Research And Application Of Synthesis Technology Of High Nitrile Butadiene Rubber

Nitrile butadiene rubber（NBR）is prepared from butadiene and acrylonitrile monomers by low temperature emulsion polymerization.Because the molecular chain structure of nitrile butadiene rubber contains polar groups cyanide and unsaturated double bonds,so that it has good heat resistance and aging resistance,so it is often used as a chemical safety elastic material,to become the automobile,aviation,petroleum,copying and other industries.At present,most of the research on nitrile butadiene rubber at home and abroad focuses on medium nitrile butadiene rubber,but there are few reports on the development and utilization of nitrile butadiene rubber with more than 40%acrylonitrile content.Therefore,exploring the synthesis technology and application of high nitrile butadiene rubber has become the focus of this research.In this paper,the effect of various additives and monomer addition technology on the polymerization rate of NBR was studied in the process of low temperature emulsion polymerization of butadiene and acrylonitrile to produce high nitrile butadiene rubber.On this basis,the acrylonitrile butadiene rubber with 44.2%acrylonitrile content was synthesized.Finally,the best polymerization formula and process of high nitrile butadiene rubber was determined.At the same time,NMR technology was used to analyze the sequence structure of the synthetic acrylonitrile butadiene rubber with more than 40%acrylonitrile content.The relationship between the different acrylonitrile content and the sequence structure was explored.The relationship between the sequence structure and the property was explored by combining the curing curve and the physical and mechanical properties test,as well as the glass transition temperature measured by DSC.To provide guidance for the optimization and application of high nitrile butadiene rubber production technology;Finally,the factors affecting the thermal stability of NBR were studied in view of the heat resistance of high nitrile butadiene rubber.The research content and conclusion of this paper are as follows:In the process of low temperature emulsion polymerization,the initiator diisopropylbenzene hydrogen peroxide and the reducing agent formaldehyde sodium bisulfate have similar initiation mechanism,and the promotion efficiency of polymerization reaction is obvious.The activator ferric sodium ethylenediamine tetraacetic acid can also promote the polymerization reaction,but because its activity decreased at the late stage of the reaction,the promotion effect was slow,and it needed to be chelated with other additives.The reaction rate of polymerization system using disproportionated rosin acid soap as emulsifier is slow,and the stability of the emulsion produced by nitrile rubber is poor,so it should be used less.The emulsifying system which uses sodium dodecyl benzene sulfonate as the main emulsifier and the condensation of sodium dodecyl sulfate and sodiumβ-naphthalene sulfonate has the best emulsifying effect.It has the advantages of fast polymerization rate,high emulsion stability and low microgel content.It can be applied to the production of high nitrile butadiene rubber.Due to the different repolymerization rates of butadiene and acrylonitrile,when the proportion of acrylonitrile in the raw material liquid increases,the copolymerization tendency of the two monomers is large,will increase the polymerization rate,and the way of adding butadiene will increase the combination amount of acrylonitrile,the structure of more uniform copolymer;The addition of molecular weight regulator tertiary twelve carbon mercaptan will also affect the polymerization process of high nitrile butadiene rubber.Adding regulators will reduce the various indexes of nitrile butadiene rubber.If only increasing the amount of regulator,the physical and mechanical properties will also be improved.Finally,considering all the factors affecting the polymerization reaction,the optimum polymerization formula was determined under the condition that the ratio of butadiene and acrylonitrile monomer was 54/46.The conversion rate of 70%-80%could be achieved in 5～6h,the polymerization time was short,the NBR tensile strength was30.1Mpa,and the elongation at break was 446.5%.High nitrile NBR with 300%constant elongation stress of 18.3Mpa and excellent physical and mechanical properties.The samples of high nitrile butadiene rubber were characterized by hydrogen NMR spectroscopy and the contents of each sequence structure were calculated.The results showed that with the increase of acrylonitrile content,except for the sequence structure of ABA,BBA,BAB and BBB characteristic peaks,BAA sequence appeared in high nitrile butadiene rubber,which was not found in medium and low nitrile butadiene rubber.The contents of BAB and ABA sequences were the highest,which indicated that the copolymerized high-nitrile butadiene rubber had relatively uniform structure.It was found that BBB sequence was related to physical and mechanical properties,vulcanization characteristics,glass transition temperature,molecular weight and its distribution,and Mooney viscosity,because the high content of unsaturated double bonds in BBB sequence would affect the degree of cross-linked branching of molecular chains of NBR,making the molecular chains more soft.When the BBB sequence was reduced by 6.9%,the molecular chain of NBR was reduced by 6.9%.The positive vulcanization time is extended by 2.23min.BAB sequence reflects whether the structure of NBR is homogeneous.When BAB sequence content increases,the affectedα-methylene activity increases and the coke time(t₁₀)decreases.The thermogravimetric analysis of high nitrile butadiene rubber in air atmosphere was carried out.The results showed that the thermal degradation of NBR vulcanized rubber was divided into two stages in the air atmosphere.The thermal stability of high nitrile butadiene rubber was better than that of low nitrile rubber and that of vulcanized nitrile butadiene rubber was better than that of unvulcanized nitrile butadiene rubber by changing the heating rate,increasing the combined acrylonitrile content and vulcanized nitrile butadiene rubber.Finally,activation energy Ea was calculated by Kissinger method.The results show that the first stage is more stable and has better safety performance.