• Advances in nano research
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• 제16권2호
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• pp.127-140
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• 2024

Upon direct/indirect exposure to flame or heat, composite structures may burn or thermally buckle. This issue becomes more important in the natural fiber-based composite structures with higher flammability and lower mechanical properties. The main goal of the present study was to obtain an optimal eco-friendly composite system with low flammability and high thermal buckling resistance. The studied composite consisted of polypropylene (PP) and short abaca fiber (AF) with eggshell powder (ESP) and halloysite clay nanotubes (HNTs) additives. An optimal base composite, consisting of 30 wt.% AF and 70 wt.% PP, abbreviated as OAP, was initially introduced based on burning rate (BR) and the Young's modulus determined by horizontal burning test (HBT) and tensile test, respectively. The effects of adding ESP to the base composite were then investigated with the same experimental tests. The results indicated that though the BR significantly decreased with the increase of ESP content up to 6 wt.%, it had a very destructive influence on the stiffness of the composite. To compensate for the damaging effect of ESP, small amount of HNT was used. The performance of OAP composite with 6 wt.% ESP and 3 wt.% HNT (OAPEH) was explored by conducting HBT, cone calorimeter test (CCT) and tensile test. The experimental results indicated a 9~23 % reduction in almost all flammability parameters such as heat release rate (HRR), total heat released (THR), maximum average rate of heat emission (MARHE), total smoke released (TSR), total smoke production (TSP), and mass loss (ML) during combustion. Furthermore, the combination of 6 wt.% ESP and 3 wt.% HNT reduced the stiffness of OAP to an insignificant amount by maximum 3%. Moreover, the char residue analysis revealed the distinct differences in the formation of char between AF/PP and AF/PP/ESP/HNT composites. Afterward, dilatometry test was carried out to examine the coefficient of thermal expansion (CTE) of OAP and OAPEH samples. The obtained results showed that the CTE of OAPEH composite was about 18% less than that of OAP. Finally, a theoretical model was used based on first-order shear deformation theory (FSDT) to predict the critical bucking temperatures of the OAP and OAPEH composite plates. It was shown that in the absence of mechanical load, the critical buckling temperatures of OAPEH composite plates were higher than those of OAP composites, such that the difference between the buckling temperatures increased with the increase of thickness. On the contrary, the positive effect of CTE reduction on the buckling temperature decreased by raising the axial compressive mechanical load on the composite plates which can be assigned to the reduction of stiffness after the incorporation of ESP. The results of present study generally stated that a suitable combination of AF, PP, ESP, and HNT can result in a relatively optimal and environmentally friendly composite with proper flame and thermal buckling resistance with no significant decline in the stiffness.

• 전기화학회지
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• 제27권3호
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• pp.88-96
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• 2024

리튬금속(Li metal)은 높은 비용량과 에너지 밀도, 낮은 표준 전극 전위로 인해 유망한 음극활 물질로 각광받아온 재료이지만, 충·방전 시 발생하는 수지상 결정인 덴드라이트(dendrite)로 인해 안전성 및 수명안정성에 한계가 있었다. 본 연구에서는 나노 파이버(Nano Fiber) 형태의 도전재인 vapor grown carbon fiber (VGCF)와 은(Ag)의 복합체가 코팅된 분리막을 개발하였으며, 해당 분리막이 리튬금속 음극의 전기화학 특성에 미치는 영향을 연구하였다. VGCF와 Ag의 시너지 효과를 확인하기 위하여 표면 처리되지 않은 분리막, VGCF만 단면 코팅 처리된 분리막을 각각 준비하여 Ag-VGCF 분리막과 비교 평가하였다. Bare 분리막의 경우, 초기 충·방전 과정에서 리튬금속 표면이 덴드라이트로 뒤덮인 반면, VGCF 분리막 및 Ag-VGCF 분리막 모두 분리막 표면에 코팅된 전도성 코팅층 내부에 리튬이 석출되는 거동을 보였다. 또한 Ag-VGCF 분리막은 VGCF 분리막 대비 더욱 균일한 형상의 석출 형태를 보였다. 그 결과 Ag-VGCF 분리막은 Bare 분리막 및 VGCF 분리막 대비 향상된 전기화학적 특성을 보였다.

