| Nitrile-butadiene rubber(NBR)is one of a rubber compound with good oil resistance.It is widely used in the production of various oil-resistant rubber products.NBR is an essential elastic material in automotive,aerospace,petrochemical and other industries.The molecular chain structure of NBR is the source and key to all its properties.The disordered arrangement of butadiene structural units and acrylonitrile structural units constitutes the molecular chain of NBR.Sequence structure distribution of nitrile-butadiene rubber(NBR)has an important influence on its vulcanization performance and mechanical properties.However,there are few studies on sequence structure of NBR at present.Most studies only focus on butadiene or acrylonitrile,which is a single structural unit,but do not systematically explore the combination of the two.With the help of advanced ~1H-NMR technology,the sequence structure content and distribution of 8 different brands of NBR were determined accurately and effectively.The effects of sequence structure of NBR on its vulcanization properties and mechanical properties were investigated in depth based on the results of vulcanization properties and mechanical properties of its vulcanizates.CKH3365 was selected as the main object of further research.At present,the vulcanizate of nitrile-butadiene rubber(NBR)generally has a problem that it is difficult to take into account both the vulcanization rate and the mechanical properties.The physical and mechanical properties of products with high curing rate are not high,and the curing time of vulcanizates with outstanding physical and mechanical properties is too long.Therefore,how to make NBR vulcanized products fast and good vulcanization has always been the goal of the community.In this paper,three kinds of carbon black with different properties were used as reinforcing fillers of nitrile-butadiene rubber.The effects of the amount of carbon black on the vulcanization properties and mechanical properties of nitrile-butadiene rubber CKH3365 were studied.The effects of the Micro-properties of carbon black on the vulcanization rate and physical and mechanical properties of nitrile-butadiene rubber vulcanized were investigated.The regularity was found and the improvement of nitrile-butadiene rubber CKH3365 was put forward on the basis of A new process for application properties of vulcanizates.Finally,the application properties and section morphology of NBR foaming materials were characterized and analyzed by scanning electron microscopy,and the physical and mechanical properties and cell structure of CKH3365 foaming rubber materials were mainly compared.The mechanism of the effect of temperature,foaming agent AC and flame retardant aluminium hydroxide on the properties and structure of foamed rubber was analyzed,and the feasible technology and formula for improving the application properties of CKH3365 foamed rubber were explored.The main contents and results of this paper are as follows:(1)The sequence structure distribution and content,glass transition temperature,vulcanization properties and mechanical properties of acrylonitrile-butadiene rubber(NBR)with 28%and 33%acrylonitrile content were studied by ~1H-NMR,DSC,vulcanization characteristics and physical andmechanical properties.The structure-activity relationship was analyzed in depth.The results showed that the sequence structure of the molecular chains of NBR with 28%and 33%acrylonitrile content mainly consisted of BAB,BBB,BBA/ABB and ABA.The sequence structure content of NBR with the same acrylonitrile content is quite different from that of butadiene.The structure content of BAB sequence on NBR2907 and NBR3308molecular chains can reach 33.4%and 41.0%,respectively,and that on JSR240S and NANTEX1052 molecular chains can reach 41.9%and 28.8%,respectively.The effect of sequence structure on the corresponding properties of NBR is mainly manifested in the low glass transition temperature of NBR with high BBB sequence structure content,the good cold resistance of materials,the increase of BBB sequence structure content by 7.2%,and the decrease of glass transition temperature by 14.52?.According to the analysis of vulcanization characteristics,the structure of BAB sequence promotes the burning stage of NBR vulcanization.The structure content of BAB sequence increases by 2.7%,and the burning time decreases by 0.48 min.The structure content of BBB sequence has some influence on the positive vulcanization time of NBR,but the regularity is limited.According to the mechanical properties of vulcanized rubber,the content of BAB sequence structure promoted the tensile strength and elongation at break of NBR.The content of BAB sequence structure increased by 2.7%,the tensile strength increased by 2.34 MPa and the elongation at break increased by 80.52%.According to the analysis of oil resistance of vulcanized rubber,the structure content of BAB sequence is high,and the oil resistance of NBR is good;the structure content of BBB sequence is high,and the oil resistance of NBR is poor.The above results show that the sequence structure of NBR has a significant effect on the performance of NBR.(2)Because the vulcanization rate of nitrile-butadiene rubber CKH3365 is faster but its mechanical properties are lower,its application performance has higher room for improvement.By adjusting the particle size and content of reinforced carbon black,it was found that N330,a high wear-resistant carbon black with large particle size and small specific surface area,could increase the vulcanization rate of NBR and shorten the vulcanization time by 28.19%.The mechanical test found that increasing the amount of carbon black can effectively improve the tensile strength and elongation of CKH3365 vulcanizate,but also reduce the elongation at break.Among them,the black N115 with small particle size and large specific surface area can increase the tensile strength by 15.83%and the elongation at break by 173.37%without reducing the vulcanization rate.(3)By testing the mechanical properties and cell structure of nitrile-butadiene rubber foam material CKH3365,it was found that compared with NBR3308,the expansion volume of CKH3365 foam rubber was much larger,although the mechanical properties were slightly insufficient,but the density was 57.9%,indicating that it had a wider application range.Through the study of foaming temperature,the results show that although the foamed rubber has smooth appearance and uniform cellular structure,the overall density of the material is higher due to the insufficient thermal decomposition rate of the foaming agent and the high crosslinking density of the rubber compound.Although the physical and mechanical properties are outstanding,the number of foams is small.The performance is insufficient.The thermal decomposition rate of rubber foaming agent coincides with the vulcanization rate in the temperature range from 165?to 175?.The foam cell of rubber foaming agent is large and uniform.With the increase of temperature,the foam wall becomes thinner and the distribution of the foam cell is more and more dense.Scanning electron microscopy(SEM)photos of the cross-section morphology of the foamed materials show that the main structure of the cell is round or elliptical closed-cell structure,and the clusters of small bubbles surround the larger vesicles,which become the structural materials with two main cell sizes.When the foaming temperature is over 180 C,more and more open cell structures are formed,and the cell structure is not uniform,and the size distribution is larger and larger.At the same time,the surface of foamed rubber cracks because of the intense release of gas,so it has no service performance at all.The mechanical properties and cell structure of nitrile-butadiene rubber foam material CKH3365 were tested.It was also found that when the addition of blowing agent AC increased from 10 phr to 18 phr,the density of foaming material decreased and the physical and mechanical properties decreased.However,the foamed materials with smooth surface can be prepared.However,the cell structure will increase with the increase of the amount of foaming agent,and the cell wall will become thinner.When the amount of foaming agent reaches 18 phr,the opening structure will be more due to the cell rupture.At last,the mechanical properties and cellular structure of NBR foamed materials were investigated by flame retardant ATH.It was found that flame retardant ATH could improve the mechanical properties of NBR,but the density of products would increase with the increase of the amount of flame retardant ATH. |
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