The Study Of Synthesis And Modification Of Waterborne Polyurethane Emulsion

Waterborne polyurethane (WPU) is green and environmentally friendly polymer materials.Scholar, experts and enterprises pay attention to waterborne polyurethane, because it hasexcellent performance and characteristic of environmental pollution-free. However,performance of waterborne polyurethane is bad in water resistance, hardness, solid contentand so on. Therefore, scientific workers need to try their best efforts to improve or eveneliminate the defect of performance. Consequently, the study of waterborne polyurethanehas important practical significance.The research shows that reaction monomers are added via two-step method, the first stepreation temperature is controlled at85℃, the second step reaction temperature is controlledat80℃, both reaction time is controlled2h, respectively. The viscosity of prepolymer isadjusted by solvents of acetone and1-methyl-2-pyrrolidone in the reaction process.According to the above requirements, we can obtain waterborne polyurethane emulsion withgood resistance to water and high solid content. The research of waterborne polyurethaneemulsion modified by epoxy resin shows that the method of adding monomer is the same asthe before modification. When the reaction temperatures of the first and the second steps areperspectively85℃and75℃, their reaction time is respectively2h and4h, we can obtainwaterborne polyurethane emulsion modified by epoxy resin with excellent performance.The reaction monomer study shows that when mole ratio (R) of the isocyanate group ofisophorone diisocyanate and the hydroxyl group of polypropylene glycol is (3.8-4.6):1, themass fraction of dihydroxy methyl propionic acid is between5.0%and6.0%, the massfraction of1,4-butanediol is between8.0%and9.0%, the content of ethylenediamine isabout0.004%, waterborne polyurethane emoulsion with well performance is able to besynthetized. Waterborne polyurethane emulsion modified by only one epoxy resin is able tobe synthetized, when the contents of E-06, E-12, E-20and E-44are below2.0%,2.0%,6.0%and8.0%, respectively. When the mass fractions of E-20and E-44are respectively2.0%and4.0%, the perporty of waterborne polyurethane emulsion modified by them isbetter than that modified by only one kind of epoxy resin.Paticle size analysis shows that the size of emulsion is non-uniform and the level ofmicron. FTIR analysis shows that the characteristic peaks of isocyanate group and hydroxyldisappear and the characteristic peak of carbamate appears in the infrared spectra, whichshows isocyanate group and hydroxyl react completely. Meanwhile, waterbornepolyurethane is synthesized. The FTIR spectra of waterborne polyurethane modified epoxyresin shows that the characteristic peak of epoxy group disappear, and the characteristicpeak of season carbon atoms of epoxy resin appear, which shows that the epoxy resin hasbeen grafted successfully to waterborne polyurethane. Thermo gravimetric analysis showedthat the property of heat resisitance of the modified waterborne polyurethane is improvedgreatly than that of the unmodified waterborne polyurethane. Electrochemical analysisshows that when the mass fraction of dihydroxy methyl acrylic acid is5.0%, thepolarization resistance of the unmodified waterborne polyurethane is50k·cm2, that of themodified waterborne polyurethane is57.3k·cm2, the latter has higher polarizationresistance than the former, having better corrosion resistance performance. Comprehensive performance test results show that the various properties of waterbornepolyurethane is very well, and these properties is conform to our country’s technicalrequirements of building exterior wall emulsion coating. Waterborne polyurethane modifiedby epoxy resin is also able to be used for emulsion of anti-corrosion coatings.