Research On Outdoor Coating Films By Water-borne Polyurethane

In this paper, self-emulsifying method was applied to synthesize water-borne polyurethane(WPU) dispersion with natural raw material castor oil, which was used as polyol, and toluene diisocyanate (TDI). Meanwhile, hydrophilic chain extender dimethylolpropionic acid was introduced in the process of polymerization.The significance of this research was that, by advantage of Functionality2.7of castor oil, linear macromolecule, which consisted of a few branched-chain, could be synthesized. In this way, the coating property of WPU could be improved. For no-NCO group was residued in the products, the present process was non-toxic and lightly polluting. Two processes were investigated in the thesis, i.e., alcoholysis of castor oil and synthesis of WPU.For alcoholysis of castor oil, the effects of castor oil/glycerol ratio, reaction temperature and time on the products of alcoholysis were studied. The contents of monoglyceride were measured by tolerate-degree which was applied to determine the end point of alcoholysis. The conversion of primary hydroxyl into secondary hydroxyl was detected by FT-IR. The results showed that when the castor oil/glycerol ratio was0.55:1, temperature was in the range of240～245℃and reaction time was about2～2.5h, alcoholysis products with good performance could be obtained which was in favor of the next polymerization process.For synthesis of WPU, the effects of-NCO/-OH ratio and DMPA dosage on the appearance, stability, particle size, viscosity and coating property of WPU dispersion were studied. The results showed that with the increasing of-NCO/-OH ratio (R value), the particle size of polyurethane increased gradually, the stability decreased, hardness and smoothness of coating increased, the adhesion of coating increased, resistance to artificial aging degraded. With the increasing of hydrophilic monomer, transparency of dispersion increased, the particle size of polyurethane declined, viscosity increased, the stability of polyurethane dispersion increased, water-resistance of WPU declined. When-NCO/-OH ratio was in the range of0.60:1～0.70:1and the dosage of DMPA was in the range of2.3%～2.5%, stable polyurethane dispersions could be obtained, and the properties of the drying time, adhesion, water-resistance, artificial aging resistance of coating films were optimal.The products had good mobility and could be easily sprayed on the surface of the outdoor debris to form hard layers. This overlay was capable of preventing environmental pollution caused by flying upwards in a way after forming bulwark, at the same time it also protected the debris.