Wood










    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
 

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