Development and Characterization of Sustainable Plant-Based Lubricants for Minimum Quantity Lubrication (MQL) Applications

Introduction: Minimum Quantity Lubrication (MQL) has become one of the most promising sustainable lubrication strategies for machining, significantly reducing lubricant consumption while maintaining process performance. Although plant-based lubricants offer important environmental advantages over mineral oils, formulating them to achieve the physicochemical and tribological properties required for effective MQL operation remains challenging. This work presents a starting point for the formulation and characterization of plant-based lubricants intended for machining applications.

Methods: Five plant-based lubricant formulations were prepared and experimentally characterized. Lubricants were spiked with sustainable and endless additives from the land (green sources) and sea & ocean (blue sources). Their performance was compared with that of commercial MQL lubricants through viscosity measurements, friction coefficient evaluation under different tribological conditions, contact angle measurements on carbide substrates to assess wettability, and energy dissipation analysis during tribological testing. Based on the experimental results, environmentally friendly and non-toxic additives were incorporated to improve the lubricant properties and achieve the target performance values.

Results: The characterization identified the influence of the proposed additives on lubricant behavior. The best-performing formulations achieved physicochemical and tribological properties close to those of commercial products: a viscosity of approximately 45 cSt, an energy dissipation of about 300 J during tribological tests, and a contact angle of approximately 11° on carbide tools. These results demonstrate that renewable plant-based lubricants can be tailored to satisfy the key requirements for MQL applications while reducing their environmental impact and risk exposure.

Conclusions: The proposed methodology establishes an initial framework for the development of plant-based lubricants with properties comparable to those of commercial MQL fluids. The best formulations constitute a promising starting point for environmentally friendly and non-toxic machining applications. Future work will focus on validating their performance under practical turning, milling, and drilling conditions by evaluating tool wear, cutting forces, surface finish, and lubricant consumption.