Avaliação da estabilidade de bases lubrificantes minerais e sintéticas por calorimetria diferencial de varredura e oxidação acelerada

Abstract

Lubricating oils are formulated from the blend of basic oils and additives. The mineral-based oils are classified as paraffinic or naphthenic and are obtained by petroleum refining processes. In this study, the feedstock used to produce synthetic-based oils was the fatty acids of bovine tallow, soybean and castor oils. The feedstock composition is decisive in the characteristics of its products. Biolubricants are esters produced from bio-oils and long chain alcohols which have lubricating properties, such as mineral-based oils, with the advantage of being renewable, non-toxic and biodegradable. However, they have poor thermal and oxidative stability, which leads to failures in the application or use of the material. The comparative study of the blend of biolubricants and antioxidants aims to improve the bio-based lubricants properties. In this context, the evaluation of the thermal and oxidative stability of lubricating oils in accelerated tests, such as Differential Scanning Calorimeter (DSC) and Rancimat, is important for the development of these products before their application. For the DSC, the cooling curves at low temperatures and the oxidation onset temperature (OOT) were evaluated. In Rancimat, the induction time was analyzed until the sample reaches a certain level of oxidation in hours from the pure biolubricants and with increments at different concentrations of the antioxidant additives Di-tert-butyl metyl phenol (BHT) and tert-butyl-hidroquinone (TBHQ). These results were compared to those of the mineral lubricants bases commercially available in Brazil. The castor oil biolubricant achieved similar or higher properties than the mineral bases in all the studied analysis, except for the acidity index. Soybean and bovine tallow biolubricants also obtained similar properties, except for the melting point and cold properties, for the bovine tallow, and oxidative stability in the case of soybean biolubricant. However, these problems can be solved using other types and concentrations of additives.