Study On Synthesis Of Anionic Waterborne Polyurethane Resin

Aqueous polyurethane dispersions are a versatile class of materials having a wide range of applications. Compared to the conventional solvent-based systems, water-based polyurethanes greatly reduce the content of volatile organic compounds(VOCs) and their harm to the environment, meet increasingly stringent air pollutant emission standards and are expected to show superior performance, such as gloss, transparency, non-flammability, adhesion with most substrates, solvents and chemicals resistance and weather stability, so they have earned more attention.It is well known that aqueous resin dispersions have some flaws such as long drying time, large shrinkage and crackling easily, which mainly result from large latent vaporization heat of water, few reactive functional groups and low degree of crosslinking. Therefore, it is imperative to address the aforementioned problems of waterborne polyurethane for the enhancement of performance and promotion of application.A proposed solution was increasing the functionality of the resin to improve its degree of crosslinking for self-crosslinking or two-component systems in this wok. The key was to find a polyfunctional substance used as a blocking reagent to achieve this idea. Herein, F, a polyhydroxyl capping reagent with hydroxyl and amino simultaneously was introduced.In this work, aqueous and hydroxy-terminated polyurethanes(AHPUs) were prepared using isophorone diisocyanate(IPDI), dimethylolpropionic acid(DMPA), poly(caprolactone) glycol(PCL-210N) as main raw materials, trimethylolpropane(TMP) as crosslinking agent, ethylenediamine(EDA) as chain extender, and F as chain terminator. With content of DMPA and TMP, molar ratio of isocyanate to hydroxyl in the prepolymerization step, and the molar ratio of amino group in EDA to residual isocyanate of prepolymerization(chain extension ratio) as main factors, while with the evaluation index of properties of dispersions(transmittance, relative viscosity and particle size of dispersions), L16(45) orthogonal experiment was elected to optimize synthesis technology of AHPUs. And the properties of coatings, such as tack-free drying time, gloss, hardness, adhesion, water resistance, were characterized.The results showed that the prepared AHPUs had good performance in relative viscosity, transmittance and particle size when synthsis parameters were 7.0 wt% DMPA, molar(isocyanate)/ molar(hydroxyl) = 1.6 in prepolymerization step and chain extension ratio = 0.2.The two-component polyurethane coatings were prepared with polyurethane dispersions obtained under the aforementioned optimization conditions, and the tests showed that films had good air-drying ability, gloss, hardness, adhesion and water resistance.