Improving characteristics of melamine–urea–formaldehyde resin by addition of blocked polyurethane prepolymer

In this paper, the effect of blocked polyurethane prepolymer (BPUP) with four R values (the ratio of –NCO to –OH) and different blending proportions on the characteristics of melamine–urea–formaldehyde (MUF) resin were first investigated. The properties of the modified adhesive systems were examined by dynamic wettability and shear strength. The results indicated that the bonding performance and the wettability of high R value blending modification were superior to that of low R value case. In addition, the optimal bonding performance came from the MUF resin modified by 15% BPUP (R = 5) addition. Besides, the K value on wood substrates with different moisture contents (MC) was calculated by wetting model to interpret the wetting kinetics. The polymer blending adhesive has a potential capacity for making wood-based panels from high-moisture raw materials.