The Preparation And Modification Studies Of Waterborne Epoxy Resin Emulsion

Because of the excellent adhesive property, chemical resistance, mechanical property and electrical insulation performance, epoxy resin is widely used. The common epoxy resin is insoluble in water, but soluble in organic solvents, causing serious environmental pollution. As an increasing need for protecting the environment, waterborne epoxy resin emulsion is heavily favored today due to its safety, environmental protection and low-VOC. Therefore, the modified epoxy resin is an important research direction of waterborne epoxy resin.In this paper, we selected bisphenol A type epoxy resin as matrix, using unsaturated acid modified method, and obtained waterborne epoxy-styrene acrylic graft copolymerization emulsion. The course of reaction and the rates of reactors were studied. The optimum reaction conditions was that epoxy resin E-06 react as main body, n-butyl alcohol and ethylene glycol butyl ether react as cosolvent, the best ratio of them was 5:6, benzoyl peroxid react as initiator, the optimum amount of initiator was about 4 %, the best grafted temperature was 120 ?, the best grafted time was 5 h, the best ratio of grafted monomer with epoxy resin was 4:5, the amount of methacrylic acid was 25 %, the neutralization degree was 100 %, the salt temperature was 55 ?. By analyzing the performance of the obtained waterborne epoxy resin emulsion, we found that epoxy resin and acrylic monomers occurred polymerization reaction successfully. The appearance, Ca²⁺ stability, dilution stability, freeze-thaw stability and the mechanical stability of the emulsion were up to standard. And glossiness of coating was higher. But the thermal stability of modified emulsion was a little lower, and the improvement of flexibility was not so obvious, needing further modification.Based on waterborne epoxy-styrene acrylic graft copolymerization emulsion, we selected PAM and PPG as modifiers to modify copolymer emulsion. And we found that the modification effect was not so ideal when the modifiers were added individually. When adding them together to the waterborne epoxy emulsion, we studied the effect of their dosage and ratio to the emulsion and film. We found that when the content of modifiers was 8 % and their ratio was 1:1, the emulsion had a minimal viscosity and the film had the lowest water absorption. Two kinds of modifier respectively played their unique role, and there were no conflicting phenomenon. The structure of modified epoxy emulsion was characterized by FT-IR and we can find the characteristic absorption peak of PAM and PPG, meaning that they were grafted to epoxy resin system successfully. The results of TG showed that the thermal stability of modified copolymer did not have obvious enhancement, but its fire resistance was improved. What's more, the poor flexibility of epoxy resin was improved after modified, and the comprehensive performance of emulsion and film was excellent.And then, we used nano-TiO₂ to modify waterborne epoxy-styrene acrylic graft copolymerization emulsion. Before that, nano-TiO₂ needed the surface modification with silane coupling agent KH-550. We studied the dispersing stability of nanoparticles in acetone solution with different modification temperature, modification time and amount of addition of modifier, and found the optimum reaction conditions: the reaction temperature was 80 ?, the reaction time was 5 h and the amount of modifier was 20 %. Through the study of the performance analysis of modified nano-TiO₂, we found that the modified nano-TiO₂ can be stable for a long time to disperse in organic solvent and its hydrophobic performance and dispersity were improved.Then, we used the modified nano-TiO₂ to modify waterborne epoxy-styrene acrylic graft copolymerization emulsion. Through the analysis the influence of addition amount of nano-TiO₂ to water absorption and viscosity, determining the best addition amount of nano-TiO₂ was 0.6 %. By analyzing the performance of the modified epoxy emulsion we found that nano-TiO₂ had modified the waterborne epoxy emulsion successfully. And nano particle in resin matrix distributed dispersedly and there were no agglomeration. The resistance of wettability of the film had been improved and the film had a better hydrolytic resistance. The emulsion modified had a better stability and lower water absorption. Besides, the thermal stability and flexibility of epoxy resin had been improved.