Structural characterization and transport properties of organically modified montmorillonite/polyurethane nanocomposites

Samples of polyurethane and organically modified montmorillonite (OMont) were prepared, covering a wide range of inorganic composition, up to 40 wt%. They were obtained by a three step process using diphenylmethane diisocyanate, poly(epsilon-caprolactone), di(ethylene glycol) and poly(epsilon-caprolactone)-OMont (NPCL) nanocomposites. The NPCL nanocomposites were used as soft segments for a partial replacement of the di(ethylene glycol) in the hard-segment of the polymeric chains. The X-ray analysis showed that exfoliation occurred for low montmorillonite content, whereas for higher contents the intercalated clay rearranged to a minor extent. The mechanical and dynamic-mechanical analysis showed an improvement of the elastic modulus and yield stress, but a decrease of the stress and strain at breaking on increasing the clay content. Sorption and diffusion were measured for two different vapors, i.e. water vapor as hydrophilic permeant and dichloromethane as hydrophobic one. For both vapors the sorption did not drastically change on increasing the clay content. At variance the zero-concentration diffusion parameter (D-0) strongly decreased on increasing the inorganic content. The permeability, calculated as the product of the sorption (S) and the zero-concentration diffusion coefficient (D-0) showed a remarkable decrease up to 20% of clay and a leveling off at higher contents. It was largely dominated by the diffusion parameter. (C) 2002 Published by Elsevier Science Ltd.