• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.106-111
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• 2008

Polypropylene (PP)/corn starch master batch (starch-MB)/silicate composites with different corn starch compositions of 10, 20, 30, 40 and 50 were prepared by melt compounding at $200^{\circ}C$, using lab scale Brabender mixer. The content of silicate was fixed at 5 wt%. The composition of starch-MB in composites was confirmed by the existence of hydroxy group and peak intensity in fourier-transform-infrared (FT-IR) spectrum. The thermal properties of the PP/starch-MB/silicate composites were investigated by differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA). There was no district change in melting temperature, and TGA curve indicates a decrease in degradation temperature with the increase of starch-MB content. The silicate dispersion of the composites was measured by X-ray diffraction (XRD) and transmission electron microscope (TEM). The degree of silicate dispersion in PP/starch-MB/silicate composites depended on the content of starch-MB. There was detectable change in d-spacing and peak intensity of the composite when the content of starch-MB was higher than 20 wt%. The rheological behavior of the composites was explained by both shear thinning effect and elastic property with the starch-MB amount. These effects were remarkable when the content of starch-MB was higher than 20 wt%. These were confirmed by an oscillatory viscometer at $200^{\circ}C$.

• Journal of IKEEE
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• v.19 no.4
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• pp.491-499
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• 2015

Silicon Carbide(SiC) has large advantage in high temperature and high voltage applications because of its high thermal conductivity and large band gap energy. When using SiC to design power semiconductor devices, edge termination techniques have to be adjusted for its maximum breakdown voltage characteristics. Many edge termination techniques have been proposed, and the most appropriate technique for SiC device is Junction Termination Extension(JTE). In this paper, the change of breakdown voltage efficiency ratio according to the change of doping concentration and passivation oxide charge of each JTE techniques is demonstrated. As a result, the maximum breakdown voltage ratio of Single Zone JTE(SZ-JTE), Double Zone JTE(DZ-JTE), Multiple Floating Zone JTE(MFZ-JTE), and Space Modulated JTE(SM-JTE) is 98.24%, 99.02%, 98.98%, 99.22% each. MFZ-JTE has the smallest and SZ-JTE has the largest sensitivity of breakdown voltage ratios according to the change of JTE doping concentration. Additionally the degradation of breakdown voltage due to the passivation oxide charge is analyzed, and the sensitivity is largest in SZ-JTE and smallest in MFZ-JTE, too. In this paper, DZ-JTE and SM-JTE is the best efficiency JTE techniques than MFZ-JTE which needs large doping concentration in short JTE width.

• Polymer(Korea)
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• v.36 no.2
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• pp.155-162
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• 2012

Sulfonated poly(ether ether ketone) (SPEEK) nanofibers were prepared by electrospinning. The nanofibrous membrane for polymer electrolyte membrane fuel cell (PEMFC) was fabricated by compression molding. The maximum degree of sulfonation was 95% and the initial thermal degradation temperature was $280^{\circ}C$ and it's value was lower than that of PEEK. The contact angle of SPEEK increased with decreasing the degree of sulfonation. The optimum voltage, flow rate, tip to collector distance (TCD) and concentration of electrospinning conditions were 22 kV, 0.3 mL/hr, 15 cm, and 23 wt%, respectively. The average nanofibrous diameter was 47.6 nm. The water uptake and ion exchange capacity of SPEEK nanofibrous membrane increased with increasing the sulfonation time and the amount of sulfonating agent. The electrical resistance and proton ionic conductivity of SPEEK membrane increased with decreasing and increasing the sulfonation time, respectively. Their values were 0.58~0.06 ${\Omega}{\cdot}cm^2$and 0.099 S/cm.

