Thermal Conductivity and Thermal Expansion Behavior of Pseudo-Unidirectional and 2-Directional Quasi-Carbon Fiber/Phenolic Composites

Cho, Donghwan,Choi, Yusong,Park, Jong Kyoo,Lee, Jinyong,Yoon, Byung Il,Lim, Yun Soo The Korean Fiber Society 2004 Fibers and polymers Vol.5 No.1

In the present paper, a variety of fiber reinforcements, for instance, stabilized OXI-PAN fibers, quasi-carbon fibers, commercial carbon fibers, and their woven fabric forms, have been utilized to fabricate pseudo-unidirectional (pseudo-UD) and 2-directional (2D) phenolic matrix composites using a compression molding method. Prior to fabricating quasi-carbon fiber/phenolic (QC/P) composites, stabilized OXI-PAN fibers and fabrics were heat-treated under low temperature carbonization processes to prepare quasi-carbon fibers and fabrics. The thermal conductivity and thermal expansion/contraction behavior of QC/P composites have been investigated and compared with those of carbon fiber/phenolic (C/P) and stabilized fiber/phenolic composites. Also, the chemical compositions of the fibers used have been characterized. The results suggest that use of proper quasi-carbonization process may control effectively not only the chemical compositions of resulting quasi-carbon fibers but also the thermal conductivity and thermal expansion behavior of quasi-carbon fibers/phenolic composites in the intermediate range between stabilized PAN fiber- and carbon fiber-reinforced phenolic composites.

Fluorescence Characterization of LaRC PETI-5, BMI, and LaRC PETI-5/BMI Blends

Cho, Donghwan,Yang, Gyeongmo The Korean Fiber Society 2002 Fibers and polymers Vol.3 No.2

In the present study, the fluorescence behavior ova phenylethynyl-terminated imide (LaRC PETI-5) resin, a bismaleimide (BMI) resin, and various LaRC PETI-5/BMI blends with different blend compositions has been characterized as a function of heat-treatment temperature, using a steady-state fluorescence technique with a front-face illumination method far solid-state films. It is observed that there are distinguishable changes in the spectral shape, size, and position of fluorescence with varying heat-treatment temperature in the pure and blend samples. The result is qualitatively explained in terms of charge transfer complex formation as well as microenvironmental change with local mobility and viscosity occurring in the LaRC PETI-5, BMI, and their blends during the cure process. The result also implies that a steady-state fluorescence technique may be a useful tool to understand the processing conditions of polyimides and their blends in the film form on the basis of their thermo-photophysical responses.

Effect of Applied Voltage on the Fluorescence Behavior of E7/NOA-65 PDLC Films

Cho Donghwan,Yang Gyeongmo,Lee Sang Cheol,Bang Dae-Suk The Polymer Society of Korea 2005 Macromolecular Research Vol.13 No.3

Effect of Thermal Imidization and Curing on Fluorescence Behavior of a Phenylethynyl-Terminated Poly(amic acid)

Cho, Donghwan,Yang, Gyeongmo,Drzal, Lawrence T. The Polymer Society of Korea 2003 Macromolecular Research Vol.11 No.5

The imidization and cure reaction of a thermosetting phenylethynyl-terminated amic acid (LaRC PETI-5) in film form have been monitored as a function of temperature by means of a steady-state fluorescence technique using a front-face illumination method. The variation of the fluorescence emission spectra of LaRC PETI-5 can be divided into four temperature regions; Region I: below 15$0^{\circ}C$, Region II: 150-25$0^{\circ}C$, Region III: 250-35$0^{\circ}C$, and Region IV: above 35$0^{\circ}C$. The fluorescence spectra in Region I are largely influenced by residual N-methyl-2pyrrolidinone in the polymer and also slightly by partial imidization of the polymer. There is a combined effect of imidization and solvent removal on the fluorescence behavior in Region II. The spectra in Regions III and IV are due significantly to the cure reaction of LaRC PETI-5 and to a post-cure effect of the polyimide, respectively. This spectroscopic evidence indicating the transformation of the amic acid imide oligomer into the corresponding polyimide via imidization and cure, agrees well with thermal analysis results obtained previously. The intermediate stage of cure in the range of 250-30$0^{\circ}C$ predominantly influences the change of the fluorescence intensity. The later stage above 30$0^{\circ}C$ significantly influences the position of the spectrum. This fluorescence study also supports the mechanism proposed in earlier work that the crosslinking reaction takes place at the reaction sites in the conjugated polyene and the phenylethynyl end group in the polyimide chain.

