Influence of the process on water permeability of semi-crystalline PLA nanocomposites: solvent casting versus annealing of melt-blended films

Semi-crystalline PLA nanocomposites containing fillers of different types have been prepared by melt blending followed by annealing treatment or by solvent casting. Annealed melt blended samples exhibit higher crystallinity (around 47%) than solvent cast films (around 36%) independently of the filler type. The glass transition temperature remains similar (around 56 °C) for all investigated films. The filler dispersion, investigated by Transmission Electron Microscopy, has been found to be better with the melt-mixing/annealing process than with the solvent casting process. The water vapor permeability of nanocomposites prepared by solvent casting shows a decrease of the permeability with the addition of fillers whereas it is not the case for annealed nanocomposites for which the permeability is often higher than the one of the annealed unfilled PLA. The permeability cannot be only related to the filler dispersion state but results also from the filler/matrix interfacial properties that depend on the filler type with respect to the matrix, but also on the process used to obtain semi-crystalline nanocomposites. It has been shown that, for silica, halloysite nanotubes and graphene, the melt blending/annealing process has a detrimental impact on the filler/matrix interfacial properties and the water barrier properties which is not the case for montmorillonite for which a 60% decrease in permeability is reached when using 10 vol% of fillers. • A wide range of semi-crystalline PLA nanocomposites were prepared from 2 processes • Annealed melt blended films exhibited higher crystallinity than solvent cast ones • Melt blending/annealing yielded better filler dispersion than solvent casting. • Microstructure-permeability relations have been established. • The process had a significant impact on the nanocomposite water barrier properties.