Study On Preparation And Application Of Emulsifiable Polyisocyanate

The purpose of the study was to prepare emulsifiable polyisocyanate prepolymer which was synthesized by reaction between four kinds of hydrophilic modifier(different quantity of EO) and polyisocyanate(PAPI). Then a stable emulsion was obtained by dispersing prepolymer in water in that condition a little stabilizing agent and surface active agent exist. The effect of process parameters such as different kind of prepolymer, molar ratio of NCO and OH, concentration of emulsifier on the properties of prepolymers and emulsions is discussed in detail. The results show that the viscosity of emulsions and prepolymers increased with the increase of molecular weight of hydrophilic modifier, and different hydrophilic modifier lead to different pot life. FTIR analysis results show that the hydroxy of hydrophilic modifier reacted completely with NCO. That is to say, hydrophilic groups have been grafted in molecule chain of polyisocyanate; As the molar ratio of NCO/OH increases, the viscosity of prepolymer and emulsion decreases, the smaller the molar ratio of NCO/OH is, the better hydrophilic of the prepolymer is, but the remaining NCO in the emulsion is less. Different molar ratio of NCO/OH cause different pot life; Concentration of emulsifier is proportional to viscosity of mulsion and prepolymer. the pot life extended gradually with the increase of the concentration of emulsifie, and the pot life bagan to decrease when the concentration reached a certain value. To sum up, two kinds of emulsifiable polyisocyanate have excellent performance which can be obtained. The polyisocyanate(PAPI) was hydrophilic modified by modifier C, and the molar ratio of NCO/OH was 60:1, and the prepolymer was dispersed in the water which contained 3%emulsifier and 0.5%stabilizer, and the pot life was more than 120 minutes; the polyisocyanate(PAPI) was hydrophilic modified by modifier D, and the molar ratio of NCO/OH was 50:1, and the prepolymer was dispersed in the water which contained 5% emulsifier and 0.5%stabilizer, and the pot life was more than 150 minutes.Prepare plywood with low molar ratio UF resin which was modified by the above two emulsifiable polyisocyanate with excellent performance. Effect of different kind of prepolymer and mass fraction of prepolymer on the properties of composite adhesives was investigated. X-ray photoelectron spectroscopy (XPS) had been used to analyze the chemical structure of bonding interface. The results showed that the composite adhesive consisting of UF resin and emulsifiable polyisocyanate content of 7.5% and curing agent content of 6% was used in plywood with best properties. At the same time, the pot life of composite adhesive was 90 minutes, bonding strength(dry) and bonding strength(wet) were 1.21MPa and 1.42MPa respectively, the formaldehyde emission (0.28mg/L) reached the E0 grade.