Testing, application, and future development of environmentally friendly ester base fluids

Abstract

Biodegradation test methods have been compared with regard to test conditions and test parameters. It has been shown that three methods are, in principle, suitable for non-water soluble products. These are the Sturm test (OECD no. 301B), the MITI test (OECD 301 C), and the CEC L-33-T-82 test method. A comparison in an actual test showed that the CEC test gives the highest biodegradation values, while the Sturm test and the MITI test give lower values. It is noted that the CEC test measures the amount of material used for both energy production and growth of the biomass, while the other methods measure only the material used for energy production. A possible explanation for the difference between the Sturm and the MITI test results is given. The CEC test is shown to be more suitable for the lubricant industry. Applications of biodegradable lubricants are reviewed, particularly hydraulic fluids. It is shown that rape seed oil (natural ester) and synthetic polyol esters have similarities regarding structure but also significant differences. This results in much better thermal and oxidative stability for the synthetic esters. These also offer the possibility of making a range of products of different ISO grades with similar properties. Brief consideration is given to future potential, notably for biodegradable four-stroke lubricants. Finally, there is a timely reminder that, owing to the present limited availability of natural oils and fats and their cost, only 19% of the market for mineral oil base fluids could be replaced by natural oils and fats and their derivatives.