Preparation And Properties Of High Solid Content Waterborne Polyurethane

With the strengthening of environmental awareness in society,research on waterborne polyurethane has gradually become popular.Compared with solvent-based polyurethanes,water-based polyurethanes have problems such as high latent heat of vaporization,slow drying speed,and high viscosity in the preparation process,resulting in high production and application costs,and thus the market is still dominated by solvent-based polyurethane products.In the preparation process of the existing waterborne polyurethane,a small amount of organic solvent is often added to adjust the dispersibility of the system.In a strict sense,it is not true to waterborne polyurethane,and the addition of the solvent still affects the environment,and the organic solvent is eliminated.It is also not conducive to the improvement of solid content.In addition,research on the application of waterborne polyurethanes is abundant,but there is not much literature on the study of its structure and performance systems.In this paper,high-solid solvent-free waterborne polyurethane was prepared by adjusting the branched structure.Study the effect of the types of cross-linking agent,the amount of cross-linking agent introduced,the solid content on stability,viscosity,thixotropy and viscoelasticity of aqueous polyurethane emulsion and foam.The test was characterized by infrared spectroscopy(FT-IR),electron microscopy,rotary viscometer and plate rheometer.Among them,pentaerythritol,dipentaerythritol and hyperbranched polyester H103 were used as crosslinking agents.The result shows:(1)By adjusting the branch structure,the early phase transition point can appear,the solid content of the emulsion can reach 55 wt.%,especially the solid content of H103 emulsion can reach 60 wt.%;the increase of cross-linking degree of the system can make the cross-linking network structure more perfect and the emulsion is stable.The increase in crosslink density affects the rheology of the emulsion,the crosslink density increases,the non-Newtonian fluid properties increase,the thixotropy decreases,the fluidity increases,and the viscoelastic behavior increases.The foaming property and foam stability can be controlled to some extent by changing the crosslinking density.At lower or higher crosslinking degree,the foaming property of the emulsion is small and the half life of the foam is short;the branched structure also affects the rheology of the foam.Within a certain range,the branch structure increases,the foam viscosity decreases substantially,the non-Newtonian fluid characteristics are obvious,the thixotropic properties decrease,and the viscoelasticity increases.In addition,the crosslink density also affects the solvent resistance of the film,the crosslinking density increases,and the water resistance and solvent resistance of the film increase.(2)By adjusting the solid content,it can affect the rheology of the emulsion.The decrease of solid content will cause the emulsion to be diluted,the viscosity of the emulsion will decrease,the characteristics of non-Newtonian fluid will be insignificant,and the thixotropic and viscoelasticity will decrease.The decrease of solid content will also increase the internal difference of the system.The reaction of cyanate with water affects the expansion ratio and foam stability;the rheology of foam is also affected by the solid content.Within a certain range,the decrease of solid content leads to the decrease of foam viscosity,the reduction of thixotropy and the decrease of viscoelasticity.Water participates in the reaction to form a urea bond,so that the membrane also has a certain degree of crosslinking at a low solid content,but the solid content is too low,and the dilution effect of water is enhanced.