Enhancing dimensional stability and weathering resistance of poplar wood through low-formaldehyde melamine resin impregnation and curing

<i>Populus deltoides</i> wood is highly susceptible to dimensional instability and degradation under outdoor exposure. This study evaluated improvements obtained through impregnation with low-formaldehyde melamine-formaldehyde (MF) resin at concentrations of 7%, 15%, 27%, and 35% using a vacuum–pressure process followed by staged curing. Physical, mechanical, surface, and weathering properties were determined. Resin treatment reduced water absorption and volumetric swelling, with maximum reductions at 35% concentration. Density, anti-swelling efficiency, modulus of rupture, modulus of elasticity, compressive strength, and hardness all increased significantly in treated specimens. Impact resistance decreased slightly at higher concentrations, indicating increased brittleness. Accelerated weathering confirmed superior color stability, with ΔE reduced from 13.3 in the control to 5.8 in MF-35%, along with lower surface roughness and sustained hydrophobicity after 750 hours of UV–moisture exposure. FTIR analysis showed chemical changes in the wood cell wall after MF treatment, including reduced lignin signals and relatively stable polysaccharide bands, suggesting partial modification rather than full stabilization. The results demonstrate MF resin as an effective modification for enhancing durability and structural integrity of poplar for outdoor use.