3.2. Viscosity of EpSS
In general, viscosity of the polymer solution is important since it
determines the processability of a polymer. For example, when the
viscosity is too high more energy would be needed for fabrication,
while too low the solution would not maintain its form until solidification
is completed. In the case of the aqueous HS solution, low
viscosity was a problem. A viscous aqueous SS solution could not
be prepared due to the limited solubility of HS in water and gelation
of HS at high concentration. Previously we prepared a highly
concentrated HS solution up to 30 wt.% by changing the solvent
from water to a LiCl/DMSO solvent and fabricated SS into beads
and fibers [4]. Therefore a LiCl/DMSO solvent could be a good solvent
for the fabrication of SS. Fig. 1 shows the viscosity of HS and
EpSS at the same concentration (20 wt.%) in 1M LiCl/DMSO. All of
the EpSS solutions exhibited higher viscosity than HS and EpSS25
shows the highest viscosity among EpSSs. However, the viscosity
of EpSS25 was too high and it was difficult to pass it through the
orifice of a syringe needle. The increased viscosity of EpSS enabled
fabrication of SS into beads and fibers even at a lower concentration
compared to HS [22]. Since the viscosity of each sample was measured
at the same concentration and temperature, the differences
in viscosity between HS and EpSS and among EpSS might be due to
the differences in their molecular weight distribution.