Effect of hemicellulose molecular structure on wettability and surface adhesion to urea-formaldehyde resin adhesives

This study examined the effect of hemicellulose molecular structure on wettability and surface adhesion to urea-formaldehyde resin adhesives to better understand the complex adhesion process of wood biopolymers. Molecular structure of two hemicelluloses, such as arabinogalactan and xylan, was characterized using Fourier transform infrared, one-dimensional, and two-dimensional nuclear magnetic resonances. As a result, arabinogalactan had a hyperbranched structure, whereas xylan was more linear, which caused a distinctive morphology in their films, with the latter having a rougher surface. Further, the surface adhesion between hemicellulose and UF resins with various formaldehyde to urea molar ratios (1.0 and 1.6) was measured. The adhesion force and work of adhesion of arabinogalactan with different UF resins were found to be greater than those of xylan due to the former film's higher surface free energy, more exposed OH groups, and smoother surface. In addition, 1.6 UF resins exhibited greater adhesion than 1.0 UF resins, regardless of the hemicellulose type, demonstrating that dispersion force was dominant in their molecular interactions.