Dielectric properties of polylactides and their nanocomposites with montmorillonite

The influence of the preparation method on the dielectric properties of two polylactides and their nanocomposites with an organoclay (Cloisite® 30B) is investigated. The samples obtained by melt-mixing followed by hot pressing and by solution casting are compared. Dielectric properties of the nanocomposites show a weak influence of the nanoclay on segmental (αS) and local (β) relaxations in PLA. Above Tg a strong increase of dc conductivity attributed to ionic species in the clay is observed. It gives rise also to the Maxwell–Wagner–Sillars interfacial polarization and both real and imaginary parts of ε∗(ω) strongly increase. In the temperature dependence of low frequency dielectric constant an additional maximum around 80–90 °C is observed due to cold crystallization of PLA which is significantly different for the two kinds of PLA. After cold crystallisation conductivity and α-relaxation decrease while MWS relaxation only shifts to higher temperatures. Dielectric spectra of solvent-cast and melt-blended nanocomposites suggest better dispersion in the latter case.