Man has been using wood since time immemorial. Fuel, building materials, furniture, musical instruments - products from it accompany us all our lives. In addition, trees are natural calendars and living historical monuments.
There is a whole branch of science - dendrochronology, which allows you to find out the age of the product, as well as in what area the tree from which it was made was cut down. Studying the sections of annual rings, you can learn about the nature and atmosphere of ancient times. Advantages and disadvantages, structure, wood as a building material, properties - all these issues deserve attention.
How things work
The properties and characteristics of the material cannot be understood without first studying the structure and composition of wood. The concept itself depends on who uses it. For an ordinary person and a builder, this is exclusively a part of a tree under the bark, which can be used in everyday life or production. For a botanist, the structure of a tree and wood is the whole complex, including all elements from roots to crown.
Krone is used in industryslightly, and the branches are used as raw materials for fibreboard and cardboard. The main thing is the trunk. On the cross section, the structure of the tree trunk opens up. The topmost layer, the cortex, protects living cells from external influences. Between the bark and the body of the trunk is a layer of living cells - cadmium. In the very center, the core passes through the entire trunk. The loose fabrics of which it is composed make it unsuitable for utilitarian purposes.
The core of the tree consists mainly of dead cells, resin deposits, dyes and tannins. The core is surrounded by sapwood, the part of the tree that is responsible for conducting water to the leaves from the roots. Accordingly, it has a lot of moisture, it passes water more and is more prone to decay. Not all trees have a pronounced core. In some of them there is no difference between the central and marginal parts of the trunk. Such rocks are called sapwood.
Microscopic structure of wood
Using a microscope, you can study the structure more deeply. Wood is generally composed of dead cells. Young plant cells consist of a shell and an inner part - the cytoplasm and the nucleus. The basis of a thin transparent membrane is cellulose or fiber. Over time, plant cells undergo metamorphosis and, depending on the inherent function, turn in their mass into either bark (corking) or wood (lignification).
Lignin is constantly formed in cells. He is the reasonlignification. There are two types of woody cells - prosenchymal and parenchymal. The first type makes up the bulk of the wood, depending on the species - from 85% to 99%. In turn, they are divided according to their functions. Conductive cells are responsible for the delivery of nutrients and moisture from the roots to the foliage, while mechanical cells are responsible for the strength and stability of the tree. Parenchymal cells act as a pantry for the plant. They accumulate nutrients (fats, starches) and give them away as needed during a difficult period.
Conifers
Depending on the type of trees, their structure also differs. Wood species are divided into coniferous and deciduous. The structure of conifers is more simple. The bulk are tracheid cells. The features of conifers include the presence of cells that produce resin. In different species, they can be either randomly scattered or combined into a system of resin passages.
Hardwood
Hardwood trees and their structure are more complex. Wood consists of vessels, libriform fibers and parenchymal cells. Since deciduous trees shed their leaves in autumn, they need a large supply of food in winter. Hence the greater number of parenchymal cells responsible for the accumulation of nutrients than in conifers. This can be seen from the pronounced core.
Properties
Wood has a number of characteristic properties. The structural features are the reason for this. The strength of wood is quite high, and among buildingmaterials on this indicator, it occupies an intermediate position. And given the small specific gravity, it is comparable in this respect with the metal. The weak point of wood is that it is an anisotropic material. The ability to resist fracture depends on the direction of the force relative to the location of the fibers. The best strength values are seen when the material is exposed along the fibers.
The rigidity of wood is small, the reason for this is the specific structure. Wood is a porous, flexible material. Beams are able to restore their shape after a short-term load. But residual deformations, due to prolonged exposure, remain forever. A wooden beam will not be able to recover its shape after a long period of use.
The hardness of building materials is determined by what load is needed to press a steel ball with certain dimensions. For the hardest wood species, it is only 1000 N. At the same time, low hardness is one of the main advantages of the material. The wood is easy to process, nails, screws, self-tapping screws are firmly held in it.
The moisture content of wood is determined by the specific moisture content in the pores. In a freshly cut tree, it reaches 100%. Depending on the purpose, freshly cut wood is dried to the required levels from 40 to 15%.
Dignity
Wood has a low thermal conductivity. It can be successfully used as a heat-insulating material. Ease of processingallows you to use a wide range of tools. It is impossible to imagine any orchestra without musical instruments made of wood. The enchanting sounds of the violin are the result of such a property of wood as the ability to resonate. The wood is easily bent, and there is a wide choice for the manufacture of various bent structures. Also, wooden products have good sound-absorbing characteristics. A beautiful surface opens up room for imagination in interior design.
Flaws
The ability of wood products to take loads depends on the direction of force application. This is due to the anisotropic structure of wood. In addition, the strength characteristics also depend on the proximity to the center of the trunk, humidity, the presence of knots, cracks. This leads to spending a lot of time selecting the right material for the job.
Being an organic material, wood is defenseless against insects, mold and fungi. For long-term operation, expensive chemical treatment is required. It is worth noting that wooden structures without pre-treatment are easy prey for fire.
Wood processing
In general, there are three types of wood processing:
- The most common is the mechanical method. The tree is sawn, planed, split.
- During chemical-mechanical processing, the material is subjected to intermediate preparation. Chips, shavings are mixed with a binder and heated. A chemical polymerization reaction takes place, and at the outputreceive materials such as plywood, chipboard, fiberboard.
- During chemical treatment, wood is exposed to acids, alkalis, s alts, and subjected to heat. Of the products of such processing, one can name charcoal, rosin, gum, tannins, cellulose.
Trees are hundreds of millions of years older than man. All civilizations that have ever existed are based on the use of wood. Books, furniture, musical instruments - all this is possible thanks to this unique natural material.
