Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
fibers () are fibers made with
ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...
s or
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
s of cellulose, which can be obtained from the bark, wood or leaves of plants, or from other plant-based material. In addition to cellulose, the fibers may also contain
hemicellulose
A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all terrestrial plant cell walls.Scheller HV, Ulvskov Hemicelluloses.// Annu Rev ...
and
lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
, with different percentages of these components altering the mechanical properties of the fibers.
The main applications of cellulose fibers are in the textile industry, as chemical filters, and as fiber-reinforcement composites, due to their similar properties to engineered fibers, being another option for biocomposites and polymer composites.
History
Cellulose was discovered in 1838 by the French chemist
Anselme Payen
Anselme Payen (; 6 January 1795 – 12 May 1871) was a French chemist known for discovering the enzyme diastase, and the carbohydrate cellulose.
Biography
Payen was born in Paris. He began studying science with his father when he was a 13-yea ...
, 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. Production of rayon ("artificial silk") from cellulose began in the 1890s, and cellophane was invented in 1912. In 1893, Arthur D. Little of Boston, invented yet another cellulosic product, acetate, and developed it as a film. The first commercial textile uses for acetate in fiber form were developed by the
Celanese
Celanese Corporation, formerly known as Hoechst Celanese, is an American technology and specialty materials company headquartered in Irving, Texas. A Fortune 500 corporation, the company is the world’s leading producer of acetic acid, prod ...
Company in 1924.
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.
Cellulose structure
Cellulose is a polymer made of repeating glucose molecules attached end to end. A cellulose molecule may be from several hundred to over 10,000 glucose units long. Cellulose is similar in form to complex carbohydrates like starch and glycogen. These polysaccharides are also made from multiple subunits of glucose. The difference between cellulose and other complex carbohydrate molecules is how the glucose molecules are linked together. In addition, cellulose is a straight chain polymer, and each cellulose molecule is long and rod-like. This differs from starch, which is a coiled molecule. A result of these differences in structure is that, compared to starch and other carbohydrates, cellulose cannot be broken down into its glucose subunits by any enzymes produced by animals.
Types
Natural cellulose fibers
Natural cellulose fibers are still recognizable as being from a part of the original plant because they are only processed as much as needed to clean the fibers for use. For example,
cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...
fibers look like the soft fluffy cotton balls that they come from.
Linen
Linen () is a textile made from the fibers of the flax plant.
Linen is very strong, absorbent, and dries faster than cotton. Because of these properties, linen is comfortable to wear in hot weather and is valued for use in garments. It also ...
fibers look like the strong fibrous strands of the
flax
Flax, also known as common flax or linseed, is a flowering plant, ''Linum usitatissimum'', in the family Linaceae. It is cultivated as a food and fiber crop in regions of the world with temperate climates. Textiles made from flax are known in ...
plant. All "natural" fibers go through a process where they are separated from the parts of the plant that are not used for the end product, usually through
harvesting
Harvesting is the process of gathering a ripe crop from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper. On smaller farms with minimal mechanization, harvesting is the most labor- ...
, separating from
chaff
Chaff (; ) is the dry, scaly protective casing of the seeds of cereal grains or similar fine, dry, scaly plant material (such as scaly parts of flowers or finely chopped straw). Chaff is indigestible by humans, but livestock can eat it. In agri ...
,
scouring, etc. The presence of linear chains of thousands of glucose units linked together allows a great deal of hydrogen bonding between OH groups on adjacent chains, causing them to pack closely into cellulose fibers. As a result, cellulose exhibits little interaction with water or any other solvent. Cotton and wood, for example, are completely insoluble in water and have considerable mechanical strength. Since cellulose does not have a helical structure like amylose, it does not bind to iodine to form a colored product.
Manufactured cellulose fibers
Manufactured cellulose fibers come from plants that are processed into a
pulp
Pulp may refer to:
* Pulp (fruit), the inner flesh of fruit
Engineering
* Dissolving pulp, highly purified cellulose used in fibre and film manufacture
* Pulp (paper), the fibrous material used to make paper
* Molded pulp, a packaging material
...
and then extruded in the same ways that synthetic fibers like
polyester
Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
or
nylon
Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic.
Nylon is a silk-like thermoplastic, generally made from petro ...
are made.
