Influence of polymethacrylate viscosity index improvers on friction and wear of lubricant formulations

Polyalkylmethacrylates (PAMAs) are widely used as viscosity index improvers and dispersant boosters in engine, transmission and hydraulic oils. They have been shown to be able to adsorb from oil solution on to metal surfaces, to produce thick, viscous boundary films. These films enhance lubricant film formation in slow speed and high temperature conditions and thus produce a significant reduction of friction and wear. In a recent systematic study a range of dispersant and non-dispersant PAMAs has been synthesized. The influence of different functionalities, molecular weights and architectures on both boundary film formation and friction has been explored using optical interferometry and friction-speed charting. From the results, guidelines have been developed for designing PAMAs having optimal boundary lubricating properties.

In the current paper the film forming, friction and wear properties of solutions of two functionalised PAMAs is first described. Then the impact of different lubricant additives on these friction and wear properties is explored. A number of components from all major classes of additives commonly used in commercial DI packages have been investigated. The results help the performance of PAMAs in fully formulated oils to be predicted and thus their design to be optimized.