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.
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 microns, the thickness is 0.5 1.0 microns and the visible length is
around 16 microns.
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 constitute 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
microns long and 2.5 and 1.2-2.6 microns 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-sections, 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 are joined together by a cementing tissue. The cortex
of the fibre is mainly responsible for the strength, elasticity and dyeing behaviour
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.
