Exploratory Studies on Borate Esters as Dropping Point Enhancers

摘要

Borate esters are known for enhancing the dropping point of lubricating greases containing lithium 12-hydroxystearic acid-based soap. Several vendors are supplying packages of dropping point enhancers with different compositions and formulations of borate esters. Even though this technology is not very new, the basis of selecting a suitable dropping point enhancer is not clear. There are only a few studies showing their effectiveness as complexing agents added at the end of the manufacturing process. However, more studies on storage stability and effects on other properties in comparison to complex greases with boric acid are required. The performance of these additives is thickener-dependent, and the borate may liberate alcohol which either remains in the grease or evaporates out. In this paper, the authors discuss the evaluation of different dropping point enhancer borate ester packages and the development of a lab-prepared borate ester to enhance the dropping point of lithium soap greases thickened with lithium 12-hydroxystearate with respect to process, physical and chemical properties. The dropping point of lithium 12-hydroxystearic acid-based grease was 202°C; the lab-prepared borate ester enhanced its dropping point to 269°C, and to 276°C in the presence of zinc dialkyldithiophosphate.