Study On Protection Mechanism Of Antioxidant For NR Thermo-oxidative Aging With The Combine Of Molecular Simulation And Experimental Method

Natural rubber(NR)has a wide range of uses in the industrial field.However,due to the isolated double bonds in its molecular structure which are vulnerable to be attacked.so in practical applications,the rubber materials are oxidized in the conditions of high temperature and oxygen,which results in the decrease of operational performance.In order to prevent the thermal-oxidative aging of natural rubber,a variety of antioxidants are often added in the NR during the preparation of the vulcanized rubber.The antioxidants added in the NR antioxidant can capture the active free radicals to effectively inhibit or delay the thermal-oxidative aging of natural rubber.Antioxidants commonly used in the industrial field are p-phenylenediamines and diaryl-substituted secondary amines,but the choose of antioxidants for rubber composites is still focus on the trial and error of the experiment,plus with the long aging test time and the big error fluctuation.So the analysis of the thermo-oxidative aging mechanism and the antioxidant protection mechanism still are not enough.In this study,the antioxidants selected are N-(1,3-Dimethylbutyl)-N-Phenyl-p-phenylene Diamine(antioxidant 4020)and N-phenyl-2-naphthylamine(antioxidant D).Based on the previous experimental method,the whole atom molecular simulation method was introduced to study the anti-aging mechanism.To study the antioxidants and NR thermal-oxidative aging mechanism from a variety of angles of the physical process and chemical reaction,aiming to provide a new theoretical method on the choice of antioxidants.In the experiment,firstly preparing the composites of antioxidant 4020/NR,antioxidant D/NR and antioxidant NR without antioxidant.By ATR-FTIR,the variations of structural components of the NR composites,which has been oxidized respectively for 0,1,2,4,7days at the 80?,were analyzed.It concludes that the antioxidants added participate in the earlier stage of reaction to delay and inhibit the oxidation of double bonds in the main chain of NR molecule,indicating the antioxidants added in the NR playing a protective role.At the same time,the electronic tension were used to measure the mechanical performance parameters such as the changes of tensile strength and elongation at break;Measuring the variation of magnetic crosslink density of different oxidation time using nuclear magnetic crosslink density meter;The hardness tester is used to measure the trend of surface hardness variation with different oxidation time.The results show that the NR with antioxidant'performance is better than the NR without antioxidant.And the antioxidant 4020 on NR thermo-oxidative aging protection is superior to the antioxidant D.In the simulation,using all atom molecular to calculate the cohesive energy density(CED)of antioxidant 4020,antioxidant D and NR respectively,to calculate the mean square displacement(MSD)of antioxidant 4020 and antioxidant D in NR matrix the,and also the binding energy of antioxidant 4020 with NR or antioxidant D with NR have been calculated.The calculation results show that,comparing with the antioxidant D,antioxidant 4020 and NR polymer has a good compatibility,the antioxidant 4020 has a better movement ability in NR matrix,and the binding energy of NR with antioxidant 4020 is bigger.It concludes that the antioxidant 4020 can effectively dispersed in NR matrix and have better protective effect on NR thermo-oxidative aging.In a word,the simulation results and experiment results both demonstrate the 4020 is better than antioxidant D,which shows that all atom molecular simulation method has a certain guiding significance for the selection of rubber composite antioxidant.Then the migration of antioxidant movement ability in the matrix of NR rubber is studied by the all atom molecular simulation method to calculate the MSD.In the research,the temperature,initial concentration of antioxidant,the matrix of rubber and different kinds of antioxidants which will have influences on the MSD have been studied.It concludes that the MSD is gradually increasing with the increase of temperature and initial concentration;and the MSD is gradually decreasing with the increase of molecular weight;Then the matrix of rubber have a influence on the MSD,on account of different rubber have a different interaction force with the antioxidant.