Enhancing fastening of threaded joints with sustainable lubricants from waste cooking oil

Mineral-based lubricants commonly used in industrial tightening increase reliance on fossil resources and can contribute to environmental impacts, motivating the development of high-performance alternatives from renewable and waste feedstocks. This work evaluates waste-cooking-oil-derived lubricants for repeated tightening of high-strength threaded joints under severe loading. Two different processing routes for waste cooking oil are explored: hydrogenation to obtain a grease-like product, and chemical functionalization via epoxidation followed by ring opening to produce a polar polyol. The functionalized waste cooking oil lubricant delivers stable friction and torque responses over multiple tightening cycles, approaching the performance of a commercial MoS2-containing paste and outperforming a conventional mineral engine oil as well as the minimally processed and hydrogenated waste cooking oil products in repeatability. In-depth wear analyses of the contact surfaces complement the tightening results and clarify the mechanisms behind lubricant performance. Overall, the findings indicate that appropriately tailored waste cooking oil lubricants can meet demanding joining requirements while supporting more sustainable fastening processes.