Chemical and Physical Modifications of Exfoliated Graphite Nanoplatelets with Liquid Rubber and the Composites

Donghwan CHO 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

Phenylethynyl-terminated polyimide, exfoliated graphite nanoplatelets, and the composites: an overview

Donghwan Cho,Lawrence T. Drzal 한국탄소학회 2016 Carbon Letters Vol.19 No.-

In efforts to characterize and understand the properties and processing of phenylethynylterminated imide (LaRC PETI-5, simply referred to as PETI-5) oligomers and polymers as a high-temperature sizing material for carbon fiber-reinforced polymer matrix composites, PETI-5 imidization and thermal curing behaviors have been extensively investigated based on the phenylethynyl end-group reaction. These studies are reviewed here. In addition, the use of PETI-5 to enhance interfacial adhesion between carbon fibers and a bismaleimide (BMI) matrix, as well as the dynamic mechanical properties of carbon/BMI composites, are discussed. Reports on the thermal expansion behavior of intercalated graphite flake, and the effects of exfoliated graphite nanoplatelets (xGnP) on the properties of PETI-5 matrix composites are also reviewed. The dynamic mechanical and thermal properties and the electrical resistivity of xGnP/PETI-5 composites are characterized. The effect of liquid rubber amine-terminated poly(butadiene-co-acrylonitrile) (ATBN)-coated xGnP particles incorporated into epoxy resin on the toughness of xGnP/epoxy composites is examined in terms of its impact on Izod strength. This paper provides an extensive overview from fundamental studies on PETI-5 and xGnP, as well as applied studies on relevant composite materials.

Exploring Control in Bottom-Up Information System Development Projects to Improve Software Development Performance

Donghwan Cho 한국콘텐츠학회 2019 International Journal of Contents Vol.15 No.2

납의 반복투여에 의한 랫드 신장과 간장에서 GST 발현에 미치는 영향

조정식,김철규,신동환,한범석,김준규,조용연,김신희,이근영,안진홍,조미행,고진경,양기화 식품의약품안전청 2001 식품의약품안전청 연보 Vol.5 No.-

