Properties of Cotton fiber
Properties of Cotton fiber
Cotton a unique cellulosic fiber, possesses an outstanding range of properties making it one of the most popular apparel fibers worldwide.
Physical properties
Length and width:
Cotton is the shortest natural fiber used in commercially in the textile industry ranging from 0.5-2-5 inches in length. The width of typical cotton fiber may vary between 12 to 20 microns.
Shape:
A typical, matured raw cotton fiber looks like a flattened tube and the cross section is oval or kidney shape. Under microscope, it is a long-twisted ribbon.
Strength:
Cotton is a moderately strong fiber. Tenacity of cotton fiber is 26.5-44 cN/Tex and the extension at break is about 8-10 %.
Elasticity:
Cotton is relatively rigid fiber (Less elastic). At 2% extension is has an elastic recovery of 74%, at 5% extension; the elastic recovery is 45%.
Porosity: Cotton fiber is somewhat porous, and consequential, it absorbs moisture readily.
Moisture regain:
Cotton has a moisture regain of 8.5%. At 100% humidity, cotton has an absorbency of 25-27%.
Color:
Normally the color of cotton is creamy-white.
Handle:
Cotton is naturally very soft and comfortable. That is why it is particularly favored for garments that get close to the skin.
Luster:
Cotton fiber has a natural luster which is due to the natural polish on the surface and its nearly circular cross-sectional shape. The smooth, hard primary coat of cellulose contains waxes which no doubt contributes to the luster of the fiber.
Chemical Properties
Effect of acid:
Cotton fiber is not affected by cold week acids. But whenever it is brought into contact with hot diluted acid or cold concentrated acids, degradation of cellulose takes place and the fibers loss their strength. Cotton fiber can fully dissolve in high concentrated mineral acid.
Effect of alkalis:
Cotton has an excellent resistance to alkalis. It swells in caustic alkali (mercerization) but not damaged. But the fiber is affected by hot alkali particularly in the presence of air. In this case, NaOH promotes cellulose oxidation by atmospheric oxygen resulting in the formation of oxycellulose. For this reason, it is suggested that to carry out the scouring of cotton in a hooded machine.
Effect of organic solvent:
Here are few solvents that will dissolve cotton completely. It has a high resistance to Normal solvents but it dispersed by the copper complexes cuprammonium hydroxide and cupriethylene diamine and by concentrated (70%) H2SO4
Effect of oxidizing agent:
For chemical treatment cotton fiber is treated with different types of oxidizing agents like sodium hypochlorite, sodium perborate, hydrogen peroxide, sodium chlorite etc. These reagents lead to chemical attack initially in the functional groups and then progressively cause the chain scission, lowering the DP and reducing the tensile strength.
Action of microorganism:
Cotton fiber can resist moths and most insects, but it can be attacked by fungi and bacteria. Mildew, for example, causes weakening and rotting tine cotton fiber often characterized by a musty smell. The presence of starchy material as a sizing or a finishing agent also promotes the growth of the mildew. Mildews and bacteria will flourish on cotton under moist and hot condition.
Action of water:
Water, which is very strong polar in nature, easily attracted by the polar –OH groups of the cotton fiber. So that water is able to penetrate into the cellulose network of the cotton fiber.
However, its porous structure also allows ready penetration of water molecules between the fibrils and into the amorphous region of the polymer, where they can easily from hydrogen bond with free –OH group of cellulose. This water absorption causes swelling of the fiber. Due to swelling, cotton fiber shows greater strength in the wet state than dry. This is because of the screw-shaped arrangement of the fibril in cotton fiber, which are supposed to be pressed more firmly against each other by the swelling action.
Other Properties
Effect of temperature:
Cotton fibers show an excellent resistance to thermal decomposition. They have the ability to conduct heat energy and do allow any destructive heat accumulation. Thus, they can withstand high temperature, but the stability depends to a great extend on the heating time and temperature.
Prolonged heating at 100 C shows the cotton no visible change.
Heating at 120 C for several hours shows the cotton little or no change in strength, but begins to turn yellow gradually.
Cotton decomposes markedly at 150 C.
At 240 C intensive decomposition takes place with the formation of liquid and gaseous products of different composition.
Effect of light:
There is a gradual loss of strength when cotton is exposed to sunlight for a long time and the fiber turns yellow.
The degradation of cotton takes place in presence of atmospheric oxygen (formation of oxycellulose). It is particularly at high temperature and in the presence of moisture. Much of the damage is caused by ultra-violet light and by the shorter waves of visible light.