• Composites Research
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• 제30권1호
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• pp.59-64
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• 2017

향상된 특성을 갖는 환경친화적인 복합재료의 개발은 고분자재료의 미래에 있어 필수적이며, 부분적으로 또는 완전히 재생가능한 기지재 또는 보강재에 단지 몇 %의 첨가제를 첨가함으로써 쉽게 제작할 수 있다. 본 연구에서는 마닐라삼 섬유를 보강재로, 비닐에스터를 기지재로 사용하였으며, VARTM 공정을 이용하여 복합재료를 제조하였다. 또한 마닐라삼 섬유의 알칼리표면처리를 수행하고, APP, HNT를 난연제를 첨가함으로써 기계적 물성과 난연 물성을 향상시키고자 하였다. 실험을 통하여 표면처리가 천연섬유의 친수성을 감소시키고 소수성인 기지재와의 계면접착력을 향상시켰으며, 이는 개발된 복합재료의 기계적 물성 향상을 이끌었다. 유사하게, 복합재료의 난연성도 난연제의 함량이 증가함에 따라 크게 향상되는 결과를 얻을 수 있었다.

• 한국의류학회지
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• 제38권3호
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• pp.372-385
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• 2014

Lignin is an abundant natural polymer in the biosphere and second only to cellulose; however, it is under-utilized and considered a waste. In this study, lignin was fabricated into nanofibers via electrospinning. The critical parameters that affected the electrospinnability and morphology of the resulting fibers were examined with the aim to utilize lignin as a resource for a new textile material. Poly(vinyl alcohol) (PVA) was added as a carrier polymer to facilitate the fiber formation of lignin, and the electrospun fibers were deposited on polyester (PET) nonwoven substrate. Eleven lignin/PVA hybrid solutions with a different lignin to PVA mass ratio were prepared and then electrospun to find an optimum concentration. Lignin nano-fibers were electrospun under a variety of conditions such as various feed rates, needle gauges, electric voltage, and tip-to-collector distances in order to find an optimum spinning condition. We found that the optimum concentration for electrospinning was a 5wt% PVA precursor solution upon the addition of lignin with the mass ratio of PVA:lignin=1:5.6. The viscosity of the lignin/PVA hybrid solution was determined as an important parameter that affected the electrospinning process; in addition, the interrelation between the viscosity of hybrid solution and the electrospinnability was examined. The solution viscosity increased with lignin loading, but exhibited a shear thinning behavior beyond a certain concentration that resulted in needle clogging. A steep increase in viscosity was also noted when the electrospun system started to form fibers. Consequently, the viscosity range to produce bead-free lignin nanofibers was revealed. The energy dispersive X-ray analysis confirmed that lignin remained after being transformed into nanofibers. The results indicate the possibility of developing a new fiber material that utilizes biomass with resulting fibers that can be applied to various applications such as filtration to wound dressing.

• Carbon letters
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• 제21권
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• pp.23-32
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• 2017

A drop weight impact test was conducted in this study to analyze the mechanical and thermal properties caused by the changes in the ratio of carbon fiber reinforced plastic (CFRP) to ethylene vinyl acetate (EVA) laminations. The ratios of CFRP to EVA were changed from 10:0 (pure CFRP) to 9:1, 8:2, 6:4, and 5:5 by manufacturing five different types of samples, and at the same time, the mechanical/thermal properties were analyzed with thermo-graphic images. As the ratio of the CFRP lamination was increased, in which the energy absorbance is dispersed by the fibers, it was more likely for the brittle failure mode to occur. In the cases of Type 3 through Type 5, in which the role of the EVA sheet is more prominent because it absorbs the impact energy rather than dispersing it, a clear form of puncture failure mode was observed. Based on the above results, it was found that all the observation values decreased as the EVA lamination increased compared with the CFRP lamination. The EVA lamination was thus found to have a very important role in reducing the impact. However, the strain and temperature were inversely propositional.

• Composites Research
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• 제33권4호
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• pp.191-197
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• 2020

본 연구에서는 향상된 내구성을 가진 고효율 전자파차폐용 랜덤배향 시트 소재를 개발하기 위해 구리(Copper: Cu)와 니켈 (Nickel: Ni)이 코팅된 탄소섬유(Carbon fiber: CF)와 같은 하이브리드 소재를 습식공정을 통해 제조 하였다. 제조된 시트 소재는 69.4~93.0 dB의 높은 전자파 차폐효율을 보여주었다. 또한 하이브리드 금속으로 코팅된 Ni-Cu/CFs 시트는 Ni표면의 유효한 부식저항성과 기계적 저항성 때문에 가혹한 화학적/열적 환경하에서 매우 우수한 내구성을 보여주었다. 이와 관련하여 Ni-Cu/CF 시트는 Cu/CF 시트와 비교하여 1.7배 긴 수명을 가지는 것을 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제25권1호
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• pp.63-68
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• 2004

