Cellulose

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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
9004-34-6 YesY
ChEMBL ChEMBL1201676 N
ChemSpider  YesY
EC-number 232-674-9
UNII SMD1X3XO9M YesY
Properties
(C
6
H
10
O
5
)
n
Appearance white powder
Density 1.5 g/cm3
Melting point 260–270 °C; 500–518 °F; 533–543 K decomposes[2]
none
Thermochemistry
−963 kJ mol−1
−2828 kJ mol−1
Hazards
EU Index not listed
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
US health exposure limits (NIOSH):
TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[2]
TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)[2]
N.D.[2]
Related compounds
Related compounds
Starch
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N verify (what isYesY/N?)
Infobox references

Cellulose is an organic compound with the formula (C
6
H
10
O
5
)
n
, a polysaccharide(多糖類) 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 of 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(重合体,高分子) on Earth.[6] The cellulose(セルロース) content of cotton fiber is 90%, that of wood is 40–50% and that of dried hemp(大麻) 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(セルロース) from energy crops into biofuels such as cellulosic ethanol((No gloss)) 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(白蟻), can digest cellulose(セルロース) with the help of symbiotic((No gloss)) micro-organisms((No gloss)) that live in their guts, such as Trichonympha. In humans, cellulose(セルロース) acts as a hydrophilic bulking agent for feces(ふん,排出物,糞便(ふんべん),かす) and is often referred to as a "dietary fiber".

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(重合体,高分子), celluloid(セルロイド), by Hyatt Manufacturing Company in 1870. Production of rayon ("artificial silk") from cellulose(セルロース) began in the 1890s and cellophane was invented in 1912. Hermann Staudinger determined the polymer(重合体,高分子) structure of cellulose(セルロース) in 1920. The compound was first chemically((No gloss)) 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,(無臭の) is hydrophilic with the contact angle of 20–30,[13] is insoluble((No gloss)) in water and most organic solvents, is chiral and is biodegradable((No gloss)). It can be broken down chemically((No gloss)) 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(関連,連関) motif contrasts with that for α(1→4)-glycosidic bonds present in starch, glycogen((No gloss)), and other carbohydrates. Cellulose is a straight chain polymer:(重合体,高分子) unlike starch, no coiling or branching occurs, and the molecule adopts an extended and rather stiff rod-like conformation,((No gloss)) aided by the equatorial(赤道の(付近の)) conformation((No gloss)) of the glucose residues. The multiple hydroxyl((No gloss)) 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(堅く,しっかりと,断固) together side-by-side and forming microfibrils with high tensile strength. This confers tensile strength in cell walls, where cellulose(セルロース) microfibrils are meshed into a polysaccharide(多糖類) 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(セルロース) is also much more crystalline(結晶質). Whereas starch undergoes a crystalline(結晶質) to amorphous(1.一定の形を持たない,無定形の,明確な形のない,非結晶の,不定形の,まとまりのない,無構造の,形の定まらない,2.アモルファス,非結晶質) transition when heated beyond 60–70 °C in water (as in cooking), cellulose(セルロース) requires a temperature of 320 °C and pressure of 25 MPa to become amorphous(1.一定の形を持たない,無定形の,明確な形のない,非結晶の,不定形の,まとまりのない,無構造の,形の定まらない,2.アモルファス,非結晶質) in water.[14]

Several different crystalline(結晶質) structures of cellulose(セルロース) are known, corresponding to the location of hydrogen bonds between and within strands. Natural cellulose(セルロース) is cellulose(セルロース) I, with structures Iα and Iβ. Cellulose produced by bacteria and algae is enriched in Iα while cellulose(セルロース) of higher plants consists mainly of Iβ. Cellulose in regenerated(再び生じさせる,を改心させる,を更生させる,を再建する,を再生利用する,刷新する,革新する) cellulose(セルロース) fibers is cellulose(セルロース) II. The conversion of cellulose(セルロース) I to cellulose(セルロース) II is irreversible,(逆にできない,逆転できない,撤回不可能の,取り消しできない) suggesting that cellulose(セルロース) I is metastable and cellulose(セルロース) II is stable. With various chemical treatments it is possible to produce the structures cellulose(セルロース) III and cellulose(セルロース) IV.[15]

