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

Abstract

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 lignincontaining 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/m3), 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.