What Is Wood?

What Is Wood?

Wood is an amazingly versatile material, used throughout history for construction and furnishings. It has natural strength and beauty and is an excellent insulator, requiring much less energy to heat a building than other materials. Wood is also very recyclable, a fact that helps reduce the environmental impact of our buildings.

When a tree grows, cambial cells divide to create two essential tissues - xylem and phloem (Image 1). Xylem transports water and minerals between the roots and the leaves, and between the crown and trunk. Phloem transports photosynthate, the sugary substance produced in leaves, to the rest of the tree.

In addition to these important functions, wood is a good insulator and stores carbon. It is also a naturally fire-resistant material that requires little energy to produce. Wood is a renewable resource that will continue to grow, and its use reduces the need for new energy sources.

A woodworking project is an opportunity for children to apply both design and practical skills. Design involves defining the task, making a plan of action and responding to what is happening as work evolves. The practical skills of woodwork, or craft, transform the designs into things that can be held and admired. Both processes can be fluid and it is common for children to revisit their initial plans, adapting them as they develop.

Wood is a strong and flexible material with a high capacity to stretch and bend. This makes it ideal for curved or irregular shapes and for creating a wide variety of finishes and textures. It can be made into furniture, musical instruments and many other products.

The main components of wood are cellulose (41-43%), hemicellulose (20%), and lignin (10-30%). Cellulose is a strong, crystalline polymer that forms the basis of wood fibers. Hemicellulose is a semi-crystalline polymer that acts as a matrix or binder for the cellulose, binding it together into strong wood fibers. Lignin is a more amorphous organic compound that confers the hydrophobic properties of wood, as well as its colour and aroma.

At the microscopic level, wood is comprised of long cells in the axial direction and thin cells in the radial and tangential directions. The axial cells are lined with a cell wall, which contains a soluble sugar called sucrose. These dissolved sugars, along with the water they carry, provide wood with its tensile strength. The thin cellular walls of the radial and tangential cells, along with the lignin, give wood its stiffness.

As trees grow, they form rings of xylem, which are the visible growth-rings that people use to gauge a tree’s age. Early in the growing season, cambial cells produce what is known as earlywood. This wood has large conductive pores and thin cell walls, giving it a light-colour appearance and lower density than latewood.

As a result of this ring-porous structure, earlywood is generally stronger than latewood for a given thickness. Nevertheless, the overall strength of wood is not solely dependent on its growth rate because woods of medium growth tend to be stronger than very fast or very slow growing woods.

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