The role of hollow silica nanospheres and rigid silica nanoparticles on acoustic wave absorption of flexible polyurethane foam nanocomposites

Pure polyurethane foam and nanocomposite foam are used to absorb sound. In this study, hollow silica nanospheres and rigid silica nanoparticles were added to the polyurethane matrix and their sound absorption properties were investigated by impedance tube and compared with pure polyurethane foam. Reinforcement phase influences on the morphology of the matrix were studied by scanning electron microscopy. Due to greater effects of the rigid silica nanoparticles on the morphology of the matrix, it was expected to increase the sound absorption coefficient of the rigid silica nanoparticles/polyurethane, more than hollow silica nanospheres/polyurethane, but the results show that the hollow silica nanospheres increased absorption coefficient of the composite more efficiently. The crust of hollow silica nanospheres increases the number of boundaries in a sound wave, and the air gap inside them cause the sound wave to damp. So the intrinsic property of the hollow silica nanospheres is more effective than the matrix morphology. Thus, by the same content of reinforcement in the matrix, hollow silica nanosphere/polyurethane sample with sound absorption coefficient of 0.87 for a thickness of 9 cm has the highest sound absorption coefficient compared to the rigid silica nanoparticles/polyurethane sample and pure polyurethane foam. In pure and nanocomposite samples, sound absorption coefficient increased by increasing the thickness of samples.