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.