Meeting the Challenges Posed by Environmentally Acceptable Lubricants: Thickener Systems for Unsaturated Polyol Ester Base Oils Mark Wilkinson & Steve Nolan R S Clare & Co Ltd Liverpool, Englandt
Introduction
ἀ ere has been an increasing and continuing trend in recent years towards biodegradable, low ecotoxicity greases. ἀ e recent introduction of the Vessel General Permit (2013) regulations, which mandate the use of Environmentally Acceptable Lubricants, has focussed the grease industry’s attention on the issue of formulating such greases. A wide range of biodegradable base oils has been available for many years. However, substantial market penetration has been limited by a combination of commercial and technical challenges. ἀ e commercial challenge has been the high price of most biodegradable base oils; high performance esters, such as the fully saturated diesters used in high-
temperature applications, are several times as expensive as typical Group I or Group II mineral oils. Even with regulation requiring the use of biodegradable base oils, such a price difference will present a substantial commercial obstacle to their use. ἀ e most commercially attractive – in other words, the cheapest – biodegradable base oils are vegetable oils and their synthetic analogues, the TMP esters. Vegetable oils have been assumed to present difficult technical challenges for manufacturers; the poor thermal and oxidative stability of the polyunsaturated component has deterred investigation of their use as bases for lithium soap greases. Synthetic TMP oleate appears to offer a useful compromise for such greases, with better stability than -6VOLUME 79, NUMBER 2
vegetable oils and lower price than saturated diesters. An alternative approach would be to reduce the thermal stress on the oil by use of a different soap. A lithium/calcium mixed base soap would typically reduce the maximum temperature required during processing by 10-15 °C; using an anhydrous calcium soap would reduce the temperature by 50 °C or more compared to a pure lithium soap. Where the grease is not intended to be subjected to high temperatures – and this will include most marine applications impacted by the VGP regulations – such thickener systems would seem to be appropriate. We have therefore decided to
