Page 407 - Handbook of Properties of Textile and Technical Fibres

380 Handbook of Properties of Textile and Technical Fibres

The oriented amorphous domains are primarily in the intrafibrillar region and the
unoriented components are mainly in the interfibrillar region (see Fig. 12.13). These
amorphous phases are different in packing density and interchain structure. The chain
segments inside the oriented amorphous region are more densely packed and their
interchain interactions are more like crystals. Interactions for the unoriented amorphous
region are similar to those in the polymer melt. This structural disparity leads to the
two amorphous domains responding differently in processing (i.e., drawing and heat
setting) and environmental conditions (i.e., humidity and temperature). The unoriented
components probably have a greater influence on the dye/moisture diffusion rate than
oriented amorphous components.
The basic characteristic of the noncrystalline phase is the glass transition
temperature T g since it has a considerable effect on both the processing and properties
of the polyamide fibers. It defines the temperature at which mobility of chain segments
or structural units begins. Processes affecting this phase have a corresponding effect on
the glass transition temperature. This is particularly evident in its response to the
concentration of water absorbed in polyamides. An increase in water content results

in a steady decrease of T g towards a limiting value (83% in C from dry T g for PA
6 and 77% from dry T g for PA 66) (Yang, 2006).
This phenomenon may be explained by a sorption mechanism according to which
3 mol of water interacts with two neighboring amide groups (see Fig. 12.14).
Polymers crystallizing from the melt are free from external stresses exhibited by
spherulitic structures (see Fig. 12.15). Spherulites originate from their crystal nuclei
and grow radially in all directions.
Typical, is the radial arrangement of individual crystallite-fibrils in formation with
the spherical symmetry. The radial fibrils normally diverge. When they are branching
(creating more fibrils at greater radial distances) the spherulite space will be uniformly
filled (Puffr and Kubanek, 1991a).
During deformation up to high strains (usually due to elongational flow in melt spin-
ning and plastic deformation in drawing), almost all isotropic spherulites are transformed

Figure 12.14 Interaction of water
with polyamides.
C O
H
HN
C O H O HN O
H
HN H C O
H
O
H
C O
H
C O H O HN O
HN
HN H H
C O