Abstract: [Objective] Urea-formaldehyde resin adhesive was the most widely used adhesive in the world. When the molar ratio of urea/formaldehyde reduced, the corresponding formaldehyde-emission decreased greatly, but at the same time the strength of plywood also declined dramatically. Therefore, many researches showed that the adhesives modified by melamine can effectively reduce formaldehyde-emission, and the wet strength of adhesives with low molar ratio was improved. However, low-formaldehyde-emission urea-formaldehyde resin modified by melamine resulted in extending the gel time, which cannot be solved by adding curing agent. [Method] Aiming at shortening the curing time and enhance production efficiency, different activators in urea-formaldehyde were studied by analyzing solid content, curing time, free formaldehyde content and hydroxymethyl content. DSC was applied on the dynamic analysis of curing reaction. DEA was used to investigate the resin curing process. moreover, FTIR analysis was also carried out to compare functional groups after adding different additives to select an appropriate catalyst for shorting the resin curing time and reducing formaldehyde-emission.[Result] Adding the ammonium chloride, ammonium boric acid, ammonium phosphate and ammonium sulfate respectively during addition polymerization, the curing rate of low molar ratio urea-formaldehyde resin was all improved significantly. Four kinds of activators had played an significant role in reducing the curing reaction activation energy, especially for the ammonium boric acid and ammonium sulfate. According to the results of DEA, four kinds of activators obviously accelerated resin curing, particularly for the ammonium boric acid and ammonium sulfate. After adding four kinds of activators, the strength of hot-pressing plywood almost remain unchanged and formaldehyde-emission reduced.[Conclusion] when the amount of (NH₄)₂SO₄ was 0.3% of the total weight during addition stage, the activation energy of the cure reaction was greatly decreased, and the curing time was also considerably reduced. Moreover, the formaldehyde emission of the plywood can meet the requirement of F^**** for JIS.

Key words: activators for urea-formaldehyde resin with low-formaldehyde-emission, DSC, DEA, curing rate, FTIR