Friction and wear of PTFE — a review

Polytetrafluoroethylene (PTFE) is an important engineering material. When rubbed or slid against a hard surface, PTFE exhibits a low coefficient of friction but a high rate of wear. These unique properties of the polymer have encouraged many mechanistic and physical examinations of the processes involved in the friction and wear of this polymer. A section of such work carried out over the past 30 years is reviewed here. When rubbed against a hard surface, the PTFE chain undergoes scission, creating active groups which chemically react with the counterface. This results in strong adhesion and a coherent transfer film. Further interaction between the bulk polymer and the transfer film gives rise to anisotropic deformation of the unit cell, which results in closeness of adjacent chains and easy shear between chains. Sliding brings about growth in as well as reorientation of crystallites situated in a very thin subsurface region of the bulk polymer. Such structural rearrangement facilitates the joining of adjacent aligned crystallites to form films and ribbons which emerge as debris.