Summary
The springback of compressed wood caused by built-up internal stresses results in excessive thickness swelling of wood-based composites when exposed to moisture. Steam pretreatment can cause partial hydrolysis of hemicellulose for both hardwoods and softwoods which markedly increases the compressibility of wood and in turn significantly reduces the build-up of internal stresses in composites during hot pressing. This steam pretreatment process is a very effective method for producing dimensionally stable wood-based composites. Mild steam pretreatments (e.g. 3 to 4 min at 1.55 MPa) cause a significant reduction of the water insoluble xylan content in hardwoods and the amount of xylan, mannan and galactan in softwoods without any apparent changes in the cellulose or lignin content.
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The authors wish to thank G. Bastien and B. S. Lethbridge for technical assistance. W. Schwald is grateful to the ‘Fonds zur Förderung der wissenschaftlichen Forschung’, Vienna, Austria for granting an ‘Erwin-Schrödinger scholarship’ (Proj. No. J0128C)
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Hsu, W.E., Schwald, W., Schwald, J. et al. Chemical and physical changes required for producing dimensionally stable wood-based composites. Wood Sci.Technol. 22, 281–289 (1988). https://doi.org/10.1007/BF00386023
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DOI: https://doi.org/10.1007/BF00386023