Type of Commercial Cotton

1.       Sea Island Cotton: This is the highest quality and the most valuable of all commercial cotton fibers. It

grows on the coast of the Gulf and Flarido, in Barbados and other adjacent islands where the climates are favorable. The average length of this fibre is about 2 inch (51 mm) and the diameter is 1/1500 inch (0.0175 mm). It is famous for uniformity, maturity, and highly developed luster, twist and softness. The color of this fiber is white to cream.

2.       Egyptian Cotton: There are two kinds of Egyptian cotton; one is Brown and another is White. Like Sea Island cotton, this type of cotton is very regular i.e. uniformity is good and contains few immature or dead fibers. The average length of this fiber is 1.5 inch to 1.75 inch (38 – 44 mm), diameter is about 1/1500 inch (0.0175 mm).

3.       South American Cotton: The cotton has a staple length of 1 inch to 1.5 inch (25 – 38 mm). It has a mean diameter of 1/1300 inch (0.0195 mm) and is suitable for mixing with regenerated menmade fibers.

4.       North American Cotton: This type of cotton is cultivated in United States and sometimes in Mexico. Its staple length is 0.9 inch 1.25 inch (23 – 32 mm) and the diameter is about 1/1200 inch (0.0211 mm).

5.       Indian Cotton: This is short fiber cotton and the length ranges from 0.6 inch to 0.8 inch (13 – 20 mm).

6.       Chinese Cotton: This is the lowest commercially accepted grade, length ranges from 0.5 inch to 0.7 inch (13 – 18 mm). Its twist is not highly developed and rather harsh. It is not suitable for spinning a good quality yarn and is usually used in a mixture with better qualities.

7.       Bangladeshi Cotton: Mainly American cotton is being produced in Bangladesh. Commercially hybrid types of cotton are now being produced in Meherpur, Jessore, Kustia, Gazipur and tribal area. The qualities of Bangladeshi cotton are now improving and lengths, color maturity are fair to good. It is possible to produce maximum 60s Ne yearn from Bangladeshi cotton.

Functional groups in cotton:

The most important chemical groups cotton polymer are hydraxyl groups (-OH, which are olso present as methylol groups (-CH2OH). Their polarity gives rise to hydrogen bond between – OH groups of adjacent cotton polymers. Less significant Van der Waal’s forces also occurs. Each glucose unit contains one primary hydroxyl group (as – OH) at C₂ and C₃ positions. Again one end of the glucose unit has an additional secondary hydraxyl group at C₄ position and the other end has on oldihyde or hemi-acetal group at c₁ position.

Polymer system cotton:

Cotton is a crystalline fiber. It consists of about 65 – 70% crystalline zone and corresponding 30 – 35% amerphous region. The repeating unit in the cotton polymer is celebiose which consists of two glucose units. Its DP is about 5,000 – 10,000. It is about 5000 mm in length and about 0.8 mm thick.

These convolutions and kidney-shoped cross-section of cotton fiber contribute.

·         Rondom contract with the skin which is more compatible with human skin physiology and therefore, more comfortable.

·         Increase the moisture absorbency due to the contless minute air spaces because of these convolutions and kidney-shape, and thus makes the cotton fiber fabric more comfortable to wear.

Cotton fibers are amongst the finest in common use. They have a length from about 10 mm to 65 mm, depending upon the quality, and diometer is range from about 11 μm to 22μm.

Layer 2: The primary wall is made up to chains of cellulose called fibrils. Those fibrils spiral around the fiber at 20 – 30 degree angles. Mature cotton fibers have thick primary walls, immature fibers do not and often collapse and tangle/twist, causing meps when the fibers are being corded and spun.

Layer 3: The winding layer is really the first part of the secondary wall. It is made up of fibrils that run at 40 – 70 degrees and spiral around the fiber. This layer helps support the rest of the secondary.

Layer 4 : The secondary wall is the last layer and it is actually made up of many layers of fiberls, each layer grows over a day and forms rings, kind of like a tree. The fibrils in the secondary wall are different in the way they grow, they do not really spiral, they change direction somewhat or random, making for a zig zag kind of formation. Weak spots can occur in the spots where the fibrils change direction and the winding layer helps compensate for this.

Layer 5: The lumen is not really a layer per say but rather the hallow tube that runs through the center of the fiber. When the fibers are growing this tube is filled with fluid (cell sap, preteins, sugars, etc.) but during processing it empties and collapses, which result in the flat appearance of the fibers and the kidney / bean appearance of cross section of the fibers. The lumen is also pert of what makes cotton so very absorbent.

Al these layers of fibers make for a densely pocked fibers. Also, as the fibrils layer around each other they make tons of microscopic capillaries, which also ups cottons absorbency. Cotton is a very hydrophilic (water loving) fiber and the cool thing about cotton fiber is when it is gets wet it swells and unlike a lot of other fibers (like silk or rayon) instead of getting weaker, it gets stronger.

Now the question is, why? the best explanation is that when water molecules penetrate into the fiber, it lies between the fibrils and into the amorphous regians of the polymer. Where it forms hydrogen bonds with the free-OH groups of the cellulose. This water absorption couses swelling also cements the cellulose chains and fibrils together by hydrogen bonding thus increasing the strength.

Chemically Modified Cotton:

Partially Acatylated Cotton (PA Cottton)

Treatment of cotton with acetic anhydride in acetic acid conderts it to partially acetylated cotton (PA cotton). This materials looks like original cotton and it has no smell and is non toxic. But in many of its properties PA cotton differs from the normal cotton fibers. Most important of all it has greater resistance to heat than normal cotton fibers. At 250℃ normal cotton loses one-third of its strength in there minutes, whereas PA cotton loses one-third of its strength after twenty-five minutes at the same temperature.

For this properly, PA cotton can be used to make laundry press cover and give lasting for long time. It also withstands the attack of micro-organisms of mildew and rotting. It has chemical resistance in 20% HCL, it loses only one-third of its strength after eight hours, whereas ordinary cotton loses about two-thirds. It is a better electrical insulate.

Uses: Sand bag, fishing nets and lines etc. Where a high resistant to rot fabric is necessary.

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