A-level Applied Science/Colour Chemistry/Fibres/Cellulose

Cellulose


Cellulose(C6H10O5)n is a long-chain polymeric polysaccharide carbohydrate, of beta-glucose. It forms the primary structural component of green plants. The primary cell wall of green plants is made primarily of cellulose.

History and applications
Cellulose is found in all plant material. It is the most abundant form of living terrestrial biomass.

Cellulose is the major constituent of paper; further processing can be performed to make cellophane]] and rayon, and more recently Modal, a textile derived from beechwood cellulose. Viscose is a very important fibre made out of cellulose and has been used for textiles since the beginning of the 20th century.

Chemistry
Cellulose monomers (β-glucose) are linked together through ß1→4 glycosidic bonds by condensation. This is in contrast to the α 1->4 glycosidic bonds present in other carbohydrates like starch.

Cellulose is a straight chain polymer: unlike starch, no coiling occurs, and the molecule adopts an extended rod-like conformation. In microfibrils, the multiple hydroxyl (OH-) groups on the glucose residues hydrogen bond with each other, holding the chains firmly together and contributing to their high tensile strength. This strength is important in cell walls, where they are meshed into a carbohydrate matrix, helping keep plant cells rigid.

Derivatives
The hydroxyl groups of cellulose can be partially or fully reacted with various chemicals to provide derivates 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 triacetate, which are film- and fibre-forming materials that find a variety of uses.

Cotton


Cotton is a soft fibre that grows around the seeds of the cotton plant (Gossypium spp.), a shrub native to the tropical and subtropical regions. The fibre is most often spun into thread and used to make a soft, breathable textile, which is the most widely used natural-fibre cloth in clothing today.

Cotton fibre (once processed to remove seeds and traces of wax, protein, etc.) consists of nearly pure cellulose, a natural polymer. The cellulose is arranged in a way that gives cotton fibres a high degree of strength, durability, and absorbency. Each fibre is made up of twenty to thirty layers of cellulose coiled in a neat series of natural springs. When the cotton boll (seed case) is opened the fibres dry into flat, twisted, ribbon-like shapes and become kinked together and interlocked. This interlocked form is ideal for spinning into a fine yarn.

Uses of cotton
Cotton is used to make a number of textile products. These include terrycloth, used to make highly absorbent bath towels and robes, denim, used to make blue jeans, chambray, popularly used in the manufacture of blue work shirts (from which we get the term "blue-collar"), along with corduroy, seersucker, and cotton twill. Socks, underwear, and most T-shirts are made from cotton. Bed sheets are also often made from cotton. Cotton is also used to make yarn used in crochet and knitting. While many fabrics are made completely of cotton, some materials blend cotton with synthetic or processed fibres such as polyester or rayon. In addition to the textile industry, cotton is used in fishnets, coffee filters, tents and in bookbinding. The first Chinese paper was made of cotton fibre, as is the modern US dollar bill and federal stationery. Fire hoses were once made of cotton.

Mercerisation is a treatment for cotton fabric and thread mostly employed to give cotton a lustrous appearance. The series of processes was devised by John Mercer in the middle of the 19th century.

Mercerised cotton is sometimes referred to in the crafts as pearl or pearle cotton. It is cotton yarn or fabric which has been put through a series of processes, primarily to increase lustre. The added desirable water handling properties gained are a secondary bonus.

Cotton thread (or cotton-covered thread with a polyester core) is treated with sodium hydroxide (caustic soda, NaOH). The thread is given a caustic soda bath that is then neutralised with an acid bath. This treatment increases strength, lustre, affinity to dye and resistance to mildew, and also reduces lint. Long staple fibre lengths respond best to mercerisation.

References and further reading

 * The Thames and Hudson Manual of Dyes and Fabrics, Joyce Storey, 1978

History and uses of cotton

 * Cotton's journey - Educational website
 * Glossary of cotton terms
 * Naturally coloured cotton

Research

 * ACSA International Cotton Institute
 * U.S. Department of Agriculture
 * UNCTAD Information on Cotton

Rayon
Rayon is a manufactured regenerated cellulosic fibre.



History of rayon
Rayon was the first fibre to be manufactured; it is produced from naturally occurring polymers and therefore it is not a synthetic fibre, but a manufactured regenerated cellulosic fibre. The fibre was sold as artificial silk until the name "rayon" was adopted in 1924. In Europe it is known as "viscose".

Major fibre properties of rayon
Rayon is a very versatile fibre and has the same comfort properties as other natural fibres and can imitate the feel and texture of silk, wool, cotton and linen. The fibres are easily dyed in a wide range of colours. Rayon fabrics are soft, smooth, cool, comfortable, and highly absorbent, but do not insulate body heat making them ideal for use in hot and humid climates. The durability and appearance retention of regular rayon are low, especially when wet; also rayon has the lowest elastic recovery of any fibre. However, HWM rayon is much stronger and exhibits higher durability and appearance retention. Recommended care for regular rayon is dry-cleaning only, HWM Rayon can also be machine washed.

