| With the development of society,the progress of science and technology,coatings are developing in the direction of green and environmental protection.Waterborne polyurethane coating is a kind of coating.It is a polyurethane system with water as dispersant.It has the characteristics of low toxicity and low harm.However,due to the poor heat resistance,water resistance and chemical resistance of waterborne polyurethane,there is a large gap between waterborne polyurethane and solvent polyurethane coatings,which limits the development of waterborne polyurethane coatings to a certain extent.Waterborne polyurethane anti-corrosion coating is a field of waterborne polyurethane coating development,but the anti-corrosion performance of pure waterborne polyurethane coating is not good.Generally,other substances are introduced into the polyurethane system to improve the performance and anti-corrosion ability of waterborne polyurethane.Firstly,a series of waterborne polyurethane were synthesized with polypropylene carbonate glycol（PPC）and IPDI as the main raw materials.The effects of different addition time of DMPA,DMPA content,hard segment content and different kinds of diols on the basic properties and salt water resistance of waterborne polyurethane were studied.On this basis,this thesis also used epoxy resin to modify waterborne polyurethane,explored the influence of different amount of epoxy resin on the basic properties of waterborne polyurethane,and focused on the influence on the corrosion resistance such as salt spray resistance and electrochemical impedance spectroscopy（EIS）.In this thesis,silane coupling agent was used to modify waterborne polyurethane alone,silane coupling agent and epoxy resin were used to modify waterborne polyurethane.The effects of different content of silane coupling agent on the basic properties of waterborne polyurethane were explored,with emphasis on the effects on the corrosion resistance such as salt spray resistance and EIS.The structure and heat resistance of the film were analyzed by infrared spectroscopy and thermogravimetric analyzer.The results are as follows:（1）In the different time of adding DMPA,the emulsion prepared by DMPA before prepolymerization had the worst appearance,the largest particle size,the worst adhesion force and the worst comprehensive performance.The comprehensive properties of the emulsion prepared by one-pot method are similar to those prepared by adding DMPA in prepolymerization and DMPA after prepolymerization,but the one-pot method is simple and easy to operate.The content of DMPA,the content of hard segment and polyols has a certain effect on the emulsion and coating.With the increase of DMPA content,the appearance of emulsion improved,the particle size became smaller,the water resistance of the film became worse,and the salt resistance was slightly worse.When the DMPA content was too low,the emulsion storage was unstable.With the increase of hard segment content,the appearance of emulsion increased,the particle size increased,the adhesive force and water resistance of film increased,the salt resistance increased slightly.Polycarbonate type waterborne polyurethane emulsion has good comprehensive properties such as appearance,stability,adhesion,water absorption and salt resistance.Polyester emulsion has poor appearance,but low water absorption and salt tolerance is similar to polycarbonate type.Polyether emulsion has higher water absorption and poor salt resistance.（2）The heat resistance of waterborne polyurethane modified by epoxy resin had been improved.The stability and freeze-thaw resistance of the emulsion were good in the range of0% ～ 15% epoxy resin.With the increase of epoxy resin content,the particle size of the modified emulsion first decreases and then increases,and the pencil hardness,adhesion and water resistance of the coating first became better and then became worse.In the corrosion resistance test of the coating,with the increase of the amount of epoxy resin,the salt spray resistance and EIS of the coating first got better and then got worse.It was found that when the amount of epoxy resin is 10%,the particle size of emulsion was the smallest,the hardness of the coating reaches H,the adhesion force reaches 1,and the water absorption rate was 11%.In the corrosion resistance test,the coating did not see obvious corrosion products after 168 h salt spray resistance test,and the salt spray resistance was the best;EIS test shows that the impedance modulus of the coating was the highest and the corrosion resistance was the best after soaking in Na Cl solution for 30 min,21d and 42 d.（3）Three silane coupling agents（KH-550,KH560 and kh-792）were used to modify waterborne polyurethane respectively,which affected the water resistance of waterborne polyurethane to varying degrees.Among them,kh-792 was the most obvious,and the water absorption was only 6.6% at 72 h.（4）The heat resistance of waterborne polyurethane modified by organosilicon and epoxy resin has been improved.The stability and freeze-thaw resistance of the emulsion are good at the 0% ～ 3% content of KH-792.With the increase of KH-792 content,the particle size of the modified emulsion increases,the pencils hardness and adhesion of coatings became worse,and the water resistance became better.The comprehensive performance was the best when the content of kh-792 is 2%.In the corrosion resistance test,after 72 h salt spray resistance test,it was found that with the increase of kh-792 content,the corrosion products of the coating near the scribed line first became less and then more,and the corrosion resistance first became better and then worse.Among them,the modified waterborne polyurethane coating with the content of kh-792 of 2% had the lightest corrosion degree near the scribed line and the best salt spray resistance.EIS test results showed that the impedance modulus of the coating soaked in Na Cl solution for 30 minutes increased with the increase of the amount of kh-792,but with the extension of soaking time,the impedance modulus of the coating decreases.When reaching 42 days,the impedance modulus of the coating with the amount of kh-792 of 2% was the highest,there were no obvious corrosion products on the surface,and the corrosion resistance was the best. |
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