Silylated montmorillonite as nanofillers for plasticized PVC nanocomposites: Effect of the plasticizer

• Epoxidized soybean oil or dioctyl phthalate as physical intercalant for MMT.
• Preparation of thermostable mercapto- and amino-silanes treated montmorillonites.
• Improvement of thermal and mechanical properties of PVC nanocomposites.

Poly(vinyl chloride) (PVC) nanocomposites were prepared by compounding PVC with different clay minerals, which were previously dispersed into dioctyl phthalate (DOP) or epoxidized soybean oil (ESO) as plasticizers, with the help of an ultrasonication. Sodium montmorillonite (Na+-Mt) and those obtained from its functionalization with N-(2-aminoethyl-)-3-aminopropyl-trimethoxy-silane (NH2-Mt) or 3-mercaptopropyl-trimethoxy-silane (SH-Mt), as well as a commercial organoclay, Cloisite 30B, were employed as the nanoparticles. The incorporation of amino or mercaptosilane on the Na+-Mt surface was estimated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The clay PVC nanocomposites containing 2.5 phr of different clay minerals were characterized by XRD, dynamic mechanical analysis, thermal degradation and dielectric analysis. It was found a high exfoliation degree for the nanocomposites containing silylated clays, as suggested by the absence of reflections. Na+-Mt also displayed a high exfoliated structure for system plasticized with ESO. The presence of different clay minerals resulted in an increase of the storage modulus without affecting the glass transition temperature. Regarding thermal stability, those systems plasticized with ESO presented the best results obtained from thermogravimetric analysis, and the presence of Cloisite 30B, a clay mineral modified with ammonium salt, presented the worst performance in both plasticized systems.