Abstract
The effects of heating lab cooked never dried kraft pulp from pine and spruce at 5 % consistency to 80, 100 and 120 °C in a pressurized vessel were evaluated based on various fiber and sheet properties. The settings of pH and conductivity in the lab trial were chosen in accordance with operations such as oxygen delignification, alkaline extraction, washing or storage of pulp in an integrated paper mill. It was found that the tensile strength was reduced steadily with increasing temperature. Nuclear magnetic resonance spectroscopy showed that fiber crystallinity and pore size increased at high temperatures compared to the unheated reference. Crystallinity most likely affected the fiber flexibility and thus resulted in less and weaker fiber–fiber bonds. Atomic force microscopy indicated that the amount of precipitated lignin granules on the fiber surface was reduced with increasing temperature. The roughness of the fiber surface did not significantly change with temperature and hence did not negatively influence the tensile strength. It was remarkable that a so called reversed latency was observed. Instead of a decrease in fiber curl with temperature, the fiber became significantly more curled. A large portion of the losses in tensile strength was attributed to the increase in fiber curl and leaching of hemicelluloses from the fiber wall.
Zusammenfassung
In dieser Studie wurden die Effekte einer Temperaturbehandlung von ungebleichtem und ungemahlenem Kraftzellstoff bei 80 °C, 100 °C und 120 °C auf die Faser- und Papiereigenschaften in einer umfangreichen Laborstudie untersucht. Die Einstellungen von pH-Wert und Leitfähigkeit der 5 %igen Zellstofflösung wurden in Anlehnung an die industriellen Bedingungen in der alkalischen Wäsche, Extraktion oder Sauerstoff-Delignifizierung eingestellt. Es wurde gezeigt, dass die Zugfestigkeit mit zunehmender Temperatur im Laborreaktor signifikant geringer wurde. Nuklear Magnet Resonanz (NMR) Spektroskopie zeigte, dass im Vergleich zur unbehandelten Referenz die Faserkristallinität und der mittlere Porendurchmesser der Faserzellwand mit zunehmender Temperatur anstieg. Höchstwahrscheinlich führte die gestiegene Faserkristallinität zu einer geringeren Fasersteifigkeit, wodurch Anzahl und die Festigkeit der Faser-Faser-Bindungen abnahm. Atom Kraft Mikroskopie (AFM) belegte, dass die Anzahl der Lignin Granulate an der Faseroberfläche mit steigender Temperatur signifikant abnahmen und somit die Festigkeit nicht negativ beeinflusste. Die Rauigkeit der Faseroberfläche wurde nur unwesentlich beeinflusst und hatte somit keine Auswirkungen auf die Zugfestigkeit der Laborblätter. Die Temperaturbehandlung einer 5 %igen Zellstofflösung führte zu einer umgekehrten Faserlatenz, das heißt die Faserkräuselung nahm mit zunehmender Temperatur zu anstatt ab. Die zunehmende Faserkräuselung und der abnehmende Anteil an Hemizellulosen in der Zellwand mit steigender Temperatur hatten ebenfalls einen nicht zu vernachlässigenden negativen Einfluss auf die Festigkeitsverluste.
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Acknowledgments
The financial support by the Austrian Federal Ministry of Economy, Family and Youth and the National Foundation for Research, Technology and Development is gratefully acknowledged. The technical support of Wood Kplus’ Wood Ananlytikzentrum for the NMR studies as well as the Lenzing research group for performing the measurements of the pulp viscosity is gratefully acknowledged. The authors also want to thank the Montanuniversität Leoben, Institute of Physics and the Christian Doppler Laboratory for surface chemical and physical fundamentals of paper strength for providing the opportunity to perform the work with the AFM. Special thanks go to Mondi Frantschach GmbH for providing the laboratory equipment & wood chips and especially to Mrs. Yvonne Holzbauer for performing most of the tedious laboratory work.
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Leitner, J., Zuckerstätter, G., Schmied, F. et al. Modifications in the bulk and the surface of unbleached lignocellulosic fibers induced by heat treatment without water removal: effects on tensile properties of unrefined kraft pulp. Eur. J. Wood Prod. 71, 101–110 (2013). https://doi.org/10.1007/s00107-012-0639-2
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DOI: https://doi.org/10.1007/s00107-012-0639-2