Characteristics and Properties of cotton.

Characteristics of cotton:

Cotton is a natural fibre of vegetable origin like linen, jute or hemp. Cotton is the fruit of a shrubby plant commonly referred to as the "cotton plant". Cotton fiber has natural twists along the entire length of the fiber called convolutions. The convolutions help the fibers interlock when it is spun into yarn. Long fibers have about 300 convolutions per inch and short fibers have 200 or less. Sea Island cotton has highest number of convolutions per inch than the others:

Sea Island cotton --> 300

Egyptian cotton --> 230

American cotton --> 210

Indian cotton --> 150

Long fibre is required to produce higher and fine count. For long staple cotton fibre the ratio of length and thickness is 6000:1 where in short fibre the ratio is 3500:1. When the ratio is high than it is suitable and more easy to spun yarn.   

Cotton has a diameter of 16 to 22 micron. But surface of cotton fibre is not regular. Its middle portion is thick and tip is thin and there is no convolution at tip region. Therefore, cotton consists of a irregular surface that increases the friction between the fibres during spinning  and yarn becomes strong.

Cotton is not circular in cross-section. It looks like kidney in cross-sectional view under microscope. Due to its convolution and kidney like cross-section air, can pass through the cotton fabric and we feel comfort.

Color of cotton is ranges from white to grey. The color of the fibers is affected by climatic conditions, impact of insects and fungi, type of soil, storage conditions etc. There are five recognized groups of color: white, gray, spotted, tinged, and yellow stained. As the color of cotton deteriorates, the process ability of the fibers decreases.

Cotton has about 55% -70% crystalline region and 30%-35% amorphousregion. That’s why the molecules of cotton polymer are arranged in a specific sequence and probably no part is 0.5nm far from the crystalline part. 0.5nm is the maximum distance to form Hydrogen bond in a polymer. These Hydrogen bonds among the polymers make the fibre strong. When cotton is wetted some molecules of amorphous region arranged in a balance way. As a result, 5% Hydrogen bond increases and that’s why wet cotton has greater strength than dried cotton.

Due to higher crystalline region cotton has less elasticity and its tendency of creasing is higher than any other natural fibre.

Cotton fabric becomes dirty easily because of its uneven surface but can be removed quite easily as it has good resistance to bleaching agent and not damaged into hot water.

Properties and uses of cotton:

Properties of cotton mean mainly physical and chemical properties. These are here:

Physical properties of cotton:

Length: 0.5-2.5 inch or 0.3-6 cm.

Diameter: 16-20microns.

Cross section: Kidney shape.

Color: White, grey, cream.

Luster: High.

Dimensional stability: Good.

Tenacity (gm/den): In dry state 3.0-5.0, In wet state 3.6-6.0

Elasticity: 74% recovery at 2% deformation and 45% at 5% deformation.

Elongation at break: 3.0-7.0%

Co-efficient of friction: 0.25.

Drapability: Good.

Resiliency: Low.

Moisture regain: 8.5% and raised to around 25-30% at 100% Relative humidity.

Specific gravity: 1.54

Chemical properties of cotton:

Effects of Acid and Alkalis: Concentrated acid or hot but low concentrated acid damages cotton. Cotton dissolved in high concentrated mineral acids such as HCl, H₂SO₄ but high resistant to alkalis. That’s why NaOH, Na₂CO₃ are used for scouring of cotton. Concentrated NaOH is also used for cotton mercerizing.

Effects of Bleaches: Resistance to bleach, but H₂O₂, NaOCl, NaOCl₂, Ca(OCl)Cl are used as bleaching agents for cotton processing.

Effect of heat: Cotton has an excellent resistance to degradation by heat. It begins to turn yellow after several hours at 120⁰C and decomposes at 150⁰C as a result of oxidation. It damaged at 240⁰C, flame at 390⁰C and burns in air and smell is like paper burning.

Effect of organic solvents: Have resistant ability to most organic solvents such as dry cleaning agents. A little organic solvents can damage cotton.

Dyeability: Have affinity to Direct, Reactive, Sulphur, Vat dye, Mordant, Indigo and natural colorant.

Effect of sunlight: There is a gradual loss of strength when cotton is expressed to sunlight and the fibre turns yellow. Ultraviolet ray is harmful for cotton.

Effect of weather: Acidic air spoils the strength of cotton. If cotton isstored carefully on dry condition it lasts for many years.

Effect of insects: Cotton is not attacked by moth grubs or beetles.

Micro-organism: Cotton is attacked by fungi and bacteria.

Uses of cotton:

Apparel - Wide range of wearing apparel: blouses, shirts, dresses, separates, children-wear, active wear, skirts, pants, sweaters, swimwear, suits, jackets, hosiery, neckwear.

Home Fashion - curtains, draperies, throws, sheets, bedspreads, comforters, towels, napkins, table mats, table cloths.

Medical and cosmetics – Bandage, wound plaster.

Others - fishing nets, coffee filters, cotton paper, in bookbinding, Fire hoses, tents.