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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.

This work is devoted to the rupture behavior of elastomers filled with carbon black (CB) or silica. Two elastomers have been studied: one which crystallizes under strain, natural rubber (NR), and another one which does not crystallize, styrene butadiene rubber (SBR). The study of the crack propagation of Single Edge Notched specimen (SENT) during stretching at different speeds focuses on the crack initiation and crack deviation phenomenon. This deviation is of main importance in the materials crack resistance as it leads to a large increase in the energy needed for rupture. The deviation in filled or unfilled NR is controlled by crystallization, which is a slow process. In unfilled SBR, deviation is controlled by polymer chain orientation, which is hindered by relaxation mechanisms. The introduction of fillers promotes strain amplification, and strain anisotropy in the crack tip region of the notched samples, and therefore crack deviation. In term of energy density at break of the SBR composites, the SBR filled with silica treated with a covering agent is the most efficient. Thus, a weak interface between the silica and SBR promotes better rupture properties. When comparing Silica and CB filled NR, the highest strain energy to rupture is also obtained with silica. This might be due to the weaker filler-matrix interface for silica. Thus, these results evidence the kinetic aspect of the rupture, and of the mechanisms it involves: the polymer relaxation, the crystallization (for NR), and the filler-matrix interaction and decohesion, all of them being strongly interrelated.