Cross-Linker-Free, Strong, and Multifunctional Chitin Aerogels Prepared via a Urea-Assisted Strategy for Efficient Broadband Sound Absorption

Biobased aerogels that combine intrinsic sustainability with superior sound absorption performance are emerging as efficient, eco-friendly solutions for next-generation noise control. Here, we report a urea-assisted strategy that is both cross-linker-free and readily scalable for fabricating stable monolithic chitin aerogels with tailorable pore structure. Raising the urea pretreatment solution (UPS) concentration from 2 to 6 wt % progressively decreased the average pore diameter of the chitin aerogels from 86.88 to 15.78 μm, reduced the porosity from 96.07 to 94.11%, and increased the bulk density from 0.06 to 0.09 g cm–3. A low-urea formulation (2 wt % UPS) generated a highly porous, large-pore network that endowed the aerogel with efficient broadband sound absorption and favorable thermal insulation: the effective bandwidth with absorption coefficient α > 0.9 spanned 3400 Hz (accounting for 58.6% of the measured frequency range), the peak absorption coefficient (αp) reached 0.97 at 4100 Hz, and the thermal conductivity was 0.044 W m–1 K–1. Conversely, a high-urea formulation (6 wt % UPS) produced a dense, small-pore structure that enhanced compressive resistance, ignition resistance, and visible diffuse reflection performance: the Young’s modulus increased to 260 kPa, the limiting oxygen index (LOI) reached 42.1%, and the average diffuse reflectance in the visible region was 92.16%. This study presents a straightforward strategy to tailor the macroscopic properties of chitin aerogels by engineering their pore structure, holding significant potential for advancing biobased acoustic materials across various applications.