Preparation Of High Hydroxyl Content Self-emulsifying Modified Waterborne Polyacrylate Emulsion

With the restriction of environmental laws and regulations,the traditional solvent based coatings have gradually been replaced by environmental-friendly coatings.Because they contain a large number of volatile organic compounds,causing serious air pollution and harmful to humans.On account of its excellent gloss retention,color retention,corrosion resistance,weather resistance,dielectric resistance and workability,waterborne acrylate coatings have been widely applied in many fields of construction,automobile,wood,metal coating etc.But it inevitably has some defects,such as poor heat and water resistance,the most typical of which is heat-adhesive and cold-brittleness after resin drying.In order to overcome these drawbacks,it is often,necessary to modify the polyacrylate through introducing functional monomers or other resins.The introduction of hydroxyl functional monomers is an effective way to improve the film properties of acrylate.In this work,a pre-emulsification and seeded semi-continuous emulsion polymerization method23,24 was firstly employed to synthesize the waterborne hydroxyl polyacrylate.The functional monomer HEMA was used to provide a high content of hydroxyl group,and the reactive emulsifier SE-10 was introduced to substitute for the traditional emulsifier,to solve the problems of residual emulsifier.The best conditions including polymerization process and temperature,monomer types and dropping time were determined,and the effects of emulsifier content and addition method,HEMA content,chain transfer agent content,and soft/hard monomer ratio on the properties of emulsion were investigated.The results of FTIR,GPC,TEM,DLS,DSC etc showed that we have successfully synthesized the core-shell structure of polyacrylate emulsion with average particle size of 182.7 nm,PdI of 0.06.Through the optimization of polymerization conditions and the control of the structure of particles,when the polymerization temperature was 80±2?,the monomer dropping time was 2.5-3 h,the SE-10 content was 1.5%and its distribution ratio in the seed and pre-emulsion was 1:3,the HEMA content was as high as 20%,and the soft/hard monomer ratio was 1/2,the hydroxyl polyacrylate emulsion has good performance,stability,low viscosity and solid content of 46.5%.With the amount of chain transfer agent in the range of 0-3 wt%the hydroxyl polyacrylate emulsion with good performance and stability could be obtained.The aminoacrylic coatings prepared by the hydroxyl polyacrylate had excellent film properties,which has great potential in development and application.The high hydroxyl content self-emulsifying waterborne polyacrylate emulsion still has the inherent defects of poor flexibility and impact resistance.Therefore,polyester resin was introduced for further modification.The performance of polyacrylate is improved by the good fullness,flexibility and impact resistance of polyester resin.In the experiment,the carboxyl terminated unsaturated polyester was synthesized,which was used as a monomer of emulsion polymerization to prepare the polyester modified waterborne acrylate by means of chemical modification.The influence of hydroxyl monomer was investigated.The viscosity and coagulum content of emulsion increase with the increase of HEMA content,and the optimum dosage of HEMA was 35%.After the introduction of polyester,the properties of modified resin emulsion,such as viscosity,molecular weight and particle size distribution,were compared,the effects of the ratio of polyester/acrylate on the emulsion properties,film properties,glass transition temperature and thermal stability of the resin were also investigated.By FTIR and DSC,it is proved that atactic copolymerization took place between polyester and acrylate,and there was only a glass transition temperature at 22? The results of DLS,GPC and TG showed that the emulsion viscosity increased,the molecular weight decreased,and the particle size became larger,the particle size distribution became wider,the emulsion stability was good,but the initial thermal decomposition temperature of the resin decreased significantly,and the thermal stability decreased after modification.When the polyester was too much or too little,the film appearance became bad,such as white,low transparency,soft and sticky or hard brittle cracking.When CtUPR/AC=1:5,solid content was 48%,Mn was 3050,the average particle size was 204.7 nm,PdI was 0.102,the viscosity reached 586 mPa-s,both the emulsion and film properties were better.The introduction of flexible polyester improved the flexibility and impact resistance of hydroxyl acrylate film,and made the modified resin have the advantages of both,and will further expand its range of application.