Rayon
Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose f ...
or
viscose
Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose ...
is one of the most common "manufactured" cellulose fibers, and it can be made from wood pulp.
Structure and properties
Natural fibers are composed by microfibrils of cellulose in a matrix of hemicellulose and lignin. This type of structure and the chemical composition of them is responsible for the mechanical properties that can be observed. Because the natural fibers make hydrogen bonds between the long chains, they have the necessary stiffness and strength.
Chemical composition
The major constituents of natural fibers (
lignocellulose
Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose a ...
s) are cellulose,
hemicellulose
A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all terrestrial plant cell walls.Scheller HV, Ulvskov Hemicelluloses.// Annu Rev ...
,
lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
,
pectin
Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component of ...
and
ash
Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...
. The percentage of each component varies for each different type of fiber, however, generally, are around 60-80% cellulose, 5–20% lignin, and 20% of moisture, besides hemicellulose and a small percent of residual chemical components. The properties of the fiber change depending on the amount of each component, since the hemicellulose is responsible for the moisture absorption, bio- and thermal degradation whereas lignin ensures thermal stability but is responsible for the UV degradation. The chemical composition of commons natural fibers are shown below, and can change if the fibers are a
bast fiber
Bast fibre (also called phloem fibre or skin fibre) is plant fibre collected from the phloem (the "inner bark", sometimes called "skin") or bast surrounding the stem of certain dicotyledonous plants. It supports the conductive cells of the phlo ...
(obtained from the bark), a core fiber (obtained from the wood), or a leaf fiber (obtained from the leaves).
Mechanical properties
Cellulose fiber response to
mechanical stresses change depending on fiber type and chemical structure present. Information about main mechanical properties are shown in the chart below and can be compared to properties of commonly used fibers such
glass fiber
Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass.
Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...
,
aramid fiber
Aramid fibers, short for aromatic polyamide, are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic-rated body armor fabric and ballistic composites, in marine cordage, mar ...
, and
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
.
Surface and interfacial properties
Hydrophilicity, roughness and surface charge determine the interaction of cellulose fibers with an aqueous environment. Already in 1950, the charge at the interface between cotton as the predominant cellulose fiber and an aqueous surrounding was investigated by the
streaming potential
Streaming media is multimedia that is delivered and consumed in a continuous manner from a source, with little or no intermediate storage in network elements. ''Streaming'' refers to the delivery method of content, rather than the content it ...
method to assess the surface
zeta potential
Zeta potential is the electrical potential at the slipping plane. This plane is the interface which separates mobile fluid from fluid that remains attached to the surface.
Zeta potential is a scientific term for electrokinetic potential in coll ...
. Due to the high swelling propensity of lignocellulosic fibers, a correlation between the zeta potential and the water uptake capability has been observed. Even for the use of waste fibers as a reinforcement in composite materials, sized fibers have been probed by an aqueous test solution. A review on the electrokinetic properties of natural fibers including cellulose and lignocellulosic fibers is found in the Handbook of Natural Fibers.
Applications
Composite materials
Composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
s are a class of material most often made by the combination of a fiber with a
binder material (matrix). This combination mixes the properties of the fiber with the matrix to create a new material that may be stronger than the fiber alone. When combined with
polymers
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...
, cellulose fibers are used to create some fiber-reinforced materials such as
biocomposite
A biocomposite is a composite material formed by a matrix (resin) and a reinforcement of natural fibers.
Environmental concern and cost of synthetic fibres have led the foundation of using natural fibre as reinforcement in polymeric composites. ...
s and
fiber-reinforced plastic
Fibre-reinforced plastic (FRP; also called fibre-reinforced polymer, or in American English ''fiber'') is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass (in fibreglass), carbon (in carbon-fib ...
s. The table displays different polymer matrices and the cellulose fibers they are often mixed with.
Since macroscopic characteristics of fibers influence the behavior of the resulting composite, the following physical and mechanical properties are of particular interest:
*Dimensions: The relationship between the length and diameter of the fibers is a determining factor in the transfer of efforts to the matrix. Additionally, the irregular cross-section and fibrillated appearance of plant fibers helps anchor them within a fragile matrix.