납은 체내에 축적쓸 결우 겄강을 해치는 것뜨로 알려진 대표적인 환경오염물질이다. 특히 신경계, 생식기계, 면역계, 조혈잠기 및 신장에 영향을 주는 것으로 보고되고 있다- 껑리적인 상태나 이 물질에 대한 적응 과정이 일껄을 통하여 계속 변화하기 때문에 최근에는 은해물질에 대한 연령단계별 독성 발현 연구가 활밭히 이루어지고 있다. 납의 주오-한 표적장기인 신장과 간장에서 연령별 GST 활성도 변화와 GSff 및 지방과산화의 변화를 관찰하기 위하여 1, 2, 5, 8 개월령의 수컷 랫드에 음수로 0, 0.04, 0.?, 0.8%의 lead acetate를 투여하였다. 간장의 GST는 1,2,5개월령의 고농도 lead acetate 투여군예서만 활성이 존가하는 것으로 나타났고 8개월령은 다른 연령군과 비교하여 증가한 증향을 나타내었는 페 보상성 증가라 생각된다. 진장의 GST 활성도는 투여농도에 따른 영항은 나타내지 않았고 대조군의 8개월령에서 감소하는 경향을 나타낸 것은 연령에 의한 강소라 생각된다. MDA 생성은 간장과 신장에서 또두 투여농도글 따른 변화는 관찰되지 않았고 8개월령의 랫드 간장에서 MDA 생성이 다른 연령군에 비하여 증가한 경향을 나타낸 것은 고령에 따른 지방과산화의 증가라 생각된다. 간장쑥서의 GSll 수즌은 연령예 따른 변하와 투여농도에 따른 변화를 나타내지 않았고, 8개월령의 0.8%음수 투여군에서 증가하브는데 그것은 창산화 작용의 감소에 따른 생체 보상적 반응에 의하여 증가한 것으로 생각된다 음수릎 통한 납-쏜복투여 실험에서 1, 2, 5, 8개월령의 랫드에 특징적인 G5 활성도의 변화극 4'?팔할누 .었으며, 깥찰된 변확는 연령에 따른 변화라 생각된다. 연령과 낟의 oxidative stress에 끽란 상관관계를 관찰f'기 위하여 여러 종류의 항깐화 효소 및 항산화 물질을 분석하고 고령의 랫드에 대한 연구가 이루어져야 할 것으로 생각된다. Recent studies shown that lead causes oxidative stress by inducing of reactive oxygen species, reducing the antioxidant defense system of cells via depleting glutathione, inhibiting sulfhydry-dependent enzymes, interfering with some essential metals needed for antioxidant enzyme activities, and increasing susceptibility of cells the oxidative attack by altering the membrane integrity and fatty acid composition. The age related changes in the oxidative status of glutahione, lipid peroxidation, and the activity of the enzymatic antioxidant defense system, as well as the influence of aging on the susceptibility to the effects of lead acetate were investigated in rats of different ages. The effect of repeated exposure to lead acetate on the expression of glutathione S-transferase(GST) and the levels of reduced glutathione(GSH) and malondialdehyde(MDA) was determined. Male Sprague Dawley rat at 1, 2, 5 and 8 months were exposed to 0, 0.04, 0.2 and 0.8% lead acetate in drinking water for 13 weeks and fed a commercial diet. The activity of GST was elevated in liver 1, 2 and 5 months highly exposed groups and the age associated increases in 8 months groups may be an attempt by the organism to counter balance the decreases in the reducing power of liver. MDA levels were not effected by lead exposure in liver and kidney. The increased liver MDA levels in 8 months groups compared with young rats means that increased lipoperoxidation is a consequence of aging. Glutathione levels responsible for the regulation of intracellular level of lipid peroxidation during ageing were not effected by lead exposure in liver. The increase of GSH in 8 months highly dosed group may be an adaptive response. This study demonstrates that repeated lead exposure by drinking water dose not cause dramatic changes in expression of GST, and that some changes are not a result of oxidative stress.

지중 박스 구조물 굴착시 침하형상에 대한 연구

조동환(Donghwan Cho),오정호(Jeongho Oh),박준경(Junkyung Park),김현기(HyunKi Kim) 한국철도학회 2017 한국철도학회 학술발표대회논문집 Vol.2017 No.05

기존의 원형터널은 터널굴착으로 인한 지표침하량 예측을 위한 다양한 경험식이 제안되어, 이를 활용한 침하영향범위산정 및 이완영역을 사전에 평가할 수 있는 지표로 활용되고 있다. 그러나, 지중박스구조물 굴착시 침하형상에 대한 연구는 미진한 실정으로, 본 연구에서는 2차원 유한요소해석을 이용하여 구형단면 터널에 대한 침하형상곡선에 대한 연구를 수행하였다. 매개변수분석을 통해 지하수위조건, 토피고, 터널단면형상, 시공조건등의 변화시 지표침하거동을 분석하여 기존 경험식의 적용가능성을 검토하고, 수치해석 결과를 바탕으로 지중박스구조물 굴착시 적용가능한 침하형상곡선식을 제안하였다. Various empirical equations have been proposed to predict the ground settlement profile due to excavation of conventional circular tunnels, and used to estimate the settlement influential range along with evaluate the relaxation area in advance. However, the study on ground movements for the underground box strurtures has not been fully studied. In this study, the ground settlement induced from underground box excavations is investigated using the two dimensional finite element analyses. A formulation to assess the settlement profile applicable to underground box structure is proposed based on the parametric analyses by the changes of ground condition, geometric condition of structure, and construction conditions.

