Morphological, acoustical, and physical properties of free-rising polyurethane foams depending on the flow directions

Polyurethane foam is widely used for automobile compartments as sound absorption materials due to its excellent noise dissipation characteristics. This sound absorption property is strongly dependent on the cavity and pore structures of the foams, and the cell morphology can be modulated by controlling experimental parameters. Two types of gelling catalysts were demonstrated in fabrications of polyurethane foams to control the cell morphology. The cell morphology of the free-rising polyurethane foams was investigated using dibutyltin-dilaurate and triethylenediamnine gelling catalysts, and the cell structures were analyzed from the free-rising samples obtained in various sampling heights and flow directions. The finer cell morphology was obtained with the organotin type catalyst by the faster gelling reactivity, compared with the amine type catalyst. In addition, the spherical small cavities in the samples obtained from horizontal planes of the free-rising foams revealed higher sound absorption coefficient and physical toughness than the elliptical irregular cavities from vertical planes, due to the higher homogeneity of cavity distributions in the horizontal planes.