Cellulose
Template:Short description Template:Cs1 config Template:Use mdy dates
Cellulose is an organic compound with the formula Template:Chem, a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units.<ref name="Crawford-1981">Template:Cite book</ref><ref name="Updegraff-1969">Template:Cite journal</ref> Cellulose is an important structural component of the cell walls of green plants, many forms of algae, and the oomycetes. Some species of bacteria secrete it to form biofilms.<ref>Template:Cite book</ref> Cellulose is the most abundant organic polymer on Earth.<ref name="Klemm-2005">Template:Cite journal</ref> The cellulose content of cotton fibre is 90%, that of wood is 40–50%, and that of dried hemp is approximately 57%.<ref>Cellulose. (2008). In Encyclopædia Britannica. Retrieved January 11, 2008, from Encyclopædia Britannica Online.</ref><ref>Chemical Composition of Wood. Template:Webarchive. ipst.gatech.edu.</ref><ref>Piotrowski, Stephan and Carus, Michael (May 2011) Multi-criteria evaluation of lignocellulosic niche crops for use in biorefinery processes Template:Webarchive. nova-Institut GmbH, Hürth, Germany.</ref>
Cellulose is used mainly 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 development as a renewable fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton.<ref name="Klemm-2005"/> In addition, cellulose exhibits pronounced susceptibility to direct interactions with certain organic liquids, notably formamide, DMSO, and short-chain amines (methylamine, ethylamine), among other, are recognized as highly effective swelling agents.<ref>Template:Cite journal</ref>
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 human nutrition, cellulose is a non-digestible constituent of insoluble dietary fiber, acting as a hydrophilic bulking agent for feces and potentially aiding in defecation.
History
Cellulose was discovered in 1838 by the French chemist Anselme Payen, who isolated it from plant matter and determined its chemical formula.<ref name="Crawford-1981" /><ref>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, reltes 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), [ Template:Google books pp. 21–31].</ref><ref name="Young-1986">Template:Cite book</ref> 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.<ref>Template:Cite journal</ref>
Structure and properties
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Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30 degrees,<ref>Template:Cite book</ref> is insoluble in water and most organic solvents, is chiral and is biodegradable. It was shown to melt at 467 °C in pulse tests made by Dauenhauer et al. (2016).<ref name="Dauenhauer-2016">Template:Cite journal</ref> It can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature.<ref>Template:Cite journal</ref>
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 and glycogen. 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 neighbour 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. The high tensile strength of plant stems and of the tree wood also arises from the arrangement of cellulose fibers intimately distributed into the lignin matrix. The mechanical role of cellulose fibers in the wood matrix responsible for its strong structural resistance, can somewhat be compared to that of the reinforcement bars in concrete, lignin playing here the role of the hardened cement paste acting as the "glue" in between the cellulose fibres. Mechanical properties of cellulose in primary plant cell wall are correlated with growth and expansion of plant cells.<ref name="Bidhendi-2016">Template:Cite journal</ref> Live fluorescence microscopy techniques are promising in investigation of the role of cellulose in growing plant cells.<ref name="Bidhendi-2020">Template:Cite journal</ref>
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.<ref name="Deguchi-2006">Template:Cite journal</ref>
Several types of cellulose are known. These forms are distinguished according 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.<ref>Structure and morphology of cellulose Template:Webarchive by Serge Pérez and William Mackie, CERMAV-CNRS, 2001. Chapter IV.</ref>
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.<ref name="Klemm-2005"/> 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.
