paper, thin, flat sheet or tissue made usually from plant fiber but also from rags and other fibrous materials. It is used principally for printing and writing on but has many other applications. The term also includes various types of paperboard, such as cardboard and wallboard.

The Formulation of Paper

A quarter to a third of most new paper is made from waste paper. The body of paper is made up of matted cellulose fibers—since c.1860 derived principally from wood. Rags, mostly cotton cuttings from textile and garment factories, are used to make fine stationery and for such purposes as cigarette paper. For other special papers, or where wood is not available, manufacturers may use pressed sugarcane, bamboo, manila rope, cereal straws, esparto grass, or other fibers.

Preparation from Wood Pulp

Most paper is made from wood pulp. Mechanical pulp, or groundwood, prepared by grinding the wood, is used to make newsprint, tissue, towel, and other inexpensive papers. For paper whose whiteness is important, a chemical pulp must be prepared. Lignin, which holds wood fibers together, turns yellow in sunlight and therefore must be removed by alternating treatments with acid and alkaline solutions. The wood pulp, boiled under pressure and treated to dissolve the lignin binder, is thus turned into cellulose fiber. The mixture is then washed and bleached; because the resulting pulp is more than 90% water, the water is usually treated before mixing.

Once the wood pulp has been treated, washed, bleached, screened, and beaten, it is blended to achieve the characteristics required for the intended use. The pulp, suspended in water, is poured over a wire screen in one of two machines that differ mainly in the form of the screen: a belt screen is used in the Fourdrinier machine and a cylindrical one in the cylinder machine. As water drains through the screen, a layer of fibers forms, which in the Fourdrinier is shaken to turn the fibers in different directions so that they mat. A wet felt belt pressed against the screen picks up the paper for feeding through sets of drying rollers. During this stage a rubber roller may be used to imprint a watermark. At the end of the process the paper is passed through a calender (stack of iron rollers), which presses the paper and smooths its surface. Fillers—chiefly clay or starch—are used to improve the printing, texture, and wet and dry strength of paper and to produce other special properties.

Treatment for Special Properties

Book paper is any kind of printing paper except newsprint; in order to prevent rapid deterioration of the paper through a reaction between the acids in the pulp mixture and the humidity in the air, modern book paper is further treated to make it acid-free. For the best reproduction of illustrations, especially halftones, book paper is coated with a layer of mineral pigment, usually clay, mixed with an adhesive. All writing papers are "sized"; i.e., a water-resistant substance such as rosin is added to the pulp to prevent the spreading of writing ink. Hanging paper, or wallpaper, is soft and bulky; it is rosin-sized for water resistance and coated to take a printed design. Bag and wrapping papers are made of kraft paper, the product of the sulfate process, because of its strength.

The Introduction of Paper

Paper is believed to have been invented by Ts'ai Lun c.105 in China, where it reached an advanced state of development. Chinese paper was a mixture of bark and hemp. Papermaking spread to Japan c.610 and to Samarkand c.751, whence it was introduced by the Arabs into Egypt c.900 and by the Moors into Spain at Játiva c.1150. Mills were established in Italy c.1276; in France, c.1348; in Germany, 1390; and in England, 1495. European paper was usually made of flax and hemp. Primitive bark paper had been made in Mexico and Central America in pre-Columbian times. Paper was first produced in the American colonies in 1690 by William Rittenhouse at Germantown.


See J. P. Casey, Pulp and Paper (rev. ed., 2 vol., 1980); J. R. Lavigne, Pulp and Paper Dictionary (1986).

Japanese origami

Art of folding objects out of paper without cutting, pasting, or decorating. Its early history is unknown, but it seems to have developed from the older art of folding cloth. Origami has reached its greatest development in Japan, with hundreds of traditional folds and an extensive literature dealing with the art. There are two types of Japanese folds: figures used in ceremonial etiquette, and objects such as animals, flowers, furniture, and human figures. Some objects have amusing action features; best known is the bird that flaps its wings when its tail is pulled. Paper folding has also flourished in Spain, South America, and Germany.

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Type of chromatography using filter paper or other special paper as the stationary phase. Spots of sample and reference materials are applied, usually as liquids, near one edge (or corner, for two-dimensional PC) of the paper. The edge of the paper is dipped in a solvent, which travels along it by capillarity, moving the components of the sample at rates depending on their relative solubilities in the solvent. In two-dimensional PC, the paper is then turned 90° and the new edge dipped in a different solvent. The components of the sample mixture, visible as separated spots, are identified by comparing the distances they have traveled with those of the known reference materials. PC is especially useful for complex mixtures of amino acids, peptides, carbohydrates, steroids, and many other organic compounds and inorganic ions.

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Ornamental, shade, and timber tree (Betula papyrifera) of the birch family, native to northern and central North America. Also called canoe birch, silver birch, or white birch, it is one of the best-known birches. The smooth, varicolored or white bark of young trees peels horizontally in thin sheets, which once were used as writing surfaces as well as for roofing, canoes, and shoes. The water-impervious bark, which burns even when wet, is a boon to campers and hikers.

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Matted or felted sheet, usually made of cellulose fibres, formed on a wire screen from water suspension. Source materials include wood pulp, rags, and recycled paper. The fibres are separated (by processes that may be mechanical, chemical, or both) and wetted to produce paper pulp, or stock. The pulp is filtered on a woven screen to form a sheet of fibre, which is pressed and compacted to squeeze out most of the water. The remaining water is removed by evaporation, and the dry sheet is further compressed and often (depending on the intended use) coated or infused with other substances. Types of paper in common use include bond paper, book paper, bristol (or bristol board), groundwood and newsprint, kraft paper, paperboard, and sanitary paper (for towels, napkins, etc.). Seealso calendering; Fourdrinier machine; kraft process.

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