Abstract
The aim of this work was to evaluate the changes of the chemical components in birch wood (Betula pendula Roth) caused by steaming with saturated steam at three temperatures—105 °C, 125 °C and 135 °C. In the samples of the original wood and wood after steaming, select chemical characteristics were determined, and wood, isolated holocellulose and Seiferts’s cellulose were analysed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The greatest changes in the birch wood characteristics were observed in steaming mode III (135 °C). The differential spectra of the birch wood samples indicated that the hemicelluloses were significantly degraded and that the dehydration reactions were able to proceed. A clear increase in both unconjugated and conjugated carbonyls was seen only in mode III. The findings also confirmed the greater sensitivity of the guaiacyl lignin contained in broadleaves to elevated steaming temperatures, as well as the course of the thermal oxidation reactions and the formation of new carboxyls in mode III. The decrease in the ratio of absorbances H 1732/2900 and H 1243/2900 demonstrated the cleavage of acyl (acetyl and formyl) groups from birch wood hemicelluloses. The qualitative and quantitative changes of the hemicelluloses and extractive substances in birch wood during steaming were well-correlated with the measured pH values and wood colour.
Highlights
Hydrothermal treatment is a method often applied to pretreat wood materials, which must obtain certain external and internal wood properties, for example, relating to colour, plasticity and durability
The aim of this work was to evaluate changes in select chemical characteristics of birch wood caused by steaming with saturated steam under operating conditions for 12 h at three different temperatures—105 ◦ C, 125 ◦ C and 135 ◦ C—and to identify and explain the changes of select chemical characteristics that occur upon changes in the pH value and wood colour using attenuated total reflectance (ATR)-FTIR spectroscopy
Birch wood samples with dimensions of 32 mm × 90 mm × 600 mm, density ρ = 704 ± 61 kgm−3 and humidity wa > 45% were thermally treated with saturated steam in an APDZ
Summary
Hydrothermal treatment is a method often applied to pretreat wood materials, which must obtain certain external and internal wood properties, for example, relating to colour, plasticity and durability. The wood is treated with water respectively with water vapor at different modes—temperature, pressure, time, hydro module [1]. Chen et al [2] used saturated steam at a lower temperature and at a higher humidity of wood for obvious discolouration with no effect on polysaccharide components. The saturated steam method effectively induces discolouring, it has so far received less attention by the wood industry. Goal-directed changes in colour by hydrothermal treatment of full volumes of wood have great practical importance, especially in the production of furniture, decorative products and other wood products [3]
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