Patrick Leong, age 11, of Visalia, Calif., for his question:
HOW IS PAPER MADE FROM LUMBER?
Paper can be made from dozens of different fibrous materials—and the most suitable fibers are created by the plant world. The very best material is the tough cellulose that plants manufacture to build their cell walls. And naturally we find concentrated supplies of this cellulose in a woody tree trunk.
Plants manufacture tough cellulose and mix its finer than fine threads with various gummy cements to build boxy walls around their cells. Lumber is made from these boxy cell walls. In making paper, the trick is to separate the fibrous cellulose from the cements and other materials. Then the cleaned fibers are mixed in a soupy mash, dried and rolled out into flat sheets of paper.
The ancient Chinese patiently hand made sheets of paper from the cellulose fibers in mulberry bark. But we need large-scale, economical processes to manufacture all the paper we use.
Our most plentiful supply of suitable cellulose fibers is in the woody lumber from such trees as firs, pines and poplars, hemlocks and tamaracks. The forested logs may be floated downstream to the paper mill, which saves transportation costs. The mill uses various chemical processes to separate the unwanted ingredients from the cellulose fibers.
Much of the wood is shaved into small chips on a grindstone. The wood chips then go to a large vat called a digester, which contains a steamy mixture of chemicals. The soupy mixture may contain calcium bisulfate or sodium sulfite and caustic soda. A steamy bath in caustic soda also will do the job of separating the unwanted plant materials from the sturdy fibers of cellulose.
The soupy wood pulp then is washed and rewashed to rinse out the chemicals and the unwanted plant materials. The pulp is bleached, perhaps with chlorine, drained and sent to machines that brush, cut and paddle the clean fibers. The fibers are matted in a moist mishmash. Now it is time to press, dry and wind the mixture into huge rolls of paper.
The finished paper is a dried, flattened layer of matted cellulose fibers processed from woody lumber. At one stage, it may be coated to give it a smooth surface. Various changes in the basic recipe produce tissues and cardboard, newsprint and copy paper—plus about 7,000 other kinds of paper used in our modern world.