Acetylated Wood
The Science Behind the Material
Dr. Callum Hill FIWSc
Senior Lecturer in Renewable Materials
School of the Environment and Natural Resources
University of Wales, Bangor
Abridged by KJN, Feb 2009
Background
Timber can be viewed as a classic renewable material. Trees absorb carbon dioxide and utilise water plus sunlight to produce a material that can be used in construction, to produce paper, or to provide chemical feedstocks; with the production of oxygen as a by-product. Furthermore, at the end of a product lifecycle, the material constituents can be combusted, or composted to return the chemical constituents to the ‘grand cycles’. In essence, timber use represents a classic example of a cyclic materials flow, mimicking the flows of materials through natural cycles. Provided we manage our forests well and do not harvest beyond the capacity of the planet to provide timber, we have at our disposal an inexhaustible resource available in perpetuity...........................................
Increasing quantities of timber are being sourced from managed plantation forests, which are now being established at a rate of over 3 million ha per year. ....................
Due to environmental concerns regarding the use of certain classes of preservatives (such as copper, chromium and arsenic), there has recently been a renewed interest in wood modification. Wood modification represents a process that is used to improve the material properties of wood, but produces a material that may be disposed of at the end of a product life-cycle without presenting an environmental hazard any greater than that associated with the disposal of unmodified wood. Although wood modification has been the subject of a great deal of study at an academic level for over 50 years, it is only comparatively recently that there has been significant commercial development.
Dimensional Stabilisation
When wood is acetylated it is far less susceptible to shrinking and swelling in the presence of varying atmospheric conditions. The reason for this is simply explained:
The cell wall is now filled with chemically bonded acetyl groups which take up space within the cell wall. As a consequence the wood is already in a swollen condition, the extent of which depends upon the level of modification, there is very little residual swelling when the wood is soaked in water. This can be proved by reacting with a range of anhydrides..................................
Biological degradation
For more than fifty years there has been discussion as to why it is that acetylated wood is protected against attack by microorganisms......
So what is the mechanism?.......................
The conclusions from this study were that the reduction in cell wall moisture content due to the space occupied by the acetyl groups was responsible for the decay resistance.
The future
We are now in a position where acetylated wood will be appearing in the market in significant quantities.....
As acetylated wood becomes established as a mainstream product it will become necessary to address the issue of disposal of this material.
Due to its nature, it could be ground down to a form suitable for composting, or incinerated without release of toxic materials into the environment.
A more appropriate strategy would be to develop a materials cascade approach. Acetylated wood would be used as a feedstock for particleboard, MDF or other reconstituted wood products to make more dimensionally stable products. At the end of life of these products pyrolysis would be used to release bonded acetyl as acetic acid which would then be used as a feedstock for new acetic anhydride. The residue from this process would then be burnt to provide process energy for the acetylation plant.
This would then be a truly cyclic materials flow process.
Read the full unabridged report here:
http://www.accoya.com/wp-content/uploads/2011/05/Acetylated-wood.pdf
More on the subject from Dr Callum Hill
http://www.bfafh.de/inst4/45/ppt/7ecology.pdf
http://accessscience.com/content/Accoya%20wood/YB081390
The Science Behind the Material
Dr. Callum Hill FIWSc
Senior Lecturer in Renewable Materials
School of the Environment and Natural Resources
University of Wales, Bangor
Abridged by KJN, Feb 2009
Background
Timber can be viewed as a classic renewable material. Trees absorb carbon dioxide and utilise water plus sunlight to produce a material that can be used in construction, to produce paper, or to provide chemical feedstocks; with the production of oxygen as a by-product. Furthermore, at the end of a product lifecycle, the material constituents can be combusted, or composted to return the chemical constituents to the ‘grand cycles’. In essence, timber use represents a classic example of a cyclic materials flow, mimicking the flows of materials through natural cycles. Provided we manage our forests well and do not harvest beyond the capacity of the planet to provide timber, we have at our disposal an inexhaustible resource available in perpetuity...........................................
Increasing quantities of timber are being sourced from managed plantation forests, which are now being established at a rate of over 3 million ha per year. ....................
Due to environmental concerns regarding the use of certain classes of preservatives (such as copper, chromium and arsenic), there has recently been a renewed interest in wood modification. Wood modification represents a process that is used to improve the material properties of wood, but produces a material that may be disposed of at the end of a product life-cycle without presenting an environmental hazard any greater than that associated with the disposal of unmodified wood. Although wood modification has been the subject of a great deal of study at an academic level for over 50 years, it is only comparatively recently that there has been significant commercial development.
Dimensional Stabilisation
When wood is acetylated it is far less susceptible to shrinking and swelling in the presence of varying atmospheric conditions. The reason for this is simply explained:
The cell wall is now filled with chemically bonded acetyl groups which take up space within the cell wall. As a consequence the wood is already in a swollen condition, the extent of which depends upon the level of modification, there is very little residual swelling when the wood is soaked in water. This can be proved by reacting with a range of anhydrides..................................
Biological degradation
For more than fifty years there has been discussion as to why it is that acetylated wood is protected against attack by microorganisms......
So what is the mechanism?.......................
The conclusions from this study were that the reduction in cell wall moisture content due to the space occupied by the acetyl groups was responsible for the decay resistance.
The future
We are now in a position where acetylated wood will be appearing in the market in significant quantities.....
As acetylated wood becomes established as a mainstream product it will become necessary to address the issue of disposal of this material.
Due to its nature, it could be ground down to a form suitable for composting, or incinerated without release of toxic materials into the environment.
A more appropriate strategy would be to develop a materials cascade approach. Acetylated wood would be used as a feedstock for particleboard, MDF or other reconstituted wood products to make more dimensionally stable products. At the end of life of these products pyrolysis would be used to release bonded acetyl as acetic acid which would then be used as a feedstock for new acetic anhydride. The residue from this process would then be burnt to provide process energy for the acetylation plant.
This would then be a truly cyclic materials flow process.
Read the full unabridged report here:
http://www.accoya.com/wp-content/uploads/2011/05/Acetylated-wood.pdf
More on the subject from Dr Callum Hill
http://www.bfafh.de/inst4/45/ppt/7ecology.pdf
http://accessscience.com/content/Accoya%20wood/YB081390
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