Page 412 - Handbook of Properties of Textile and Technical Fibres

The chemistry, manufacture, and tensile behavior of polyamide fibers 385

application to molecular orientation measurements in PA 6 fibers has been verified.
They also proved that the fluorescence technique can be used to measure the effects
and structural changes to nylon 6 in the drawing process.

12.4 Production and processing of polyamide fibers

The basic chemical routes of polyamide preparation are comprehensively described in
manypublications (Deopura et al., 2008; Yang, 2006; Estes and Schweizer, 1987; Mather
and Wardman, 2015; Puffr and Kubanek, 1991a; Deopura and Mukherjee, 1997):
The important types of synthesis for the industrial preparation of polyamides are
(Richards, 2005; Hopff et al., 1954):
1. the condensation of diamines with diacids,
2. the self-condensation of amino acids,
3. the hydrolytic polymerization of lactams, which involves partial hydrolysis of the lactam to
an amino acid, and
4. the anhydrous addition polymerization of lactams.

By different methods it is possible to obtain polyamides with required molecular
mass and content of oligomeric substances according to the type of monomers used.
The details about the synthesis of some basic types of polyamides have been thor-
oughly discussed in books by (Deopura et al., 2008; Yang, 2006; Mather and Ward-
man, 2015; Deopura and Mukherjee, 1997).
The formation of polyamide fibers consists of three basic operations:
1. spinning,
2. drawing, and
3. heat setting.
These operations are realized under different conditions with the aim of obtaining
required properties for specific applications and to select the most economic techno-
logical method especially for standard fibers used for clothing purposes.

12.4.1 Spinning
For the production of PA fibers, the technologies of melt spinning, dry spinning, wet
spinning, and gel spinning can be used (Najafi et al., 2017b). Polyamide fibers produced
by conventional melt spinning show low tenacity, low modulus, and high elongation
at break, which are useful for clothing purposes only. Mechanical characteristics of
polyamide fibers can be tuned by drawing and heat setting (annealing). The highest
draw ratio for commercial nylon fibers of about 5e6 is not sufficient to create high-
performance fibers. The maximum tenacity and initial modulus for technical polyamide
fibers/filaments are about 1 N/tex (approx. 1 GPa) and 9 N/tex (approx. 9 GPa) (Yang,
2006), which are far from the corresponding theoretical values of 28.3e31.9 GPa and
183e263 GPa (Lim et al., 1989). Higher modulus and tenacity of PA fiber can be
obtained possibly by breaking/weakening the hydrogen bonds (Gupta, 2008).