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In-situ SAXS/WAXS investigations of the mechanically-induced phase transitions in semi-crystalline polyamides

Abstract : The structural evolution under uniaxial tension of both Polyamide-11 (PA11) and Polyamide-6 (PA6) crystallized under various crystal forms has been investigated as a function of draw temperature with respect to the Brill transition. The use of in-situ synchrotron two-dimensional wide-angle X-ray diffraction and small-angle X-ray scattering allows to discriminate thermal from mechanical effects, leading to a revisited scheme of the strain-induced phase transitions in polyamides. It is demonstrated that only the H-bonded sheet-like structures transform mechanically into a pseudo-hexagonal form with a random distribution of H bonds around the chain axis. This order-disorder transition occurs during the fibrillar transformation and seems systematically preceded by a twinning mechanism at low deformation. By contrast, the mesophases and the High Temperature forms are mechanically stable, the latter transforming thermally into the H-bonded sheet-like structures as soon as samples are cooled down below the Brill transition temperature.
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Submitted on : Friday, October 22, 2021 - 9:35:33 PM
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Julie Pepin, Valérie Gaucher, Cyrille Rochas, Jean Marc Lefebvre. In-situ SAXS/WAXS investigations of the mechanically-induced phase transitions in semi-crystalline polyamides. Polymer, Elsevier, 2019, Polymer, pp.87-98. ⟨10.1016/j.polymer.2019.04.073⟩. ⟨hal-02448905⟩

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