A review of water interaction in cellulosic-systems, particularly wood, is presented.Discussed are the different states of water in these systems according to Nuclear Magnetic Resonance results, the BET, Dent, and Hailwood and Horrobin sorption isotherm models. The discussion includes details of water structure, and, conformational analysis of cellulose crystals and amorphous cellulose. The water cluster theory is used to more adequately explain the sigrnoid curve of the wood isotherm.

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Wood is relatively transparent to terahertz (THz) radiation with wavelengths in the submillimeter range. This radiation has a high potential for sensing and imaging wood with a good spatial resolution. THz is especially sensitive to moisture content, fiber alignment, and density – all of which are critical in the manufacturing of wood products. In this work, a systematic study was undertaken on 46 very different wood species by means of THz time-domain spectroscopy with density determination in focus. The dielectric response of wood was modeled based on the Maxwell-Garnett effective medium theory. The dielectric function of the cell wall material was found to be extremely consistent over this large number of species with very different properties. This renders possible to determine wood density by THz time-domain spectroscopy. A strong correlation between the measured and predicted densities has been observed for all the samples investigated.

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