Sodium Bisulfite Blocking Isocyanate With Phase-Transfer Catalyst

In the recent decades, the research of the wood adhesives was focused on the blocking isocyanate adhesives. It has been researched widely to block the isocyanate with organic reagents, but in the side of the wood of the protection of environment, some researchers has researched the blocking isocyanate with inorganic agants.Based on the theory of the blocking reaction between the active hydrogen of the sodium bisulfate and the isocyanate, it was researched that the conditions of blocking reaction between the powder or solution of the sodium bisulfate and the polymethylene polyphenyl polyisocyanate(PAPI),for example, the temperatrue, the mole ratio of the catalyst, the mole ratio of the materials, the catalyst and the solvent. The blocking reaction between the sodium bisulfate and PAPI was improved with the tebrabutyl ammonium bromides(TEBA)and the hexadecyl trimethyl ammonium bromide. The best condition of blocking reaction was definited. The higher blocking ratio was received blocking the PAPI with the powder of the sodium bisulfate than the solution of the sodium bisulfate, because the PAPI reacts easily with the water in the solution. The blocking ratio of the reaction between the PAPI and the powder of the sodium bisulfate with TEBA reached 69%.The best conditions of the reaction is that the temperature of reaction is 30℃,that the mole ratio of the catalyst is 1%,that the volume ratio of the solvent to PAPI is 1:1,that the mole ratio of -NCO and the powder of the sodium bisulfate is 1.1:1.It was researched systematically with IR and the method of titration of the free-NCO, that the content of the free-NCO in the system changed with the different condition and the kinetics data of the blocking reaction. At 15℃,the reaction between the TDI in the solvent and the solution of the sodium bisulfate occurred at a certain time, dropping and stirring. The blocking ratio of isocyanate could reach to 80%. The strcture of blocked isocyanate was characterized by FTIR. The unblocking temperature range of blocked isocyanate is from 54℃to 68℃by DSC.