Page 419 - Handbook of Properties of Textile and Technical Fibres

392 Handbook of Properties of Textile and Technical Fibres

Textured yarn: paradox “absence of texture (structure)”

Multifilament flat yarns

Staple yarns
Textured yarns (false twist)

Textured yarns (air jet)

Textured yarn:
crimped, bulked, stretched
Figure 12.28 Appearance of flat, textured, and staple yarns.

in the amorphous regions of PA 6 are weakened or broken above 70e120 C, which
facilitates orientation of polymeric chains during hot-drawing (Kunugi et al., 1998).
In the production of bulked continuous filament yarn the spinning-drawing-
texturing process is used. In this process, a lower draw ratio (2.6) is used and drawing

is carried out in one stage only, at 180 C. After drawing, the fibers are texturized
usually by air jet or stuffer box texturing. If the LOY material is delivered for texturing,
a sequential drawing-texturing process is used, i.e., the texturing machine is provided
with an independent drawing zone. With the POY material the drawing-texturing
process is simultaneous, i.e., the material is additionally drawn at the same time as
texturing takes place (Puffr and Kubanek, 1991b). The differences between flat mul-
tifilaments, textured multifilaments, and staple yarns are shown in Fig. 12.28.

12.4.3 Heat setting
The creation of a fibrous structure is completed during the heat-induced stabilization
stage (fixation of structure) by heat setting (Sengupta, 1997b; Gupta, 2002). During
stabilization, relaxation of internal stresses and recrystallization due to heating or
swelling occurs. There exist three basic setting methods:
1. Isotonic setting (under constant tension) takes place when fibers are shrunk, chains are
retracted, and stress relaxation combined with recrystallization occurs. This setting often
occurs in the free-state during which dimensional changes are not constrained.
2. Isometric setting (under constant length) results in the geometry of fibers not being changed.
Stress relaxation combined with chain sliding and crystallization under stress occurs. The
fiber orientation and strength remain practically constant. This setting is realized at a constant
fiber length.
3. Post drawing, additional tensile deformation is applied. Stress relaxation and recrystallization
occur due to the higher temperature.