**4. Conclusion**

PVA/starch biohybrid films are widely becoming an eco-friendly alternative to petrochemical-based plastics due to their biodegradability and for being suitable , generally obtainable, and less expensive materials. These biohybrid films have been obtained by using casting (sol-gel or mixing) and thermal processing (extruder or extrusion) methods. A great number of components in PVA/starch biobased films have been added to the matrix in order to improve physicochemical and mechanical properties. Moreover, various additives such as plasticizers, cross-linkers, fillers, and natural raw materials as well as thermoplastic starch have been used to improve the mechanical, thermal, and morphological properties of PVA/starch-based biodegradable hybrid films.

Plasticization in starch and PVA involves place in the amorphous area for higher molecular dynamism as well as their flexibility. Elasticity and other properties of biobased films are significantly affected by the functional groups (carboxyl and hydroxyl groups) of plasticizers. The using of cohydroxyl/carboxyl group as

a functional group increases the flexibility and physicochemical and mechanical properties of films. Cross-linking modifications in biobased films increase amorphous zone in molecular structure. This formation is effective to enhance the physicochemical and mechanical properties. These modifications improve the TS [2], modulus of elasticity [33], water resistance [49], thermal resistance [16], swelling behavior [8], and antibacterial activity of biofilms [15], unlike %E [2]. The filler in PVA/starch biobased films has a high potential class. Nature and the geometry of the filler-added biobased films have enhanced their properties such as gas barrier, mechanical stiffness, transparency, and thermal stability. The chemical modifications occur in the carboxyl group in molecular structure of PVA and starch because of oxidation. With increasing of carboxyl groups, the hydrogen bonds in biobased films were stronger than those of nonmodified ones. This stronger hydrogen bonding has improved physical-biological-chemical properties of biobased films because of the changing molecular structure of blend. Moreover, applied physical modifications to biobased films also significantly affect their physicomechanical properties. Consequently, these modifications applied to starch and PVA cause the esterification, etherification, hydrogen bonding, and oxidation in their molecular structure.
