Study On Urea Formaldehyde Resins Adhesive For E0Grade Plywood

A low toxicity urea formaldehyde resin used in EO grade plywood was synthesized by low n(F):n(U) mole ratio and the addition of melamine and polyvinyl alcohol in this paper, the impact of different addition stage mole ratio and the additives on the performance of the resin and adhesive bonding properties were also discussed, at time same time the analysis instruments such as DSC, FTIR and TGA were taken advantage of to study the curing temperature, molecular structure and stability of cured and curing reaction process of resin. The result shows that:With the increasing of the synthesis molar ratio, the integrated performance of the resin turned superior. The UF resin with synthesis molar ratio of1.80had the lowest free formaldehyde content while poor stability, more difficult curing and lower bonding strength of plywood. Taking into account the reaction process and storage stability, when n(F):n(U1)=1.85the comprehensive performance is better. When the dosage of melamine reached3-4%of the total weight of urea, the content of free formaldehyde reached the lowest point while the bonding strength reached the maximum. The influence of polyvinyl alcohol on the performance of the resin was obvious, when the dosage was1.0%the performance indicators achieved optimal, continuing to increase the dosage would decline the properties. So when the dosage of polyvinyl alcohol and melamine were separately1.0%and3%of the total weight of urea, the properties of the resin are best, the bonding properties of the plywood could meet the GB/T9846.3-2004Ⅱ standard and the formaldehyde emission reached the E0grade standard which is environmental-friendly by this process. For the UF resin synthesized in this test, the moisture content of the veneer should be controlled below10%otherwise the bongding properties would get worse. The resin with the synthesis molar ratio of1.85and curing agent which was more than6%had the best pre-pressure performance. The different curing system caused different curing effect and different cured resin structure, the mechanical properties and the formaldehyde emission capacity were also different. The low toxicity urea formaldehyde resins under No.1curing system had the lower Ea than under the other two curing systems and the cured substance of No.1curing system had the highest decomposition activation energy which indicated that the cured effect of curing system A was best.