RHEOLOGICAL AND MECHANICAL-PROPERTIES OF FILLED RUBBER - SILICA-SILICONE

This work focuses on the relationship between the morphology of filled rubbers and their behavior at small and large deformations. Composites were made from vinyl terminated polydimethylsiloxane (PDMS) and different fumed silicas. Filler concentration range was kept between 0 to 40 phr(parts of silica per hundred parts of PDMS). Small deformation tests done in oscillatory shear showed that there is coupling of the filler agglomeration and crosslinking effects at high crosslink density while the coupling is negligible at low crosslinking levels. Since crosslinking (hydrosilation) proceeds through the end vinyl groups of the PDMS, lower molecular weight polymers produce rubbers with higher elastic modulus than do high molecular weight silicones. However, the rubbers formed from low molecular weight PDMS break at lower extensions. As in the case of uncured composites, the moduli of the samples increase with silica concentration and amount of silanols on the silica. A silica treated with divinyltetramethyldisilazane gave rubbers of high modulus similar to those obtained from untreated silicas, highlighting the importance of good adhesion between filler and polymer.