Everything about Cellulose totally explained
Cellulose is an
organic compound with the
formula, a
polysaccharide consisting of a linear chain of several hundred to over nine thousand β(1→4) linked
D-
glucose units.
Cellulose is the 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.
Cellulose is the most common organic compound on Earth. About 33 percent of all plant matter is cellulose (the cellulose content of
cotton is 90 percent and that of wood is 50 percent).
For industrial use, cellulose is mainly obtained from
wood pulp and
cotton. It is mainly used to produce
cardboard and
paper; to a smaller extent it's converted into a wide variety of derivative products such as
cellophane and
rayon.
Some animals, particularly
ruminants and
termites, can
digest cellulose with the help of
symbiotic micro-organisms that live in their guts. Cellulose isn't digestible by
humans and is often referred to as '
dietary fiber' or 'roughage', acting as a
hydrophilic bulking agent for
feces.
History
Cellulose was discovered in 1838 by the French chemist
Anselme Payen, who isolated it from plant matter and determined its chemical formula. Cellulose was used to produce the first successful
thermoplastic polymer,
celluloid, by Hyatt Manufacturing Company in 1870.
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.
Commercial products
Cellulose is the major constituent of paper and cardboard and of textiles made from
cotton,
linen, and other plant fibers.
Cellulose can be converted into
cellophane, a thin transparent film, and into
rayon, an important fiber that has been used for textiles since the beginning of the 20th century. Both cellophane and rayon are known as "regenerated cellulose fibers"; they're identical to cellulose in chemical structure and are usually made from
viscose, a
viscous solution made from cellulose. A more recent and environmentally friendly method to produce rayon is the
Lyocell process.
Cellulose is used in the laboratory as the stationary phase for
thin layer chromatography. It is the raw material in the manufacture of
nitrocellulose (cellulose nitrate) which was historically used in
smokeless gunpowder and as the base material for
celluloid used for photographic and movie films until the mid 1930s.
Cellulose insulation made from recycled newsprint is becoming popular as an environmentally preferable material for
building insulation.
Cellulose is used to make
hydrophilic and highly absorbent sponges, as well as water-soluble
adhesives and
binders such as
methyl cellulose and
carboxymethyl cellulose which are used in
wallpaper paste.
Microcrystalline cellulose (
E460i) and powdered cellulose (E460ii) are used as inactive fillers in tablets and as thickeners and stabilizers in processed foods.
Cellulose source and energy crops
The major
combustible component of non-food
energy crops is cellulose, with
lignin second. Non-food energy crops are more
sustainable than edible energy crops (which have a large
starch component), but still compete with food crops for agricultural land and water resources. Typical non-food energy crops include
industrial hemp,
switchgrass,
Miscanthus,
Salix (
willow), and
Populus (
poplar) species.
Some bacteria can convert cellulose into
ethanol which can then be used as a fuel; see
cellulosic ethanol.
Structure and properties
Cellulose has no taste, is odorless, is
hydrophilic, is insoluble in
water and most organic
solvents, is
chiral and is biodegradable.
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 occurs, and the molecule adopts an extended and rather stiff rod-like conformation. The multiple
hydroxyl groups on the glucose residues from one chain form
hydrogen bonds with oxygen molecules on another chain, holding the chains firmly together side-by-side and forming
microfibrils with high
tensile strength. This strength is important in cell walls, where they're meshed into a carbohydrate
matrix, conferring rigidity to plant cells.
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.
Chemically, cellulose can be broken down into its glucose units by treating it with concentrated acids at high temperature.
Many properties of cellulose depend on its
degree of polymerization or chain length, 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 celluloses have chain lengths ranging from 800 to 10,000 units. Each RTC floats in the cell's plasma membrane and "spins" a microfibril into the cell wall.
The RTC's contain at least three different cellulose synthases, encoded by
CesA genes, in an unknown
stoichiometry. Separate sets of
CesA genes are involved in primary and secondary
cell wall biosynthesis.
Cellulose synthase utilizes
UDP-D-glucose precursors to generate microcrystalline cellulose. Cellulose synthesis requires chain initiation and elongation, and the two processes are separate.
CesA glucosyltransferase initiates cellulose polymerization using a
steroid primer, 'sitosterol-beta-glucoside' and UDP-glucose. A
cellulase may function to cleave the primer from the mature chain.
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 break down of other polysaccharides.
Mammals don't have the ability to break down cellulose directly. Some
ruminants like cows and sheep contain certain
symbiotic anaerobic bacteria (like
Cellulomonas) in the flora of the gut wall, and these bacteria produce
enzymes to break down cellulose; the break down products are then used by the mammal. Similarly, lower
termites contain in their
hindguts certain
flagellate protozoa which produce such enzymes; higher termites contain bacteria for the job.
Fungi, which in nature are responsible for recycling of nutrients, are also able to break down cellulose.
The enzymes utilized to 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 cellulose binding modules; these complexes are in some cases referred to as
cellulosomes.
Hemicellulose
Hemicellulose is a polysaccharide related to cellulose that comprises ca. 20% of the biomass of most plants. In contrast to cellulose, hemicellulose is derived from several sugars in addition to glucose, including especially
xylose but also
mannose,
galactose,
rhamnose, and
arabinose. Hemicellulose consists of shorter chains - around 200 sugar units as opposed to 7,000 - 15,000 glucose molecules in the average cellulose polymer. Furthermore, hemicellulose is branched, whereas cellulose is unbranched.
Derivatives
The
hydroxyl groups of cellulose can be partially or fully reacted with various
reagents to afford derivatives with useful properties. Cellulose
esters and cellulose
ethers are the most important commercial materials. In principle, though not always in current industrial practice, cellulosic polymers are renewable resources.
Among the esters are
cellulose acetate and
cellulose triacetate, which are film- and fiber-forming materials that find a variety of uses. The inorganic ester
nitrocellulose was initially used as an explosive and was an early film forming material.
Ether derivatives include
Further Information
Get more info on 'Cellulose'.
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