Structure Design And Mechanism Of LDHs As Multifunctional Antioxidant For Lubricating Oil

Under the influence of heat and light,lubricating oil and grease will be oxidized.Their performance will gradually fail,and even lead to corrosion of metal devices or equipment damage.The solution of oxidation delay and inhibition is adding antioxidants.Antioxidants have important commercial value,but there are still some problems and challenges in the research of antioxidants:(1)The commonly used antioxidants in the market are organic compounds,and there are obvious shortcomings: the thermal stability of phenolic antioxidants is poor;mine antioxidants have high toxicity,high cost and easy discoloration;ZDDP antioxidants have serious phosphorus and sulfur pollution;heterocyclic antioxidants are expensive.(2)Most antioxidants rely on capturing free radicals to achieve antioxidant,so they are consumer antioxidants,and they have short service life,so they are difficult to be applied in complex and extreme conditions,and the research on antioxidant mechanism lacks experimental and theoretical support.In view of the above problems,the main research contents are as follows:1.MgAl-LDHs with different metal ratios were prepared by hydrothermal method and nucleation crystallization isolation method.The free radical capture EPR experiment proved that LDHs had the ability to capture free radicals.The antioxidant properties of LDHs were systematically evaluated by DPPH and ABTS free radical scavenging experiments and ORAC oxygen free radical absorption capacity method.The antioxidant capacities of LDHs with different metal ratios were different,and the antioxidant capacities were as follows:2:1MgAl-LDH>3:1MgAl-LDH>4:1MgAl-LDH.Most importantly,the antioxidant mechanism of LDHs antioxidants was revealed by means of isotope tracer technology,synchrotron radiation,solid-state NMR and model simplification reaction.MgAl-LDHs is a kind of catalytic antioxidant,its antioxidant mechanism is the following three steps: Firstly,LDHs adsorbed lubricating oil.Then,the hydroxyl dehydrogenation of LDHs laminates quenches the free radicals,interrupts the chain reaction,and forms hydrogen vacancies in the laminates to form De-LDHs.Finally,the hydrogen vacancies in the De-LDHs laminates were restored.There are two hydrogen donors with hydrogen vacancies,on the one hand,H comes from the HOO· radical of the system;another source is the H· free radicals generated by alkanes in the lubricating oil system to fill the hydrogen vacancy and realize the regeneration of LDHs.The catalytic oxidation process of LDHs is a dynamic equilibrium process.Its unique non-stoichiometric consumption mechanism determines that LDHs is a long-life,green and environmentally friendly antioxidant.2.Based on LDHs intercalation assembly structure advantage,organic antioxidant diphenylamine(DPA)was intercalated into the LDHs interlayer.DPA-LDHs were prepared by co-precipitation method to study the synergistic antioxidant effect of different antioxidants.The ability of scavenging DPPH and ABTS free radicals was evaluated.The comprehensive evaluation of oxidation stability was carried out through the differential scanning calorimetry(PDSC)of lubricating oil and grease,rotating oxygen bomb test of lubricating oil and oxygen bomb test lubricating grease.The order of antioxidant capacity was3:1DPA-LDH > 2:1DPA-LDH > LDHs.There is a synergistic effect between LDHs laminates and interlayer guests in terms of antioxidant properties.Furthermore,based on the excellent UV resistance of LDHs material,Ultraviolet aging test and UV spectrophotometer were used to study the antiUV aging ability of oil added with LDHs.It was found that the addition of LDHs antioxidant significantly improved the UV resistance of lubricating oil.Therefore,LDHs is a kind of ’one-agent multi-functional’ lubricant additive with both antioxidant and UV resistance.