Cellulose-based functional materials from Posidonia oceanica: a sustainable valorization approach

The valorization of Posidonia oceanica residues, an abundant lignocellulosic biomass deposited along Mediterranean coasts, represents a sustainable strategy to reduce coastal waste while generating high-value bioproducts. In this study, we developed a biorefinery approach to convert Posidonia egagropili into composite insulating panels and cellulose-based films. Mechanical and chemical pretreatments were optimized to minimize processing steps and waste generation while maximizing cellulose accessibility. Chemical characterization of raw and treated biomass confirmed a composition rich in cellulose and lignin, comparable to other lignocellulosic feedstocks. The entire biomass was exploited to produce low-density insulating panels through two consolidation strategies in which Posidonia served as both filler and binder. Among the tested delignification methods, H₂O₂/NaOH treatment proved most effective in isolating a cellulose-enriched fraction. Cellulose solubilization in DMSO/LiCl enabled direct use of the biomass-derived solution as a binder, yielding panels with a thermal conductivity of 0.038 ± 0.005 W m⁻1 K⁻1, comparable to or better than commercial wood-based insulators. The cellulose-rich solution was also successfully used to prepare flexible films, incorporating tailored additives to modulate mechanical behavior and surface properties. Overall, the proposed process provides an efficient, scalable, and environmentally friendly route for fully valorizing Posidonia oceanica, producing renewable, lightweight, thermally efficient biomaterials for construction.