Designing Ice-Templated Microstructures for Efficient Acoustic and Mechanical Properties of Hydroxypropyl Methylcellulose Cryogels

High Resolution Image Download MS PowerPoint Slide This study investigated the relationships between microstructure and the mechanical and acoustic properties of hydroxypropyl methylcellulose (HPMC) cryogels prepared by an ice-templating technique under different freezing conditions. Both random and unidirectional freeze-casting yield cryogels with low density (0.031–0.036 g cm –3 ) and high porosity (>96%). Isotropic cryogels obtained by random freezing exhibited a higher compression modulus (131 ± 16 kPa) and lower deformation (∼20%), attributed to their highly interconnected porous network. Anisotropic cryogels prepared at a lower freezing temperature (−196 °C) showed narrower interlamellar spacing (∼65 μm) and stiffness comparable to isotropic samples under longitudinal compression but reduced strength linked to poor pore connectivity, resulting in strains up to 55%. Freezing at a higher temperature (−38 °C) led to wider lamellar pores (∼106 μm) and the formation of secondary pores on the lamellae of the cryogel, which reduced the modulus to 78 ± 12 kPa. These microstructural differences also affected the acoustic response, indicating that sound absorption performance could be optimized by tailoring interlamellar spacing and secondary pore formation through control of the freezing temperature. All 20 mm-thick cryogels exhibited broadband sound absorption in the 200 Hz to 6.3 kHz frequency range, which falls within the audible frequency range for humans. The bilayer cryogel, bid-HPMC, formed by sequential freezing at −196 °C and −38 °C, exhibited a hierarchical anisotropic structure and superior acoustic performance, with a sound absorption coefficient (SAC) peak of 0.93 at 2000–3150 Hz and noise reduction coefficient (NRC) of 0.53, outperforming conventional absorbers (melamine and PET wool). Inverse characterization with iterative optimized algorithms allowed estimation of the airflow resistivity, tortuosity, and viscous and thermal characteristic length values that control the sound energy dissipation. These findings underscore the potential of ice-templating as a versatile approach for designing high-performance, biobased porous materials for sustainable building materials.