*3.1. Appearance and Color*

All biodegradable films developed in this study appeared to be homogeneous. Figure 1 shows the starch-chitosan composite films with different proportions of the poloxamer pluronic F127 stored for 0 and 16 months; the images were captured on a black background

difference.

difference.

for contrast. All films presented a translucent white color, as seen in Figure 1, and exhibited no significant visible changes during the 16-month storage process. They did not become brittle or more brittle to handle with time in storage. No visibly considerable color change was noted in the films when compared to the initial time (0) with the samples stored for 16 months. However, when evaluating the film color using a colorimeter, it was observed that the samples did change their coloration after 16 months of storage when compared to the initial time, as indicated by the values of the *L\**, *a\**, and *b\** color parameters in Table 1. exhibited no significant visible changes during the 16-month storage process. They did not become brittle or more brittle to handle with time in storage. No visibly considerable color change was noted in the films when compared to the initial time (0) with the samples stored for 16 months. However, when evaluating the film color using a colorimeter, it was observed that the samples did change their coloration after 16 months of storage when compared to the initial time, as indicated by the values of the *L\**, *a\**, and *b\** color parameters in Table 1. ground for contrast. All films presented a translucent white color, as seen in Figure 1, and exhibited no significant visible changes during the 16-month storage process. They did not become brittle or more brittle to handle with time in storage. No visibly considerable color change was noted in the films when compared to the initial time (0) with the samples stored for 16 months. However, when evaluating the film color using a colorimeter, it was observed that the samples did change their coloration after 16 months of storage when compared to the initial time, as indicated by the values of the *L\**, *a\**, and *b\** color parameters in Table 1.

All biodegradable films developed in this study appeared to be homogeneous. Figure 1 shows the starch-chitosan composite films with different proportions of the poloxamer pluronic F127 stored for 0 and 16 months; the images were captured on a black background for contrast. All films presented a translucent white color, as seen in Figure 1, and

All biodegradable films developed in this study appeared to be homogeneous. Figure 1 shows the starch-chitosan composite films with different proportions of the poloxamer pluronic F127 stored for 0 and 16 months; the images were captured on a black back-

**Figure 1.** Biodegradable films based on corn starch and chitosan with pluronic F127 at 0%, 1%, 3%, and 5%; images were captured in the initial storage time (time 0) and after 16 months of storage at room temperature; the photos of the films at 16 months were taken at higher magnification. **Figure 1.** Biodegradable films based on corn starch and chitosan with pluronic F127 at 0%, 1%, 3%, and 5%; images were captured in the initial storage time (time 0) and after 16 months of storage at room temperature; the photos of the films at 16 months were taken at higher magnification. **Figure 1.** Biodegradable films based on corn starch and chitosan with pluronic F127 at 0%, 1%, 3%, and 5%; images were captured in the initial storage time (time 0) and after 16 months of storage at room temperature; the photos of the films at 16 months were taken at higher magnification.

**Table 1.** Effect of poloxamer content and storage time on water solubility, color, contact angle, and mechanical properties of corn starch-chitosan biodegradable films. **Table 1.** Effect of poloxamer content and storage time on water solubility, color, contact angle, and mechanical properties of corn starch-chitosan biodegradable films. **Table 1.** Effect of poloxamer content and storage time on water solubility, color, contact angle, and mechanical properties of corn starch-chitosan biodegradable films.

*Polymers* **2021**, *13*, x FOR PEER REVIEW 4 of 10

*Polymers* **2021**, *13*, x FOR PEER REVIEW 4 of 10

**3. Results and Discussion**  *3.1. Appearance and Color* 

**3. Results and Discussion**  *3.1. Appearance and Color* 


Mean values of at least three replicates. § Experimental data and significant difference taken from Fonseca-García, Jiménez-Regalado [11]. 1 Hunter color parameters, *L\**: color coordinate, lightness (0 = black, 100 = white); *a\**: color coordinate, F127 5% 56.98 3.27 a 12.40 a 89.53 1.30 −6.02 50.74 Mean values of at least three replicates. § Experimental data and significant difference taken from Fonseca-García, Jiménez-Regalado [11]. 1 Hunter color parameters, *L\**: color coordinate, lightness (0 = black, 100 = white); *a\**: color coordinate, Mean values of at least three replicates. § Experimental data and significant difference taken from Fonseca-García, Jiménez-Regalado [11]. <sup>1</sup> Hunter color parameters, *L\**: color coordinate, lightness (0 = black, 100 = white); *a\**: color coordinate, greenness and redness (+ = red, − = green); *b\**: color coordinate, blueness to yellowness (+ = yellow, − = blue). *L\** standard= 91.76, *a\** standard = 2.14, and *b\** standard = <sup>−</sup>10.64. a,b,c: values with different letter in a same column denote significant difference.

