Overcoming Obstacles in Water Resistant H1 Specialty Greases Using Polymers Erik Willett, PhD Functional Products Inc. Macedonia, OH USA
Abstract Water resistance is a critical performance aspect of grease that often becomes an obstacle in developing non-industrial greases for the H1 incidental food contact or biobased grease markets. A specialty grease formulation may perform well in many categories but fail water resistance testing by methods such as ASTM D4049 (water sprayoff) or ASTM D1264 (water washout). Improving water resistance late in the grease development process can involve extensive changes to the formulation. For example, HX1 base stocks are highly refined, which results in greases with low cohesion and little ability to resist the ingress of water as well as poor solubility for additives needed to fix the problem. This work shows how two HX1 grease polymers may be used in combination with a diverse range of HX1 base stocks to improve the water resistance of full PAO/mPAO base oil blends at significant cost reduction. Conversely, greases formulated from biobased oils have high cohesion, but most natural or synthetic esters are limited to low ISO viscosity grades and have affinity for water. A higher treat rate of thickener is often used, but this can hinder fluidity and have a negative effect on the economics of the grease. This paper includes examples of how biobased viscosity modifiers can be used to build base oil viscosity, reduce thickener treat rates, and greatly improve water resistance of biobased grease. In this work, the greases were made using hydrous calcium and calcium complex thickener from pre-formed salts, but the principles discussed in this paper apply broadly to other thickener types. Introduction Much of the longstanding experience in the grease industry is based on petroleum oils. Production-wise, 70% of reported grease production is lithium or lithium complex grease, and 86% uses conventional mineral oil with 7%, 5%, and 1% using synthetic, semi-synthetic, or biobased oils, respectively.1 Best practices and starting points for high performance grease formulating are well established based on the structure and properties of paraffinic or naphthenic oils and bright stocks and their interactions with additive chemistries that were developed alongside greases. Trends continue to push for reducing the use of petroleum oils in lubricants and greases for various reasons. Highly refined or synthetic base stocks offer improved oxidative and thermal stability and the potential for longer service life. Removal of organic substances containing aromatic carbon groups can greatly reduce the aquatic toxicity of greases, especially those used in environmentally sensitive applications. Whichever the reason, formulators who wish to develop greases in the specialty areas of NSF H1 incidental food contact (which tend to include synthetic base oils such as polyalphaolefins or PAOs) or environmentally acceptable lubricants often find unique challenges that were easily solved under standard practices in petroleum oil. The body of knowledge and experience is largely focused on industrial lithium grease, while specialty grease formulators are often confronted by a constrained list of allowable raw materials plus a shortage of know-how when exploring new greases or markets. -8NLGI Spokesman | VOLUME 85, NUMBER 6 | January/February 2022
