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Wood

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Wood is the hard fibrous tissue found in many plants. It is produced as a secondary xylem in the stems of trees and other woody plants. It consists largely of cellulose and lignin. Wood has been used for centuries both as a fuel and a construction material.

Parts of Wood

Bark

The outer layer of the wood is the bark. Although the rough outer bark on a tree trunk is dead, it protects the living tisues inside.

Cambium

Just underneath the bark area is the cambium. This is the part of the tree that grows. Each year, the cambium forms two new cell layers: the inner bark, which carries food made in the leaves down to the roots, and the sapwood, which carries water and nutrients up from the roots. Wood increases in diameter by this process leading to the formation of growth rings.

Sapwood

Sapwood is the softer, younger portion of a tree that lies between the cambium and the heartwood. It is lighter in color, more permeable and less durable compared to the heartwood.

Heartwood

Heartwood is the older and harder central portion of a tree. It usually contains deposit of various materials giving it a darker color. It is denser, less permeable and more durable compared to sapwood.

Kinds of Wood

Softwood

Softwoods are coniferous or needle-bearing trees. They are composed of simple cell structures and grows faster than hardwoods. Examples of softwood trees are pine, cedar, fir, hemlock, redwood, spruce and yew.

Hardwood

Hardwoods are deciduous or leaf-bearing trees. They have a more complex cell structure and are generally stronger than softwoods. Examples of hardwood trees are alder, ash, amaranth, basswood, beech, birch, blackwood, cherry, chestnut, ebony, elm, hickory, maple, oak, olive, rosewood, sycamore, teak, wanut and yellow poplar

Wood Products

Lumber vs. Timber

Although timber is predominantly defined as the wood that is still attached to the ground while lumber refers to processed wood that has been cut and dried. The two terms are interchangeably used since timber also refers to lumber with smallest dimension not less than 5 inches.

Plywood

Plywood is made of two or more wood veneers glued together. A number of layers is usually glued in a different direction to counteract warping. Plywood is strong, lightweight and adaptable for many uses. It resists blows and is not easily cracked or broken.

Fiberboard and Particleboard

Fiberboards are made of wood fibers felted and pressed together. Natural adhesives in the wood keep the fibers firmly together. For greater strength, a resin adhesive is sometimes added. Particleboards are made of wood chips or flakes bonded together with a synthetic resin, heated and pressed into shape.

Pulp and Paper

Pulp is produced mostly from softwoods, although low-grade logs, small logs, waste pieces from sawmills cut into chips are also used. Pulp is used in the manufacture of paper, container boards and also dissolved to make products such as rayon and cellophane.

Chemical Products

Wood cellulose are chemically treated to yield sugars, industrial alcohol and other chemicals. Heating wood in a closed chamber known as destructive distillation yields methyl alcohol, acetic acid, wood tar and charcoal. A by-product from pulp mills, lignin is used as a binder of fiberboard, as a source of other chemicals in the manufacture of plastics and vanilla flavoring. Lignin compounds are also used as adhesives.

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