Dong Ouk Kim

Synthesis of Lignin-Based Thermoplastic Copolyester Using Kraft Lignin as a Macromonomer

Lignin-based thermoplastic copolyester was synthesized for eco-friendly polymers and composite applications using lignin as a macromonomer to form a high molecular weight polymer. Kraft lignin was polymerized with sebacoyl chloride in the presence of triethylamine in N,N-dimethylacetamide (DMAc), and the molecular weight of the synthesized polymer was controlled by the polymerization temperatures and [COCl]/[OH] ratios providing up to 39 000 corresponding to 4–5 repeating units of lignin macromonomers. The glass transition temperature of the synthesized polymer was difficult to measure due to the random distribution of functional groups and irregular configurational or conformational arrangement of natural lignin. Therefore, the complex electric modulus (CEM) technique was used to determine the glass transition of the synthesized polymer to give around 70°C measured by the peak of the imaginary part of CEM. The synthesized lignin-copolyester exhibited good thermal stability up to 200°C in TGA analysis and, thus, it was possible to shape the synthesized polymer using the solvent casting or hot-melt processing techniques at 120°C–140°C without generating odor, fume or irritation. Although the molecular weight should further be increased in the future, the developed methodology may help to exploit new applications for eco-friendly sustainable materials in various fields.

Synthesis of Platinum Nanoparticles Using Electrostatic Stabilization and Cluster Duplication of Perfluorinated Ionomer

Platinum (Pt) nanoparticles were prepared by the liquid-phase reduction of tetraammineplatinum (II) chloride ([Pt(NH3)4]Cl2) using Nafion as a stabilizer under various conditions of the Nafion phase. This method is novel in its use of electrostatic interactions between the Pt complex ions and sulfonic groups in the hydrated Nafion molecules. The synthesized Pt nanoparticles of the recast film system had a cubic shape. In the case of the Nafion solution system, the Pt nanoparticles mainly had a spherical shape. The shapes and sizes of the Pt nanoparticles were strongly influenced by the Nafion phase.

Morphological Characteristics of Electrospun Poly(Methyl Methacrylate) Nanofibers Containing Multi-Walled Carbon Nanotubes

The electrospinning process was investigated to embed multi-walled carbon nanotubes (MWNTs) in the electrospun nanofibers of poly(methyl methacrylate) (PMMA) for anisotropic alignment and effective dispersion of carbon nanotubes in the transparent polymer substrate. The morphology of MWNT-incorporated electrospun nanofibers was substantially influenced by the types of solvent and the content of carbon nanotubes exhibiting various forms of beads, undulated fibers, or uniform fibers. In the fibrous forms of electrospun PMMA, the MWNTs were mostly attached on the surface of polymer by physical interlocking. On the other hand, when the bead-shaped PMMA was produced by the electrospinning process, most of the MWNTs were embedded in the PMMA matrix without being exposed on the polymer surfaces. Using the O2 plasma treatment for cutting-off the polymer-rich surface layer of the beads, the embedded MWNTs were exposed out of the beads and subsequently an urchin-shaped structure was obtained. The protruded MWNTs of the urchin-shaped beads could stabilize the polymer beads by the steric stabilization in the solution state and provide facile electronic pathway and percolation in the condensed solid state.