Mississippi State University
Walters, Keisha B.
Lewis, Edwin A.
Hill, Priscilla J.
Elmore, Billy B.
Date of Degree
Dissertation - Open Access
Doctor of Philosophy (Ph.D)
James Worth Bagley College of Engineering
Dave C. Swalm School of Chemical Engineering
The overall goal of this research was to explore new living radical polymerization methods and the blending of renewable polymers. Towards this latter goal, polylactic acid (PLA) was blended with a new renewable polymer, poly(trimethylene-malonate) (PTM), with the aim of improving mechanical properties, imparting faster degradation, and examining the relationship between degradation and mechanical properties. Blend films of PLA and PTM with various ratios (5, 10, and 20 wt %) were cast from chloroform. Partially miscible blends exhibited Young’s modulus and elongation-to-break values that significantly extend PLA’s usefulness. Atomic force microscopy (AFM) data showed that incorporation of 10 wt% PTM into PLA matrix exhibited a Young’s modulus of 4.61 GPa, which is significantly higher than that of neat PLA (1.69 GPa). The second part of the bioplastics study involved a one-week hydrolytic degradation study of PTM and another new bioplastic, poly(trimethylene itaconate) (PTI) using DI water (pH 5.4) at room temperature, and the effects of degradation on crystallinity and mechanical properties of these films were examined by differential scanning calorimetry (DSC) and AFM. PTI showed an increase in crystallinity with degradation, which was attributed to predominately degradation of free amorphous regions. Depending on the crystallinity, the elastic modulus increased at first, and decreased slightly. Both bulk and surface-tethered stimuli-responsive polymers were studied on amine functionalized magnetite (Fe3O4) nanoparticles. Stimuli-responsive polymers studied, including poly(N-isopropylacrylamide) (PNIPAM), poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), and poly(itaconic acid) (PIA), were grafted via surface-initiated aqueous atom transfer radical polymerization (SI-ATRP). Both Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) spectroscopies showed the progression of the grafting. The change in particle size as a function of temperature was measured using dynamic light scattering (DLS). Once the PIA was grafted from the Fe3O4 nanoparticles for 13 h, the PIA thickness was around 13 nm. After the PNIPAM was grafted for 6 h, the stimuli-responsive nanocomposites with a lower critical solution temperature (LCST) of 32 °C exhibited a particle size of 236 nm. Moreover, a variety of stimuli-responsive bulk block copolymers were synthesized. The stimuli-responsive nanocomposites could be good candidates as drug carriers for the targeted and controllable drug delivery.
Eyiler, Ersan, "Development of Degradable Renewable Polymers and Stimuli-Responsive Nanocomposites" (2013). Theses and Dissertations. 1458.