Biomedical Engineering Reference
In-Depth Information
10.0 um
FIGURE 4.79
Raw PAN fibers.
10.0 um
FIGURE 4.80
After oxidation (cross-linked)—before activation.
A positive potential was applied to the polymer solution by attaching the lead
to the high-voltage power supply directly to the outside of the hypodermic needle.
The collection screen was a 10-
10-cm aluminum foil placed 20 cm horizontally
from the tip of the needle as the grounded counterelectrode. The potential difference
between the needle and the counterelectrode used to electrospin the polymer solution
was 20 kV (electrical field strength, 1 kV/cm). The fiber diameter and polymer
morphology of the electrospun polyacrylonitrile fibers were determined using scan-
ning electron microscopy (SEM) (fig. 4.81).
The activation of PAN requires inducing cross-linking by the formation of
pyridine rings by low-temperature annealing and, subsequently, converting nitrile
groups to carboxylic acid groups by saponification with sodium or lithium hydroxide.
The degree of cross-linking depends on annealing temperature and time, which in
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