## 2 Materials and Methods
### Preparation Method  
In order to obtain potato peels, the locally sourced potatoes were initially washed to remove soil residues, and then the peels were carefully separated from the tubers. The peels were subsequently processed to prepare a fine powder. For this purpose, the peels were first dried in the drying apparatus at 50 \({}^{\circ}\)C for 24 h. Following that, the dried material was subjected to grinding and then processed using a Retsch MM400 ball mill machine (Retsch GmbH, Haan, Germany) at a frequency of 30 Hz for a duration of four minutes to  
Figure 1: The “egg-box” model of crosslinking of sodium alginate by Ca\({}^{2+}\) ions.  
achieve finely powdered potato peel waste (PW). The resulting powder was then sieved using a 200-mesh sieve to ensure uniform particle size and stored for use in film fabrication.  
To evaluate the impact of sodium alginate, its molecular weight, and the crosslinking on the properties of pure PW film, three film types were analyzed: pure PW, binary films (PW/SA), and crosslinked films with calcium chloride. The binary and crosslinked films were formulated using two grades of SA: low-viscosity grade SA (lvSA) and high-viscosity SA (hvSA).  
Pure PW films were prepared by dissolving 10 g of PW powder in 200 mL of distilled water, followed by stirring for 5 min. The 5% solid content was selected based on previous studies, indicating that this concentration provides an optimal balance between tensile strength, flexibility, moisture barrier, and film integrity [22; 23]. The mixture was then processed in a high-speed homogenizer at 4500 rpm for 15 min. To prevent foam formation, a few drops of organic antifoam were added during the homogenization process. The solution was subsequently subjected to ultrasonic irradiation using a probe ultrasonic device (Q700, Qsonica, LLC, Newtown, CT, USA) for 15 min at 70% of the total amplitude to enhance solution uniformity and improve film integrity. After obtaining a well-dispersed solution, glycerol was introduced as a plasticizer at a concentration of 35% relative to the dry weight. The mixture was then stirred at 400 rpm at 80 \({}^{\circ}\)C for 1 h. For each sample, the specified amount of the solution was cast onto Petri dishes and allowed to dry in the oven at 40 \({}^{\circ}\)C for 24 h, after which the films were removed for analysis.  
In the binary mixtures, an 80:20 ratio of PW powder to SA was evaluated. To prepare the solution, 2 g of SA was dissolved in 100 g of distilled water in a separate beaker, stirring at 400 rpm and 80 \({}^{\circ}\)C for 50 min. This solution was then added to the homogenized and ultrasonicated PW solution (containing 8 g of PW powder in 100 g of distilled water), with 35% glycerol added as a plasticizer. The mixture was stirred for 1 h at 400 rpm and 80 \({}^{\circ}\)C. Following the cooking process, the solution was cast onto Petri dishes for drying. For the crosslinked mixtures, a CaCl\({}_{2}\) solution was prepared, and an amount equivalent to 7% of the total SA was added dropwise to the PW/SA mixture using a syringe and needle during agitation. To prevent gelation and ensure a uniform solution, the mixture underwent high-speed homogenization at 1000 rpm for 10 min. Finally, a predetermined amount of the solution was poured onto Petri dishes. The amount of SA was determined by the total weight of the dried samples, while the percentage of CaCl\({}_{2}\) was calculated based on the content of SA within the samples. Figure 2 presents a photograph of the PW, PAlv, and PAlvx films after casting.  
Figure 2: Photograph of dried films after casting of PW, PW/SA (PAlv), and crosslinked PW/SA film (PAlvx).