## 1 Introduction  
In recent years, with the change from conventional petrol-based food packaging materials such as polyethylene (PE), polyvinyl alcohols (PVA) and nylon [1], to biodegradable, natural and environmentally friendly counterparts, pressure has been observed in the food packaging industry to adapt to the responsibilities and duties of this new reality [2]. The food packaging industry has had many decades of studying and improving conventional plastic packages from the scope of improving mechanical, barrier and cost properties, which, in the case of biodegradable and environmentally friendly food packages, has not been observed to such an extent due to the great amount of time and testing needed on these products. Research directions in food packaging include active (which modifies the condition of food to increase shelf life and safety) and intelligent (which monitors the condition of food) packaging. These directions, although widely explored in experimental studies, have not reached the market to a great extent [3]. Current issues in the food packaging industry that should be addressed by the development of biodegradable food packaging materials include greener packaging, waste reduction and sustainability [3]. Finally, a life cycle assessment of biodegradable food packaging materials should be studied in order to fully assess their environmental and ecological impact [4]. Between the varieties of biodegradable, natural film forming polymers, the most common one is starch because of several reasons, including its abundance, its ease of processing in order to produce films and the ability to customize the film forming procedure in order to manufacture films with different attributes. Starch, which is one of the most abundant natural polymers, consists of amylose and amylopectin. amylose is the linear polysaccharide of starch, consisting of glucose units linked by a-(1\(\rightarrow\)4) glycosidic bonds and is the main film forming factor, whereas amylopectin is the branched polysaccharide of starch consisting of both a-(1\(\rightarrow\)4) and a-(1\(\rightarrow\)6) glycosidic bonds [5]. The film forming procedure of starch includes the gelatinization of starch in an excess water content during heating at a specific temperature with the presence of a secondary plasticizer, such as glycerol. Starch is organized in granules, which in their physical state are semi-crystalline and insoluble in water. However, during heat treatment at a specific temperature for each starch species called gelatinization temperature, in an aqueous environment, starch granules tend to absorb water and swell, subsequently leading to their disruption and causing amylose chains to leach out into the solution. The gelatinization of amylose is the process that enables water absorption by amylose and the transition from a crystalline to amorphous state and, further, allows the formation of a continuous amylose matrix in which the water is entrapped [6]. The aqueous dispersion, which includes the gelatinized amylose with the secondary plasticizer, is called thermoplastic starch and, when it is dried, the films occur. As it happens with all natural systems, these non-spontaneous reactions based on thermodynamics--such as gelatinization, which needs energy to happen--are reversible, which means that, after some time, the amorphous state of starch is submitted to physicochemical reactions leading to retrogradation or a return to the crystalline state, which begins with the removal of water from the amylose matrix. Retrogradation has negative effects on the matrix and, therefore, on the occurring films, leading to the high britteness and low integrity of the film. For these reasons, the use of secondary plasticizers, such as glycerol [7], is necessary, since they delay and hinder starch retrogradation by reducing the high intermolecular forces [8; 9].