1. Physical and Chemical Properties of Cotton Fibre
Staple length of cotton fibre varies from 10mm – 80mm.
1.2. Fibre Fineness
Wall thickness of different cotton ranges from 3.2-10µ (Micron). Ribbon width ranges from 12-25µ. Cotton fibre fineness is measured at middle portion of fibre because the tip and end of the fibre is slightly tapered.
1.3. Fibre surface
The surface of cotton fibre, seen at high magnification is wrinkled and striated and its cross section is kidney shaped.
1.4. Tensile Strength
Cotton is a moderately strong fibre, tenacity is 3.0-5.0 g/den. The strength is affected greatly by moisture and by the test conditions such as rate of loading, and length of fibre section tested. The long, fine cottons, such as Sea Island and Egyptian, yield the strongest yarns and materials. Long and fine fibres of good strength can thus be spun into finer yarns.
Cotton does not stretch easily. It’s elongation at break of 5-10%.
1.6. Elastic Properties
Cotton is a relatively inelastic, rigid fibre. At 2% extension it has an elastic recovery of 74%; at 5% extension, the elastic recovery is 45%.
The density of the cotton fibre is 1.54 gm/cm3.
1.8. Effects of Moisture
Under Standard atmospheric conditions, cotton takes up about 6-8% of moisture regain. At 100% humidity, cotton has an absorbency of 25-27%.
Each unhydroglucose unit in cellulose has three hydroxyl groups. On an average one out of these three hydroxyl groups on each glucose residue is a site for moisture absorption. Amount of moisture in cotton depends on temperature and relative humidity (R.H.).
The tensile properties of cotton fibres and yarns are affected appreciably by the amount of moisture absorbed by the fibres. Cotton yarns will continue to become stronger at high relative humidity. Up to a relative humidity of 100%, absorption of water by the cotton cellulose results in an increase in fibre strength. At higher humidity fibre absorbs more water due to breakage of hydrogen bonds in amorphous region and availability of more hydroxyl groups. Also Fibres saturated with water are about 20% stronger than dry fibres. The swelling of cotton yarns and fabrics in water is accompanied by some shrinkage.
1.9. Effect of Heat
Cotton has an excellent resistance to degradation by heat. It begins to turn yellow after several hours at 1200C and decomposes markedly at 1500C, as a result of oxidation. Cotton is severely damaged after a few minutes at 2400C. Cotton ignites easily and burns readily in air with odor similar to that of burning paper.
1.10. Effect of Aging
Cotton shows only a small loss of strength when stored carefully. It can be kept in the warehouse for long periods without any significant deterioration. After 50 years of storage, cotton may differ only slightly from fibre a year or two old. Ancient samples of cotton fabric taken from tombs more than 500 years old had four fifths of the strength of new material.
1.11.Effect of Sunlight
There is a gradual loss of strength when cotton is exposed to sunlight, and yellow. The degradation of cotton by oxidation when heated is promoted and encouraged by sunlight. It is particularly severe at high temperatures and in the presence of moisture. Much of the damage is caused by ultra-violet light and by the shorter Waves of visible light. Under certain the effects of weathering in direct sunlight can be serious. The cotton can be protected to some degree by using suitable dyes.
1.12.Effect of Acids
Cotton is attacked by hot dilute acids or cold concentrated acids, in which it disintegrates. It is not affected by cold weak acids.
1.13.Effect of Alkali
Cotton has an excellent resistance to alkalis. It swells in caustic alkali but is not damaged. It can be washed repeatedly in soap solutions without harm.
Cotton can be mercerized by treating with or without tension in a strong solution of alkali like sodium hydroxide (NaOH). Due to the mercerization the swelling of the fibre takes place. The proper can be improved like:
- Shrinkage in yarn or fabric due to swelling
- Improvement in luster
- Improvement in tensile strength
- Improvement in dyeabiliy and its uniformity
- Improvement in dimensional stability
1.14. Effect of Organic Solvents
There are very few solvents that will dissolve cotton completely. It has a high resistance to normal solvents but is dispersed by the copper complexes cuprammonium hydroxide and cupriethylene diamine, and by concentrated (70%) H2S04
Cotton is attacked by fungi, bacteria. Mildews, for example, will feed on cotton because of this rotting (decomposing) and weakening the material takes place. They have a characteristic musty smell and stain the fabric with naturally produced pigments. Mildews are particularly troublesome on cotton that has been treated with starchy finishes, and much of the damage can be avoided by thorough scouring. The pure cellulose is a less attractive food for mildew than the starch Mildews and bacteria will flourish on cotton under hot, moist conditions. When cottonfabrics are to be used under conditions favorable to attack by micro-organisms, they can be protected by impregnation with certain types of chemical. Copper compounds, such as copper naphthenate, will destroy organisms that would otherwise attack the cotton cellulose.
2. Applications of Cotton
- Poplins, voiles are made by using Cotton.
- Cotton is used in great quantity as a fabric for hot weather wear.
- The absorbency of cotton makes it an excellent material for household fabrics such as sheets and towels.
- Cotton is widely used in making rainwear fabrics. It can be woven tightly to keep out the driving wind arid rain, yet the fabric will allow perspiration to escape.
- Ventile fabrics, for example, are close-woven cotton materials of this sort which are given additional water resistance by a chemical proofing.
- It goes into clothing (shirts, T-shirts, trousers, denim, etc.), undergarments, boots and shoes, carpets and curtains, hats, etc.
- Heavy cotton yarns and materials are used for tyre cords and marquees, tarpaulins and industrial fabrics of all descriptions.
- Cotton can be blended with other fibres like polyester, rayon to manufacture fabric for different applications.