PLA Nanocomposites Based on Silica and Organo-Modified Montmorillonite: A Comparative Investigation of Different Solvent-Free Synthesis Routes on the Morphology and Water Permeability

Amorphous PLA nanocomposites based on hydrophobic silica or organo-modified montmorillonite (Cloisite 30B) have been prepared according to two different routes: melt blending and in situ polymerization for a filler range up to 10 vol %. The process and conditions used for in situ polymerization have been optimized for each filler type in order to obtain nonbrittle self-standing films. While direct reactive processing could be successfully carried out for in situ polymerization in the presence of silica, a two-step process, consisting first of the in situ synthesis of a masterbatch and then diluting in commercial PLA, had to be used and optimized with montmorillonite. The formation of lower average molar mass PLA chains by in situ polymerization routes led, whatever the filler, to a lower glass transition temperature of the PLA matrix with respect to commercial PLA. Based on the obtained nanocomposite series, filler dispersion as well as filler/matrix interactions have been investigated and discussed as a function of the synthesis route and filler type. PLA chain grafting from organomodified montmorillonite was evidenced by FTIR analysis for the samples prepared by in situ polymerization. For both silica and montmorillonite, better filler dispersion states were obtained from the in situ polymerization route for filler content above 5 vol % leading to higher water barrier properties.