• Food Science and Preservation
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• v.24 no.6
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• pp.820-826
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• 2017

Soybean is one of the most common food materials for making traditional Korean foods such as soybean paste, soy source and soy snack, and their manufacturing processes include heat treatment of soybean. This study was carried out to investigate the effect of heat treatment on the physicochemical properties of soybean. All samples were heat treated under commercial steamed, puffed or air-fried conditions, and then the protein molecular weight distribution, thermal properties, fluorescence intensity, protein solubility, and water and oil holding ability of the heat treated soybeans were examined. Sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that heat treatment caused fragmentation of polypeptide chain in soybean, showing the band of low molecular ranging from 17 to 40 kDa. The differential scanning calorimetric analysis showed the decrease of enthalpy values (${\Delta}H$) by heat treatment. Fluorescence spectroscopy indicated that the heat treatment caused lipid oxidation as proved by increasing emission intensity. The protein solubility at pH 3-6, and water holding capacity of heat treated soybeans were the higher than no treatment. These results suggest that the heat treatment resulted in decreased enthalpy values, and increased protein degradation, lipid oxidation and water affinity of soybean. Moreover, the effect of heat treatment on physiochemical properties of soybeans was more significant under air-fried condition.

• KSBB Journal
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• v.21 no.2
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• pp.133-139
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• 2006

In 'solid-phase' PEGylation, the conjugation reaction occurs as the proteins are attached to a solid matrix, and thus it can have distinct advantages over the conventional, solution-phase process. We report a case study: rhIFN-${\alpha}$-2a was first adsorbed to cation exchange resin and then N-terminally PEGylated by aldehyde mPEG of 5, 10, and 20 kD through reductive alkylation. After the PEGylation, salt gradient elution efficiently recovered the mono-PEGylate in a purified form from the unwanted species such as unmodified IFN, unreacted PEG, and others. The mono-PEGylation and its purification were integrated in a single chromatographic step. Depending on the molecular weight of the mPEG aldehyde used, the mono-PEGylation yield ranged 50-64%. We could overcome the major problems of random, or uncontrollable, multi-PEGylation and the post-PEGylation purification difficulties associated with the solution-phase process. N-terminal sequencing and MALDI-TOF MS confirmed that a PEG molecule was conjugated only to the N-terminus. Compared with the unmodified IFN, the mono-PEGylate showed the reduced anti-viral activity as measured by the cell proliferation assay. The bioactivity was reduced more as the higher molecular weight PEG was conjugated. Immunoreactivity, evaluated indirectly by antibody binding activity using a surface plasmon resonance biosensor, also decreased. Nevertheless, trypsin resistance as well as thermal stability was considerably improved.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.162-168
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• 2013

$Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn) nano-composite is a promising cathode material for xEV application due to its high theoretic capacity. However high voltage operating system of $Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn) has worked as a hurdle in its application because of the inherent demerits, such as cycle life degradation and gas evolution. In order to enhance cell performance of $Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn)/graphite cell, we examined electrolyte mainly composed of FEC, fluroalkyl ether and $LiPF_6$ (F-based EL). F-based EL showed much better discharging retention ratio than 1.3 M $LiPF_6$ EC/EMC/DMC (3/4/3, v/v/v) (STD). Furthermore gas evolution, especially CO and $CO_2$ during $60^{\circ}C$ storage for 30 days was dramatically reduced owing to thermal stable SEI formation effect of F-based EL.

• Polymer(Korea)
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• v.37 no.6
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• pp.744-752
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• 2013

The miscibility between poly(L-lactide) (PLLA) and poly(methyl methacrylate) (PMMA) was investigated using thermal analyses for the purpose of developing birefringence-free material at oriented state. The effect of methyl acrylate (MA) units as comonomer of PMMA on the miscibility was also studied. All the blends prepared in this study show composition-dependent single $T_g$'s between those of blend components and high transparency over the visible region, indicating the miscibility at molecular level and no discernible effect of MA units on it. No phase separation was observed at elevated temperature of $280^{\circ}C$, higher than the degradation of PLLA and PMMA. The interaction energy density in PLLA/PMMA blends with 17 mol% of MA was measured to be $-0.74J/cm^3$ from the equilibrium melting temperature depression based on the Hoffman-Weeks method. The blends show zero-${\Delta}$n behavior at a specific mixing ratio and the drawing ratio of 3 due to compensation of intrinsic orientation birefringence. Birefringence dispersion of PLLA/PMMA5 blends was also measured to examine the possibility for quarter-wave plates or polarizer protective films.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.357-363
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• 2011

