Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE Figure 9. Results of the beverage bottle tests.
As expected, the results of the series of tests show that the hydrolytic stability of pentaerytrithol is greater than that of trimethylol propane, which, in turn, is greater than that of neopentyl glycol.
According to the test results very hydrolytic stable products can also be produced with complex esters which screen the ester bond even more effectively. Furthermore, the partially aromatic structures of the dicarboxylic acids used have structures that lead to an additional resonance stabilisation. This property plays an important role especially in the production of lubricating greases.
Thermal stability Figure 10 shows the results of the high-pressure DSC measurement. The graphs, on which Figure 10 is based, have a significant exothermic peak at approx. 180°C up to 200°C in the range greater than -30 J/g. An explanation for this reaction could not be found. Since this occurs in both, saturated and unsaturated variants, participation of the double bond can be excluded. The energy tint of the peak is too high for a secondary reaction with any existing free fatty acid. In a standard DSC under normal pressure, this behaviour does not occur.
A clear reaction peak can be seen for all esters at approx. 440°C which could not be completely
LUBE MAGAZINE NO.150 APRIL 2019 33 Figure 10. Results of the HP DSC under N2 [100 bar]. Summary
The suitability of an ester as the base fluid is decided by a wide range of properties, mainly those listed in Figure 11. The selection of raw materials or the modification of the manufacturing process, can have a big impact on these properties. However, it is not possible to improve all the criteria at the same time. In the case of the iodine value of the fatty acids considered here, the reduction leads to improved thermal and oxidative stability. At the same time, however, the esters have a significantly worse cold behaviour, as well as a poorer hydrolytic stability. The esters must be carefully matched to the respective application. General statements, such as saturated esters are more stable, are not, in general, correct.
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recorded due to the maximum measuring temperature. Therefore the “onset” was evaluated. As can be seen in the Figure 10, this will enter into force for all investigated products at approximately the same temperature, regardless of the presence of unsaturated groups or the molecular weight. It is, therefore, concluded that there is a pyrolysis with subsequent evaporation.
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