Effect of low molecular weight melamine-urea-formaldehyde resin impregnation on poplar wood pore size distribution and water sorption

This study aimed to investigate the relationship between the properties of pore size distribution and water sorption in melamine-urea-formaldehyde (MUF) resin-impregnated wood by scanning electron microscopy (SEM), nitrogen adsorption (NAD) measurement, mercury intrusion porosimetry (MIP), water-soaking, and moisture adsorption over saturated salt solutions. The results showed that MUF resin not only filled the macropores and mesopores of the wood, such as those of vessels and wood fibers, but also penetrated the cell walls and replaced some hygroscopic groups of cell wall polymers, thus significantly reducing the water sorption. The porosity and cumulative pore volume of the RI140 and RII140 samples (impregnated with 10% and 20% MUF resin solution, respectively, with each dried at 140 ℃) were 19.25% and 1.20 mL·g−1, and 9.85% and 0.89 mL·g−1, respectively, which were lower than those obtained for the control group (CK). The specific surface area of RII140 was lower than that of CK. The pore size range of the CK and RII140 samples was 3.1–22.9 nm and 2.5–5.1 nm, respectively. The water absorption rate and equilibrium moisture content values for MUF resin-impregnated wood were inversely proportional to the drying temperatures and weight percent gain (WPG). The MUF resin leaching efficiency was inversely proportional to the drying temperature but proportional to the WPG.