| Synthesis and construction process of polyurethane in traditional way require a large amount of organic solvents, the remaining of which would cause serious health problems of staff and consumers. With the development of society and the improvement of people's environmental awareness, VOC is limited in many countries. In this situation, aqueous polyurethane, which is used as an alternative dispersion medium instead of organic solvents, has great potential application in environmental protection.This paper mainly focused on the synthesis of aqueous polyurethane. The aqueous polyurethane prepolymer was made through step-growth polymerization of diphenylmethane diisocyanate with polyester glycol and dimethylol propionic acid, which was neutralized by triethylamine to form the stable transparent aqueous polyurethane dispersion. The remaining number of -NCO group was measured by di-n-butylamine titration method and the results showed that its remaining amount had great effect on the properties and stability of aqueous polyurethane. The morphology of the polyurethane dispersion was characterized by TEM and the properties of the PU films were also tested. The experimental results revealed several facts. Firstly, with the increase of n(NCO)/n(OH) ratio, both water resistance and tensile strength of samples were improved, while the elongation rate at break decreased. Secondly, with the increase of the DMPA content, the water resistance fell, the tensile strength enhanced, and the elongation rate at break increased initially but decreased later. Further more, emulsion stability and water resistance of samples degraded with the increase of the neutralization degree. Finally, after adding ethylenediamine, a chain-extension agent, into the dispersion in the process of emulsification, both of the tensile strength and the elongation at break enhanced, while the water absorptivity decreased to 4% obviously which overcame the intrinsic defect of polyurethane emulsion film fabricated by internal emulsification-high water absorption rate.Through mechanical blending, aqueous polyurethane emulsion and microspheres with hollow structures were mixed together. The mechanical properties of the film formed later were studied. The experimental results showed that its mechanical properties fell and no ideal conclusion was made.There exist many disadvantage of the single APU emulsion, such as poor self-thickening, low solid content, weak water resistance, lower mechanical strength compared to acrylic resin and high cost. However, the property of polyacrylate(PA) emulsion and polyurethane emulsion could complement each other, which has great potential application. Organic silicone resin with low surface energy, good water resistance, fine weatherability and excellent air permeability has been widely used in polyurethane modification. Modification of aqueous polyurethane-polyacrylate using organosilicon by suitable chemical methods could obtain coating with excellent properties, such as water resistance and mechanical properties.A novel modification method, dual-modification of acrylic acid and organosilicon, was adopted in the experiment. Double bond is introduced to the molecular chain of product, utilizing the reaction between-OH and -NCO group in HEMA. Then free radical polymerization occurres between double bond and C=C double bond of vinyl silane, which results in the organosilicon modification of APU. This method was supposed to achieve the acrylic acid and organosilicon modification effect. The structure and properties of the obtained samples were investigated in the experiment. The results revealed that although the thermal performance and water-resistance of the novel emulsion improved, its stability and filming property degraded. These factors discussed above limits the usage of this emulsion.
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