o A
mature cotton fiber has the following six parts.
o
The “cuticle” is the outer waxy layer,
which contains pectins and proteinaceous materials. It serves as a smooth,
water-resistant coating, which protects the fiber. This layer is removed from
the fiber by scouring.
o
The “primary wall” is the original thin
cell wall. Mainly cellulose, it is made up of a network of fine fibrils (small
strands of cellulose).
This makes for a well-organized system of continuous, very fine capillaries. It
is well known that fine capillaries rob liquids from coarse capillaries. The
fine surface capillaries of each cotton fiber contribute greatly to cotton’s
wipe-dry performance.
o
The “winding layer” (also called the S1
layer) is the first layer of secondary thickening. It differs in structure from
both the primary wall and the remainder of the secondary wall. It consists of
fibrils aligned at 40 to 70-degree angles to the fiber axis in an open netting
type of pattern.
o
The “secondary wall” (also called the S2
layer) consists of concentric layers of cellulose, which constitute the main
portion of the cotton fiber.
After the fiber has attained its maximum diameter, new layers of cellulose are
added to form the secondary wall. The fibrils are deposited at 70 to 80-degree
angles to the
fiber
axis, reversing angle at points along the length of the fiber. The fibrils are
packed close together, again, forming small capillaries.
o
The “lumen wall” (also called the S3
layer) separates the secondary wall from the lumen and appears to be more
resistant to certain reagents than the secondary wall layers.
o
The “lumen” is the hollow canal that
runs the length of the fiber. It is filled with living protoplast during the growth
period. After the fiber matures and the boll opens, the protoplast dries up,
and the lumen naturally collapses, leaving a central void, or pore space, in
each fiber.
o
Figure shows a schematic structure of a mature
cotton fiber, identifying its six parts.
o Throughout the fiber structure,
there are variously sized pores or capillary spaces between the variously sized
fibrils in each of the six fiber parts. Thus, the cotton fiber can be viewed as
a microscopic physical sponge with a complex porous structure. This internal
structure makes cotton fibers accessible to liquids and vapors. The capillary
action of the fibrils pulls liquid in, where it is held in pores between the
fibrils. This structure accounts for cotton’s wickability and
unique absorbing capacity.
o
The
cotton fiber, when observed in its entirety, is a flat, twisted ribbon, with 50
to 100 convolutions per inch. The fiber is tapered on one end and fibrillated
on the other, where it was joined to the cottonseed. This provides the fiber
with a soft touch or feel, because it has no sharply cut ends, as do synthetic
staple fibers.