Lesson 7.01: Properties of Wood

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In this lesson, we will answer three primary questions.

1. What are the chemical properties of wood?
2. What are the physical properties of wood?
3. What is the difference in properties between softwood and hardwood species?

What are the chemical properties of wood?

Wood is often thought of as the hard, fibrous substance that forms the greatest part of the stems and branches. There are several chemical properties of wood.

Wood is made up of about 50 percent cellulose, 28 percent lignin, and minor quantities of other materials.

1. Cellulose and lignin are responsible for some of the properties of a wood, such as the wood’s ability to absorb moisture and its resistance to corrosion by salt water.
• Hardwoods have less lignin than softwoods.
2. Cellulose forms the framework of the cell walls and is the product used in the manufacture of paper.
3. Lignin is the cementing material that binds the cells together and is also found mixed with cellulose in the cell walls. When the lignin is dissolved with chemicals, the cells may be separated for papermaking.
4. Characteristics like color, odor, and natural resistance to decay cannot be attributed to cellulose or lignin, but rather to other materials in the wood.

View the following video content from Discovery Education Streaming. Click here to view the instructions for logging in to Discovery Education Streaming videos. Wood's Structure (4:01)

What are the physical characteristics of wood?

Wood is indispensable in our everyday lives, and many products are derived from trees. There are several physical characteristics of wood.

1. The relationship between moisture and wood is very important in understanding wood behavior. The wood-water relationship causes most of the problems in using wood products.
   • Nearly all wood properties are affected by the amount of water in wood. The amount of water in wood is affected by changes in temperature and humidity.
   • The water found in wood originates in the living tree. When a tree is harvested, most of the cells still contain a high percentage of water.
2. Woods can be divided into two groups: those without pores (non-porous)and those with pores (porous).
   • The porous woods are further divided into ring-porous and diffuse-porous.
3. In the manufacturing of furniture it is sometimes necessary to bend wood. Some hardwoods are more readily softened by heat and moisture for bending than are other hardwoods.
   • A variety of chemicals are used to aid in the bending of wood. Urea, dimethyl sulfoxide, and liquid ammonia are a few.
4. Other physical properties of wood include:
   • Resin ducts or canals, found in pine, are intercellular passages surrounded by resin-secreting cells. The ducts are often filled with resin. Resin is a vegetable substance secreted by certain plants and trees and is a characteristic of coniferous trees.
   • Properties such as color, luster, taste, hardness, odor, and texture are important in wood identification.
   • Properties such as weight, strength, stiffness, bending and woodworking qualities, hardness, durability, permeability to staining and shrinkage are among the most important characteristics to someone using wood.

What are the characteristics of hardwoods and softwoods?

Trees are divided into two classes: hardwoods, which have broad leaves, and softwoods, which have needlelike leaves or scale leaves and are called conifers. No degree of hardness divides the hardwoods from the softwoods. Some hardwoods are soft and some softwoods are hard.

1. The term softwood originated in New England, where the loggers applied it to the light wood of white pine, a conifer. The term was applied to all conifers, regardless of their wood density.
2. Hardwood was the term given to hard maple, a dense wood, and there after to all deciduous species.
3. Wood can readily be identified as a hardwood or softwood by the presence or absence of pores when viewed in a transverse section.
   • If no pores are present, the section is a softwood. Pines show small, fairly evenly distributed resin ducts on a transverse surface. Resin dust should not be confused with the pores in hardwoods. The pores in hardwoods are closer together than are the resin ducts in softwoods.
4. Hardwoods have specialized pores or vessels for conducting sap. The pores in hardwoods vary in size depending on the species. Some are visible to the naked eye.
   • Hardwood vessels are cells with open ends, one above the other, and continuing as open passages for long distances.
   • The strength giving elements of hardwood are called wood fibers. Usually wood fibers have small cavities and thick walls. In the fiber walls are found pits by which the sap passes from one cavity to another.

View the following resources on products that are produced from trees. As you review the material, think about how the physical or chemical properties of wood allow for these products to be produced. Click here to view the instructions for logging in to Discovery Education.

• Taxol
• Rayon
• Latex

How do the properties of wood affect your everyday life? You may be suprised to learn that many everyday items are produced from trees!

Read Trees in Your Life. Begin reading the section titled From Plants to Pulp to Paper and read to the end of the page.