Generation of microcellular polyurethane with supercritical carbon dioxide

Abstract

We examined the formation of microcellular foam in a thermoplastic polyurethane elastomer (TPU) with supercritical carbon dioxide. Measurements of the permeability and impregnation with carbon dioxide suggested that the impregnation of TPU with carbon dioxide was affected by the soft‐segment chain length and soft‐segment concentration in TPU and that carbon dioxide was mainly present in the soft‐segment area. Thus, it seemed likely that the nucleation and growth of the nuclei in the microcells occurred in the soft‐segment area. In addition, scanning electron microscopy of the microcells indicated that the higher the saturation pressure was, the smaller the mean cell diameter was; that is, the higher the cell number density was, the lower the foaming temperature was, the smaller the mean cell diameter was, and the lower the saturation pressure was, the more conspicuous this phenomenon was. These results showed that the saturation pressure and foaming temperature affected the cell structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Towards maximal cell density predictions for polymeric foams

“…Clearly, a prediction of the smallest possible bubble size alone under given conditions is not sufficient to predict the "quality" of a foam. The prediction of higher cell densities with increased blowing agent is consistent with the observations of Goel and Beckman [13] and later observations, for example, references [15,32,33,34]. Surprisingly, the critical radius does not correspond to the maximal bubble surface area per polymer volume.…”

“…Overall, we find that, consistent with experimental experience [13,15,32,33,34], to get the "best" possible foam one should dissolve the greatest amount of blowing agent into the polymer melt while remaining away from the spinodal point, that is, the point of absolute instability of the mixture. SCFT can then be used to predict the smallest possible radius for which the interior of a typical bubble remains well segregated.…”

Gas Permeability of Thermoplastic Polyurethane Elastomers

“…In our laboratory, the fabrication of microcellular polyurethanes by the use of carbon dioxide is under study. 8 The application of TPU to food packaging materials also is under study. Hence, we need a fundamental knowledge of the solubility of carbon dioxide in TPU and oxygen gas-barrier property of TPU.…”

Development and characterization of piezoresistive porous TPU-MWNT nanocomposites

“…The single phase solid solution was prepared by saturating the nanocomposite inside a high pressure vessel filled with CO2 gas at 4.13 MPa (600 psi) for 22 hr. Based on diffusion half-length calculations using properties available in literature [18,19], 22 hr was deemed a sufficient enough period for saturating 0.5 mm thick TPU samples with carbon-dioxide. After saturation, the vessel was rapidly depressurized and samples were immersed in a heated water bath at 95 °C for 10s causing gas-polymer phase separation.…”