Estimating the hydrolytic durability of cured wood adhesives by measuring formaldehyde liberation and structural stability

The durability of different commonly used thermosetting wood adhesives (UF, MUF, MUPF) was determined from the hydrolytically induced mass loss and the amount of liberated formaldehyde. Both methods showed high reproducibility. Different methodical aspects were investigated for further improvement. The hydrolytically induced mass loss and formaldehyde liberation depend on the particle size of the cured resins. Additionally, more severe hydrolytic conditions (time, pH, temperature) caused elevated mass losses and formaldehyde liberations. The hydrolytic stability of the cured resins could be well determined by gravimetric analysis. However, a distinct graduation of the adhesive durability according to formaldehyde liberation appeared to be more difficult. These findings were reinforced by correlating the hydrolytic indicators and wet strength properties of particle boards according to different test methods (V70, V100, EN 321, Werzalit cycle test).