*3.2. FTIR Spectra Analysis*

Figure 2a shows the FTIR spectra of the GA, PA66 films and GA/PA66 films with various weight ratios. For the GA film, the broad stretching band at 3000 to 3750 cm<sup>−</sup><sup>1</sup> (amide A) was related to N–H stretching vibrations and O–H, and three characteristic peaks of GA were observed at around 1647 cm<sup>−</sup><sup>1</sup> (amide I) corresponding to C=O and C–N stretching vibrations, 1542 cm<sup>−</sup><sup>1</sup> (amide II) corresponding to N–H bending and C–H stretching vibration, and 1259 cm<sup>−</sup><sup>1</sup> (amide III) [9,36]. For PA66 film, the adsorption peak appearing at 3305 cm<sup>−</sup><sup>1</sup> belonged to the N–H stretching band of amine group and the peaks at 1641 cm<sup>−</sup><sup>1</sup> and 1540 cm<sup>−</sup><sup>1</sup> [37]; and the characteristic peak at 2934 cm<sup>−</sup><sup>1</sup> corresponding to the stretching vibration of C–H also confirmed solid evidence of the existence of PA66 [38].

**Figure 1.** Pictures and scanning electron microscopy (SEM) images of the solution blowing spun gelatin (GA) (**a**), GA/PA66 (2:1) (**b**), GA/PA66 (1:1) (**c**), GA/PA66 (1:2) (**d**), PA66 (**e**) nanofibers.

**Figure 2.** (**a**) Fourier transform infrared (FTIR) spectra and (**b**) X-ray diffraction (XRD) patterns of the GA, GA/PA66 (2:1), GA/PA66 (1:1), GA/PA66 (1:2), PA66 nanofibers.

The absence of peak splitting in all mixed nanofibers indicates that gelatin and PA66 were uniformly dispersed in the fibers. Overall, the GA/PA66 composite films exhibited similar major peaks, but with different amplitudes. The characteristic peaks of PA66 at around 3305 and 2934 cm<sup>−</sup>1, and three characteristic peaks of at around 1647, 1542 and 1259 cm<sup>−</sup><sup>1</sup> belonging to GA, were observed in the GA/PA66 composite films, indicating that the introduction of PA66 did not disrupt the structure of GA and the homogeneous mixing in the GA/PA66 composite film. In addition, it can be observed that the peak around 3436 cm<sup>−</sup><sup>1</sup> in GA shifted to a higher band at about 3305 cm<sup>−</sup>1. The lower intensity of the peak in the range 3125 cm<sup>−</sup><sup>1</sup> and 3400 cm<sup>−</sup><sup>1</sup> may be attributed to the interaction between the O–H and N–H groups of gelatin and PA66 molecules resulting in more intermolecular or intramolecular hydrogen bonding [20]. This result may also explain the phenomenon of improved GA spinnability mentioned above.
