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© 2007 American Scientific Publishers. The authors wish to thank the CICYT, MAT 2004-00825 and the Spanish Ministry of Science and Technology (MCYT), PPQ2003-03299, for financial support and Dr. López Manchado for the concession of a Ramón y Cajal contract (MCYT)., Novel millable polyurethane (PU)/organoclay nanocomposites have been successfully prepared by conventional transformation techniques. One natural (C6A) and two organically modified (C15A and C30B) montmorillonites have been used as clays for preparing PU nanocomposites. The optimum dispersion of nanofiller at a nanometer scale in PU matrix was confirmed by X-ray diffraction patterns and transmission electron microscopy. A substantial improvement of the PU properties by addition of only a small amount of organoclay was observed. It is worthy to note that the organoclays show a different interfacial interaction with the PU matrix, which was reflected in different macroscopic properties. Thus, C30B organoclay seems to react with PU chains to form covalent bonds, while C15A only interacts physically with PU chains. Mechanical and barrier properties are analyzed., CICYT, Spanish Ministry of Science and Technology (MCYT), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2007 Elsevier Ltd. The authors of this study gratefully acknowledge the financial support of the Ministry of Science and Technology (MCYT, Spain) through its project No. PPQ2003-03299 and MAT 2004-00825. Dr. López Manchado also acknowledges the concession of a Ramón & Cajal contract from the MCYT., Polypropylene membranes modified with natural and organically modified montmorillonite clays were prepared. The permeability, diffusivity and solubility of helium, oxygen and nitrogen were determined for the unfilled and filled membranes over the temperature range 25-65 degrees C. Physical properties of polypropylene membranes were investigated using X-ray diffraction, thermogravimetric analyser, tensile testing and differential scanning calorimetry. The results showed that the filled membranes exhibit lower gas permeability compared to the unfilled polypropylene membrane. For helium, a reduced diffusivity is mainly responsible for the reduction in the permeability, in contrast, for nitrogen and oxygen, both diffusivity and solubility were reduced by the presence of fillers. The X-ray diffraction spectra showed that the incorporation of the unmodified and modified clay did not affect the crystallographic nature of polypropylene., Ministry of Science and Technology (MCYT, Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub