What is Wood?
Wood, known for its fibrous and porous structure, is one of the few renewable natural resources. It comprises cellulose fibers embedded in a lignin matrix, providing trees with strength and facilitating nutrient transportation. The product plays a vital role in our daily lives and the economy, finding applications in textile fabrics, fuelwood, bridges, railway sleepers, and organic chemicals.
Humans have relied on wood for shelter and protection since ancient times. However, deforestation and slow tree growth have recently led to an increase in the value of wood. Wood serves various purposes, including roofing, woodwork, and scaffolding. The byproducts from the wood industry are used in making man-made materials such as chipboard and plywood.
Composition of Wood
Wood consists primarily of cellulose, a polysaccharide produced by plants, as well as other natural polymers such as lignin (25%) and hemicellulose (25%), as well as other organic components such as resins, waxes, and lipids.
Its main atomic components are carbon (50%) and oxygen (42%), with small amounts of hydrogen (6%) and nitrogen (2%).
Structure of Wood
Bark: The tree has numerous visible levels. The outer bark is the first layer of protection for the tree. It is very thin for a few species, like poplar. For some trees, like Douglas Fir, it can be very thick, sometimes more than 10 cm. Inner bark is the layer that covers the cambium layer. The inner bark stores nutrients and transports them down the tree. The bark protects the sapwood and phloem from drying out and insulates the tree against temperature exposure.
Cambium Layer: The cambium is the layer of a tree that lies between the epidermis and the sapwood. This layer contains fluid that has not yet transformed into sapwood, or it is the reproductive layer responsible for the formation of new tissue.
Sapwood: Sapwood refers to the few outer annual rings. This particular part of the tree is actively growing. It functions actively by transporting nutrients from the roots to the leaves, storing them, and supporting the tree.
Heartwood: The inactive layer below the sapwood is the heartwood. The heartwood is typically darker than the sapwood, because there is no sap flow.
Pith: The pith or medulla is the innermost centre part that has all of the cell tissue. The stem plays a crucial role in promoting new growth. It also initiates new growth, both upward and downward, at twigs and roots.
Medullary Rays: Composed of cellular tissue these are narrow radial lines that extend from the pith to the cambium layer.
Process of Obtaining Wood
The process of wood’s journey, from the tree to becoming the roof over your head, the bookshelf in your room, or the chair you’re using, is a complex and detailed procedure that includes harvesting, seasoning, preservation, treatment, and cutting. An overview of the procedures involves follows.
Harvesting
Cutting down trees is not an option, and the growth of fresh wood must be closely monitored to determine when it is ready to be harvested. Sustainability is essential, so a management plan determines yearly yield and removal methods, including clear-cutting large areas or selective cutting of trees. Sustained-yield management ensures periodic timber removal based on net tree growth.
Ecological labeling (ecolabeling) promotes sustainable practices. The harvest timing is not based on ripening but takes into account various factors such as personnel, machinery, nesting birds, and forest protection against damage, fungi, and insects. Harvesting can occur year-round depending on processing speed.
Seasoning
Freshly cut trees appear like sponges and must be dried or seasoned before use. Seasoning offers numerous benefits, such as reducing wood’s moisture content, making it less prone to rot and decay, lighter for transportation, and versatile for various applications. Properly dried wood, especially for firewood, burns more easily and efficiently.
Seasoning can occur through air-drying, which may take several months to a year, or kiln drying, which shortens the process to days or weeks. Seasoned wood typically has a moisture content ranging from 5 to 20 percent, depending on the duration and method of curing.
Preservation and Additional Treatment
Preservatives play a vital role in extending the lifespan of wood by safeguarding it against moisture and insect-related damages. Various preservatives work differently; paint acts as an outer skin, preventing fungi and insects from harming the wood, but it may crack and flake over time.
Creosote, once commonly used, derived from coal-tar, offers superior protection against wood-eating organisms. However, environmental concerns have prompted the exploration of alternative options. Different treatment methods can protect wood and make it fire-resistant, ensuring its safe and long-lasting use.
Cutting
The process of cutting wood varies depending on the intended final product. Some items, such as utility poles or fence posts, only require the removal of branches from the tree (roundwood). To create timber or sawnwood, trees undergo further processing in sawmills. By cutting logs in different orientations, flat pieces of wood are produced with distinct grain patterns.
Plain Sawn (flatsawn) wood exhibits ovals or curves on its largest flat surface, while quartersawn wood features grain running in broad, parallel stripes along the surface. The skilled carving and woodworking during the cutting process determine the characteristics of the final product, whether it’s a chair, a bookshelf, or other wooden items used in everyday life.
Benefits of Using Wood
1. Sustainability
Wood is readily available, recyclable, and reusable, making it a more sustainable alternative to materials like steel.
2. Thermal Insulation
Wood keeps spaces warm and reduces energy usage, leading to cost savings on electricity bills.
3. Acoustic Insulation
Wood absorbs sound, making it ideal for creating quiet and harmonious environments.
4. Adaptability
Wood can be easily recycled and reused for various purposes.
5. Health Benefits
Wooden structures moderate humidity levels, improve breathing, and promote emotional well-being.
