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Kim H.-J.,Korea Institute of Industrial Technology | Jung R.,Korea Institute of Industrial Technology | Jung R.,Samsung | Hwang D.-K.,Small and Medium Business Corporation | And 2 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2014

The surface of commercial carbon black was modified by pyrolysis of acetonitrile in attempt to obtain the graphitic carbon coating layer. It was confirmed that the surface of carbon black was partially graphitized, having 0.23 of graphitization index and 1.87 nm of mean stack height. From the electrochemical oxidation test of carbon, the carbon-coated carbon black showed higher corrosion resistance than the untreated carbon black although the core of the carbon black support still remained untreated. When it was applied to the support for platinum electrocatalyst, the enhanced stability was observed. From those corrosion tests as well as XPS results, it can be suggested that the partially crystalline graphitic carbon surface facilitates the relatively more reduced surface of platinum. Copyright © 2014 American Scientific Publishers.

Hwang D.K.,Small and Medium Business Corporation | Shul Y.G.,Yonsei University | Chu Y.H.,Sangji University
Polymer Composites | Year: 2015

Photocatalytic degradation mechanism of the polycarbonate(PC)/TiO2 composite films was studied under the ambient air condition in order to investigate the feasibility of the PC/TiO2 composite as a photodegradable polymer. TiO2 composition in the PC/TiO2 composite was changed from 0 wt% to 4 wt%. Photodegradation behaviors of the composite films were compared with that of the pure PC films by performing the weight loss monitoring under UV irradiation, FTIR spectroscopy, color measurement analysis, SEM, and XPS analysis. The weight loss rate of the PC/TiO2 composite film (33% weight loss after 300 h) with 4 wt% TiO2 was twice as high as the pure PC films (14% weight loss after 300 h). The increase in the FTIR hydroxyl peak, and carbonyl peak intensity and the yellowing observation during the photodegradation were due to the formation of the photoproducts (aliphatic, aromatic chain-ketones, aromatic, and OH radical) and the structural modification of polycarbonate. XPS analysis of composite film showed the photodegradation of the polymer surface and TiO2 particles exposure on the surface of the composite films matrix. © 2014 Society of Plastics Engineers.

Hwang D.K.,Small and Medium Business Corporation | Shul Y.-G.,Yonsei University | Oh K.,Inha Technical College
Industrial and Engineering Chemistry Research | Year: 2013

Nanosize Au-TiO2 is becoming popular to photocatalytic application in visible light. A new fabrication process of photocatalyst is introduced for the purpose of its potential utilization under sunlight. A mixture of photocatalyst and polycarbonate (PC) was cast on a glass substrate to form a film. The photocatalytic experiment was performed in the UV region and visible region separately with powdery samples first, followed by composite films. When powdery Au-TiO2 was applied to decompose of acetaldehyde, activity inferior to Degussa P-25 was observed in UV light, but superior activity was observed in visible light. In the case of Au-TiO2 in PC composite film, evidence of acetaldehyde decomposition was observed, unlike the case of P-25 in PC composite, which showed negligible traces of acetaldehyde decomposition. © 2013 American Chemical Society.

Hwang D.K.,Small and Medium Business Corporation | Lee H.S.,Dong - A University | Kim H.J.,Korea Institute of Industrial Technology | Shul Y.G.,Yonsei University | Oh K.,Inha Technical College
Polymer Engineering and Science | Year: 2014

Crystallization of polycarbonate (PC) was attempted by a precipitated method in a ternary system of PC/solvent/nonsolvent. Chloroform was used as a solvent, and isopropanol was used as a nonsolvent. Crystallization of PC was clearly observed as a powdery state when chloroform/isopropanol mixtures were prepared by 68/32 and 61/39 vol%. Crystallinity of PC was evaluated by differential scanning calorimeter and X-ray diffractometer. As the difference of solubility parameters between PC and binary solvent/nonsolvent mixtures became smaller, the relative crystallinity of PC was increased. The highest degree of PC crystallization was obtained when chloroform/isopropanol was mixed by 61/39 vol%. Subsequently, crystallized PC was used as a filler to high-density polyethylene (HDPE) composite. HDPE composite incorporated by crystallized PC filler improved its mechanical and thermal properties. Flexural modulus was increased from 620 to 990 N/mm2, and flexural strength was increased from 720 to 1080 N/mm2. And heat deflection temperature measurement and flammability test supported the enhancement of thermal property when crystallized PC was added to HDPE composite up to 40 wt%. POLYM. ENG. SCI., 54:1893-1899, 2014. © 2013 Society of Plastics Engineers.

Hwang D.K.,Small and Medium Business Corporation | Oh K.,Inha Technical College
Iranian Polymer Journal (English Edition) | Year: 2014

Reducing cycle time in injection molding process is important because it can save operational cost and increase product yield. Cycle time can be categorized by six criteria, which are metering time, time for closing a mold, packing time, holding time, cooling time, and the time needed to open a mold and to eject the molded product. It was found that the metering time is crucial to predict the cycle time of glass fiber reinforced syndiotactic polystyrene (sPS/GF, 60/40 by weight). In many cases, however, cycle time could be reduced by saving cooling time. This study is motivated by the demand to reduce the cycle time of sPS/GF composite. Since the increase of thermal conductivity leads to the reduction of cooling time, silicon carbide (SiC) is employed to evaluate if it can increase the thermal conductivity of sPS/GF composite. When SiC is added to replace entire GF in sPS/GF composite, the mechanical property of the resulting sPS/SiC (60/40 by weight) composite was not satisfied even though its thermal conductivity was enhanced to about 62 %. Within tolerable ranges in mechanical properties, SiC was added to replace a half amount of existing GF filler. sPS/GF/SiC (60/20/20 by weight) composite achieved the enhancement of thermal conductivity from 0.230 to 0.308 W/m K (34 %) which resulted in the effective reduction of both cooling time and cycle time from 16 to 10 s and from 47 to 38 s, respectively. It should be noted that additional time saving was obtained by 3 s between 6 s in cooling and 9 s in overall cycle time. It can be interpreted by the fact that the increase of thermal conductivity also accelerated the heating rate of sPS/GF/SiC composite. © 2014 Iran Polymer and Petrochemical Institute.

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