Shear-induced nonisothermal crystallization of two grades of PLA |
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| Affiliation: | 1. Centro de Tecnología Repsol, Carretera Extremadura, A-5, km. 18, 28935 Móstoles, Spain;2. Departamento de Ingeniería Química, Centro de Investigación en Tecnología de Productos y Procesos Químicos (Pro2TecS), Campus de ‘El Carmen’, Universidad de Huelva, 21071 Huelva, Spain;1. Department of Life, Health and Chemical Sciences, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK;2. International Institute for Nanocomposites Manufacturing (IINM), WMG, University of Warwick, Coventry, CV4 7AL, UK;3. WMG, University of Warwick, Coventry, CV4 7AL, UK;4. Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK;5. School of Mechanical & Aerospace Engineering, Queen''s University Belfast, BT9 5AH, UK;1. Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis, #08-03, Singapore 138634, Singapore;2. Department of Materials Science and Engineering, National University of Singapore, Singapore 117574, Singapore;1. Department of Polymer Materials, Shanghai University, 200444, Shanghai, China;2. Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 130022, Changchun, China |
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| Abstract: | Shear-induced nonisothermal crystallization of two commercial polylactides (PLAs) differing in optical purity was studied. The molten polymers were sheared at selected temperatures (Ts) and subsequently cooled. The crystallization was followed by a light depolarization method, whereas the specimens were analysed ex-situ by DSC, 2D-WAXS and SEM after etching. It was found that the effect of shear, especially on the crystallinity developed during post-shearing cooling, intensified with a decrease of Ts from 160 to 146 °C, and with increasing shear rate and strain. Moreover, the effect of shear on PLA1.5 with d-lactide content of 1.5% was stronger than PLA2.8 with 2.8% of d-lactide, although maximum crystallinity of both polymers was practically the same. A decrease of cooling rate from 30 to 10 °C/min increased crystallinity of both PLAs, except for those shearing conditions which induced high crystallinity even during faster cooling. Although SEM examination revealed some row-nucleated forms, no significant crystal orientation was detected by 2D-WAXS, indicating that, under the experimental conditions, the shear induced predominantly point-like nuclei. |
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| Keywords: | Biodegradable polymers Polylactide Shear-induced crystallization Structure Melting behavior |
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