Wood | Research & Encyclopedia Articles

Wood

Wood is the hard, fibrous substance found beneath the bark in trees, shrubs, and other similar plants. It is a result of the secondary growth processes of these plants. The cambium layer (the region between the xylem and phloem in vascular plants) divides to produce various new tissues in a process that results in secondary thickening. This increases the girth of the tree by the production of the new wood. Wood is actually a very complex organic material made of a variety of carbohydrates, lignin, inorganic materials, and other organic materials. Wood has and still continues to be used in the construction industry and in the manufacture of pulp and paper.Charcoal i s produced from wood by slow combustion in a low supply of oxygen. Charcoal can be used as a fuel by burning it in excess oxygen, as a reducing agent in industrial chemistry, and it can be used to absorb gases and other particles. Charcoal is often one of the active ingredients in simple gas masks.

One of the main constituents of wood is cellulose, a carbohydrate polymer. Cellulose is used to manufacture rayon (viscose). Firstly, the cellulose is treated with an alkali and then carbon disulfide, to yield xanthated cellulose, that upon extrusion into an acid bath, gives rayon. When wood is pulped (as is done during paper manufacture) a liquid fraction is collected that is called tall oil. Tall oil contains mainly fatty acids and it can be used as a protective coating (a varnish), in the production of soaps (saponification), and as a plasticizer (a compound added to plastic or paint to improve the flexibility). Annual production of tall oil in the 1990s in the United States is in excess of 1 megatonne. Also from tall oil a solid resin called rosin (or colophony) can be obtained. Rosin is a translucent, amber solid that can also be found in the oil from pine trees. Rosin is mainly resin acids (monocarboxylic acids). Rosin can be used as a plasticizer, in the manufacture of varnishes and printing inks, and also to treat bows for stringed instruments. Steam distillation or chromatography of wood and wood residues can release terpenes. Terpenes are a large class of organic compounds that are widely employed in the pharmaceutical industry. Different terpenes can be obtained from different wood types and have characteristic physical properties often including distinctive odors. Terpenes are particularly common in the resins of coniferous trees. It is the terpenes that give the resins of conifers their characteristic smells.

Wood (along with other plant material), fossilised during the carboniferous period, is responsible for our coal and oil reserves.

Some wood can be produced very quickly and consequently it is usually a cheap and easily renewed resource. As a result of this it is still used extensively as a fuel and a building material. Wood can be divided into two types, hard and soft wood. Each has different physical properties. Hard wood is very dense and strong, and it is much slower growing and consequently is more expensive than soft wood. Hard woods are used where strength is needed. For example, the large wooden ships of the past were built of hard wood such as oak. Soft woods such as that obtained from conifers can be used where less physical strength is needed. They can be used in the manufacture of smaller structures or as is more common in the production of paper and pulp. Soft wood such as that obtained from conifers is very quick to grow and as such it is relatively cheap and easily renewable.

Wood is a versatile, natural product. It can be used directly as a building material or fuel. With minor treatment paper and pulp can be manufactured. With greater treatment a number of commercially important compounds can be obtained. Wood is obtained from trees as a result of secondary growth and different trees produce wood with different physical and chemical characteristics.