Summary
The known requirements for the sorption and swelling of wood are reviewed. These are shown to be compatible, in the case of softwoods, with the following simplified model. The fibers are continuous with either rectangular or circular cross sections and lumen of the same shape with a constant size. The fiber walls consist of concentric lamina made up of small repeating units 100 Å by 100 Å, consisting of a microcrystalline core surrounded by an amorphous sheath. All sorption and swelling occurs at the surfaces of or within the amorphous sheath. The major portion of the sorption and swelling is inter-laminar with just sufficient intra-laminar sorption and swelling to avoid laminar distortion. Calculations give the generally accepted internal sorption surface for water of about 200 square meters per gram. The portion of the total sorption that is intra-laminar varies from 5 ... 20 percent in going from wood with a specific gravity of 0.3 ... 1.0. Thickness of sorption in water molecules per sorption site vary from 6.1 ... 4.9 for inter-laminar sorption and 0.35 ... 1.35 for intra-laminar sorption in going from wood with a specific gravity of 0.3 to one of 1.0. Similar values are obtained from experimental swelling data where lumen cross sections change. Similar calculations for super swelling of wood and pulps show that laminar separations may become sufficiently great to be microscopically visible. The calculations show that bound water fiber saturation points for wood normally fall in the range of 25 ... 40 percent. Super swollen wood, chemically isolated fibers and beaten fibers may as a result of reduced restraints have fiber saturation points greater than 150 percent. The latter are attributed to dispersion or diffusion forces rather than the conventional bound water forces of hydrogen bonding for intact wood.
Zusammenfassung
Die bekannten Bedingungen für die Sorption und Quellung von Holz werden erörtert. Sie sind auf Nadelholz unter Anwendung des folgenden, vereinfachten Modells anwendbar. Die Fasern sind durchgehend und haben rechteckigen oder kreisförmigen Querschnitt, mit Zellhohlräumen gleicher Form und konstanter Größe. Die Faserwände bestehen aus konzentrisch angeordneten Schichten, die wiederum aus kleinen, sich wiederholenden 100 Å×100 Å großen Einheiten zusammengesetzt sind; diese wiederum bestehen aus einem mikrokristallinen Kern, umgeben von einer amorphen Auflagerung. Alle Sorptions- und Quellungsvorgänge finden an der Oberfläche oder innerhalb dieser amorphen Auflagerung statt; sie spielen sich in der Hauptsache in der Schicht selbst ab (inter-laminar), jedoch findet genügend Zwischenschicht-Sorption und-Quellung (intra-laminar) statt, um Verformungen der Schichten zu vermeiden. Durch Berechnung erhält man die allgemein anerkannte Größe der inneren Sorptionsfläche für Wasser von etwa 200 m2/g. Der Anteil der intra-laminaren Sorption an der Gesamtsorption schwankt zwischen 5 und 20% bei Holz mit Rohdichten von 0.3 bis 1.0. Die Schichtdicke der sorbierten Wassermoleküle je Sorptionsstelle liegt für inter-laminare Sorption zwischen 6.1 und 4.9, und für intra-laminare Sorption zwischen 0.35 und 1.35 bei Holz mit Rohdichten zwischen 0.3 bis 1.0. Ähnliche Werte ergaben sich aus experimentell ermittelten Quellungsdaten bei Zellhohlräumen mit sich änderndem Querschnitt. Vergleichbare Berechnungen der Super-Quellung des Holzes und des Zellstoffes zeigen, daß laminare Abtrennungen so groß werden können, daß sie mikroskopisch sichtbar werden. Sie zeigen ferner, daß die Fasersättigungspunkte bei gebundenem Wasser meist zwischen 25 und 40% liegen. Extrem gequollenes Holz, chemisch herausgelöste und gemahlene Fasern können aufgrund verringerter Behinderung Fasersättigungspunkte über 150% erreichen. Diese letztere Erscheinung ist eher den Dispersions- oder Diffusionskräften zuzuschreiben als den Kräften aus Wasserstoffbrücken des gebundenen Wassers im intakten Holz.
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Paper No. 2743 of the Journal Series of the N. C. State University Agricultural Experiment Station, Raleigh, North Carolina.
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Stamm, A.J., Smith, W.E. Laminar sorption and swelling theory for wood and cellulose. Wood Science and Technology 3, 301–323 (1969). https://doi.org/10.1007/BF00352304
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DOI: https://doi.org/10.1007/BF00352304