Abstract. Micronic and submicronic mineral fillers recently appeared as efficient reinforcing agents for polyolefins in addition to the benefit of bypassing the exfoliation/dispersion problem encountered in the case of incorporation of nanoscopic fillers such as clay. Submicronic-talc, designated as µ-talc, belongs to this kind of new fillers. This work was aimed at searching to optimize the crystallinity ratio of isotactic polypropylene in the presence of µ-talc in relation to the filler ratio of the composites and the cooling rate from the melt. In order to highlight the efficiency of the µ-talc on the crystallization of polypropylene comparison has been made with PP composites containing conventional talc particles. The study has been carried out on samples having µ-talc weight fractions covering the range 3-30%. In the context of optimizing the crystallinity ratio of the polypropylene matrix in the composites, calorimetric experiments have been planned using a full factorial design. The results were statistically processed by analysis of the variance via mathematical models for predicting the crystallinity ratio in relation to the cooling rate and the filler ratio. Contour graphs have been plotted to determine the effect of each parameter on crystallinity. The cooling rate proved to have a significantly stronger influence on crystallinity than the type and content of filler.
ABSTRACT:The effects of interfacial adhesion strength on the mechanical behavior of composites of polyamide 66 and precipitated calcium carbonate (CaCO 3 ) particles have been investigated. The 50 nm average diameter particles have been surface-treated using two kinds of coupling agent having various affinities with respect to the matrix. The surface-modified particles have been incorporated into the polyamide matrix via melt processing. Tensile and impact tests, associated with dynamical mechanical analysis, have been performed on injection-molded samples. The structural characterization of the specimens has been carried out using differential scanning calorimetry and wide-angle X-ray scattering. It is observed that the matrix structure is roughly insensitive to the surface treatment, despite a weak nucleating effect of the filler particles. In contrast, the particle surface treatment strongly influences the particle dispersion in the polymer matrix. Although dispersion was not optimized, the elastic properties of the reinforced polyamide increase with the CaCO 3 content, below as well as above the glass transition temperature. Impact toughness decreases for CaCO 3 weight fraction greater than 5%. Scanning electron microscopy investigation reveals that the interfacial adhesion affects local deformation processes, such as debonding and fibrillation of the polymer matrix around the particles, during the macroscopic deformation of the composites.
Injected polypropylene/talc composites were studied to evaluate the conditions leading to the formation of a mixed talc/polymer crystalline lamella percolating network and the influence of such a network on the nanocomposite mechanical properties. The talc was either conventional micrometer-sized (conventional talc) or submicrometer-sized particles (l-talc). In the case of l-talc, several talc fractions were studied, ranging from 3 to 30 wt %. The nanocomposite crystallinity was characterized with differential scanning calorimetry and wide-angle Xray scattering. Talc was found to act as a nucleating agent, and only the a phase was detected. Through quantification on a Wilchinsky diagram, the talc particles were found to lie in the sample plane, the polypropylene crystalline lamellae being orthotropically distributed perpendicularly to the talc particles. The mechanical properties of the composites were tested in different directions by tensile and compression tests. The mechanical behavior of the composites confirmed the microstructural model. For low talc loadings, the composite moduli could not be well fitted by a law of mixtures. The large difference between the observed and predicted moduli was attributed to the formation of a mixed percolating network, including talc particles and polypropylene crystalline lamellae. At high talc loadings, when the mixed percolating network was completely formed, the reinforcement could well be described by parallel coupling, which indicated a classical reinforcement mechanism. Finally, the value of the critical talc fraction, at which the mixed percolating network was formed, was examined as a function of talc.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.