| Under the catalysis of phosphotungstic acid,the waterborne resin emulsion was obtained by modifying the epoxy resin with high epoxy value,low epoxy value and high epoxy value epoxy-acrylic resin by phosphoric acid.The preparation conditions were optimized by single factor experiment,response surface method and orthogonal experiment,respectively.FT-IR,1HNMR,31PNMR and 13CNMR were used to characterize waterborne resin emulsions.The mechanism of synthesis process of phosphoric acid-modified resin for waterborne resin emulsions was investigated,and the reaction kinetic model was obtained.The properties of the waterborne resin emulsions were studied.Meanwhile,waterborne epoxy emulsion was applied to Dacro coating to investigate its application.The main research contents and results are as follows:(1)A type of epoxy resin with low epoxy value(named DER671)was modified by phosphoric acid.The effects of the molar ratio of epoxy resin to phosphoric acid,reaction temperature,stirring speed,reaction time,both dosage of solvent and dosage of catalyst for total reaction amount on the conversion rate of epoxy group were investigated by single factor experiment.The process conditions were optimized by response surface method and the products were characterized.The catalysis mechanism of phosphotungstic acid was studied,and the waterborne epoxy emulsion was applied to Dacro coating to for its application.The results showed that when the stirring speed was 300r/min and the molar ratio of epoxy resin to phosphoric acid was 3:1,the order of influence of various factors on the conversion rate of epoxy group was as follows:phosphotungstic acid amount>reaction temperature>reaction time>solvent amount.The quadratic polynomial equation of the response surface is as follows:Y=+90.88+2.88A+1.63B+2.75C-1.42D-0.74AB-0.96AC-0.11AD-0.56B C+0.75BD+0.55CD-1.71A2-0.19B2-0.91C2-0.76D2.The conversion rate of 93.27%for the epoxy group was achieved under the following optimum process conditions:1.15%of the dosage of phosphotungstic acid,160min of the reaction time,53°C of the reaction temperature,26m L of the amount of solvent.The results of FT-IR and NMR analysis showed that the formation of phosphoric ester compounds was considered to be attributable to the ring-opening reaction between phosphoric acid and epoxy resin.Furthermore,the results showed that the waterborne epoxy emulsion had good water dispersion and stability.The results for dacro coating test showed that the emulsion was easy to be in combination with the metal matrix due to both the film-forming material containing phosphorusand organic attachment.Therefore,the bonding force was enhanced,and the protective effect was also stronger.The hardness and impact resistance of the coating physical properties are both excellent,corrosion resistance indicators are good.The possible catalytic mechanism is that the hydrogen ions generated in the ionization process of phosphotungstic acid solution,which made the epoxy group open the ring and form carbocation,and then reacted with the negatively-charged hydrogen phosphate ion dissociated from the phosphoric acid in the solution to form the epoxy phosphate ester.(2)A type of epoxy resin DER331 with high epoxy value(named DER331)was modified by phosphoric acid.The effects of different ratio of reactants,reaction time,dosage of phosphotungstic acid in catalyst,reaction temperature,dosage of acetone in solvent and stirring speed on the conversion rate of epoxy group were investigated by single factor experiment,and the process conditions were optimum by orthogonal experiment.Then,under the optimized conditions,the effects of reaction temperature on the conversion rate was studied,and the kinetic model was studied.Furthermore,the kinetic equation of the reaction was obtained.The structural changes before and after modification were characterized and the properties of the emulsion were studied.The results showed that when the stirring rate was 300r/min,the order of influence of various factors on the conversion rate of epoxy group was as follows:reaction temperature>solvent amount>reaction material ratio>catalyst amount>reaction time.The average conversion rate of 98.07%for the epoxy group was achieved after 5 parallel experiments under the following optimized process conditions:1:2 of epoxy/phosphoric acid,1.3%of phosphotungstic acid content,45°C of reaction temperature,15m L of solvent content,130min of reaction time.The results of IR and NMR analysis showed that the formation of phosphoric ester compounds was considered to be attributable to the ring-opening reaction between phosphoric acid and epoxy resin.By fitting the nonlinear equation with the data of the conversion rate changing with temperature at different times,the reactions at 35°C,45°C and 55°C are the second order reactions,and the isothermal kinetic equation is R=1520.36*e-26.2048/RT*C2,Ea=26.6048 k J/mol.(3)A type of epoxy-acrylic resin with high epoxy value was modified by phosphoric acid.A ring-opening reaction was carried out between acrylic acid and epoxy resin with high epoxy value(named DER331),and then phosphoric acid was added to modify it in water.Fanally,it was copolymerized with acrylic acid,methyl methacrylate,butyl acrylate and styrene to obtain waterborne epoxy-acrylic resin emulsion.For the first step,the acrylic acid was reacted with DER331.The effect of the ratio of reactants,reaction time,the dosage of catalyst N,N-dimethylethanolamine,reaction temperature,the dosage of n-butanol solvent and stirring speed on the esterification rate of acrylic acid and retention efficiency of epoxy groups were investigated,respectively.The effects of different ratio of reactants,reaction time,amount of phosphotungstic acid,reaction temperature and stirring speed on the retention efficiency of epoxy group in the second step of modification experiment via phosphoric acid were studied by single factor experiments.The structures of resin before and after modification were characterized.The solid content,dilution stability and mechanical stability of the emulsion were investigated and analyzed.The results showed that the synthesis condition for epoxy-acrylic resin modified by phosphoric acid was as follows:0.5 of acrylic acid/epoxy group,2.0%of N,N-dimethylethanolamine,115°C of reaction temperature=,20m L of solvent,4h of reaction time=,300r/min of stirring speed.A modified epoxy resin with an epoxy retention rate of 8.15%and an esterification degree of acrylic acid of 98.37%was obtained by the following processes:2:3 of epoxy group/phosphoric acid,2.0%of phosphotungstic acid content,105°C of reaction temperature=3.5h of reaction time and 300r/min of stirring speed.Both the water dispersion and stability of the emulsion were good. |
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