*3.8. Solvent Resistance*

Figure 7 shows the morphologies of the PA66 films and GA/PA66 films after immersing them in 1 × PBS for 24 h and drying. The pure gelatin film (Figure 7a) swelled in 1 × PBS solution, completely losing their fibrous structure and dried to form a transparent solid with a block-like structure, while the pure PA66 film (Figure 7e) remained intact in its fibrous form. With the addition of PA66, the fiber structure of the composite films (Figure 7b–d) was well maintained, indicating that the addition of PA66 could effectively improve the ability of GA to resist dissolution and thus maintained the various advantages brought by its nanometer size. The explanation for this could be that the PA66 network provided good support in an aqueous environment to maintain the basic structure of the gelatin. This intact fiber structure could improve the barrier performance of the fiber film in humid environments. The above results are consistent with the observation of Deng et al.'s work [16], which found that zein particles were distributed nicely in the gelatin network and helped preserve the compact structure by co-electrospinning. As reported by Ahammed et al. [49], the resistance to water of GA was also improved with the solubility in water decreased from 100% to 40% after the introduction of zein. The improved solvent

resistance allows GA/PA66 composite films to be used for packaging of foods that generate water vapor due to respiration, such as fruits and vegetables.

**Figure 7.** Morphologies of the GA (**a**), GA/PA66 (2:1) (**b**), GA/PA66 (1:1) (**c**), GA/PA66 (1:2) (**d**) and PA66 (**e**) films after immersed in 1 × phosphate-buffered saline (PBS) for 24 h.
