*2.2.1 Polysaccharides: starch polymers*

The main polysaccharides explored in various applications are starch and cellulose-based derivatives [7]. Owing to being abundant, low in cost, and biodegradable, starch-based polymers are among the most extensively studied biodegradable polymer and are considered one of the most favorable candidates for sustainable materials [2, 6, 7, 14–16, 19, 20, 25, 28, 29]. Starches are hydrophilic carbohydrate materials that are regenerated by photosynthesis from plants such as wheat, corn, rice, and potato [6, 28].

Starch is primarily composed of two glucose homopolymers: (1) linear amylase and (2) highly branched amylopectin [1, 16]. Different sources yield different proportions of the homopolymers in the range of 10–25% amylose and 75–90% amylopectin [6]. This leads to variable properties, where high amylose content in starch leads to an improvement in mechanical properties such strength and elongation [7, 20]. Additionally, the hydroxyl side groups present in the polymeric chain aid in the rapid biodegradation of the biopolymer [6]. The polymer is considered as highly sustainable, where it is worth noting that during the natural assimilation process, starch is hydrolyzed into glucose that is further metabolized into CO2 and H2O. Afterwards, an ecological equilibrium is created, whereas aforementioned the starch is regenerated by the natural photosynthesis process of plants as they absorb the processed CO2 [6, 27]. Nevertheless, it is important to note that native starch by itself cannot be processed and it must undergo a modification process to improve its processability.