Producers of rayon
Trade names are used within the rayon industry to determine the type of rayon used.

Bemberg, for example, is a trade name for cuprammonium rayon that is only produced in Italy due to EPA regulations in the US.

MODAL is a widely used form of rayon produced by Lenzing Fibres Corp. which is based out of northern Austria.

Galaxy, Danufil, and Viloft are rayon brands produced by Kelheim Fibres, a German manufacturer.

Acordis is a major manufacturer of cellulose based fibres and yarns. Production facilities can be found throughout Europe, the U.S. and Brazil.

Visil rayon is a flame retardant form of viscose which has silica built into the content of the fibre during manufacturing.

Uses of rayon
Some major Rayon fibre uses include apparel (e.g. blouses, dresses, jackets, lingerie, linings, suits, ties), furnishings (e.g. bedspreads, blankets, window treatments, upholstery, slipcovers), industrial uses (e.g. medical surgery products, non-woven products, tire cord), and other uses (e.g. feminine hygiene products).

Viscose
Cellulose fibres from wood, cotton or hemp are dissolved in alkali to make a solution called viscose. Viscose used in Europe as the name of the fibre rayon.

Cellophane is a thin, transparent sheet made of processed cellulose. It is made when viscose solution is extruded through a slit into an acid bath to reconvert the viscose into cellulose. A similar process, using a hole instead of a slit (a spinneret), is used to make a fibre called rayon.

Cellophane
See Viscose

Modal
See Rayon

Triacetate
Triacetate also known as 'cellulose triacetate', is manufactured from cellulose and acetate. Triacetate is typically used for the creation of fibres and film base. It is similar chemically to cellulose acetate, with the distinguishing characteristics being that in triacetate, according to the Federal Trade Commission definition, at least "92 percent of the hydroxyl groups are acetylated". During the manufacture of triacetate the cellulose is completely acetylated whereas in regular cellulose acetate or cellulose diacetate, it is only partially acetylated. Triacetate is significantly more heat resistant than cellulose acetate.

Production of triacetate
Triacetate is derived from cellulose by combining cellulose with acetate from acetic acid and acetic anhydride. The cellulose acetate is dissolved in a mixture of dichloromethane and methanol for spinning. As the filaments emerge from a spinneret, the solvent is evaporated in warm air, in a process known as dry spinning, leaving a fibre of almost pure triacetate.

A finishing process called S-Finishing or surface saponification is sometimes applied to acetate and triacetate fabrics using a sodium hydroxide solution. This removes part or all of the acetyl groups from the surface of the fibres leaving them with a cellulose coating. This reduces the tendency for the fibres to acquire static.

Chemistry
CAS number 9012-09-3

Characteristics

 * Shrink resistant
 * Wrinkle resistant
 * Easily washable
 * Generally washable at high temperatures
 * Maintains creases and pleats well

Usage Scenarios
Particularly effective in clothing where crease or pleat rentention is important, such as skirts and dresses

General Care Tips
Always refer to individual garment care labels


 * Ironable up to 200 °C
 * Pleated garments are best hand laundered. Most other garments containing 100% triacetate can be machine washed and dried
 * Articles containing triacetate fibres require very little special care due mainly to the fibre's resistance to high temperatures

Cellulose acetate
Cellulose acetate is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, and as a component in some adhesives; it is also used as a synthetic fibre.

Acetate Fibre and Triacetate Fibre
Acetate and Triacetate are mistakenly referred to as the same fibre, although they are similar, their chemical compounds differ. Triacetate is known as a generic description or primary acetate containing no hydroxyl group. Acetate fibre is known as modified or secondary acetate having a few hydroxyl groups. Triacetate fibres, although no longer produced in the United States, contain a higher ratio of acetate-to-cellulose than do acetate fibres[1].

Fibre
Cellulose acetate or acetate rayon fibre (1924) is one of the earliest synthetic fibres and is based on cotton or tree pulp cellulose ("biopolymers"). These "cellulosic fibres" have passed their peak as cheap petro-based fibres (nylon and polyester) and have displaced regenerated pulp fibres.

