Production and Properties of Paper

        Papyrus, more commonly known as paper, is used commonly for various purposes. The deceivingly simple object that we come into contact with nearly every day in fact goes through a complex process to become the writing paper that we are so familiar with. Common belief holds that paper always comes from trees, but many non-woody plants are also used. Besides writing paper, we also use paper in the form of containerboards, cotton fiber, tissue, newspaper, and money. The process through which various types of paper are created involves many biological, as well as chemical and physical, aspects. It also has many biological properties that result from its makeup and creation process.

        The most important ingredient in the creation of paper is cellulose, which is found in plants. Wood from trees is made up of cellulose fibers, which are connected by a natural adhesive substance called lignin. Cellulose is a polysaccharide fiber, with glucose units connected by beta linkages, that usually forms the framework of most cell walls in plants. It is the most abundant organic compound on the planet. Lignin is a complex polymer that is mostly responsible for rigidity and strength in the structure of plants.

In order to extract the cellulose, the wood goes through a process called pulping, which can be done either mechanically or chemically. Chemically, the wood is cooked with chemicals that serve to dissolve the lignin. Mechanically, the wood is finely ground or chopped to separate the cellulose. However, mechanically processed pulp still contains much of the lignin, which can cause undesirable effects in the resultant paper. The process also tends to produce fibers that are short and stiff, and which yield paper that isn't very strong. For that reason, mechanical pulps are mainly used for packaging, newsprint, and other low-strength applications. Mechanical pulp is sometimes blended with chemical pulp to produce a middle-level product with low cost and reasonable strength and color properties. There is also another method known as the “kraft” process during which lignin is removed in a pressurized vessel called a digester. The pulp is then washed to remove the “black liquor,” which is the waste from the digester, made up of lignin and pulping chemicals. It is usually burned in a recovery boiler, producing energy at the paper mill. Paper made through the “kraft” process is often stronger than paper made from traditional mechanical and chemical pulping methods.

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After the pulp goes through these processes, the resulting product is a dark brown unbleached pulp. To achieve the desired whiteness of paper, the pulp must be bleached. Depending on the type of paper desired, the amount of bleach will vary. For writing papers with high brightness, it is often sent to a bleaching tower. Chemically processed pulp is usually easier to bleach because of lower lignin content, while mechanically processed pulp may require more bleaching. Common bleaching agents used are chlorine, sodium hydroxide, and hydrogen peroxide.

Once bleached, the pulp is diluted with water in large amounts. This ...

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