Page 409 - Handbook of Properties of Textile and Technical Fibres

382 Handbook of Properties of Textile and Technical Fibres

Cross-section

Taut tie Microfibrils
molecules

Crystallites
Longitudinal
view
Amorphous part

Figure 12.17 Structural model of PA fibers.

Crystalline phase Taut tie molecules

C
Crystallinity: TT
l c 40%–50%
Orientation >0.9 Portion:
0.05%–1.5%
A
Orientation >0.6

ν TT
Amorphous phase
Figure 12.18 Three-phase model of polyamide fibers.

This model is composed mainly of crystalline and amorphous phases and oriented
tie molecules. The dimensions of crystallites are 5e20 nm in all directions.
The basic structural elements are microfibrils of thickness of 10e20 nm and a
length of tens of micrometers. Microfibrils are composed of alternating amorphous
layers and crystalline blocks (see Figs. 12.17 and 12.18). The long period (the sum
of crystal block thickness and amorphous layer thickness) depends on the temperature
and rate of drawing.
The crystalline blocks in microfibrils and adjacent microfibrils are laterally
connected by numerous tie molecules (10% to 30%). Tie molecules result from chain
unfolding during the drawing process, and their strength and length significantly affect
the process of fiber breakage.
Bundles of microfibrils are densely packed and aligned into fibrils (length 3e6 mm).
The packing density of microfibrils within a fibril is more perfect than the lateral