Multifunctional biodegradable polyvinyl alcohol/ nanolignin composite films of optical, photoluminescence, antimicrobial properties and enhanced fruit preservation ability

Lignin is the second most abundant natural polymer after cellulose. It is an affordable renewable material with versatile properties that enable its utilization in many technological applications. This work is concerned with the preparation of nanocomposite biodegradable films based on nanolignin (NL) and polyvinyl alcohol (PVA). Different ratios of NL ranging from 0.5% to 8% were added to the PVA solutions, and free-standing films are obtained by casting technique. The formed films were characterized using FTIR and XRD and their morphology was studied using high- resolution scanning electron microscope (HRSEM). Studying the optical properties of the films revealed that the films have a high UV-shielding ability that is boosted with an increasing ratio of NL in the film. Moreover, the presence of NL reduced the optical band gap of polyvinyl alcohol. The concentration of NL determines the equilibrium between PL enhancements and quenching, demonstrating a concentration-sensitive interaction between the lignin-conjugated electrons and the PVA matrix. Antimicrobial activities toward different microorganisms are boosted by increasing the amount of NL in the prepared films. The films demonstrated obvious antioxidant properties (radical scavenging activity, RSA%), and films containing 8% NL showed 82% RSA. Moreover, gas barrier properties and the ability of the prepared formulations to preserve plum fruit in terms of weight and color are examined. The obtained nanocomposite films demonstrated versatile properties that enable variable applications, including active packaging material.