Wood modification
Wood modification , also wood modification in the narrower sense, refers to the improvement of the durability of wood through chemical or thermal treatment or impregnation resins . In a broader sense, other impregnation processes for wood modification can also be counted.
In particular, colonization by wood-degrading fungi or insects should be delayed. Ideally, biocidal wood preservatives can then be dispensed with. At the same time, this often results in a change in other wood properties, e.g. B. the reduction in the equilibrium moisture content , greater dimensional stability and an increase or decrease in strength compared to untreated wood.
Types of wood modification
Thermal-physical processes or heat treatment processes
At temperatures above 150 ° C, hydrolytic cleavage and condensation reactions occur . Due to the partial degradation of cell wall components, thermally modified wood (thermowood) has a lower density and strength than untreated wood. The durability of the wood usually increases with the heat and exposure time used, while the strength of the wood decreases at the same time. Heat-treated wood turns dark. It is also known as thermowood.
Waterproofing with oils, resins and waxes
By storing water-repellent substances such as oils or waxes , the moisture is kept away from the wood, thus significantly reducing infestation by fungi. Treatment with oils alone is often not enough to guarantee permanent protection against wood-degrading fungi, as oils in the exterior are washed off the wood surface or decomposed. Stand oil or oil mixed with natural resins is more resistant .
However , German pine impregnated with wax has a significantly increased durability; the compressive strength of the wax-impregnated wood is 20–80% higher than that of untreated pine. The fungus resistance of the wood treated with wax in this way reaches at least that of oak heartwood ( durability class II according to EN 350-2).
Waxes and resins only penetrate the pore spaces of the wood if impregnation is carried out under pressure or vacuum. See: pressure impregnation
Chemical modification
In the chemical modification of wood, reactive chemicals are used that can react with the functional groups of cellulose or lignin . Most of the time, the hydroxyl groups on the cell wall react, as in the production of acetylated wood . Chemicals such as formaldehyde can also cross-link the hydroxyl groups in the cell wall. In addition, some chemicals are able to store themselves in the wood cell wall and polymerize there ( impregnation with melamine resins , phenol-formaldehyde resin , urea resin , furfurylation with furfuryl alcohol from biomass and others). Wood treatment with silicon compounds also leads to a reduction in water absorption and can thus contribute to better durability against wood-degrading fungi.
Stabilized wood
The term stabilized wood is used by some manufacturers for wooden work pieces that are impregnated with synthetic resins to improve the mechanical and chemical properties and to increase the decorative effect of the grain.
Often, PMMA resin used with which the pores of the wood by the vacuum and pressure treatment are almost completely filled.
literature
- André Wagenführ, Frieder Scholz (Ed.): Pocket book of wood technology. Hanser Verlag, Munich 2008
- Heinz Geza Ambrozy, Zuzana Giertlová: Planning manual for wood-based materials. Technology, construction, application. Springer Verlag, Vienna 2005
- Alfred Teischinger (Ed.) (2002) Modified Wood - Properties and Markets. Lignovisionen Volume 3, series of publications at the Institute for Wood Research, BOKU Vienna, September 2002, ISSN 1681-2808
Web links
Individual evidence
- ↑ Thermally tempered wood at waldwissen.net, accessed on November 18, 2015.
- ↑ Complete impregnation of modified wood with wax at link.springer.com, accessed on November 18, 2015.
- ↑ Carsten Mai: Processes of chemical wood modification at technikredaktion-weis.de, accessed on November 18, 2015.
- ↑ Holger Militz: Chemical modification of beech wood PDF file, accessed on November 18, 2015.
- ↑ Description of stabilized wood from the manufacturer Raffin ( Memento of the original from January 6, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed August 2015.
