| In recent years,it has become one of the research hotspots in the application field of epoxy coatings to develop new waterborne epoxy coatings instead of the traditional solventborne epoxy coatings with high VOC content.Waterborne epoxy curing agent is the key component which determines the performance of two-component waterborne epoxy coatings.However,the coatings film made from the widely used ionic waterborne epoxy curing agent in China at present has some defects such as poor water resistance and corrosion resistance,which limits the application of waterborne epoxy coatings in the field of metal corrosion protection.Therefore,developing new nonionic waterborne epoxy curing agent with excellent corrosion resistance is of great significance for the promotion and application of waterborne epoxy coatings.Based on this,the following works have been done in this paper:Using triethylenetetramine(TETA),epoxy resin E44,polyethylene glycol diglycidyl ether(PEGDGE)and n-butyl glycidyl ether(BGE)as raw materials,a new nonionic waterborne epoxy-polyamine curing agent was synthesized by a two-step reaction method.Taking the epoxy conversion rate as the judgment standard,the single-factor parallel experiment and multifactor orthogonal experiment were adopted to determine the optimal process conditions of the first and second reaction step.In the first step,the reaction temperature of polyamine and mixture of E44 and PEGDGE was 65?,the reaction time was 4h,and the molar ratio was 2.1: 1.In the second step,the blocking time of the blocking reaction was 2h,and the adding amount of the blocking agent was 120%.At the same time,the influence of nonionic hydrophilic segment content on curing performance of curing agent was emphatically investigated.Through DSC,water absorption,EIS,mechanical properties and other tests,it was found that when n(E44):n(PEGDGE)was 7:3 under normal temperature curing conditions and 8:2 under high temperature curing conditions,a balance between hydrophilicity and water resistance was achieved by the synthesized curing agent while maintaining good water solubility and corrosion resistance.Finally,different types of polyamine and blocking agent were compared,and the results showed that when polyamine IPDA and blocking agent CGE were used,the coating films had better water resistance and corrosion resistance.Based on the two-step synthesis of IPDA-E44/PEGDGE-CGE nonionic waterborne epoxy curing agent,an epoxy-terminated phenyltrisiloxane(PEPDMS)was introduced to synthesize silicone modified waterborne epoxy curing agent IPDA-E44/PEGDGE-PEPDMS-CGE.Water absorption and contact angle tests showed that with the increase of PEPDMS,the water absorption of the coating film was decreased and the surface contact angle was increased.The mechanical property test results showed that the coatings had the best adhesion when the PEPDMS addition is 40% of the theoretical addition.The films cured by curing agents before and after modification were compared.SEM analysis showed that the modified films were smoother.TG and DSC analysis showed that the modified films had better thermal stability and higher glass transition temperature.Electrochemical tests showed that the modified films had better corrosion resistance.On the basis of previous studies,a two-component room temperature curing waterborne epoxy anticorrosion primer was prepared by using the synthesized IPDA-E44/PEGDGEPEPDMS-CGE waterborne epoxy curing agent and a commercially available waterborne epoxy resin 3EE101 W.Firstly,it was found,when the molar ratio of active hydrogen of curing agent to epoxy group of epoxy resin was 0.9,the coating film had the best mechanical properties and corrosion resistance.Then,the best pigment volume concentration(PVC)of primer was determined to be 30% by water absorption and EIS tests.Finally,the corrosion resistance of the coating films made from the synthesized and the commercially available waterborne epoxy curing agent were investigated.The results showed that,after soaking in 3.5 wt% Na Cl solution for 30 days,the coating film still maintained a good corrosion resistance and paint film state and its mechanical properties,water resistance and corrosion resistance of the coating films made from the synthesized waterborne epoxy curing agent had reached or even were partially superior to those of the two commercially available waterborne epoxy curing agents. |
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