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

POLYMER

卷:175

Article

Pepin, Julie¹  Gaucher, Valerie¹  Rochas, Cyrille²  Lefebvre, Jean-Marc¹ 

[1] Univ Lille, CNRS, INRA, ENSCL,UMR 8207,UMET, F-59000 Lille, France

[2] CERMAV, UPR CNRS 5301, Grenoble, France

关键词: Polyamide;    Polymorphism;    Structural evolution;    In-situ observations;    Hydrogen bond;    Twinning;   

DOI  :  10.1016/j.polymer.2019.04.073

来源: Elsevier

【 摘 要 】

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.

【 授权许可】

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