Papers by Author: Byung Hyun Park

Abstract: In this study, poly(ε-caprolactone) (PCL)/multiwalled carbon nanotube (MWCNT) composites with different contents of MWCNTs were successfully prepared by solution compounding, a method which could make them good competitors for commodity materials such as general purpose plastics, while allowing them to keep their complete biodegradability. For the homogeneous dispersion of the MWCNTs in the polymer matrix, oxygen-containing groups were introduced on their surface. The mechanical properties of the PCL/MWCNT composites were effectively increased due to the incorporation of the MWCNTs. The composites were characterized using scanning electron microscopy, in order to obtain information on the dispersion of the MWCNTs in the polymeric matrix. In the case of the composites containing 2.0 wt% of MWCNTs in their matrix, the strength and modulus of the composites were increased by 18.4% and 178.4%, respectively. In addition, the dispersion of the MWCNTs in the PCL matrix resulted in a substantial decrease in the electrical resistivity of the composites as the MWCNT loading was increased from 0 to 2.0 wt%.

Abstract: Poly(ε-caprolactone)/multiwalled carbon nanotube (PCL/MWCNT) composites with different MWCNT contents were successfully prepared by in situ bulk polymerization, which could make them good competitors for commodity materials such as general purpose plastics, while allowing them to completely retain their biodegradability. The mechanical properties of the PCL/MWCNT composites were effectively increased due to the incorporation of the MWCNTs. The composites were characterized using scanning electron microscopy, in order to obtain information on the dispersion of the MWCNTs in the polymeric matrix. In the case where 0.5 wt% of MWCNTs were dispersed in the matrix, the strength and modulus of the composite increased by 23% and 71%, respectively. In addition, the dispersion of the MWCNTs in the PCL matrix resulted in a substantial decrease in the electrical resistivity of the composites being observed as the MWCNTs loading was increased from 0 wt% to 0.5 wt%.

Abstract: Polycarbonate/multiwalled carbon nanotubes (PC/MWNT) nanocomposites with different contents of MWNT were successfully prepared by melt compounding. The mechanical properties of the PC/MWNT nanocomposites were effectively increased due to the incorporation of MWNTs. The composites were characterized using scanning electron microscopy in order to obtain the information on the dispersion of MWNT in the polymeric matrix. In case of 0.3 wt% of MWNT in the matrix, strength and modulus of the composite increased by 30% and 20%, respectively. In addition, the dispersion of MWNTs in the PC matrix resulted in substantial decrease in the electrical resistivity of the composites as the MWNTs loading was increased from 1.0 wt% to 1.5 wt%.

Abstract: Polymeric carbon nanotube composites constitute one of the most promising alternatives to conventional filled polymers. The dispersion of nanometer-sized carbon nanotubes in a polymer matrix markedly improves its physical properties. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(L-lactic acid) (PLLA), which has been receiving an increasing amount of attention due to environmental concerns. In this study, the mechanical properties of PLLA were enhanced by the incorporation of a small amount of carbon nanotubes (0.8 wt%) in the solution state, which could make this material a good competitor for commodity materials such as general purpose plastics, while allowing it to retain its biodegradability. In order to obtain a homogeneous dispersion of the carbon nanotubes in the matrix, oxygen-containing groups were introduced on the surface of the MWNTs. The good dispersion of the nanotubes in the PLLA matrix observed by scanning electron microscopy was attributed to the fact that the PLLA was compatible with the functionalized MWNTs during the compounding process. The electrical conductivity of the composites was also investigated.

Abstract: Biodegradable composites consisting of poly(butylene succinate) (PBS) and carbon nanotube (CNT)-coated silk (Bombxy mori) fibers were prepared by melt compression molding. The results show that even with addition of a small amount of reinforcements (about 3 wt%), the tensile strength and modulus of the composites improved dramatically by about 195% and 121%, respectively, compared with PBS. The improvement is attributed to stronger interfacial shear strength between the PBS matrix and the CNT-coated surface of silk fiber, which was obtained by the microbond droplet test between PBS matrix and fibers. Furthermore, scanning electron microscopy images indicated that the interfacial adhesion between PBS matrix and CNT-coated fiber improved in the composites.

Abstract: By severe plastic deformation of metals, an ultra fine grain size can be obtained. In the present study an AA 1050 Aluminium alloy has been severe deformed by Equal channel angular pressing (ECAP). A study on the microstructure and the texture of the samples after ECAP and subsequent heat treatment has been carried out. The specimens after ECAP showed a very fine grain size, a decrease of <100> // ND, and an increase of <111> // ND textures. The {111}<112>, {123}<634>, {110}<001>, {112}<111>, {110}<111>, and {013}<231> texture components were increased in the specimens after the ECAP and subsequent heat-treatment at 400° C for 1 hour. One of the most important properties in sheet metals is formability. The r-value or plastic strain ratio has been used as a parameter that expresses the formability of sheet metals. The change of the plastic strain ratios after the ECAP and subsequent heat-treatment conditions has been investigated and it was found that they were two times higher than those of the initial Al sheets. This could be attributed to the formation above texture components through the ECAP and subsequent heat-treatment.

Abstract: . Equal channel angular pressing (ECAP) is useful method to obtain the ultra-fine grained and the high hardened metal. The microstructure, the hardness, and the texture of the 1050 Al sheets by ECAP are changed by a severe shear deformation. The change of the microstructure, the hardness, and the texture were investigated on the 1050 Al sheets that were prepared by ECAP and annealing.

Abstract: Electrodeposited Ni films were produced by using four types of electrodeposition methods, direct current without additive (DC), direct current with additive (AD), square pulse without additive (SP) and square pulse with additive (AS). The <100> texture was obtained by using the DC method at about 20 °C and by using the AD and the AS methods at about 80°C. The <110> texture was obtained by using the DC and the SP methods at about 80 °C. When using the AS method, the surface roughness of Ni deposit was lower than that of Ni deposits after using the other electrodepositon methods and the microstructure of Ni deposits showed nanocrystalline grain size. The <100> textures of Ni deposits using the DC and the AS methods remained unchanged after the recrystallization process. The <110> texture of Ni deposits using the SP method at about 80 °C changed to < 3 1 0> orientation after the recrystallization process.