Bio-based dual-hollow PLA/chitosan/SiO₂ thermoacoustic aerogels with broadband acoustic absorption

This study addresses the interconnected challenges of thermal management, noise pollution, and unsustainable materials in urban construction and transportation. We introduce a dual-hollow composite aerogel engineered via multiscale pore design that combines melt spinning and freeze-drying. The aerogel features a three-dimensional framework of polylactic acid (PLA) hollow fibers, chitosan as a binder, and silica hollow microspheres (SiO₂ HMs) as fillers. At the macroscale, PLA channels and chitosan networks form interconnected labyrinths that extend sound paths and enhance acoustic insulation. At the mesoscale, Helmholtz resonance units formed by the cavities of SiO₂ HMs and PLA channels selectively absorb sound in the 500-2000 Hz range. At the nanoscale, SiO₂ surfaces reduce heat transfer through Knudsen diffusion, while phonon scattering at the PLA-SiO₂ interface lowers solid-phase thermal conductivity. The resulting SiO₂/PLA composite aerogel exhibits a density of 0.024 g·cm^-3 and a thermal conductivity of 0.027 W·m^-1·K^-1-comparable to stagnant air and 63.5 % lower than commercial polyurethane foam. It achieves a high sound absorption coefficient (0.87 over 500-5500 Hz; NRC = 0.63) and biodegrades within 90 days via enzymatic action in soil, enabling PLA and SiO₂ recovery through acid-assisted separation.