| Resumo: | This work reports an investigation on the solid state uniaxial deformation of neat poly(ethylene terephthalate), PET, and its nanocomposites with montmorillonite, MMT, and nanosilica, SiO2, followed by in situ WAXS/SAXS (under X-ray synchrotron source radiation). The nanocomposites were produced via direct melt blending with addition of 0.3wt% of nanoparticles. Structural characterization by TEM revealed relatively good dispersion of both types nanofillers, namely intercalated morphology for the PET/MMT nanocomposite and agglomerate sizes (c.a. 80 nm) for the PET/ SiO2 nanocomposites. Despite the type of nanoreinforcements, three common stages of multiscale structure evolution were indentified: - Stage I, before necking, is characterized by a small amount of amorphous phase evolving into mesophase at almost constant molecular orientation level; - Stage II, at neck propagation, where a rapid increase of polymer molecular orientation is accompanied by a sharp increase of the mesophase and by the formation of a periodical mesophase; it is also observed the appearance of crazes in the polymer matrix, and voids within the nanoparticles agglomerates 1-4. - Stage III, during necking, corresponds to the transformation of crazes and voids into micro-voids, at a plateau of average molecular orientation. The highest periodical mesophase content is achieved together with a slight increment of mesophase1-4. In comparison to the neat PET structure evolution, all kind of nanocomposites showed: i) improved amount of mesophase and maximum periodical mesophase formed at earlier deformations; ii) retarded crazes widening/growing within the polymer bulk, and iii) similar maximum orientation level are achieved. Multiscale structures modelling are suggested based on the results obtained.
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