Thermo-oxydation des polyamides

Abstract : Some metal components of automotive engine are bound to be replaced by polyamide parts. However, despite their thermal resistance polyamides are sensitive to oxygen leading to thermal oxidation chain reactions responsible for their long-term properties. While durability is critical for polyamide users, only a few studies deal with the elaboration of a kinetic model capable of predicting polyamide lifetime (time to embrittlement) in contrary to polyolefins (especially polyethylene). This PhD thesis is a contribution to the understanding of aliphatic polyamide thermal degradation by considering chemical and physical aspects of oxidation process in order to build a kinetic model. Our approach is based on a multi-scale physicochemical characterization of oxidized PA11 film samples under air between 90 and 165 °C but also under oxygen pressure. The proposed kinetic model coupling oxidation and solid state polymerization is able to simulate the whole experimental data (hydroperoxides, carbonyls and molar mass changes). In a same time, an intrinsic criterion for embrittlement is assessed to predict lifetime whatever the exposure conditions. Finally, the influence of phenols and copper salts on the oxidation kinetic is investigated. A first kinetic model including the phenol stabilizing effect is capable of simulating the main observed trends for stabilized PA11 such as the appearance of the pseudo induction period which contributes to the significant improvement of PA11 durability.
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Octavie Okamba Diogo. Thermo-oxydation des polyamides. Mécanique des matériaux [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2015. Français. ⟨NNT : 2015ENAM0002⟩. ⟨tel-01346299⟩

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