Regulation Of Graphene Oxide Structure And Its Effect On Electrochemical Behaviors Of Epoxy Composite Coatings

Epoxy resin(EP)is a thermosetting resin with excellent chemical resistance,adhesion strength and heat resistance.It has been widely used as anti-corrosion coating in many fields such as pipes,buildings,automobiles and ships.It is a complex and harsh corrosive environment in the the ocean.There are many aggressive ions and cyclical forces such as tides and sea breeze,which make the metal materials face serious anti-corrosion challenges.Therefore,it is urgent to develop coatings with high anti-corrosion performance.Among the already known methods,modification by two-dimensional nanofiller is considered as an effective way to enhance the corrosion resistance of epoxy coatings.As the thinnest two-dimensional carbon material,graphene has high aspect ratio,excellent permeability resistance and good chemical stability.It is considered to be an ideal anti-corrosion reinforcing filler,but graphene is difficult to form a good dispersion in the coating matrix due to van der Waals force and ?-? interaction,which limits its application in the field of corrosion protection.However,graphene oxide(GO)not only inherits many excellent properties of graphene,but also has abundant oxygen-containing functional groups as modified active sites,which has great potential for enhancing the anticorrosive performance of epoxy coatings.Based on the construction of graphene oxide modified epoxy composite coating system,the effect of sheet-like structure,organic polymer modification,fluorination treatment and inorganic nanoparticle loading on dispersion and compatibility of graphene oxide in epoxy coating were systematically investigated.The anti-corrosion performance and corrosion protection mechanism of GO/EP composite coatings were also explored at micro/nano-scale.Firstly,three kinds of graphene oxides with different aspect ratios were prepared by adjusting the oxidation conditions of modified Hummers method.Three kinds of GO/EP composite coatings were also prepared by introducing graphene oxide into waterborne epoxy resin by physical dispersion.The structure-activity relationshipbetween the aspect ratio of graphene oxide and the corrosion resistance of GO/EP composite coatings was investigated.The results show that the higher the aspect ratio of graphene oxide,the better the anti-corrosion performance of GO/EP coatings.This is attributed to the fact that graphene oxide sheets with high aspect ratio can form more tortuous permeation paths in epoxy coatings,thus exhibiting much better barrier properties.Secondly,the graphene oxide was chemically modified with an amine-rich organic polymer chain(polyethyleneimine),and the corrosion behaviors of graphene oxide modified epoxy composite coatings with different contents(0.1 wt%,0.25 wt%and 0.5 wt%)were compared with pure epoxy coating.When the content of polyethyleneimine modified graphene oxide is 0.25 wt%,the epoxy composite coating displays the best corrosion resistance,and when its content reaches 0.5 wt%,graphere oxide is prone to agglomeration in the epoxy coating,which results in a decline in coating corrosion resistance.Compared with unmodified graphene oxide,polyethyleneimine can bridge graphene oxide and epoxy resin to improve the interfacial compatibility between graphene oxide and epoxy resin,thereby enhancing the corrosion resistance of graphene oxide modified epoxy composite coating.Finally,three kinds of fluorinated graphene oxide(LFG,MFG and HFG)were obtained by adjusting the preparation parameters,which were also loaded by inorganic nanoparticles(cerium oxide).The effect of fluorination degree on the loading of cerium oxide nanoparticle was investigated.The corrosion resistance of epoxy composite coatings containing FG with different fluorination degree was compared.The effect of cerium oxide nanoparticles loading on the corrosion resistance of FG/EP composite coatings was also studied.For FG/EP composite coatings,HFG with high fluorination degree has positive effect on corrosion resistance of coating due to its lower surface energy and stronger hydrophobicity.For cerium oxide nanoparticles modified FG/EP composite coating,LFG with low fluorination degree exhibits the best corrosion resistance because of the large amount of cerium oxide loaded on it,which can play a better corrosion inhibition and barrier role.