Furfurylated wood

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Example of furfurylated wood (Pinus Radiata with a loading level of 30-35%)

Furfurylated wood (English: furfurylated wood ) describes the end product of a treatment of wood with furfuryl alcohol . This process is also called furfurylation . Furfurylation is a modification process used commercially to improve the properties of wood. Here the cell walls of the wood are swollen with furfuryl alcohol, which polymerizes within the cell walls . With this treatment, the water absorption capacity of the wood is reduced and the tendency for wood to deform when there is a change in humidity is reduced. The hardness and rot resistance of the modified wood is also improved compared to that of native wood. The furfuryl alcohol used is obtained by hydrogenating furfural from biological residues such as husks or bagasse .

Physical and chemical processes

When wood is furfurylated, the cell wall membranes of the wood cells are first swollen with furfuryl alcohol; the furfuryl alcohol penetrates the cell wall due to its polarity and size. The polymerisation of furfuryl alcohol in wood is a complex reaction, the processes of which are not yet fully understood. It is not yet clear whether the furfuryl alcohol only reacts with itself and polymerizes within the cell, or whether the furfuryl alcohol also reacts with the cell wall components such as cellulose . The wood cells are rendered hydrophobic by the polymerized furfuryl alcohol inside the cell.

history

The furfurylation of wood is a process that was first researched by Alfred Stamm in the USA in the 1950s , but which has not yet been widely used in the market. The first industrial production of furfurylated wood in the USA started in the 1960s . In the 1980s , a working group led by Professor Marc Schneider in Canada developed a two-step process. The wood was first impregnated with a catalyst and then with the furfuryl alcohol. Furfurylated wood produced in this way could not be produced at the prices demanded on the market because of the high costs of the two-stage impregnation. In 1997, Wood Polymer Technologies ASA was founded in Norway to build a pilot plant for the single-stage manufacturing process. From 2000, furfurylated wood is marketed in the USA and Europe. In 2004 the production capacity in Porsgrunn , Norway was 3,000 m³ per year. In 2008 the capacity was increased to 25,000 m³ per year.

Manufacturing

In order to produce furfurylated wood, the following steps are necessary:

  1. Storage and mixing of the impregnation solution: Here approx. 40% furfuryl alcohol, water, polymerization initiators, catalysts and surfactants are mixed and then filled into a storage tank.
  2. Impregnation: The wood is soaked in a pressure vessel in a three-stage process. First, a vacuum is applied to draw the remaining air out of the wood. In the second step, the wood is soaked with the soaking solution at a pressure of 13 bar . Step three represents a short relaxation phase in which the boiler is brought to ambient pressure. The entire vacuum vessel can be tilted by 5 ° to allow the excess impregnation solution to run off the boards.
  3. Drying and polymerisation: The soaked wood is dried in a vacuum dryer by direct heating with steam. Due to the high boiling point of furfuryl alcohol of 170 ° C, it is possible to first dry the water out of the wood and then carry out the polymerization at a second, higher temperature level. The condensate that arises during drying is fed to the impregnation solution for further use.
  4. Post-drying: The modified wood is post-dried at moderate temperatures to minimize emissions and to set the final moisture content.

For the production of furfurylated wood, about 80% pine ( Pinus Sylvestris ) is used; other types of wood used are southern yellow pine ( Pinus palustris ), beech ( Fagus sylvatica ) and maple ( Acer saccharum ).

properties

The properties of the modified wood are strongly dependent on the amount and concentration of the furfuryl alcohol added. The amount of furfuryl alcohol introduced can be controlled through the proportion of furfuryl alcohol in an aqueous impregnation solution. So it is possible to adjust the properties of the modified wood.

With a load of 30–35%, the hardness, weight, mechanical properties, dimensional stability and resistance to insects, fungi and chemicals increase to such an extent that the product is classified in durability class 1. As a result of the process, the wood darkens considerably, especially when high amounts of furfuryl alcohol are introduced, which is why it is traded and used as a substitute for tropical wood in terms of both properties and color. The only disadvantage of heavily modified wood is an increase in the brittleness of the wood.

