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“What are the differences between biodegradable lubricants and bio-based lubricants?”
Because environmentally friendly lubricants are somewhat new and not as clearly defined as other lubrication concepts, many people struggle with certain terms such as bio-based and biodegradable. When discussing these types of lubricants, it is imperative to apply the proper terminology and to understand why these words should not be used interchangeably.
The term bio-based specifies the origin of a lubricant. This involves the annually renewable raw material utilized to construct the lubricant’s base stock. Some examples of these base stock materials would be soybean, rapeseed and sunflower products. These base stocks can offer good lubricity, flash point and viscosity index properties but often are inferior in regard to their oxidation stability. Although their usage is not widespread, they have their place in certain hydraulics, total-loss systems and environmentally sensitive areas.
Just as what characterizes bio-based lubricants centers on the front end of the lubricant’s creation, what identifies biodegradable lubricants is more focused on the back end. It considers how the environment has a tendency to break down the lubricant, if exposed, as well as the function and timeframe for this breakdown to occur.
The ASTM D6064 standard defines biodegradability as “a function of degree of degradation, time and test methodology.” Other terms generally used to describe a lubricant’s level of biodegradability are “readily biodegradable” or “primary degradation” and “inherently biodegradable” or “ultimate degradation.”
Primary degradation measures the reduction in the carbon-hydrogen bond and is determined with infrared spectroscopy. Ultimate degradation assesses the evolution of carbon dioxide through the degradation process. The ASTM D5864 standard is one of the most common methods for verifying this level of biodegradability.
It is important to understand the differences between biodegradable and bio-based lubricants. While some lubricants may be bio-based, this does not necessarily make them biodegradable. This is true for a couple of reasons. First, a bio-based lubricant might not be the only base stock in the lubricating oil. Second, in rare occasions, the bio-based base stock, though agrarian in nature, may not be biodegradable. On the other hand, some synthetic base stock lubricating oils can offer biodegradable benefits as well.
By recognizing these differences and knowing that specific test parameters exist to determine whether a lubricant is biodegradable, you should be able to apply the proper terms when discussing environmentally friendly lubricants.