Water-induced structural changes in poly(lactic acid) and PLLA-clay nanocomposites
| Autor: | Freddys R. Beltrán, María L. Cerrada, J. Martínez Urreaga, M.U. de la Orden, Vicente Lorenzo, Ernesto Pérez |
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| Rok vydání: | 2016 |
| Předmět: |
Materials science
Polymers and Plastics 02 engineering and technology engineering.material 010402 general chemistry 01 natural sciences Halloysite Catalysis law.invention chemistry.chemical_compound Crystallinity Differential scanning calorimetry law Polymer chemistry Materials Chemistry Crystallization Fourier transform infrared spectroscopy Nanocomposite Organic Chemistry 021001 nanoscience & nanotechnology 0104 chemical sciences Montmorillonite chemistry Chemical engineering engineering sense organs 0210 nano-technology |
| Zdroj: | Polymer. 107:211-222 |
| ISSN: | 0032-3861 |
| DOI: | 10.1016/j.polymer.2016.11.031 |
| Popis: | The influence of nanoclays on the structural changes of hydrated poly(l-lactic acid) (PLLA) was investigated at two temperatures, above and below its Tg. Samples of a commercial PLLA and nanocomposites with 2 wt% of an organically modified montmorillonite and an unmodified halloysite were kept in a phosphate buffered solution for different times at 37 and 58 °C and then characterized. The crystallinity degrees and the nature of the crystalline structures developed were determined by differential scanning calorimetry, X-Ray Diffraction and Fourier Transform infrared spectroscopy. While in the cold crystallization of PLLA in dry conditions the α form is obtained only above 100 °C, different mixtures of α and α′ forms were obtained in water at 58 °C, depending on the clay used. The hydrolytic degradation of PLLA played a main role in the structural transformations found at long immersion times, since the short chains formed allowed greater crystallinity degrees and leaded to more perfect crystals. PLLA structure is changed by clays because of its ability as nucleating agents but also due to its effect on the hydrolytic degradation. The unmodified tubular halloysite inhibited degradation, so that lower degrees of crystallinity were obtained in the halloysite based nanocomposite. On the other hand, the modified montmorillonite acted as catalyst of degradation, which explained the appearance of crystalline structures in the nanocomposite with montmorillonite after 84 days of immersion at 37 °C. |
| Databáze: | OpenAIRE |
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