Studied On The Copolymerization Modification Of Melamine-Urea-Formaldehyde Resin Adhesive

As a main adhesive used in wood industry, Urea formaldehyde resin (UF resin)has many advantages such as available raw materials, excellent as well as excellent agglutinative intension, so which has wildly application in wood processing industry. However, it has some disadvantages:poor water-fast quality, brittle layer, especially high content of free formaldehyde which seriously hinders UF resin application range and its product quality. Therefore, for these shortcomings, using a certain amount of melamine to copolymerization modification, which not only combined the advantages of the MF, but also making up for their own shortcomings.In the course of film faced plywood and multi-layer parquet production, in order to make the product to achieve quasi-water resistance-level, needing to use the phenolic resin adhesive. In the premise of reducing cost and ensured the quality of products, May be used melamine modified urea formaldehyde resin. In order to meet the requirements of the water resistance-level product, generally used this method:first copolymer and then blending. In the premise of simplifying the production process, in this paper, take over the one-step method, that is using melamine to modify UF resin, Studied the effects of the amount of melamine, the adding methods and the molar ratio of n(F):n(U) and n(F):n(U1)on the UF performance, at time same time, take advantage of the analysis instrument such as DSC, FTIR, GPC, TGA and TBA, studied on the curing temperature, molecular weight and distribution of molecular weight, molecular structure and stability of cured and curing reaction process of resin. The result shows that:Along with the increased of molar ratio of n (F):n (U1) and amount of melamine, the bonding strength was increased and the formaldehyde emission was decreased obviously. At the same time, the bonding strength and formaldehyde emission were all improved significantly with the increased of molar ratio of n (F):n (U) but secondary batching could decrease the formaldehyde emission efficiently. As well, the mechanical properties of cured substance are different along with the different curing systems. The curing system A(ammonium chloride, formic acid) lead to the lowest peak temperature, the fastest curing ratio, the better curing degree, relatively high thermal stability and the best bonding strength, At the same time, with the increasing of the mole ratio of poly-condensation stage(n(F):n(U1)), the boning strength was elevated and the formaldehyde emission was decreased. So when the n(F):n(U)=1.3:1, n(F):n(U1)=1.9:1 and The V(A curing system):m(glue)6 mL:100 g, the mechanical properties of plywood are best; at the same time, The bonding properties reached to 0.8MPa, met the GB/T9846.3-2004 I standard, the formaldehyde emission (0.35mg/l) reached the E0 grade.Process different, MUF resin, its molecular structure is different, Mw and Mn had the same trend during resin synthesization of MUF resin; that is having the trend:first increasing, then decreasing, Different polycondensation molar ratio made molecular weight ups and downs. With the increasing of the condensation stage of the molar ratio, molecular weight increased, distribution coefficient is lower. While, secondary batching cause molecular weight distribution broadens, molecular weight distribution unbalanced. But, the polycondensation mole ratio had no definitely action on macromolecule, but on low molecular weight fraction.