Prazosin의 항고혈압 효과에 대한 임상적 관찰

서세웅,이균태,김연호,조성락,신영우,신영기 최신의학사 1984 最新醫學 Vol.27 No.8

Batch Unscented Transformation for Satellite Orbit Determination Using A Satellite Laser Ranging (SLR)

Seo, Kyoung-Seok,Park, Sang-Young,Park, Eun-Seo,Kim, Young-Rok,Choi, Kyu-Hong 한국우주과학회 2008 한국우주과학회보 Vol.17 No.2

Fused Filament Fabrication of Poly (Lactic Acid) Reinforced with Silane-Treated Cellulose Fiber for 3D Printing

( Young-rok Seo ),( Birm-june Kim ) 한국목재공학회 2024 목재공학 Vol.52 No.3

Various polylactic acid (PLA) blends were reinforced with untreated or silane-treated micro-sized cellulose fiber (MCF), successfully prepared as 3D printing filaments and then printed using a fused filament fabrication (FFF) 3D printer. In this study, we focused on developing 3D-printed MCF/PLA composites through silane treatment of MCF and investigating the effect of silane treatment on the various properties of FFF 3D-printed composites. Fourier transform infrared spectra confirmed the increase in hydrophobic properties of silane-treated MCF by showing the new absorption peaks at 1,100 cm^-1, 1,030 cm^-1, and 815 cm^-1 representing C-NH₂, Si-O-Si, and Si-CH₂ bonds, respectively. In scanning electron microscope images of silane-treated MCF filled PLA composites, the improved interfacial adhesion between MCF and PLA matrix was observed. The mechanical properties of the 3D-printed MCF/PLA composites with silane-treated MCF were improved compared to those of the 3D-printed MCF/PLA composites with untreated MCF. In particular, the highest tensile and flexural modulus values were observed for S-MCF10 (5,784.77 MPa) and S-MCF5 (2,441.67 MPa), respectively. The thermal stability of silane-treated MCF was enhanced by delaying the initial thermal decomposition temperature compared to untreated MCF. The thermal decomposition temperature difference at T₉₅ was around 26℃. This study suggests that the effect of silane treatment on the 3D-printed MCF/PLA composites is effective and promising.

< 전시-P-44 > Effect of Nanoclay and Carbon Fiber on the Water Absorption and X-Ray Diffraction Properties of Recycled WPCs

( Young-rok Seo ),( Sang-u Bae ),( Jae-gyoung Gwon ),( Sun-young Lee ),( Birm-june Kim ) 한국목재공학회 2019 한국목재공학회 학술발표논문집 Vol.2019 No.1

Since the waste resources in our daily lives have an impact on environmental pollution, research on sustainable resources through recycling has attracted worldwide attention. So far, research on the recycling of wood or plastic has actively conducted, but there is little research on the recycling of waste wood plastic composites (W-WPCs). W-WPCs was deteriorated in performance, especially, water absorption. Therefore, in this study, various recycled WPCs (R-WPCs) based on W-WPCs was manufactured using functional fillers to improve performances. R-WPCs were prepared with different proportions of W-WPCs, nanoclay (NC) and carbon fiber (CF). The composite specimens used in this study were prepared by melt compounding and injection molding processing. The water absorption properties of R-WPCs were measured by water absorption and thickness swelling rate after immersion in distilled water for a certain period of time. X-ray diffraction (XRD) properties were analyzed to confirm the intercalation of NC in the composite matrix. In water absorption property results, CF filled R-WPCs showed very low water absorption rate and percentage. As the content of NC in R-WPCs increased, the water absorption decreased. This means the presence of high aspect ratio nano filler can create tortuous pathway for water molecules to diffuse into the composites. Similar trends were observed in thickness swelling properties as well. This suggests that the presence of NC in R-WPCs prevents the expansion of thickness caused by water and gives a dimensional stability to R-WPCs. In the XRD results, patterns of R-WPCs filled with both NC and CF showed broader peaks compared to R-WPCs without CF. This probably indicates that NC retains its original crystalline structure and shows a similar peak in the NC filled R-WPCs, but it is partially exfoliated in the NC/CF filled R-WPCs due to the presence of CF. Therefore, this study suggests that NC and CF are suitable functional fillers for the recycling of W-WPCs with deteriorated performances.

