Bangalore
Structure of Cotton Fiber
What makes cotton so breathable and strong? Dive into the microscopic structure of cotton fiber from its outer cuticle to its inner lumen.
SohaniSharma
Introduction
Cotton is obtained from a plant and is classified as a natural, cellulose, seed, mono-cellular, staple fiber. Cotton is the most important natural textile fiber, as well as cellulose textile fiber, in the world, used to produce apparel, home furnishings, and industrial products.
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Composition of Typical Cotton Fibers
Specifications of Cotton Fiber
- Length: 1 cm to 6.5 cm
- Diameter: 11 micrometers to 22 micrometers
- Length-to-width ratio: 6000:1 to 350:1
- Convolution: Sixty per cm
- Specific gravity: 1.52
- Color: Generally white, but maybe creamy or brown.
- Strength tenacity: at dry = 3.0-5.0 g/d; at wet = 3.3-6.0 g/d
- Light reflection: Low luster, dull appearance
- Dimensional stability: Medium
- Elasticity: Low breaking extension 5% to 7%
- Moisture regain: 8.5%
- Resiliency: Low
- Abrasion resistance: Medium
Microstructure and Morphology of Cotton Fiber
The cotton fiber is made up of a cuticle, primary wall, secondary wall, and lumen. The cotton fiber is a single plant cell.
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| Structure of a Cotton Fiber |
Cuticle
- The cuticle is the very outer layer or skin of the cotton fiber.
- It is composed of a waxy layer only a few molecules thick.
- This outer layer protects the rest of the fiber against chemicals and other degrading agents.
Primary Cell Wall
- It is immediately underneath the cuticle and is about 200 nm thick.
- It is composed of very fine threads of cellulose, called fibrils, which are about 20 nm thick.
- The fibrils are at about 70% of the fiber axis. This spiraling imparts strength to the primary cell wall and hence to the fiber.
Secondary Cell Wall
- Beneath the primary cell wall lies the secondary cell wall, which forms the bulk of the fiber.
- The fibrils are about 10 nm thick and of undefined length.
- Near the primary cell wall, the fibrils of the secondary wall spiral at about 20° to 30° to the fiber axis. This spiral angle widens to about 20° to 45° for the fibrillar layers nearer the lumen.
Lumen
- The hollow canal running the length of the fiber is called the lumen.
- The walls are the innermost, concentric layers of the spirals of the secondary cell wall.
- It is full of cell sap, which is composed of a dilute, aqueous solution of proteins, sugars, minerals, and cell waste products.
- Further, as the sap evaporated, the pressure inside the fiber became less than the atmospheric pressure on the outside. This causes the fiber to collapse inward, resulting in the characteristic kidney-shaped cross-section of the cotton fiber.
