Functionalized Graphene Reinforced Waterborne Heavy Duty Anti-corrosion Coatings

In this thesis,high-corrosion-resistant epoxy composite coatings were prepared by adding functionalized graphene as barrier reinforcement,which can be used as a primer coating.Self-repairing waterborne polyurethane coatings were prepared,which can be used as the topcoatings for heavy-duty anti-corrosion.The main research work includes the following aspects:(1)The effect of sulfonated graphene(SG)on the corrosion resistance of waterborne epoxy(WEP)coatings was systematically investigated.Sulfonic acid groups were grafted on the edges of graphene sheets.SG can be stably dispersed in water and WEP emulsions,while graphene oxide(GO)caused demulsification of epoxy emulsions.Assembly of SG sheets at oil/water interfaces in WEP emulsions was proposed,which co-stabilized the WEP emulsions.SG reinforced WEP coatings were fabricated on carbon steel plates for corrosion protection.When the SG content was 0.2 wt%,SG sheets were nanoscopicly well dispersed in WEP coatings.With increasing of the SG content,the SG sheets tended to assemble parallelly in short range,leaving a distance of 20-30 nm between the neighboring sheets.The corrosion protection properties of the coatings were significantly improved by the dispersed SG sheets,as well as the parallelly assembled SG sheets.The most remarkable improvement was achieved by adding 1.0 wt% of SG in the WEP coatings,where the impedance modulus at 0.1Hz was 200 times higher than the neat WEP coatings after 150 days of immersion in electrolytes.The outstanding corrosion protection properties were attributed to the stable waterborne epoxy emulsions,the physical barrier properties of SG,the high SG content,as well as the sufficient distance between the parallelly assembled SG.(2)Based on the research of the corrosion resistance of the SG/WEP coatings,the impact of the graphene size on the corrosion resistance of the coatings was further studied.SG nanosheets with different size were fabricated based on the different size of GO nanosheets,the average size of SG was 4 ?m(SSG)and 35 ?m(LSG).The impact of the size of SG nanosheets on the epoxy emulsions and the corrosion resistance was characterized.The experimental results showed that,compared with SSG,LSG was more conducive to the stability of epoxy emulsions.The electrochemical impedance spectroscopy(EIS)results showed that there was no significant difference between SSG/WEP composite coatings and LSG/WEP composite coatings.The size of the SG did not take effect on inhibiting the diffusion of the corrosive medium in the coatings.The salt spray test(SST)results showed that the corrosion resistance of the LSG/WEP composite coatings was significantly better than the SSG/WEP composite coatings.The intiation of corrosion product accumulation was 30 days for LSG/WEP composite coatings and 18 days for SSG/WEP composite coatings.LSG helped the stabilization of the epoxy emulsions,thereby improving the film-forming properties of the coatings,which in turn improved corrosion resistance of the LSG/WEP coatings.(3)Linseed oil-loaded microcapsules with the protection of cross-linked GO shells were fabricated based on Pickering emulsions.We chose polyetheramine molecules(D-2000)to dissolve in linseed oil(LO),so that it could diffuse from LO to the oil/water interface and reacted with GO sheets from the core side of the microcapsules.Chemical stitching of GO sheets by D-2000 were employed to enhance the chemical stability of the microcapsules.With the protection of cross-linked GO sheets,both Pickering emulsions and the microcapsules exhibited good chemical stability in a variety of organic solvents that otherwise lead to the destruction of Pickering emulsions and the microcapsules.The microcapsules contained 97.2 wt% of LO as the healing agent.The self-healing function of the coatings was well realized by embedding the microcapsules in waterborne polyurethane(WPU)matrix.