Machinery Lubrication magazine published by Noria Corporation
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degradation rate is low above 80 percent but high in the 30- to 70-percent range. This led the technical development group in an earlier stage to switch from the "high" reference oil (RL 130) used in the L-33 test with 80- to 90-percent degradation to an alterna- tive synthetic (RL 245) with degradation values near 70 percent. Nevertheless, the precision data of the new test marked a big step forward in comparison to existing tests, as the repro- ducibility of the CEC-L-33 test had been 19 to 38 percent in 1991, and the reproducibility of the Organization for Economic Cooperation and Development's test (OECD-301) using only water-soluble chemicals had been 19 to 40 percent in 1988. The round-robin exercise made the effect of the individual inocula (bacterial batches) quite obvious. Using two different inocula in the same lab brought the repeatability figures up into the range of the reproducibility. Thus, the relative activity of the micro-organisms was a factor with equal importance as the indi- vidual lab and operator. Two options were found to minimize or remove this undesired variation through microbial activity. First, each candidate test result must be achieved consecutively with a test of RL 245. In addition, the test result is valid only if the RL result is within the 10-percent range of the last round-robin test's average. Second, inoculum preconditioning, which involves putting each inoculum into a well-defined environment of standard nutrients before the oil test, was shown to reduce the number of individual species and the individual behavior of the inoculum. Benefits of the New Test Method The new test procedure is equally suitable for all types of lubricating oils, base stocks and formulations except water-sol- uble products. It avoids the use of toxic or harmful chemicals, reduces the overall consumption of chemicals and biomass, and increases test precision. It also offers a good way to simulate the fate of lubricating oil spilled in small quantities within the envi- ronment, such as during the operation of chainsaws or two-stroke engines. Laboratories beginning to perform this new test procedure will need training and experience until they are able to produce valid results. However, the test description contains a number of hurdles and checkpoints that help make insufficient accuracy obvious and grant a high degree of reliability for all valid results. Of course, there remain several issues that are not sufficiently covered by this or other test methods. For instance, no standard test method exists for simulating biodegradation of severe oil spills in a limited volume of water or soil, as in the cases of acci- dents with tank cars or mobile hydraulic systems. The main problem in such accidents is oxygen starvation that can lead to severe environmental damage. More research and possibly new test methods may be required to rate products for these real- world conditions. In addition, during the technical development group's work, a few tests were conducted with lubricating greases, which produced reasonable results. However, these tests were performed only with low NLGI grades and in a limited number, so the new test procedure cannot be recommended for lubri- cating greases in general. This may be the subject of further investigation and possibly an optimized test procedure. Please note that CEC test methods do not define limits for "good" or "acceptable" behavior of candidate oils. This is gener- ally left to those who use CEC test procedures to set specifications, such as the DEKRA product-specific rules guideline for sustain- able hydraulic fluids, which was the first specification using the new CEC-L-103 test. INdUstrY FoCUs Biodegradation of oils after 21 days 26 March - April 2014 | www.machinerylubrication.com The new test method (CEC-L-103-12) provides a procedure to evaluate the biodegradability of lubricants in natural water. It is performed in direct comparison with at least one reference oil. Lubricants tested may be base oils or contain usual additives. Base oils can be conventional mineral, hydrogenated/hydrocracked oils, PAOs, synthetics, natural (vegetable) esters or mixtures thereof. The required hardware for the test includes standard glassware, a shaker tablet and a high-temperature gas-chromatographic column and analyzer. The test medium is natural water from a defined source (comprising a defined level of micro-organisms) enriched with defined nutrient mineral salts. The test is set up to simulate biodegradation in natural water, i.e., ground water or open rivers, lakes or sea. There is also good correla- tion with biodegradation in wet soil with the presence of sufficient air/oxygen as well as in biological sewage plants. The lubricants tested are introduced by pre-dilution with a special solvent. After a 21-day degradation period, the oil content of the test flasks is compared with the original oil concentration and with poisoned (abiotic) reference flasks using oil extraction and a high-temperature GC analyzer. This procedure ensures all original oil and the products of primary biodegradation (long- and medi- um-chain hydrocarbons, esters, alcohols and fatty acids) are counted as "non-degraded" in the final test evaluation. Test results provide the percentage of biodegradation over three weeks. For example, a result of 70 percent would indicate that 70 percent of the test material has been degraded biologically over 21 days down to carbon dioxide, protein (cell material) or metabolites that are readily soluble in water and are on a direct biochemical path to ultimate degradation. Summary of the New Lubricant Biodegradability Test Procedure