Morphological structure of wool

The morphological structure of the wool fibre is shown in the figure. It consists of three structural parts.

(a) Epidermis or Cuticle
(b) Cortex

(c) Medulla. Cuticle.


Morphological structure of wool

The cuticular

The layer is the outer surface of the fibre. It is made up of flat, irregular horny scales which overlap with the projecting edges pointing. Towards the fibre tip. This serrated pattern is similar to fish scales or like that of tiles of a roof. This scaly epidermis serves as a protection for the main part of the fibre, and also gives it rigidity.

The cuticle cell width is around 36 micron, the thickness is 0.5 1.0 micron and the visible length is around 16 micron. The size and density of the scales vary along with the fibre and from fibre to fibre. In fine wool, one scale is enough to go all the way around the fibre, so that it looks like a series of funnels set inside each other.

When the diameter increases, the number of scales also increases. The scaly layer consists of three separate fractions ie. epicuticle (outermost exocuticle and endocuticle (innermost) which constitutes the scales. The epicuticle is an extremely thin layer, reputed to have a thickness of 50-250A.


Cortex

The cortex constitutes the main portion or body of the wool fibre. It consists of long, slightly flattened and twisted spindle-shaped cells. The cells are approximately 80-110 micron long and 2.5 and 1.2-2.6 micron for the major and minor diameters respectively.
The cross-section of the fibre may be circular but more often they are elliptical. For circular cross-section, the diameter of the cortex cells is the same. The cortex may be divided into its cells by treatment with enzymes. These cells, in turn, consist of fibri!s- that are oriented along the length of the cell.

The cells appear to have an enclosing membrane and joined together by a cementing tissue. The cortex of the fibre is mainly responsible for the strength, elasticity and dyeing behavior of wool.

  Medulla


In some of the medium or coarser wool, there is a central core or medulla that runs lengthwise through the fibre. This medulla arises from the growing root and is loosely filled with many superimposed cells of various shapes, often polygonal.

The size of the medulla varies greatly and the volume of wool fibres occupied by the medulla may run from 10-80%. It is probably through the medulla that solutions to wet processing treatment and dyes penetrate the fibre. 

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