Nitrated lignin-reinforced polyvinyl alcohol films with enhanced optical and mechanical properties

Lignin is recognized as a biodegradable, eco-friendly, and sustainable material that can be applied in various industries, including biomass-embedded film manufacturing. However, several challenges associated with the low chemical compatibility of lignin towards polymer matrix need to be adequately addressed to enable the widespread use of lignin-containing composite films. This study aims to investigate the effects of lignin-derived additives with adjusted molecular weight and functional group content on the mechanical and UV-shielding properties of polyvinyl alcohol (PVA) films. Due to their enhanced chemical compatibility, nitric acid-treated lignin powders with reduced molecular weight were homogeneously blended with PVA. The resulting lignin-containing films exhibited excellent UV-blocking activity in the wavelength range of 290–400 nm and showed significantly enhanced mechanical properties due to hydrogen bonding between the additives and PVA, with tensile strength reaching 123.7 MPa, accompanied by a reduction in elongation at break. Additionally, the incorporation of polyethylene glycol (PEG) significantly improved the toughness (up to 25.2–25.5 MJ/m 3 ), while UV-blocking performance remained excellent, with an ultraviolet protection factor (UPF) rating of 50 + . Overall, this work presents a sustainable and scalable approach for producing lignin-containing functional films with tunable optical and mechanical properties, contributing to the advancement of renewable, bio-based materials for sustainable engineering applications. • Lignin-derived additives impart excellent UV-blocking properties. • Nitrated lignin additives improve tensile strength of PVA films due to improved hydrogen bonding. • PEG blending improves film flexibility and overall toughness.