Dynamic mechanical and morphological studies of isotactic polypropylene/fumed silica nanocomposites with enhanced gas barrier properties V. Vladimirov a , C. Betchev a , A. Vassiliou b , G. Papageorgiou b , D. Bikiaris b, * a Central Scientific and Research Laboratory, University of Chemical Technology and Metallurgy, 8, Kliment Ohridski Blvd., 1756 Sofia, Bulgaria b Laboratory of Organic Chemical Technology, Department of Chemistry, Aristotle University of Thessaloniki, GR-541 24 Thessaloniki, Macedonia, Greece Received 11 January 2006; received in revised form 7 February 2006; accepted 12 February 2006 Available online 31 March 2006 Abstract Polypropylene/fumed silica nanocomposites were prepared via melt mixing using a twin-screw co-rotating extruder. To improve the dispersion degree of the nanoparticles, maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer. From transmis- sion electron microscopy it was found that agglomerations of silica particles into the PP matrix increased in average size with increasing silica contents whilst they decreased at higher PP-g-MA amounts. Storage modulus values of prepared nanocomposites measured by DMTA were sensitive to the microstructure of the nanocomposites. Higher silica contents resulted in higher storage modulus, evidence revealing that the material became stiffer. By adding the PP-g-MA copolymer a further increase of storage modulus was observed due to the finer dispersion of the filler in the matrix and the increased interfacial adhesion. Both permitted a much more efficient transfer of stresses from the polymer matrix to the SiO 2 nanoparticles. Crystallization rates were found to increase by increasing silica nanoparticles as well as PP-g-MA content. In fact for a given PP-g-MA content increasing the silica content up to 5–7.5 wt% accelerated the crystal- lization. Further increase of the nanoparticles amount did not have any effect. Permeability rates of O 2 and N 2 through films of iPP/SiO 2 were also measured. Lower rates were observed compared to pure iPP, most notably for O 2 , which decreased with increasing concen- trations of silica. This was attributed to the more tortuous path which must be covered by the gas molecules, since silica nanoparticles are considered impenetrable by them. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Nanocomposites; Polypropylene; Fumed silica nanoparticles; Poly(propylene-g-maleic anhydride); Dynamic mechanical properties; Permeability 1. Introduction Polymeric nanocomposites have been recently estab- lished as an exciting new class of materials that are parti- cle-filled, with at least one dimension of the dispersed particles being in the nanometer range, and which usually exhibit superior mechanical performance and improved barrier properties at very low loading levels compared to conventional filler composites. Improvements on mechani- cal properties, such as stiffness and toughness, dimensional, barrier and thermal properties as well as retardant enhancements, with respect to the bulk polymer, are usu- ally observed [1–8]. These are usually attributed to the dra- matic increase of the interfacial area between the filler and the polymeric matrix [9]. The dispersion degree of the filler greatly influences the enhancement efficiency. Typical filler amounts of less than 5 wt% result in effective enhancement of the nanocomposite, unique and quite different from con- ventional composites. A remarkable aspect of these new materials is that although current micromechanics theories predict that the effective properties of composite materials 0266-3538/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2006.02.010 * Corresponding author. Tel.: +30 2310 997812; fax: +30 2310 997667. E-mail address: dbic@chem.auth.gr (D. Bikiaris). www.elsevier.com/locate/compscitech Composites Science and Technology 66 (2006) 2935–2944 COMPOSITES SCIENCE AND TECHNOLOGY