Additives Modifying the Rheological Properties of Lubricating Oils

1 Additives Modifying the Rheological Properties of Lubricating Oils 

A lubricant should be characterized by its viscosity at low temperature (-18°C) to account for its behavior during cold weather starting and by its viscosity at high temperature (100°C). Values of these two viscosities are based on the SAE classification. See Chapter 6. 

A refinery lubricant base stock is obtained having an viscosity index around 100, certain hydrotreatments result in Vi s of 130, and paraffin hydroisomerization provides oils with a VI close to 150. 

Nevertheless, a great majority of lubricating oils is obtained having bases whose VI is around 100. 

The function of viscosity additives is to improve the viscosity index so as to obtain multigrade oils. The problem is to use materials that, by only slightly increasing the low temperature viscosity, are capable of counterbalancing the decrease in viscosity when the temperature increases. 

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