Synthesis Of Organic-Inorganic Compound Antioxidants For Ester Oils And Evaluation Of Their Antioxidation Properties

Lubricants,as the significant and indispensable compositions in the modern mechanical systems,play an important role in ensuring the safety and reliability during the service life of mechanical systems.Along with the enforcement of various more and more restrictive regulations for environmental protection,the development of novel biodegradable lubricants becomes increasingly urgent while the environmental awareness rises all over the world.Driven by this,a series of synthetic ester-based lubricants have been developed due to their high biodegradability,low toxicity,and environmentally benign nature.Their anti-oxidation stability,however,still needs to be improved in association with the reduction in life-cycle cost.But most of the organic antioxidants,especially sterically-hindered phenol and diphenylamine,have small molecular weight,which make them unstable and volatile,which affects the oxidation resistance of lubricating oil at high temperature.This paper is expected to improve the thermal stability of antioxidants through the combination of organic antioxidants and inorganic nanomaterials which includes carrying organic antioxidants through inorganic nano mesoporous materials,preparation of nanomaterials using the method of in situ encapsulation or modification.(1)Methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate(brand name T512)was loaded by mesoporous silica nanospheres(MSNs)to afford the antioxidant for synthetic ester lubricant oil.Rotary oxygen bomb tests,pressure differential scanning calorimetry and oven oxidation tests were conducted to investigate the effect of the as-prepared antioxidant on the antioxidant stability of di-iso-octylsebacate(denoted as DIOS).When MSNs are combined with T512 at a properly selected mass ratio,the oxidation of the DIOS base oil is greatly slowed down while the oxidation induction time is significantly prolonged.This may be attributed to the gradual release of T512 from the MSNs and the adsorption of the oxidation products into the channels of MSNs.(2)The mesoporous alumina was prepared by soft template method by using aluminum isopropanol as the aluminum source,poly(epoxy ethane)-poly(epoxy propane)-poly(epoxy ethane)three block copolymer as template.The effects of sintering temperature on the pore structure of alumina were investigated by IR,nitrogen adsorption desorption curves and transmission electron microscopy.The effect of the compound antioxidant of 3-(3,5-ditert butyl-4-hydroxyphenyl)propionate on the oxidation induction time of the ester lubricating oil was studied by a rotating oxygen bomb tester,high pressure differential scanning calorimetry and oven oxidation experiment.The results showed that compound antioxidant could significantly improve the antioxidant capacity of ester oil DIOS,and delay the change of acid value,viscosity and color to a certain extent.The mechanism of oxygen resistance is that organic antioxidants enhance the antioxidant capacity of lubricants through slow release after loading mesoporous alumina.(3)SiO2 coated octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate(denoted as T512@SiO2)was synthesized.The morphology and microstructure of the prepared sample were analyzed with a transmission electron microscope and a Fourier transfer infrared spectrometer.Moreover,the antioxidant performance of the prepared sample in di-iso-octylsebacate(denoted as DIOS)was evaluated by a series of methods including the oven oxidation stability test,rotary oxygen bomb test and pressure differential scanning calorimetry.All the tests showed that the T512@SiO2 exhibit excellent antioxidant capacity using as antioxidant additive for DIOS and can effectively inhibit the increase of the kinematic viscosity and acid value of oil during the oxidation process.(4)3-(3,5-Di-tert-butyl-4-hydroxyphenyl)propionic acid(DBHP)functionalized ZnO nanoparticles were synthesized by in situ surface modification technology.DBHP as an organic hindered phenol antioxidant was used as surface modifier,which can improve the dispersion stability of the prepared composite nanoantioxidant in the lubrication oil and scavenge free radicals produced during the oxidation process of oil.The structure and morphology of the composite antioxidant were investigated by FTIR,TEM,XRD and TG.The results demonstrate the thermal stability of the prepared composite antioxidants is greatly enhanced compared with DBHP.Moreover,rotary oxygen bomb test,pressurized differential scanning calorimetry and free radical scavenging method were utilized to evaluate the antioxidant behaviors of the prepared sample,which can effectively improve the antioxidant stability of the based oil.In addition,activation energy of the oxidation process was analyzed by model-free methods,including Flynn-Wall-Ozawa and Kissinger methods.The results indicated DBHP-ZnO had better antioxidant properties than DBHP under high temperature.