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Crystallization, mechanical, and fracture behaviors of spherical alumina-filled polypropylene nanocomposites



The objectives of this paper are to study the crystallization behavior and fracture characteristics of spherical alumina (Al2O3) nanoparticle-filled polypropylene (PP) composites. Nanocomposites containing 1.5–5.0 wt % of the Al2O3 nanoparticles (pretreated with silane coupling agent) were prepared for this investigation. Wide angle X-ray diffraction (WAXD) results show that a small amount of β-crystal of PP forms after adding the Al2O3 nanoparticles. According to differential scanning calorimetric (DSC) and optical microscopy (OM) measurements, the Al2O3 nanoparticles make PP spherulite size reduced and crystallization temperature of PP enhanced, by acting as effective nucleating agents. However, there are no obvious differences in the crystallinity for the virgin PP and the Al2O3/PP nanocomposites. Tensile test shows that both the Young's modulus and the yield strength of the Al2O3/PP nanocomposites increase with the particle content increasing, suggesting that the interfacial interaction between the nanoparticles and PP matrix is relatively strong. Under quasi-static loading rate, the fracture toughness (KIC) of the Al2O3/PP nanocomposites was found to be insensitive to nanoparticle content. Under impact loading rate, the Izod impact strength and the impact fracture toughness (Gc) indicate that the impact fracture toughness increases initially with the addition of 1.5 wt % of the Al2O3 nanofillers into the PP matrix. However, with the further addition of up to 3.0 and 5.0 wt % nanoparticles, both the Izod impact strength and impact Gc change very little. By observing the single-edge-double-notch (SEDN) specimens with optical microscopy after four point bending (4PB) tests, it was found that numerous crazes and microcracks form around the subcritical crack tip, indicating that crazing and microcracking are the dominant fracture mechanisms. Scanning electron microscopy (SEM) observation confirms this result. In addition, when the strain rate of 4PB tests was increased, some wave-like branches were formed along the fractured edge for the Al2O3/PP nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3652–3664, 2005