Study On The Synthesis Of Hydroxyl Component Of The Two-component Waterborne Polyurethane And Its Curing Properties

At present, the waterborne polyurethane coatings, the majority of which are one-component system, are eco-friendly; but they are difficult to meet the extensive market demand due to the obvious disadvantages in the film properties. The two-component waterborne polyurethane, which can form the crosslinking coating and result in effective improvement in the film properties, has become a research hotspot in recent years. In this paper, we first synthesized the aqueous polyurethane polyol dispersion component, then selected the curing agent component to match it, and finally prepared two-component waterborne polyurethane system by mixing the polyol dispersion component and the curing agent component together.A polyurethane polyol dispersions component of the two-component waterborne polyurethane system has been successfully synthesized with the diethanolamine (DEA) as the blocking agent for introducing hydroxy-terminated on to the end-NCO polyurethane prepolymers, which was previously prepared with isophorone diisocyanate (IPDI), polyether binary alcohol (DL-1000), dimethylol propionic acid (DMPA), trimethylolpropane(TMP) as the main raw material by "prepolymer method" Some composition factors such as-NCO/-OH of prepolymer stage, DMPA content, crosslinked chain extender TMP content, the proportion of amine chain extender, and the hydroxy contents have been studied.The effects of different types of water-soluble isocyanate curing agents and as-prepared the polyol composition mentioned above on the film properties have been discussed. The ion-modified curing agent exhibits the best performance; but its reaction with polyols is too fast, compared with that of the non-ionic modified curing agent. The non-ionic modified curing agent is more moderate. The Arocura360, which is more balanced between the mixed state and the film properties, was selected as curing agent components.The influences of curing conditions on the two-component waterborne polyurethane film performance have also been investigated. The appropriate conditions for curing progress have been decided according to the final film performane:1.5～1.7of molar ratio of curing agents to dispersions, increasing the curing temperature as much as possible in the range of20℃-50℃. When curing for72h, the gel rate has almost no change, and the crosslinking reaction between the polyol component and the curing agent component has almost completed.The synthesis of polyol components and the film properties of two-component products were tested, characterized and analyzed. Laser particle size analyzer tests show that the hydroxy component has narrow size distribution with the average size about100nm. Fourier transform infrared (FTIR) is used for tracing synthetic process and characterizing structures of the polyurethane polyols. The FTIR contrastive analysis of the polyols and the final film prove that during the curing stage, the cross-linking reaction occurs between the polyol and the curing agent. Scanning electron microscopy (SEM) shows the changes of surface crack spacing and regularity of the film. The thermogravimetry (TG) curves indicate that the final film has good heat resistance. The differential scanning calorimetry (DSC) shows that the cured two-component waterborne polyurethane films have three phase transition peaks.