Effect of natural and organically modified montmorillonite clays on the properties of polydimethylsiloxane rubber

The effects of natural (MT) and organically modified (O-MT) montmorillonite clays on the properties of polydimethylsiloxane (PDMS) rubber were evaluated. Rubber composites with different clay contents were prepared by a compounding procedure in in open two-roll mill, which was followed by a compression-molding step in which the PDMS matrix was peroxide crosslinked. The clay rubber composites were characterized by swelling measurements in toluene, thermogravimetric analyses, X-ray diffraction, scanning electron microscopy, and tensile tests. The introduction of NIT restricted the solvent swelling and increased the crosslinking density of the rubber, which indicated the formation of a covalent filler-matrix interface. The enhanced interaction between NIT and PDMS reduced the aggregation size of MT particles in the MT composites and promoted an increase in the separation of the clay layers. When the rubber was filled with O-MT, a higher solvent amount was incorporated in the material, and this trend increased with the clay content. Moreover, the low interaction between O-MT and the PDMS chains resulted in larger clay aggregates in the O-MT composites compared to those with MT. Despite the different interface natures, both clays enhanced thermal stability and acted as reinforcing fillers in relation to Young's modulus and tensile strength. (C) 2008 Wiley Periodicals, Inc.10842587259