| The corrosion of metals causes great losses to the national economy every year,and one of the most commonly used and effective methods to inhibit corrosion is organic coatings.According to different corrosion environment and coating thickness,anticorrosive coatings can be divided into heavy and light anticorrosive coatings.Thereinto,light anticorrosive coatings are mostly used in conventional corrosion environment.The newfashioned waterborne light anticorrosive coatings have received too much concern because of the massive VOC emission of solvent-based paint and grievous damage on environment and human health,waterborne polyurethane?WPU?has become the hot spot.However,the poor water and medium resistance of WPU limits its application in the field of light anticorrosion and promote further modification.In this paper,a series of WPU products with good corrosion resistance were prepared with the easily designed property of WPU molecule and different modification methods,the comprehensive properties of WPU were characterized by a variety of methods.The research contents of this paper are as follows:Polytetrahydrofuran ether diol?PTMEG?,isophorone diisocyanate?IPDI?,hydrophilic chain extender dimethylol propionic acid?DMPA?,small molecule chain extender ethylenediamine?EDA?,triethylamine?TEA?and other raw materials were used to prepare a series of waterborne polyurethane?WPU?products with different molecular structures by a two-step method.The molecular structure of WPU was characterized by fourier transform-infrared spectroscopy?FTIR?,and the expected products were synthesized.The optimum reaction temperature and reaction time of WPU prepolymer were discussed and the emulsifying technology of WPU was optimized,while the effects of chain extender dosage,DMPA content and neutralization degree on the comprehensive properties of WPU emulsion and coatings were studied to obtain the best formula for the better water resistance and dielectric resistance of WPU.On the basis of WPU,a series of epoxy modified waterborne polyurethane?EP-WPU?products with different epoxy content were prepared through graft polymerization,while the molecular structure was characterized by FTIR and the ring opening mechanism of epoxy group was studied.The optimum epoxy content formula was investigated through the viscosity,particle size,stability,physical properties,dielectric resistance and water absorption tests of EP-WPU.The results showed that the EP-WPU with 7 wt.%epoxy content behaved better on the stability,physical properties,water resistance,alkali resistance and salt water resistance compared with other samples,but the performance in acid-resistant medium was still poor.Electrochemical tests revealed that the Ecorr of 7 wt.%EP-WPU coating was the largest,the icorr was the smallest and the|Z|f=0.1 HZ was the highest after soaking in 3.5wt.%NaCl solution for 120 h.In order to further improve the corrosion resistance of the coatings,graphene oxide?GO?was modified by 3-aminopropyltriethoxysilane?APTES?,which was further reacted with epoxy resin to obtain functionalized graphene oxide?MGO?and then a series of nanocomposite emulsions and coatings?MGO/EP-WPU?were prpared by blending EP-WPU and GO or MGO in different ratios.FTIR,X-ray diffraction?XRD?and thermogravimetic?TG?analysis showed that the modification of GO was obtained successfully and the settlement of MGO and its dispersivity in composite emulsion were studied by naked eyes.Furthermore,the physical properties,water absorption and dielectric resistance of composite coatings were characterized and the influence of MGO content on corrosion resistance was studied by electrochemical method.The results showed the composite coating with 1 wt.‰MGO content had no change in acid,alkali and saline solution for 24 h,the medium resistance was improved obviously.And low water absorption of 10.36%after 72 h immersion revealed excellent water resistance of the coating.After 23 days immersion in 3.5 wt.%NaCl solution,the OCP was-0.406 V,the icorr was 4.227×10-7 A cm-2 and the|Z|f=0.1HZ=0.1HZ was maintained at 2.37×106?cm2.The Rc was decreased from 9.2×104 to 5.27×104?cm2.The uniform dispersion of MGO in EP-WPU effectively improved the corrosion resistance of the coating. |
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