Research On Preparation And Properities Of Graphene Modified Waterborne Functional Coatings

Organic coating with resin as the main component can form a dense layer on the surface of substrate after curing,which can prevent the erosive medium to penetrate into the substrate and enhance its durability.In recent years,the development tendency of organic coating is water-based and functional,which put forward the functional performance requirements for the coating,such as corrosion resistance,static conduction and electromagnetic shielding etc.This paper applies graphene with high-barrier and high-conductivity as the reinforcement to enhance the impermeability,corrosion resistance and electrical conductivity.of waterborne epoxy coatings.In this study,graphene oxide(GO)was first prepared form graphite powder.Based on this,we developed a green approach to synthesize CeO2/reduced graphene oxide nanocomposites(CeO2@rGO)through combined hydrothermal and calcination processes,and in-situ produce CeO2 nanoparticles(NPs)with controlled dispersion,sizes and shapes on reduced graphene oxide(rGO).Then,GO/epoxy nanocomposite coatings(GO/EP)based on concrete substrates and CeO2@rGO/epoxy nanocomposite coatings(CeO2@rGO/EP)based on metal substrates were prepared and coated on corresponding substrates,respectively.The microstructures of the fillers and the nanocomposite coatings were characterized.And the resistance to chloride ion penetration,corrosion resistance and conductivity of the nanocomposite coatings were tested.Experimental results show:1.The CeO2 NPs with size of 2～60nm was in-situ grown on rGO sheets through combined hydrothermal and calcination processes with trivalent cerium salt and GO prepared by Hummer’s method as raw materials.When the dosage of cerium salt is 12mM and the calcination temperature is 750℃,the CeO2 loading,dispersion and grain size(～5.5nm)in the CeO2@rGO composite powder were most appropriate.The in-situ growth mechanism of CeO2 NPs can be explained as follows.During calcination,the oxygen-containing functional groups in rGO such as-OH and C=O are transformed into H2O and CO2,and these H2O and CO2 act as a oxidizing agent to react with cerium ions to finally produce CeO2 NPs on rGO.2.In the GO/EP nanocomposite coatings,the GOs were uniformly dispersed inside the epoxy matrix,and covalent cross-links were formed between the GO and epoxy matrix.Water surface contact angles of concrete coated with the nanocomposites coatings were found to increase firstly but then decrease with the increase of the added GO contents.When the GO content was 0.3 wt%,the contact angle was 96.1°±0.3°,whereas that of pure epoxy resin was 77.5°±0.3°.At the same GO content,water absorption(～1.28%)and chloride diffusion coefficient of the coated concrete(～1.12×10-12m2/s)are much lower than those of the uncoated samples.The enhancement mechanisms for the chloride ion penetration resistance are attributed to the formation of cross-linking in the composite coating,improved hydrophobicity and shielding effects of the GOs.3.The TEM images of the CeO2@rGO/EP nanocomposite coating showed that CeO2@rGO was uniformly dispersed in the epoxy resin and formed a dense interfacial layer with the epoxy matrix.The electrical conductivity of CeO2@rGO/EP nanocomposite coatings enhanced with the content of CeO2@rGO increasing.And the percolation threshold of the nanocomposite coating is 0.231 vol%.The corrosion protection of CeO2@rGO/EP nanocomposite coatings were fluctuated by addition of CeO2@rGO.When the 0.50wt.%CeO2@rGO was added to the CeO2@rGO/EP,the self-corrosion potential was the highest and the self-corrosion current density was the lowest.And the corresponding scratched coating also exhibited the highest electrochemical impedance,which reached the best corrosion protection.At the same time,the conductivity of 0.50wt.%CeO2@rGO/EP also reached up to antistatic level of 10-5S/m with the best comprehensive corrosion resistance/antistatic performance.