Effects of synthesized conditions of urea resin on the formaldehyde emission and the bond strength of plywood

摘要

The mechanism of initial formaldehyde emission from plywood prepared with urea-formaldehyde resin adhesive synthesized under various conditions was investigated by chemical analysis of resin adhesive. Moreover, the relationship between synthesized conditions and bond strength properties of plywood were studied. Within 500 hours after plywood preparation, the amount of formaldehyde emission decreased greatly over time, and there was a correlation between the coefficients of formaldehyde emission rate and the free formaldehyde in resin. Moreover, the relative intensity ratios of some chemical functional groups and bonds measured by means of 13{sup left}CNMR were linearly correlated with the coefficients of formaldehyde emission rate. Thus, within 500 hours after plywood preparation, it was clarified that the free formaldehyde in resin, and some chemical functional groups and bonds that could form formaldehyde in the curing reaction, principally influence formaldehyde emission from plywood. As the molar ratio of urea to formaldehyde decreased, bond strength in wet condition were decreased also.