Cellulose

Cellulose

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Cellulose[1]
Identifiers
CAS Registry Number
ChEMBL
ChemSpider
EC number
UNII
Properties
Chemical formula
Appearance
Density
Melting point
Solubility in water
Thermochemistry
Std enthalpy of
formation (ΔfHo298)
Std enthalpy of
combustion(ΔcHo298)
Hazards
NFPA 704
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
IDLH (Immediate danger
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cellulose is an organic compound with the formula (C
6H
10O
5)
n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units.[3][4] Cellulose is an important structural component of the primary cell wall ofgreen plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms.[5] Cellulose is the most abundant organic polymer on Earth.[6] The cellulose content of cotton fiber is 90%, that of wood is 40–50% and that of dried hemp is approximately 45%.[7][8][9]

Cellulose is mainly used to produce paperboard and paper. Smaller quantities are converted into a wide variety of derivative products such as cellophane and rayon. Conversion of cellulose from energy crops into biofuels such as cellulosic ethanol is under investigation as an alternative fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton.[6]

Some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts, such as Trichonympha. In humans, cellulose acts as a hydrophilic bulking agent for feces and is often referred to as a "dietary fiber".

Contents

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History[edit]

Cellulose was discovered in 1838 by the French chemist Anselme Payen, who isolated it from plant matter and determined its chemical formula.[3][10][11] Cellulose was used to produce the first successful thermoplastic polymer, celluloid, by Hyatt Manufacturing Company in 1870. Production of rayon ("artificial silk") from cellulose began in the 1890s and cellophane was invented in 1912.Hermann Staudinger determined the polymer structure of cellulose in 1920. The compound was first chemically synthesized (without the use of any biologically derived enzymes) in 1992, by Kobayashi and Shoda.[12]

The arrangement of cellulose and other polysaccharides in a plant cell wall.

Structure and properties[edit]

Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30,[13] is insoluble in water and most organic solvents, is chiral and is biodegradable. It can be broken down chemically into its glucose units by treating it with concentrated acids at high temperature.

Cellulose is derived from D-glucose units, which condense through β(1→4)-glycosidic bonds. This linkage motif contrasts with that for α(1→4)-glycosidic bonds present in starch, glycogen, and other carbohydrates. Cellulose is a straight chain polymer: unlike starch, no coiling or branching occurs, and the molecule adopts an extended and rather stiff rod-like conformation, aided by the equatorial conformation of the glucose residues. The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen atoms on the same or on a neighbor chain, holding the chains firmly together side-by-side and forming microfibrils with high tensile strength. This confers tensile strength in cell walls, where cellulose microfibrils are meshed into a polysaccharide matrix.

A triple strand of cellulose showing the hydrogen bonds (cyan lines) between glucose strands

Cotton fibres represent the purest natural form of cellulose, containing more than 90% of this polysaccharide.

Compared to starch, cellulose is also much more crystalline. Whereas starch undergoes a crystalline to amorphous transition when heated beyond 60–70 °C in water (as in cooking), cellulose requires a temperature of 320 °C and pressure of 25 MPa to become amorphous in water.[14]

Several different crystalline structures of cellulose are known, corresponding to the location of hydrogen bonds between and within strands. Natural cellulose is cellulose I, with structures Iα and Iβ. Cellulose produced by bacteria and algae is enriched in Iα while cellulose of higher plants consists mainly of Iβ. Cellulose in regenerated cellulose fibers is cellulose II. The conversion of cellulose I to cellulose II is irreversible, suggesting that cellulose I is metastable and cellulose II is stable. With various chemical treatments it is possible to produce the structures cellulose III and cellulose IV.[15]

Many properties of cellulose depend on its chain length or degree of polymerization, the number of glucose units that make up one polymer molecule. Cellulose from wood pulp has typical chain lengths between 300 and 1700 units; cotton and other plant fibers as well as bacterial cellulose have chain lengths ranging from 800 to 10,000 units.[6] Molecules with very small chain length resulting from the breakdown of cellulose are known as cellodextrins; in contrast to long-chain cellulose, cellodextrins are typically soluble in water and organic solvents.

