Cellulose
Overview
Cellulose (SELL-you-lohs) is a colorless to white, tasteless, odorless, polysaccharide fiber found in the cell walls of all land plants and some bacteria, seaweeds, algae, and fungi. Polysaccharides (the term means "many sugars") are polymers consisting of monosaccharide (simple sugar) monomers joined together in very large molecules. The monomer of which cellulose is made is glucose, also known as blood sugar, dextrose, or grape sugar. The subscript "n" at the end of the chemical formula indicates that a large number of these monomers combine to make the polymer. Cellulose provides the structural support for plants and other organisms in which it occurs. It is generally regarded as the most common organic compound found in nature.
Key Facts
Other Names:
None
Formula:
(C6H10O5)n
Elements:
Carbon, hydrogen, oxygen
Compound Type:
Polysaccharide (carbohydrate polymer; organic)
State:
Solid
Molecular Weight:
Very large, in excess of 100,000 g/mol
Melting Point:
Decomposes at temperatures above 260°C (500°F)
Boiling Point:
Not applicable
Solubility:
Insoluble in water and all common organic solvents
Cellulose never occurs in nature in a pure form. Cotton is the purest natural form, consisting of about 90 percent cellulose. Flax (linen fiber) consists of about 70 to 75 percent cellulose, wood of about 40 to 50 percent cellulose, and seaweeds and algae of about 25 to 30 percent cellulose.
Cellulose was first discovered in 1819 by the French naturalist Henri Braconnot (1781–1855). The compound was first isolated and analyzed fifteen years later by the French botanist Anselme Payen (1795–1871), who gave it its modern name of cellulose based on its origin ("cell" ) plus the suffix -ose. The earliest chemical studies of cellulose were conducted by a team of English chemists, Charles Frederick Cross (1855–1935), Edward John Bevan (1856–1921), and Clayton Beadle (1868–1917), who identified the compound we now know as cellulose and reported on its structure and properties in the 1890s and early 1900s.
Cellulose, in its natural forms such as wood, cotton, and linen, has countless numbers of uses as food, clothing, construction materials, and other applications. It also serves as the raw material in making derivatives such as cellulose acetate, cellulose nitrate, and cellulose xanthate with many other uses and applications.
How It Is Made
Cellulose is synthesized in plants and some microorganisms through the process known as photosynthesis. In that process, carbon dioxide (CO2) and water (H2O) are combined in a complex series of reactions to produce glucose (C6H10O5) and oxygen (O2). Glucose molecules are then linked to each other to from successively larger and more complex molecules, eventually resulting in the formation of cellulose.
Commercially, most cellulose is extracted from wood by one of two methods, the kraft (sulfate) process or the steam explosion process. The product of these reactions is wood pulp, which consists primarily of cellulose. In the kraft process, wood chips are treated with a solution of sodium hydroxide (NaOH) and sodium sulfide (Na2S) at temperatures of about 175°C (350°F) for two to six hours. This process usually results in a yield of about 40 to 45 percent wood pulp. The pulp is then treated with a bleaching agent, such as calcium or sodium hypochlorite (Ca(OCl)2 or NaClO) or chlorine dioxide (ClO2) to remove the color of lignin and other impurities.
Interesting Facts
- Scientists estimate that plants worldwide synthesize up to one trillion metric tons of cellulose annually.
In the steam explosion process, wood chips are saturated with moisture and then exposed to temperatures of 200°C to 250°C (400°F to 500°F) at pressures of one to five atmospheres. In this process, cellulose fibers are physically separated from lignin fibers, which are the other major constituent of wood. In either process, yields of up to 99 percent pure cellulose can be obtained.
Common Uses and Potential Hazards
The number of products made from pure cellulose is almost endless. The largest volume of such products include paper and paper products, including (with 2001 production numbers): newsprint (5.8 million metric tons; 6.4 million short tons), printing and writing paper (22.1 million metric tons; 24.4 million short tons), packaging and related uses (3.9 million metric tons; 4.3 million short tons), tissue paper (6.4 million metric tons; 7.0 million short tons), containerboard (26.6 million metric tons; 29.3 million short tons), and boxboard (7.7 million metric tons; 8.5 million short tons). Other uses of cellulose include:
- Manufacture of cotton products, such as items of clothing, sheeting, and industrial fabrics;
- Production of other organic products, especially ethanol (ethyl alcohol; grain alcohol) and methanol (methyl alcohol; wood alcohol);
- As insulation and soundproofing;
- As a food additive, where it is used to thicken and add bulk to food products;
- In equipment used in analytical chemistry, such as chromatographic devices used to separate the components of a mixture.
Words to Know
A compound consisting of very large molecules made of one or two small repeated units called monomers. A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.A major industrial use of cellulose is in the preparation of various cellulose derivatives, primarily cellulose acetate, cellulose nitrate, and cellulose xanthate, each of which has a number of applications.
For Further Information
"Cellulose." Fibersource. http://www.fibersource.com/f-tutor/cellulose.htm (accessed on September 30, 2005).
"Cellulose." London South Bank University. http://www.lsbu.ac.uk/water/hycel.html (accessed on September 30, 2005).
"Cellulose Processing." Organic Materials Review Institute. http://www.omri.org/cellulose_final.pdf (accessed on September 30, 2005).
Cross, Charles, Clayton Beadle, Edward Bevan. Cellulose. An Out line of the Chemistry of the Structural Elements of Plants, with Reference to Their Natural History and Industrial Uses. Elibron. Replica of 1895 edition by Longmans, Green, and Co., London. http://www.elibron.com/english/other/item_detail.phtml?msg_id=10006054 (accessed on September 30, 2005).
See Also
Cellulose Acetate; Cellulose Nitrate; Cellulose Xanthate
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