Benchmarking and State of the art for Modified wood

Benchmarking and State of the art for Modified wood With an increased awareness of the fragility of our environment and the need for durability in wood products, new technologies have been developed to increase the service life of wood materials without the use of toxic chemicals. Issues of sustainability, carbon sequestration and performance converge in this search for environmentally friendly methods of wood preservation. For wood to be used in exterior applications, dimensional stability and fungal resistance is of crucial importance. There are really only three routes that can be considered as a complement to traditional pressure impregnation or naturally durable wood species, namely acetylation, furfurylation and thermal treatment. Reductions in hygroscopicity, increased dimensional stability and decay resistance of thermally treated wood depend on decomposition of a large portion of the hemicelluloses in the wood cell wall. In theory, these hemicelluloses are converted to water and furantype intermediates that can polymerize in the cell wall. Furfuryl alcohol is a low-viscosity liquid that can be impregnated into wood and swells the wood cell walls. It reacts strongly with itself at low (acid) pH to form a dark, highly-resistant, hard, cross-linked polymer. Recent studies have shown that the FA also covalently bonds to the wood cell wall during polymerization.Reductions in hygroscopicity and improved dimensional stability of acetylated wood depends on esterification by means of reacting the cell wall polymers with acetic anhydride, reducing hydrogen bonding with water, and bulking the cell wall back to its green volume. The cell wall moisture content is too low in acetylated wood to support fungal attack so the initial enzymatic attack starting the colonization does not take place. Strength properties are reduced in thermally treated wood as a result of the degradation of the cell wall matrix, while strength properties are not significantly changed in furfurylated and acetylated wood.