Hydrothermal Densification of Oak Wood: A Microstructural, Physical and Chemical Study Toward Composite Material Applications

Wood has been employed for millennia as a versatile structural material in various applications, from furnishings and household items to components in the automotive, aerospace, and energy sectors. However, its limited strength and toughness often constrain its use in highperformance applications. To address these limitations, numerous densification methods—often relying on aggressive chemical or thermal modifications—have been developed to improve wood’s mechanical properties and dimensional stability under moisture variation. In this study, a sustainable, low-cost hydrothermal densification method using a Teflon-lined system is proposed as a green alternative to conventional alkali-based processes. The investigation compares the effects of traditional alkali treatment and the proposed hydrothermal method on the structural integrity of oak wood cell walls. Various analytical techniques, including Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Dynamic Mechanical Analysis (DMA), were employed to evaluate surface color changes, microstructural alterations, and chemical composition of both as received and treated wood samples. Results reveal that the degree of cell wall degradation varies significantly depending on the treatment and temperature. Alkali-treated samples exhibited the most pronounced structural damage, while the hydrothermally treated wood retained a porous microstructure with finer pore distribution. FTIR analysis confirmed hemicellulose degradation in both treatments, indicated by the reduction or disappearance of the C=O absorption peak. Importantly, the hydrothermal method achieved up to a 19.6% increase in storage modulus compared to alkali-treated samples, suggesting improved mechanical performance with lower environmental impact. These findings underscore the potential of the hydrothermal densification process as an environmentally friendly and effective pre-treatment for enhancing wood properties, making it a promising strategy for future integration into composite material manufacturing.