scale analysis of the impact of polylactide morphology on gas barrier properties. Polymer, Elsevier, 2017, 108, pp.163-172. 10.1016/j.polymer.2016 Multi-scale analysis of the impact of polylactide morphology on gas barrier properties Samira Fernandes Nassar t r a c tSemicrystalline polylactide (PLA) films with controlled morphology were produced by thermal crystallization to optimize the oxygen barrier properties. The crystalline morphology of PLA at the scales of the lamella and the spherulite was investigated and the mobile amorphous phase dynamics were studied. The crystalline morphology had a negligible impact on the oxygen diffusion coefficient. The occurrence of a rigid amorphous fraction (RAF) in the amorphous phase due to its insufficient decoupling from the crystalline phase provided an accelerated pathway for diffusion, though. As a conclusion, for reaching optimal barrier properties, semicrystalline PLA should be pre-nucleated and rapidly crystallized from the glass in the a-polymorph in the aim to reach a high crystallinity degree and decoupling of the amorphous and the crystalline phase. These recommendations can benefit to industry for the optimization of PLA annealing treatments.

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Multi-nanolayered Polystyrene/Poly(L,L-lactide) (PS/PLLA) films were obtained by the layermultiplying co-extrusion process, with an individual PLLA layer thickness as thin as 20 nm. The confinement of the amorphous PLLA induced a change in the molecular mobility, evidenced by a drop of the Cooperative Rearranging Region (CRR) size at the glass transition. The annealing of confined PLLA layers revealed slower crystallization kinetics and two-dimensional crystalline growth geometry. Furthermore, the annealing of PLLA in confined layers allowed a decoupling between the amorphous and crystalline phase, evidenced by the absence of a Rigid Amorphous Fraction (RAF). As a consequence, the dynamic heterogeneity at the glass transition remained unaffected by the annealing procedure. In bulk polymers, where the level of coupling between amorphous and crystals is high, the glass transition temperature increased significantly whereas the CRR size fell. It is deduced that the glass transition dynamics in semi-crystalline polymers is strongly related to the mobility landscape at the interface with crystals.