A Fresh Look at Lithium Complex Greases Part 1: How Did We Get Here? J. Andrew Waynick NCH Corporation
Abstract In 1942, five U.S. Patents were issued with Clarence E. Earle as named inventor. These five patents defined simple lithium soap greases for subsequent decades. However, simple lithium soap greases were limited in their high temperature utility owing, at least in part, to their dropping points – typically about 200 C. In August, 1959, only months after the Earle patents expired, a lithium complex grease patent issued that featured for the first time what would become the most common compositional approach. Stearic acid was used as the long chain fatty acid. An alkyl diester of sebacic acid was also used. Reaction with aqueous lithium hydroxide accomplished the thickener formation. Reported dropping points were between 248 C and 276 C or higher when mineral oil was used as the base oil. Since that 1959 patent, many modifications and advances in lithium complex grease formulation and manufacturing have been documented. All such development work can be placed into one or more of only three categories: formulation change, process change, or manufacturing equipment change. Interestingly, no organized and critical review of all the decades of development of lithium complex greases can be found in the published literature. Due to the very large amount of such development work, an exhaustive review is beyond the scope of this paper. However, a review that focuses on some of the most important of those developments can be provided. This paper provides such a review. By doing so, explanations of certain physical and chemical behavior never fully documented are brought into full focus. This, in turn, allows those involved in the formulation and manufacture of lithium complex greases to gain an improved perspective on potential future paths to improve the cost-effectiveness of these greases. Given the recent sharp rise in lithium prices, such an improved perspective is more relevant now than ever before. Beginnings As early as the late 1930’s, it had been reported that lithium soaps were not effective grease thickeners.[1] This was proven incorrect when five U.S. patents with Clarence E. Earle as the named inventor issued in 1942.[2-6] Those patents used lithium stearate as the thickener and provided the defining foundation for every lithium-based lubricating grease that would be subsequently developed. Within less than one year of the issuance of the Earle patents, Harold M. Fraser filed for a U.S. patent using lithium 12-hydroxystearate as the thickener. That patent issued in 1946.[7] Fraser claimed that such greases had several improvements over lithium stearate-thickened greases, including superior batch to batch consistency, improved initial structure, and improved shear stability. These improvements were optimized by mixing the batch as it cooled from its nearly melted state at about 218 C. This was in contrast to lithium stearate greases where such mixing resulted in less initial structural uniformity and inferior structural stability. However, by the time Fraser’s patent issued, additional developments in lithium-based lubricating greases were well underway. A good discussion of those developments has already been provided elsewhere.[8] A few representative examples are discussed here. - 10 NLGI Spokesman | VOLUME 85, NUMBER 1 | March/April 2021
