Preparation Of Blocking Isocyanate And Study On The Unblocking

The isocyanate blocking technology is of great significance to the further development and application of isocyanate adhesives. The blocked isocyanate adhesives that applied as wood adhesive should be unblocked under less than 100°C, and the good blocking ability and good storage at room temperature are demanded. Of abundant blocking agents, the bisulphate salt has special properties such as low unblocking temperature, low price and almost no pollution. Besides, the sodium bisulfate blocked isocyanate might be self-emulsified due to the high polar group with ionBased on the previous study, the blocking technologies of TDI oligomer with sodium bisulfate were well studied, which included the content of S₁ solvent, mole ratio of TDI oligomer, blocking time, charging method of each component, and blocking temperature. The unblocking temperature of blocked TDI oligomer started from 80℃ characterized by DSC.Based on the works on the TDI oligomer blocking with sodium bisulfate, it also well discussed the blocking technology of PAPI with sodium bisulfate and the effects of each technological parameters on the blocking reaction. After evaluating the effects of each key parameter on the blocking percentages and stabilities of each reactants, the best blocking technology for PAPI was optimized. The key parameters evaluated were charging method, stirring speed, loading speed, combined solvent, blocking temperature and time, content of S₁ solvent, NaHSO₃/NCO mole ratio, and initial NaHSO₃ concentration.By means of DSC, the unblocking temperature of blocked isocyanate adhesives and the key parameters that affected the unblocking were discussed. The analytic results by DSC were verified by aniline titration analysis and FTIR analysis, which further indicated that it was available to block isocyanate by sodium bisulfate. DSC analysis also implied that blocked isocyanate could be used to modify the urea-formaldehyde (UF) resin and would accelerate the UF curing. The best content of blocked isocyanate was 3% when it used to modify UF resin.