PROJECT DESCRIPTION
BACKGROUND
At present 30.000 tonnes of toxic preservatives e.g. copper, chromium, arsenic, creosote, etc. are used par annum for weed preservation in Western Europe (6 millions cubic meters of wood is treated per annum and 5 kg of preservative is used per cubic meter). Acetylation of wood is an alternative, environmentally friendly treatment to improve the durability and stability of woods (a reduction in swelling and shrinkage and an increase of 30 % of the hardness). It is a non toxic treatment because alteration of the molecular structure is used as a mechanism instead of toxic chemicals. Acetylation modifies the arrangement of cellulose and lignin molecules and improves the characteristics of the wood. The process could be an alternative for current less environmentally friendly preservation methods of wood.
OBJECTIVES
The objective of the project was the design and construction of a prototype in order to investigate the feasibility of the acetylation process applied to solid wood. To achieve this, the process needed further elaboration and some technical uncertainties had to be solved. It was expected that the application of the acetylation technology as an alternative to the commonly used preservation method would lead to a reduction of 30,000 tons of toxic preservatives products. Furthermore, the substitution of other building materials like plastics, steel and aluminum would lead to(i)a trap of CO2 by the use of woods, and (ii) less CO2 production during the production of the other materials. Finally, it would also lead to a large reduction of the consumption of (VOC-containing) paints.
RESULTS
When the project ended, the following general conclusions could be drawn: • The investment costs for an industrial acetylation plant are high. • The production costs of acetylated wood are higher than other treatments (for window frame uses (laminated, profiled etc), around 1.477 € per m3, while around 1.091 € for other products such as Meranti, or around 727 € for untreated Pine. • Although the ketene route (by-product) shows more efficient input of acetic anhydride, the additional investments are very high; • The complexity of the production process, especially when combined with a ketene plant,is high. Although the product qualities of acetylated wood seem superior to any present competitor on the market, acetylated wood in the joinery market is too complex and expensive. Although the technical results are very promising, the economic feasibility is limited and needs further attention. The project faced several problems as outlined below: 1. Administrative issues In 1997, the beneficiary submitted the original proposal to Senter (Dutch executing agency of the Ministry of Economic Affairs). This proposal was approved by Senter in January/February 1998, before the approval of the LIFE application. Due to this, only a limited part of the project has been financed by LIFE. 2. Technical issues • The problem of withdrawing the acid from the wood - By using a mixture of acetic anhydride ((CH3CO)2O) and acetic acid (CH3COOH) more or less the same acetylation level is reached in comparison with treatment with pure acetic anhydride with the same process. These results show that using mixtures of acetic anhydride and acetic acid could reduce the usage of acetic anhydride. - Steaming to reduce the amount of acetic acid proved not to be a successful post treatment; the wood degrades and too much acetic acid remains. - Water impregnation followed by high temperature drying to reduce the amount of acetic acid darkens the wood, but is successful • The problem of the byproducts It would be better for the environment to build a re-processing plant next to the acetylation plant. This should be done for the re-processing ketene (C2H2O, used as acetylation agent) derived from acetic acid. • The problem of the proof Acetylation had positive as well as negative effects on all the mechanical properties tested. In some cases the mechanical properties were increased by acetylation, especially with Scots pine and poplar. On the other hand, the Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) were decreased by the acetylation of Radiata pine. Almost no change in mechanical properties applied for beech. The effect of acetic acid on long-term mechanical properties is unknown at the moment. 3. Financial issue The beneficiary has decided not to continue the project, as the financial feasibility appears to be very limited. The beneficiary decided to give up his research and investment on the wood acetylation. Other companies seem however to be working on this technology.