The wood is a vegetable Tissu (the Xylème) which plays a double part at the vascular Plante S: driver of the rough Sap and fabric of support which gives their resistance to the Tige S. It is used also sometimes as fabric of reserve.
It is a Matériau appreciated for its properties Mécanique S, for its calorific value and a raw material for chemical industry , which one draws mainly from the trunk of the Arbre S and of the Bambou S. It has many uses in the building and the industry and as a Combustible.
The Norme NF B 50-003 (vocabulary of wood) defines it as “a whole of secondary resistant fabrics (of support, conduction, and retention) which form the trunks, branches and roots of the woody plants. Resulting from the operation of the peripheral Cambium, it is located between this one and the Moelle”.
A wood is also a planted place of Arbre S, generally of small surface (in opposition to a Forêt, which indicates a great wooded extent).
Characteristics of wood
StructureWood is composed of various types of fabric plants: vascular fabric, fibers, Parenchyma S of reserve.
Fibers: beams of resistant cells, laid out in the axial direction, which ensures the rigidity and the mechanical resistance of wood. It is about a bio-composite made up of cellulose, hemicellulose and lignin.
- vascular Fabric: formed of vessels, hollow cells which are used to lead the crude sap since the roots to the sheets. In the coniferous trees these vessels are Trachéide S. These vessels are often associated with parenchymatous cells (also called parenchyma) which contribute to the transport of the nutrients. These parenchymas, associated with the vessels, give reasons particular to each gasoline (particularly tropical gasolines) on the transverse section (perpendicular to the axis of the trunk).
- woody Rays: cells of reserve (parenchymatous) to thickened and lignified walls, which accompany vascular fabric. These cells take part moreover in the function of support. Their orientation is transverse and radiant on the basis of the longitudinal axis of the tree. The photograph of right-hand side shows some woody rays which leave the center of the trunk.
This one is characteristic of each gasoline. For example, it what is called gives “the maillure”, which is the aspect of the radial cut of wood (longitudinal section in the direction of the ray of the tree). This maillure is characteristic at the Oak, the Beech, the Plane tree or Niangon and the Mahogany tree.
The general orientation of the cells and fibers is in the axial direction, which determines the “wire of wood”.
Chemical compositionWood is made up mainly of organic matters (cellulose and lignin) and of a small percentage (from 1 to 1,5%) of biogenic salts. It also contains a variable share of moisture.
- Cellulose (40 to 50%)
- Lignin (20 to 30%)
- Hemicellulose (15 to 25%)
- Other organic substances: Polysaccharide S, Pentosan S, Hexosane S, resin S, Tannin S, Dye S, Wax S, Alkaloid S…
Actually, there exist three types of water in wood.
the interstitial water, it is the water which is present in the green heart Schématiquement, it is the water which is contained in sponge. During the evacuation of this water, wood does not take withdrawal.
- bound water, it is the water which uses the composition of fibers. It is that which causes the withdrawal during drying. For our sponge, it is about the water which is contained in the matter but that we cannot dry. During drying, it is the water which is withdrawn between 30% and 0% of moisture.
- the water boiler feed, it is the water which uses the chemical composition of the molecules of wood. Its elimination involves the destruction of wood (by the fire for example).
- Impact strength
- Tensile strength and to compression
- Density: the density of wood is generally lower than 1 (wood floats) because of the vacuums in its structure. This density strongly varies according to its percentage of moisture; it depends on the gasoline and also on the station. It is the most important parameter to characterize a wood. One normally expresses it for a water content equal to 15% (average between the anhydrous state and the state of saturation). The density with 15% generally ranges between 0,5 and 0,7, but can vary considerably, of 0,1 for the balsa, 0,4 for wood light (Sapin, spruce, Peuplier), 0,8 to 1 for wood hard (yew, Teck, olive-tree), 1,1-1,2 for the Azobé and 1,3-1,4 for the Gaïac (iron wood).
