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Molecular Mobility in the Amorphous Phase Determines the Critical Strain of Fibrillation in the Tensile Stretching of Polyethylene

  • Rui Li
  • Guo-Xing Yang
  • Ya-Nan Qin
  • Li Liu
  • Zhi-Yong JiangEmail author
Article
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Abstract

The microstructural development of bimodal high density polyethylene subjected to tensile deformation was investigated as a function of strain after annealing at different temperatures by means of a scanning synchrotron small angle X-ray scattering (SAXS) technique. Two different deformation mechanisms were activated in sequence upon tensile deformation: intralamellar slipping of crystalline blocks dominates the deformation behavior at small deformations whereas a stress-induced crystalline block fragmentation and recrystallization process occurs at a critical strain yielding new crystallites with the molecular chains preferentially oriented along the drawing direction. The critical strain associated with the lamellar-to-fibrillar transition was found to be ca. 0.9 in bimodal sample, which is significantly larger than that observed for unimodal high-density polyethylene (0.4). This observation is primarily due to the fact that the bimodal sample possesses a greater mobility of the amorphous phase and thereby a reduced modulus of the entangled amorphous network. The conclusion of the mobility of the amorphous phase as a determining factor for the critical strain was further proven by the 1H-NMR T2 relaxation time. All these findings contribute to our understanding of the excellent slow crack growth resistance of bimodal polyethylene for pipe application.

Keywords

SAXS Bimodal high density polyethylene Molecular mobility 

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Notes

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (No. 21674119) and Jilin Scientific and Technological Development Program (No. 20180519001JH). We thank Prof. Yongfeng Men and Dr. Victor Litvinov for helpful discussions.

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Copyright information

© Chinese Chemical Society Institute of Chemistry, Chinese Academy of Sciences Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Rui Li
    • 1
    • 2
  • Guo-Xing Yang
    • 2
  • Ya-Nan Qin
    • 3
  • Li Liu
    • 1
  • Zhi-Yong Jiang
    • 3
    Email author
  1. 1.School of Chemistry and Chemical Engineering, State Key Laboratory of Urban Water Resource and EnvironmentHarbin Institute of TechnologyHarbinChina
  2. 2.Daqing Petrochemical Research Center, Petrochemical Research InstituteChina National Petroleum CorporationDaqingChina
  3. 3.State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied ChemistryChinese Academy of SciencesChangchunChina

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