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Lube-Tech


can alter the behaviour of elastomers and therefore also have an effect on seals. These influences include pressure, temperature and exposure to solar radiation, for example, but also contact with the lubricant itself. Contact with the lubricant may result in lubricant constituents lodging in the seal or the dislodging of sealing material components (Vidović, 2014). Seals swell or shrink accordingly when this happens.


The results shown in figure 8 were obtained for acrylonitrile butadiene rubber (NBR1), which is regarded as moderately compatible with ester oils. The swelling behaviour of the ester is influenced by the polarity, the molecule size and steric effects but also by the accompanying substances.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.131 page 5


Biodegradability Biodegradable lubricants are becoming even more important since the emission of substances into the environment cannot be completely avoided in a number of applications. This applies not only in the case of loss lubrication. For example, in agriculture, forestry or the building industry, significant amounts of lubricant can get into the environment due to leaks and other defects. The maritime ecosystems are particularly sensitive. This is why there are now a number of laws, regulations and bodies such as the Vessel General Permit (VGP), EU Ecolabel and Oslo and Paris Conventions (OSPAR) which prescribe the use of biodegradable lubricants.


Figure 8: Results of seal compatibility according to DIN ISO 6072


Saturated short-chain esters only perform little beneficial here and for low ISO-VG classes often lie above the critical level of 10% swelling. The behaviour of the unsaturated esters is far better due to their long-chain monocarboxylic acids.


In a direct comparison the estolide is almost on a par with the unsaturated complex ester, even though it has a saturated component due to the capping fatty acid. However, this is situated in the immediate vicinity of the base fatty acid where the influence is able to develop less strongly.


30 LUBE MAGAZINE NO.160 DECEMBER 2020


An important role in biodegradability is played by the molecule size and polarity but also by the resistance to hydrolysis of products. Thus the biodegradability of the ester oils decreases with increasing ISO VG class. As can be gathered from Figure 9 the biodegradability of the unsaturated complex ester is slightly lower than that of the saturated variant due to the improved resistance to hydrolysis. All the more astonishing is the estolide’s very good biodegradability with similarly good resistance to hydrolysis and a high ISO VG class. This can be partly explained by the emulsion properties of the estolide. Besides the aforementioned factors, an important role is undoubtedly played by other effects such as transportability across biological membranes.


Figure 9: Results of biodegradability (28 days)


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