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Mechanics of bio-based thermosetting polymers and water-induced rejuvenation

Abstract : In order to meet growing environmental concerns, there has been a considerable interest in generating bio-based polymers with a view to replacing the traditional oil-based chemistries. This thesis focuses on polyester thermosetting resins derived from renewable feedstock. Product optimization is however currently impeded by the limited knowledge about the mechanical properties of these new polymers. Indeed, the material foamability coupled to fast polymerization during processing prevents the fabrication and characterization of macroscopic polymer samples under technologically relevant conditions.To overcome this limitation, we prepare samples with micrometric sizes (typically in the 10 textmu m range) and controlled geometries from a model bio-based polyester resin. The mechanical behaviour of these micro samples is investigated experimentally using various micro mechanical characterization techniques. Because of its large hydrophilicity, the model polymer exhibits a large change in its mechanical properties upon exposure to humidity. For increasing humidity, pristine specimens undergo a water-triggered glass transition from a glassy to a water-swollen gel state which is attributed to the dramatic plasticization of the material by water. We also evidence the influence of hygric history on the mechanical, structural and sorption properties of the polymer and show that this dependence bears close similarities with the effect of thermo-mechanical physical ageing on polymer glasses. Finally, when subjected to long-term hygrothermal ageing conditions, the polymer exhibits an irreversible degradation of its mechanical properties which may be ascribed to the existence of hydrolysis process.
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  • HAL Id : tel-02631729, version 1

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Raphaëlle Kulis. Mechanics of bio-based thermosetting polymers and water-induced rejuvenation. Chemical Physics [physics.chem-ph]. Université Paris sciences et lettres, 2019. English. ⟨NNT : 2019PSLET003⟩. ⟨tel-02631729⟩

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