Biodegradable fluids are a recent addition to the family of hydraulic fluids. Growing industrialization and its impact on environmental degradation due in part to the misuse and mishandling of lubricants has prompted European nations, Germany in particular, to formulate performance criteria for biodegradable hydraulic fluids and also to evolve standards for biodegradability [1, 2]. In Germany alone, per 1992 estimates, 50 million liters (13.2 million gallons) of mineral oils per annum were dumped into the drain water and ground, and 27 million liters (7.13 million gallons) of hydraulic oil disposed of into the surroundings [3, 4]. Today, those figures are probably much higher. The situation in the U.S. and other countries is similar. Per the National Fluid Power Association (NFPA) data, of 830 million gallons of industrial lubricants used in the U.S., only 75 million gallons are recycled—hardly 9% . The rest, it seems, are dumped into the environment. The impact of mineral oil polluting the environment is detailed in Chapter 9. Work is under way to address this problem before it becomes unmanageable; the basic approach seems to be “prevention is better than cure.” So as a first step, efforts are being made to reduce—if not eliminate—the usage of mineral oils. In this direction, steps have been taken to end the use of mineral oils in equipment that operates in water or near water sources and other environmentally sensitive areas. In addition, a range of biodegradable hydraulic fluids are now commercially available.
Biodegradable lubricants made their first appearance in 1980 to meet the needs of two-stroke engine oils. Ester-based fluids were first used in hydraulic systems in the late 1980s ; but vegetable-based fluids have also been in use since the 1980s. Applications of biodegradable lubricants have since expanded and include engine, gear, turbine, and slide way lubricants; metal cutting fluids; steel rolling oils; engine coolants; textile loom oil; and mould release oils [7, 8, 31]. Yet despite their wide range of availability, these fluids are still not widely used. In Germany, for example, annual consumption of these fluids  is estimated to be only 2.7 million to 4.5 million liters, which is indeed a small market share. A survey conducted by the British Fluid Power Association  also suggests that usage of these fluids is currently limited to hydraulic systems installed in highly sensitive watercourses where leaks or accidental spillage of mineral oil can contaminate soil, water, or groundwater. Biodegradable fluids have yet to make a significant mark in the industrial applications, and this is apparently due to the absence of either legal or technical compulsions. Admittedly, biodegradable fluids do not perform as well as other lubricants in use today. Nevertheless, given the importance of environmental protection and the demands of the future, users of hydraulic fluids must become aware of and understand the technicalities of biodegradable hydraulic fluids. Hence, a concise overview on this topic is outlined in this chapter.