Fibre Properties
Acetate is a very valuable manufactured fibre that is low in cost and has good draping qualities. Properties of acetate have promoted it as the “beauty fibre”[1]. Acetate is used in fabrics such as satins, brocades, and taffetas to accentuate luster, body, drape and beauty.
 * Hand: soft, smooth, dry, crisp, resilient
 * Comfort: breathes, wicks, dries quickly, no static cling
 * Drape: linings move with the body linings conform to the garment
 * Colour: deep brilliant shades with atmospheric dyeing meet colourfastness requirements
 * Luster: light reflection creates a signature appearance
 * Performance: colourfast to perspiration staining, colourfast to dry cleaning, air and vapor permeable
 * Tenacity: weak fibre with breaking tenacity of 1.2 to 1.4 g/d; loses strength when wet
 * Environmentally friendly: made from wood pulp of reforested trees
 * Abrasion: poor resistance
 * Heat retention: poor thermal retention; no allergenic potential (hypoallergenic)
 * Dyeability: (two methods) cross-dying method where yarns of one fibre and those of another fibre are woven into a fabric in a desired pattern; solution-dying method provides excellent colour fastness under the effects of sunlight, perspiration, air contaminants and washing [1,2]

Acetate usually requires dry cleaning.

Production
The Federal Trade Commission definition for acetate fibre is "A manufactured fibre in which the fibre-forming substance is cellulose acetate. Where not less than 92 percent of the hydroxyl groups are acetylated, the term triacetate may be used as a generic description of the fibre."

Acetate is derived from cellulose by deconstructing wood pulp into a purified fluffy white cellulose. The cellulose is then reacted with acetic acid and acetic anhydride in the presence of sulfuric acid. It is then put through a controlled, partial hydrolysis to remove the sulfate and a sufficient number of acetate groups to give the product the desired properties. The anhydroglucose unit is the fundamental repeating structure of cellulose and has three hydroxyl groups which can react to form acetate esters. The most common form of cellulose acetate fibre has an acetate group on approximately two of every three hydroxyls. This cellulose diacetate is known as secondary acetate, or simply as "acetate".

After it is formed, cellulose acetate is dissolved in acetone into a viscose resin for extrusion through spinnerets (which resemble a shower head). As the filaments emerge, the solvent is evaporated in warm air via dry spinning, producing fine cellulose acetate fibres.

First U.S. Commercial Acetate Fibre Production: 1924, Celanese Corporation

Current U.S. Acetate Fibre Producers: Celanese Acetate, Eastman Chemical Company

Production Method

 * 1) Purified cellulose from wood pulp or cotton linters
 * 2) Mixed with glacial acetic acid, acetic anhydride, and a catalyst
 * 3) Aged 20 hours- partial hydrolysis occurs
 * 4) Precipitated as acid-resin flakes
 * 5) Flakes dissolved in acetone
 * 6) Solution is filtered
 * 7) Spinning solution extruded in column of warm air. Solvent recovered
 * 8) Filaments are stretched and wound onto beams, cones, or bobbins ready for use [1]

Trademarks [4]
Trade Names---Manufacturer
 * Celanese (forms produced: flake and tow)--*Celanese Acetate
 * Celstar--*Celanese Acetate
 * Chromspun--*Eastman Chemical Company
 * Estron--*Eastman Chemical Company
 * MicroSafe--*Celanese Acetate

* Voridian Company is an operating division of Eastman Chemical Company

Voridian introduced acetate tow in 1952 and remains a leading manufacturer today. Voridian sells acetate tow under the trademark Estron[5].

Acetate Fibre Characteristics

 * cellulosic and thermoplastic
 * selective absorption and removal of low levels of certain organic chemicals
 * easily bonded with plasticisers, heat, and pressure
 * acetate is soluble in many common solvents (especially acetone and other organic solvents) and can be modified to be soluble in alternative solvents, including water
 * hydrophilic: acetate wets easily, with good liquid transport and excellent absorption; in textile applications, it provides comfort and absorbency, but also loses strength when wet
 * acetate fibres are hypoallergenic
 * high surface area
 * made from a renewable resource: reforested trees.
 * can be composted or incinerated
 * can be dyed, however special dyes and pigments are required since acetate does not accept dyes ordinarily used for cotton and rayon (this also allows cross-dyeing)
 * resistant to mold and mildew
 * easily weakened by strong alkaline solutions and strong oxidizing agents.
 * can usually be wet cleaned or dry cleaned and generally does not shrink

Major industrial acetate fibre uses

 * apparel: linings, blouses, dresses, wedding and party attire, home furnishings, draperies, upholstery and slip covers
 * high absorbency products: nappies, feminine hygiene products, cigarette filters, surgical products, and other filters
 * Ink reservoirs for fibre tip pens, industrial fabrics, holiday [5]

Paper
Paper is a thin, flat material produced by the compression of fibres. The fibres used are usually natural and composed of cellulose. The most common source of these kinds of fibres is wood pulp from pulpwood trees, (largely softwoods) such as spruce. However, other vegetable fibre materials including cotton], hemp, linen, and rice may be used.