Showing papers by "Nam Hoon Kim published in 2010"

Synergy effect of hybrid fillers on the positive temperature coefficient behavior of polypropylene/ultra‐high molecular weight polyethylene composites

Abstract: Hybrid nanocomposites of polypropylene/ultra-high molecular weight polyethylene (PP/UHMWPE, 70/30) with various amounts of carbon black (CB) and carboxylated multiwalled carbon nanotubes (c-MWNTs) were prepared by the solution mixing and melt blending techniques. The effects of the mixture of CB and c-MWNTs on the positive-temperature-coefficient (PTC) behavior and the negative-temperature-coefficient (NTC) behavior, as well as the room temperature resistivity, were studied. The transmission electron microscopy (TEM) images showed that the CB particles were aggregated at the interface, between PP and UHMWPE. This selective localization of the CB particles at the interface along with the formation of continuous conducting media leads to the formation of additional conducting networks, resulting in a percolation threshold at a low CB content. A synergy effect of the hybrid conducting fillers of CB and c-MWNTs on the PTC behavior of the hybrid blends was also observed. The room temperature resistivity was reduced significantly by the incorporation of the c-MWNTs into the PP/UHMWPE/CB composite. The intensity and repeatability of the PTC effect in the nanocomposites were improved and the NTC effect weakened by incorporating a small amount (0.5 wt %) of c-MWNTs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effects of the surface treatment on the properties of polyaniline coated carbon nanotubes/epoxy composites

Abstract: The effects of a surface treatment of carbon nanotubes (CNTs) on the electrical conductivity and the hydrophilicity of a polyaniline (PAni) coated CNTs (PAni-CNTs)/epoxy (EP) composites were examined. The surface of the CNTs was treated with various chemicals, such as acid mixtures (HNO 3 :H 2 SO 4 ), potassium persulfate (KPS) and sodium dodecyl sulfate (SDS), to improve their dispersion and reactivity with PAni. The electrical conductivity and hydrophilicity of PAni-CNTs and their EP composites were strongly affected by the surface treatment of the CNTs. The surface-treating materials remained on the surface of the CNTs affected the reactivity of the CNTs surface to PAni, and thus resulted in different PAni amounts in the PAni-CNTs. The electrical conductivity of the PAni-CNTs/EP composites decreased, but the hydrophilicity increased, with increasing the amount of PAni coating on the CNTs surface.

Synthesis of water soluble sulfonated polyaniline and determination of crystal structure

Abstract: A polyaniline (PANI) was synthesized by the oxidative polymerization using ammonium persulfate as an oxidizing agent. The PANI was then stirred with excess fuming sulfuric acid at room temperature for 6 h to obtain water soluble sulfonated polyaniline (SPANI). The degree of sulfonation was found to be 93–94% from the Fourier transform infrared (FTIR) and elemental analysis. The solubility of the SPANI in water was 1.25 g/L at room temperature and appeared as a green color solution. Conductivity of the PANI was decreased after sulfonation. A proliferation of hydrophilic nature of the PANI after sulfonation was observed from the water contact angle measurement. From the UV analysis, it was revealed that the energies required for the π–π* and bipolaron/polaron transitions are less and the intensity of these transitions are lower in SPANI compared to those of PANI. A detailed study on the crystal structures of PANI and SPANI were accomplished from the powder X-ray diffraction analysis. The SPANI exhibited a more ordered structure having a higher degree of crystallinity and crystallite sizes with an increased unit cell volume compared to the PANI. After sulfonation the morphology of PANI was transformed from a rod-like shape to a flat-plate shape. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

One-Step Process for the Exfoliation and Surface Modification of Graphene by Electrochemical Method

Abstract: SDBS modified graphene was prepared by electrochemical method using Sodium dodecylbenzenesulfonate (SDBS) as electrolyte and graphite rod as electrode. The anode graphite rod was corroded and deposited at the bottom of the electrolyte solution. The obtained graphene was characterized by Atomic force microscopy (AFM), Raman and Fourier transform infrared spectra (FT-IR). AFM images indicated that most of the layers had the thickness of less than 2 nm, suggesting the fromation of single layer of graphene. The resulting graphene showed very good dispersion stability both in water and in organic solvents (ethanol, acetone).