In this paper, high temperature oxidation behavior of newly developed alloys, Ti-6Al-4Fe and Ti-6Al-1Fe, is examined. To understand the effect of Fe on the air oxidation behavior of the Ti-Al-Fe alloy system, thermal oxidation tests are carried out at $700^{\circ}C$ and $800^{\circ}C$ for 96 hours. Ti-6Al-4V alloy is also prepared and tested under the same conditions for comparison with the developed alloys. The oxidation resistance of the Ti-Al-Fe alloy system is superior to that of Ti-6Al-4V alloy. Ti-6Al-4V shows the worst oxidation resistance for all test conditions. This is not a result of the addition of Fe, but rather it is due to the elimination of V, which has deleterious effects on high temperature oxidation. The oxidation of the Ti-Al-Fe alloy system follows the parabolic rate law. At $700^{\circ}C$, Fe addition does not have a noticeable influence on the amount of weight gain of all specimens. However, at $800^{\circ}C$, Ti-6Al-4Fe alloy shows remarkable degradation compared to Ti-6Al-1Fe and Ti-6Al. It is discovered that the formation of $Al_2O_3$, a diffusion resistance layer, is remarkably hindered by a relative decrease of the ${\alpha}$ volume fraction. This is because Fe addition increases the volume fraction of ${\beta}$ phase within the Ti-6Al-xFe alloy system. Activities of Al, Ti, and Fe with respect to the formation of oxide layers are calculated and analyzed to explore the oxidation mechanism.

• Korean Journal of Materials Research
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• v.19 no.1
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• pp.28-32
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• 2009

Silicon carbide (SiC) is a promising material for power device applications due to its wide band gap (3.26 eV for 4H-SiC), high critical electric field and excellent thermal conductivity. The Schottky barrier diode is the representative high-power device that is currently available commercially. A field plate edge-terminated 4H-SiC was fabricated using a lift-off process for opening the Schottky contacts. In this case, Ni/Ti dual-metal contacts were unintentionally formed at the edge of the Schottky contacts and resulted in the degradation of the electrical properties of the diodes. The breakdown voltage and Schottky barrier height (SBH, ${\Phi}_B$) was 107 V and 0.67 eV, respectively. To form homogeneous single-metal Ni/4H-SiC Schottky contacts, a deposition and etching method was employed, and the electrical properties of the diodes were improved. The modified SBDs showed enhanced electrical properties, as witnessed by a breakdown voltage of 635 V, a Schottky barrier height of ${\Phi}_B$=1.48 eV, an ideality factor of n=1.04 (close to one), a forward voltage drop of $V_F$=1.6 V, a specific on resistance of $R_{on}=2.1m{\Omega}-cm^2$ and a power loss of $P_L=79.6Wcm^{-2}$.

• Korean Journal of Food Science and Technology
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• v.32 no.5
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• pp.1015-1021
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• 2000

Volatile flavor components (VFCs) in cooked black rices (Suwon-415 and Chindo) were studied. The major reactions during cooking, which result in aroma volatiles, are the Maillard reaction between amino acids and reducing sugars, and thermal degradation of lipid. Black rices washed with water were soaked in 1.5 folds water and heated at $110^{\circ}C$ in oil bath for 30min. VFCs in cooked black rices were extracted for three hours by SDE and were analyzed by GC and GC/MS. A total of 91, 82 volatiles were identified in Suwon-415 and Chindo black rice, respectively. Suwon-415 was composed of 26 alcohols, 10 aldehydes, 5 acids, 11 esters, 15 ketones, 9 hydrocarbons, 3 furans, 3 nitrogen containing compounds and 9 sulfur containing compounds. Chindo was composed of 28 alcohols, 9 aldehydes, 4 acids, 12 esters, 14 ketones, 5 hydrocarbons, 3 furans, 3 nitrogen containing compounds and 4 sulfur containing compounds.