Many properties of cellulose(セルロース) depend on its chain length or degree of polymerization, the number of glucose units that make up one polymer(重合体,高分子) molecule. Cellulose from wood pulp has typical chain lengths between 300 and 1700 units; cotton and other plant fibers as well as bacterial cellulose(セルロース) have chain lengths ranging from 800 to 10,000 units.[6] Molecules with very small chain length resulting from the breakdown of cellulose(セルロース) are known as cellodextrins; in contrast to long-chain cellulose,(セルロース) cellodextrins are typically soluble(溶解できる,(物質が)溶けやすい,(問題が)解決できる,溶性の) in water and organic solvents.

Plant-derived cellulose(セルロース) is usually found in a mixture with hemicellulose, lignin, pectin((No gloss)) and other substances, while bacterial cellulose(セルロース) is quite pure, has a much higher water content and higher tensile strength due to higher chain lengths.[6]:3384

Cellulose is soluble(溶解できる,(物質が)溶けやすい,(問題が)解決できる,溶性の) in Schweizer's reagent(試薬), cupriethylenediamine (CED), cadmiumethylenediamine (Cadoxen), N-methylmorpholine N-oxide, and lithium(リチウム) chloride / dimethylacetamide.[16] This is used in the production of regenerated(再び生じさせる,を改心させる,を更生させる,を再建する,を再生利用する,刷新する,革新する) celluloses (such as viscose and cellophane) from dissolving pulp. Cellulose is also soluble(溶解できる,(物質が)溶けやすい,(問題が)解決できる,溶性の) in many kinds of ionic liquids.[17]

Cellulose consists of crystalline(結晶質) and amorphous(1.一定の形を持たない,無定形の,明確な形のない,非結晶の,不定形の,まとまりのない,無構造の,形の定まらない,2.アモルファス,非結晶質) regions. By treating it with strong acid, the amorphous(1.一定の形を持たない,無定形の,明確な形のない,非結晶の,不定形の,まとまりのない,無構造の,形の定まらない,2.アモルファス,非結晶質) regions can be broken up, thereby producing nanocrystalline cellulose(セルロース), a novel material with many desirable properties.[18] Recently, nanocrystalline cellulose(セルロース) was used as the filler phase in bio-based((No gloss)) polymer(重合体,高分子) matrices to produce nanocomposites with superior thermal and mechanical properties.[19]

Processing[edit]

Assay[edit]

Given a cellulose-containing(セルロース) material, the carbohydrate portion that does not dissolve in a 17.5% solution of sodium hydroxide at 20 °C is α cellulose(セルロース), which is true cellulose(セルロース)[clarification(1.浄化,2.説明,解明(making clear and intelligible)) needed]. Acidification of the extract precipitates(1.投げ落とす,凝結させる,早める,促進する,沈殿させる,真逆様に落とす,急がせる,2.沈澱物) β cellulose(セルロース). The portion that dissolves in base but does not precipitate(1.投げ落とす,凝結させる,早める,促進する,沈殿させる,真逆様に落とす,急がせる,2.沈澱物) with acid is γ cellulose(セルロース)[citation needed].

Cellulose can be assayed using a method described by Updegraff in 1969, where the fiber is dissolved in acetic(酸っぱい,酢の) and nitric acid to remove lignin, hemicellulose, and xylosans. The resulting cellulose(セルロース) is allowed to react with anthrone in sulfuric acid. The resulting coloured((No gloss)) compound is assayed spectrophotometrically at a wavelength of approximately 635 nm.

