• Applied Chemistry for Engineering
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• v.9 no.4
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• pp.523-528
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• 1998

The electrochemical characteristics of $V_2O_5$ as working electrode were studied in the cell (1-butene+$O_2$, $V_2O_5{\mid}YSZ{\mid}Ag$, $O_2$) with a YSZ solid electrolyte. The sintering of Ag as a counter electrode was occurred after calcination, and the structure which has the pores of over $3{\mu}m$ was achieved. In particular, the peak of (010) plane of the working electrode on the XRD spectrum which is responsible for selective oxidation appeared after calcination. The major product of 1-butene oxidation over $V_2O_5$ was butadiene. The technique of SEP (solid electrolyte potentiometry) was used to monitor the chemical potential of chemical species adsorbed on the working electrode. Over a wide range of gas compositions of 1-butene and oxygen, open circuit voltage (OCV) exhibited the mixed potential of surface oxygen activity.

• Elastomers and Composites
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• v.38 no.3
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• pp.251-261
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• 2003

The flame retardancy and foaming properties of NBR foams containing waste ground tire rubber (GTR) were studied. When the composition ratios of NBR/GTR were ranged in $100/0{\sim}80/20$ (w/w) and rubbers/flame retardants were in the range of $1/1.95{\sim}3.70 wt%$, the considerably optimized foam for flame retardancy was obtained with high limiting oxygen indices (LOI, $29.4{\sim}40.0$), low heat release rate(HRR), closed/semi-closed cell of uniformity, and reasonable expandability ($215{\sim}300 %$). The LOI was increased and the heat release rate was decreased with increasing the amount of GTR content.

• Korean Chemical Engineering Research
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• v.52 no.2
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• pp.266-271
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• 2014

The effects of antioxidants on the properties of Polycarbonate/Acrylonitrile-Butadiene-Styrene(PC/ABS) blends were studied for the functions of the screw speed and loaded duration of high shear rate processing in order to investigate the degradation for PC/ABS blends. Tris-(2,4-di-tert-butyl-phenyl phosphate) (A1) and Bis(2,4-dicumylphenyl) pentaerythritol diphosphite (A3) as phosphite antioxidants and Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (A2) as a phenolic antioxidant are used. The thermal properties were detected by TGA and severely decreased, after the processing. The stress-induced and thermal degradation for PC/ABS blends with the antioxidant A3 was retarded better than the others. By using UTM, the mechanical properties also showed individually decreased according to the antioxidants, after the processing, especially, the elongations showed considerable decline behaviors, while the tensile strengths of PC/ABS blends changed very little. For example, in the operating conditions of 1000rpm of screw speed and 20 seconds of loaded period, the elongations decreased from 148% before the processing, to 91.6% with the A1, to 63% with the A2 and to 131% with the A3 after the processing, respectively. In order to get the morphological properties, the size distributions of the dispersed phases for PC/ABS were investigated by SEM analysis and tended to decrease, as the screw speed and loaded period of the processing increased. Therefore, we confirmed that the antioxidant A3 was the best of all of three to inhibit the stress-induced degradation of PC/ABS blends during the high shear rate processing.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.32 no.2
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• pp.153-162
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• 2022

Objectives: Fused deposition modeling (FDM) 3D printer which is one of the material extrusion (MEX) technologies is an additive manufacturing (AM) process. 3D printers have been distributed widely in Korea, particularly in school and office, even at home. Several studies have shown that nanoparticles and volatile organic compounds (VOCs) were emitted from an FDM 3D printing process. The objective of this study was to identify types of chemicals possibly emitted from FDM 3D printing materials such as PLA (polylactic acid), ABS (acrylonitrile butadiene styrene), nylon, PETG (polyethylene terephthalate glycol), PVA (polyvinyl alcohol), PC (polycarbonate) filaments. Methods: 19 FDM 3D printing filaments which have been distributed in Korea were selected and analyzed VOCs emitted of 3D printing materials by headspace gas chromatography mass spectrometry (headspace GC-MS). Subsamples were put into a vial and heated up to 200℃ (500 rpm) during 20 minutes before analyzing FDM 3D printing filaments. Results: In the case of PLA filament, lactide and methyl methacrylate, the monomer components of one, were detected, and the volume ratio ranged 27~93%, 0.5~37% respectively. In the case of ABS filaments, styrene (50.5~59.1%), the monomer components of one, was detected. Several VOCs among acetaldehyde, toluene, ethylbenzene, xylene, etc were detected from each FDM 3D printing filaments. Conclusions: Several VOCs, semi-VOCs were emitted from FDM 3D printing filaments in this study and previous studies. Users were possibly exposed to ones so that we strongly believe that we recommend to install the ventilation system such as a local exhaust ventilation (LEV) when they operate the FDM 3D printers in a workplace.

