Abstract
Pleating is an optimal way to increase bendability of wood used in diverse industrial applications. It results in the excessive buckling of cell walls and modifications of constitutive polymers. However, thoughtful understanding of the physical–chemical mechanisms of that modification process is very limited. The main purpose of the present study was to identify changes in functional groups of wood polymers induced by longitudinal compression. Four types of wood samples prepared from beech and sessile oak (untreated, steamed, longitudinally compressed and fixated for 1 min as well as longitudinally compressed and fixated for 18 h) were assessed by infrared spectroscopy. The spectra interpretation revealed that changes can be observed in hydroxyl as well as in carbon–oxygen single and carbon-hydrogen functional groups of polysaccharides and lignin. Beech wood seems to be more susceptible to investigated modification processes as compared to oak. Detailed interpretation of infrared spectra allows identification of changes in the hygroscopicity of wood as well as alterations in the linkage between structural elements in the polymer matrix of wood induced by the applied treatments.Graphic
Highlights
As described in earlier papers (Hanemann 1917; Stevens and Turner 1948; Vorreiter 1949; Bader and Nemeth 2017), the aim of longitudinal wood compression is to make the material pliable
An important difference between chemical content of beech and oak species lays in composition of hemicelluloses
The share of xylan extracted from hydrolysed beech wood is more than double of the same polymer extracted from oak, assuming the same mass loss
Summary
As described in earlier papers (Hanemann 1917; Stevens and Turner 1948; Vorreiter 1949; Bader and Nemeth 2017), the aim of longitudinal wood compression is to make the material pliable. The compression process results in excessive buckling of the cell wall, which allows much higher elongation without break during the proper wood bending. The glass transition temperature decreases till the fiber saturation point FSP and the temperature remains relatively constant It reaches approximately 80 °C for lignin in beech wood with MC [ 35.6% or oak [ 24.5% MC (Molnar 2004). Hemicelluloses pass their glass transition point already at room temperature if the moisture content exceeds FSP (Lenth and Kamke 2001)
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