| As people continue to pay attention to the safety of marine engineering structures,the durability and smoke suppression of various engineering structures in the marine environment have received more and more attention.As a protective coating that has emerged in the past two decades,polyurea coating is not only convenient for construction,but also has good mechanical properties.However,due to the harsh marine environment,polyurea materials will change their aging resistance and smoke suppression performance due to factors such as sunlight radiation,corrosive ion erosion,and environmental temperature instability during service.This paper examines the different changes of the new polyurea coating after natural exposure,different environmental temperatures(high temperature of 50?,low temperature of-15? and high and low temperature alternate)and various corrosive media(15% sulfuric acid,30% Na OH and 20%Na Cl solution)experiment,including basic mechanical properties such as hardness,mechanical strength,elongation at break,surface conditions such as gloss,contact angle,and changes in thermal stability and smoke suppression properties.And through Fourier infrared spectroscopy(ATR-FTIR),scanning electron microscope(SEM),atomic force microscope(AFM)these research methods to characterize and analyze the microstructure and morphology of the coating.The main conclusions obtained under different experimental conditions are as follows:(1)The experimental results under natural exposure conditions showed that the hardness,tensile strength,breaking strength,elongation at break,gloss and smoke density of the polyurea coating after exposure for 180 days were all reduced,and the wettability and thermal stability of the coating were improved after exposure;SEM showed that the surface of the coating was cracked after exposure;AFM study showed that the surface of the coating had obvious microphase separation after 30 days of exposure,and the roughness Rrms and Ra increased from 7.858 nm and 4.577 nm to 156 nm and 119.209 nm,respectively.The exposure process has a greater impact on the chemical structure of the coating.The FTIR study showed that important chemical bonds such as N-H bonds and C=O bonds on the coating surface were broken.Quantitative analysis showed that the hydrogen bond length and the degree of hydrogen bonding of the polyurea coating decreased from 2.94(?) and 87.8% before exposure to2.90(?) and 44.3% after exposure.It can be seen that the exposure environment had a very obvious influence on the structure and performance of the coating.(2)The macroscopic properties and microstructure changes of polyurea coatings after immersing in 15% sulfuric acid,30% Na OH and 20% Na Cl solutions were studied.The results showed that the hardness,tensile strength,tear strength,elongation at break and gloss of the polyurea coating decreased after 180 days of soaking in three solutions,and the smoke density grade of the coating after immersing in the three solutions for210 d also decreased,but the wettability and thermal stability of the coating were improved after being immersed in the solution for 180 d.The SEM experiment results of the coating showed that degradation products were attached to the surface of the coating after soaking in acid and alkaline media,and cracks and holes appeared on the surface of the coating after soaking in chloride medium.The results of AFM study showed that the coating appeared microphase separation state after being corroded by alkaline and chloride salt media.Their Rrms increased to 50.345 nm and 89.764 nm,respectively,and their Ra increased to 45.232 nm and 95.893 nm,respectively.Observing the infrared spectrum of the coating after immersing in alkaline and chloride salt media for 180 days,it can be seen that the chemical bond structure of the coating such as N-H and C=O has changed,and the degree of hydrogen bonding of the coating had decreased by 4.1% and 5.4%,respectively.By comparison,it can be seen that the coating was most severely damaged in the chloride salt solution,and its microstructure and macroscopic properties had the most obvious changes.(3)The performance and structure changes of polyurea coatings under high temperature of 50?,low temperature of-15? and high and low temperature alternating conditions were studied.The results showed that the hardness,tensile strength,tear strength,elongation at break and gloss of the coating decreased after being placed for 180 days under different temperature conditions,but the wettability and thermal stability of the coating increased.The smoke suppression performance of the coatings after the experiment at high temperature of 50°C and low temperature of-15°C for 210 days was studied,and the results showed that their smoke density grades were all decreased.Observing the microscopic morphology of the coating after 180 d experiments at high temperature of 50? and low temperature of-15?,it can be seen that degradation products were attached to the coating surface under high temperature conditions,the relative content of the soft and hard segments of the coating changed in a state of microphase separation,and its Rrms and Ra increased to 28.814 nm and45.510 nm,respectively.Under low temperature conditions,pores are formed on the coating surface and the maximum diameter of the pores was about 40 ?m.The FTIR analysis of the coating after 180 days of experiment at high temperature of 50? and low temperature of-15? showed that the microstructure of the coating was destroyed after the experiment.The degree of hydrogen bonding decreased by 3.6% and 10.3%,and the hydrogen bond length increased to 2.95(?),so the hydrogen bond of the coating was weakened.Comprehensive analysis of this experiment showed that extreme temperature changes the structure and performance of the coating,and low temperature had a greater effect... |
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