## 1 Introduction  
In 20 years, the planet has produced more plastic than in the previous 50 years. Thus, the use of non-biodegradable polymers in everyday life is one of the sources of environmental problems. To overcome these problems, researchers have sought sustainable alternatives [1; 2]. To replace non-renewable petrochemical materials, starch and its modifications are good candidates [3; 4]. As renewable source adhesives, chitosan [5; 6], cellulose, lignin [7] and alginate [8], polylactic acid (PLA), polyhydroxybutyrate (PHB) and polycaprolactone (PCL) [9] have proved to be very effective. Since these films are fragile in nature, they are not recommended for large-scale use in packaging manufacturing [10]. To overcome this problem, plasticizers are interpenetrating connections of polymers are developed to modify the interactions and/or the structure of the polymer chain in order to optimize the mechanical and physicochemical properties of biofilms and to have interesting functions for applications in the field of food packaging [11; 12]. Sorbitol, glycerol and polyethylene glycol (PEG) are now commonly used to improve the plasticity of biopolymers [6]. Their actions are at the level of the flexibility of biopolymers by decreasing the glass transition temperature (Tg) [13]. Having low molecular weights (between 300 and 600 kDa) and linear or cyclic carbon chains, these plasticizers can intercalate between polymers by reducing the formation of hydrogen bonds between the polymer chains [6]. Regarding the use of films based on biopolymers, Glycerol (GL) is a very good candidate of natural plasticizer which improves their mechanical properties [14]. Starch is a complex sugar with the molecular formula (C\({}_{6}\)H\({}_{10}\)O\({}_{5}\))\({}_{n}\). Being produced by photosynthesis, it comes in the form of grains ranging in size from 1 to 200 \(\upmu\)m. Starch grains also have different aspect of shapes like spherical or oval. Starch serves as a carbohydrate reserve in plants like glycogen in animals [15]. This carbohydrate reserve is a mixture of two polysaccharides, amylose and amylopectin. The proportions of these two polysaccharides are vary according to the types of starch. In the native form, it comes in the form of grains which consist, on average, of 15 to 30% amylose and 70 to 100% amylopectin [16]. In order to obtain a starch-based food film, it is necessary to transform the native starch into thermoplastic starch. Indeed, in the native state, the melting temperature of starch is higher than its degradation temperature (about 300 \({}^{\circ}\)C), due to the presence of numerous intermolecular hydrogen interactions. These properties make native starch very malleable and unsuitable for processing [15; 16]. The plasticization of starch consists of incorporating a plasticizer and applying hydro-thermal and/or thermomechanical treatments in order to destructure the crystalline structure of the starch, and thus lower its melting and glass transition temperatures. The added plasticizer will insert itself between the starch chains and break the inter-starch chain hydrogen bonds. This will make it possible to create new hydrogen bonds between the starch and the plasticizer and thus increase the mobility of the chains. The effects of plasticization are reflected during the characterization of the films by a reduction in the breaking stress and an increase in the elongation at break, which is linked to a reduction in the Young's modulus [15; 16]. Alginate is an edible heteropolysaccharide abundantly available in brown algae [17]. The two major molecules that compose it are D-mannuronic acid (M) and L-glucuron acid (G) [17]. Alginate, and more particularly sodium alginate, have many properties that seem to make them interesting materials for forming films. These algae could improve food safety and extend the shelf life of packaged foods. Indeed, these films are non-toxic, biodegradable, transparent and uniform and have antimicrobial properties.