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Melt-state and solid state mechanical properties and thermal stability of polylactide layered silicate nanocomposites elaborated by melt intercalation were studied as a function of clay content. Wide angle X-ray scattering results, transmission electron microscopy observations, and rheological measurements indicated that the clay was finely distributed in the polylactide matrix. Contrary to nonlinear mechanical properties, thermal and linear mechanical properties were shown to increase with increasing clay fraction. The nanoindentation measurements confirm the significant increase of linear mechanical properties previously observed by tensile tests. The good correlation of linear mechanical properties at the macrometric and nanometric scales is explained by the high dispersion degree of the nanofiller in the biodegradable polymer matrix.

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Full Paper: The objective of this work is aimed at determining the kinetics of HALS photografting in PP films as a function of the additive concentration under both natural weathering and accelerated UV conditions. The stabilizer studied had a single structure that combined HALS and a UV absorbing unit detectable at 308 nm in the UV spectrum of PP, capable of inducing a photoreaction with the polymer matrix. The kinetics of HALS photografting on PP films at various additive concentrations was determined by direct spectroscopic measurements on film samples through the absorption band of the stabilizer positioned at 308 nm in the UV spectra, which was attributed to the highly conjugated methylenic double bond. The content of free HALS was determined as a function of exposure time by UV spectroscopy for all the additive concentration ratios used. It is shown that the kinetics of HALS photografting increase with a decrease in the additive concentration ratio. The whole grafting process under conditions of natural weathering occurred in the PP film after almost 350 h of exposure, while approximately 20 h were necessary under accelerated UV conditions. Moreover, these kinetics are well described by a third order polynomial model, validated by a maximum value of the coefficient of correlation close to unity. This was also confirmed by a comparison of the time values measured at 50% of the total grafting calculated from the model with those observed experimentally. This finding was consistent with the data obtained on the free HALS content determined by UV spectroscopy.

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