Contribution of lignin to the reactivity of wood in chemical modifications II: influence of delignification on reaction with vaporous formaldehyde |
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Authors: | Kazuya Minato Hiroyuki Hosoo Shingo Kawaguchi |
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Institution: | (1) Graduate School of Agriculture, Kyoto Prefectural University, Shimogamo Hangi-cho, Sakyo-ku, Kyoto 606-8522, Japan;(2) Faculty of Agriculture, Kyoto Prefectural University, Kyoto 606-8522, Japan |
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Abstract: | Participation of lignin in the reaction between vapor-phase formaldehyde and wood was examined by using gradually delignified
wood meal. A fi rst-order rate equation was successfully applied to the weight gain data. From the estimated reaction parameters
such as rate constant, k, and ultimate weight gain, a, the reactivity toward formaldehyde was discussed among wood components, and compared with that for acetylation. k decreased monotonously with progress of the elimination of lignin, suggesting that the reaction rate of lignin is dominant
over that of whole wood, and the decrease in the ratio of lignin retarded the reaction of wood as a whole. On the other hand,
a increased with decreasing lignin content. This may be attributable to the enhanced reactivity of the remaining lignin due
to some structural changes and to the increase in the number of reactive sites in polysaccharides as a result of their exposure
accompanying the elimination of lignin. The dependencies of k and a on the lignin content were not similar to the case for acetylation, probably because of the difference in the reaction phase.
In vapor-phase formaldehyde treatment, the remaining lignin reacts as it is, whereas in liquid-phase acetylation it would
undergo rearrangement or swelling of the structure in the reaction solution. |
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Keywords: | Chemical modification Formaldehyde treatment Lignin content Reactivity Reaction parameter |
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