November / December 2019 NLGI Spokesman

Viscometric and Low Temperature Behavior of Lubricants with Blended VI Improvers Erik Willett, Andrew DeVore, Daniel Vargo Functional Products Inc. 8282 Bavaria Road, Macedonia, OH 44056 USA www.functionalproducts.com Abstract Polymeric viscosity index improvers (VII’s) are routinely used to modify oils to the proper viscosity and VI for lubricant applications. There are many commercially available polymer chemistries to choose from when selecting a VII product for formulation. Improper selection of a polymer can drastically influence low temperature behavior of lubricants. This study investigates the appropriateness of different polymer chemistries in Group II, Group III, and PAO fluids and the polymers’ effects on pour point (PP) at low temperatures (down to -60 C). This study finds that the effects of polymers on VI and PP depend on the base oil. A number of cases are reported and explained on the basis of the dilute to semi-dilute transition, c*, of the polymer and changes in base oil solvency with polymer content. This paper also proposes several lubricant formulation strategies for synergistic combinations of VII’s for maximum VI improvement and minimal effect on PP and low temperature viscosity. These results provide useful information for development of new greases with desirable low temperature performance.

1. Introduction Viscosity Index and Lubrication The viscosity of oil decreases as its temperature increases. This occurs because the increased thermal (kinetic) energy allows the individual oil molecules to move faster and overcome the attraction or ‘cohesion’ between molecules. Variation in viscosity of in-service lubricant with temperature during start-up and operation of equipment or aging can cause the lubricant to fall out of the viscosity grade for the application. The rate at which viscosity declines with temperature, from 40 to 100 C, is expressed as the viscosity index (VI).[1] In petroleum-based oils, VI can range from <60 in naphthenic oils between 80 and 120 in paraffinic API Groups I and II and >120 in Group III oils. Synthetic oils and esters can reach VI’s of over 200.

Commercial lubricant VI varies widely. For example, industrial gear oil specification ANSI AGMA 9005 specifies four distinct ranges of VI for industrial applications: 90, 120, 160, and 240.[2] In many cases, a modest VI (< 90) is sufficient and presents the lowest cost up front. However, vehicles, mobile equipment, and other applications in areas that experience wide seasonal temperature swings benefit from multi-grade (all season) oils. In varying temperature environments, it is necessary to replace low VI products to meet changing lubrication requirements. This shortens oil drain intervals, increases downtime, and poses the risk of cross-contaminating old and new lubricants.

Applicability in Greases While the basis of this work - simple formulations of VI improvers in various fluids – applies most directly to lube oil formulators, the results of this work may be useful for grease making. This study addresses two issues relevant to the grease community, effects of polymers on grease properties and formulation guidelines.

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