Molecular Mobility in the Amorphous Phase Determines the Critical Strain of Fibrillation in the Tensile Stretching of Polyethylene
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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.
KeywordsSAXS Bimodal high density polyethylene Molecular mobility
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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.
- 3.Strobl, G. The physics of polymers. Springer, Berlin, 2006.Google Scholar
- 5.Men, Y. F.; Rieger, J.; Strobl, G. Role of the entangled amorphous networks in tensile deformation of semicrystalline polymers. Phys. Rev. Lett. 2003, 91, 095502.Google Scholar
- 10.Men, Y.; Strobl, G. From crystalline block slips to dominance of network stretching—mechanisms of tensile deformation in semi-crystalline polymers. Chinese J. Polym. Sci. 2002, 20, 161–170.Google Scholar
- 11.Jiang, Z. Y.; Tang, Y. J.; Rieger, J.; Enderle, H. F.; Lilge, D.; Roth, S. V.; Gehrke, R.; Wu, Z.; Li, Z.; Men, Y. F. Structural evolution of tensile deformed high-density polyethylene at elevated temperatures: Scanning synchrotron small- and wide-angle X-ray scattering studies. Polymer 2009, 50, 4101–4111.CrossRefGoogle Scholar
- 19.Meinel, G.; Peterlin, A. Plastic deformation of polyethylene. Colloid Polym. Sci. 1970, 242, 1151–1160.Google Scholar
- 24.Scheirs, J.; Bohm, L. L; Boot, J. C; Leevers, P. S. PE100 resins for pipe applications: continuing the development into the 21st century. Trends Polym. Sci. 1996, 4, 408–415.Google Scholar
- 29.Men, Y. F.; Rieger, J.; Lindner, P.; Enderle, H.; Lilge, D.; Kristen, M.; Mihan, S.; Jiang, S. Structural changes and chain radius of gyration in cold drawn polyethylene after annealing: small- and wide-angle X-ray scattering and small angle neutron scattering studies. J. Phys. Chem. B2005, 109, 16650–16657.CrossRefGoogle Scholar
- 33.Glatter, O.; Kratky, O. Small-angle X-ray scattering. Academic Press, London, 1982.Google Scholar