A near-infrared study of thermally induced structural changes in polyethylene crystal |
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Authors: | Shin Watanabe Ji?í Dybal Yukihiro Ozaki |
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Affiliation: | a Research and Development Department, EurLAsia Analytical, Analytical Department, Kobe Technical Center, Procter and Gamble Far East Inc., 1-17 Naka, Koyo-cho, Higashi-Nada, Kobe 658-0032, Japan b Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq.2, 162 06 Prague, Czech Republic c Department of Future Industry-oriented Basic Science and Materials, Graduate School of Engineering, Toyota Technological Institute, Tempaku, Nagoya 468-8511, Japan d Department of Chemistry, School of Science and Technology, Kwansei-Gakuin University, Gakuen, Sanda, Hyogo 669-1337, Japan |
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Abstract: | Thermally induced structural changes of polyethylene (PE) have been studied by means of near-infrared (NIR) spectroscopy in the course of heating up to the melting temperature. NIR bands characteristic of the regular orthorhombic phase, the conformationally disordered hexagonal phase, and the amorphous phase have been successfully identified. It has been found that for the unoriented PE sample, the disordering process of orthorhombic lattice starts above room temperature and that it mostly occurs above 100 °C for the uniaxially oriented PE sample. In the latter case, the enhancement of crystallinity has clearly been detected just below Tm due to the reorganization of crystalline lattice. For the geometrically constrained ultradrawn PE sample, the phase transition from orthorhombic to hexagonal phase has been detected immediately below the melting point. The NIR bands characteristic of the hexagonal phase have been confirmed definitely. Usefulness of NIR spectroscopy has been demonstrated successfully in such a study of thermally induced phase transition behavior of PE samples with appreciable thickness, for which mid-IR spectroscopy is difficult to apply because of the intensity saturation of various key bands. |
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Keywords: | Polyethylene Near-infrared (NIR) Phase transition |
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