The Research On The Low Toxic Urea-Formaldehyde Resin Adhesive In Artificial Board

The adhesive industry has become bigger and stronger with our country economy development in 20 years, and had more and more importance for other industry in simplifying technique, saving energy, reducing costs and increasing benefit. At the present time, our country has been a big artificial broad industry country in world, the use of wood adhesive has been over 4 million ton. Because artificial broad product in our country most used in furniture manufacture and indoor fitment, adhesive in artificial board were most urea-formaldehyde resin adhesive.The urea-formaldehyde resin adhesive had a lot of good points such as price cheap, high bonding strength, solidify rapidity, compounding easy, et.al. There were also some problems just like high dissociated formaldehyde and formaldehyde release in using product, which made harm and pollution to people and environment. This paper researched how to reduce dissociated formaldehyde of urea-formaldehyde resin adhesive aiming at its problems on controlling costs and guaranteeing bonding strength basis.This study selected the optimized compound formulation and technique by twice orthogonality experiment and analysis of the detected result, and a low dissociated formaldehyde urea-formaldehyde resin adhesive was synthesized. The experimental results turned out:adjusting the molar ratio of formaldehyde to urea to 1.1, adding 10% of melamine in medium time, using the ratio of urea wisely to 60:15:25, controlling the pH value of adding stage to 7.5-8.0, regulating the pH value of polycondensation stage to 4.8-5.1, and keeping the temperature of polycondensation stage to 88～92℃, a low toxic urea-formaldehyde resin adhesive was obtained which contained 0.08% dissociated formaldehyde, reaching the E1 standard. The bonding strength of the plywood reached theⅡnational standard, and the amount of formaldehyde release was 0.7mg/L, reaching the E1 standard.Reducing the molar ratio of formaldehyde to urea could increase urea amount to neutralizethe dissociated formaldehyde but decrease two hydroxyl methyl which has viscosity; using the ratio of urea wisely could react formaldehyde to urea adequately to be good for generate two hydroxyl methyl carbamide; adding melamine could react with urea instead of formaldehyde to raise resin joining degree; controlling the pH value of adding stage could be the key of generating hydroxyl methyl carbamide; regulating the pH value of polycondensation stage could influence second methyl producing and resin reacting; regulating the pH value of polycondensation stage could control the molecular weight to effect solidify rate and bonding strength.This paper analyzed forward compounding stages samples of urea-formaldehyde resin adhesive by Fourier transform infrared spectroscopy, and investigated active radical and compounding mechanism. The experimental results turned out:reducing the pH value made the-OH to lower, adding the subsequent urea made the reactive mode to equilibrium and the absorbency of aldehyde group to fall off, controlling the amount of-CH2OH in compounding process was benefit for decreasing dissociated formaldehyde and maintaining bonding quality.This study investigated systematically the compound formulation and technique to reduce dissociated formaldehyde, and supplied theoretical principle for expanding the urea-formaldehyde resin adhesive in artificial broad to advance the artificial broad industry development.