Received: 30 July 2009, Revised: 27 September 2009, Accepted: 28 September 2009, Published online in Wiley InterScience: 2009 Comparison of the effect of mica and talc and chemical coupling on the rheology, morphology, and mechanical properties of polypropylene composites Yousef Jahani a * The effect of filler types of mica and talc on the oscillatory shear rheological properties, mechanical performance, and morphology of the chemically coupled polypropylene composites is studied in this work. The Maleic Anhydride grafted Polypropylene (MAPP) was used as an adhesion promoter for coupling mineral particles with the poly- propylene matrix. The samples were prepared by a co-rotating, L/D ¼ 40, 25 mm twin screw extruder. The tensile tests carried out on the injection molded samples showed a reinforcing effect of talc up to 20 wt% on the Polypropylene (PP). The tensile strength of PP-mica composites showed a slight decrease at all percentages of mica. The effect of chemical coupling by using MAPP on the tensile strength was more pronounced in increasing the tensile strength for PP-mica than PP-talc composites. The complex viscosity curve of pure PP and the composites, showed a Newtonian plateau (h 0 ) up to 30 wt% at low frequency terminal zone. By increasing the filler content to 40 and 50 wt%, the complex viscosity at very low shear rates sharply increased and showed yield behavior that can be due to the formation of filler particles networks in the melt. At the optimum amount of coupling agent, a minimum in cross over frequency curve against MAPP content is observed. The optimum amount of coupling agent for PP-talc composites is about 1.5%, and about 3% for PP-mica formulations. The analysis of viscosity behavior at power-law high region, revealed the more shear thinning effect of mica than talc on the PP matrix resin. Copyright ß 2009 John Wiley & Sons, Ltd. Keywords: mica; morphology; polypropylene; rheology; talc INTRODUCTION Polypropylene (PP) is a widely used commodity plastic with good mechanical properties, excellent chemical resistance, low price, acceptable range of modulus, and good processability, which makes it an attractive candidate for many engineering applications. [1] Mineral fillers are normally used in polypropylene (PP) resins [2] to improve its stiffness and dimensional stability. Talc and mica are the most frequently used mineral filler for the stiffening of PP resins, increasing dimensional stability, and reducing the production cost. [3,4] The incorporation of filler may also adversely affect the ductility, strength, and processability of composites. [5,6] For some years, particular attention has been given to PP-talc and PP-mica composites for their superior stiffness and low linear thermal expansion coefficient and are therefore suitable for jointless connections and zero-gap parts such as automotive bumpers. [5] Mica and talc are mineral materials with high surface energy, and inherently poor interactions with non-polar polypropylene with low surface tension. There are several methods for improving the interfacial interactions between minerals and polymers. [7] Changing the surface chemistry of minerals by low molecular weight coupling agents, such as silane and isocya- nate, [8] is a way to reduce the surface tension of minerals, material, and a better adhesion between the two phases by a chemical reaction is achieved. [9] Maleic anhydride grafted PP (MAPP) has shown the maximum potential in improving the mechanical properties of the composites through reactive compatibilization, [10–13] and react- ing the maleic anhydride group with active groups of fillers, to strengthen the adhesion between fillers and PP resins. [13,14] The processing systems and type of coupling agents significantly affect the interfacial structure and mechanical properties of the composites. [15] The study of the mechanical and electrical properties of talc and mica-filled PP has been the subject of many research works. [15,16] The rheological measurements can be used as a means to evaluate the flow behavior which is vital for processing of the polymer, as well as characterizing the microstructure and polymer-filler interaction. There are a few studies on the rheological behavior of PP-mica and PP-talc composites. [13,17] There is not available released report on the comparison of the effects of mica and talc and maleic anhydride- grafted PP on the dynamic rheological behavior of PP composites. (www.interscience.wiley.com) DOI: 10.1002/pat.1600 Research Article * Correspondence to: Y. Jahani, Faculty of Polymer Processing, Iran Polymer and Petrochemical Institute, PO Box 14965/115, Tehran, Iran. E-mail: y.jahani@ippi.ac.ir a Y. Jahani Faculty of Polymer Processing, Iran Polymer and Petrochemical Institute, Tehran, Iran Polym. Adv. Technol. (2009) Copyright ß 2009 John Wiley & Sons, Ltd. 1