Impregnation of Beech Wood (Fagus sylvatica L.) with Corn Oil: A Comprehensive Evaluation of Hygroscopic Behavior, Surface Properties, and Artificial Weathering

Beech (Fagus sylvatica L.) is a widely used hardwood species whose limited natural durability and dimensional instability under moisture restrict its outdoor applications. This study investigated the effect of vacuum impregnation with corn oil (Zea mays L.), a low-cost and underexplored vegetable oil, on the surface and hygroscopic properties of beech wood. Specimens were impregnated for 30 or 60 min and characterized, together with non-impregnated controls, for weight percentage gain (WPG), dimensional change, FTIR spectra, color, hardness, surface roughness, and contact angle, before and after accelerated artificial weathering in a Xenon chamber; hygroscopic behavior was further assessed through water absorption and dimensional swelling during 24 h of water immersion. FTIR analysis confirmed effective oil penetration into the wood structure through characteristic triglyceride absorption bands. Impregnation resulted in high oil uptake (WPG > 45%) at both durations without inducing substantial dimensional change and significantly increased the contact angle and reduced water absorption (by 65%–66%) and radial and tangential swelling relative to the controls (p < 0.05), while surface hardness remained unaffected (p = 0.263). Color difference (ΔE*) after artificial weathering was significantly higher in impregnated specimens than in the controls (p < 0.001), reflecting the natural yellowish hue of the oil rather than material degradation. Overall, corn oil impregnation, applied for as little as 30 min, improved the hydrophobicity and dimensional stability of beech wood without compromising its hardness, supporting its potential as a sustainable, bio-based wood modification medium.