European ecolabels for biodegradable hydraulic oils — a challenge to base material producers and formulators

‘ Ecolabels’ are a means to guide the user to more environmentally favourable products. With regard to lubricants, the German Blue Angel UZ-79 and the Swedish standard SS 155434 for biodegradable hydraulic fluidsare perhaps the most important. Whereas the Blue Angel is optional, the Swedish standard SS 155434 is a legal requirement: hydraulic fluidsnot fulfilling the criteria of SS 155434 are not permitted on the Swedish market. Version 4 of SS 155434, which came into effect in July 2000, introduced new and more stringent ecological requirements. In view of the growing importance of the Swedish market for biodegradable hydraulic oils, the authors' company launched a research programme in early 2000 with the aim of offering SS-155434-compliant oleochemical base oilsby the end of the year. First, the effects and the plausibility of the new assessment criteria for the ready biodegradability of raw materials were studied. A systematic comparison based on chemical oxygen demand (COD) and theoretical oxygen demand(ThOD) evaluations confirmed that unqualified reliance on the COD parameter can lead to false positive evaluations. The studies also showed, however, that results based on COD determined by chemical analysis are valid, provided a suitable oxidation method is used and the completeness of the oxidation is carefully monitored. Moreover, it was shown that the required use of the reference parameter ThOD does not necessarily require complicated elementary analyses of the test substance. Even in the case of oleochemicalproducts with indefinable structural formulas(C-chain fractions, alkoxylatedcompounds), structural estimatesenabled sufficiently accurate ultimate oxidation values to be calculated. The studies also showed that the restriction to only two degradation test methods is scientifically unfounded. An extension of the approved test methods to include the scientifically accepted CO2 headspace test and two-phase closed bottle test would enable existing data to be used without detracting from the environmental standard. On the basis of more recent degradation studies, it has been shown that synthetic esters, especilay various saturated and unsaturated TMP fatty acid esters, satisfy the stringent sriteria of the new SS 155434, Supplementary studies of low-viscocity XXX-oils (hydrocrackates) and mixtures of XXX-oils and synthetic esters indicated that this product class could be optimised to make it satisfy the criteria of the Swedish ecolabel.