The chemical formula of cellulose is (C6H10O5)n where n is the degree of polymerization and represents the number of glucose groups.<ref>Template:Cite book</ref>
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.<ref name="Klemm-2005"/>Template:Rp
Cellulose consists of fibrils with crystalline and amorphous regions.<ref>Template:Cite web</ref> These cellulose fibrils may be individualized by mechanical treatment of cellulose pulp, often assisted by chemical oxidation or enzymatic treatment, yielding semi-flexible cellulose nanofibrils generally 200 nm to 1 μm in length depending on the treatment intensity.<ref>Template:Cite journal</ref> Cellulose pulp may also be treated with strong acid to hydrolyze the amorphous fibril regions, thereby producing short rigid cellulose nanocrystals a few 100 nm in length.<ref>Template:Cite journal</ref> These nanocelluloses are of high technological interest due to their self-assembly into cholesteric liquid crystals,<ref>Template:Cite journal</ref> production of hydrogels or aerogels,<ref>Template:Cite journal</ref> use in nanocomposites with superior thermal and mechanical properties,<ref>Template:Cite journal</ref> and use as Pickering stabilizers for emulsions.<ref>Template:Cite journal</ref>
Processing
Biosynthesis
In 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.<ref>Template:Cite journal</ref> Each RTC floats in the cell's plasma membrane and "spins" a microfibril into the cell wall.Template:Citation needed
RTCs contain at least three different cellulose synthases, encoded by CesA (Ces is short for "cellulose synthase") genes, in an unknown stoichiometry.<ref>Template:Cite journal</ref> Separate sets of CesA genes are involved in primary and secondary cell wall biosynthesis. There are known to be about seven subfamilies in the plant CesA superfamily, some of which include the more cryptic, tentatively-named Csl (cellulose synthase-like) enzymes. These cellulose syntheses use UDP-glucose to form the β(1→4)-linked cellulose.<ref name="Richmond-2000">Template:Cite journal</ref>
Bacterial cellulose is produced using the same family of proteins, although the gene is called BcsA for "bacterial cellulose synthase" or CelA for "cellulose" in many instances.<ref name="Omadjela-2013"/> In fact, plants acquired CesA from the endosymbiosis event that produced the chloroplast.<ref name="Popper-2011">Template:Cite journal</ref> All cellulose synthases known belongs to glycosyltransferase family 2 (GT2).<ref name="Omadjela-2013">Template:Cite journal</ref>
Cellulose synthesis requires chain initiation and elongation, and the two processes are separate. Cellulose synthase (CesA) initiates cellulose polymerization using a steroid primer, sitosterol-beta-glucoside, and UDP-glucose. It then utilises UDP-D-glucose precursors to elongate the growing cellulose chain. A cellulase may function to cleave the primer from the mature chain.<ref>Template:Cite journal</ref>
Cellulose is also synthesised by tunicate animals, particularly in the tests of ascidians (where the cellulose was historically termed "tunicine" (tunicin)).<ref>Template:Cite journal</ref>
Breakdown (cellulolysis)
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.<ref>Template:Cite journal</ref> However, this process can be significantly intensified in a proper solvent, e.g. in an ionic liquid.<ref name="Ignatyev-2011">Template:Cite journal</ref>
Most mammals have limited ability to digest dietary fibre such as cellulose. Some ruminants like cows and sheep contain certain symbiotic anaerobic bacteria (such as Cellulomonas and Ruminococcus spp.) in the flora of the rumen, and these bacteria produce enzymes called cellulases that hydrolyze cellulose. The breakdown products are then used by the bacteria for proliferation.<ref name="La Reau-2018">Template:Cite journal</ref> The bacterial mass is later digested by the ruminant in its digestive system (stomach and small intestine). Horses use cellulose in their diet by fermentation in their hindgut.<ref>Template:Cite web</ref> Some termites contain in their hindguts certain flagellate protozoa producing such enzymes, whereas others contain bacteria or may produce cellulase.<ref>Template:Cite journal</ref>
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.<ref>Template:Cite journal</ref>
Breakdown (thermolysis)
Template:See also At temperatures above 350 °C, cellulose undergoes thermolysis (also called 'pyrolysis'), decomposing into solid char, vapors, aerosols, and gases such as carbon dioxide.<ref>Template:Cite journal</ref> Maximum yield of vapors which condense to a liquid called bio-oil is obtained at 500 °C.<ref>Template:Cite journal</ref>