The mechanical properties of the wood improve even with a low level of loading, but the resistance to pests such as fungi and insects is not given, and the dark discoloration of the wood is also weaker. Slightly modified wood is therefore used indoors, mostly as flooring.

At a loading level of 50%, there is a high resistance to maritime ship drills such as the shipworm ( Teredo navalis ).

Furfurylated wood is traded as an ecologically harmless product, since both the wood and the furfuryl alcohol are produced from renewable raw materials.

market

Currently there is only one manufacturer of furfurylated wood with the name Kebony and based in Oslo , Norway . This company produces 22,000 m³ of furfurylated wood at various locations in Europe. The company has a capacity of at least 25,000 m³.

Web links

Individual evidence

  1. ↑ H. Militz, C. Mai: Other remuneration methods . In: A. Wagenführ, F. Scholz (Hrsg.): Taschenbuch der Holztechnik . 2., updated Edition. Fachbuchverlag Leipzig im Hanser Verlag, Leipzig 2012, ISBN 978-3-446-42605-4 , p. 485-500 .
  2. ↑ D. Sandberg, A. Kutnar, G. Mantanis: Wood modification technologies - a review . In: iForest - Biogeosciences and Forestry . tape 10 , no. 6 , 2017, ISSN  1971-7458 , p. 895-908 , doi : 10.3832 / ifor2380-010 .
  3. ↑ a b G. I. Mantanis: Chemical Modification of Wood by acetylation or Furfurylation: A Review of the Present Scaled-up Technologies . In: BioResources . tape 12 , no. 2 , May 1, 2017, p. 4478-4489 .
  4. ↑ a b Callum AS Hill: Wood Modification: Chemical, Thermal and Other Processes . John Wiley and Sons, Chichester 2006, ISBN 0-470-02172-1 .
  5. ^ MH Schneider, AE Witt: History of wood polymer composite commercialization . In: Forest Products Journal . tape 2 , 2004, p. 19-24 .
  6. ^ MH Schneider: Furan polymer impregnated wood . PCT laid-open specification WO 2002/060660 A1, 08.08.2002, 2001.
  7. ↑ a b c C. May: Processes of chemical wood modification . In: wood technology . tape 51 . Dresden 2010.
  8. ↑ a b Stig Lande, Mats Westin, Marc Schneider: Properties of furfurylated wood . In: Scandinavian Journal of Forest Research . tape 19 , sup5, December 1, 2004, ISSN  0282-7581 , p. 22-30 , doi : 10.1080 / 0282758041001915 .
  9. ↑ Pia Larsson Brelid: Benchmarking and state of the art for Modified wood. (PDF) Retrieved January 9, 2018 (English).
  10. ^ A b P. Brynildsen, R. Bendiktsen, F. Englund, CAS Hill, H. Militz, BK Segerholm: State-of-the-art Kebony factory and its main products. Proc. of the 4th European conference on wood modification . Ed .: BK Segerholm. Stockholm 2009, p. 37-42 .
  11. ^ Philippe Gérardin: New alternatives for wood preservation based on thermal and chemical modification of Wood - a review . In: Annals of Forest Science . tape 73 , no. 3 , September 1, 2016, ISSN  1286-4560 , p. 559-570 , doi : 10.1007 / s13595-015-0531-4 .
  12. ↑ M. Westin, P. Larsson-Brelid, T. Nilsson, A. Rapp, JP Dickerson, S. Lande, S. Cragg: Marine borer resistance of acetylated and furfurylated wood - Results from up to 16 years of field exposure. In: Proceedings of the “47th Annual Meeting of the International Research Group (IRG) on Wood Protection” . Stockholm May 2016, p. 10 ff .
  13. ^ Philippe Gérardin: New alternatives for wood preservation based on thermal and chemical modification of wood - a review . In: Annals of Forest Science . tape 73 , no. 3 , September 1, 2016, ISSN  1286-4560 , p. 559-570 , doi : 10.1007 / s13595-015-0531-4 .