Cotton Fiber Morphology

The macro structure of cotton-

# Under a microscope, a cotton fiber appears as a very fine, regular fiber.
# It ranges in length ½” to 2 ¾ “, depending upon the quality of the fiber.
It is the finest in common use, ranges 11µm to 22µm .

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# The fiber length to breadth ratio of cotton ranges from about 6000:1 for the longest and best types, to about 350:1 for the shortest coarsest cotton type. the greater the ratio, the more readily can the cotton fibers be spun into yarn.

# The color of cotton fibers depends on its type, environment, soil and climatic conditions under which it is grown.

The microscopic appearance of cotton-

# Under the microscope, the cotton fiber looks like a twisted ribbon or a collapsed and twisted tube. These twists or convolutions identify the cotton fiber under the microscope.

# The seed end of the fiber is quite irregular, having been torn, during ginning, from the epidermis or skin of the cotton seed.

Picture4# The main part of the fiber, about 3/4th to
5/6th of its length, is regular, with a thick fiber wall, a canal along the center of the fiber called the lumen, and about 16 convolutions/cm.

# fiber tip is less than 1/4th of the fiber length.
At this end, the fiber tapers to a cylindrical, pointed tip, and has no convolutions.

# The convolutions are formed after the cotton boll bursts open, the limp, sap-filled cotton seed hairs begin to dry out, their cell walls collapse inward, decreasing the size of the lumen. When the cotton seed hairs cease shrinking, twisting and collapsing inward, they become the valuable, convoluted cotton fiber

The micro-structure of cotton fiber-

# Its cross-section is oval, compared with the normal hexagonal plant cell. However, like all plant cells, cotton has a distinct cuticle, well developed primary and secondary walls, and a lumen.

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# The cuticle is the’ very-outside’ or ‘skin’ of the cotton fiber. It is composed of a waxy layer (pectin) only a few molecules thick. The waxy nature of the cuticle enables it to adhere tenaciously to the primary wall of the fiber.

# The primary cell wall, which is immediately underneath the cuticle, is about 200nm thick. It is composed of very fine threads of cellulose, called fibrils.

# These fibrils are about 20nm thick, but length is not known. The fibrils spiral at about 70° to the fiber axis. This spiraling imparts strength to the primary cell wall and hence, to the

#Secondary cell wall, which forms the bulk of the fiber. Concentric layers of spiraling, cellulosic fibrils, not unlike the growth rings of trees, make up the secondary wall.

#The hollow canal, running the length of the fiber, Is called the lumen.
The lumen was once the central vacuole of the growing cotton fiber. It was full of cell sap, which was composed of a dilute, aqueous solution of proteins, sugars, minerals and cell-waste products.

#When the sap evaporated, its constituents remained behind to contribute to the color of the cotton fiber

#This caused the fiber to collapse inward resulting in the characteristics kidney-shaped cross-section of the cotton fiber.

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