• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.12
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• pp.820-824
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• 2008

Electret filter media are used in general ventilation filters, disposable respirators, vehicle cabin filters, vacuum cleaners and room air cleaners. There are basic mechanisms of interception, inertial impaction, diffusion, gravitational settling, electrostatic attraction by which an aerosol particle can be deposited onto a fiber in a filter. The ability of fine particle removal strongly depends on the electrostatic forces between particles and polarized fibers. Thus, the stability of the fiber polarization is a major factor in the reliability of electret filters. In this study, the electret filter is made by electrospinning process using Polystyrene which is dissolved by 5 : 5 of Tetrahydrofuran (THF) and Dimethylformamide (DMF). Also the electrical properties and the filtration performances of electrospun filter media are Quantitatively investigated. Electrical properties of electrospun filters have been studied on surface charge potential and surface charge density. Also the filtration performance of the electret filters are evaluated on collection efficiency. The surface charge potential and the surface charge density of electrospun PS filters are increased with increasing applied voltage and saturated at 30 kV of applied voltage. Also collection efficiency of electro spun filters is increased with increasing surface charge potential and surface charge density. But the surface charge potential is decreased by natural decay and it causes deterioration of particle collection efficiency.

• Journal of Korean Society on Water Environment
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• v.38 no.2
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• pp.72-81
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• 2022

Numerous studies have investigated the occurrence and fate of microplastics in the environment; however, only limited effort has been devoted to exploring the characteristics of dissolved organic matter (DOM) leached from microplastics. In microplastic (MP)-contaminated environment, MPs are typically mixed with naturally-occurring particles, which interferes with their detection in the environment. Thus, it is necessary to distinguish between the DOM leached from MPs and those leached from natural particles and also to characterize their properties. This study investigated DOM leaching behavior from MPs (polystyrene: PS, polyvinylchloride: PVC) and natural particulates (forest soil: FS, litter leaves: LL) under light, which is considered one of the main weathering processes that affect MPs in the environment. The leached DOM concentrations and fluorescence characteristics were compared under dark versus light conditions. Regardless of the origins, UV light promoted DOM release from all the particulates. More DOM was released from natural particles than from MPs under both conditions. However, the effect of promoting DOM release by UV was more pronounced for MPs than for natural particles. It was observed from fluorescence spectra that the intensity of the humic-like region was substantially reduced when MP-derived DOM was exposed to UV light, whereas the change of intensity was very little for natural particles. Under light conditions, the ratio of protein-like to humic-like fluorescence of MP-derived DOM was higher than that of DOM from natural particles. This study implies that a substantial amount of DOM could be leached from MPs even in MP-polluted environment under UV irradiation. Protein/humic fluorescence ratio could be utilized as a fast probing indicator to separate the two sources of particles under light.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.232-232
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• 2023

고속도로 및 편의시설 건설로 불투수층의 면적이 증가하여 강우 시 고속도로 및 편의시설에서 발생하는 오염원에 의한 하천의 수질 영향도 커지고 있다. 특히 휴게소에서는 자동차의 급가속, 급감속으로 더욱 많은 분진과 오염물질이 발생할 수 있으며 타이어 마모 입자, 자동차 배기가스, 중금속 및 오일류 등이 휴게소나 도로 지표에 집적되어 있다. 이렇게 발생한 오염물질은 우기에 강우와 함께 불투수면을 침투하지 못하고 배수로를 통해 유출되어 인근 하천의 수생태 및 토양의 주요 오염원으로 작용하고 있다. 이에 따라 고속도로 및 인근 휴게소의 비점오염 저감대책이 필요하며 효율적인 비점오염원 저감을 위해 장기적인 모니터링, 지속적인 자료 수집 및 분석이 필요하다. 본 연구에서는 강원지역 고속도로 및 인근 휴게소에서 강우 시 강우유출수 모니터링을 통해 강우유출수 유량가중평균농도 (Event Mean Concentration) 산정하고 강우유출수 수문곡선 (hydrograph)을 작성하였다. 또한 강우사상에 따른 분석항목별 초기세척효과(First Flush Effects)와 오염부하량을 산정하였다. 추가적으로 차량 기인 입자를 확인하기 위해 μ-FT-IR 현미경 분석 실험을 하였다. 모니터링 장소는 휴게소 및 고속도로 일원이며, 모니터링은 선행무강우일수 2일 이상, 강우량 10mm 이상일 때 실시하였으며 2022년 6월부터 10월까지 총 4회 실시하였다. 모니터링 결과 타이어 및 브레이크 패드 마모와 관련된 중금속인 Zn, Cu, Pb 등의 중금속이 높게 분석되었으며 이러한 중금속의 오염부하량 역시 높게 산정되었다. 강우유출수 수문곡선에서 강우 초기 오염물질의 세척효과가 나타났다. MFFn 산정 결과 강우 30% 구간에서 초기세척효과를 보였다. μ-FT-IR 현미경 분석 결과 PE (Polyethylene)가 가장 많이 검출되었고 PP (Polypropylene), PS (Polystyrene) 순으로 검출되었다. 이러한 강우유출수 모니터링 데이터는 향후 고속도로 휴게소 및 고속도로 주변 오염저감 시설 설치 및 사회적 동참을 위한 타당한 근거 확보를 위한 기초자료로서 제공될 수 있을 것이다.

