Valorization of Invasive Kans Grass for Fabrication of PVA-Reinforced Multifunctional Cellulose Nanofibril-Based Composite Aerogels for Advanced Insulation and Fire Safety

The valorization of abundant lignocellulosic waste, such as invasive Kans grass (Saccharum spontaneum), into high-value, sustainable materials is a critical pursuit for a circular economy. This study reports the fabrication and comprehensive characterization of multifunctional cellulose nanofibril composite aerogels derived from this biomass and prepared via freeze-drying. The aerogels were modified with poly(vinyl alcohol) for mechanical reinforcement, hexadecyltrimethoxysilane for hydrophobicity, and varying concentrations of phytic acid (0–3 wt %) to impart flame retardancy. The resulting composites were comprehensively evaluated for a suite of functional properties, including their physicochemical, morphological, mechanical, thermal, acoustic, and hydrophobic characteristics. The aerogels exhibited low densities (0.0606–0.0738 g/cm3), high porosities (>93%), and excellent thermal insulation, with thermal conductivity ranging from 28.05 to 38.2 mW/(m·K). Incorporation of phytic acid, particularly at 1–2 wt %, significantly enhanced compressive strength (up to 0.928 MPa at 70% strain). It also imparted self-extinguishing behavior, withstanding 30 s of direct flame exposure, achieving a limiting oxygen index of up to 30.4%, and maintaining stable water contact angles of up to 121° over time. These findings highlight a robust strategy for engineering multifunctional aerogels from invasive biomass with potential applications in thermal/acoustic insulation and fire safety.