What Is Cellulose? Facts and Functions

Cellulose [(C₆H₁₀O₅)_n] is an organic compound and the most abundant biopolymer on Earth. It is a complex carbohydrate or polysaccharide consisting of hundreds to thousands of glucose molecules, linked together to form a chain. While animals don't produce cellulose, it is made by plants, algae, and some bacteria and other microorganisms. Cellulose is the main structural molecule in the cell walls of plants and algae.

History

French chemist Anselme Payen discovered and isolated cellulose in 1838. Payen also determined the chemical formula. In 1870, the first thermoplastic polymer, celluloid, was produced by Hyatt Manufacturing Company using cellulose. From there, cellulose was used to produce rayon in the 1890s and cellophane in 1912. Hermann Staudinger determined the chemical structure of cellulose in 1920. In 1992, Kobayashi and Shoda synthesized cellulose without using any biological enzymes.

Chemical Structure and Properties

Cellulose forms via β(1→4)-glycosidic bonds between D-glucose units. In contrast, starch and glycogen form by α(1→4)-glycosidic bonds between glucose molecules. The linkages in cellulose make it a straight chain polymer. The hydroxyl groups on the glucose molecules form hydrogen bonds with oxygen atoms, holding the chains in place and conferring high tensile strength to the fibers. In plant cell walls, multiple chains bond together to form microfibrils.

Pure cellulose is odorless, flavorless, hydrophilic, insoluble in water, and biodegradable. It has melting point of 467 degrees Celsius and can be degraded into glucose by acid treatment at high temperature.

Cellulose Functions

Cellulose is a structural protein in plants and algae. Cellulose fibers are enmeshed in a polysaccharide matrix to support plant cell walls. Plant stems and wood are supported by cellulose fibers distributed in a lignin matrix, where the cellulose acts like reinforcing bars and the lignin acts like concrete. The purest natural form of cellulose is cotton, which consists of over 90% cellulose. In contrast, wood consists of 40-50% cellulose.

Some types of bacteria secrete cellulose to produce biofilms. The biofilms provide an attachment surface for the microorganisms and allow them to organize into colonies.

While animals cannot produce cellulose, it is important to their survival. Some insects use cellulose as a building material and food. Ruminants use symbiotic microorganisms to digest cellulose. Humans can't digest cellulose, but it is the main source of insoluble dietary fiber, which affects nutrient absorption and aids defecation.

Important Derivatives

Many important cellulose derivatives exist. Many of these polymers are biodegradable and are renewable resources. Cellulose-derived compounds tend to be non-toxic and non-allergenic. Cellulose derivatives include:

• Celluloid
• Cellophane
• Rayon
• Cellulose acetate
• Cellulose triacetate
• Nitrocellulose
• Methylcellulose
• Cellulose sulfate
• Ethulose
• Ethyl hydroxyethyl cellulose
• Hydroxypropyl methyl cellulose
• Carboxymethyl cellulose (cellulose gum)

Commercial Uses

The principal commercial use for cellulose is paper manufacturing, where the kraft process is used to separate cellulose from lignin. Cellulose fibers are used in the textile industry. Cotton, linen, and other natural fibers may be used directly or processed to make rayon. Microcrystalline cellulose and powdered cellulose are used as drug fillers and as food thickeners, emulsifiers, and stabilizers. Scientists use cellulose in liquid filtration and thin layer chromatography. Cellulose is used as building material and electrical insulator. It is used in everyday household materials, like coffee filters, sponges, glues, eye drops, laxatives, and films. While cellulose from plants has always been an important fuel, cellulose from animal waste can also be processed to make butanol biofuel.

Sources

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• Klemm, Dieter; Heublein, Brigitte; Fink, Hans-Peter; Bohn, Andreas (2005). "Cellulose: Fascinating Biopolymer and Sustainable Raw Material." Angew. Chem. Int. Ed. 44 (22): 3358–93. doi:10.1002/anie.200460587
• Mettler, Matthew S.; Mushrif, Samir H.; Paulsen, Alex D.; Javadekar, Ashay D.; Vlachos, Dionisios G.; Dauenhauer, Paul J. (2012). "Revealing pyrolysis chemistry for biofuels production: Conversion of cellulose to furans and small oxygenates." Energy Environ. Sci. 5: 5414–5424. doi:10.1039/C1EE02743C
• Nishiyama, Yoshiharu; Langan, Paul; Chanzy, Henri (2002). "Crystal Structure and Hydrogen-Bonding System in Cellulose Iβ from Synchrotron X-ray and Neutron Fiber Diffraction." J. Am. Chem. Soc. 124 (31): 9074–82. doi:10.1021/ja0257319
• Stenius, Per (2000). Forest Products Chemistry. Papermaking Science and Technology. Vol. 3. Finland: Fapet OY. ISBN 978-952-5216-03-5.