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Wood properties, influenced by type, structure, environment, and history, are divided into physical-mechanical, biological, and chemical categories. These properties vary significantly in raw timber compared to engineered wood products and differ within a trunk and by location. Wood is heterogeneous and anisotropic, with varying cell types and chemical compositions.
This guide covers the relevant properties of Norwegian timber.
Lone Ross
Director
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Division of Forest and Forest Resources
(+47) 911 97 268 lone.ross@nibio.no Office Location: Ås H8
The density of wood describes the relationship between mass and volume. The cell wall of all wood species has approximately the same density, about 1500 kg/m³ in an absolutely dry state. Therefore, it is the ratio between the cell wall and the cell lumen in the wood that determines the density. Wood absorbs moisture from the environment, and the density will therefore vary with moisture content. To describe density, the specific moisture content must be specified. There are many variants and different terms used to describe density in various contexts.
Carbon, hydrogen, and oxygen combine to form the primary organic components of wood: cellulose, hemicellulose, and lignin. These components cannot be easily identified. Separation and quantitative determination of each component can be achieved in the laboratory through the use of solvents or through thermo-gravimetric analysis.
The proportions of cellulose, hemicellulose, and lignin are as follows (in percent of the oven-dry weight of wood):
Cellulose is composed of glucose molecules (C6H12O6), a monosaccharide produced through photosynthesis from atmospheric carbon dioxide (CO2). These glucose molecules are linked together to form long cellulose chain molecules.
Hemicellulose is chemically related to cellulose, as both are carbohydrates. Carbohydrates are chemical substances composed of carbon, hydrogen, and oxygen, with the latter two elements present in the same proportions as in water.
Lignin is the cell wall component that distinguishes wood from other cellulosic materials produced by nature. The process of lignification, which involves the deposition of lignin, marks the final stage of cell wall development. Lignin is produced only by living cells. Notably, lignin always occurs in association with cellulose, whereas cellulose can be found almost pure in nature (e.g. in cotton). Lignin is not a carbohydrate. It is predominantly aromatic in nature. The composition of lignin differs between softwoods ("guaiacyl" lignin) and hardwoods ("syringyl" lignin) and also varies especially among different hardwood species.
Tsoumis G. 1991. Science and technology of wood - structure, properties, utilization, 494 pp., Van Nostrand Reinhold, New York. The properties of wood are divided into physical-mechanical, biological, and chemical characteristics. These properties are influenced by the type of wood, its structural composition, environmental conditions, and history. Moreover, the properties of raw timber exhibit considerably more variability than those of engineered wood products, such as chipboards and other wood panels. These properties can vary significantly within a single trunk and based on geographical location.
Additionally, wood is not a homogeneous material in structural or chemical terms but is instead described as heterogeneous and anisotropic. It consists of different cell types and behaves differently in radial, tangential, or axial directions. Depending on the type of wood species, the chemical construction of wood also varies, and the composition of hemicellulose, cellulose, and lignin can differ. Beyond that, other chemical elements present in the wood can influence its properties.
Here, we aim to provide information about timber in Norway and the various properties relevant to all those who utilise wood.
