Other than food, wood and wood products are the most useful materials derived from plants. The widest and most familiar use of wood is in the form of lumber and plywood used for building and construction. However, wood is also commercially important as fuel, pulp, and paper.
Fuel: A Past and Present Energy Source
Throughout the course of human history, wood has been the chief source of fuel and in many developing nations, the vast majority of harvested wood is still used as fuel. About 1.5 billion people depend on wood or charcoal for 90% of their energy needs for heating and cooking. Another billion people use wood for about half of their energy needs. It is estimated that 50% of the wood harvested worldwide each year goes to fuel.
In addition to being burned directly, wood can also be converted into charcoal by partial combustion in an oven or other enclosure that restricts air flow. Charcoal is almost pure carbon and burns at a much higher temperature than wood, so hot that it can be used for smelting ores into metals.
Wood Pulp: Useful Mush
Wood pulp is a watery suspension of pulverized wood. In industrialized nations, approximately 50% of the harvested wood goes into wood pulp, with the vast majority of pulp used in the manufacture of paper.
Wood pulp is produced by two methods: mechanical and chemical. The mechanical process involves grinding the wood with water, making a slurry. This process produces the greatest yield, but paper produced from such pulp is weak and yellow quickly. Newsprint, catalogs, and paper towels are manufactured using this process.
Chemical processes attack and dissolve the lignin in the wood. In one method, wood chips are dissolved in sodium hydroxide, while sulfites or sulfates are employed in other chemical processing methods. These methods will produce paper that is quite strong and resistance to yellowing.
In addition to paper, wood pulp is used in the manufacture of cardboard and fiberboard, as well as rayon and cellophane.
Paper: The Basis of Modern Communication
Written human communication has come a long way from its humble beginnings as pressed symbols on clay tablets. Although today the Internet promises worldwide computer link-up and instantaneous electronic exchanges, paper is still the major medium of written communication in modern society.
The United States accounts for over one-third of the world’s production and use of paper and cardboard. Each year about one billion trees are cut down to meet the demand for paper and paper products, with each American directly or indirectly using approximately 600 pounds of paper.
Paper made from wood pulp can be traced back to China, early in the second century, where paper was made using a process not all that different from contemporary production. For about 500 years, papermaking remained the intellectual property of the Chinese. Knowledge of the process then slowly made its way to Japan, then to Central Asia, the Near East, and into Egypt.
The Moors introduced the use of paper to Europe, and the first European paper was made in Spain around 1150. The introduction of movable type in the fifteenth century provided a major stimulus for the production of paper.
In 1803, British papermakers Henry and Sealy Fourdrinier, developed the Fourdrinier screen, a continuous belt of wire cloth onto which pulp is deposited. The water drains through the screen, leaving a mat of fibers that comprise a sheet of paper.
At present wood pulp is the major source of the world’s paper supply. However, cotton and linen rags were the sources for the necessary fibers in the early forms of paper. Today fine quality stationery and paper for permanent records still contain a large percentage of rags.
As demand grows and deforestation occurs at breakneck speed, it becomes imperative that we find alternatives to wood pulp. Just the Sunday edition of the New York Times alone consumes about 150 acres of forest.
The most promising alternative may be kenaf, a herbaceous plant in the mallow family. It grows from seed to maturity in four to five months. Southern pine, main source of wood pulp, takes seven to 15 years to reach harvest size. Moreover, fiber yield from an acre of kenaf is three to five times the yield for an acre of pine.
From lumber and plywood to pulp and paper and from fibers and cellophane to fuel and cardboard, wood is an amazingly versatile material that has proven to be indispensable to humanity.
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