Cellulose fiber


Cellulose fibers are fibers made with ethers or esters 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 and lignin, 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, 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 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 Company in 1924. Hermann Staudinger determined the polymer structure of cellulose in 1920. The compound was first chemically synthesized 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 fibers look like the soft fluffy cotton balls that they come from. Linen fibers look like the strong fibrous strands of the flax 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, separating from chaff, 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 and then extruded in the same ways that synthetic fibers like polyester or nylon are made. Rayon or 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 are cellulose, hemicellulose, lignin, pectin and 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, a core fiber, or a leaf fiber.

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, aramid fiber, and carbon fiber.
FiberDensity Elongation Tensile strength Young's modulus
Cotton1.5–1.63.0–10.0287–5975.5–12.6
Jute1.3–1.461.5–1.8393–80010–30
Flax1.4–1.51.2–3.2345–150027.6–80
Hemp1.481.6550–90070
Ramie1.52.0–3.8220–93844–128
Sisal1.33–1.52.0–14400–7009.0–38.0
Coir1.215.0–30.0175–2204.0–6.0
Softwood kraft1.5–100040.0
E–glass2.52.5–3.02000–350070.0
S–glass2.52.8457086.0
Aramid1.43.3–3.73000–315063.0–67.0
Carbon1.41.4–1.84000230.0–240.0

Applications

Composite materials

MatrixFiber
EpoxyAbaca, bamboo, jute
Natural rubberCoir, sisal
Nitrile rubberJute
Phenol-formaldehydeJute
PolyethyleneKenaf, pineapple, sisal, wood fiber
PolypropyleneFlax, jute, kenaf, sunhemp, wheat straw, wood fiber
PolystyreneWood
PolyurethaneWood
Polyvinyl chlorideWood
PolyesterBanana, jute, pineapple, sunhemp
Styrene-butadieneJute
RubberOil palm

Composite materials are a class of material most often made by the combination of a fiber with a binder material. 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, cellulose fibers are used to create some fiber-reinforced materials such as biocomposites and fiber-reinforced plastics. 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:
In the textile industry regenerated cellulose is used as fibers such as rayon,. Cellulose fibers are manufactured from dissolving pulp. 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 acetates.
The first artificial fiber, known as artificial silk, became known as viscose around 1894, and finally rayon in 1924. A similar product known as cellulose acetate was discovered in 1865. Rayon and acetate are both artificial fibers, but not truly synthetic, being made from wood. 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:
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 plants, but instead a highly processed bamboo pulp that is extruded as fibers. Although the process is not as environmentally friendly 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.