engleski

Correlation between orientations of nanoclay and natural rubber crystallites in natural rubber / clay nanocomposites

Orientations of the nanoclay platelets (organically modified montmorillonite, OMMT) and natural rubber (NR) crystallites in NR/OMMT nanocomposites were studied during uniaxial stretching by using various methods of X-ray diffraction (XRD). Uniaxial preferred orientation of the NR crystallites in pristine NR and conventional NR composites is well known, as well as the preferred orientation of the clay platelets parallel (in average) to the pressing or calendaring surface. Wide-angle XRD study of NR/OMMT nanocomposites during rotation around the stretching axes showed biaxial character of the NR crystallites` orientation in the presence of clay. TEM study of an unstretched sample indicated large fluctuations of the orientation of the nanoclay platelets throughout the sample, which led us to perform an XRD study at more local level, using micro-diffraction. It allowed the recording of both the clay and the NR (200) diffraction ring, in different depths from the sample surface, in steps of 0.02 mm. Azimuthal profiles from this series of diffraction patterns were corrected and analysed using Maier-Saupe distribution function, in order to quantify the deviation of the average orientation with respect to the surface normal and to calculate order parameters, for both phases for every position. The results provided direct proof of the filler geometry on the strain induced crystallization and confirmed the correlation between nanoclays` and NR crystallites` orientation. In the light of the results, a mechanism of reinforcement is discussed.

natural rubber; nanoclay; montmorillonite; X-ray diffraction; TEM; crystallites

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