An experimental evidence of a remarkable enhancement of strain-induced crystallization in natural rubber nanocomposite under uniaxial stretching, due to the presence of nanoclay particles, is described. Synchroton wide-angle X-ray diffraction (WAXD) have been used to monitor structure changes and crystallinity development during deformation. The results showed a dual crystallization mechanism in nanocomposites, which consists of spatial reorganization of organoclay at low strains, followed by rapid strain-induced crystallization of natural rubber. The presence of nanoparticles introduces new energy-dissipating mechanisms, and the mechanical property enhancement refers to the nanoparticle mobility and orientation during deformation. In-situ experiments were also carried out to relate the stress-strain behavior with structure determination using WAXD.

The authors gratefully acknowledge the financial support of the Spanish Ministry of Education (MEC) through its project MAT 2004-00825. J. Carretero-González wishes to thank the Spanish Ministry of Education (MEC) for the concession of a FPI grant and R. Verdejo also acknowledges a Juan de la Cierva contract from the MEC. BH also acknowledges the support by the NSF (DMR-0405432).

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