environmental contamination and mitigates anthropogenic climate change compared to conventional petroleum-based oils. This review synthesizes the current knowledge on bio-based lubricants, focusing on three key aspects: (i) the market growth of biolubricants, (ii) the role of nanofillers in enhancing tribological performance, and (iii) the impact of nanofiller integration on the tribological and thermophysical properties of bio-based lubricants. Additionally, the paper discusses the challenges and future opportunities for the development and application of bio-based lubricants.