Estimation of Reinforcement in Compatibilized Polypropylene Nanocomposites by Extensional Rheology Stephan Laske, 1 Milan Kracalik, 1 Michael Gschweitl, 1 Michael Feuchter, 2 Gu¨nther Maier, 3 Gerald Pinter, 2 Ralf Thomann, 4 Walter Friesenbichler, 1 Gu¨nter Ru ¨diger Langecker 1 1 Institute of Plastics Processing, University of Leoben, Leoben 8700, Austria 2 Institute of Materials Science and Testing of Plastics, University of Leoben, Leoben 8700, Austria 3 Materials Center Leoben Forschung GmbH, Roseggerstrasse 12, Leoben 8700, Austria 4 Freiburg Materials Research Center, University of Freiburg, Freiburg 79104, Germany Received 23 April 2008; accepted 9 August 2008 DOI 10.1002/app.29163 Published online 13 November 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Structural characterization in polymer nano- composites is usually performed using X-ray scattering and microscopic techniques, whereas the improvements in proc- essing and mechanical properties are commonly investi- gated by rotational rheometry and tensile testing. However, all of these techniques are time consuming and require quite expensive scientific equipment. It has been shown that a fast and efficient way of estimating the level of reinforcement in polymer nanocomposites can be performed by melt exten- sional rheology, because it is possible to correlate the level of melt strength with mechanical properties, which reflect both the 3D network formed by the clay platelets/polymer chains as well as final molecular structure in the filled system. The physical network made of silicate filler and polymer matrix has been evaluated by X-ray diffraction and transmission electron microscopy. Extensional rheometry and tensile test- ing have been used to measure efficiency of the compatibil- izer amountin a polypropylene-nanoclay system. V V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2253–2259, 2009 Key words: nanocomposites; melt compounding;melt strength INTRODUCTION Nanocompositesusing different polymer matrices and layered silicates have been intensively investi- gated because of the improvements in their process- ing and use properties.Consequently, it is possible to prepare new, tailored,materials 1 or to use nanofil- lers in polymer recycling. 2–4 The improvementin material propertiesdue to nanoclay addition has usually been evaluated using a combination of trans- mission electron microscopy (TEM) and morphologi- cal (X-ray diffraction (XRD), mechanical(tensile testing),and sometimes also rheological (rotational rheometry)analyses.However, these conventional methods require quite expensivescientific equip- ment and long sample preparation and characteriza- tion times.Generally,intercalated and delaminated (partially exfoliated) polymer nanocomposites reveal significantenhancements in their properties: higher elastic modulus,tensile strength, thermalresistivity, lower gas and liquid permeability, reduced flamma- bility, 5 and improved rheological properties (e.g., higher melt strength)compared with the unfilled polymer matrix. 1 The high level of possible rein- forcement due to the addition of the layered silicates results from their large active surface area (in the case of montmorillonite 700–800 m 2 /g). 6 In the case of highly dispersed systems, a 3D physicalnetwork is achieved,formed by the silicate platelets and the polymer chains. This phenomenon can be investi- gated by analyzing the melt elasticity using rota- tional rheometry. 1–4,6–22 A fast way to evaluate this network effectis using elongationalrheometry, 23–26 which provides information about the melt strength. To disperse the clay in hydrophobic polypropyl- ene (PP), a compatibilizer(mostly PP grafted with maleic acid anhydride (MA)) must be admixed. However,the molecular weight of the compatibilizer is usually lower than thatof the PP matrix due to the grafting reaction and the presence of free MA molecules. 27 We have already presented 23,24 that the effective level of reinforcement in PP nanocomposites cannot be based solely on an evaluation of the delamination level (increase in interlayer distance) determined by X-ray scattering. In the PP-PPMA-nanoclay system, the simple rule ‘‘higher delamination leadsto an improvementin material properties’’is not always Journal of Applied Polymer Science, Vol. 111, 2253–2259 (2009) V V C 2008 Wiley Periodicals, Inc. Correspondence to: M. Kracalik (Milan.Kracalik@ mu-leoben.at). Contractgrant sponsor:PlaComp1 Project(NanoComp research project cluster founded by the Austrian Nanoinitiative).