Síntese de ésteres lubrificantes a partir de óleos de moringa (Moringa oleifera Lam.) e da tilápia do nilo (Oreochromis niloticus) e polióis sem o hidrogênio β

Abstract

Sustainability has been established as a research area over the last few years, raising a series of themes related to environmental preservation. In view of this, the search for biosafe and efficient alternatives to fossil products is increasingly necessary. The development of lubricants from renewable oleaginous sources (biolubricants) has stood out, since these products have desirable characteristics, such as high viscosity, low volatility and, above all, they are non-toxic and biodegradable. The inedible oils extracted from the seeds of moringa (Moringa oleifera Lam.) and the viscera of the Nile tilapia (Oreochromis niloticus) can be used as raw material for the production of biolubricants, as they have high levels of oleic acid, which provides good thermal stability, and are produced with good yields. However, the presence of unstable groups in the triacylglycerol (TAG) chain limits its use in extreme temperatures. Thus, chemical modifications in the TAG chain can be used to optimize the use of vegetable and animal oils in lubrication processes. In this perspective, the objective of this work is to synthesize new esters from moringa, Nile tilapia, and oleic acid oils using commercial and non-commercial polyols that do not contain β-hydrogen. The proposed synthetic strategy began with the hydrolysis of TAGs from moringa and tilapia to obtain free fatty acids (FFAs), followed by the esterification reaction of FFAs with polyols without β-hydrogen (trimethylolpropane – TMP and pentaerythritol – PE). Additionally, five polyols analogous to TMP and neopentylglycol (NPG) were synthesized and used for the synthesis of polyesters with oleic acid. All polyesters synthesized in this research showed high results for viscosity, viscosity index (VI between 153 and 221) and thermo-oxidative stability (Tonset between 258 and 323 ºC). DSC analyses have shown that the use of NPG and TMP polyesters are ideal in low temperature applications (melting point between -47 and -0.1 °C). On the other hand, PE polyesters are in a gel-like form at room temperature. Rheological tests performed with tilapia and oleic acid polyesters indicated a predominantly Newtonian behaviour at temperatures of 20, 40 and 60 ºC. The tribological behaviour of oleates, verified through the four-ball test, showed the formation of an efficient tribofilm with low values of friction coefficient and wear scar diameter, indicating that non-commercial polyols analogous to TMP and NPG are promising for the synthesis of new lubricants. Furthermore, all polyesters were considered biosafe (non-toxic) when tested with the Artemia salina and Zebrafish models. The results of this research demonstrate that polyesters obtained from natural sources are advantageous substitutes for fossil lubricants, as they present good thermal stability, are biosafe and, above all, come from renewable sources