With people ever more conscious of preserving the planet, the lubricants industry sees increased interest in products that minimize environmental impact. The industry has several tools for providing such products – one of them being tests that measure the biodegradability of lubricating oils.
Europes leading developer of test methods for lubricants is close to adopting a new one for biodegradability. Developers say it is more accurate and more convenient than existing methods. As such, they predict the new method will be used more widely, giving industry better assessments of the environmental threats posed by various products.
Lubricants are almost never good for the environment, so minimizing their impact comes down to two things: making them less toxic and ensuring that they degrade quickly. For 30 years, a method for testing biodegradability has been on the books of the CEC (the Coordinating European Council for the Development of Performance Tests for Fuels, Lubricants and Other Fluids). The method, CEC-L-33, was last updated in 2001, and it has been unpopular with some in the industry for a number of reasons, according to Martin Voeltz, an independent consultant based in Norderstedt, Germany.
The solvents used in this test procedure were identified as carcinogenic or hazardous for the environment, he wrote in a technical paper presented in January at the International Colloquium on Tribology, hosted by Technische Akademie Esslingen in Ostfildern, Germany. Voeltz is also chairman of a test development group, TDG-L-103, that CEC created in 2008 to rewrite the method. The solvents may not present hazards to lab employees conducting the test, but they forced labs to take special precautions when disposing of them.
CEC-L-103 is included in specifications for lubricants such as chainsaw oils and two-stroke marine engine oils, which are expelled during operation. It is also used for lubricants used in applications with high potential for spills into sensitive ecosystems, such as hydroelectric dams, or machinery at ports.
Oil and Water
According to the 2001 method, the test is conducted by introducing the candidate base oil or lubricant into a beaker of water, using a solvent to create a dispersion. The mixture is left for a prescribed time, allowing microorganisms to break down the oil molecules. The remaining oil is then extracted from the water using a hydrocarbon and analyzed to assess the extent to which it has degraded.
TDG-L-103 Secretary Ben Mueller-Zermini presented Voeltzs paper to the colloquium and discussed another problem with the 2001 version. The method suggested a few techniques for introducing the oil to the water, but did not prescribe one in particular.
So the labs are free to find out and choose the option that gives the best – or desired – results, Mueller-Zermini said, adding that this compromises the integrity of the test. The introduction procedure can have a or great impact on results, he explained. Researchers tested different procedures on bees wax and found that biodegradation over 28 days ranged from 13 percent to 82 percent.
There are alternatives to CECs biodegradability test. One of the best known is the Organization for Economic Cooperation and Developments OECD-301. Voeltz acknowledged that many lubricant formulators have used other tests because of dissatisfaction with CEC-L-33, but he contended that the OECD method is a poorer gauge for lubricants.
The CEC method is the only method written specifically to test the biodegradability of lubricants, he said. The OECD method was developed to test water-soluble substances with clearly defined chemistries. Base oils and lubricants are not water soluble, and lubricants, of course, are blends with components of different chemistries. Technically, OECD-301 is not meant to be used on them.
The CECs test development group set out in late 2008 to prescribe one specific method for introducing oils to water and to replace the toxic solvents used in the existing method. The groups work took so long because both tasks proved more difficult than expected. The group tried out a number of materials that proved to be inadequate replacements for the solvents.
Hydrocarbons are less hazardous, but unlike the incumbent materials, which included fluorine and chlorine, they allow the oil to rise to the waters surface, rather than sink. Once on the surface, oils that are particularly repellent to water can actually climb the glass walls of the flasks. When they are no longer in contact with the water, the microorganisms cant do their work.
Other substances disperse some oils better than others. This was unsatisfactory because it would lead to test results based on dispersion quality and not on biological criteria, Mueller-Zermini said. The group also tested a number of detergents and emulsifiers used in other applications to break up oil. Some of these did indeed prove to be effective dispersants, but researchers then had difficulty when it came time to extract the oil for analysis.
The test development group even tried several solid carriers, such as silica gel and glass fiber filters. However, these either did not hold the oil strongly enough or again did not allow adequate extraction.
A Mystery Material
In the end, the group settled on a substance with which they seem very pleased. It is a good trick for combining oil and water, Voeltz said. The CEC has declined to publicly identify the substance, other than to say it is a polar ether that is well known and readily available. The substance will be identified in the new method, which the CEC will offer for sale once it has been approved.
Voeltz said the test development group feels it has come up with a good method. According to his paper, the test demonstrated good discrimination between different oils and good repeatability at a test laboratory. At the time of the TAE colloquium, some work remained, including round-robin tests at other labs. According to the CECs website, that work has now been satisfactorily completed, and a vote to approve it is expected by July.
Voeltz noted that the new test, if approved, will be just part of the larger effort to reduce the environmental impact of lubricants. Water-borne microorganisms eventually break down most lubricating oils, so in some cases the key is to ensure that the lubricant does not kill wild-life before breaking down.
Depending on the duration of contact between the oil and water, it becomes more and more important for parallel tests of toxicity, he said. If the contact is to be very long, then eco-toxicity tests are even more important than biodegradability.