What Is Viscosity Index Improver?
Viscosity index improver is also called viscosity modifier. It increases the viscosity of lubricating oils and temperature-viscosity performance, and expands the range of working temperature for oils.
There are a few indicators to consider when choosing a viscosity index improver: the ability to thicken the oil (thickening ability) and improve temperature-viscosity performance, shear stability and thermal stability. Generally speaking, for the same type of viscosity index improvers, the higher the molecular weight, the better the thickening ability, and the worse the shear stability and thermal stability.
For internal combustion machine oil, the performance of each types of additives is shown as follows:
Shear stability and thermal stability
Poly-isobutylene (PIB) > polystyrene copolymer > ethylene-propylene copolymer (OCPs) > polymethacrylate (PMA)Viscosity index improvers have high molecular weight, highly viscous, some types are in the solid form. As a commodity, some solid viscosity index improvers are diluted in the base oil for the convenience to use. As the shear and thermal stability is a concern, viscosity index improvers could not be added a great amount.