CELLULOSE FIBERS

Cellulose fibers (/ˈsɛl.jəˌloʊsˈfaɪ.bər/) are fibers made with ether or esters of cellulose, which can be obtained from the bark, wood or leaves of plants, or from a plant-based material. Besides cellulose, these fibers are compound of hemicellulose and lignin, and different percentages of these components are responsible for different mechanical properties observed.

The main applications of cellulose fibers are in textile industry, as chemical filter, and fiber-reinforcement composite, 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 ("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 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 chains linked by hydrogen bonds

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 Celullose Fibers

Natural cellulose fibers are fibers that 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 Fiber

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 compose 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 (lignocelluloses) are cellulose, hemicellulose, lignin, pectin and ash. The percentage of each component varies for each different type of fiber, however, generally, are present around 60-80% cellulose, 5–20% lignin, and until 20% of moisture, besides hemicellulose and a small percent of residual chemical components. The amount of these components affect directly the properties of the fiber, 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 showed below and can change if the fibers are a bast fiber (obtained from the bark), a core fiber (obtained from the wood), or a leaf fiber (obtained from the leaves).

Type of fiber		Cellulose (%)	Lignin(%)	Hemicellulose (%)	Pectin (%)	Ash (%)
Bast fiber	Fiber flax	71	2.2	18.6 – 20.6	2.3	–
	Seed flax	43–47	21–23	24–26	–	5
	Kenaf	31–57	15–19	21.5–23	–	2–5
	Jute	45–71.5	12–26	13.6–21	0.2	0.5–2
	Hemp	57–77	3.7–13	14–22.4	0.9	0.8
	Ramie	68.6–91	0.6–0.7	5–16.7	1.9	–
Core fiber	Kenaf	37–49	15–21	18–24	–	2–4
	Jute	41–48	21–24	18–22	–	0.8
Leaf fiber	Abaca	56–63	7–9	15–17	–	3
	Sisal	47–78	7–11	10–24	10	0.6–1
	Henequen	77.6	13.1	4–8	–	–

Mechanical Properties

Cellulose fiber response to mechanical stresses change depending of 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.

Fiber	Density (g/cm³)	Elongation (%)	Tensile strength (MPa)	Young’s modulus (GPa)
Cotton	1.5–1.6	3.0–10.0	287–597	5.5–12.6
Jute	1.3–1.46	1.5–1.8	393–800	10–30
Flax	1.4–1.5	1.2–3.2	345–1500	27.6–80
Hemp	1.48	1.6	550–900	70
Ramie	1.5	2.0–3.8	220–938	44–128
Sisal	1.33–1.5	2.0–14	400–700	9.0–38.0
Coir	1.2	15.0–30.0	175–220	4.0–6.0
Softwood kraft	1.5	–	1000	40.0
E–glass	2.5	2.5–3.0	2000–3500	70.0
S–glass	2.5	2.8	4570	86.0
Aramid	1.4	3.3–3.7	3000–3150	63.0–67.0
Carbon	1.4	1.4–1.8	4000	230.0–240.00

Applications
Composite Materials

Matrix	Fiber
Epoxy	Abaca, Bamboo, Jute
Natural Rubber	Coir, Sisal
Nitrile Rubber	Jute
Phenol-formaldehyde	Jute
Polyethylene	Kenaf, pineapple, Sisal, Wood fiber
Polypropylene	Flax, Jute, Kenaf, Sunhemp, Wheat Straw, Wood fiber
Polystyrene	Wood
Polyurethane	Wood
Polyvinyl chloride	Wood
Polyester	Banana, Jute, Pinneapple, Sunhemp
Styrene-butadiene	Jute
Rubber	Oil palm

Composite materials are a class of material, made usually by the combination of a matrix and a fiber. This combination mix the ductility of the matrix with the high strength of the fiber, and create a stronger material. Recently, cellulose fibers began to be used as a fiber-reinforcement material, especially in conjunction with polymers (as can be observed in the table) in biocomposites and fibre-reinforced plastic. As macroscopic characteristics of major interest in fibers are those related behavior the resulting composites. So, usually interest as following physical and mechanical properties of cellulosic fibers:

• Dimensions: The relationship between length and diameter of the fibers is a determining factor in the transfer of efforts to matrix. Another interesting point is the irregular cross section of plant fibers as well as their appearance fibrillated, which exert a positive influence on the anchoring of the fibers with the fragile matrix.
• Void volume and water absorption: Because of the large volume percentage of permeable voids, the absorption is very high within the first moments of immersion. As a direct consequence, comes interference negative in relation water - binder matrix, swelling and subsequent shrinkage of the fiber. Furthermore, the high void volume contributes to reduced weight, increased acoustic absorption and low thermal conductivity the obtained components.
• Tensile strength: Similar, on average, the polypropylene’s fibers.
• Elastic Modulus: Cellulosic fibers are classified as low modulus determining factor for 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 is used as fibers such as rayon, (including modal, and the more recently developed Lyocell). 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 in filtration/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 others 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 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 is much more sustainable and environmentally friendly than harvesting more slow growing trees and clearing existing forest habitats for timber plantations.

References

1. ^ "Cellulose Fiber - definition of cellulose fiber in the Free Online Enciclopedy. The Free Online Dictionary. Retrieved December 7, 2014.
2. ^ Xue, L. G.; Tabil, L.; Panigrahi, S. (2007). "Chemical Treatments of Natural Fiber for Use in Natural Fiber-Reinforced Composites: A Review". Journal of Polymers and the Environment 15 (1): 25–33. doi: 10.1007/s10924-006-0042-3.
3. ^ Saheb, D. N.; Jog, J. P. (1991). "Natural fiber polymer composites: A review". Advances in Polymer Technology 18 (4): 351–363. doi:10.1002/(SICI)1098-2329(199924)18:4.
4. ^ Mohanty, A. K.; Misra, M.; Hinrichsen, G. (2000). "Biofibres, biodegradable polymers and biocomposites: An overview". Macromolecular Materials and Engineering. 276-277 (1): 1–24. doi: 0.1002/(SICI)1439-2054(20000301)276:1<1::AID-MAME1>3.0.CO;2-W.

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