Maturity of Cotton Fiber (Development of the Cell Wall)

What is the Maturity of Cotton Fiber? When the cotton fiber starts developing on a cotton plant, initially it is like a hollow tube having only a primary wall. As time passes, the second wall takes place inside the pad of the primary wall and starts filling up the hollow tube. When the cotton fiber is fully developed, ideally the secondary wall occupies 85 – 90% of the cross-section of the fiber leaving a small capillary at the center called a lumen.

Importance of Maturity for Cotton Fiber:

i) Gives more strength and rigidity.
ii) Gives fiber better mechanical properties.
iii) Gives high flexibility.

Problems of Immature Cotton Fiber:

1. The size of the lumen is bigger.
2. Lower strength.
3. Less rigidity.
4. Worst mechanical properties.
5. Form more entanglements during processing.

Matured Cotton Fiber: The cotton fiber has a well-developed secondary wall and a very small lumen is called matured cotton fiber.

1. Primary wall
2. Secondly wall
3. Lumen

You may read: Identification of Cotton Fiber

Immature Cotton Fiber: The cotton fiber that has a thinner secondary wall and larger lumen is called immature cotton fiber.

1. Primary wall
2. Secondary wall
3. Lumen

Dead fiber: The fiber that has only the primary wall and the lumen occupying the bulk of fiber is called dead fiber.

1. Primary wall
2. Lumen

Convolution of Fiber: After the bursting of the mature cotton boll, the wall of the fiber shrinks and collapses to relieve internal stress during drying. Thus the cylindrical cross section is converted into a twisted ribbon which is called the convolution of cotton fiber. 

1. Undried cylinder
2. Convolution beginning
3. Dry fiber

Importance of convolution:

1. Make only random contact with the skin.
2. Increases inter-fiber friction.

Enables fine cotton yarns of sufficient strength to be cut.

Morphological Structure of Cotton Fiber: 

Cuticle:

1. The outermost layer of cotton is known as the cuticle.
2. It consists of wax, a mixture of fats and oils.
3. It protects the fiber from chemical and mechanical damage.

Primary wall:

1. Inside the cuticle, the primary wall is composed mainly of cellulose
2. It consists of wax, protein, and pertinacious substances.
3. Fibrils are arranged in a crisscross pattern at about 70⁰ to the fiber axis.   31/128 

Secondary wall:

1. Under the primary wall, the secondary wall is composed of cellulose.
2. It consists of concentric layers of cellulosic fibril in a spiral formation.
3.  Spiral angle changes slightly between 20º – 30º 

Lumen:

1. The hollow empty canal of cotton fiber is called lumen.
2. During the growth stage of cotton fiber, it was full of aqueous solution of proteins, sugar, and minerals.
3. After drying, the liquid disappears and leaves an almost empty canal.

Chemical Structure of Cotton Fiber:

• Cotton fiber
• Fibrils 
• Cellulose
• Molecules

Polymer System of Cotton:

1. The cotton polymer is about 5000 nm in length and about 0.8 nm thick.
2. The repeating unit is cellobiose
3. The degree of polymerization (DP) is about 5000.
4. It is about 65 – 70 % crystalline and 30 – 35% amorphous.
5. Functional groups are OH & CH₂OH