Synthesis Of Hydroxyl Constituent Of Epoxy-polyurethane Dispersion

At present,waterborne polyurethane resin is the basic materials of high performance water coatings.Using epoxy resin to modify waterborne polyurethane is a method to enhance its corrosion resistance and abrasion resistance.Directly adding epoxy resin into synthesis process of polyurethane has been considered as the most extensive method to modify the properties of waterborne polyurethane in many papers,however it could easily gel during the experiment.Therefore the amount of added epoxy resin is limited,which could not get the expected result.The residual epoxy group can react with some active initiators(urethane groups,carboxyl groups,amines),which would reduce the storage ability of emulsion.In order to eliminate the negative effects of epoxy group and improve the addition of epoxy resin,this research selected chemical modified epoxy resin to modify waterborne polyurethane,and the dispersion could be used as hydroxyl constituent in the two-component polyurethane.Firstly,the epoxy resin was modified by diethanol amine to prepare epoxy-based polyol.The influence of epoxy resin’s different average molecular weight on dispersions and films were studied.At last the bisphenol-A type epoxy resin(CYD-011)was used,epoxide number 0.21,average molecular weight 950.The conditions of epoxy resin chemically reacted with diethanol amine were studied.The optimized condition was 1:1(the mole ratio of epoxy group to diethanol amine)at the temperature of 80℃ for 6 h.Secondly,the hydroxyl constituent of epoxy-polyurethane dispersion was synthesised by some main raw materials,such as toluene diisocyante(TDI-80),polyether polyols(DL2000),dimethyol propionic acid(DMPA)and epoxy-based polyol.The factors during the synthesis process of dispersions were discussed,for instance,the mole ratio of-NCO/-OH in the prepolymer stage,the content of DMPA,the blocking percentage,the addition of epoxy-based polyol and the neutralization degree to dispersions and films.When the mole ratio of-NCO/-OH in the prepolymer stage was 15,the content of DMPA reached 8%,the blocking percentage was 50%,the addition of epoxy-based polyol reached 23～25%,and the neutralization degree was 100%,so the properties of dispersions and films had high performance and appearance.Thirdly,two component polyurethanes were composed by the hydroxyl constituent of epoxy-polyurethane dispersion and five water-soluble isocyanate curing agents.The research selected Aquolin 161 as the curing agent of two component polyurethane by observing the mixture stage and testing the physo-chemical properties of cured films.The hardness,heat resistance,water and chemical resistance were in optimized conditions when the mole ratio of-NCO/-OH in curing agent/dispersion was 1.5～1.7.(4)Lastly,the structure of epoxy-based polyol,epoxy-polyurethane dispersion and two component polyurethane films were analysised by Fourier transform infrared(FTIR).The surface crack spacing and regularity changes of the two-package waterborne polyurethane films were observed by Scanning electron microscopy(SEM).The heat resistance of two component polyurethane films and one component films was investaged by Thermogravimetric analysis(TG).