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Cotton

Textile Fibers

Polymeric

Natural

Regenerated

Synthetic

Inorganic

Natural

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Manmade

Engineered

Bicomponent

Unconventional

4DG
Hollow

Cotton fiber is seed hair, a long single cell closed at one end. The central lumen runs through the fiber. With ginning, the cotton fibers are separated from the seeds. Cotton grading is based on fiber length, uniformity, diameter, strength, maturity, color and the amount of foreign matter.

Topics:

Facts about Cotton Fiber

The Morphological Structure of Cotton

The Molecular Structure of Cotton

Chemical Modification

Facts about Cotton Fiber:

Cotton is an important textile fiber.

² Cotton fiber is 65-70% crystalline.

² Cotton fiber is a porous material, 20-41% is volume occupied. Also, there are spaces between fibrils in fiber walls.

² The most important constituent group is hydroxyl group (-OH).

² Cotton is hydrophilic, high regain due to the hydroxyl groups wrecking H₂O between fibrils, layer and walls.

² Cotton has low elastic recovery due to the breaking and reforming of hydrogen bonds.

² Cotton fabrics are comfortable. Cotton absorbs water vapor emitted by body. The yarn and fabric structure is relatively open that permits passage of H₂O vapor.

² Cotton is highly resistant to alkaline degradation but degrades with acids.

² Silver fish eat cellulose.

² Prolonged sun exposure causes cotton fiber to yellow and degrade.

² Cotton has high heat conduction. It is not thermoplastic due to the extremely long polymers and numerous hydroxyl bonds.

² Cotton demonstrates comfortable low luster because of the convoluted surface,

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The Morphological Structure of Cotton

Details of the morphology of the cotton fiber include fiber length, fiber fineness, fiber convolutions, the shape of the cross-section, the wall thickness and the fibrillar wall structure.

Length:

The average length of the cotton fiber varies from variety to another. The range of average length in spinnable cotton is 12-36 mm.

To demonstrate the length distribution of cotton, staple diagram is always used, which is a graphical representation of fiber arranged in order of decreasing length.

The full length of the cotton fiber is attained in about 25 days from flowering. Most of this stage the fiber is bounded only by the primary wall with the cuticle on its exterior surface. The thickening of the fibers occurs by deposition of the secondary wall on the interior surface of the primary wall. This begins several days before the growing fiber reaches its full length and continues for a further 35-40 days. The rate of increase in thickness is relatively slow.

Cuticle:

Cuticle is just few molecule thick, a very think layer moulded to the outside of the primary wall tightly. Cuticle is a surface deposit of cotton wax that is a complex mixture of fats, waxes and resins.

The Primary Wall:

The primary cell wall composes of fibrils spiraling around fiber axis. It is built up from cellulose. Fibrills spiral at an angle of about 70° around the fiber axis.

The Secondary Wall:

The secondary cell wall is bulk of fiber concentric layers of spiraling fibers. It contributes most of the weight of the cotton fibers. Also, it is composed mainly of cellulose as the primary wall. But it’s not laid down uniformly but consist of concentric layers of fibrils in spiral formations at an angle of about 20-30° around the fiber axis.

The Lumen:

Lumen is the hollow canal, used to be full of sap. Typically, the lumen area of a typically fully developed fiber in the closed boll occupies about 1/3 of the total area of the cross-section. In the dried state lumen occupies only about 5%. The lumen contents are largely evaporated after the boll-split. In the dried state of the cotton fiber, the lumen contains the desiccated remains of the protoplasm and nucleus.

Related Concepts:

Dead Cotton, Immature Fibers, Fuzz Fibers, Cotton Linters, Fiber Weight.

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The Molecular Structure of Cotton

Cotton is mainly composed of cellulose. The repeating unit in the cellulose molecule is the glucose reside.

ß-D-Glucose

Cellulose

Two glucose residues (GR) arse held together by the glycoside link (GR-O-GR).

The chain-length of cotton cellulose purified by careful chemical treatment is at least 2,000 units. There are two hydroxyl endgroups for each cellulose molecule.

The properties of cotton are influenced by the nature of the 3 structural features of its molecules:

1. The glycoside links,

2. The hydroxyl end-groups

3. The glucose residues.

There are three hydroxyl groups for every glucose residue, two of which are in secondary alcohol groups and the third is in a primary alcohol group.

Hydrolysis of the glycoside link will shorten the molecular weight and produce hydrocellulose.

In a undegraded cotton molecule, there is only one pair of end groups to some 2,000 chain links. It’s few that we can neglect them. But since the number is doubled when a single glycoside link is opened by hydrolysis, the nature of the hydroxyl end groups will be expected to be of rapidly growing importance as the hydrocellulose formations process.

For quantitatively measurements of reducing value, alkaline solutions of copper salt are generally used and the amount of copper precipated is determined is determined by analysis.

The weight of copper precipated under standard conditions by a standard weight of the chemically modified cotton is called copper number. The copper number of undegraded cotton is almost zero, but it rises progressively as hydroxylitic degradation occurs under the continued action of acid on the cotton.

There are four types of chemical reactions that might happen to alcohol groups of the cellulose molecules: esterification, ionization, hydrogen bonding and oxidation.

Esterification:

The esterification of cellulos with an acid is often accompanied by hydrocellulose formation and its characteristic degradation.

It is possible to esterify the hydroxyl groups in the cellulose groups in the cellulose molecule without appreciable rupture of chain-links by the acid. This is called no-degradative esterification ( nitration, acetylation, etc). There are very few liquids capable of dissolving cotton cellulose without at the same time causing a rupture of the cellulose molecular chain. One of them is cuprammonium hydroxide, called cuprammonium for short.

Ionization:

Related concepts:

Cation(+), anion(-), H⁺(Hydrogen cation), Cl^-(chloride anion)

Hydrogen bonding:

The direct association of one hydroxyl group in one molecule with that in another.

Oxidation:

Related concepts:

Aldehyde group(-CHO), carboxyl group(-COOH)

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