Flow cytometry 기법을 이용한 간 손상 평가법 연구

김철규,신동환,한범석,김준규,조용연,김신희,이근영,안진홍,조미행,고진경,조정식 식품의약품안전청 2001 식품의약품안전청 연보 Vol.5 No.-

화학물질f) 의해 발생하는 간발암 과정중 initiation 단계와 PrOmOtiOH 단계에서 간세포의 증식은 중요한 역할을 한다. 설치류에f·1 혈중 지방감소제나 플라스틱가소제인 phthalate 예스테르 같은 과산화쇼체 증가물질(peroxisome proliferator)을 장기간 투여했을 때, 간 종양이 발껑한다고 알려져 있다.diisodecyl phthalate(DIDP)는 현재 대량생산되어 사용되고 있는 플라스틱 가소제로 주로 풍선, 비닐잉 3, 렌트, 장난감, 직물류의 코.팅 등에 이용되고 있다. 다른 프탈레이트 계통의 가소제와 같이 DIDP 또 할 Pt'c에 혼합되어 이용퇴고 있고 곽산화소체 증가물질로 알려져 있다. 파산화소체 증가물질인 DIDP에 의끌 간세포꼭 DNA함량 변화 및 세포증식 변화를 관찰하고, flolr c반emoter를 이용한 DNA합성지표 및 세포증식지표의 2차원적 분석 기댑을 확립하고자 본 연구를 수행하였다. 430-4509의 Sprague Bawley 랫드를 4 군으로 나누어 DIDP를 0, 300, 600, 1200 mgAg 씩 corn oil에 희석하여 2주간 투여하였다. 극치군에저 대조군자 비교하여 20%, 24%, 33% 정도 간장의 비대에 의한 무게 증가를 나타내었다. 2차원적 리ow cytometer 분석을 이용하여 묘rd린 표지 세포왁 PCNA 발현 양성 간세포의 수와 각각의 세포 주기의 분포는 대조군과 투여군에서 관간 유의차를 나타내지 않았다. BrdU 표지 세포와 PCNA 발현 양성 세포가 대조군과 비교하여 투여굴에서 유의차를 나타내지 않은 것은 DIDP의 영향보 다 성장에 의한 간세포 증식이 활발하여 나타난 결과라 생각된다. 본 실험에서 과산화소체 증가물질인 DIDP의 반닦투여에 의한 간세포의 DNA함쏠 변화 및 세포증식 변후에 미치는 유의차는 관찰되지 않았고, 포르말린 고정한 표본이나 신선하게 분리한 간세포에서 flow c?·tometer를 이용한 DNA합성지표 및 세포증식지표의 2차원적 분석 기댑은 유해물질의 세포증식에 대한 영향을 독성병리학적 관점에서 평가할수 있는 유용글 지표라 생각한다. Peroxisome proliferators are belived to induce liver tumors in rodents due to sustained increase in cell proliferation and oxidative stress resulting from the induction of peroxisomal enzymes. Diisodecyl phthalate(DIDP), a plasticizer produced in a large amount, is use for balloon, ink, tent, toys, coated fabrics and wire cable. Liver effects, including indications of an increase in certain subcellular structure(peroxisomes), occurred in rats fed DIDP. The objective of this study was to conduct a analysis of the changes in cell cycle and rat liver DNA synthesis after treatment with a peroxisome proliferator. Immunofluorescent detection of proliferating cell nuclear antigen (PCNA) and bromodeoxyuridine (BrdU) incorporation into DAN during S phase were used to assess rat heapatocyte proliferation in vivo during administration of DIDP, a known peroxisome proliferator in rodents. Sprague Dawley rat at 430-450g were exposed to 0, 300, 600 and 1200mg/kg body weight DIDP in corn oil for 2 weeks and fed a commercial diet. DIDP treated rats showed marked hepatomegaly wih liver weight increased approximately 20, 24, 33% in groups of 300, 600, 1200 mg/kg, respectively. Isolated liver nuclei labeled with fluorescein isothiocyanate (FITC)-anti-BrdU/PI and FITC-anti-PCNA/PI were analyzed for S-phase kinetics using flow cytometry. BrdU labeling index, PCNA lebeling index and distribution of cells in G_(0)-G₁, S phase, G₂-M did not differ significantly from controls. S-phase cells constitute approximately 35% of the total population in control rat liver, a significantly higher number than reported earlier. The use of relatively young rat in the present study might have led to high levels of S-phase nuclei in control rats and too no differences in distribution of cells. It is reasonable to conclude that the marked hepatomegaly, associate with DIDP treatment, that the flow cytometric analysis of isolated nuclei from formalin fixed samples and freshly isolated hepatocytes and potentially other useful markers would provide a useful tool for retrospective assessment of the cell proliferation in toxicological pathology.