Sound absorption improvement of polyurethane foam through sequential arrangement of its cellular morphology

We designed four distinct polyurethane foam (PUF) cellular morphologies by employing low-molecular-weight polyols and two types of gelling catalysts. The cellular morphologies contained cavity sizes ranging from 458 mu m to 287 mu m and open porosities between 0.97 and 0.63. The highest values of the sound absorption coefficient from the four individual specimens were observed at specific frequencies (1,550, 2,000, 2,650, 3,800 Hz) owing to their distinct morphological characteristics. Specimen combinations showed enhanced sound absorption compared to their individual specimens due to the synergistic effect between its highly open porosity, which dissipates high-frequency waves, and its small cavity, which diffracts low-frequency waves. The acoustic activity reached to the highest (0.82) value from the double-layered sample with the front small and back large cavities. The small front cavities resulted in a high noise reduction coefficient because of the destructive interference effect of the low-frequency waves through the relatively large cavity of the back layer. However, its reversely arranged specimen showed increased noise reduction coefficient (0.53) due to the air gap effect. Therefore, suitable layer combinations of the different cellular structures can assist in achieving high sound absorption in PUF systems and be utilized in various practical engineering applications.