Page 427 - Handbook of Properties of Textile and Technical Fibres

400 Handbook of Properties of Textile and Technical Fibres

of an induction period and can be initiated in the presence of cationic catalysts such as
protic acids, lewis acid derivatives, salts of acids with amines, or ammonia.
The degree of polymerization n for spinnable products is between about 130 and
250 (lower values for textile fibers, higher values for tire yarn and technical fibers)
(Fourné, 1999).
Spinning of the PA 6 fibers is carried out by melt spinning. Melt spinning temper-
ature is selected according to the molecular mass of PA 6 so as to have the same melt

viscosity. For textile fibers this temperature is 260e285 C, for technical fibers it is
280e290 C, and for tire cord 285e300 C. Spinning speed depends on the type of

end-product. For standard PA 6 fibers cold-drawing is usual and for technical yarns
hot-drawing is used.
There exists a continuous effort to improve the mechanical properties of PA 6 fibers
for technical applications. Recent developments are comprehensively discussed in a
book by Najafi et al. (2017b) and a thesis by (Gupta, 2008). The main techniques
up to 1993 are presented in Table 12.5 in which the main methods (Wu et al., 2004;
Acierno et al., 1979; Zachariades and Porter, 1979; Richardson and Ward, 1981; Shi-
mada and Porter, 1981; Kunugi et al., 1982; Gogolewski and Pennings, 1985; Chuah
and Porter, 1986a,b; Kunugi et al., 1993; Suzuki et al., 1993) for PA 6 preparation with
the chief researchers and obtained maximum values of the initial modulus (E) and ten-
sile strength (s) are summarized.
There are many interesting methods in the list, for example, the spinning of a
mixture of nylon 6 and lithium halide by Ciferris et al (Acierno et al., 1979) and
Ward et al (Richardson and Ward, 1981), the plasticization with ammonia or iodine
by Porter et al (Zachariades and Porter, 1979; Chuah and Porter, 1986a), and
the dry spinning of nylon 6 solution in formic acid/chloroform by Pennings et al
(Gogolewski and Pennings, 1985). However, the moduli which were achieved were
still low; even the maximum value was only 12.7% of the crystal modulus along
the PA 6 molecular chains of 165 GPa (Sakurada and Kaji, 1970). To overcome
this situation, Kunugi et al. (1998) had applied the vibrating hot-drawing and zone-
annealing method to the nylon 6 fiber, which succeeded in a further improvement of
the mechanical properties. Recent improvements described by Najafi et al. (2017b)
look more promising.

12.4.7 Other polyamides
In addition to the popular polyamides like PA 6 and PA 66, there are several other
polyamides that have been introduced for use as fibers in specialty applications where
certain combinations of properties are desired. The major specialty nylons include PA
3, PA 4, PA 46, PA 5, PA 610, PA 7, PA 8, PA 11, and PA 12 (Fourné, 1999; Kohan
and Zimmerman, 2003). Major properties of these polyamides are summarized in a
book by Ellis and Smith (2009).
12.4.7.1 PA 46

PA 46 is created by polycondensation of diamine butane and ADA. These com-
pounds make adduct (salt) able to polymerize in water to produce a solution of