Page 174 - Handbook of Properties of Textile and Technical Fibres

Silk: fibers, films, and compositesdtypes, processing, structure, and mechanics 151

(a)
Spinneret / head
Anterior tube

Central part
Sericins

Posterior part
Fibroin

(b)

Figure 5.6 Schematic of the pair of Bombyx mori silk glands. (a) Each gland is composed of
posterior, middle, and anterior regions, the middle region itself being composed of three parts. A
microphotograph of a gland “dried” is given in (b); the animal head is on the top left side
(close to the interference artefact).

to kill the worms, or pupas. The cocoons are then dipped into hot water to loosen the
tightly woven filaments. These filaments are unwound onto a spool. Each cocoon is
made up of a filament between 500 and 1500 m long! Between five and eight of these
superfine filaments are twisted together to make one thread (flotte). Finally this thread
is used by silk makers and woven into yarn, and then into textiles or used for embroi-
dery work. Degummingdremoval of the sericin coatingdand dyeing can take place
before or after weaving (Fig. 5.7).
The silkworm extrudes the silk through its mouth, and it is the sideways movement
of the head after initially sticking the fiber end tip at one spot, which permits the silk to
be spun or extruded and which may induce axial orientation in the fiber structure
through shearing of the polymer. If the silkworm wants to stop the production, it
has to cut its fiber. Production speed is around 10 mm/s (Kiyosawa et al., 1999).
The cocoon is made up of one continuous fiber the diameter of which reduces
throughout the cocoon with the inner most part, the last part to be produced by the