Page 400 - Handbook of Properties of Textile and Technical Fibres

The chemistry, manufacture, and tensile behavior of polyamide fibers 373

Table 12.1 Selected properties of PA 6 and PA 66 (Brandrup and
Immergut, 1989; Polymer properties database)

Property PA 66 PA 6

Melting point [ C] 256 220
Enthalpy of fusion [kJ/mol] 42.566 30.271

Glass transition T g [ C] a 52 a 40 a

Glass transition T g [ C] (0% water) 74 60
0.5
Solubility parameter [MPa ] 26 25.5
Birefringence Dn 0.063 0.05
Mean polymerization degree 50e100 100e200
Molar volume [mL/mol] 211.5 104.4
van-der-Waals volume [mL/mol] 137.65 68.83
Molar cohesive energy [kJ/mol] 143.1 67.6
Entanglement molecular weight [g/mol] 2200 2400
1
Molar heat capacity [J (mol K) ] 343 171
Boiling water shrinkage [%] 5.3 10
Time of half crystallization [s] 0.42 5
NH 2 end groups [meq/kg] 36e45 54
COOH end groups [meq/kg] 75 100
Isoelectric point [pH] 3e3.5 5.4
Moisture regain (65% RH) [%] 3.5 4.5
Softening temperature [ C] 236 210

a
Values depend on evaluation technique. Calculated values are 51 C for both polyamides (Polymer properties database).
For AB polyamides, there are a lot of properties dependent on the number of
carbon atoms in the elementary unit (numeral m). It is interesting that AB polyamides
with low m have more hydrophilic behaviors and systematically higher densities
in comparison with AB polyamides with high m (see Table 12.3). The structural,
physical, mechanical, and other properties of various polyamides are summarized in
the book (Ellis and Smith, 2009).

12.3 Morphology of polyamide fibers

The term “morphology” refers to the size, shape of crystals, crystal aggregates, and the
arrangement of crystalline and amorphous regions. Polyamides are morphologically
very complex and their morphology changes during their processing and