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Mechanical properties of talc- and CaCO3-reinforced high-crystallinity polypropylene composites

Weon, J.-I., Sue, H.-J.
Journal of materials science 2006 v.41 no.8 pp. 2291-2300
calcium carbonate, crystallization, crystals, mechanical properties, nanocomposites, nanoparticles, polypropylenes, talc, temperature, thermodynamics
Toughening mechanisms and mechanical properties of two high-crystallinity polypropylene (hcPP)-based composite systems, hcPP/talc and hcPP/CaCO₃, are investigated. Significant improvement in tensile modulus is observed in the PP/talc composite, but only a moderate improvement is found for hcPP/CaCO₃. The introduction of CaCO₃ nanoparticles to hcPP helps nucleate a measurable amount of β-phase crystals and results in a significant drop in crystallization temperature, suggesting a possible retardation of hcPP crystallization. In addition, the hcPP/CaCO₃ nanocomposite shows more pronounced damping characteristics than that of hcPP/talc, throughout the temperature range studied. A detailed investigation of fracture mechanisms suggests that well-dispersed, highly oriented talc particles cause embrittlement of hcPP. Only when the crack extends toward the edges of the specimen will the crack deflection/bifurcation and microcracking mechanisms initiate. In the case of hcPP/CaCO₃, the CaCO₃ nanoparticles help trigger massive crazing and shear yielding if the testing speed is in quasi-static. The presence of β-phase crystals around the CaCO₃ particles could facilitate the formation of crazes throughout the hcPP matrix. Approaches for toughening hcPP are discussed.