Study On The Preparation And Application Of Blocked Waterborne Polyurethane

Waterborne polyurethane has been widely used in coating, adhesive, leather, paper making, textile finishing, polymer surfactant industry with its good performance of environmental protection, safety, good mechanical properties and easy modification etc. The methods to prepare waterborne polyurethane emulsion include the pre-polymer, blocked, acetone method, and so on. To acquire the comparable properties with conventional solvent-based polyurethane, we have to make modification on the basis. So it becomes a hot spot to research for new methods to modify waterborne polyurethane. At this stage, the commonly used methods have:Crosslinking modification, blending modification, copolymerization modification and organic silicon/fluorine modification.In the invention, the blocked waterborne polyurethane was synthesized with polyethylene glycol (PEG-400/PEG-1000), methylhexahydrophthalic anhydride(MHHPA), diphenyl-methane-diisocyanate (MDI) and then reacted with epsilon-Caprolactam to cap-NCO terminal groups. Finally, the stable, yellow, transparent water-borne polyurethane resin was prepared. When added curing agent XCT-802, a novel solvent-free, environment-friendly, aqueous adhesive for wood had been prepared. Discussed the-NCO content, resin viscosity, hydrophilic and stability of the emulsion under different polyethylene glycol, MHHPA and MDI mole ratio.The molecular structure of polyester polyols and blocked waterborne polyurethane were characterized by Fourier transform infrared spectroscopy (FT-IR), and then investigated the effects of some factors such as deblocking time, deblocking temperature and curing agent content on the mechanical properties of the adhesive. The results revealed that when the curing agent content was35%of the resin, curing temperature was150℃and the curing time was120min, the F-BWPU system deblocked completely and showed good mechanical properties:The tensile shear strength was4.119MPa and the elongation at break was14.37%. when the amount of crosslinking agent was35%of the F-BWPU system, curing temperature was150℃, curing time was120min, the tensile shear strength was only1.013MPa. To improve the comprehensive performance of the system, we added waterborne epoxy emulsion.The results showed that for T-BWPU crosslinking system, the addition of waterborne epoxy emulsion have little improvements to its mechanical properties, and with the increase of curing temperature, the tensile shear strength was reduced. What’s more,when the curing temperature increased to170℃,the glue line turned to powder.while for F-BWPU crosslinking system, the results showed that the composite not only improved the toughness of epoxy curing system but also decreased the de-blocking temperature of the blocked waterborne polyurethane to some extent, meanwhile when the ratio was1:1,curing process:25℃/12h+145℃/2h,the layer exhibited better mechanical properties:Tensile shear strength above11MPa, elongation at break above60%and water absorption lower than5%within15days, it’s a perfect adhesive for wood.