Wood is a material much taken for granted and little understood, yet so useful in our everyday life. Wood is a fantasticly complex material that is not only polymeric but a composite of a complexity that current synthetic methods can only dream to parallel. Wood primarily consists of a polysaccharide called cellulose and other biopolymers such as lignin and other living tissues such as tracheids and parenchyma cells that act to keep the tissue living.
There
are several different diagnostic features of wood in relation to their
commercial value, among these are porosity, early or late wood, growth
rings, rays, sapwood or heartwood and grain and figure. There are
many distinct morphologies with regard to porosity in wood when seen in
cross section.
Here
is an example of ring porous wood in which pores are arranged in concentric
circles.
Another
pore morphology is pictured here that is referred to as a nonporous wood,
due to the lack of pores
and yet another form of porosity can be seen in the diffuse porous wood in which pore sizes and positions are random
Early wood or late wood refers to growth seasons where early wood is the first wood formed in the spring and is different in morphology due to the need for more conductive tissues and late wood is the denser type of wood laid down with thicher walled cells. In the following image the dark wvy lines are early wood and the light areas are late wood of white ash.
ash cross section where the light regions are late wood and the dark regions are early wood.
Rays are
morphologies arising from sheets or ribbons consisting mainly of parenchyma
cells oriented at right angles to the axis of the stem
Sapwood
and heartwood are differentiated by the fact that the sapwood is the living
tissue and the heart wood is the biologically inactive wood.
Grain
and figure refer to the structural arrangement of various wood elements
and the design or pattern that appears on the surface respectively.
All of these defining charachteristics of wood are either characteristic
of or the cause of different structural properties of wood..
These different properties include the crushing strength, tensile strength, shearing strength cross-breaking strength, stiffness, toughness, hardness, and cleavability.
These
terms refer to the structural integrity of the wood with respect to different
forces applied and there exist standard charachterization methods to evaluate
wood and wood containing materials.
The different structural
properties of the wood are determined by such factors as density, moisture
content, and defects. To learn more about physical testing of wood
or wood like materials click here.
Due to the good structural properties of wood it has been and is used as a common building material In light of the structural properties and all the contributing morphologies and external factors wood is a vary versatile material. Consequently wood has either been improved with various chemical treatment or reinforcement or utilized in composite formation in which properties of another bulk material has been attempted to be improved. Also due to the unique chemical nature of wood components a variety of other composite applications have been developed..
To learn more click on the
following