- Durability: although it is about a biodegradable material, wood can last under certain conditions several centuries, as testify some to many frames of old monuments. The parameters favorable to the durability of wood are the maintenance in dry atmosphere, the raised density, the chemical composition, been dependant on the gasoline (presence of resins, oleoresins, Tanin S). The wood of heart is more durable than the Aubier, richer in fermentable matters. Among the most durable species, one classifies the Cèdre, the Séquoïa, the Mélèze, the Chêne, the Châtaignier… and among the least durable: the Fir tree, the spruce, the Beech, the Poplar, the Lime…
- insulating Properties : because of its cellular structure, which imprisons air in the form of small volumes, wood is a bad driver of heat. However its thermal Conductibilité is very variable according to its percentage of moisture, its density and the gasoline considered, as well as orientation compared to the wire of wood: it is better driver in the axial direction than in the radial direction. One usually uses panels agglomerated in wood particles like heat insulators.
A wood glare is called a splinter .
Deteriorations of wood
The mushrooms attack mainly the lignin of wood but they can also degrade cellulose. One often speaks about mushrooms lignivores.
The mushrooms attack wood when it contains more than 20% of moisture. A seasoned wood (< 20% of moisture) is never attacked by mushrooms.
There exist various deteriorations which are is visual, mechanical or both at the same time.
Much coniferous and leafy timber turns blue when they remain exposed with the bad weather. This deterioration is only esthetic and does not deteriorate of anything the properties attacked wood.
On the other hand, the white rot, the cubic rot (brown calcined wood aspect) or the brown rot are mechanical deteriorations of wood.
The white rot is due to a mushroom lignivore. By degrading the lignin which is yellow, the mushroom leaves behind him the cellulose and the hemicellulose which are white. The brown rot functions contrary, it is the cellulose which is attacked.
In general, the attack of a wood by mushrooms can be measured simply. Any attack is characterized by a loss of mass of wood. This loss can go up to 80% of the initial mass.
The mushroom the most known east can be Mérule which is typically appeared as a large white task fluffy that one finds under tight grounds posed on wood floors which were exposed to water.
Xylophagous attacks of insects
Many a Insecte S attacks wood that it is on foot, in barks after demolition in Forêt (xylophagous of the forests) or dryness once implemented (xylophagous of wood dry).
In fact the Larve S dig galleries in wood. The adult insects lay in wood and the larvae develop in that Ci by eating its components. At the ultimate stage of its development, the larva becomes adult and leaves its habitat to reproduce. They is precise at this time which the insect dig the hole of exit that one sees on wood attacked. In general, when one notes wood wormeaten, the attack is finished. The size, the geometry and the nature of the worm-holes make it possible to define which insect attacked wood.
One fights against these insects by the application of Insecticide S steeping, pulverization… It is a preventive medication. As regards the curative step, two cases arise. That is to say wood are still mechanically viable (in the case of a carrying element) and in this case a curative treatment can be applied. It can be a question of injection or pulverization after sanding. That is to say wood are very attacked then it will be necessary to replace them and burn wood infested.
Certain wood, rich in active ingredients (insecticidal, natural fungicides), are naturally resistant to the attacks of insects. One speaks about naturally durable gasolines.
Among the principal xylophagous insects of wood dry, let us quote:
In France, the occupant of a building which notes a infestation by the termites must immediately declare it in town hall (Law n° 99-471 of June 8th, 1999 tending to protect the purchasers and owners from buildings against the xylophagous termites and other insects).
See also the List of the xylophagous insects.
It is possible to protect wood from the deteriorations caused by mushrooms and the insects.
It is a question of applying a preventive medication which contains an insecticidal and fungicidal base. This treatment is done mainly by steeping (immersion in a vat containing the product). For the wood of structure, the obligatory treatment is a treatment classifies 2. The product used can be colorless, yellow, green or red. It can also be in phase solvent or aqueous phase.
