Hydrothermal treatment-induced changes in wood iron concentrations and colour: a technological study

This study aimed to reveal the changes in Fe concentration and colour in the wood obtained from selected tree species: Pinus sylvestris L., Picea abies (L.) H. Karst., Pseudotsuga menziesii (Mirb.) Franco, Juglans regia L., and Acer platanoides L. at different stages of the hydrothermal treatment with additive Fe2O3 in combination with tannic acid. The study results showed that wood obtained from deciduous and coniferous trees responded slightly differently to the duration of treatment, and the temperature applied. In all cases, the higher Fe concentrations were found the outer wood layers, which directly contacted the modifying solvent. In deeper wood layers, Fe concentrations gradually decreased. Higher Fe concentration determined darkening of the colour. The longer treatment time and the higher temperature caused the higher Fe concentrations in all wood layers. For the most reliable and efficient technological process, the treatment temperature could be optimised up to 90 degrees C, when the wood is exposed to the solvent made of water with the addition of Fe2O3 and tannic acid. The duration of the full hydrothermal process could be optimised up to 120 h for the wood from coniferous species, and it could be prolonged up to 150-240 h for deciduous species.