The Influence of Linear and Rotating Motions on the Friction of Polymers

Abstract

A series of experiments are described where combined linear and rotating motions are imposed upon a polymer while it is in contact with a smooth and clean counterface. Friction data are presented for a series of polymers, which reflect the main tribological groups, for a range of linear and angular velocities. The main conclusion is that within certain ranges of contact conditions, which the paper defines in part, three polymers, PTFE, high density polythene and ultrahigh molecular weight polythene, exhibit a response which is markedly different from that of the other polymers investigated. For the PTFE group of polymers the measured force attains a pronounced maximum value as rotation is introduced. The other polymers show no such effect. The phenomena are associated with the natural tendency of PTFE type polymers to undergo reorientation of the matrix at the interface during sliding. The results suggest a method of sensing the nature of the energy dissipation process during sliding and also accounts for an artefact which may be observed with PTFE materials when their friction is monitored in a pin-on-disk configuration.