Preparation And Properties Of Functionalized Graphene Epoxy Composite Anticorrosive Coatings

Graphene has become a new type of two-dimensional carbon nanofiller with outstanding development space because of its high specific surface area,special conductivity and superior mechanical properties.However,the Vander Waals force and high specific surface area between the reduced graphene oxide?RGO?layer and layer make its agglomeration in the polymer matrix hinder its application.Therefore,it is necessary to improve the dissolution and dispersion of reduced graphene oxide in polymer matrix by functionalization of covalent or non-covalent bonds and broaden its application scope.In this paper,HDI-RGO and Tri-HDI-RGO functionalized graphene were synthesized by modifying graphene with hexamethylene diisocyanate?HDI?and HDI trimer?Tri-HDI?respectively.The functionalized graphene/waterborne epoxy nanocomposites with good stability and compatibility were obtained by using waterborne epoxy resin as the base material.The following are specific descriptions:?1?Graphene oxide?GO?was obtained by improved Hummers method,then modified by HDI or Tri-HDI,and reduced by hydrazine hydrate.HDI-RGO and Tri-HDI-RGO functionalized graphene were successfully synthesized.The effects of HDI and Tri-HDI dosage,reaction temperature and time on the modification of graphene were discussed.The optimum preparation scheme was determined as follows:the mass ratio of GO to HDI was 1:10,the reaction temperature was 70? and the reaction time is 8 h;the mass ratio of GO to Tri-HDI was 1:5,the reaction temperature was 70? and the reaction time was 8h.?2?The elemental composition and interlayer spacing of RGO,HDI-RGO and Tri-HDI-RGO were characterized by XPS and XRD.The micro-morphology of reduced graphene oxide and functionalized graphene were observed by TEM and SEM.The thermal stability of HDI-RGO and Tri-HDI-RGO were characterized by thermogravimetric instrument.From the test results we can get that,comparing with RGO,the intensity of N 1s peaks in XPS survey spectrum of HDI-RGO and Tri-HDI-RGO increased significantly,C-N bond peaks and HN-C=O bond peaks appeared in their N1s XPS spectrum,and the C/O ratio increased.HDI-RGO and Tri-HDI-RGO had a larger spacing than the RGO layer,and both exhibited a two-dimensional pleated thin layer structure.Compared with GO,the thermal weight loss rate of the decomposition of the last stage carbon layer of HDI-RGO and Tri-HDI-RGO was significantly reduced,and the thermal stability was improved.?3?A series of HDI modified graphene/epoxy resin?EP/HDIG?and Tri-HDI modified graphene/epoxy resin?EP/Tri-HDIG?nanocomposite emulsions were prepared by using HDI-RGO and Tri-HDI-RGO as nano fillers and waterborne epoxy resin?EP?as matrix resin.The effects of different contents of HDI-RGO and Tri-HDI-RGO on the morphology,mechanical properties,heat resistance and water resistance of the composite film were studied by means of SEM,tensile test,thermogravimetric analysis and water resistance test.The results showed that with the increase of HDI-RGO and Tri-HDI-RGO content,the roughness and tortuous paths of the film increased,and the roughness continued uniformly throughout the nanocomposite film.The mechanical properties,heat resistance and water resistance of the film showed a trend of increasing first and then decreasing.When the content of HDI-RGO and Tri-HDI-RGO was 0.7%,the water resistance,heat resistance and the mechanical properties of the nano-composite latex film were optimized.The anti-corrosion properties of EP/HDIG and EP/Tri-HDIG composites were investigated and compared by electrochemical tests.According to the electrochemical impedance spectroscopy?EIS?test,the impedance modulus of EP/Tri-HDIG composite coating increasesd from 3.71×10⁵ to 3.64×10¹⁰?.cm²,which was increased by five orders of magnitude compared with pure EP.EP/Tri-HDIG coating resistance increased from 6.81×10⁴ to 3.87×10¹⁰?.cm²,much higher than the impedance modulus of EP/HDIG?1.28×10⁹?.cm²?and coating resistance?1.36×10⁹?.cm²?.Because Tri-HDI-RGO improved the shielding properties and ionic resistance of the coating,the EP/Tri-HDIG nanocomposite coating had excellent long-term corrosion resistance.