Biolubricants derived from Brazilian Cerrado for drilling under hybrid lubrication/cooling

• Biolubricants were synthesized via transesterification, epoxidation, and ring opening. • In drilling, wettability and viscosity are more critical than oxidative stability. • Macaúba and pequi biolubricants provide adequate lubrication in drilling. • The hybrid MQL/vortex tube approach reduces thrust force, torque, and temperature. • Biolubricants improved the machined surface quality of AISI H13 steel. Amid the intensification of extreme climatic events, the demand to transition from an economy reliant on fossil resources to sustainable alternatives has become critical, particularly in industrial processes that depend heavily on petroleum-derived products, such as conventional cutting fluids. In this context, the present study investigates a hybrid lubrication-cooling strategy utilizing biolubricants derived from native species of the Brazilian Cerrado, macaúba and pequi, as environmentally responsible alternatives to conventional cutting fluids. These biolubricants were synthesized via a sequence of transesterification, epoxidation, and epoxide ring-opening. The structural and physicochemical properties were characterized through FTIR, NMR, thermogravimetric analysis, and Rancimat testing. Chemical modification significantly enhanced both wettability and rheological behavior, thereby reducing contact angles and improving viscosity under shear and elevated temperatures. During the drilling of AISI H13 steel under a hybrid system of minimum quantity lubrication (MQL) assisted by a vortex tube, both biolubricants demonstrated performance comparable to a commercial cutting fluid and superior to dry cutting, despite the absence of additives in their formulations. Long-wavelength infrared thermography, combined with contact temperature measurements, was used to assess the thermal performance of cutting fluids across different cutting parameters relative to dry cutting. Under severe drilling conditions, the hybrid lubrication-cooling strategy resulted in reductions of 11% in thrust force, 14% in torque, and approximately 45% in drilling temperature, accompanied by improvements in hole surface roughness of up to 112%. These findings highlight the technical and environmental feasibility of hybrid MQL-vortex tube systems using biolubricants as eco-friendly solutions for drilling processes.