Page 431 - Handbook of Properties of Textile and Technical Fibres

404 Handbook of Properties of Textile and Technical Fibres

long periods without deterioration. Spinning is carried out in a manner similar to that
used in PA 6 production.
The melting point of PA 11 is on the lower side for general textile use, and great
care must be taken in ironing and other elevated temperature treatments. The initial
modulus of PA 11 is higher than those of the other nylons (44.1 cN/dtex), resulting
in increased stiffness, stress-crack resistance, and rigidity. This is advantageous in
applications such as brush bristles, and it also helps for easier processing.
PA 11 fibers, Rilsan, have a silk like handleability but they have lost their signif-
icance as a fiber material. PA 11 yarns do not stretchsoeasily when subjectedto
physical processing such as winding. The high initial modulus of PA 11 suggests
that this is a useful material for the huge tire cord market. Tires reinforced with
PA 11 would not be subjected to flat-spotting to the extent that PA 6 and PA 66 rein-
forced tires are. The low moisture absorption of PA 11 enables it to retain its excel-
lent insulation properties at higher humidities. This is a useful characteristic in
electrical applications. PA 11, with a density similar to water, is a very light fiber,
with much greater recovery power than the other polyamides. PA 11 has been
made as multifilament yarns, monofilaments, staple, and tow, in a range of deniers
and staple lengths.

12.4.7.10 PA 12

PA 12 fibers are spun from polylaurylamide. PA 12 has a melting point at 180 C, a
3
density of 1010 kg/m and a moisture regain of 0.9% at 65% RH and 4.5% at 100%
RH (amorphous) (Aharoni, 1997; Cook, 2001).
PA 12 is inherently expensive, however, and it is unlikely that it could become of
importance as a general purpose polyamide fiber.
The starting material is butadiene. Polycondensation of the lauryl lactam is carried
out in the usual way and polymers may be obtained without difficulty. PA 12 polymer
contains only a very small proportion of oligomers (0.75% extractable with water).

12.4.8 Modification of polyamide fibers

Modification of polyamide fibers is an effective way to improve desired properties,
suppress unwanted properties, and add new properties according to the type of appli-
cation envisaged. Major types of modification are physical, chemical, and combined
modifications.

12.4.8.1 Physical modification
The cross-sectional shape of a fiber has a governing influence on many important
characteristics, and polyamides are produced in a variety of noncircular cross-
sections (see Fig. 12.33).
Multilobal cross-section polyamides have advantages like increased cover; crisp,
silk-like, firm handle; reduced pilling in spun yarn fabrics; increased bulk; sparkle