Microfibrillated-cellulose-modified urea-formaldehyde adhesives with different F/U molar ratios for wood-based composites

The relationship between urea–formaldehyde (UF) adhesives (E0 and E1 classes) and microfibrillated-cellulose (MFC) and its effect on the mechanical properties of laminated veneer lumbers (LVLs) were investigated. Bending strength, modulus of elasticity in bending, and tensile shear strength of the LVLs were determined. The morphology, gel time, viscosity, and acidity of the modified UF adhesives were also investigated. The tensile shear strength of the LVLs significantly increased (2.89 to 3.35 N/mm2) as the MFC suspension was increased to 3.75 g in the 7.50 g E0 class UF adhesive, while it slightly increased (3.10 to 3.16 N/mm2) as the MFC suspension was increased to 2.5 g in the 8.75 g E1 class UF adhesive. The results showed that the bond performance of the E0 class adhesive with the MFC was better than that of the E1 class adhesive with the MFC. The MFC was found to be valuable nanoscale reinforcing filler for the improvement of bond performance of UF adhesive, in particular, E0 class adhesive, in the production of wood-based composites.