Molecular and Genomic Approaches on Nickel Toxicity and Carcinogenicity

Seo, Young-Rok,Kim, Byung-Joo,Ryu, Jae-Chun The Korean Society of Toxicogenomics and Toxicopro 2005 Molecular & cellular toxicology Vol.1 No.2

Nickel is the one of potent environmental, the occupational pollutants and the classified human carcinogens. It is a serious hazard to human health, when the metal exposure. To prevent human diseases from the heavy metals, it is seemingly important that understanding of how nickel exerts their toxicity and carcinogenic effect at a molecular and a genomic level. The process of nickel absorption has been demonstrated as phagocytosis, iron channel and diffusion. Uptaked nickel has been suggested to induce carcinogenesis via two pathways, a direct DNA damaging pathway and an indirect DNA damaging pathway. The former was originated from the ability of metal to generate Reactive Oxygen Species (ROS) and the reactive intermediates to interact with DNA directly. Ni-generated ROS or Nickel itself, interacts with DNAs and histones to cause DNA damage and chromosomal abnormality. The latter was originated from an indirect DNA damage via inhibition of DNA repair, or condensation and methylation of DNA. Cells have ability to protect from the genotoxic stresses by changing gene expression. Microarray analysis of the cells treated with nickel or nickel compounds, show the specific altered gene expression profile. For example, HIF-I (Hypoxia-Inducible Factor I) and p53 were well known as transcription factors, which are upregulated in response to stress and activated by both soluble and insoluble nickel compounds. The induction of these important transcription factors exert potent selective pressure and leading to cell transformation. Genes of metallothionein and family of heat shock proteins which have been known to play role in protection and damage control, were also induced by nickel treatment. These gene expressions may give us a clue to understand of the carcinogenesis mechanism of nickel. Further discussions on molecular and genomic, are need in order to understand the specific mechanism of nickel toxicity and carcinogenicity.

Effects of Silane Treatment on 3D Printed PLA/MFC Composites Fabricated by Fused Deposition Modeling

( Young-rok Seo ),( Sang-u Bae ),( Birm-june Kim ),( Min Lee ) 한국목재공학회 2020 한국목재공학회 학술발표논문집 Vol.2020 No.1

Recently, interest in 3D printing has increased in the technical field because complex objects can be manufactured without special tools. Among the various 3D printing methods, fused deposition modeling (FDM) is the most popular. In terms of polymer matrix, polylatic acid (PLA) is most widely used to make filaments in FDM 3D printing. However, PLA has fundamental drawbacks of high cost, poor toughness and high density, which limit its applicability. To overcome this, research is underway to apply the most abundant renewable natural resource, cellulose fiber, as a filler. Microfibrillated cellulose (MFC) is a filler with a high aspect ratio and is known to be useful in successfully transferring the stresses generated by external impacts. But, hydrophilic groups at the end of the MFC cause agglomeration, and to address this problem, the surface of the MFC was modified with a silane coupling agent. After that, PLA/MFC based FDM 3D printing filaments were fabricated. In our study, the silane-treated MFC was observed to be compatible with PLA by Fourier transform infrared spectra and scanning electron micrographs. Also, the addition of silane-treated MFC to 3D printed PLA/MFC composites improved mechanical properties (impact, tensile, and flexure) compared to untreated-MFC. Additionally, thermogravimetric analysis showed that in 3D printed PLA/MFC composites, silane-treated MFC delays thermal decomposition and imparts thermal stability compared to untreated MFC. In conclusion, the silane-treated MFC presented its applicability as a suitable filler for FDM 3D printing filaments based on PLA. - 84

< 전시-P-43 > A Study on the Thermal Properties of Nanoclay and Carbon Fiber Reinforced Recycled WPCs

( Young-rok Seo ),( Sang-u Bae ),( Jae-gyoung Gwon ),( Sun-young Lee ),( Birm-june Kim ) 한국목재공학회 2019 한국목재공학회 학술발표논문집 Vol.2019 No.1

Waste wood plastic composites (W-WPCs), one of the growing waste resources in our daily lives, must be identified as a sustainable resource through recycling. However, in general, waste resources that have been exposed to outdoor conditions for a long time have deteriorated thermal properties. Thus, this study intended to improve the thermal properties of W-WPCs by incorporating hybrid functional fillers. Nanoclay (NC) and carbon fiber (CF) were used as fillers for the preparation of recycled WPCs (R-WPCs) based on W-WPCs. NC is being applied in various fields because it can achieve a balanced performance even if only a small amount is used. CF is increasingly available in advanced engineering materials because its performance is maintained at high temperatures. R-WPCs were prepared with different proportions of W-WPCs, NC and CF, and then melt-compounded. Thermal properties of R-WPCs were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA results showed that the thermal stabilities of the R-WPCs were improved as the amount of fillers (NC and CF) increased. This is because the diffusion delay effect of the thermal decomposition products of NC and the heat resistance of CF exerted synergistic effect. In DSC results, melting point and cold crystallization temperature showed no difference between R-WPCs. Melting enthalpy is an important parameter since its magnitude is directly proportional to the overall level of the crystallinity possessed by the polymer. NC and CF used in this study are masterbatches containing 50% of polypropylene and 50% of fillers. As the amounts of fillers (NC and CF) increased, the amount of PP increased accordingly. As a result, the crystallinity values were increased. Also, the crystallization behavior of the composites is affected by amount and dispersion of fillers. Thereby, as the NC and CF were well dispersed in the R-WPCs, the hybrid filled composites showed the improvements of nucleating effect and crystallinity values. Therefore, the results of this study suggest that the hybrid incorporation of nano and engineering fillers (NC and CF) played an important role in improving the thermal properties of R-WPCs.