Plant-derived cellulose is usually found in a mixture with hemicellulose, lignin, pectin and other substances, while bacterial cellulose is quite pure, has a much higher water content and higher tensile strength due to higher chain lengths.[6]:3384

Cellulose is soluble in Schweizer's reagent, cupriethylenediamine (CED), cadmiumethylenediamine (Cadoxen), N-methylmorpholine N-oxide, and lithium chloride / dimethylacetamide.[16] This is used in the production of regenerated celluloses (such as viscose andcellophane) from dissolving pulp. Cellulose is also soluble in many kinds of ionic liquids.[17]

Cellulose consists of crystalline and amorphous regions. By treating it with strong acid, the amorphous regions can be broken up, thereby producing nanocrystalline cellulose, a novel material with many desirable properties.[18] Recently, nanocrystalline cellulose was used as the filler phase in bio-based polymer matrices to produce nanocomposites with superior thermal and mechanical properties.[19]

Processing[edit]

Assay[edit]

Given a cellulose-containing material, the carbohydrate portion that does not dissolve in a 17.5% solution of sodium hydroxide at 20 °C isα cellulose, which is true cellulose[clarification needed]. Acidification of the extract precipitates β cellulose. The portion that dissolves in base but does not precipitate with acid is γ cellulose[citation needed].

Cellulose can be assayed using a method described by Updegraff in 1969, where the fiber is dissolved in acetic and nitric acid to removelignin, hemicellulose, and xylosans. The resulting cellulose is allowed to react with anthrone in sulfuric acid. The resulting coloured compound is assayed spectrophotometrically at a wavelength of approximately 635 nm.

In addition, cellulose is represented by the difference between acid detergent fiber (ADF) and acid detergent lignin (ADL).

Biosynthesis[edit]

In vascular plants cellulose is synthesized at the plasma membrane by rosette terminal complexes (RTCs). The RTCs are hexameric protein structures, approximately 25 nm in diameter, that contain the cellulose synthase enzymes that synthesise the individual cellulose chains.[20] Each RTC floats in the cell's plasma membrane and "spins" a microfibril into the cell wall.

RTCs contain at least three different cellulose synthases, encoded by CesA genes, in an unknown stoichiometry.[21] Separate sets of CesA genes are involved in primary and secondary cell wall biosynthesis. There are known to be about seven subfamilies in the CesA superfamily. These cellulose synthases use UDP-glucose to form the β(1→4)-linked cellulose.[22]

Cellulose synthesis requires chain initiation and elongation, and the two processes are separate. CesA glucosyltransferase initiates cellulose polymerization using a steroidprimer, sitosterol-beta-glucoside, and UDP-glucose.[23] Cellulose synthase utilizes UDP-D-glucose precursors to elongate the growing cellulose chain. A cellulase may function to cleave the primer from the mature chain.

Cellulose is also synthesised by animals, particularly in the tests of ascidians (where the cellulose was historically termed "tunicine") although it is also a minor component ofmammalian connective tissue.[24]

Breakdown (cellulolysis)[edit]

Cellulolysis is the process of breaking down cellulose into smaller polysaccharides called cellodextrins or completely into glucose units; this is a hydrolysis reaction. Because cellulose molecules bind strongly to each other, cellulolysis is relatively difficult compared to the breakdown of other polysaccharides.[25] However, this process can be significantly intensified in a proper solvent, e.g. in an ionic liquid.[26]

Most mammals have limited ability to digest dietary fiber such as cellulose. Some ruminants like cows and sheep contain certain symbiotic anaerobic bacteria (like Cellulomonas) in the flora of the rumen, and these bacteria produce enzymes called cellulases that help the microorganism to digest cellulose; the breakdown products are then used by the bacteria for proliferation. The bacterial mass is later digested by the ruminant in its digestive system (stomach and small intestine). Horses use cellulose in their diet byfermentation in their hindgut via symbiotic bacteria which produce cellulase to digest cellulose.[citation needed] Similarly, some termites contain in their hindguts certain flagellateprotozoa producing such enzymes, whereas others contain bacteria or may produce cellulase.[27]

The enzymes used to cleave the glycosidic linkage in cellulose are glycoside hydrolases including endo-acting cellulases and exo-acting glucosidases. Such enzymes are usually secreted as part of multienzyme complexes that may include dockerins and carbohydrate-binding modules.[28]

Hemicellulose[edit]

Main article: Hemicellulose

Hemicellulose is a polysaccharide related to cellulose that comprises about 20% of the biomass of most plants. In contrast to cellulose, hemicellulose is derived from several sugars in addition to glucose, especially xylose but also including mannose, galactose, rhamnose, and arabinose. Hemicellulose consists of shorter chains – between 500 and 3000 sugar units.[29] Furthermore, hemicellulose is branched, whereas cellulose is unbranched.

Derivatives[edit]

The hydroxyl groups (-OH) of cellulose can be partially or fully reacted with various reagents to afford derivatives with useful properties like mainly cellulose esters and celluloseethers (-OR). In principle, though not always in current industrial practice, cellulosic polymers are renewable resources.

