A Proposed Adhesive Mechanism of Boundary Lubrication for Polyphenylene Oxide and Silicone Fluid

Abstract

This paper is concerned with the application of Rubenstein's mechanism of the boundary lubrication of polymers together with Bowden and Tabor's mechanism of the boundary lubrication of metals, to explain the data recently obtained from experiments with polyphenylene oxide (PPO) sliding against steel in the presence of silicone fluid under truly boundary lubrication conditions. It is shown that it is possible to find the variation with speed of (i) the fraction (α) of the true area of contact at which polymer/metal contact occurs, (ii) the shear strength (S) of the polymer/metal contacts and (iii) the shear strength of the boundary lubricant (SL). These variations are then used to predict values of the coefficient of friction (μ) at other speeds within the boundary lubrication regime. It is found that there is a very good agreement between these predictions and the experimental values of μ versus speed, thereby verifying that changes in physical properties do occur when plasticization takes place during sliding contact and that the dominant mechanism is an adhesive one.