Photo-oxidation of semicrystalline polymers: Damage nucleation versus growth

Abstract : The relative roles of damage nucleation and growth in the oxidative embrittlement of polymers has been investigated in tension. Additive-free polyamide-6 was used, taking advantage of prior knowledge of damage mechanisms in the unaged condition. Accelerated aging was carried out on bulk and thin specimens, which were then mechanically tested to fracture. Videos of the tests enabled the measurement of specimen deformation and detection of surface microcracks and their evolution. In addition, in situ synchrotron tomography was used to observe damage nucleation and growth in the thin specimens. It was found that distributed cracking occurred well before the load maximum and that the density of microcracks increased with both strain and oxidation levels. Using a combination of video-based extensometry and digital image correlation, significant strain-induced dilatations were measured for both unaged and oxidized specimens. In addition, damage nucleation by chain scission was found to be heterogeneous, as the molar mass between entanglements, inferred from the true strain hardening rate, was unaffected by oxidation. Finally, a chemical-stress based model is invoked to interpret gradual ductile-to-brittle transitions in oxidative embrittlement.
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K.N. Cundiff, Yazid Madi, A.A. Benzerga. Photo-oxidation of semicrystalline polymers: Damage nucleation versus growth. Polymer, Elsevier, 2020, 188, pp.122090. ⟨10.1016/j.polymer.2019.122090⟩. ⟨hal-02437226⟩



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