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are not well defined and have often been used interchangeably within the lubricant industry. Therefore, it may create confusion among people regarding its environmental impact. If a lubricant is termed ‘biobased’, it does not always mean fossil- free or biodegradable. Companies often use the ‘bio’ tagged terms to advertise lubricants as having desirable environmental properties which may have lower environmental impact to some extent.
Dr. Lou A. Honary from Environmental Lubricants Manufacturing, Inc. has summarised the differences between biobased and biodegradable lubricants [1]. According to him, biobased lubricants are made with renewable oils and are biodegradable, while biodegradable lubricants may come from mineral oils that are not biobased. For instance, canola or soybean oil-based lubricants are biobased and biodegradable lubricants. On the other hand, PAO-based oil can be biodegradable if it passes the OECD 301 biodegradability test, but it is not biobased.
Water-based or water-soluble lubricants are composed of water either as base fluid or as additives depending on applications and formulations. In WBLs, the water content can vary from roughly 10% to 70%. Water can be mixed with esters or glycols in equal proportion along with other performance additives. On the other hand, water can also be used as an additive with base fluid such as glycerol. In all cases, the associated chemical compounds should be water-soluble, non-toxic, and biodegradable to enhance the sustainability aspect.
There are several environment-friendly lubricant categories such as biobased/biodegradable, sustainable, and Environmentally Acceptable Lubricant (EAL). The point to notice here is that WBLs can be regarded as sustainable lubricants by revisiting the definition of sustainable lubricant. However, a complete life cycle analysis of the WBLs is necessary in order to classify it as a biobased or biodegradable lubricant.
Advantages of water-based lubricants It is very difficult to find an eco-friendly solution that can deliver similar performance as a fully formulated fossil-based lubricant. Currently, researchers have been exploring different innovative environment- friendly lubricant technologies to fulfil the upcoming requirements. The research interest in water-based lubrication has grown due to its many advantages over conventional lubricants, including lower friction, easy degradability, low emissions, environmental friendliness, exceptional cooling performance and flame retardancy.
Figure 1: Comparison of friction behaviour among mineral oil, synthetic oil and WBL [2]
Figure 2: Hydrogen-bonded layer in glycerol aqueous solution confined between ferrous substrates [3]
As mentioned earlier, water alone cannot deliver the lubrication and tribological performance that is required in highly loaded bearings and gears contact. Therefore, compounds such as polyglycol, glycerol, esters and different ionic liquids are used with water in different concentrations depending on the application. Recently, glycerol and water solution has caught the attention of the research community due to its tremendous friction reduction capacity as
10 LUBE MAGAZINE NO.179 FEBRUARY 2024
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