Characterizing polymorphism and crystal transformation of polylactide by terahertz time-domain spectroscopy |
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| Institution: | 1. Department of Materials Science and Engineering, China University of Petroleum, Beijing 102249, China;2. College of Science, Minzu University of China, Beijing 100081, China;1. Department of Power Mechanical Engineering, National Formosa University, Yunlin 632, Taiwan;2. Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, Keelung, Taiwan;3. Electronics and Optoelectronics Research Laboratories (EORL), Industrial Technology Research Institute (ITRI), Taiwan;1. Tecnológico Nacional de México/Centro Nacional de Investigación y Desarrollo Tecnológico (CENIDET), Prolongación Palmira s/n esq, Apatzingán, Col. Palmira, Cuernavaca, Morelos, Mexico;2. CIICAp/FCQeI/Universidad Autónoma del Estado de Morelos Av, Universidad 1001 Col, Chamilpa C.P, 62209 Cuernavaca, Morelos, Mexico;3. Facultad de Química/ICF/Universidad Nacional Autónoma de México, Coyoacán, D. F. C. P. 04510, Mexico;1. Enersol Pty Ltd, 235 Nelson St, Annandale, NSW, 2038, Australia;2. United Nations Population Fund, UN City, Marmorvej 51, 2100, Copenhagen, Denmark;1. Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia;2. Department of Mechanical Engineering, École Polytechnique, P.O. Box 6079, Station Centre Ville, Montréal, Qc, H3C 3A7, Canada |
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| Abstract: | Terahertz time-domain spectroscopy (THz-TDS), which has been proved to show promising application in complex polymer systems, was employed to investigate the polymorphism phenomenon and crystal transformation of polylactide (PLA) in this study. The THz-TDS shows sensitive response on the crystal structure. The α'-form, α-form and stereocomplex crystals exhibit absorption peaks of lattice vibration at 1.82, 2.01 and 2.09 THz, respectively. THz-TDS has no direct chirality identification on the difference between poly (d-lactide) (PDLA) and poly(l-lactide) (PLLA). However, the PLA stereocomplex shows an extra and distinctive absorption peak at 1.43 THz compared with homo-PLA, and the peak was proved to be stemmed from the collective vibration of L-lactic unit and D-lactic unit pairs connecting by hydrogen bonds. This is the first time that THz-TDS has been proved to be of great potential in identification of polymer stereocomplex crystal. Also, the α'→α crystal transformation of PLA were intuitively investigated at 120 °C using THz-TDS, while the transformation rate was quite slow. |
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| Keywords: | Terahertz time-domain spectroscopy Polylactide Crystal transformation Stereocomplex |
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