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1 Manufacture of wood pulp

Wood pulp is made in several stages:

1. First the bark is removed from the wood. This can be done with or without water (wet stripping). The bark is generally recovered to use as fuel in the pulp and paper making process.
2. The cellulose fibres that keep the wood together are then separated. This can be done in a number of ways:
   • The wood can be crushed with grinders (huge grindstones) and then soaked in water to produce groundwood (GW). Mechanical pulps are used for products that require less strength, such as newsprint and paperboards.
   • The wood can be crushed with refiners using steam at high pressures and temperatures to produce thermomechanical pulp (TMP). TMP differs in quality from groundwood.
   • In additional to the refiners, chemicals can be used to break up the cellulose fibres. Pulp produced this way is known as chemithermomechanical pulp (CTMP). GW, TMP and CTMP are all considered as mechanical pulps. The mechanical pulps tend to turn yellow in time, because of the binding material, lignin, in the pulp.
   • Chemical pulp is produced by combining wood chips and chemicals in huge vats known as digesters. The effect of the heat and the chemicals dissolves the lignin, that binds the cellulose fibers together, without breaking the wood fibres. The fluid that contains lignin and other dissolved material is then dried and used as fuel. Chemical pulp is used for materials that need to be stronger or combined with mechanical pulps to give a product different characteristics. Chemical pulps include kraft pulp (or sulphate pulp).
   • Pulp can also be made out of waste paper and paperboard. Recycled pulp is most often used to make paperboard, newsprint or sanitary paper.
   • Research is under way to develop biological pulping, similar to chemical pulping but using certain species of fungiChytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus are a large group of organisms ranked as a kingdom within the Domain Eukaryota. Included are the conspicuous mushrooms, but also many microscopic forms such as molds and yeast that are able to break down the unwanted lignin, but not the cellulose fibres. This could have major environmentAn environment is a complex of external factors that acts on a system and determines its course and form of existence. An environment may be thought of as a superset, of which the given system is a subset. An environment may have one or more parameters, pal benefits in reducing the pollution associated with chemical pulping.
3. The pulp produced up to this point in the process can be bleached to produce a white paper product. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to chlorineChlorine (from Gr. Chloros meaning "pale green"), is the chemical element with atomic number 17 and symbol Cl . It is a halogen, found in the periodic table in group 17. Chlorine gas is greenish yellow, is two and one half times as heavy as air, has an in, such as oxygenOxygen is the chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O, often called free oxygen on Earth is thermodynamically un, ozoneOzone (O) is a molecule consisting of three oxygen atoms. At standard temperature and pressure Ozone is a blue gas. Ozone forms a dark blue liquid, below -112 °C, and a dark blue solid, below -193 °C. Ozone is a powerful oxidizing agent, and is unstable, and hydrogen peroxideProperties General Name Hydrogen peroxide Chemical formula H O Appearance Colourless liquid Physical Formula weight 34. 0 amu Melting point 272. 4 °C) Boiling point 423 K (150 °C) Density 1. 4 ×103 kg/ m3 Solubility miscible Thermochemistry ΔH0 -136.
4. The pulp mixture is now sent to the paper machine, where it is shaped and dried.