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Dissociation of phenolic groups in kraft lignin at elevated temperatures
2000 (English)In: Holzforschung, ISSN 0018-3830, Vol. 54, no 5, 519-527 p.Article in journal (Refereed) Published
Abstract [en]

The dissociation of the phenolic groups in a polydisperse, low molecular weight kraft lignin (Indulin AT) was studied in alkaline aqueous solutions in the temperature interval 21-70 degrees C, using a UV-spectrophorometric method. It was found that at a constant concentration of hydroxide ions, the degree of dissociation was decreasing when the temperature was elevated. Dissociation curves and apparent pK(0) values were also calculated for the polydisperse sample at the same conditions, using the van't Hoff and the Poisson-Boltzmann equations. At degrees of dissociation exceeding alpha approximate to 0.4, the outcome of the theoretical approach showed to be in good agreement with the experimentally obtained results. Furthermore, calculations were performed for different molecular weights of kraft lignin and from this it was found that the apparent pK(0) is shifted to higher values by increasing molecular weight, due to an increased electrostatic attraction of the hydrogen ions, which is arising from a less curved surface. Predictions of the dissociation behavior at temperatures reached in the kraft process were performed and under these conditions, higher molecular weight lignin fragments seem never to reach the point of complete dissociation. It was also found that an increase in temperature results in phase separation in kraft lignin solutions with high ionic strengths and pH values close to the pK(a) of the phenolic groups.

Place, publisher, year, edition, pages
2000. Vol. 54, no 5, 519-527 p.
Keyword [en]
dissociation of elevated temperature, pKa of phenolic groups, kraft lignin, Poisson-Boltzmann equation, phase separation of kraft lignin, association, components, water
URN: urn:nbn:se:kth:diva-20071DOI: 10.1016/j.colsurfa.2007.02.032ISI: 000089643300014OAI: diva2:338764
QC 20100525Available from: 2010-08-10 Created: 2010-08-10Bibliographically approved

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Norgren, Magnus
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