Ester derivatives include:

Cellulose ester Reagent Example Reagent Group R
Organic esters Organic acids Cellulose acetate Acetic acid and acetic anhydride H or -(C=O)CH3
Cellulose triacetate Acetic acid and acetic anhydride -(C=O)CH3
Cellulose propionate Propanoic acid H or -(C=O)CH2CH3
Cellulose acetate propionate (CAP) Acetic acid and propanoic acid H or -(C=O)CH3 or -(C=O)CH2CH3
Cellulose acetate butyrate (CAB) Acetic acid and butyric acid H or -(C=O)CH3 or -(C=O)CH2CH2CH3
Inorganic esters Inorganic acids Nitrocellulose (cellulose nitrate) Nitric acid or another powerful nitrating agent H or -NO2
Cellulose sulfate Sulfuric acid or another powerful sulfuring agent H or -SO3H

The cellulose acetate and cellulose triacetate are film- and fiber-forming materials that find a variety of uses. The nitrocellulose was initially used as an explosive and was an early film forming material. With camphor, nitrocellulose gives celluloid.

Ether derivatives include:

Cellulose ethers Reagent Example Reagent Group R = H or Water solubility Application E number
Alkyl Halogenoalkanes Methylcellulose Chloromethane -CH3 Cold water-soluble E461
Ethylcellulose Chloroethane -CH2CH3 Water-insoluble A commercial thermoplastic used in coatings, inks, binders, and controlled-release drug tablets E462
Ethyl methyl cellulose Chloromethane and chloroethane -CH3 or -CH2CH3 E465
Hydroxyalkyl Epoxides Hydroxyethyl cellulose Ethylene oxide -CH2CH2OH Cold/hot water-soluble Gelling and thickening agent
Hydroxypropyl cellulose (HPC) Propylene oxide -CH2CH(OH)CH3 Cold water-soluble E463
Hydroxyethyl methyl cellulose Chloromethane and ethylene oxide -CH3 or -CH2CH2OH Cold water-soluble Production of cellulose films
Hydroxypropyl methyl cellulose (HPMC) Chloromethane and propylene oxide -CH3 or -CH2CH(OH)CH3 Cold water-soluble Viscosity modifier, gelling, foaming and binding agent E464
Ethyl hydroxyethyl cellulose Chloroethane and ethylene oxide -CH2CH3 or—CH2CH2OH E467
Carboxyalkyl Halogenated carboxylic acids Carboxymethyl cellulose (CMC) Chloroacetic acid -CH2COOH Cold/Hot water-soluble Often used as its sodium salt, sodium carboxymethyl cellulose (NaCMC) E466

The sodium carboxymethyl cellulose can be cross-linked to give the croscarmellose sodium (E468) for use as a disintegrant in pharmaceutical formulations.

Applications[edit]

A strand of cellulose (conformation Iα), showing the hydrogen bonds(dashed) within and between cellulose molecules.

See also: dissolving pulp and pulp (paper)

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2015)

Cellulose for industrial use is mainly obtained from wood pulp and cotton.[6] The kraft process is used to separate cellulose from lignin, another major component of plant matter.

Main article: Energy crop

The major combustible component of non-food energy crops is cellulose, with lignin second. Non-food energy crops produce more usable energy than edible energy crops (which have a large starch component), but still compete with food crops for agricultural land and water resources.[31] Typical non-food energy crops include industrial hemp(though outlawed in some countries), switchgrass, Miscanthus, Salix (willow), and Populus (poplar) species.

References[edit]

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  2. ^ Jump up to:a b c d "NIOSH Pocket Guide to Chemical Hazards #0110". National Institute for Occupational Safety and Health (NIOSH).

  3. ^ Jump up to:a b Crawford, R. L. (1981). Lignin biodegradation and transformation. New York: John Wiley and Sons. ISBN 0-471-05743-6.

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  6. ^ Jump up to:a b c d e Klemm, Dieter; Heublein, Brigitte; Fink, Hans-Peter; Bohn, Andreas (2005). "Cellulose: Fascinating Biopolymer and Sustainable Raw Material". Angew. Chem. Int. Ed.44 (22). doi:10.1002/anie.200460587.

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  10. Jump up^ Payen, A. (1838) "Mémoire sur la composition du tissu propre des plantes et du ligneux" (Memoir on the composition of the tissue of plants and of woody [material]), Comptes rendus, vol. 7, pp. 1052–1056. Payen added appendices to this paper on December 24, 1838 (see: Comptes rendus, vol. 8, p. 169 (1839)) and on February 4, 1839 (see: Comptes rendus, vol. 9, p. 149 (1839)). A committee of the French Academy of Sciences reviewed Payen's findings in : Jean-Baptiste Dumas (1839) "Rapport sur un mémoire de M. Payen, relatif à la composition de la matière ligneuse" (Report on a memoir of Mr. Payen, regarding the composition of woody matter), Comptes rendus, vol. 8, pp. 51–53. In this report, the word "cellulose" is coined and author points out the similarity between the empirical formula of cellulose and that of "dextrine" (starch). The above articles are reprinted in: Brongniart and Guillemin, eds., Annales des sciences naturelles ..., 2nd series, vol. 11 (Paris, France: Crochard et Cie., 1839), pp. 21–31.