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

Biosynthesis[edit]

In vascular((No gloss)) plants cellulose(セルロース) is synthesized at the plasma(プラズマ,血漿,リンパ漿,乳漿,原形質) membrane by rosette terminal complexes (RTCs). The RTCs are hexameric protein structures, approximately 25 nm in diameter, that contain the cellulose(セルロース) synthase enzymes that synthesise the individual cellulose(セルロース) chains.[20] Each RTC floats in the cell's plasma(プラズマ,血漿,リンパ漿,乳漿,原形質) membrane and "spins" a microfibril into the cell wall.

RTCs contain at least three different cellulose(セルロース) synthases, encoded(符合化する) 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(セルロース) synthases use UDP-glucose to form the β(1→4)-linked cellulose.(セルロース)[22]

Cellulose synthesis requires chain initiation and elongation, and the two processes are separate. CesA glucosyltransferase initiates cellulose(セルロース) polymerization using a steroid((No gloss)) primer,(点火装置,活字,雷管,入門書,手引書) sitosterol-beta-glucoside, and UDP-glucose.[23] Cellulose synthase utilizes UDP-D-glucose precursors to elongate(長くする) the growing cellulose(セルロース) chain. A cellulase((No gloss)) may function to cleave the primer(点火装置,活字,雷管,入門書,手引書) from the mature chain.

Cellulose is also synthesised by animals, particularly in the tests of ascidians (where the cellulose(セルロース) was historically(歴史的に,歴史上) termed "tunicine") although it is also a minor component of mammalian((No gloss)) connective(【文法】連結詞) tissue.[24]

Breakdown (cellulolysis)[edit]

Cellulolysis is the process of breaking down cellulose(セルロース) into smaller polysaccharides called cellodextrins or completely into glucose units; this is a hydrolysis((No gloss)) reaction. Because cellulose(セルロース) molecules bind strongly to each other, cellulolysis is relatively difficult compared to the breakdown of other polysaccharides.[25] However, this process can be significantly(きわめて,意味深く,意味ありげに) intensified in a proper solvent, e.g. in an ionic liquid. [26] Most mammals have only very limited ability to digest dietary fibres such as cellulose.(セルロース) Some ruminants like cows and sheep contain certain symbiotic((No gloss)) anaerobic((No gloss)) bacteria (like Cellulomonas) in the flora of the rumen, and these bacteria produce enzymes called cellulases that help the microorganism((No gloss)) to break down cellulose;(セルロース) 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). Similarly, lower termites(白蟻) contain in their hindguts certain flagellate protozoa((No gloss)) which produce such enzymes; higher termites(白蟻) contain bacteria for the job. Some termites(白蟻) may also produce cellulase((No gloss)) of their own.[27] Fungi, which in nature are responsible for recycling of nutrients, are also able to break down cellulose.(セルロース)

The enzymes utilized to cleave the glycosidic linkage(関連,連関) in cellulose(セルロース) 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(多糖類) related to cellulose(セルロース) that comprises about 20% of the biomass of most plants. In contrast to cellulose,(セルロース) 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(セルロース) is unbranched.

Derivatives[edit]

The hydroxyl((No gloss)) groups (-OH) of cellulose(セルロース) can be partially or fully reacted with various reagents to afford derivatives with useful properties like mainly cellulose(セルロース) esters and cellulose(セルロース) ethers (-OR). In principle, though not always in current industrial practice, cellulosic polymers(重合体,高分子) 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(セルロース) acetate and cellulose(セルロース) 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(セルロイド).

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(セルロース) can be cross-linked to give the croscarmellose sodium (E468) for use as a disintegrant in pharmaceutical formulations.

Applications[edit]

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

A strand of cellulose (conformation Iα), showing the hydrogen bonds (dashed) within and between cellulose molecules.
  • Biofuel: TU-103, a strain of Clostridium bacteria found in zebra waste, can convert nearly any form of cellulose into butanol fuel.[32][33]
  • 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.[34] 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.
  • 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.

References[edit]

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External links[edit]