# Edible Packaging: A Technological Update for the Sustainable Future of the Food Industry
## 3 Results
### Production of Edible Films and Coatings
#### 3.3.2 Dry Process  
In the dry process, added contents are converted into films by using the thermoplastic behavior at low moisture levels [14]. The dry process is more varied and consists of the extrusion method, compression molding, injection molding, etc. [3].  
The extrusion process is a method of producing edible films on a commercial scale that consists of three zones: feeding, kneading, and heating. This method can change the structural properties and improve the physicochemical characteristics of extruded films [15]. In the feeding zone, film components are mixed, and air compression is applied to minimize the moisture content of these components. This process is also known as a \"dry process\" because it functions best with a small amount of water or solvents. As the ingredients move through the kneading zone, the strain, temperature, and density of the mixture rise. Then, these materials are heated above their glass transition temperature to facilitate a conversion into a melt form, which is extruded through a suitably shaped nozzle by the rotating force of an extrusion screw. The resulting materials are then subjected to cooling to form the film [16]. Mechanical and thermal energy are used in this process for the production of extruder-based films. Screw speed also has a role in specific mechanical energy. Different screw speeds alter film properties such as shear rate, homogeneity, and stress, as well as the control of residence time, which allows for the addition and removal  
Figure 1: Schematic representation of the production of edible films (Casting method) and coatings.  
of additives like stabilizers. As the screw speed increases, the torque value of the extrusion method to obtain films decreases. Other factors such as screw speed, barrel temperature, feed moisture content, die diameter and pressure, energy input, etc., are necessary to ensure that the extrusion process affects the final products. Figure 2 shows a schematic representation of the extrusion process of edible film production [13; 14].  
The extrusion method has better mechanical and optical properties than the casting process, and it also requires less energy and time to process the material. Extrusion processing is also a widely employed commercial technique in the food industry that offers high performance at a reasonable cost. However, the extrusion method has some drawbacks, which are limited to materials with low temperature tolerance and low moisture levels. For example, chitosan is not a thermoplastic material and cannot be extruded [14].  
Compression molding is one of the oldest methods and is considered a sustainable process due to its low energy requirement and rapid formation. Here, the film-forming contents are heated under high pressure in the mold until they solidify. Processing time is also a critical parameter for determining the properties of films. This step is usually used in combination with the extrusion method to prepare the film-forming material before its main thermoforming process. [PERSON] et al. [17] developed an edible film from starch and yerba mate extract using extrusion and compression molding. Their study revealed that films produced via the compression-mold technique with yerba mate extract can improve the shelf life of foods, providing a promising active food packaging material.  
The injection molding method is mainly used to make plastic items, but it is also appropriate for the mass production of edible films. This method consists of three stages, namely, filling, packing, and cooling, and its parameters are injection pressure, molding temperature, and pre-injection pressure temperature [18]. This method can be used in conjunction with the extrusion method to obtain a film. Studies on the injection molding method are scarce [14].