Abstract
Acetylated wood (WAc) shows improved properties largely due to the reduced amount of water in its cell wall, but the exact mechanism of water reduction remains unclear. Acetylation reduces hydroxyl (OH) content by acetyl (Ac) substitution but may also limit water access to unmodified OH groups by steric hindrance. In the present work, the accessibility of OH groups in acetylated or propionylated Radiata pine (Pinus radiata D. Don) wood (WAc and WPr) was investigated by deuterium exchange, saponification in sodium hydroxide followed by high-performance liquid chromatography (HPLC) analysis and weight percentage gain determination of the modified samples. Acetylation reduced OH accessibility (OHA) to a greater extent than would be predicted, if OH substitution were the only responsible mechanism for accessibility reduction. The combination of deuterium exchange and saponification results provides strong evidence that steric hindrance plays a key role in reduction of water accessibility to unmodified OH groups in WAc. The supramolecular architecture of WPr samples seems to be modified by the propionylation reaction, which leads to increased OHA at low levels of substitution. This suggests that molecular restructuring within the cell wall exposes new OH groups after propionylation. At higher levels of substitution, however, the WPr exhibited less OHA than expected indicating steric hindrance from the propionyl groups.
References
Hill, C.A.S. Wood Modification: Chemical, Thermal and Other Processes. John Wiley & Sons, Hoboken, NJ, 2007.10.1002/0470021748Search in Google Scholar
Hill, C.A.S., Jones, D. (1996) A chemical kinetics study of the propionic anhydride modification of Corsican pine: determination of activation energies. J. Wood Chem. Technol. 16:235–247.10.1080/02773819608545806Search in Google Scholar
Hill, C.A.S., Jones, D., Strickland, G., Cetin, N.S. (1998) Kinetic and mechanistic aspects of the acetylation of wood with acetic anhydride. Holzforschung 52:623–629.10.1515/hfsg.1998.52.6.623Search in Google Scholar
ICC Evaluation Service, Inc. (2005) AC 297. Acceptance criteria for acetylated wood preservative systems.Search in Google Scholar
Jeffries, R. (1963) An infra-red study of the deuteration of cellulose and cellulose derivatives. Polymer 4:375–389.10.1016/0032-3861(63)90044-2Search in Google Scholar
Kumar, S. (1994) Chemical modification of wood. Wood Fiber Sci. 26:270–280.Search in Google Scholar
Kymäläinen, M., Rautkari, L., Hill, C.A.S. (2015) Sorption behaviour of torrefied wood and charcoal determined by dynamic vapour sorption. J. Mater. Sci. 50:7673–7680.10.1007/s10853-015-9332-2Search in Google Scholar
Lee, K.Y., Quero, F., Blaker, J.J., Hill, C.A.S., Eichhorn, S.J., Bismarck, A. (2011) Surface only modification of bacterial cellulose nanofibres with organic acids. Cellulose 18:595–605.10.1007/s10570-011-9525-zSearch in Google Scholar
Moore, W.E., Johnson, D.B. Procedures for the Chemical Analysis of Wood and Wood Products. USDA Forest Service Forest Products Laboratory, Madison, WI, 1967.Search in Google Scholar
Morrison, J. (1960) Deuterium-hydrogen exchange between water and macromolecules: accessibility of cellulose. Nature 185:160–161.10.1038/185160a0Search in Google Scholar
Papadopoulos, A.N., Hill, C.A.S. (2002) The biological effectiveness of wood modified with linear chain carboxylic acid anhydrides against Coniophora puteana. Holz Roh- Werkst. 60:329–332.10.1007/s00107-002-0327-8Search in Google Scholar
Pönni, R., Rautkari, L., Hill, C.A.S., Vuorinen, T. (2014) Accessibility of hydroxyl groups in birch kraft pulps quantified by deuterium exchange in D2O vapor. Cellulose 21:1217–1226.10.1007/s10570-014-0166-xSearch in Google Scholar
Popescu, C.M., Hill, C.A.S., Curling, S., Ormondroyd, G., Xie, Y. (2014) The water vapour sorption behaviour of acetylated birch wood: how acetylation affects the sorption isotherm and accessible hydroxyl content. J. Mater. Sci. 49:2362–2371.10.1007/s10853-013-7937-xSearch in Google Scholar
Rautkari, L., Hill, C.A.S., Curling, S., Jalaludin, Z., Ormondroyd, G. (2013) What is the role of the accessibility of wood hydroxyl groups in controlling moisture content? J. Mater. Sci. 48: 6352–6356.10.1007/s10853-013-7434-2Search in Google Scholar
Rowell, R.M., Simonson, R., Hess, S., Plackett, D.V., Cronshaw, D., Dunningham, E. (1994) Acetyl distribution in acetylated whole wood and reactivity of isolated wood cell-wall components to acetic anhydride. Wood Fiber Sci. 26:11–8.Search in Google Scholar
Rowell, R.M. Handbook of Wood Chemistry and Wood Composites. CRC Press, Boca Raton, FL, 2005.10.1201/9780203492437Search in Google Scholar
Sepall, O., Mason, S.G. (1961) Hydrogen exchange between cellulose and water: I. measurement of accessibility. Can. J. Chem. 39:1934–1943.10.1139/v61-260Search in Google Scholar
Stamm, A.J. (1956) Thermal degradation of wood and cellulose. Ind. Eng. Chem. 48:413–417.10.1021/ie51398a022Search in Google Scholar
Taniguchi, T., Harada, H., Nakato, K. (1978) Determination of water adsorption sites in wood by a hydrogen–deuterium exchange. Nature 272:230–231.10.1038/272230a0Search in Google Scholar
Thybring, E.E. (2013) The decay resistance of modified wood influenced by moisture exclusion and swelling reduction. Int. Biodeter. Biodegr. 82:87–95.10.1016/j.ibiod.2013.02.004Search in Google Scholar
Thybring, E.E., Thygesen, L.G., Burgert, I. (2017) Hydroxyl accessibility in wood cell walls as affected by drying and re-wetting procedures. Cellulose 24:2375–2384.10.1007/s10570-017-1278-xSearch in Google Scholar
Thygesen, L., Elder, T. (2008) Moisture in untreated, acetylated, and furfurylated Norway spruce studied during drying using time domain NMR. Wood Fiber Sci. 40:309–20.Search in Google Scholar
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