Abstract: [Objective]The aim of this study is to explore the influence of different post-treatment and drying methods on weight percent gain (WPG) and dimensional stability of the melamine-urea-formaldehyde (MUF) resin impregnated wood, to provide reference to modification technique with resin-impregnation.[Method]The MUF resin solutions with concentrations of 5%, 10%, 15%, 25% were used to impregnate poplar wood (Populus tomentosa) using the full cell treatment schedule. After the impregnation, specimens were treated respectively under 4 conditions:air drying for seven days, storing in high humidity condition for seven days, soaked in the resin solution for seven days, and no post-treatment. Subsequently, the post-treated specimens were sorted into two groups and took direct drying and wet drying respectively, followed by the measurements of the WPG and bulking. Finally, resin treated specimens and untreated specimens were immersed in distilled water for fourteen days. Once the specimens were taken out from the distilled water, the anti-swelling efficiency and the ratio of radial swelling to tangential swelling were determined.[Result]It was found that there was a significant positive correlation between WPG and resin content. The WPG of specimens impregnated with resin content of 5%, 10%, 15%, and 25% was 9.7%, 19.1%, 28.4%, and 50.0% respectively,and no obvious differences in WPG was observed between specimens with different post-treatments. After the same post-treatment, specimens through direct drying had a slightly lower WPG than those through wet drying. Specimens stored in a high humidity condition or soaked in the resin solution after resin impregnation had a higher bulking ratio than those through other post-treatments. Wet drying resulted in a higher bulking ratio than direct drying after the same post-treatment except for the air drying. The changes in anti-swelling efficiency for resin impregnated specimens under different post-treatments corresponded to those in bulking ratio. The radial and tangential swelling of the resin impregnated wood decreased with the increase in WPG, while the ratio of radial swelling to tangential swelling also increased. The ratio of radial swelling to tangential swelling of the resin impregnated specimens at low WPG was smaller than that of the untreated wood, but larger than that of the untreated wood with WPG above about 30%.[Conclusion]1) Post-treatment has less influence on WPG than the drying process. The wet drying process is conducive to resin fixation in wood pores, resulting in a higher WPG. 2) Cell wall bulking ratio is influenced by the post-treatment method as well as the drying process. Storing the specimens in high humidity condition or soaking them into the resin solution after the resin impregnation would result in more resin penetrating into the cell wall. Wet drying process would favor more resin penetrating through and fixing at cell walls, and therefore, result in higher bulking ratio. 3) Anti-swelling efficiency correlates with cell wall bulking ratio of the resin-impregnated specimens, and the higher bulking ratio would results in higher anti-swelling efficiency and better dimensional stability. 4) The ratio of radial swelling to tangential swelling increases with the increase in WPG.

Key words: low molecular weight resin, diffusion, water solubility, weight percent gain, dimensional stability