Effect of isocyanate molecular structures in fabricating flexible polyurethane foams on sound absorption behavior

Flexible polyurethane foams have attracted significant attention as sound absorption materials for automotive components. Molecular structure of isocyanate components in the fabrication of the foams has a strong effect on the formation of interconnecting pores. Two competitive mechanisms of microphase separation and drainage flow in the polyurethane urea matrix determine the fractional ratio of closed, partially and fully open pores. This fractional ratio of pore types is crucial for the sound absorption efficiency of the final foam materials. The addition of modified isocyanate containing uretonimine linkages increases, not only the microphase separation of hard domains in the matrix, but also drainage flow in the cell wall. In addition, the decrease of toluene diisocyanate content increases the phase separation of hard domains in polyurethane urea matrix. The optimum amount of uretonimine linkages in the isocyanate for good sound absorption is 4.3 × 10^-5 mol/g, showing the highest partially open pore fraction. Foam properties were analyzed by Fourier transform infrared spectroscopy, atomic force microscopy and scanning electron microscopy. Sound absorption efficiency was analyzed with an impedance tube.