Formation of Interpenetrating-Phase Composites Based on the Combined Effects of Open-Cell PIF and Porous TPU Microstructures for Enhanced Mechanical and Acoustical Characteristics

The open-cell foam is a highly preferred sound-absorbing material used for improving indoor sound quality. Herein, polyimide foam (PIF) with an open-cell structure was synthesized through the introduction of oxalic acid dihydrate (H 2 C 2 O 4 ·2H 2 O). The introduction and subsequent decomposition of H 2 C 2 O 4 ·2H 2 O provided additional heterogeneous nucleation sites during foaming and promoted the formation of open-cell structures. The relation between H 2 C 2 O 4 ·2H 2 O content and pore structure, the formation mechanism of open-cell structures, and the effect of H 2 C 2 O 4 ·2H 2 O content on the sound absorption performance were analyzed. Furthermore, interpenetrating-phase thermoplastic polyurethane (TPU)/PIF composites were prepared via non-solvent-induced phase separation on the basis of the open-cell PIF. The formation of porous TPU microstructures and improvement of mechanical and acoustic properties of the interpenetrating-phase composites were discussed. Two main forms of TPU existed in the interpenetrating composites: microparticle TPU structure and microporous TPU structure. The compression strength (125.54 kPa) and sound insulation capacity of 10%TPU/PIF3 were 3.47 and approximately 5 times those of open-cell PIF3, respectively. Moreover, the average sound absorption coefficient (1000–6400 Hz) increased by 58.43% compared to that of open-cell PIF3. The design based on the open-cell PIF promoted the enrichment of internal channels, and the construction of the internal channels with porous TPU microstructures achieved reflection enhancement and viscoelastic damping dissipation. Finally, the combined effects of the two designs synchronously enhanced the mechanical properties, sound absorption, and sound insulation properties of TPU/PIF materials, providing a thought for improving the acoustic properties of serialized polymer foam materials.