The discovery of paper contributed greatly to civilization. Writings have been traced back thousands of years to a time when signs and words were made on bark, bricks, skins, and other surfaces.
If man had observed nature and watched paper-making wasps use wood pulp, he might have made paper earlier. The wasps chew the pulp and spread it in thin layers to form the walls of their nests.
Today there are about five thousand different types of paper with almost as many uses. The consumption of paper in the United States is enormous. Over four hundred pounds per person are used in a single year.
Paper is made from cellulose or vegetable fibers. In the early days of paper-making, rags were the chief source of fiber for paper. Today the chief source of cellulose for paper is wood. When the forests were abundant, preferred woods were selected. Today, many kinds of wood are used for pulp, including pine, spruce, hemlock, fir, poplar, beech, birch, maple, and aspen.
Many successful experiments have been made to produce paper from fibrous materials other than wood. But while the supply of wood lasts, it seems to be the easiest and most economical pulp material. Paper has been made from hemp, turf, moss, potato skins, tobacco waste, coconut husks, bean stalks, cabbage leaves, bamboo, and many other vegetable materials. The important considerations for pulp material are the need for long enough fibers to make strong paper, the ease of changing the material to fiber form and eliminating impurities, availability of large supplies of low cost material, and economical means of getting the pulp materials to the mills.
If a sheet of medium-weight paper is held up to a good light, the paper can be seen to be made up of small fibers matted together. The logs that arrive at a pulp mill have to be reduced to these small fibers. One of the methods used is mechanical, the others are chemical. In the mechanical, or ground-wood method, pulp is produced by grinding the wood with grindstones under water. The chemical process takes wood chips that have come through a chipping machine, combines them in a digester, an enormous pressure cooker, with chemicals and cooks them to pulp. Different chemicals are used depending on the kind of wood used and the kind and grade of paper desired. There are sulfite (acid), sulfate (alkaline), and soda processes used in chemical methods.
The pulp, which is about 95 per cent water, is usually bleached and then goes to the paper machine. The pulp is spread onto a screen-like bed, which moves forward as it drains off some of the water and jostles from side to side to mat the fibers. The pulp is rolled between felt rollers to absorb moisture and pressed and dried as it goes through a series of rollers. The continuous sheet emerges and is wound in large rolls as finished paper to be used in manufacturing paper products.
