Environmental limitations of PTFE for ultralow friction composites and alternatives to using liquid lubricants

The importance of reducing energy-related environmental and economic issues by extending the lifetime and efficiency of mechanical systems has increased. The use of ultralow friction composite materials is one approach to eliminate frictional wear. Polytetrafluoroethylene (PTFE) has excellent low friction properties and has been used to reduce frictional wear in various industrial fields. However, degradation of PTFE in natural environments poses challenges owing to its stable chemical structure, which is characterized by strong C‒F bonds. Furthermore, PTFE can accumulate in the living body and environment over a long period of time. Consequently, it is resistant to physiological filtration or decomposition. Hence, it is sometimes called a “forever chemical”. Therefore, PTFE, which is a type of poly- and perfluoroalkyl substance (PFAS), is increasingly being adopted as a regulated substance. This review focuses on several aspects of PTFE and PFAS, reasons for their adoption as regulated chemicals, and research on alternatives to PTFE, particularly the use of liquid lubricants.