1. WOOD
The substance making up the central part of the trunk and
branches of a tree. Used as a material for construction, to
manufacture various items, etc. or as fuel is Wood.
2. STRUCTURE OF WOOD
Wood is
a heterogeneous, hygroscopic, cellular and anisotropic material.
It consists of cells, and the cell walls are composed of micro-
fibrils of cellulose(40% – 50%) and hemicellulose (15% – 25%)
impregnated with lignin (15% – 30%).
In coniferous or softwood species the wood cells are mostly of
one kind, tracheids, and as a result the material is much more
uniform in structure than that of most hardwoods.
The structure of hardwoods is more complex.
3. TYPES OF WOODS
SOFTWOOD
Softwoods are gymnosperms. These plants let seeds fall to the ground as is, with no covering. Pine
trees, which grow seeds in hard cones
HARDWOOD
Hardwood trees are angiosperms, plants that produce seeds with some sort of covering. This might be a
fruit, such as an apple, or a hard shell, such as an acorn.
7. Physical
A physical property is a characteristic that can be seen or measured without changing
the material. Examples are odor, color, shape and texture.
The principle physical properties of wood are strength, hardness, stiffness and density.
8. Chemical
The chemical composition of wood varies from species to species, but is
approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other
elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by
weight. Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in
small quantity.
9. Aesthetic
Wood is a biological material with inherent aesthetic properties which can give the final
product a competitive advantage over other materials. The beauty of wood is that it
engages all of our senses. Its appeal in design and construction is a natural one, as of
course, all of the sensual elements (rich, warm etc) are present when we build with
wood.
Structure of wood
Take a tree and peel off the outer "skin" or bark and what you'll find is two kinds of wood. Closest to the edge there's a moist, light, living layer called sapwood packed with tubes called xylem that help a tree pipe water and nutrients up from its roots to its leaves; inside the sapwood there's a much darker, harder, part of the tree called the heartwood, which is dead, where the xylem tubes have blocked up with resins or gums and stopped working. Around the outer edge of the sapwood (and the trunk) is a thin active layer called the cambium where the tree is actually growing outward by a little bit each year, forming those famous annual rings that tell us how old a tree is. Slice horizontally through a tree, running the saw parallel to the ground (perpendicular to the trunk), and you'll see the annual rings (one new one added each year) making up the cross-section. Cut vertically through a tree trunk and you'll see lines inside running parallel to the trunk formed by the xylem tubes, forming the inner structure of the wood known as its grain. You'll also see occasional wonky ovals interrupting the grain called knots, which are the places where the branches grew out from the trunk of a tree. Knots can make wood look attractive, but they can also weaken its structure.