Semi-crystalline cellulose polymers react at pyrolysis temperatures (350–600 °C) in a few seconds; this transformation has been shown to occur via a solid-to-liquid-to-vapor transition, with the liquid (called intermediate liquid cellulose or molten cellulose) existing for only a fraction of a second.<ref>Template:Cite journal</ref> Glycosidic bond cleavage produces short cellulose chains of two-to-seven monomers comprising the melt. Vapor bubbling of intermediate liquid cellulose produces aerosols, which consist of short chain anhydro-oligomers derived from the melt.<ref>Template:Cite journal</ref>
Continuing decomposition of molten cellulose produces volatile compounds including levoglucosan, furans, pyrans, light oxygenates, and gases via primary reactions.<ref>Template:Cite journal</ref> Within thick cellulose samples, volatile compounds such as levoglucosan undergo 'secondary reactions' to volatile products including pyrans and light oxygenates such as glycolaldehyde.<ref>Template:Cite journal</ref>
Hemicellulose
Template:Main Hemicelluloses are polysaccharides related to cellulose that comprises about 20% of the biomass of land plants. In contrast to cellulose, hemicelluloses (which include xylans, xyloglucans, (gluco)mannans, and mixed-linkage glucans) are derived from several sugars in addition to glucose, especially xylose but also including mannose, galactose, glucuronic acid, fucose, and arabinose. Hemicelluloses consist of shorter chains – between 500 and 3000 sugar units.<ref name="Gibson-2013">Template:Cite journal</ref> Furthermore, hemicelluloses are often branched, whereas cellulose is unbranched.<ref>Template:Cite journal</ref>
Regenerated cellulose
Cellulose is soluble in several kinds of media, several of which are the basis of commercial technologies. These dissolution processes are reversible and are used in the production of regenerated celluloses (such as viscose and cellophane) from dissolving pulp.<ref>Template:Cite journal</ref>
The most important solubilizing agent is carbon disulfide in the presence of alkali. Other agents include Schweizer's reagent, N-methylmorpholine N-oxide, and lithium chloride in dimethylacetamide. In general, these agents modify the cellulose, rendering it soluble. The agents are then removed concomitant with the formation of fibers.<ref>Template:Cite book</ref> Cellulose is also soluble in many kinds of ionic liquids.<ref>Template:Cite journal</ref>
The history of regenerated cellulose is often cited as beginning with George Audemars, who first manufactured regenerated nitrocellulose fibers in 1855.<ref name="Abetz-2005">Template:Cite book</ref> Although these fibers were soft and strong -resembling silk- they had the drawback of being highly flammable. Hilaire de Chardonnet perfected production of nitrocellulose fibers, but manufacturing of these fibers by his process was relatively uneconomical.<ref name="Abetz-2005" /> In 1890, L.H. Despeissis invented the cuprammonium process – which uses a cuprammonium solution to solubilize cellulose – a method still used today for production of artificial silk.<ref>Template:Cite book</ref> In 1891, it was discovered that treatment of cellulose with alkali and carbon disulfide generated a soluble cellulose derivative known as viscose.<ref name="Abetz-2005" /> This process, patented by the founders of the Viscose Development Company, is the most widely used method for manufacturing regenerated cellulose products. Courtaulds purchased the patents for this process in 1904, leading to significant growth of viscose fiber production.<ref name="Borbély-2008">Template:Cite journal</ref> By 1931, expiration of patents for the viscose process led to its adoption worldwide. Global production of regenerated cellulose fiber peaked in 1973 at 3,856,000 tons.<ref name="Abetz-2005" />
Regenerated cellulose can be used to manufacture a wide variety of products. While the first application of regenerated cellulose was as a clothing textile, this class of materials is also used in the production of disposable medical devices as well as fabrication of artificial membranes.<ref name="Borbély-2008" />
Cellulose esters and ethers
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 cellulose ethers (−OR). In principle, although 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 | Propionic 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 sulfating agent | H or −SO3H |
Cellulose acetate and cellulose triacetate are film- and fiber-forming materials that find a variety of uses. Nitrocellulose was initially used as an explosive and was an early film forming material. When plasticized with camphor, nitrocellulose gives celluloid.
