Collagen Nanofiber-Lignin Composite Sponges with Adjustable Hierarchical Pore Structure for Efficient Low-Frequency Sound Absorption

Current sound-absorbing materials, reliant on nonrenewable resources, pose sustainability and disposal challenges. This study introduces a novel collagen-lignin sponge (CLS), a renewable biomass-based material that combines collagen's acoustic properties with lignin's structural benefits. CLSs demonstrate high porosity (>0.97), lightweight (10 mg cm^{- 3}), and exceptional broadband noise absorption performance (sound absorption coefficient exceeding 0.9 across 2000-6300 Hz). Due to their unique hierarchical and aligned pore structure, CLSs display superior low-frequency sound-absorbing capabilities and a high noise-reduction coefficient of 0.64 (for a 30-mm-thick sample). A geometric model is also developed to evaluate and predict the sound absorption performance with high consistency to the experimental results. Additionally, the inclusion of lignin as a green crosslinker has significantly improved the thermal stability and compressive strength by ≈600% compared to collagen sponges alone. The innovative integration of collagen and lignin in this study not only leverages the benefits of renewable resources but also presents a cost-effective and straightforward preparation process, positioning CLS as a promising alternative for the construction of sound-absorbing materials seeking sustainable solutions.