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  14. Jump up^ Deguchi, Shigeru; Tsujii, Kaoru; Horikoshi, Koki (2006). "Cooking cellulose in hot and compressed water". Chemical Communications (31): 3293. doi:10.1039/b605812d.

  15. Jump up^ Structure and morphology of cellulose by Serge Pérez and William Mackie, CERMAV-CNRS, 2001. Chapter IV.

  16. Jump up^ Stenius, Per (2000). "Ch. 1". Forest Products Chemistry. Papermaking Science and Technology. Vol. 3. Finland: Fapet OY. p. 35. ISBN 952-5216-03-9.

  17. Jump up^ [H. Wang, G. Gurau, and R. D. Rogers. "Ionic liquid processing of cellulose" Chem. Soc. Rev., 2012, 41, 1519–1537

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  19. Jump up^ Pranger, L.; Tannenbaum, R. (2008). "Biobased Nanocomposites Prepared by in Situ Polymerization of Furfuryl Alcohol with Cellulose Whiskers or Montmorillonite Clay".Macromolecules 41 (22): 8682. doi:10.1021/ma8020213.

  20. Jump up^ Kimura, S; Laosinchai, W; Itoh, T; Cui, X; Linder, CR; Brown Jr, RM (1999)."Immunogold labeling of rosette terminal cellulose-synthesizing complexes in the vascular plant vigna angularis". The Plant cell 11 (11): 2075–86. doi:10.2307/3871010.JSTOR 3871010. PMC 144118. PMID 10559435.

  21. Jump up^ Taylor, N. G. (2003). "Interactions among three distinct CesA proteins essential for cellulose synthesis". Proceedings of the National Academy of Sciences 100 (3): 1450.doi:10.1073/pnas.0337628100.

  22. Jump up^ Richmond, Todd A; Somerville, Chris R (October 2000). "The Cellulose Synthase Superfamily". Plant Physiology 124 (2): 495–498. doi:10.1104/pp.124.2.495. Retrieved14 December 2014.

  23. Jump up^ Peng, L; Kawagoe, Y; Hogan, P; Delmer, D (2002). "Sitosterol-beta-glucoside as primer for cellulose synthesis in plants". Science 295 (5552): 147–50.doi:10.1126/science.1064281. PMID 11778054.

  24. Jump up^ Endean, R (1961). "The Test of the Ascidian, Phallusia mammillata" (PDF). Quarterly Journal of Microscopical Science 102 (1): 107–117.

  25. Jump up^ Barkalow, David G. and Whistler, Roy L. "Cellulose". AccessScience, McGraw-Hill.

  26. Jump up^ Ignatyev, Igor; Charlie Van Doorslaer; Pascal G.N. Mertens; Koen Binnemans; Dirk. E. de Vos (2011). "Synthesis of glucose esters from cellulose in ionic liquids".Holzforschung 66 (4): 417–425. doi:10.1515/hf.2011.161.

  27. Jump up^ Tokuda, G; Watanabe, H (22 June 2007). "Hidden cellulases in termites: revision of an old hypothesis". Biology Letters 3 (3): 336–339. doi:10.1098/rsbl.2007.0073.PMC 2464699. PMID 17374589.

  28. Jump up^ Brás, Natércia; N. M. F. S. A. Cerqueira; P. A. Fernandes; M. J. Ramos (2008). "Carbohydrate Binding Modules from family 11: Understanding the binding mode of polysaccharides". International Journal of Quantum Chemistry 108 (11): 2030–2040.doi:10.1002/qua.21755.

  29. Jump up^ Gibson LJ (2013). "The hierarchical structure and mechanics of plant materials".Journal of the Royal Society Interface 9 (76): 2749–2766. PMC 3479918.PMID 22874093.

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  31. Jump up^ Holt-Gimenez, Eric (2007). Biofuels: Myths of the Agrofuels Transition. Backgrounder. Institute for Food and Development Policy, Oakland, CA. 13:2 [1] [2]

  32. Jump up^ Kathryn Hobgood Ray (August 25, 2011). "Cars Could Run on Recycled Newspaper, Tulane Scientists Say". Tulane University news webpage. Tulane University. RetrievedMarch 14, 2012.

  33. Jump up^ Laurie Balbo (January 29, 2012). "Put a Zebra in Your Tank: A Chemical Crapshoot?". Greenprophet.com. Retrieved November 17, 2012.

  34. Jump up^ "Zeoform: The eco-friendly building material of the future?". Gizmag.com. Retrieved2013-08-30.

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