Cellulose Ether<ref>Template:Cite web</ref> derivatives include:
| Cellulose ethers | Reagent | Example | Reagent | Group R = H or | Water solubility | Application | E number |
|---|---|---|---|---|---|---|---|
| Alkyl | Halogenoalkanes | Methylcellulose | Chloromethane | −CH3 | Cold/Hot water-soluble<ref>Template:Cite web</ref> | E461 | |
| Ethylcellulose (EC) | Chloroethane | −CH2CH3 | Water-insoluble | A commercial thermoplastic used in coatings, inks, binders, and controlled-release drug tablets,<ref name="Maita-2023">Template:Cite journal</ref> also employed in the production of oleogels and bioplastics<ref>Template:Cite journal</ref> | 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<ref name="Orlanducci-2022">Template:Cite journal</ref> | |
| Hydroxypropyl cellulose (HPC) | Propylene oxide | −CH2CH(OH)CH3 | Cold water-soluble | filming properties, coating properties, pharmaceuticals, cultural heritage restoration, electronic applications, cosmetic sector<ref name="Maita-2023"/><ref name="Orlanducci-2022"/><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> | 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. Furthermore, by the covalent attachment of thiol groups to cellulose ethers such as sodium carboxymethyl cellulose, ethyl cellulose, or hydroxyethyl cellulose mucoadhesive and permeation enhancing properties can be introduced.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Thiolated cellulose derivatives (see thiomers) exhibit also high binding properties for metal ions.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
Commercial applications
Template:See also Cellulose for industrial use is mainly obtained from wood pulp and from cotton.<ref name="Klemm-2005"/>
- Paper products: Cellulose is the major constituent of paper, paperboard, and card stock. Electrical insulation paper: Cellulose is used in diverse forms as insulation in transformers, cables, and other electrical equipment.<ref>Template:Cite journal</ref>
- Fibres: Cellulose is the main ingredient of textiles. Cotton and synthetics (nylons) each have about 40% market by volume. Other plant fibres (jute, sisal, hemp) represent about 20% of the market. Rayon, cellophane, and other "regenerated cellulose fibres" are a small portion (5%).Template:Citation needed
- Consumables: Microcrystalline cellulose (E460i) and powdered cellulose (E460ii) are used as inactive fillers in drug tablets<ref>
Template:Cite book</ref> and a wide range of soluble cellulose derivatives, E numbers E461 to E469, are used as emulsifiers, thickeners, and stabilizers in processed foods. Cellulose powder is, for example, used in processed cheese to prevent caking inside the package. Cellulose occurs naturally in some foods and is an additive in manufactured foods, contributing an indigestible component used for texture and bulk, potentially aiding in defecation.<ref>Template:Cite journal</ref>
- Building material: Hydroxyl bonding of cellulose in water produces a sprayable, moldable material as an alternative to the use of plastics and resins. The recyclable material can be made water- and fire-resistant. It provides sufficient strength for use as a building material.<ref>Template:Cite web</ref> Cellulose insulation made from recycled paper is becoming popular as an environmentally preferable material for building insulation. It can be treated with boric acid as a fire retardant.Template:Citation needed
- Miscellaneous: Cellulose can be converted into cellophane, a thin transparent film. It is the base material for the celluloid that was used for photographic and movie films until the mid-1930s. Cellulose is used to make water-soluble adhesives and binders such as methyl cellulose and carboxymethyl cellulose which are used in wallpaper paste. Cellulose is further used to make hydrophilic and highly absorbent sponges. Cellulose is the raw material in the manufacture of nitrocellulose (cellulose nitrate) which is used in smokeless gunpowder.Template:Citation needed
- Pharmaceuticals: Cellulose derivatives, such as microcrystalline cellulose (MCC), have the advantages of retaining water, being a stabilizer and thickening agent, and in reinforcement of drug tablets.<ref>Template:Cite journal</ref>
Aspirational
Energy crops: Template:Main 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.<ref>Holt-Gimenez, Eric (2007). Biofuels: Myths of the Agrofuels Transition. Backgrounder. Institute for Food and Development Policy, Oakland, CA. 13:2 Template:Cite web Template:Cite web</ref> Typical non-food energy crops include industrial hemp, switchgrass, Miscanthus, Salix (willow), and Populus (poplar) species. A strain of Clostridium bacteria found in zebra dung can convert nearly any form of cellulose into butanol fuel.<ref>MullinD, Velankar H.2012.Isolated bacteria, methods for use, and methods for isolation.World patent WO 2012/021678 A2</ref><ref>Template:Cite journal</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref>
Another possible application is as Insect repellents.<ref>Template:Cite news</ref>
Dung-geneering
Cellulose has been extracted from cow dung using pressurized spinning from a horizontal vessel capable of structuring small structure nano-fibers.<ref>Template:Cite journal</ref>
See also
- Gluconic acid
- Isosaccharinic acid, a degradation product of cellulose
- Lignin
- Zeoform
References
External links
- Template:Cite EB1911
- Structure and morphology of cellulose by Serge Pérez and William Mackie, CERMAV-CNRS
- Cellulose, by Martin Chaplin, London South Bank University
- Clear description of a cellulose assay method at the Cotton Fiber Biosciences unit of the USDA.
- Cellulose films could provide flapping wings and cheap artificial muscles for robots – TechnologyReview.com
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