Durability-related performance of reinforced bondline by phenol formaldehyde/nano SiO₂ composite in Laminated Veneer Lumber (LVL)

The development of bonding performance and cohesion of the constituent members is of great interest in the wood-based composites production process. This work presents an investigation for assessment of bondline in reinforced laminated veneer lumber. Phenol-formaldehyde was modified with silicon dioxide nanoparticles (SiO₂-NPs), before applying as the binder. Experimentally, the bonding quality and durability were investigated based on penetration parameters, shear strength, apparent cohesive wood failure, and delamination ratio. Results verified that SiO₂-NPs had catalytic impacts on the polymerization mechanism of phenol-formaldehyde resin. Bondline morphology was affected by SiO₂-NPs presence, in a way that the penetration parameters were reduced under the influence of the viscosity rising and polymerization behavior of phenol-formaldehyde/nano SiO₂ composite. With the shorter hot-pressing time, the brittle resin failed cohesively in the bondline, while the reinforced bondline by phenol-formaldehyde/nano SiO₂ composite failed by delamination in the wood fibers. The highest shear strength in the core layer was recorded when 2% SiO₂-NPs were presented in the bondline. The optimum shear strength and delamination ratio were observed at ≈ 135 and 330 μm penetration depth for effective penetration and maximum penetration, respectively. The SiO₂-NPs promoted the bonding durability performance of the bondline, especially in the core layer of the laminated veneer lumbers with shortened hot-pressing time. This reinforced product indicated applicability of being used as a building material in high humid/exterior conditions.