The Production of Paper
Paper is an important
commodity in the world, and is used internationally
by the tonne. However, it is also a major
issue environmentally due to pollution created during its production, and also due to deforestation
How Paper is Made
Paper is produced from cellulose fibers
found in plant walls. Cellulose is produced in the tree as a carbohydrate, and is made through the process of photosynthesis
. The plant uses air and the sunlight around it to produce glucose, and from the glucose it is then able to make cellulose. The manufacture of glucose follows this equation:
+ 6 H2
O ⇒ C6
The glucose in the above equation is then taken, and through the process of photosynthesis cellulose is made:
)n + H2
Cellulose structures are held together in plants by a complex chemical called lignin. To remove the cellulose fibers from the tree they are chopped down, debarked, chipped into finer pieces and then pulped through two different means, either chemical pulping or mechanical pulping. Both processes remove the fibers that are needed to make paper.
In mechanical pulping the chips are heated and go through a machine called a refiner, which consists of fast, rotating disks that break the chips into individual fibers, whereas in chemical pulping various chemicals are used to dissolve the lignin between the fibers in the wood. In a sulfite process, the chips are steam heated with an acid solution, but in a different method sulfate can be used to remove the fibers.
Sodium hydroxide can be used in a pulping method, both to help dissolve the lignin from between the fibers and to maintain the acidity of the solution at a neutral level.
After either of these processes the pulp must be washed to remove the excess materials and chemicals around the cellulose fibers. The paper is also put through several fine sieves to remove knots and any other unwanted materials. The paper may also be bleached to produce a whiter paper. If chlorine is used as a hypochlorite then the excess chlorine needs to be removed. To remove chlorine from solutions used to bleach the paper thiosulfate ion is used, seen in this equation converting hypochlorite to chloride:
HOCl + 2 S2O32- ⇒ Cl- + S4O62- + OH2-
By removing the extra chlorine from the solution it is not discharged into the environment as wastewater. Thiosulfate can also be used as a whitening agent.
Once the paper is bleached, it is then refined between rotating disks, making the fibers more flexible by unraveling the cell walls of the cellulose. The length of time that paper is refined determines the quality of the paper. The paper is then rolled between steam-heated cylinders to dry the paper, and it can be sliced as it is rolled, or can go straight onto a large paper reel.
Many years ago the process took a long time as it was all hand made, but today paper making machines can make a single sheet of paper that is up to 10 meters wide, and they can move at speeds faster then 1,700 meters per minute.
Paper and the Environment
Paper is an important
commodity in society, as paper is used for many reasons, including as pages in book
s, as paper towel
s, packaging and writing material. As paper is so necessary in society it is very important to continue its production, however, the rate at which paper is currently consumed is taking a great toll on the world’s forests. Approximately 315 million metric tonnes
of paper is used every year worldwide. Since between 10 and 17 trees are needed to produce one tonne of paper, an approximate 70,000 hectares of trees are cut down each year to help produce paper for Australia
The lack of trees and the necessity of machinery to deforest this large amount of paper produces an enormous amount of pollution. Pollution is also produced during the pulping and bleaching process, and the chemicals used can be toxic to the environment. For example the chlorine used to bleach paper white is toxic to ocean life, lakes and other water sources.
Another issue involving paper production and pollution is the dangerous gases that can be released into the atmosphere during the manufacturing of paper. Oxides of nitrogen and sulfur can be released, both of which are toxic to humans and the ozone layer.
In order to reduce the amount of pollution caused by paper manufacturing paper-made items such as newspapers, paper towels and paper napkins are made from recycled paper.
Without the production of paper many things would not be available to today’s society. However, care must be taken with its manufacture so as not to cause unnecessary harm to the environment.
World Book, Inc 2005 The World Book Encyclopaedia, Chicago; Vol. 15, Pages 134, 135
Dunn, K. M. 2002, Caveman Chemistry, viewed 16.02.08 http://cavemanchemistry.com/cavebook/chstring2.html
Hackworth, Heide 2008, Paper Production and the Environment, viewed 12.02.08 http://www.earthgreetings.com.au/htm%20pages/environment/paper&environment.html
Senese, F. 2005, General Chemistry Online, viewed 16.02.08 http://antoine.frostburg.edu/chem/senese/101/compounds/faq/thiosulfate.shtml
Paper Online, viewed 12.02.08 http://www.paperonline.org/cycle/paperboard/paperboard_frame.html
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