Effects of nanofillers on water resistance and dimensional stability of solid wood modified by melamine-urea-formaldehyde resin

The water absorption and dimensional stability of wood impregnated with melamine-urea-formaldehyde (MUF) and wood impregnated with different nanofiller/MUF formulations were investigated. Three kinds of nanoparticles, Cloisite (R) 30B, Claytone (R) APA, and Cloisite (R) Na+, were selected and mixed with MUF resin, and subsequently impregnated into solid aspen wood through a vacuum and pressure process. The wood polymer nanocomposites were prepared by in situ condensation polymerization of the impregnated wood under specific conditions. Significant improvements in water repellency and better dimensional stabilities were obtained for the nanofiller/MUF-treated wood. The untreated wood absorbed around 63% of moisture after 24 h soaking in water, while water uptake was about 125% after 1 week immersion in water. The MUF resin-impregnated wood absorbed about 8.3% and 38.5% of moisture after 24 h and 1 week immersion in water, respectively. For the organophilic nanoclay/MUF resin-impregnated wood, much lower water absorption in the amounts of around 5% water uptake in 24 h and 22% after 1 week was observed. The antiswelling efficiency (ASE) was also improved from 63.3% to 125.6% for the nanofiller/MUF-treated wood. The significant improvement in water resistance and dimensional stability of the resulting wood polymer nanocomposites can be attributed to the introduction of MUF and nanofillers into the wood. X-ray fluorescence shows that some nanoparticles have migrated into the wood cell wall. Wood treatments with MUF and nanofiller/MUF showed no significant influence on the color of the wood, which is important for practical application of the treated wood in some specific areas such as flooring.