The characterizations of nanofluid type urea formaldehyde resins

For reducing the emission of formaldehyde, urea formaldehyde (UF) resin adhesives used in the wood-based panel industry are mainly synthesized by adding urea in stages to reduce the molar ratio of formaldehyde and urea. Although the lower molar ratio UF resin has lower formaldehyde emissions, it also has the defects of longer curing time and lower bonding strength when being used in wood-based panel products. In this study, nanofluid type UF resins adhesives were prepared by dispersing SiO ₂ and TiO ₂ nanoparticles with six concentrations levels, 0%, 0.2%, 0.4%, 0.6%, 0.8% and 1% into UF resins with 1.0 and 1.3 M ratio by the assistance of ultrasound, respectively. It was found that the excellent thermal conductivity of the nanofluid type adhesives could eliminate the defects of the low molar ratio UF resins. When nano-SiO ₂ and nano-TiO ₂ were incorporated, the viscosity increased as the nanoparticles concentration increased, the maximum viscosity increased by 11.7% (1.0UF) and 15.0% (1.3UF) with nano-SiO ₂, the free formaldehyde content, curing time, and pot life of UF resins declined in varying degrees with nanoparticles loading level increased, the maximum amount of free formaldehyde content reduced by 41.2% (1.0UF) and 43.9% (1.3UF) with nano-TiO ₂, the maximum reduction of curing time was 25.80% (1.0UF) and 42.6% (1.3UF) with nano-TiO ₂, the pot life maximum decreased by 39.7% (1.0UF) and 43.0% (1.3UF) with nano-SiO ₂. Nanofluid type UF resins had much higher bonding strength with lower formaldehyde emission than pristine UF resins after being treated with same hot-pressing in plywood manufacture. The maximum of bonding strength increased by 28.1% (1.0UF) and 28.8% (1.3UF) with nano-SiO ₂, and the maximum amount of formaldehyde emissions reduced by 48.7% (1.0UF) with nano-SiO ₂ and 41.9% (1.3UF) with nano-TiO ₂. Meanwhile, the results showed that nanofluid type UF resin used in plywood manufacture exhibited the ability to decrease the hot-pressing temperature or shorten the hot-pressing time.