Chemical extractives of the tropical wood

1 Wallaba (Eperua falcata) is a tropical wood which is known to have naturally low swelling 2 characteristics. Samples of wallaba heartwood were subjected to differential solvent 3 extraction. Wood pieces that were extracted with methanol experienced significantly higher 4 swelling after rehydration from oven dry to 96% relative humidity in comparison to non-5 extracted samples and samples extracted with other solvents. Methanol soluble wallaba 6 heartwood extract was purified by high pressure liquid chromatography and the compounds 7 present were characterised by nuclear magnetic resonance spectroscopy. Methanol extract was 8 found to contain a very high relative proportion of polar compounds which are proposed to 9 bind to the polymeric cell wall by multiple hydrogen bonds restricting the association of water 10 and therefore acting as natural anti-swelling agents. 12 13 Introduction 14 Wood cellulose is organized in crystalline networks of nanofibres coated by hemicellulose 15 macromolecules and then by lignin. In the cell walls, the organization of these layers of fibre 16 composite and the orientation of those fibres are determining factors of hygroscopic 17 properties (Skaar 1988). Water induces dimensional variations in wood and it is present in 2 18 mains forms; commonly called " bound water " or " free water ". Bound water is either 19 intimately associated into the lignocellulosic network or associated onto wood cell wall 20 through hydrogen bonding; in the latter case this is termed " water of saturation " or " water of 21 surface absorption. " Free water, sometimes termed " interstitial water, " is contained in cell 22 lumens when the fibre saturation point is exceeded (approximately 30% wood moisture 23 content). The absorbtion or desorption of free water does not influence swelling of wood 24