Physical and Chemical Changes in Hydrothermally Modified Wood

In this study, the simulation of artificial conditions, containing various chemical additives similar to a bog environment, was hypothesised as a relatively short way to develop a more sustainable wood product with better properties. This study aimed to determine how hydrothermal treatment with different iron additives with and without tannic acid, performed at 100 °C for 75 h, changed the mass and density of wood of different tree species (Pinus sylvestris L., Picea abies (L.) H. Karst., Pseudotsuga menziesii (Mirb.) Franco, Juglans regia L., and Acer platanoides L.); total phenolic compounds in biobased solvents after the hydrothermal processing andiron concentration in different wood layers. We also aimed to determine the wood chemical composition using Fourier-transform infrared technique. The study results showed that the softwood samples were more susceptible to hydrothermal modification than the hardwood samples, indicated by minorly different intensities on infrared spectra. The FTIR results showed bands of hardwood and softwood samples which along with the spectral characterisation of the wood constituents, which can further be utilized for creating a larger FTIR spectral database of wood samples for their identification. The factors with the most significant effect on the hydrothermal modification were tannic acid and inorganic Fe3O2 salt, used as an additive. The results indicated the suitability of inorganic Fe3O2 salt and tannic acid combination applied in this type of modification, because a higher concentration of iron was distributed on the inner and intermediate sublayers of wood samples. The hydrothermal modification approach to anchor tannic acid–Fe macromolecules in wood shown in this study has promising capabilities and may attract interest in the field of wood protection against weathering.