Design and engineering of barrier materials including nano-adsorbents

Abstract : A material is defined as “barrier” when it is able to delay the diffusion of a penetrant. There are few possibilities to modulate the barrier properties of a prescribed material (e.g. packaging material). Most of conventional technological strategies aim at increasing the tortuosity path of the penetrant by adding obstacles. Such obstacles could be obtained either by creating a crystalline morphology or by adding of nano-fillers. The gain in diffusion barrier depends on the shape factor of obstacles, their concentration and orientation according to the main direction of transfer. In this PhD work, a novel direction to improve the barrier property has been studied; its principles have been early formalized independently from theoretical considerations on random walk on heterogeneous energy surfaces and from modeling of reactivity in heterogeneous catalysis. The central idea relies on increasing retention times instead of diffusion path lengths by incorporating nano-adsorbents (i.e. active obstacles) in the material. In this case, the considered material becomes a barrier specific to one or a family of solutes. This new concept has been tested on organic solutes to develop new barrier materials (e.g. biobased food packaging, materials for fuel tank…). The results brought out the engineering principles of such materials and experimental evidences to support the concepts. In particular, an extended free-volume theory has been developed to separate interactions with active surfaces (i.e. montmorillonites (MMT) in this work) from free-volume related effects in the polymer. Sorption properties of pristine MMT and organo-modified ones have been characterized experimentally and by molecular simulation to derive conditions where the partition coefficient Kcontrast between the surface of MMT and tested polymers (i.e. polycaprolactone (PCL), polyvinyl alcohol (PVA)) could be much greater than unity. PVA materials containing pristine MMT exhibited the most promising barrier properties to studied model solutes, which can be activated by decreasing temperature and whose selectivity can be controlled by varying the relative humidity. The blocking effects were in good agreement with the proposed description of “trapping” of organic solutes by intercalation in MMT galleries and on its enthalpic and entropic control.
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Xiaoyi Fang. Design and engineering of barrier materials including nano-adsorbents. Food engineering. AgroParisTech, 2013. English. ⟨NNT : 2013AGPT0055⟩. ⟨tel-01139146⟩

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