Melt compounding of syndiotactic polypropylene nanocomposites containing organophilic layered silicates and in situ formed core/shell nanoparticles

Syndiotactic polypropylene (sPP) compounds containing organophilic layered silicates were prepared by means of melt extrusion at 220 C using a corotating twin screw extruder in order to examine the influence of the silicate modification and the addition of maleic-anhydride-grafted isotactic polypropylene (iPP-g-MA) as compatibilizer on morphology development and mechanical properties. Synthetic sodium fluoromica was used as water-swellable layered silicate, which was rendered organophilic by means of cation exchange with protonated octadecylamine. Only compounding of the modified silicate in conjunction with iPP-g-MA afforded exfoliation and dispersion of individual silicate layers, encapsulated in an iPP-g-MA shell, within the polypropylene matrix. Interlayer distance increased with increasing content and increasing molecular weight of the compatibilizer. The Young's modulus of the nanocomposite increased fivefold from 490 to 2640 MPa. This was attributed to silicate nanoreinforcement and nucleation of sPP crystallization via the iPP-g-MA shell of the dispersed organophilic silicate nanoparticles. The yield stress was increased to 29 MPa with respect to 16 MPa for the bulk sPP. Morphology and mechanical properties were examined as a function of the silicate-and compatibilizer content. (C) 2002 Elsevier Science Ltd. All rights reserved.