Direct measurement of surface adhesion between thin films of nanocellulose and urea–formaldehyde resin adhesives

Abstract

When applying an adhesive to wood, the chemical heterogeneity of the wood cell walls makes it difficult to understand the contribution they make to the interfacial adhesion between the adhesive and the wood as the adhesion is a very complex physical and chemical phenomenon.This study, for the first time, directly measured the surface adhesion between cellulose, a major component of wood, and urea-formaldehyde (UF) resin adhesives. The adhesion between thin, smooth nanocellulose films, such as cellulose nanofibrils (CNFs), carboxymethylated nanofibrils (CM)-CNFs, and carboxylated cellulose nanocrystals (C-CNCs), and UF resins with two formaldehyde to urea (F/U) molar ratios of 1.0 and 1.6 was measured using two approaches: 1) direct measurement of the adhesion force between nanocellulose films and liquid droplets of the UF resins, and 2) calculation of the work of adhesion between films of the nanocelluloses and UF resins using the contact angle and the van Oss-Chaudhury-Good (OCG) method. The results show that the total surface energies, either between the different nanocelluloses or between the two UF resins are somewhat similar, indicating the similarity in their surface properties.However, the adhesion force and work of adhesion of 1.6 UF resins with different types of nanocellulose are higher than those of 1.0 UF resins, which shows that van der Waals forces are dominant in their molecular interactions. These results suggest that the adhesion between 1.6 UF resins and nanocellulose is stronger than that when 1.0 UF resins are used because the 1.6 UF resins have a more branched structure, smoother surface, and higher surface energy.

Performance of Particleboard Made of Agroforestry Residues Bonded with Thermosetting Adhesive Derived from Waste Styrofoam

“…The smoothness of the adhesive film can have a considerable impact on adhesion in bonding wood veneer [ 38 ]. Smoother adhesive films frequently result in greater adhesive–wood surface interaction by enhancing molecular interactions between the adhesive and wood [ 39 ]. As supported by the FTIR results ( Figure 4 and Figure 5 ), the modification of WPS with MDI resulted in –NH and –C=O of urethane groups.…”

Two-Dimensional Nuclear Magnetic Resonance Analysis of Hydrogen-Bond Formation in Thermosetting Crystalline Urea–Formaldehyde Resins at a Low Molar Ratio

“…UF resins with high and low F/U molar ratios (1.6 and 1.0) were synthesized using an established alkaline−acid−alkaline three-step procedure. 36 First, a formalin solution was placed into a four-neck glass reactor, the pH was adjusted to 8.0 using NaOH (20 wt %), and the temperature was increased to 40 °C. Subsequently, urea was fed into the reactor to achieve an initial F/U molar ratio of 2.0.…”