Effects of Filler Treatments on the Mechanical, Flow, Thermal, and Morphological Properties of Talc and Calcium Carbonate Filled Polypropylene Hybrid Composites Y. W. Leong, M. B. Abu Bakar, Z. A. Mohd. Ishak, A. Ariffin School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Seberang Perai Selatan, Penang, Malaysia Received 21 April 2003; accepted 12 October 2004 DOI 10.1002/app.21507 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Commercially available neoalkoxy titanate (Lica 12) and organosilane (3-aminopropyltriethoxysilane) coupling agents were used to treat talc and calcium carbon- ate (CaCO 3 ) to compare their effects with those of untreated fillers upon their incorporation into polypropylene (PP). Commercial stearic acid treated CaCO 3 was also used to widen the scope of the study. Single-filler PP composites (containing either talc or CaCO 3 ) and hybrid-filler compos- ites (containing a mixture of talc and CaCO 3 ) were com- pounded on a twin-screw extruder and subsequently injec- tion-molded into dumbbells. The silane and titanate treat- ments dramatically increased the elongation at break for both the single-filler and hybrid-filler composites, whereas stearic acid did not. There was also a moderate improve- ment in the impact strength of the composites, particularly those treated with Lica 12. The hybrid composites, through the synergistic coalescence of positive characteristics from talc and CaCO 3 , had exceptionally good impact properties, more so with the aid of the coupling agents. For example, the impact strength value of a Lica 12 treated hybrid com- posite was the greatest for all the composites studied, over- shadowing the superiority of the CaCO 3 -filled PP compos- ites, which predominantly had the highest impact proper- ties. Further investigations of the thermal and morphological properties were also conducted to facilitate the determination of the coupling mechanisms and their interesting effects on the hybrid composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 413– 426, 2005 Key words: composites; poly(propylene) (PP); fillers INTRODUCTION Polypropylene (PP) filled with particulate fillers has been widely studied, the amount of PP research is still increasing. The versatility of PP and its good process- ability characteristics have also made it favorable for research and development. The incorporation of fillers such as calcium carbon- ate (CaCO 3 ) and talc in thermoplastics is a common practice in the plastics industry to reduce the produc- tion costs of molded products. Fillers are also used to improve the working properties of thermoplastics, such as strength, rigidity, durability, and hardness. 1 Considerable experimental data can also be found in recent studies dealing with the mechanical properties of PP filled with CaCO 3 , 2–4 talc, 5–7 rice husk ash, 8 and organic fibers. 9,10 Particulate-filled polymers must be continuously upgraded to meet the specific requirements of various new applications. One of the possible ways of doing this is the modification of the filler surface to alter the filler–matrix interfacial interaction. 4 Although the par- ticle size can be changed to modify the interaction, the range is still narrow. Thus, the incorporation of cou- pling agents onto the filler surface is an obvious way of modifying interactions by a change in the size of the interface or an alteration in the strength of the inter- action. Silane and titanate types of coupling agents have been gaining importance in recent time, and many claims and counterclaims have been made about its efficacy. Sharma et al. 11 in their article on the effect of a titanate coupling agent on the performance of CaCO 3 -filled PP showed that upon the treatment of the filler with an isopropoxy triisostearoyl titanate coupling agent, a 20% improvement in the impact strength was recorded, whereas the elongation at break of the composite was slightly less than that of virgin PP. They also claimed that this increase in the impact strength was not as evident as reported by Han et al., 12 who also worked on PP/CaCO 3 systems pre- viously, even though the fillers were also treated with titanate coupling agents. The elongation at break, as Correspondence to: Z. A. Mohd. Ishak (zarifin@usm.eng.my). Contract grant sponsor: Malaysian Ministry of Science, Technology, and Environment Intensification of Research in Priority Areas (IRPA); contract grant number: 305/PTE- KIND/6101003. Journal of Applied Polymer Science, Vol. 98, 413– 426 (2005) © 2005 Wiley Periodicals, Inc.