using nozzle diameters of 200 μm instead 300 μm. In
addition, it can be clearly seen that all obtained mats more
resemble those of pure gelatin, while the wavy net behavior
of the PU component is not expressed at all as result of the
simultaneous spinning of DMF, acetic and formic acid
polymer solutions.
Fiber diameters were generally in the range of 2 to 12 μm
in all cases, GPU1 having the best distribution centered at
about 7 μm. It must be mentioned that well outside the main
domain investigated using Image J software were observed
agglutinated fiber parts (Figure 7(c)) and residual sparse
fibers in the nanometer range (Figures 7(a) and 7(c)). These
fibers show diameters of about 100-200 nm and can be
better viewed at higher magnification (Figures 7(d) and
7(f)). The thin fibers formation is related to the G/PU ratio,
and in particular to the proportion between gelatin solvents
and DMF, rising from a negligible amount for GPU2 to
about 20 % for GPU3. Furthermore, the solvents used are
miscible, but gelatin solubility in DMF is very low whereas
the others may precipitate the polyurethanes. As a consequence,
the resulting vapors interfere with the viscosity
and stretching behavior of extruded jet. Obviously, these
interferences are enhanced by increasing the amount of the
higher volatile solvents. Thus, the process seems to involve
the different stretching of filaments in the air flow enriched
by an increased amount of vapors coming from the higher
volatile solvents [10] rather than subsidiary jets formation
and backbone emitted nanofibers observed at the electrospinning
of complex mixtures [7,24]. This supposition is also supported
by the results obtained at gelatin and polyurethane nonmixed
mats (Figures 4(c) and 5(a)), where fibers distributions
include fractions of relative similar diameters. The solvents
interference may also compromise the jets stability, inducing
coalescence and bead formation. Both effects are clearly
shown in Figure 7, where the G/PU ratio of 2:1 (GPU3)
(Figures 7(c) and 7(f)) was led to the lowest quality mats,
characterized by relative frequent coalescence and a high