## 3 Results and Discussion
### Characterization of Starch/MCC Films
#### 3.2.5 Surface Wettability  
The surface wettability of packaging films plays a crucial role in maintaining the integrity of the packaged product. Excessive wetting, especially in highly wettable or hydrophilic films, can lead to liquid infiltration, potentially causing damage to the enclosed product. Therefore, it is imperative for packaging films to exhibit low wettability or high hydrophobicity. Wettability, quantified by the water contact angle, serves as a key metric to assess a material's surface hydrophilicity or hydrophobicity [44]. A surface is deemed hydrophobic when the water contact angle falls within the range of 150\({}^{\circ}\) to 90\({}^{\circ}\). If the water contact angle surpasses 150\({}^{\circ}\), the surface is classified as superhydrophobic. Conversely, a surface is labeled hydrophilic when the water contact angle ranges between 90\({}^{\circ}\) and 10\({}^{\circ}\). Surfaces with water contact angles below 10\({}^{\circ}\) are considered superhydrophilic. Figure 7 depicts the water contact angle of cassava starch films with and without MCC. Initially, the water contact angle of the starch films is measured at 69.17\({}^{\circ}\), indicating the hydrophilic nature of the film surface. Upon the addition of MCC into the films, up to 3% (\(w/w\) of starch), a noticeable increase in the water contact angle is observed, reaching 102.82\({}^{\circ}\). It is noteworthy that there is no significant difference in the water contact angle between the starch/3%MCC and starch/5%MCC films. This suggests that the presence of MCC substantially enhances the hydrophobicity of the film surface. The FTIR spectra depicted in Figure 4 validate the strong interaction between MCC and cassava starch via hydrogen bonds, leading to the formation of a network among the polymer chains of starch. This interaction effectively diminishes the affinity between water and the film surface, thereby inhibiting water penetration [11]. Additionally, MCC diminishes the free space between the molecules of cassava starch films, thereby restricting water absorption [45]. [PERSON] et al. (2020) and [PERSON] et al. (2022) have also reported that the incorporation of MCC can decrease the hydrophilicity of biocomposite films [11; 46]. The findings of the present study suggest that MCC could serve as a promising filler to enhance the hydrophobicity of cassava starch films for packaging applications. The investigation of water dynamic contact angle on films revealed intriguing findings as shown in Figure 8. Initially, all films displayed a decline in water contact angle from 1 to 60 min of exposure. Specifically, starch films and starch/1%MCC exhibited a contact angle below 90\({}^{\circ}\) after 10 min of water contact, indicative of increased water penetration and swelling at 60 min. Starch/3%MCC and starch/5%MCC initially demonstrated contact angle exceeding 90\({}^{\circ}\) after 10 min of water exposure. However, over time, their contact angle decreased, falling below 90\({}^{\circ}\) between 10 and 60 min. This observation suggested that starch/3%MCC and starch/5%MCC initially inhibited water penetration into the film surfaces within the first 10 min. Nonetheless, as the water contact time surpassed 10 min, the hydrophobicity of the films diminished, facilitating water penetration. The observation of starch/3%MCC and starch/5%MCC initially exhibited a contact angle above 90\({}^{\circ}\) after 10 min of water exposure, implying a temporary resistance to water penetration, attributed to the enhanced hydrophobicity conferred by MCC. This finding underscores the potential of MCC to modify the surface properties of starch films, rendering them less susceptible to immediate water infiltration. However, the subsequent reduction in contact angles beyond 10 min signifies a transition towards increased water permeability, indicating a compromise in the hydrophobic barrier provided by MCC.