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Lube-Tech


The resulting estolide still has a free acid group on the starting fatty acid which can be further esterified with alcohols. Linear or branched alcohols, both saturated and unsaturated, can be used here, for example. In this way, it is possible to produce estolides with a lower viscosity. Another alternative is to use polyols with a neopentyl structure, which results in very good cold- temperature behaviour and both good oxidative and thermal stability.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.131 page 2


The following explanations are intended to show that the estolides can go beyond the previous restrictions and, through the combination of the strengths of both complex esters, come close to an ideal type of ester.


Oxidation stability


Lubricants based on esters can be impaired at high temperatures due to oxidation and/or thermal decomposition processes and are thereby severely limited in their lubricating properties and effects. Decomposition breaks the lubricant down into volatile low molecular mass components. The consequences are unwanted variations in viscosity, loss of oil and excessive vapour formation due to evaporation of these volatile components. This also results in a loss of lubricating effect. The lubricants also lose their lubricating effect due to polymerisation and the products that arise from this.


Table 1: Modifications of the estolide ester and their effect


Table 1 shows the properties of the estolide with regard to various relevant parameters for the lubricants industry in direct comparison to a saturated and an unsaturated complex ester from the same viscosity class (ISO VG 320). It is clear that the complex esters achieve a good to very good performance while the strengths of the saturated and unsaturated variants lie in different areas.


Figure 3: Results of oxidation stability according to ASTM 2272 Figure 2: General comparison of estolides versus complex esters


Figure 3 shows the oxidation stability of the estolide compared to complex esters. In each case 1% of an additive package was used. As expected, the results show that the double bonds of the unsaturated complex ester favour radical oxidation. Hence the saturated complex ester performs far better than the unsaturated variant with regard to oxidation stability. Although the estolide molecule also contains double bonds, it exhibits better values not just in comparison to the unsaturated complex ester. In a


LUBE MAGAZINE NO.160 DECEMBER 2020 27


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