H. Dodiuk, G. Goldberg, S. Kenig Department of Plastics Engineering, Shenkar College, 12 Anna Frank St, Ramat-Gan 52526, Israel The effect of multiwall carbon nanotubes (MWCNTs) and Tungsten Disulfide nanotubes (WS2- INTs) on the bulk and adhesion properties of room temperature vulcanized silicone nanocomposites was investigated. The MWCNTs were functionalized by methacryloxy or vinyl based silanes. The nanocomposites were prepared by solvent mixing, in the high viscosity silicone matrix, of the nanotubes. It was found that the optimal concentration of both treated and untreated MWCNTs in the silicone was 1 wt.%. Above this threshold value the nanocomposites properties decreased. In the case of WS2-INT the optimal properties were obtained at 2%wt, exhibiting 33% higher storage modulus, 6% improvement in tensile strength, 17%reduction in the coefficient of linear thermal expansion and 13% improvement in shear strength. Above this threshold value the nanocomposites adhesion properties decreased as was the case for MWCNTs. Furthermore, the silane treatment of the MWCNTs was proven to be an effective process that resulted in a significant increase in the nanocomposites properties compared to the neat polymer, leading to higher storage modulus, up to 27.5% improvement in the tensile strength, 20-30% reduction in the thermal expansion coefficient, 220-300% enhancement in crystallinity, and up to 56% improvement in lap shear strength together with significant changes in fracture morphologies. As the WS2- INTs are larger in diameter (by an order of magnitude) compared to MWCNTs, the “nano-effect" is limited in the case of WS2- INTs relative to MWCNTs where a significant enhancement in crystallization, fracture and simultaneous increase in strength and toughness were obtained. Keywords: MWCNTs, WS2- INTs, RTV silicone adhesives, nanocomposite properties