Synthesis, tribological properties and oxidative stability of polyol esters base oils containing pentaerythritol complex esters

Abstract

The performance requirements for extreme pressure and anti-wear properties, as well as oxidative stability, are increasingly stringent for MIL-PRF-23699G Enhanced Ester (EE) for aviation turbine engine lubricants. An oligomerization reaction of pentaerythritol through direct esterification using pentaerythritol and dibasic acid catalyzed by tetrabutyl titanate in xylene solvent, was employed to achieve the low-polymerization reaction of dibasic acid and pentaerythritol. A two-step synthesis process yielded a mixed ester comprising dibasic acid pentaerythritol complex ester and pentaerythritol tetrapentanoate. These mixed esters demonstrate excellent viscosity-temperature performance and good oxidative stability, significantly enhancing the extreme load-carrying properties and anti-wear properties of pentaerythritol tetrapentanoate. Molecular dynamics (MD) calculations indicate that complex esters possess higher adsorption energy and molecular interaction energy, enhancing the possibility of ester molecules adsorbing on metal surfaces and producing stronger oil film that can withstand large loads. The novel 5 mm2/s pentaerythritol ester containing diacid pentaerythritol complex esters exhibits improved viscosity-temperature performance, high-temperature oxidation resistance, and better tribological properties. Therefore, the novel pentaerythritol esters show potential for application in 5 mm2/s EE aircraft engine lubricants.