Multifunctional composite film based on biodegradable grape skin and polyvinyl alcohol

In winemaking, large amounts of grape skin (GS) are generated as by-products, which contain not only abundant degradable cellulose, hemicellulose, and pectin but various functional polyphenols. In contrast to most studies focusing on the utilization of extractives, the current study investigates the use of ultrasonicated grape skin (UGS) containing all components to develop a multifunctional composite film. Owing to dissociation during ultrasonication, all GS components were well dispersed in water to obtain the UGS suspension. Transmission electron microscopy (TEM) indicated that the celluloses were successfully transformed into cellulose nanofibers, which can improve the uniformity of the composite film. Subsequently, biodegradable and multifunctional composite films were fabricated by combining the UGS and polyvinyl alcohol (PVA). The UGS and PVA formed a good interface, which was attributable to strong hydrogen bonds, and the resulting films exhibited excellent thermal stability and moisture-sensitive mechanical properties. The polyphenols in the UGS suspension endowed the composite film with multiple functions, including pH-responsive color change, excellent antioxidant activity, ultraviolet shielding, and antimicrobial properties. The use of PVA enhanced the flexibility, strength, and elongation of the UGS film. Therefore, the easily prepared, tailored, multifunctional, and biodegradable UGS/PVA composite film exhibits superior potential for application in agriculture, cosmetics, and healthcare. Graphic abstract