< 전시-P-42 > A Study on the Mechanical and Morphological Properties of Nanoclay and Carbon Fiber Reinforced Recycled WPCs

( Young-rok Seo ),( Sang-u Bae ),( Jae-gyoung Gwon ),( Sun-young Lee ),( Birm-june Kim ) 한국목재공학회 2019 한국목재공학회 학술발표논문집 Vol.2019 No.1

Wood-plastic composites (WPCs) are a kind of composite material combining wood-based elements with plastics. Currently, WPCs are mainly used for exterior decking, fencing and railing, roofing, and patio furniture. Hence, WPC products are inevitably exposed to various outdoor conditions leading to degradation. Somewhat degraded WPCs are regarded as waste WPCs (W-WPCs) and there is a need to recycle the W-WPCs. Since the W-WPCs have deteriorated properties, to manufacture recycled WPCs (R-WPCs) having reliable performance, nanoclay (NC) and carbon fiber (CF) were selected as functional fillers. NC imparts balanced performance to filled composites by controlling dispersibility even if only a small amount is used. CF has been extensively used as a reinforcing filler in advanced engineered composites due to its low density and excellent performances. R-WPCs were prepared by adding different proportions of NC and CF (50/50 masterbatch pellets) into W-WPC granules. Composite specimens used in this study were fabricated by melt compounding and injection molding processing. Mechanical properties (impact, flexural, and tensile properties) of R-WPCs were investigated by universal testing machine (UTM) and impact tester. Morphological properties were observed by scanning electron microscope (SEM). The impact, flexural and tensile strength results showed that the strength improved by incorporation of NC and CF. This is because CF had a long fiber length with high aspect ratio and the surface sizing of CF enhanced the interfacial bonding between the polymer matrix and CF. But, the impact strength decreased with the incorporation of more than 5wt.% NC. This indicates that the incorporation of an appropriate amount of NC showed better toughening effects with CF, but a large amount of NC incorporation resulted in fracture failure due to aggregation of NC. The flexural and tensile modulus were improved with the incorporation of CF, but were not significantly changed by incorporation of NC. This is because CF has strong rigidity and increase the longitudinal fiber orientation in R-WPCs, while NC causes aggregations and weakens the interfacial bonding between the polymer matrix and NC. SEM images showed good adhesions between the polymer matrix and fillers. As a results of this study, the incorporation of appropriate functional fillers (NC and CF) can be expected to improve the performances of R-WPCs.

< 전시-P-25 > A study on the Mechanical and Morphological Properties of Glass Fiber and Nanoclay Reinforced Recycled WPCs

( Young-rok Seo ),( Sang-u Bae ),( Jae-gyoung Gwon ),( Sun-young Lee ),( Birm-june Kim ) 한국목재공학회 2018 한국목재공학회 학술발표논문집 Vol.2018 No.2

< 전시-P-40 > A study on the Thermal Properties of Wood Flour/SEBS-g-MAH/Nano Clay-filled Polylactic Acid Composites

( Young-rok Seo ),( Sang-u Bae ),( Jae-kyung Cha ),( Birm-june Kim ) 한국목재공학회 2018 한국목재공학회 학술발표논문집 Vol.2018 No.1

Recently, as interest in environmentally friendly materials has increased, studies on the development of new materials using various biodegradable plastics have been conducted. Poly(lactic acid)(PLA), one of the biodegradable plastics, synthesized from renewable resources has become popular due to their sustainability, biodegradability, and transparency. In this study, PLA composites were prepared by incorporating wood flour(WF), maleic anhydride grafted styrene-ethylene/butylene-styrene copolymer(SEBS-g-MAH), and nano clay. SEBS-g-MAH and nano clay were mixed at the same ratio and used as a master batch. The materials used in the study were first compounded with a twin screw extruder and then pelletized using a pelletizer. Thermal properties of PLA composites were analyzed by thermogravimetric analysis(TGA) and differential scanning calorimetry(DSC). GA results showed that the thermal stability of PLA/WF composite was reduced compared to PLA only due to the relatively low thermal decomposition temperature of WF. However, the thermal stabilities of the PLA/WF composites were improved in the presence of SEBS-g-MAH/nano clay master batch. This is because the SEBS-g-MAH having thermally stable styrene component binds to the WF surface and forms strong interfacial bondings between WF and PLA matrix. In DSC results of the PLA/WF composites, decreases in glass transition temperatures were observed. It is considered that the addition of WF interferes with the interaction of the PLA polymer chain, which increases the fluidity of the polymer. Besides, the crystallinity of PLA composites decreased with the addition of SEBS-g-MAH/nano clay master batch. This suggests that the presence of SEBS-g-MAH affects the efficiency of nucleation in the crystallization of PLA. SEBS-g-MAH, therefore, effectively improved the thermal properties of PLA/WF composites and it could be used as an promising additive in PLA/WF composites.