Alumina-Filled Polystyrene Micro- and Nanocomposites Prepared by Melt Mixing with and Without Latex Precompounding: Structure and Properties S. Siengchin, 1 J. Karger-Kocsis, 1 R. Thomann 2 1 Institute for Composite Materials (Institut fu ¨ r Verbundwerkstoffe GmbH), Kaiserslautern University of Technology, Erwin Schro ¨dinger Str., D-67663 Kaiserslautern, Germany 2 Institut fu ¨ r Makromolekulare Chemie und Freiburger Materialforschungszentrum, Albert-Ludwigs-Universita ¨t Freiburg, Stefan-Meier-Str. 31, D-79104 Freiburg, Germany Received 2 December 2006; accepted 4 March 2007 DOI 10.1002/app.26505 Published online 16 May 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Alumina fillers were incorporated in poly- styrene (PS) in 4.5 wt % by melt blending with and with- out latex precompounding. Latex precompounding was used for the latex-mediated predispersion of the alumina particles. The related masterbatch was produced by mixing PS latex with water dispersible boehmite alumina in vari- ous particle sizes followed by drying. The dispersion of the alumina in the PS was studied by transmission and scanning electron microscopy (TEM and SEM, respec- tively). The mechanical and thermomechanical properties of the PS composites were determined in uniaxial tensile, dynamic-mechanical thermal analysis (DMTA), and short- time creep tests performed at various temperatures. In addition, the melt flow of the composites was character- ized in a plate/plate rheometer. It was found that direct melt mixing of the alumina with PS resulted in micro-, whereas the masterbatch technique in nanocomposites. The stiffness and resistance to creep (summarized in mas- ter curves) of the nanocomposites were improved com- pared to those of the microcomposites. The properties of the composites were upgraded by decreasing nominal size of the water dispersible alumina. The preparation tech- nique and the size of the alumina particles affected the tensile strength, melt viscosity, and heat distortion temper- ature in lesser extent than the stiffness and thus compli- ance data. Ó 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 2963–2972, 2007 Key words: polystyrene; nanocomposite; creep; structure- property relations; thermal properties; stiffness INTRODUCTION Nowadays, great effects are undertaken to improve the mechanical, thermal, and other properties (e.g., flame resistance, barrier properties, electric conduc- tivity) of polymers using fillers of various shape fac- tors, which may be dispersed on nanoscale in the resulting composites. For the modification of polysty- rene (PS), for example, metal oxides, 1,2 organophilic modified layered silicates, 3–14 and single and multi- wall carbon nanotubes 15–17 were already tried. It was recognized earlier that the preparation technique of the nanocomposites has a strong impact on the dis- persion of the nanoparticles. One differentiates usu- ally between in situ polymerization, melt blending, and solution/dispersion preparation techniques. 18 The latter grouping also covers the latex compound- ing/latex coagulation methods. Major benefits of the ‘‘latex route’’ are listed below. It is noteworthy that for the production of rubber nanocomposites, the la- tex coagulation is already widely used. 19–22 Many polymers are produced by suspension and emulsion polymerizations in aqueous media. The related suspension, emulsions, or latices (for rubbers) can be easy modified with water swellable or water dispersi- ble particles. Water swellable are for example several layered silicates (montmorillonites, bentonites) bear- ing intergallery Na 1 ions. Via hydration of the inter- gallery cations intercalated and exfoliated structures can be achieved. Among the water dispersible com- mercially available nanofillers, alumina should be mentioned. To produce nanocomposites using aque- ous dispersions, slurries are not only an affordable method (no organophilic modification is needed for the fillers) but are also associated with reduced health hazard. Recall that the particles introduced are in micron range and become nanoscaled only in the aqueous media. In the follow-up steps (coagulation, drying etc.), the nanoparticles are embedded in the polymer, which guarantees easy handling and mini- mized health risk. Apart from rubbers, 19–22 this ‘‘la- tex-route’’ is followed for various polymers, including PS, 23–28 to produce various nanocomposites. There is a further scientific beauty with this approach: it is possible to produce micro- and nanocomposites using Correspondence to: J. Karger-Kocsis (karger@ivw.uni-kl. de). Journal of Applied Polymer Science, Vol. 105, 2963–2972 (2007) V V C 2007 Wiley Periodicals, Inc.