6. Easy to Obtain
Wood is readily available in the environment, making it a cost-effective building material.
Types of wood
Wood can be divided into two main classes: softwoods and hardwoods. Softwoods come from coniferous species, while hardwoods come from angiosperms. The terms “softwood” and “hardwood” can be misleading, as not all softwoods are necessarily soft, and not all hardwoods are hard.
However, these general terms are still useful when discussing the woods from these two significant groups of trees.
Comparison of softwood vs. hardwood:
| Characteristics | Softwood | Hardwood |
| Source | Coniferous trees (evergreen) | Deciduous trees (broad-leaved) |
| Growth Rate | Faster-growing | Slower-growing |
| Availability | More readily available and less expensive | Higher cost and less widespread availability |
| Weight | Generally lighter | Generally heavier |
| Density | Generally less dense | Generally denser |
| Common Uses | Construction, furniture, paper products | Flooring, cabinetry, fine furniture, woodworking, high-traffic areas |
| Examples | Pine, spruce, cedar | Oak, maple, cherry |
Hardwood
The following are the different types of Hardwood:
| Attribute | Black Cherry | Oak Wood | Black Walnut | Maple |
|---|---|---|---|---|
| Common Names | Cherry, Wild Black Cherry, Wild Cherry | White oak, chestnut oak, post oak, etc. | American Black Walnut (Black Walnut) | Sugar maple, black maple, silver maple, etc. |
| Native Range | Southeastern Canada, Eastern United States | South, South Atlantic, Central States, etc. | Vermont to Great Plains, Louisiana, Texas | Principally from Middle Atlantic and Lake States |
| Sapwood | Nearly white | Nearly white | Nearly white, up to 3 inches wide | Commonly white with a reddish-brown tinge, etc. |
| Heartwood Color | Light to dark reddish brown | Generally grayish brown | Light to dark brown | Usually light reddish brown, sometimes darker |
| Wood Texture | Fairly uniform | Various grain patterns, often straight grained | Normally straight grained | Fine, uniform texture |
| Workability | Very good | Varies based on species | Easily worked with tools | Easy to work |
| Weight | Moderately heavy | Higher in weight than red oaks | Heavy, hard, strong, stiff | Hard maple: Heavy, strong, stiff |
| Strength | Strong and stiff | Generally strong and stiff | Strong, stiff, good resistance to shock | Soft maple: Not as heavy as hard maple |
| Common Uses | Furniture, fine veneer panels, etc. | Furniture, railroad crossties, etc. | Furniture, architectural woodwork, etc. | Flooring, furniture, boxes, etc. |
| Additional Uses | Burial caskets, woodenware novelties, etc. | Ship planking, boat parts, millwork, etc. | Cabinets, interior finish | Flooring, shoe lasts, handles, etc. |
Softwood
The following are the different types of Softwood:
| Attribute | Alaska-cedar | Douglas-Fir | Pine Wood | Spruce Wood |
|---|---|---|---|---|
| Common Name | Alaska-cedar | Red-fir, Douglas-spruce, and yellow-fir. | Pine wood | Spruce wood |
| Native Range | Pacific coast region of North America from southeastern Alaska southward through Washington to southern Oregon | Rocky Mountains to the Pacific coast, Mexico to central British Columbia | Varies (depending on pine species) | Varies (spruces create vast forests) |
| Sapwood | Narrow, white to yellowish, hardly distinguishable from the heartwood | Narrow in old-growth trees, up to 3 inches wide in second-growth trees of commercial size | Yellowish white | No clear heartwood distinction, whitish color |
| Heartwood Color | Bright, clear yellow | Varies (reddish in young trees, yellowish brown in old trees) | Orange-brown | No clear heartwood distinction, whitish color |
| Wood Texture | Fine textured, generally straight grained | Generally straight grained | Fairly even texture with some resin content | Lightweight, very soft, rigid, moderately strong, less resin than pine |
| Workability | Smooth Workability | Varies widely in weight and strength | Easy to work with and nail | Easily worked with tools, suitable for carpentry and construction projects |
| Weight | Moderately heavy | Moderate to heavy | Light to heavy (depending on pine species) | Lightweight |
| Strength | Moderately strong and stiff | When lumber of high strength is needed for structural uses, selection can be improved by applying the density rule | Typically stiff and strong | Moderately strong, moderately rigid |
| Common Uses | Interior finish, furniture, small boats, cabinetwork, novelties | Building and construction purposes (lumber, timbers, piles, plywood, etc.), railroad crossties, cooperage stock, mine timbers, poles, fencing, sash, doors, laminated beams, general millwork, railroad-car construction, boxes, pallets, crates, flooring, furniture, ship and boat construction, tanks, plywood, cabinets, and more | Carpentry, heavy construction, structural framing, formwork, ship-building, furniture making, and others | Similar uses to soft pine, resonance properties, preferred for paper pulp, construction, carpentry |
| Additional Uses | Burial caskets, woodenware novelties, patterns, etc. | Ship planking, boat parts, doors, millwork, etc. | Crafting, shelving, molding | Musical instruments, paneling |