Preparation And Performance Research For Urea-formaldehyde Resin Adhesive With Post-crossing Modification

The paper concerns the modification of urea-formaldehyde resin for plywood. Beginning with the synthesis mechanism of urea-formaldehyde resin and the reasons of formaldehyde wood-based panel release, we focus on the ratio of raw materials during synthesis and the technical parameters in the two stages of the synthesis process. In order to reduce both the content of free formaldehyde in the resin and the formaldehyde release contained in wood-based panels to achieve the E1standard while ensuring the bonding strength of wood-based panel, we are hoped to explore a new technique, which can produce a new kind of urea-formaldehyde resin that has a low content of free formaldehyde and low formaldehyde emission but high bonding strength.In our experiments, firstly, we adopted a low molar ratio of formaldehyde to urea to reduce the content of free formaldehyde in the resin; Secondly, for the purpose of minimizing the content of-CH2-O-CH2-in the urea-formaldehyde resin structure, the process of polymerization was controlled to overcome the problem of formaldehyde release, which is caused by the decomposition of-CH2-O-CH2-. Finally, with X as a cross-linking agent, we aim to improve the poor performances (which is caused by the reduction of free formaldehyde and the low molecular weight of prepolymers) of the UF resin.Many detailed factors that impact the performance of modified resins and their bonding performances were concerned in this research. The results showed that the addition of urea for several times helped to cut down the content of formaldehyde in resins; besides, with a higher initial molar ratio, the storage of the resin increased, and a higher temperature was beneficial to enhance the performances of modified resin; we also found that, a appropriate reaction time and the value of PH during the condensation polymerization played crucial roles in the improvement of resin performances.The effect of cross-linking agent X on the resins capability was also studied in our paper. Research implied that with the cross-linking of the X1group(contained in cross-linking agent X)、imine group(contained in resin prepolymers) and some other vivid groups, the bonding strength of the resin has greatly enhanced. In the same time, for the reaction of X2group (in cross-linking agent X) with the-CH2OH group(in the resin structure), the proportion of the condensation unit contained in the resin structure, which has a continual decomposition and then lead to the release of formaldehyde, would be greatly reduced.