• Polymer(Korea)
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• v.38 no.2
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• pp.144-149
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• 2014

Large residual stresses are remained in the conventional injection molded products because of the high cavity pressure in packing phase during injection molding process. Conventional injection molding (CIM) invokes distribution of cavity pressure and it has a limitation to obtain product with uniform physical property. Multi-cavity conventional injection molding contains quality deviation among the cavities since flow imbalance occurs during filling phase. Injection compression molding (ICM) is adopted to overcome these limitations of CIM. In this study, molding characteristics of CIM and ICM have been investigated using multi-cavity injection mold. Researches were performed by both experiment and computer simulation through observations of birefringence for transparent resins, polycarbonate and polystyrene in CIM and ICM. As a result, low and uniform birefringence and mold shrinkage were showed in the specimens by ICM that could give a uniform cavity pressure. Deviation of physical property among the specimens in multi-cavity mold shown in CIM was significantly reduced in the specimens by ICM. Through this study it was concluded that the ICM in multi-cavity molding was valid for molding products with uniform property in an individual cavity and also reduced property deviation among the cavities.

• Microbiology and Biotechnology Letters
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• v.47 no.3
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• pp.332-336
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• 2019

The use of ultraviolet (UV) spectroscopy for foods is known to have a microbial inhibitory effect. UV-A having a longer wavelength than UV-C can be used for continuous or intermittent UV irradiation of food stored in containers or packages. Because UV-LED can be used effectively at a low price, this study reported the effect of UV-A 365 nm-LED on inhibiting Bacillus subtilis in accordance with the packaging conditions employed in daily use. The packaging materials were linear low-density polyethylene (LLD-PE), nylon/low density polyethylene (LDPE), polystyrene, and glass. When all packaging materials were treated with 365 nm UV-LED, B. subtilis was observed to remain inactive for 30-60 min. Further, compared with the control (-log 5), the survival rate of B. subtilis was -log 2.0-2.5 for nylon/LDPE and -log 2.58-3.61 for LLD-PE. These packaging materials showed an excellent inhibitory effect regardless of their thickness. Typically, a decrease in the viable cell count of more than 3 log indicates a 99.9% bactericidal effect. These results suggest that 365 nm UV-LED permeated the packaging material and inhibited bacterial growth.

• Journal of Food Hygiene and Safety
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• v.38 no.2
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• pp.37-45
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• 2023

