In-situ modification of wood polymer via impregnation with ultra-low molar ratio urea-formaldehyde resins

This study investigates how the impregnation of ultra-low molar ratio urea-formaldehyde (UL-UF) resins with formaldehyde to urea (F/U) mole ratio of 0.8 at various curing temperatures affects wood characteristics, including density, weight percent gain (WPG), weight loss (WL), and anti-swelling efficiency (ASE). The UL-UF resins were synthesized using a modified alkaline-acid-alkaline process, resulting in low viscosity, low crystallinity, and low curing temperature of resins. The impregnation technique started by immersing sengon (Paraserianthes falcataria L. Nielsen) wood in UL-UF resins at a volume ratio of 1.0:1.1, subjecting to a vacuum of -50 cmHg for 30 min, and applying 7 kgf.cm^-2 of pressure for 3 h at 25 ± 2 °C. The treated wood was cured at temperatures of 120, 140, 160, and 180 °C for 30 min. This research revealed that there was a successful in-situ modification of wood with UL-UF resin, as confirmed by SEM micrographs, XRD and semi-quantitative FTIR analysis. The UL-UF-impregnated wood had a higher WPG and density than untreated wood. Greater curing temperatures were linked to decrease WPG, density, and WL values, but higher ASE. Lowering the curing temperature induces higher WL and decreased ASE owing to under-curing in the core layer, while raising the curing temperature promotes faster curing and gelation time, resulting in the opposite effect.