Green Tribology: A Review of Biodegradable Lubricants-Properties, Current Status, and Future Improvement Trends

The use of lubricants to lower friction and wear in mechanical systems has been established for centuries. Growing concerns about the hazardous effects of conventional mineral lubricants on the environment have motivated scientists to search for biodegradable substitutes. This threat is particularly at a critical level in ecologically sensitive regions. Despite their lower eco-toxicity, the inherent shortcomings of biodegradable lubricants (e.g., high pour point, and poor oxidative and thermal stability, etc.) have prevented their full application in different industries. This review intends to (1) introduce various sources of biodegradable lubricants, their properties, and applications; (2) discuss the current state and most recent advances from the tribology perspective; and (3) discuss future trends regarding improving the tribological properties and overall performance of biodegradable lubricants.