Aerogels are synthetic nanoporous solids composed of up to 99.98% air by volume. Though aerogels have found applications in thermal blankets and as energy absorbers, their use in acoustic applications has been limited because of their fragility and lack of control over their macrostructure. Here, we demonstrate a novel method of 3D printing aerogel-based porous sound absorbers with controlled microstructures by combining freeze-casting and extrusion. The 3D printing process aligns the particles along the freezing direction and allows the fabrication of samples with interconnected and aligned pores. Here, we fabricate cylindrical cellulose nanocrystal aerogel bulk absorbers with unidirectional and bidirectional pore alignments and test their normal incidence acoustic absorption properties using an impedance tube setup. The printed absorbers show significantly high and broadband acoustic absorption properties and thus offer an attractive proposition of developing ultra-lightweight sound absorption devices for aerospace applications.
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