Cellulose

Source: Wikipedia, the free encyclopedia.

Cellulose[1]
Cellulose, a linear polymer of D-glucose units (two are shown) linked by β(1→4)-glycosidic bonds
Three-dimensional structure of cellulose
Identifiers
ChEMBL
ChemSpider
  • None
ECHA InfoCard
 100.029.692 Edit this at Wikidata
EC Number
  • 232-674-9
E number E460 (thickeners, ...)
KEGG
UNII
Properties
(C
12H
20O
10)
n
Molar mass 162.1406 g/mol per glucose unit
Appearance white powder
Density 1.5 g/cm3
Melting point 260–270 °C; 500–518 °F; 533–543 K Decomposes[2]
none
Thermochemistry
Std enthalpy of
formation
(ΔfH⦵298)
 −963,000 kJ/mol[clarification needed]
Std enthalpy of
combustion
(ΔcH⦵298)
 −2828,000 kJ/mol[clarification needed]
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
1
0
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[2]
REL (Recommended)
 TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)[2]
IDLH
(Immediate danger)
 N.D.[2]
Related compounds
Related compounds
 Starch
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Cellulose is an

green 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 57%.[7][8][9]

Cellulose is mainly used to produce

wood pulp and cotton.[6] Cellulose is also greatly affected by direct interaction with several organic liquids.[10]

Some animals, particularly

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.[3][11][12] 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.[13]

polysaccharides in a plant cell wall

Structure and properties

Cellulose under a microscope.

Cellulose has no taste, is odorless, is

hydrophilic with the contact angle of 20–30 degrees,[14] 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).[15] It can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature.[16]

Cellulose is derived from

reinforcement bars in concrete, lignin playing here the role of the hardened cement paste acting as the "glue" in between the cellulose fibers. Mechanical properties of cellulose in primary plant cell wall are correlated with growth and expansion of plant cells.[17] Live fluorescence microscopy techniques are promising in investigation of the role of cellulose in growing plant cells.[18]

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.[19]

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.[20]

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.

The chemical formula of cellulose is (C6H10O5)n where n is the degree of polymerization and represents the number of glucose groups.[21]

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 consists of fibrils with

emulsions.[27]

Processing

Biosynthesis

In

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.[28] 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 (Ces is short for "cellulose synthase") genes, in an unknown stoichiometry.[29] 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.[30]

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.[31] In fact, plants acquired CesA from the endosymbiosis event that produced the chloroplast.[32] All cellulose synthases known belongs to glucosyltransferase family 2 (GT2).[31]

Cellulose synthesis requires chain initiation and elongation, and the two processes are separate. Cellulose synthase (CesA) initiates cellulose polymerization using a

sitosterol-beta-glucoside, and UDP-glucose. It then utilizes UDP-D-glucose precursors to elongate the growing cellulose chain. A cellulase may function to cleave the primer from the mature chain.[33]

Cellulose is also synthesised by

ascidians (where the cellulose was historically termed "tunicine" (tunicin)).[34]

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.[35] However, this process can be significantly intensified in a proper solvent, e.g. in an ionic liquid.[36]

Most mammals have limited ability to digest dietary fiber such as cellulose. Some

digestive system (stomach and small intestine). Horses use cellulose in their diet by fermentation in their hindgut.[38] Some termites contain in their hindguts certain flagellate protozoa producing such enzymes, whereas others contain bacteria or may produce cellulase.[39]

The enzymes used to

glucosidases. Such enzymes are usually secreted as part of multienzyme complexes that may include dockerins and carbohydrate-binding modules.[40]

Breakdown (thermolysis)

See also: Wood ash § Composition

At temperatures above 350 °C, cellulose undergoes

bio-oil is obtained at 500 °C.[42]

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.

aerosols, which consist of short chain anhydro-oligomers derived from the melt.[44]

Continuing decomposition of molten cellulose produces volatile compounds including levoglucosan, furans, pyrans, light oxygenates, and gases via primary reactions.[45] Within thick cellulose samples, volatile compounds such as levoglucosan undergo 'secondary reactions' to volatile products including pyrans and light oxygenates such as glycolaldehyde.[46]

Hemicellulose

Main article: Hemicellulose

Hemicelluloses are polysaccharides related to cellulose that comprises about 20% of the biomass of land plants. In contrast to cellulose, hemicelluloses are derived from several sugars in addition to glucose, especially xylose but also including mannose, galactose, rhamnose, and arabinose. Hemicelluloses consist of shorter chains – between 500 and 3000 sugar units.[47] Furthermore, hemicelluloses are branched, whereas cellulose is unbranched.

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
.

The most important solubilizing agent is carbon disulfide in the presence of alkali. Other agents include

ionic liquids.[49]

The history of regenerated cellulose is often cited as beginning with George Audemars, who first manufactured regenerated

viscose.[50] 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.[52] 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.[50]

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.[52]

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[53] 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[54] E461
Ethylcellulose
(EC)		 Chloroethane −CH2CH3 Water-insoluble A commercial thermoplastic used in coatings, inks, binders, and controlled-release drug tablets [55] 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 [56]
Hydroxypropyl cellulose (HPC) Propylene oxide −CH2CH(OH)CH3 Cold water-soluble filming properties, coating properties, pharmaceuticals, cultural heritage restoration, electronic applications, cosmetic sector [57] [58] [59] [60] [61] 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

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.[62][63][64] Thiolated cellulose derivatives (see thiomers) exhibit also high binding properties for metal ions.[65][66]

Commercial applications

A strand of cellulose (conformation Iα), showing the hydrogen bonds (dashed) within and between cellulose molecules.
See also: dissolving pulp and pulp (paper)

Cellulose for industrial use is mainly obtained from

wood pulp and from cotton.[6]

Aspirational

Energy crops:

Main article:
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.[73][74][75][76]

Another possible application is as Insect repellents.[77]

See also

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External links

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