Synthesis And Characterization Of High Solid Content Polyester Polyurethane Dispersions Containing Polycarbodiimide

Polyurethane dispersions(PUD)synthesized from adipic acid type polyester polyols are widely used in adhesives and coatings,such as waterborne shoe adhesives,automobiles,furniture adhesives,leather,textile coatings,and so on.The ester group in the adipic acid type polyester polyol structure is easily hydrolyzed,affecting the stability of the polyurethane dispersion,resulting in poor water resistance and solvent resistance after the film formation of the emulsion,low hardness,poor heat resistance and so on.At present,there are two types of methods used in China: one is to modify polyester polyol or to add mixed polyol to make up for the deficiency of polyester polyol,but it has not been able to fundamentally solve the problem of poor hydrolysis resistance of polyester.The second method is to adding to anti-hydrolysis agents.However,these products are expensive in China and may affect the stability of the PUD system.Polycarbodiimide(PCDI)was synthesized from tetramethylxylylene diisocyanate(TMXDI).Then polyurethane dispersions(PUD)with solid content above 50% were prepared from polycarbodiimide(PCDI)based on tetramethylxylylene diisocyanate(TMXDI),polybutylene adipate diol(PBA),hexamethylene diisocyanate(HDI)and isophorone Diisocyanate(IPDI),sodium ethylenediamine sulfonate(AAS-Na),isophorone diamine(IPDA)by the acetone method.The effects of different variables on the viscosity,particle size,particle size distribution and water-resistance of high-solid polyurethane dispersions were investigated by means of dynamic light scattering particle size distribution ζ potentiometer and transmission electron microscopy(TEM).The results showed that,as the amount of PCDI added and the degree of polymerization increased,the average particle size of the dispersion increased,the viscosity decreased,and the particle size exhibited a more pronounced binary distribution;as the content of the hydrophilic group increased,the average particle size of the dispersion decreased,the viscosity increased,and the particle size distribution narrowed.Transmission electron microscopy(TEM)characterization showed that the dispersion colloidal particles demonstrated spherical structures of different sizes.The small colloidal particles in the dispersion were in the gap between the large colloidal particles,which ensured the dispersion with high solid content and good stability by reducing the viscosity of the system.The addition of PCDI in the polyurethane synthesis stage can significantly improve the hydrolysis resistance of the polyester polyurethane.The optimum addition amount of PCDI is 3wt%,and the optimum polymerization degree of PCDI is 4.PUD films were tested by infrared spectroscopy,mechanical properties,Shore hardness,thermogravimetric analysis(TG),water resistance and ethanol resistance.The mechanical properties and Shore hardness of PUD film indicated that with the increase of the amount of PCDI added,the extent of the tensile strength weakening after the hydrolysis of the film gradually decreased;when the addition amount of PCDI is the same,as the content of hydrophilic groups increases,the tensile strength of the film increases before and after hydrolysis,and the hardness increases accordingly.The water resistance and ethanol resistance test of the PUD film showed that the water absorption of the PUD film was between 6% and10%,indicating that the water resistance of PUD films was good.As the hydrophilic content increases,the water absorption rate and ethanol absorption rate of the PUD film increase.The thermal performance test of the PUD film showed that the initial decomposition temperature of the PUD film was 290 °C,and it was completely decomposed at 450 °C,and it had good thermal stability.