Fibre-Fibre Hybrid Composites for Aerospace Applications

Abstract: The extruded poly ether ether ketone (PEEK) and glass fibre were used to obtain the co-woven hybrid fibre fabrics and converted into composites using compression moulding technique. The effect of shear stress and shear rate on the shear viscosity of PEEK was investigated to optimise the process conditions for converting hybrid fabrics into composites. The mechanical properties such as flexural strength and inter laminar shear strength (ILSS) as a function of number of layers of fabric have been evaluated. Low velocity (2.1 m/s) repeated drop weight impact tests were carried out on the fabricated composites at 5 and 10 J incident energy. Dielectric properties as a function of temperature and frequency have been carried out. Flammability behaviour of composites has been carried out using cone calorimeter. The data generated shows that glass-PEEK based composites are excellent potential materials for advanced structural composites.

Preparation of Primary-Amine Functionalized Poly(2,5-benzimidazole) Membrane for Fuel Cells

Abstract: Acid doped polybenzimidazole membrane has been prepared for proton exchange membrane fuel cell. The present work aims at improving the proton conductivity without losing mechanical properties at high doping level by modifying poly (2,5-benzimidazole) (ABPBI). The nitration of ABPBI has been carried out with acid mixture of HNO3 and H2SO4 at 30oC. This nitro compound has been reduced successfully by stannous chloride/dimethylacetamide in presence of hydrochloric acid. Fourier transform infrared (FT-IR) spectra confirm the presence of primary amine groups in the ABPBI structure. The primary amine functionalized ABPBI has been cross-linked by hexamethylene diisocyanate and casted onto glass Petridis using dimethyl sulfoxide as solvent. Membrane doped with phosphoric acid shows comparatively higher proton conductivity, but lower tensile strength.

Effect of Carbon Fillers on the Performance of a Composite Bipolar Plate for Fuel Cells

Abstract: The bipolar plates were fabricated using compression molding of graphite (GR), carbon black (CB), multi-wall carbon nanotubes (MWNTs), carbon fibers (CF) and powder type epoxy resin. The electrical conductivity and flexural properties of the composites was increased with increasing the content of fibrous conducting fillers e.g., MWNTs and CF. However, when particulate fillers such as CB and GR were used, the electrical conductivity was increased, but the flexural properties deteriorated with increasing filler content up to certain content. A comparison was also made between the current-voltage (I-V) performances of fabricated composite bipolar plates and commercial graphite bipolar plate. The I-V characteristic in single cell test exhibited more uniform power density at both higher and lower current density and single cell performance increased with increasing the electrical conductivity.

Preparation and Characterization of Functionalized Graphene/Linear Low Density Polyethylene Nanocomposites

Abstract: The present work deals with the functionalization of graphene sheet and preparation of functionalized graphene/linier low density polyethylene (LLDPE) nanocomposites by solution-mix techniques. Dodecyl amine (DA) has been used for the surface modification of graphene oxide (GO) and hydrazine as reducing agent. Fourier transform infrared (FTIR) spectra exhibits the appearance of new peaks in the functionalized graphene (DA-G), which suggests the functionalization of graphene by DA. X-ray diffraction (XRD) analysis infers the formation of fully exfoliated DA-G/LLDPE nanocomposites. The tensile strength (TS) and elongation at break (EB) of the composites are higher in comparison to neat LLDPE. The nanocomposites with only 0.5 wt.% of DA-G content results in TS and EB to be 17% and 10% higher compared to neat LLDPE. TGA shows that the thermal stability of the DA-G/LLDPE nanocomposites is higher compared to pure matrix polymer.