Effets de vitesse et de transcristallinité dans l'analyse de la cristallisation de polyamides 66 d'architectures différentes

Abstract : Crystallization of three PA66 grades of different molar mass, linear or branched, has been studied in terms of crystallization kinetics and morphology.A hot stage has been used to study isothermal crystallization at high temperatures. A Hyper DSC has been used to study crystallization at constant cooling rates up to 700°C/min. Further investigations have been carried out using a Flash DSC setup increasing the reachable constant cooling rate up to 60000°C/min.Overall kinetics of crystallization have been successfully calculated thanks to Avrami model for isothermal crystallization and thanks to Ozawa model for anisothermal crystallization at constant cooling rate up to 700°C/min.Microtomed sections made with a glass knife microtome out of hot stage and Hyper DSC samples have been observed with a polarized light microscope. For one grade of PA66 studied, morphologies are very transcrystalline whereas for the two other grades, morphologies are spherulitic.The presence of transcrytalline zones while performing DSC experiments modifies the exotherms of crystallization with a contribution of surface crystallization and bulk crystallization. This leads to a polluted determination of crystallization kinetics. Then, we used the method proposed by Billon & al in order to discriminate the part of the exotherm due to transcrystalline crystallization and to bulk crystallization.Moreover, crystallization parameters as growth rate is identified thanks to the analyses of DSC crystallization trancrystalline-perturbed exotherms using two different thicknesses of DSC samples. Despite of a certain degree of uncertainty, the results obtained by this new method compare well with already published data. This method is particularly of interest when direct observation of spherulites is impossible.The lateral and folding surface free energies as well as the work of chain folding have been determined from Hoffman & Lauritzen treatment. Indeed, it allows us to see the change of growth regime from regime I to regime II and to calculate accurately growth rate vs temperature for the whole temperature range studied.
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Elio Lionel Freire. Effets de vitesse et de transcristallinité dans l'analyse de la cristallisation de polyamides 66 d'architectures différentes. Matériaux. PSL Research University, 2016. Français. ⟨NNT : 2016PSLEM042⟩. ⟨tel-01693771⟩

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