3.3.1. Mechanical Properties

The mechanical properties of films represent their ability to maintain their integrity and endure external stress during the processing, transportation, handling, and storage of packaged materials [30]. As shown in Figure 3, AGO/SPEEK film presented the highest TS (Figure 3a) and EM (Figure 3b) but the lowest EAB (Figure 3c) under the maximum load of 0.9% (*w/w*). It was attributed to the existence of numerous hydrogen bonds in the AGO/SPEEK film that caused strong cohesive energy density [12,31]. Likewise, AGO/SPEEK films also presented higher TS and EM under the same load, which was ascribed to the reaction of more –NH2 groups with SPEEK as indicated by the decrease of crystallinity shown in XRD pattern [29]. The EAB of AGO/SPEEK films (Figure 3c) was lower than that of the original film by varying degrees, which was imputed to the loading of AGO that restricted the movement of SPEEK polymer chains [32]. Moreover, extensive hydrogen bonds increased the interfacial adhesion, thereby enhancing the mechanical properties of the film [12,31]. Noteworthily, when the filling amount of the inorganic filler was between 0.1% and 0.9% (*w/w*), the EAB of films remained above 40%, showing that it still had sufficient mechanical strength and extensibility, which is required for food packaging applications [30].

**Figure 3.** Mechanical properties of AGO/SPEEK films. (**a**) Tensile strength, (**b**) elastic modulus, (**c**) elongation at break.