*Void volume and water absorption: Fibers are fairly porous with a large volume of internal voids. As a result, when the fibers are immersed in the binding material, they absorb a large amount of matrix. High absorption can cause fiber shrinkage and matrix swelling. However, a high void volume contributes to reduced weight, increased acoustic absorption, and low thermal conductivity of the final composite material.
*
Tensile strength
Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
: Similar, on average, to the polypropylene's fibers.
*
Elastic modulus
An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is ...
: Cellulosic fibers have a low modulus of elasticity. This determines its use in building components working in post-cracked stage, with high energy absorption and resistance to dynamic forces.
Textile
In the textile industry
regenerated cellulose
Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose ...
is used as
fiber
Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...
s such as
rayon
Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose f ...
, (including
modal, and the more recently developed
Lyocell
Lyocell, originally trademarked in 1982 as Tencel, is a form of regenerated cellulose. It consists of cellulose fibers, made by dissolving pulp and then reconstituting it by dry jet-wet spinning. The fiber is used to make textiles for clothing a ...
). Cellulose fibers are manufactured from
dissolving pulp Dissolving pulp, also called dissolving cellulose, is bleached wood pulp or cotton linters that has a high cellulose content (> 90%). It has special properties including a high level of brightness and uniform molecular-weight distribution. This pul ...
.
Cellulose-based fibers are of two types, regenerated or pure cellulose such as from the cupro-ammonium process and modified cellulose such as the
cellulose acetate
In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and ...
s.
The first artificial fiber, commercially promoted as
artificial silk Artificial silk or art silk is any synthetic fiber which resembles silk, but typically costs less to produce. Frequently, "artificial silk" is just a synonym for rayon. When made out of bamboo viscose it is also sometimes called bamboo silk.
Th ...
, became known as
viscose
Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose ...
around 1894, and finally
rayon
Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose f ...
in 1924. A similar product known as
cellulose acetate
In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and ...
was discovered in 1865. Rayon and acetate are both artificial fibers, but not fully
synthetic , being a product of a chemically digested
feedstock
A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials that are feedstock for future finished products. As feedst ...
comprising natural
wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
. They are also not an artificial construction of silk, which is a fibrous polymer of animal
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s. Although these artificial fibers were discovered in the mid-nineteenth century, successful modern manufacture began much later.
Filtration
The cellulose fibers infiltration/filter aid applications can provide a protective layer to filter elements as powdered cellulose, besides promoting improved throughput and clarity. As ashless and non-abrasive filtration, make cleanup effortless after the filtering process without damage in pumps or valves. They effectively filter metallic impurities and absorb up to 100% of emulsified oil and boiler condensates. In general, cellulose fibers in filtration applications can greatly improve filtration performance when used as a primary or remedial precoat in the following ways:
* Bridging gaps in the filter septum and small mechanical leaks in the gaskets and leaf seats
* Improving the stability of the filter-aid cake to make it more resistant to pressure bumps and interruptions
* Creating a more uniform precoat with no cracks for more effective filtration surface area
* Improving cake release and reducing cleaning requirements
* Preventing fine particulate bleed-through
* Precoating easily and rapidly and reducing soluble contamination
Comparison with other fibers
In comparison with engineered fibers, cellulose fibers have important advantages as low density, low cost, they can be recyclable, and are biodegradable.
Due to its advantages cellulose fibers can be used as a substituent for glass fibers in composites materials.
Environmental issues
What is often marketed as
"bamboo fiber" is actually not the fibers that grow in their natural form from the
bamboo
Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, bu ...
plants, but instead a highly processed bamboo pulp that is extruded as fibers.
Although the process is not as
environmentally friendly
Environment friendly processes, or environmental-friendly processes (also referred to as eco-friendly, nature-friendly, and green), are sustainability and marketing terms referring to goods and services, laws, guidelines and policies that clai ...
as "bamboo fiber" appears, planting & harvesting bamboo for fiber can, in certain cases, be more sustainable and environmentally friendly than harvesting slower growing trees and clearing existing forest habitats for timber plantations.
See also
*
Fiber modification
Fibre modification is a research field in which researchers aim at developing and applying technologies to impart new properties to natural fibres such as those in paper, in order to increase their functionality. Research areas in this field includ ...
References
External links
Dissolving of Cellulosics
{{Authority control
Cellulose
Fibers
Materials
Textiles