Synergistic lubrication effect of antioxidant and low content ZDDP on PFPE grease

Abstract

Purpose The purpose of this study is to reduce the use of Zinc dialkyl dithiophosphates (ZDDP) and improve the frictional properties and thermal oxidation stability of Perfluoropolyether (PFPE) grease by adding antioxidant additives. The addition of antioxidants can reduce the consumption of ZDDP as an antioxidant, thus improving the anti-wear efficiency of ZDDP and reducing the excess phosphorus element in the grease. Design/methodology/approach In this study, an antioxidant with good comprehensive performance was selected from several antioxidants by tribological tests and high-temperature tests. Then, the effect of its combination additive with ZDDP on PFPE grease was investigated. The anti-wear property, anti-friction property, thermal oxidation stability and extreme pressure property of greases containing different proportions of ZDDP and antioxidant were tested by four-ball tester and synchronous thermal analyzer (STA). The effects of additives on properties of grease were analyzed by SEM, EDS, LSCM, XPS and FT-IR. Findings The research shows that 2,6-Di-tert-butyl-4-methylphenol (BHT) can be used as an antioxidant in combined additives to reduce the antioxidant reactions of ZDDP, thus improving the anti-wear efficiency of ZDDP and further enhancing the anti-wear performance of the grease. Moreover, BHT and ZDDP have a synergistic effect on the high temperature performance of the PFPE grease due to their different antioxidant mechanisms. Social implications In this paper, the problems related to PFPE grease are studied, which has a certain guiding effect on the industrial application of fluorine grease and the related formulation design. Originality/value In this paper, the properties of PFPE grease under different lubricating condition were studied. The synergistic lubrication effect of antioxidant and ZDDP are discussed. It provides experimental and theoretical support for reducing the content of ZDDP and improving the performance of additives.

Comparative investigation on antioxidant properties of phenolic compounds in lubricants

“…For the sake of investigating the inhibitory effect of three phenolic substances on lubricants oxidation, the reaction energy barrier of phenoxy free radicals to 3, 26-dimethyl octacosane was calculated comparing with that of alkoxy free radicals to 3, 26-dimethyl octacosane, as shown in equation ( 4)- (7). The energy barrier of alkoxy radical reaction with lubricants was 156.88 kJ/mol, and that of phenoxy free radical, 2-tert-butylphenoxy and 2,6-di-tert-butylphenoxy were 146.10 kJ/mol, 224.39 kJ/mol and 459.86 kJ/mol, respectively.…”

“…(5) (6) (7) In general, the hydrogen supply capacity of molecules and the stability of free radical generated by the hydrogen supply reaction are related to the bond dissociation energy of bonds for hydrogen supply and the energy difference from the HOMO to the LUMO of molecules. The lower the bond dissociation energy of O-H bond and the energy difference from the HOMO to the LUMO of molecules, the stronger its hydrogen supply capacity, and the more stable the free radical generated by the hydrogen supply reaction [12].…”

“…At present, zinc dialkyldithiophosphate, aromatic amines and phenols are widely used antioxidants [7,8]. Zinc dialkyldithiophosphate is kind of multi-effect additive.…”

Design of a high-temperature grease by BP neural network and its preparation and high-temperature performance studies

“…Because the testing time of the UMT experiments is limited, it can only explain the high-temperature lubrication performance in a short time but long-term operation. Considering that the main failure modes of greases in high-temperature environments are oxidation deterioration and high-temperature evaporation, we have done several sets of thermal gravimetric analysis (TGA) experiments and differential scanning calorimetry (DSC) experiments of greases to judge the long-term stability of the grease in high-temperature environment (Xu et al , 2017; Zhang et al , 2021; Qi et al , 2021). Therefore, TGA and DSC experiments were done for the grease to explain its long-term lubrication performance in high temperature.…”

A review of advances in tribology in 2020–2021

“…6). Qi et al [55] found that adding antioxidants to additives to reduce the antioxidant reaction of additives can enhance the temperature stability and antiwear properties of lubricating greases.…”