Abstract
The reaction kinetics between acetic anhydride and small Pinus radiata blocks was found to be diffusion controlled over the temperature range examined (80–120 °C), with an activation energy of 34 kJ/mol obtained from initial rate constants. The rate-limiting diffusion appeared to be through the wood cell wall layers, rather than through to the cell lumen. It was possible to mathematically model the wood block reaction based on reaction time and temperature, and this model could be used to predict acetylation level for similar sized softwood samples. In addition, a technique for estimating extent of reaction of acetylated wood blocks was proposed using solid state carbon NMR spectroscopy. Overall, this study demonstrated the critical importance of the wood ultra-structure, sample size and reaction conditions in determining the rate of acetylation (diffusion- or activation-controlled) in wood and wood-based substrates.
Zusammenfassung
Es wurde gezeigt, dass die Reaktionskinetik zwischen Essigsäureanhydrid und kleinen Pinus radiata Prüfkörpern im untersuchten Temperaturbereich (80–120 °C) durch Diffusion kontrolliert wird. Die aus den Konstanten der Anfangsgeschwindigkeit bestimmte Aktivierungsenergie betrug 34 kJ/mol. Die Diffusionsgeschwindigkeit schien eher durch die Zellwandschichten als durch die Zelllumen bestimmt zu sein. Es war möglich, die Reaktion der Holzprüfkörper basierend auf Reaktionszeit und Temperatur mathematisch zu modellieren und dieses Modell konnte zur Vorhersage des Acetylierungsgrades ähnlich großer Nadelholzproben herangezogen werden. Daneben wurde ein Verfahren zur Schätzung des Ausmaßes der Reaktion von acetylierten Holzprüfkörpern mittels 13C-Festkörper NMR-Spektroskopie vorgeschlagen. Diese Studie zeigt die maßgebliche Bedeutung der Holz-Ultrastruktur, der Prüfkörpergröße und der Reaktionsbedingungen zur Bestimmung der Acetylierungsgeschwindigkeit (sowohl diffusions- als auch aktivierungskontrolliert) von Holz und Holzwerkstoffen auf.
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Acknowledgments
The author would like to acknowledge special funding from Scion for the PhD studies, support from School of Agricultural and Forestry Sciences at the University of Wales Bangor and specifically to Prof Bart Banks and Dr Callum Hill for their supervision, and the contribution of the British Council towards travel costs incurred during the collaboration. Thanks are also due to Drs Adya Singh, Ian Suckling and Mervyn Uprichard for their helpful comments on the manuscript.
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Dunningham, E.A. Kinetic studies of the acetylation reaction of small Pinus radiata blocks. Eur. J. Wood Prod. 70, 857–863 (2012). https://doi.org/10.1007/s00107-012-0632-9
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DOI: https://doi.org/10.1007/s00107-012-0632-9