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G. Weichslberger, S. Knaus, H. Gruber:
"Chemical modification of wood. Effects on surface wettability and mechanical strenght";
Poster: 12th International Symposium on Wood and Pulping Chemistry, Madison, USA; 09.06.2003 - 12.06.2003; in: "Proceedings 12th International Symposium on Wood and Pulping Chemistry", (2003).

Chemical modification is a very effective means of improving wood properties such as dimensional stability or biological resistance. The processes involved rely essentially upon forming covalent bonding between the hydroxyl groups of wood and some chemical reagent, leading to modification of the basic chemistry of the cell walls. Many studies in this area have been focused either on etherification or esterification reactions, with a particular attention on acetylation with acetic anhydride. A wide variety of other chemical reagents have also been considered to chemically modify wood. However, up to now there is little evidence in the literature of the effect of hydrophobic organosilicon compounds (OSC) upon the dimensional stabilisation of wood. The chemical grafting of such highly hydrophobic components to wood could drastically change its hygroscopicity and, as a result, decrease its dimensional instability. In order to explore the possible benefits of organosilylation, we investigated the chemical modification of spruce wood with organosilicon compounds. Reactions of spruce cellulose, spruce wood meal and solid spruce wood with trimethylchlorosilane and N,O-bis-trimethylsilylacetamide respectively, in liquid phase were compared. Silicon mass contents in the range of 3-18 wt% were achieved, depending on modifier, reaction conditions and starting material. Hydrophobization of the silylated wood meal and spruce wood was proved both by gravimetrical determination of the decrease in water uptake and by contact angle measurements, comparing untreated and modified samples. To make clear whether (a) bond formation between OSC and the wood had taken place, (b) how much of the OSC had been incorporated and (c) which parts of the wood cells reacted, proper analytical methods were developed. Bond formation between OSC and wood was confirmed by infrared spectroscopy and solid state NMR spectroscopy. A simple method was established to quantify the extent of silylation by IR-spectroscopy, replacing the time-consuming and labour-intensive gravimetrical determination commonly used. Surface wettability was strongly decreased as could be proved by contact angle measurements. Furthermore the mechanical strength was considerably lowered due to the loss of intermolecular hydrogen bonds as tensile testing results showed.

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