Thermal conductivity anisotropy in polypropylene foams prepared by supercritical CO2 dissolution |
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Authors: | Marcelo Antunes Vera Realinho José Ignacio Velasco Eusebio Solórzano Miguel-Ángel Rodríguez-Pérez José Antonio de Saja |
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Affiliation: | 1. Centre Català del Plàstic, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, BarcelonaTech. C/Colom 114, E-08222 Terrassa, Barcelona, Spain;2. Cellular Materials Laboratory (CellMat), Condensed Matter Physics Department, University of Valladolid, E-47011 Valladolid, Spain;3. SF-3 Dept., Helmholtz-Zentrum Berlin, Glienicker Strasse 100, D-14190, Berlin, Germany |
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Abstract: | Different relative density polypropylene foams were prepared by means of two foaming processes: chemical foaming by compression moulding and physical foaming by high pressure CO2 dissolution. By controlling the foaming parameters, such as blowing agent concentration, foaming temperature, pressure drop and pressure drop rate, it was possible to regulate the cellular structure, foams showing from markedly isotropic-like cellular structures to ones with highly-elongated cells in the vertical foam growth direction (honeycomb-like cell orientation). The thermal conductivity was measured using the transient plane source method. Using this technique, it was possible to measure the global conductivity and the thermal conductivity in both the axial and radial directions of a given sample. Results show that the global thermal conductivity of foams was mainly regulated by their relative density. In addition, the honeycomb-like cell orientation of the CO2 dissolution foams resulted in considerably higher values in axial direction when compared to radial, demonstrating that there was a direct influence of cellular structure on the thermal conduction behaviour of these foams, enabling the development of new polypropylene foams with direction-dependent thermal properties. |
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Keywords: | Microporous materials Thermal conductivity Microstructure Anisotropy |
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