Influence of synthesis method and melamine content of urea-melamine-formaldehyde resins to their features in cohesion, interphase, and adhesion performance

This study investigated impacts of the synthesis method and melamine content of urea-melamine-formaldehyde (UMF) resins to their cohesive and interphase features, and adhesion in bonding wood products. Melamine at three addition levels was simultaneously reacted with urea and formaldehyde to obtain melamine-urea-formaldehyde (MUF) resins, while melamine at the same levels was initially reacted with formaldehyde and then with urea to prepare melamine-formaldehyde-urea (MFU) resins. As the melamine content increased, molecular weights, curing peak temperature, activation energy, bond-line thickness, E′_max, and adhesion strength of wood products increased. These results indicated that the cohesive features of these resins mainly affected the adhesion strength in wood products while the interphase features had a partial contribution to the adhesion.