Effects of Average Molecular Weight and Concentration of Polymer Additive on Friction and Wear

Abstract

Tribological behavior with oils containing PMAs differing in average molecular weight, Mw, is examined in sliding concentrated contacts. At low loads, low PMA Mw or higher concentrations of PMA have a beneficial effect on wear, but at high loads are detrimental. The beneficial effect is attributed to EHD film formation. The most important parameter is the number of PMA molecules per unit oil volume. The prowear action can be explained by the fact that PMA molecules may accumulate in the inlet region of the contact. The polymer accumulation may block the base oil entering the contact leading to oil starvation which in turn leads to severe contacts and increases in wear. This anamalous behavior may result from the competition between the prowear action and oil film formation.