Properties of Wood

Wood is one of the most naturally available materials which has transformed the life of man.  Wood, obtained from trees, is used as firewood, for furniture, building homes and for making tools.  The benefits of wood cannot go unaccounted for and are useful because of their unique properties.

The wood that we make use of, is in fact, the xylem of the plant.  The xylem is part of the vascular structure along with the phloem that carries food, nutrients and water across the plant.  It forms the supporting and conducting tissue of the plant.    The properties of wood are, a) Physical and b) Chemical.

a)  Physical: 

Wood when examined is found to be hygroscopic, that is, it absorbs water and swells or when it loses water it shrinks and dries.  It is also very stiff and firm owing to the strong supporting tissue in it.   There are many characteristic features of wood that fall under the category of Physical attributes.

* Luster:  Ability of the surfaces of the wood to reflect light.    Luster is most prominent on the longitudinal face of the wood and also forms the basis for valuing wood for ornamental items.

* Color:  Color in wood is developed due to various substances that infiltrate, get embedded in or are part of the secondary thickening of the plant cells.  Color plays an important role in the classification and identification of wood types.  When dark wood is cut and exposed for a long time, it turns lighter. 

* Odor:  Deposits of chemical substances are responsible for the unique smell that each wood type gives out.  Wood loses most of its odor when it is cut and in the open for long.

* Density:  Density of wood, expressed as weight per cubic foot, is standard for all wood.  The density of cell wall component of the wood is greater than water and is 1.55.  Wood with thinner cell walls and broader cavities are less denser than wood with thicker cell walls and narrow cavities.    Density forms a measure of the durability and strength of the wood.

* Water content:  Water is part of the wood.  The more water there is, the more is the chance for fungal and bacterial attack and also chances for wood to rot easily.  The percentage of water in the wood also determines the density, strength, durability, weight size and texture of the wood. 

* Texture:   Texture is calculated as the size of cells making up the wood.  In the case of construction, the texture of the wood is irrelevant, but in the case of ornamental use of wood, the texture of the wood is very important and it results in a finer or a less qualified work of art.

* Figure and grain:  Grain of wood is the arrangement and position of elements of the wood.  If the wood elements are arranged from top to bottom, length-wise, it is called longitudinal or straight grained.  When it is disorganized it becomes spiral and curly.  The design that the grains display is called the figure.  Wood grain determines the mechanical strength of wood.  It is strong along the grain but weak at right angles to the grain.  Items which are used as support such as posts, floor boards, handles of spade and axe beams, etcetera are made from straight grained wood cut parallel to the long axis.

* Weight:  Weight of wood differs one from the other.  It is dependent on the cell wall thickening, amount of mineral deposits and also the amount of water present in the wood.  Wood of the same type when kept in the open and in enclosed spaces exhibit different weights owing to the fact that wood in the open dries with the help of dry atmosphere. 

* Elasticity:  Wood that absorbs water can be bent and shaped more easily than dry wood.  Using this to an advantage, many kinds of musical instruments such as violins and pianos can be fashioned and also in the making of furniture and cabinets. 

b) Chemical Properties:  Wood is obtained from trees.  It consists of chemicals in the form of long chained carbohydrates called polysaccharides.    Cellulose is the major composition of the wood.  70% of the wood is halo-cellulose which is a combination of cellulose and hemi-cellulose.  25% to 30% of of wood is lignin.  Other substances in trace amounts present in the wood are resins, gums, minerals, oils, etcetera, which affect the odor and color of the wood.