Durability Of Waterborne Epoxy Anticorrosive Coating Reinforced By Polyaniline Nanofibers/Graphene Oxide/Silicon Dioxide

Waterborne anticorrosive coatings are extensively concerned due to the advantages of green environmental protection and no VOC.However,the problems of weak permeability resistance and poor durability after curing limit the application of waterborne coatings in the industrial anticorrosion fields.It is an important strategy to improve its performance to add efficient anticorrosion components.In this paper,the waterborne epoxy polymer emulsion was synthesized by self-emulsification method,and a green and efficient waterborne anticorrosion coating was prepared by using polyaniline/graphene oxide/silicon dioxide（PANI-f/GO/SiO₂）composite as synergistic anticorrosive filler.The durability and the long-term protective mechanism of the waterborne coating was studied by electrochemical impedance,salt spray resistance,water resistance,adhesion test and basic performance.The waterborne epoxy polymer emulsion were prepared by using the method of external emulsifier and self-emulsification.The different addition of reactants such as polyethylene glycol 2000,maleic anhydride,epoxy resin（E-44）and silane coupling agent（KH550）were studied,and the ratio was optimized as follows:n（polyethylene glycol）:n（maleic anhydride）:n（epoxy resin）:n（silane coupling agent）=0.7:1.3:1.5:1.5,the reaction at 75℃for 2h and then at 100℃for 0.5h.The optimal ratio of curing agent（n（epoxy resin）:n（triethylene tetramine））was 1:3,and the dosage of curing agent was15%.The adhesion promoter was silane coupling agent KH570.The prepared aqueous emulsion had good stability,moderate hardness,low water absorption,strong salt resistant and water resistant,and the adhesion was the highest level 0.All the properties had reached the industry standard HG/T 4842--2015.Modified graphene oxide（CTGO）was obtained by the modification of GO.Polyaniline/graphene oxide（PANI-f/GO）composite with different mass ratios were prepared by in-situ polymerization in non-hydrochloric acid medium.The chemical grafting of polyaniline nanofibers（PANI-f）and CTGO was demonstrated by XRD,FTIR and UV-Vis.The composite PANI-f/GO-6（the mass ratio of CTGO and PANI-f was 1:6）had more uniform lamellar and nanofiber structure,and remained good dispersion in water after 3 days.The composite PANI-f/GO-6 was physically blended with fumed SiO₂ to obtain PANI-f/GO/SiO₂ with different mass ratios.The results of XRD,FTIR and UV-Vis showed that PANI-f/GO/SiO₂ was doped by fumed SiO₂through physical adsorption.The composite PANI-f/GO/SiO₂-3 were uniformly distributed without agglomeration,and fumed SiO₂ were uniformly adsorbed on the surface.The composite PANI-f/GO/SiO₂-3 also showed better dispersion and electrochemical activity.The waterborne epoxy polymer emulsion under the optimized conditions was used as base material,and the composite PANI-f/GO/SiO₂ was used as the anticorrosive and synergistic filler.The synergistic waterborne coating was prepared by the adhesion enhancement technology.The anticorrosion properties of the composite coating were analyzed by means of open circuit potential（OCP）,potentiodynamic polarization curve（Tafel）and electrochemical impedance（EIS）.Compared with control group（EP,CTGO-EP,PANI-f-EP and PANI-f/GO-EP）,composite coating（PANI-f/GO/SiO₂-EP）possessed good stability,blocking ability and passivation effect to protect steel from corrosion.The 0.4PANI-f/GO/SiO₂-EP had the largest corrosion potential（-0.247 V）and the smallest corrosion current density（0.316μA/cm²）,and the low-frequency impedance value reached 3.47×10⁸Ω·cm²,which showed that the 0.4PANI-f/GO/SiO₂-EP had the best anticorrosion effect.From the salt spray test and morphology of cross-section,the PANI-f/GO/SiO₂-EP had smooth surface and less corrosion products.As for the 0.4PANI-f/GO/SiO₂-EP,there was no blistering,peeling,rust and other phenomena,and the adhesion still reached the highest level 0 after being soaked in3.5wt.%Na Cl solution for 24 hours,which proved that 0.4PANI-f/GO/SiO₂-EP had good anti-corrosion durability.Molecular dynamics simulation results showed that the minimum adsorption energy of PANI-f/GO/SiO₂ on Fe surface was-3612.39 k J/mol and the radial distribution function g（r）value was less than 3.5?,which indicated that the N and O atoms of PANI-f/GO/SiO₂ could form coordination bonds with Fe atoms through chemical adsorption.The EIS test of scratch micro-area and XRD analysis of corrosion products showed that the composite coating formed a Fe₃O₄ passivation layer on the surface of carbon steel.Therefore,the composite PANI-f/GO/SiO₂ had active protection ability because of the chemical adsorption and passivation effect.According to the experimental results combined with molecular dynamics simulation analysis,the long-term anti-corrosion mechanism of the composite coating on the steel surface is proposed:The addition of fumed SiO₂ promoted the good dispersion of the composite PANI-f/GO/SiO₂ and formed an interpenetrating network in the coating,which promoted better compatibility with the waterborne coating and improved physical barrier performance of PANI-f/GO/SiO₂-EP.The composite PANI-f/GO/SiO₂ could produce chemical adsorption on the steel surface and form N-Fe and O-Fe coordination bonds,which inhibited the anodic corrosion reaction of carbon steel.In the long-term corrosion process,Fe lost electrons to form Fe²⁺and Fe³⁺when the electrolyte solution reached the surface of the steel base.The electrons were rapidly transferred through PANI-f,prompting Fe³⁺to react with OH^-to form a dense Fe₃O₄layer to further hinder the erosion of the corrosive medium.Chemical adsorption of PANI-f-GO on Fe surface and the formation of Fe₃O₄ passivation film could be served as active anti-corrosion strategies,and the physical barrier effect of PANI-f-GO composites could be used as a passive anti-corrosion strategy,which significantly improved the durability of the waterborne composite anticorrosive coating.This paper provided experimental support for the application of green composite anticorrosive coating in industry.