## 1 Introduction  
Petroleum-based polymers are the primary materials used in the packaging industry. The environmental, ecological, and safety concerns over petroleum-based polymers have raised a global trend in the use of biodegradable polymers [1]. Biodegradable plastics can be obtained from either synthetic or natural polymers. Synthetic polymers are commonly derived from non-renewable petroleum resources, while natural polymers are derived from natural/renewable sources or the by-products of food and agricultural products [2]. Biodegradable plastics can be degraded into carbon dioxide (CO\({}_{2}\)), methane (CH\({}_{4}\)), water, and inorganic compounds by the natural microorganisms present in soil or water [3] and can be used to produce edible films and coatings that have a wide application in the food industry due to their biodegradability, sustainability, mechanical, and barrier properties [4]. Moreover, these biopolymers can be used as carriers for flavours, nutrients, vitamins, antioxidants, and antimicrobial agents [5]. Synthetic polymers are more applicable in the packaging industry compared to natural polymers mainly due to their mechanical and barrier properties. However, several efforts are currently dedicated to the development of packaging materials based on natural biopolymers, such as polysaccharides, proteins, etc. [6; 7; 8]. Among them, starch is a novel biopolymer to replace conventional plastics in food packaging due to its high biodegradability, abundance in nature, chemical stability, and film-forming ability. It is one of the most abundant and cheap natural biopolymers made from glucose units that are formed in amylose and amylopectin structures. Starch's functional properties are mainly due to the amylose and amylopectin forms with high molecular weights and their physical form in the granular structure of starch [9]. Starch is a thermoplastic material and can form films in the presence of food-grade plasticizers such as polyols (glycerol, sorbitol, xylitol, etc. ), sugars (glucose, fructose, etc. ), and water [10]. During the starch heating gelation, the hydrogen bonds supporting the crystal structure of the granules break down, and the plasticizers prevent the recrystallization and improve the integrity of starch films by positioning between starch chains' hydrogen bonds. However, starch films have weaker mechanical and barrier properties compared to conventional polymers such as polyethylene [11]. Thus, additives or modification strategies have been proposed to improve the mechanical and barrier properties of starch films [11], such as blending with synthetic polymers and reinforcing with suitable nanofillers [7; 12; 13]. Among synthetic polymers, hydrophilic ones, such as poly(vinyl alcohol) (PVA), are generally safer to use and cheaper than hydrophobic polymers due to using polar solvents such as water and ethanol during the moulding technique. Poly(vinyl alcohol), which is commercially produced from the hydrolysis of poly(vinyl acetate) under alkaline conditions [14], is widely used in the food industry as a packaging material, film, and more often, lacquer due to its low permeability to gases [15]. Nano-scale reinforcing materials are a class of filler materials used to modify polymer matrices by improving their mechanical, thermal, and barrier properties [16]. Chitosan is the second most common biopolymer available in nature, and it is the main component of the exoskeletons of arthropods [2]. Chitosan, due to possessing a considerable antioxidant, antimicrobial activity, and biodegradability, has wide applications in the food industry, agriculture, medicine, and the cosmetics industry [17]. Moreover, chitosan nanoparticles (CNPs), by virtue of their high surface area, biocompatibility, low toxicity, and film-forming ability, have gained attention as potential nanofillers in different polymers [18].