Physical Chemistry and Rheological Behavior of Commercial Polymers of Viscosity Index Improver Used in Motor Oil Industry

Nowdays, production of high quality engine oils is one of the worries of ourcountry’s engine oil industry. In this study, the behavior of four commercialpolymers used in nation motor oil industry in obtaining the best viscosityindex improver was investigated. In this regard, viscometric behavior, shear stabilityand polymers’ performance for engine cranking were compared at low temperature. Inthis respect, viscometry behavior of polymer solutions with different concentrations(0.3, 0.5, 0.7 and 1% by weight) in terms of physical chemistry parameters such asspecific viscosity, intrinsic viscosity, viscosity ratio, thickening power and viscosityindex were compared with each other. The activation energy of each polymer solutionwas calculated using the Arrhenius equation and polymer performance was evaluatedwith respect to activation energy changes and lower oil temperature sensitivity.In continuation, the shear stability of these commercial polymers in solution statewas evaluated. Based on shear stability analysis an inverse relationship was foundbetween polymers’ shear stability and their molecular weights. Finally, the behaviorof the commercial polymers was investigated for determination of optimum performancein engine cranking at-15°C. Based on the obtained data, the most suitablepolymer was identified and indicated as the best to fulfil oil industry’s purposes. Inthis respect the high-tech polymers, based on their molecular structures demonstratethe best performance compared to other polymers. Paratone and Viscotech polymershave relatively shown similar behaviors, although based on viscometric behavior theViscotech is better than Paratone, and based on shear behavior the order of preferenceis reversed. Keltan polymer has just a better thickening power while, it is not consideredsuitable for high quality engine oil at low temperatures of engine cranking for itsweak shear performance and low efficiency.