Page 252 - Handbook of Properties of Textile and Technical Fibres

226 Handbook of Properties of Textile and Technical Fibres

(a) Primary wall Secondary wall-S layer
2
(approx. 0.1 μm thick) (approx. 4 μm thick)

Lumen
Secondary
wall
Winding
layer
Primary
wall
Lumen
wall
Winding-S layer Lumen (c)
1
Cuticle (approx. 0.1 μm thick)
Fiber convolutions
(b)

Figure 7.1 Structural features of cotton fiber.

cotton fibers exhibit higher tensile strengths than immature fibers, everything else
being equal. The primary wall makes for a well-organized system of continuous
very fine capillaries. These fine capillaries “rob” liquids from coarse capillaries; an
action that contributes greatly to cotton material’s wipe-dry performance. The third
part is called the winding layer or S1 layer. This is the first layer of secondary thick-
ening, and it differs in structure from either the primary wall or the remainder of
the secondary wall. It is an open “netting” pattern of fibrils that are aligned at about
40e70 degrees angles around the fiber axis (Duckett, 1975). The fourth part is the
secondary wall, which consists of concentric layers of pure cellulose constituting
the main portion of the cotton fiber (also called S2 layer). Secondary wall fibrils
that close to the primary wall lie at an approximate 45 degrees angle to the fiber
axis, while this orientation becomes aligned more closely with the fibrillar axis as
the fiber core, or lumen, is approached (El Gaiar and Cusick, 1976). The thickness
of the secondary wall, from primary wall to lumen, determines fineness and defines
the fiber’s maturity. Fibers with no secondary wall development exhibit no individual
fiber integrity and can exist only in clumps. Development of the secondary wall
provides the fiber with rigidity and fullness (Duckett, 1975). The fifth part is the lumen
wall, which is a layer separating the secondary wall from the sixth part, or the lumen. It
appears to be more resistant to certain reagents than the secondary wall layers. Finally,
the lumen is a hollow canal that runs along the fiber axis. It is filled with living
protoplasts during the growth period. After the fiber matures and the boll opens, the
protoplast dries up, and the lumen will naturally collapse.