Preparation And Properties Of Aminosalicylic Acid Doped Polyaniline/Graphene Oxide Waterborne Anticorrosive Coatings

Despite popular for their low VOC content and environment-friendly,waterborne anticorrosive coatings are limited in application of high performance anticorrosion for the poor water resistance and adhesion,durability and corrosion resistance are not as good as oily coatings.In view of the problems above,a new type of synergistic effect was developed by using a phosphate ester modified waterborne epoxy emulsion as base and amino-salicylic acid doped polyaniline/graphene oxide?PACA/GO?as synergistic filler.The anti-corrosion coatings are used to research the durability,salt spray resistance and electrochemical performance of the coatings,and also the anti-corrosion mechanism.Phosphate modified waterborne epoxy emulsion was prepared by seed emulsion polymerization.Research the influence of the type and ratio of emulsifier,reaction temperature,initiator dosage,amount of phosphate monomer,epoxy resin dosage,silane coupling,the type and amount of the binder on the properties to the emulsion and the coating,and optimize the suitable emulsion synthesis process:under the reaction temperature 80°C,OP-10/SLS is 3:1;the amount of emulsifier is 3.48%;the amount of phosphate monomer is 4%;the amount of epoxy resin is 30%;the amount of initiator is 1.51%;the amount of the silane coupling agent is 4.13%,the obtained waterborne epoxy emulsion has good stability and the properties of the emulsion reached the relevant national standards.Amino-salicylic acid doped polyaniline/graphene oxide composites?PACA/GO?with different mass ratios were prepared by using 5-amino-salicylic acid as the doping acid in-situ polymerization method.The structures of GO,PACA and PAGO composites were characterized by XRD,FTIR,UV and SEM,and the target products were identified.The suitable ratio of GO to PACA was determined by analyzing the dispersibility and electrochemical activity of GO,PACA and PACA/GO composites with different mass ratios.SEM analysis showed that PACA is uniformly dispersed on the GO sheet,GO exhibit an irregular flake structure,and PACA is a nano-spherical particle structure with slight accumulated which is well dispersed in water without any agglomeration.With the increase of GO content in the composites,the water dispersion of PAGO composites is gradually increased.Electrochemical analysis shows that the PACA/GO polymer material doped with 0.5 wt.%GO increase the electrochemical signal intensity of PACA.When the mass ratio of PACA to GO is 5:1,the composite has the best dispersibility in the emulsion.The component of phosphate modified waterborne epoxy emulsion film was optimized by formulation design,and by using PACA/GO composite as functional additive,the synergistic waterborne anticorrosive coating was prepared,which also research the effect of the amount of composite material on the coating performance.Dynamic mechanical properties?DMA?,open circuit potential?OCP?,polarization curve?Tafel?,alternating current impedance?EIS?,electrochemical fitting and salt spray corrosion experiments were used to study the dynamic mechanical properties,physical barrier and corrosion resistance of the coatings.PACA/GO composite material improves the durability and anti-corrosion performance of the coating.Salt spray corrosion test was used to compare the color,surface smoothness and corrosion width of scratches before and after salt spray test to study the corrosion resistance of coatings.The results show that the coating with 5 wt.%PACA/GO composite still has smooth surface and no rough particles and bubbles are produced during 240 hours of salt spray test.The coating exhibits good anti-permeability and corrosion resistance.With flaky nanostructure,GO can prevent electrolyte from immersing into the substrate and make the path of electrolyte into the metal surface become tortuous,thus having a good effect on physical isolation.PACA can form a passivation film on the surface of metal matrix,and produce electric field,which can hinder the transmission of electrons to the outside world,and has a good anti-corrosion effect.PACA/GO composites have good dispersibility in water-borne coatings,and the electrochemical activity of the composites is enhanced.The synergistic effect of GO and PACA is fully utilized to improve the anticorrosion performance of the coatings.It is presumed that the synergistic mechanism is that PACA is equipped with the ability of exchanging and capturing electrons,which can forcibly prevent anodic dissolution in the corrosion process.Due to the presence of PACA,Fe²⁺and Fe³⁺formed by anodic reaction were converted into Fe₂O₃ and Fe₃O₄ to form passive films,which could protect metals.Appropriate dispersion of GO nanosheets in epoxy matrix could significantly increase the length of electrolyte diffusion path.GO nanosheets provide an effective barrier layer for the diffusion of oxygen and water and prevent the diffusion.Because graphene has a strong impermeability,the path of corrosive substances to metal surface through coating becomes longer and more complex.The addition of PACA/GO to waterborne epoxy emulsion significantly enhanced the barrier properties and ion resistance of epoxy coatings.Due to the?-?stacking between GO and PACA,the strong interface formed increases the electron delocalization and promotes the charge transfer in the redox process.PACA/GO exhibits higher electrochemical activity than PACA,improves the dispersion of PACA in water,and achieves the synergy of waterborne anticorrosive coatings.This research has a guiding significance for the performance enhancement and practical application of waterborne anticorrosive coatings.