• Environmental Analysis Health and Toxicology
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• v.17 no.2
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• pp.95-107
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• 2002

This study was designed to investigate the characteristics of atmospheric concentrations of toxic volatile organic compounds (VOCs) in Korea. Target compounds included 1,3-butadiene, aromatics such as BTEX, and a number of carbonyl compounds. In this paper, as the first part of the study, the performance of sampling and analytical methods was evaluated for the measurement of selected VOCs and carbonyl compounds in the ambient air. VOCs were determined by the adsorbent tube sampling and automatic thermal desorption coupled with GC/MSD analysis, while carbonyls by the DNPH-silica cartridge sampling with HPLC analysis. The methodology was investigated with a wide range of performance criteria such as repeatability, linearity. lower detection limits, collection efficiency, thermal conditioning, breakthrough volume and calibration methods using internal standards. In addition, the sampling and analytical methods established in this study were applied to real field samples duplicately collected in various ambient environments. Precisions for the duplicate samples appeared to be comparable with the performance criteria recommended by USEPA TO-17. The overall precision of the sampling and analytical methods was estimated to be within 20 ∼ 30% for major aromatic VOCs such as BTEX, whereas the precision for major carbonyl compounds such as formaldehyde and acetaldehyde was within 10 ∼ 20% for field samples. This study demonstrated that the adsorbent sampling and thermal desorption method can be reliably applied for the measurement of BTEX in ppb levels frequently occurred in common indoor and ambient environments.

• Journal of the Korean Society of Industry Convergence
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• v.2 no.1
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• pp.69-75
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• 1999

Intending to develop a new rubber curing process using only microwave, the both the characteristics of cure and the mechanical properties of rubbers for the tire tread, for which a green styrene-butadiene compounds had been cured with 2.45 GHz microwave, have been compared with those of the custom thermal cured rubber. The unintentional hot spot formation in the compound during the microwave curing has not found where the compound has a microwave absorbing ceramic powders in 4.18 weight percents and the supplying voltage has been adjusted to 90 volts. The new microwave process accomplished preheating to 418K in a quarter of the thermal cure time. The average tensile strength of the microwave-cured rubber indicating $190kg/cm^3$ was compatible to that of the thermal cure. In conclusion, the new microwave cure had approved to be applicable in a commercial plant.

• Food Science and Biotechnology
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• v.16 no.2
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• pp.290-293
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• 2007

Cassumunar ginger (Zingiber montanum Roxb.) was grown in the experimental field at the Department of Horticulture, Kasetsart University, Thailand. The antioxidant activity and volatile oil content of rhizomes of varying age were measured. Antioxidant activity as determined using the DPPH (diphenyl-2-picrylhydrazyl) method differed significantly between samples of different ages. Antioxidant activity and rhizome age were positively correlated, with 22-month old rhizomes showing the highest radical scavenging activity (79.19%). Volatile oil was obtained by steam distillation of fresh rhizomes. The extraction yield of volatile oil was highest in l6-month old rhizomes (13.02 mL/kg). GC-FID data indicated the presence of three major compounds, sabinene, terpinen-4-ol and (E)-1-(3',4'-dimethylphenyl) butadiene (DMPBD), however none of the major components were correlated with the age of rhizome.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.651-655
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• 2004

This paper studies the designing method and application for grommets, rubber material used to absorb vibration on the air conditioner compressor. The existing grommet with hardness 40 degrees, EPDM, has the high transmissibility on the compressor that causes additional structure born sound. The problem for EPDM is transformation over long time usage possibly due to its design in which stress is concentrated on a certain position. In order to resolve it, silicon material was previously used with the same design in some models. The vibration performance did improve, but the cost became high. Below are the major developments regarding improvements in compressor rubber material, vibration performance and durability through design change, and new grommet to attain cost reduction. 1 The optimum grommet design for stress even distribution through FEM methods. 2. Comparison for grommet material and design for improved transmissibility. 3. Assess for grommets durability and product applications.

• Environmental Engineering Research
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• v.14 no.4
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• pp.212-219
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• 2009

Emission characteristics of air pollutants from three commercially operating cement kilns co-burning waste were investigated. The major heavy metals emitted were mercury (Hg), zinc (Zn), nickel (Ni), chromium (Cr), lead (Pb), cadmium (Cd), and arsenic (As) Removal efficiency of the bag filter was above 98.5% for heavy metals (except Hg), and above 60% for Hg. Higher fractions of heavy metals entering the bag filter were speciated to cement kiln dust. On average, 3.3% of the -heavy metals of medium and low toxicity (Pb, Ni, and Cr) entering the bag filter were released into the atmosphere. Among highly toxic heavy metals, 0.14% of Cd, 0.01% of As, and 40% of Hg entering the bag filter were released into the atmosphere. In passing through the bag filter, the proportion of oxidized Hg in all cases increased. Emission variations of hazardous air pollutants in cement kilns tested were related to raw materials, fuel, waste feed and operating conditions. Volatile organic compounds detected in gas emissions were toluene, acrylonitrile benzene, styrene, 1,3-butadiene, and methylene chloride. Although hazardous air pollutants in emissions from cement kilns co-burning waste were within the existing emission limit, efforts are required to minimize their levels.

• Elastomers and Composites
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• v.42 no.1
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• pp.9-19
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• 2007

In this study, SBR (Styrene-butadiene rubber: solid content: 25 wt%) nanocomposites reinforced with carbon/organoclay(C18-MMT) were manufactured by a latex method. The SBR nanocomposites was made with the dual phase fillers. The mixing ratios, i.e. carbon black/C18-MMT, were 50/0, 49/1, 48/2, 47/3, 45/5, 44/6, 40/10. Total filler content of compounds was restricted to 50 phr. Cure characteristics and mechanical properties of SBR nanocomposites with carbon black and C18-MMT were evaluated. The SBR nanocomposites containing 49/1 ratio of carbon black/C18-MMT showed good dispersity and excellent values of ODR torque, tensile strength, modulus and tear energy. It was found that the improvement of the mechanical properties was mainly due to the reinforcing effect, i.e., the improvement of dispersion of silicates in the rubber matrix.