Poly(lactic acid) blends, composites and fibers and direct pyrolysis mass spectrometry for nanoclay composites

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2017
Özdemir, Esra
In the first part of this study, poly(lactic acid)-poly(ethylene glycol), PLA-PEG, blends, composites and electrospun fibers of PLA and PLA composites, PLA-PEG blends and PLA-PEG, blends composites were prepared and characterized. X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Gel Permeation Chromatography (GPC), Simultaneous Thermal Analyzer (STA) and Direct Pyrolysis Mass Spectrometer (DP-MS) techniques were used for characterization studies. Both TGA and DP-MS analyses of PLA-PEG blends involving 10, 15 and 20 wt% PEG pointed out that the thermal decomposition occurred mainly in two steps. An interaction between COOH groups of PLA and ether linkages of PEG due to blending process was detected. Addition of 20 wt% PEG decreased the tensile strength and tensile modulus of PLA while improving its ductility due to its plasticization effect. Enhancement in the chemical interactions between PLA and PEG in the presence of Cloisite 30B (C30B) was observed. Also, tensile strength, %elongation at break and Young’s modulus were increased compared to the corresponding blends. Fiber formation not only effected thermal degradation behaviors of PLA, PLA-PEG blends and corresponding composites but also affected the morphology. The intermolecular trans-esterification reactions were enhanced upon fiber formation. Better delamination and intercalation of PLA chains into clay layers of Cloisite 15A (C15A), Cloisite 20A (C20A) and C30B were detected. On the other hand, the interaction between PLA and PEG decreased and phase separation during the electrospinning process was recorded upon fiber generation. On the contrary, in the presence of C30B, the interactions between PLA and PEG were enhanced and the phase separation was not detected for PLA-PEG composite fibers. In the second part of this study, the use of direct pyrolysis mass spectrometry to characterize polymer/organoclay systems was discussed. DP-MS analyses of poly(lactic acid) (PLA), poly(methyl methacrylate), (PMMA) and poly(ethylene) (PE) composites involving organically modified montmorillonites C15A, C20A, C25A (Cloisite 25A), C93A, (Cloisite 93A) or C30B showed that the technique supplies strong evidences for the extent and type of dispersion of clay layers in the polymer matrices. In addition, the technique allows identification of possible interactions between the polymer and the organic modifier.

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Citation Formats
E. Özdemir, “Poly(lactic acid) blends, composites and fibers and direct pyrolysis mass spectrometry for nanoclay composites,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.