The surge in food delivery systems during the coronavirus 2019 pandemic necessitated this study of heavy metal migration from food contact materials (FCMs). A total of 104 samples of FCMs, comprising 51 polypropylene (PP), 21 polyethylene (PE), and 32 polystyrene (PS) samples of six different types of FCMs (containers, covers, table utensils, cups, pouches, and wrappers) used for food delivery distributed in Korea, were collected and investigated for migration of three heavy metals (Pb, Cd, and As) using inductively coupled plasma-mass spectrometry (ICP-MS) to determine whether they complied with Korea's Standards and Specifications for Utensils, Containers, and Packages. Acetic acid (4%, v/v) was used as the food simulant, and tests were performed at 100℃ (in harsh conditions) for 30 min. Linearity of Pb, Cd, and As showed acceptable results with a coefficient of determination (R²) value of 0.9999. Limit of detection (LOD) and limit of quantification (LOQ) of Pb, Cd, and As were 0.001, 0.001, and 0.001 ㎍/L and 0.002, 0.003, and 0.003 ㎍/L, respectively. Accuracy and precision results complied with the criteria presented in the European Commission Joint Research Centre guidelines. The average concentration of Pb, Cd, and As migration detected in a total of 104 samples was 0.009-0.260 ㎍/L, which was very low compared with the migration specification set in the Standards and Specifications for Utensils, Containers, and Packages. The maximum level of Pb corresponded to 0.23% of the migration limit. There were no samples exceeding the limit. Thus, this study confirmed that the heavy metal contents of FCMs used for delivery food distributed in Korea were safely managed. The data from this study represent an invaluable source for science-based safety management of hazardous heavy metals migrating from FCMs used in the food delivery industry.

• Analytical Science and Technology
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• v.32 no.6
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• pp.243-251
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• 2019

Microplastics (MP) are found in large quantities in the oceans, posing a major threat to the ecosystem. In Korea, MPs have been reported to be detected in sea salts. In order to analyze MPs, information on their composition, size, and shape is required. FT-IR microscopy is used frequently to measure sizes larger than 20 ㎛. Recently, however, Raman microscopy, which can analyze ultrafine plastics below 20 ㎛, has been applied extensively. In this study, 10.0 g samples of commercially available salts were dissolved and filtered through a 45 ㎛ mesh filter with a size of 25.4 mm × 25.4 mm. These filtered samples were then analyzed by both FT-IR microscopy and Raman microscopy. A total of four MPs, including three polyethylene (PE) of size 70-100 ㎛ and a polypropylene (PP) of size 170 ㎛, were detected by FT-IR microscopy, while 10 MPs, including nine PE of size 10-120 ㎛ and one polystyrene (PS) of size 40 ㎛, were detected by Raman microscopy. Approximately, 1,000 MPs/kg was estimated, which was almost two times higher than the previous reported levels (~550-681 particles/kg in sea salts); this is because Raman microscopy can detect much smaller MPs than FT-IR microscopy. A total of 113 particles were found using Raman microscopy: Carbon (35, 31.5 %), minerals (28, 25 %), and glass (16, 14.4 %) were dominant, forming around 70% of the total, but MPs (10, 8.8 %) and cellulose (5, 4.5 %) were also found. Raman microscopy has great potential as an accurate method for measuring MPs, as it can measure smaller size MPs than FT-IR microscopy. It also has a reduced sample preparation time.

• Applied Chemistry for Engineering
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• v.23 no.2
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• pp.131-137
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• 2012

Polyaniline (PANI) and polypyrrole (Ppy) hollow sphere structures with controlled shell thicknesses can be easily synthesized than those of using a layer-by-layer method for cathode active material of lithium-ion batteries. Polystyrene (PS) core was synthesized by emulsion polymerization using an anion surfactant. The shell thicknesses of PANI and Ppy were controlled by amounts of aniline and pyrrole monomers. PS was removed by an organic solution. This structure increased in contact with an electrolyte and a specific capacity in lithium-ion batteries. But polymers have disadvantages such as the difficult control of molecular weights and low densities. These disadvantages were completed by controlled shell thicknesses. The amount of aniline monomer increased from 1.2, 2.4, 3.6, 4.8 to 6.0 mL, and the shell thicknesses were 30.2, 38.0, 42.2, 48.2, and 52.4 nm, respectively. And the amount of pyrrole monomer was 0.6, 1.2, 2.4 and 3.6 mL, the shell thicknesses were 16.0, 22.0, 27.0 and 34.0 nm, respectively. In the cathode materials with controlled shell thicknesses, shell thicknesses of the PANI hollow spheres were 30.2, 42.2, and 52.4 nm, and discharge specific capacities of after 10 cycle were ~18, ~29, and ~62 mAh/g, respectively. The shell thicknesses of the Ppy hollow spheres were 16.0, 22.0, 27.0 and 34.0 nm, and discharge specific capacities of after 15 cycle were ~15, ~36, ~56, and ~77 mAh/g, respectively. Thus, shell thicknesses of PANI and Ppy increased, the specific capacities increased.