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Incorporating Cloisite 30B (C30B) in poly(lactic acid) (PLA) matrix was investigated as functions of the content and of the hydration state of nanoclays. Two series of PLA based nanocomposites were prepared by melt compounding using nanoclays in hydrated state (undried C30B) or preliminary dried (dried C30B). Their structure was characterized by transmission electron microscopy (TEM) observations and X-ray diffraction (XRD) measurements which highlighted the coexistence of exfoliated, intercalated, and aggregated structures. Rheological measurements put forward better degrees of dispersion and of exfoliation for nanocomposites containing undried C30B. From differential scanning calorimetry (DSC) measurements, a slight change in crystallinity was measured owing to the nucleating effect induced by the nanoclays. The transport properties were analyzed from permeation and sorption kinetics. A significant improvement of the water and oxygen barrier properties was obtained, especially for nanocomposites with undried C30B, while a reduction in diffusion was evidenced. This peculiar behavior was correlated to the presence of water molecules included in C30B contributing to a better dispersion and orientation of the nanoplatelets into the PLA matrix.

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Multilayer coextrusion processing was applied to produce 2049-layer film of poly(butylene succinate-co-butylene adipate) (PBSA) confined against poly(lactic acid) (PLA) using forced assembly, where the PBSA layer thickness was about 60 nm. This unique technology allowed to process semicrystalline PBSA as confined polymer and amorphous PLA as confining polymer in a continuous manner. The continuity of PBSA layers within the 80/20 wt % PLA/PBSA layered films was clearly evidenced by atomic force microscopy (AFM). Similar thermal events to the reference films were revealed by thermal studies; indicating no diffusion of polymers during the melt-processing. Mechanical properties were measured for the multilayer film and the obtained results were those expected considering the fraction of each polymer, revealing the absence of delamination in the PLA/PBSA multinanolayer film. The confinement effect induced by PLA led to a slight orientation of the crystals, an increase of the rigid amorphous fraction (RAF) in PBSA with a densification of this fraction without changing film crystallinity. These structural changes allowed to strongly improve the water vapor and gas barrier properties of the PBSA layer into the multilayer film up to two decades in the case of CO gas. By confining the PBSA structure in very thin and continuous layers, it was then possible to improve the barrier performances of a biodegradable system and the resulting barrier properties were successfully correlated to the effect of confinement on the microstructure and the chain segment mobility of the amorphous phase. Such investigation on these multinanolayers of PLA/PBSA with the aim of evidencing relationships between microstructure implying RAF and barrier performances has never been performed yet. Besides, gas and water permeation results have shown that the barrier improvement obtained from the multilayer was mainly due to the reduction of solubility linked to the reduction of the free volume while the tortuosity effect, as usually expected, was not really observed. This work brings new insights in the field of physicochemical behaviors of new multilayer films made of biodegradable polyesters but also in interfacial processes due to the confinement effect induced in these multinanolayer structures obtained by the forced assembly coextrusion. This original coextrusion process was a very advantageous technique to produce eco-friendly materials with functional properties without the help of tie layer, additives, solvents, surface treatments, or inorganic fillers.

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