Abstract
Four commercial viscosity index improvers (VII) have been used to investigate the behavioral differences of these compounds in three types of universally applicable base oils. The used VIIs are structurally three types of co-polymer: ethylene-propylene, star isoprene, and two di-block styrene-isoprene. After dissolving of different amounts of VIIs in different base oils, the kinematic viscosities at two standard temperatures were determined and the intrinsic viscosities were calculated according to Huggins method, then the effects of changes in base oil and polymer type were investigated. Intrinsic viscosities as criteria for polymer molecules sizes were found to be higher at lower temperature than at higher temperature. Dependence of intrinsic viscosity on the polymer molecular weight was observed. In the previous works, one or two types of VIIs were studied in only one type of base oil and/or solvent, not different base oils. Furthermore, different ranges of temperatures and concentrations not necessarily applied ranges were selected, but in this work, common base oils and most commercial VIIs were used and the viscometric properties were compared at two temperatures. Viscosities at these temperatures are used for determining VI and definition of lubricant’s viscosity grades. VI improvement is the main cause of VII usage.
Highlights
Two key initial properties of each lubricant are viscosity and viscosity index
Kinematic viscosity is the fluid viscosity in non-shear/stress conditions, which is depended on temperature and pressure for a given fluid
A well-known method for expressing the viscosity-temperature relation is based on viscosity index, which is calculated from kinematic viscosities at 40 and 100 ◦C
Summary
Two key initial properties of each lubricant are viscosity and viscosity index. viscosity is the intrinsic resistance of a fluid to flow that is defined and measured in different ways. TThhee aaddvvaannttaaggee ooff PPIIBB iiss eexxcceelllleenntt sshheeaarr ssttaabbiilliittyy aanndd llooww ccoosstt. Covitch studied the change in polymer coil size at different temperatures and concentrations by two methods: SANS and intrinsic viscosities determination. He showed that polymer coil expansion is not necessarily a requirement for VI improvement [40]. The hydrodynamic volume represents the volume occupied by the polymer in the solution Based on these equations, the intrinsic viscosity is one of the parameters that are suitable for showing the change in the size of polymer coils in the solution. These three types account for more than 90% of VII consumption in the lubrication industry
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