Three types of mineral fillers-talc, calcium carbonate (CaCO 3 ), and kaolin (10 -40 wt % filler loadings)-were compounded with polypropylene (PP) with a twin-screw extruder. The composites were injectionmolded, and the effects of the filler loading on the mechanical, flow, and thermal properties for the three different types of filled composites were investigated. The aim was to compare their properties and to deduce prospective filler combinations that would yield hybrid PP composites in following studies. The results showed that in most cases, the strength and stiffness of the talc-filled PP composites was significantly higher than those of the CaCO 3 -and kaolinfilled PP composites. However, CaCO 3 , being a nonreactive filler, increased the toughness of PP. The kaolin-filled PP composites also showed some improvement in terms of strength and stiffness, although the increases in these properties were not as significant as those of the talc-filled PP composites. The effects of interfacial interactions between the fillers and PP on the mechanical properties were also evaluated with semiempirical equations. The nucleating ability of all three fillers was studied with differential scanning calorimetry, and the strongest nucleating agent of the three was talc, followed by CaCO 3 and kaolin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: [3315][3316][3317][3318][3319][3320][3321][3322][3323][3324][3325][3326] 2004

ABSTRACT:The main aim of this work was to study and compare the mechanical and thermal properties of hybrid polypropylene (PP) composites and single-filler PP composites. With two main types of mineral fillers-calcium carbonate (CaCO 3 ) and talc-PP composites of different filler weight ratios (talc/CaCO 3 ) were compounded with a twinscrew extruder and then injection-molded into dumbbell specimens with an injection-molding machine. Tensile, flexural, and impact tests were performed to determine and compare the mechanical properties of the hybrid and singlefiller PP composites. A synergistic hybridization effect was successfully achieved; the flexural strength and impact strength were highest among the hybrids when the PP/talc/ CaCO 3 weight ratio was 70:15:15. The nucleating ability of the fillers and its effects on the mechanical properties were also studied with differential scanning calorimetry. Because of the influence of talc as the main nucleating agent, the hybrid fillers showed significant improvements in terms of the nucleating ability, and this contributed to the increase in or retention of the mechanical properties of the hybrid composites.

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