To finish, preventive medication is quasi useless if wood used are dry. Indeed, the insects (and mushrooms) attack mainly wood with the top of 20% of moisture. In Europe, France is one of only the nation to impose a preventive medication of the wood of structure.
Natural defects of wood
The nodes are resurgences of branches in the tree trunk. They are of variable size according to the wood turpentines and sylviculture. They can be called healthy, adherent, sautées, bars, blacks or " bottoms of singe".
The nodes also vary according to whether a piece of wood is resulting from the ball or but log (low of the tree) located higher in the tree.
Sylviculture can largely exploit the size of the nodes. Regularly pruned trees of then their first years will present small nodes and quasi non-existent.
Another defects of wood
Among the known current defects of wood, it there a: gélivure, the rolled edge, the lunate defect, " blows of vent" , the eccentricity of the heart, resin pockets, the black core or red (for the ash and the beech in particular), the irregularity of the annual layers, grooves of the trunk, the between-bark, the wire corrugated and twisted, figured or brambly wood, broussins and the magnifying glass.
Uses of wood
Wood is employed with multiples Usage S and in multiple forms:
- Wood in the rough in the form of posts and logs, after sawing or splitting generally.
- Wood energy
- the use of wood as Combustible is its first use on the level Mondial: it brings 3000 Calorie S by kg (1 Stère of wood is equivalent to 0,147 Tonne equivalent-oil).
- Sawlog (sawn starting from barks)
- Wood of structure: Frame S, House of wood (piled up wood, house with framework wood or posts beam) and boardings, terraces, Cross-piece S of Railroads. These wood can be rough of sawing or planed. It is generally about a choice frames (choice 2 or ST 2 in France).
- timber sea: frames, bordered, espars (mast, bôme…), part of skittle
- wood aeronautics: structures of the first planes. Plywood is an invention of aeronautics. Today rather used for the small private planes in construction amateur or industrial
- rough Sawings, wood of domestic use: formwork with Concrete, scaffolding S, pallet S, Packing S…
- wood planed: Skirting, parquet floor S, Joinery
- platings: Wood unrolled or sliced. Fine gasolines cabinet work…
- Wood of engineering, wood of the second transformation: lamellate-stuck, reconstituted, joined, laminated, rolled-iron product, beam in " I" …
- Other uses: framing; Woodwork; Stringed-instrument trade; Match S…
- Wood of industry (exploited in logs)
- wood of mines, telegraph poles and different…
- pulpwood: Pulp paper, particle and fiberboards, agglomerates, wool of wood…
- Wood of turning: balls, skittles, handles with tools, toys…
- Wood of cutting: plywood…
- Split timber: Stave wood S for the Cooperage, sheeting planks (shingles of roof)…
- Bent timber: chairs “Thonet”
- Produced industrialized. Wood can be transformed elements industrialized such as:
- Elements of structure: Lamellate-stuck wood, wood pasted, wood joined (fingerjointed), beams out of I.
- Panels: Panels of large particles OSB, particle Boards or agglomerate, fiberboards average density (MDF) or high density (HDF)
- In art:
- wood is a means of expression Artistique in the Marqueterie and the Sculpture on wood,
- It is a traditional support for the Oil-base paint or with Tempera on wood panel. Since the old Egypt wood is covered with Gesso polished before being painted.
- In kitchen:
- certain parts of trees are consumed in various countries (bamboo shoots, heart of palm, etc)
EconomyThe worldwide production (year 2003, source FAO) rises with:
- Firewood: 1.797 million m ³.
- Sawlog for sawing and plating: 940 million m ³.
- Pulpwood: nc
- Other industrial roundwood: 153 million m ³.
- Chips (clipping, small plate, that one removes with an instrument slicing) and particles: 165 million m ³.
- Residues of wood: 70 million m ³.
- Sawings: 391 million m ³.
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