Preparation of low-hardness thermoplastic polyurethane microcellular foam by supercritical CO 2 process and the performance of high-frequency noise insulation

Abstract

The development of noise insulation devices is crucial in military work environments since the characteristics of military noise are intense and have multiple frequencies. This study prepared a low-hardness thermoplastic polyurethane (TPU) microcellular foam with efficient noise insulation performance, especially for high-frequency noise, using supercritical carbon dioxide (CO₂) as the foaming agent. A Shore 65A hardness TPU was used as the model compound due to its high softness. The effect of the operating parameters in the supercritical CO₂ foaming process on the foam properties was investigated. Operating at an intermediate saturation temperature and a high pressure was favorable for preparing foam with a high expansion ratio. The effect of saturation pressure and depressurization time were significant in manipulating the cell size and density. Selecting a high saturation pressure and a short depressurization time is beneficial for producing TPU foam with small cell size and high cell density. This study successfully prepared the low-hardness TPU foam by supercritical CO₂ process with an expansion ratio of up to 3.44, and the mean cell size and density could be manipulated within 6.6–194.5 μm and 2.22 × 10⁵–5.48 × 10⁹ cells/cm³, respectively. Finally, through the noise insulation test, the prepared TPU foam shows a noise reduction rating (NRR) of 27.4 dB and good noise insulation performance, especially for noise higher than 3000 Hz.