Page 432 - Handbook of Properties of Textile and Technical Fibres

The chemistry, manufacture, and tensile behavior of polyamide fibers 405

Figure 12.33 Typical cross-section of polyamide fibers.

or highlight effects; and resistance to soiling. The increase in the surface area of a mul-
tilobal filament requires more dyestuff and reduces wash-fastness (Cook, 2001).
Preparation of hollow fibers is possible by using precoalescent spinnerettes
(injection of a gas through the capillary to create the void (U.S. Pat. 3075242; U.S.
Pat. 3081490)) and post-coalescent spinnerettes (entrapment of gas by coalescence
of the molten polymer (U.S. Pat. 3745061)). The open hollow-fiber shape is created
by bicomponent yarn technology, where the filament is made from a water-soluble
copolyester core and a nylon sheath (U.S. Pat. 3394985). The final shape is obtained
by the dissolution of the core in alkalis.
Polyamide multifilaments are frequently textured and bulked by the various pro-
cesses in common use.
Bicomponent polyamide fibers are made by two filaments of different constitution,
which have been brought together during spinning to form a single bicomponent fila-
ment. Some types of bicomponent PA fibers are shown in Fig. 12.34.

(a) (b)

Core
Sheath
Figure 12.34 Examples of bicomponent polyamides (a) longitudinal and (b) cross-sectional.