Shear behaviour of polyalkylmethacrylate solutions under thin film lubrication

Abstract

Film-forming properties and traction were determined for the oils containing polyalkylmethacrylates (PAMAs) under a temperature of 40 °C and a rolling speed between 0.001 and 1 m/s with the disc-on-roller tester. Oil film thickness measurements were made under a pure rolling condition and traction measurements were made under the slide/roll ratio of 50 per cent. All the copolymers were synthesized in the base oil by a random copolymerization method. Difference in oil film thickness between polymer solutions became significant under the rolling speed below 0.1 m/s. Among non-functionalized homopolymers, PAMAs with branched alkyl group were superior to those with linear alkyl group in film-forming performance. In functionalized PAMAs, film-forming performance was affected by the functional group as well as the coexisting alkyl group. High-mole-concentration of functional group produced a greater oil film thickness than the corresponding low-mole-concentration PAMAs. This tendency was more marked for high-molecular-weight PAMAs. Among all the polymer solutions, high-molecular-weight PAMA with methyl group as a main component showed the thickest oil film, followed by high-molecular-weight PAMA containing branched alkyl group and dimethylaminoethyl group. In the low speeds of the traction–speed curves, most PAMA solutions showed the effect of friction reduction, whose extent depended upon the type of alkyl group and functional group. It was inferred that the friction behaviour in the partial elastohydrodynamic lubrication (EHL) regime was considerably affected by the friction in the thin film lubrication based on the mutual interaction between polymer molecules.