In this article, the two-dimensional distributions of cells from the cross section of some flexible polyurethane foams were cleared, and the three-dimensional distributions of cells based on Saltykov's theory were estimated further. As a result, it was found that a mean of the two-dimensional distributions of cells was a good linear relation with a mean of the three-dimensional distributions of cells, and it was confirmed that cell structure of the foams which should have been analyzed in the threedimensional distributions was evaluated by analysis of the two-dimensional distributions fully. It was also found that not only cell number but also cell distribution was necessary in the evaluation of flexible polyurethane foams, and cell diameter was closely related to the sound absorption coefficient in polyester-based flexible polyurethane foams.
ABSTRACT:In this article, the two-dimensional distributions of cells from the cross section of some flexible polyurethane foams were cleared, and the three-dimensional distributions of cells based on Saltykov's theory were estimated further. As a result, it was found that a mean of the two-dimensional distributions of cells was a good linear relation with a mean of the three-dimensional distributions of cells, and it was confirmed that cell structure of the foams which should have been analyzed in the threedimensional distributions was evaluated by analysis of the two-dimensional distributions fully. It was also found that not only cell number but also cell distribution was necessary in the evaluation of flexible polyurethane foams, and cell diameter was closely related to the sound absorption coefficient in polyester-based flexible polyurethane foams.
Effects of cell destruction on compression moduli of four closed-cell polyethylene were studied by the dynamic viscoelastic measurements in compression mode and the static compression test. In the dynamic viscoelastic measurements, dynamic modulus after cell destruction was smaller than that before cell destruction, and in foams after cell destruction the relations with the dynamic modulus and the initial shrinkage for foams of small elastic modulus was different from those for foams of large elastic modulus. In the static compression test, stress-strain curves of virgin foams gave a bend in the small strain region as observed for expanded polystyrene foams, whereas after cell destruction the stress monotonically increased with strain for foams having low elastic modulus. On the other hand for foams of high elastic modulus, stress-strain curves gave a bend in the small strain region as observed for virgin foams after cell destruction. It is considered that the ratio of the resistance against the pressure inside the cells to the total resistance varies with the elastic modulus of foams.
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