greenness and redness (+ = red, − = green); *b\**: color coordinate, blueness to yellowness (+ = yellow, − = blue). *L\** standard=

#### 91.76, *a\** standard = 2.14, and *b\** standard = −10.64. a,b,c: values with different letter in a same column denote significant greenness and redness (+ = red, − = green); *b\**: color coordinate, blueness to yellowness (+ = yellow, − = blue). *L\** standard= *3.2. Morphology by SEM*

91.76, *a\** standard = 2.14, and *b\** standard = −10.64. a,b,c: values with different letter in a same column denote significant Figure 2 shows a comparison of the films with different amounts of poloxamer evaluated at time 0 and 16 months of storage. The evaluation of the initial time (zero) showed that in the biodegradable films formulated from starch and chitosan, the presence of the poloxamer significantly improved the morphology of the surface of these materials. In the film formulated without F127, an irregular surface was observed without cracks. This appearance was gradually reduced until a smoother surface was obtained with an increase in the content of F127.

Figure 2 shows a comparison of the films with different amounts of poloxamer evaluated at time 0 and 16 months of storage. The evaluation of the initial time (zero) showed that in the biodegradable films formulated from starch and chitosan, the presence of the poloxamer significantly improved the morphology of the surface of these materials. In the film formulated without F127, an irregular surface was observed without cracks. This appearance was gradually reduced until a smoother surface was obtained with an increase

**Figure 2.** SEM images for the surface (500×) of composite films of corn starch-chitosan with pluronic F127 at ratios of 0%, 1%, 3%, and 5% stored for 0 and 16 months. **Figure 2.** SEM images for the surface (500×) of composite films of corn starch-chitosan with pluronic F127 at ratios of 0%, 1%, 3%, and 5% stored for 0 and 16 months.

A significant change was observed in the morphology of all the composite biodegradable films after 16 months of storage under ambient conditions; however, the most noticeable or drastic changes were observed in the materials containing F127 at concentrations of 3% and 5% (Figure 2). A less homogeneous morphology was observed in these films, which may be due to a change in the organizational structure of the starch chains. Garalde, Thipmanee [20] reported a similar morphology in thermoplastic starch/poly (butylene adipate-co-terephthalate) (PBAT) films, which occurred when the starch was selectively removed from the composite film. A significant change was observed in the morphology of all the composite biodegradable films after 16 months of storage under ambient conditions; however, the most noticeable or drastic changes were observed in the materials containing F127 at concentrations of 3% and 5% (Figure 2). A less homogeneous morphology was observed in these films, which may be due to a change in the organizational structure of the starch chains. Garalde, Thipmanee [20] reported a similar morphology in thermoplastic starch/poly (butylene adipate-co-terephthalate) (PBAT) films, which occurred when the starch was selectively removed from the composite film.

#### *3.3. Contact Angle 3.3. Contact Angle*

*3.2. Morphology by SEM* 

in the content of F127.

The wettability of the biodegradable films was evaluated in terms of the contact angle; Table 1 shows the contact angle values of the starch-chitosan-poloxamer (F127) films. In films F127 0% and F127 1%, after 16 months of storage, the hydrophilicity increased as the contact angle decreased from 99.93° to 67.66° and 33.22° to 31.89°, respectively. In the case of F127 3% and F127 5%, the hydrophilicity decreased as the contact angle increased from 43.88° to 46.09° and 46.25° to 50.74°, respectively. The results suggest that pluronic F127 has a considerable effect on the wettability of biodegradable starch-chitosan films. The wettability of the biodegradable films was evaluated in terms of the contact angle; Table 1 shows the contact angle values of the starch-chitosan-poloxamer (F127) films. In films F127 0% and F127 1%, after 16 months of storage, the hydrophilicity increased as the contact angle decreased from 99.93◦ to 67.66◦ and 33.22◦ to 31.89◦ , respectively. In the case of F127 3% and F127 5%, the hydrophilicity decreased as the contact angle increased from 43.88◦ to 46.09◦ and 46.25◦ to 50.74◦ , respectively. The results suggest that pluronic F127 has a considerable effect on the wettability of biodegradable starch-chitosan films.
