Page 466 - Handbook of Properties of Textile and Technical Fibres

Tensile failure of polyester fibers 439

1
Shrinkage in water at 100°C (%) 40
2
60

20

0 2000 4000 6000
Spinning speed (m/min)
Figure 13.8 Typical spinning speed effect on fiber shrinkage in boiled water. Region 1: POY;
region 2: LOY.
Krifa M: Fiber length distribution in cotton processing: dominant features and interaction
effects, Textil Res J 76:426e435, 2006.

Just before the neck formation, the viscosity suddenly decreases (Raghavan and
Cuculo, 1999).
It is generally believed that the occurrence of necking is associated with the crys-
tallization process. The stress-induced crystallization is an essential requirement for
neck formation. The position of the neck moves closer to the spinneret as the deforma-
tion rate is increased. The actual position of the neck fluctuates and from diameter mea-
surements a bimodal distribution appears (Raghavan and Cuculo, 1999). Necking is
also seen when the polymer intrinsic viscosity is increased (Ziabicki and Kawai, 1985).
High-speed spinning requires considerable energy consumption, high costs for
manufacturing the take-up bobbin, and high costs for operational safety. To obtain
orientation-induced crystallization at speeds lower than that for the high-speed spin-
ning supercooled spinning was proposed (Cao, 2006). This is achieved by setting
the nozzle temperature to 265 C, i.e., lower than the melting point of PET. The

experimental results show that high orientation and high crystallinity can be achieved
at a spinning speed of 2500 m/min, which compares well with the speed of
5000e6000 m/min used in high-speed spinning (Cao, 2006).
To obtain high-tenacity, high-modulus PET fibers, the liquid isothermal bath (LIB)
spinning process was developed (Lin et al., 1992). For the normal LIB, the liquid bath
is placed in the thread line at a position that is 150e180 cm from the spinneret. The
modified LIB process was developed with the intention of increasing the temperature
of the fibers prior to their entry into the hot liquid bath. The hot liquid reduces the cool-
ing rate of the fibers. It was found that the heating of the fibers before entering the
liquid bath induces a uniform radial structure and an increase of deformability (Huang
et al., 1997). This process makes possible the formation of high-tenacity, high-
modulus PET fibers via melt spinning at high speeds (up to 5000 m/min). For the