Sugar-based gelator p-dodecanoyl-aminophenyl- ${\beta}$-D-aldopyranosides (1-3) have been shown to self-assemble in the presence of p-aminophenyl aldopyranosides. The hydrogel 1+4 showed the double-helical structure with 3-25 nm outer diameters, which is quite different from that of 1. The gel 2+5 revealed twisted ribbon structure with 30-50 nm in widths and a few micrometers of length whereas the gel 3+4 revealed the single and the bundled fiber structures. The difference in these gel supramolecular structures has successfully been transcribed into silica structures by sol-gel polymerization of tetraethoxysilane (TEOS), resulting in the doublehelical, the twisted-ribbon, the single and the multiple (lotus-shaped) hollow fiber structures. These results indicate that novel silica structures can be created by transcription of various superstructures formed in binary gels through the hydrogen-bonding interaction, and the amino group of the p-aminophenyl aldopyranosides acts as an efficient driving force to create novel silica nanotubes. Furthermore, electron energy-loss spectroscopy (ELLS) provided strong evidence for the inner hollow structure of the double-helical silica nanotube. This is a novel and successful example that a variety of new silica structures can be created using a library of carbohydrate gel fibers as their templates.

• 한국기계가공학회지
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• 제20권5호
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• pp.135-141
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• 2021

As a trend of lightening automobiles and electronic products, several studies are currently underway to replace parts of metals with resins. In particular, heterojunctions between metals and resins are now under the spotlight. This study aims to evaluate the variation in bonding strength with process conditions when the polybutylene terephthalate (PBT) polymer is bonded to a specimen of the lightweight 6061 aluminum alloy (AL6061). Conditions of the bonding surface of the AL6061 specimen, the temperature of the injection mold, and the content of the glass fiber were considered to be process variables. Bonded specimens were manufactured for different values of these variables. Bonding strength tests were then performed on these specimens and variations were analyzed in their characteristics corresponding to those of the process conditions. Fractures in these specimens were assessed using scanning electron microscopy (SEM) to assess the fracture surface. This was then used to analyze the fracture shape and determine whether anodizing the specimen led to the development of cracks on the joint surface. Results of the above test indicated that while the surface condition of the specimen and the temperature of the injection mold significantly influenced the strength of bonding, the content of the glass fiber did not.

• Advances in nano research
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• 제10권1호
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• pp.59-69
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• 2021

Electrospinning is a cost-effective and versatile method for producing submicron fibers. Although this method is relatively simple, at the theoretical level the interactions between process parameters and their influence on the fiber morphology are not yet fully understood. In this paper, the aim was finding optimal electrospinning parameters in order to obtain the smallest fiber diameter by using Taguchi's methodology. The nanofibers produced by electrospinning a solution of Thermoplastic Polyurethane (TPU) in Dimethylformamide (DMF). Polymer concentration and process parameters were considered as the effective factors. Taguchi's L9 orthogonal design (4 parameters, 3 levels) was applied to the experiential design. Optimal electrospinning conditions were determined using the signal-to-noise (S/N) ratio with Minitab 17 software. The morphology of the nanofibers was studied by a Scanning Electron Microscope (SEM). Thereafter, a tensile tester machine was used to assess mechanical properties of nanofibrous scaffolds. The analysis of DoE experiments showed that TPU concentration was the most significant parameter. An optimum combination to reach smallest diameters was yielded at 12 wt% polymer concentration, 16 kV of the supply voltage, 0.1 ml/h feed rate and 15 cm tip-to-distance. An empirical model was extracted and verified using confirmation test. The average diameter of nanofibers at the optimum conditions was in the range of 242.10 to 257.92 nm at a confidence level 95% which was in close agreement with the predicted value by the Taguchi technique. Also, the mechanical properties increased with decreasing fibers diameter. This study demonstrated Taguchi method was successfully applied to the optimization of electrospinning conditions for TPU nanofibers and the presented scaffold can mimic the structure of Extracellular Matrix (ECM).

• Composites Research
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• 제35권4호
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• pp.255-260
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• 2022

소화전 탱크의 경량화는 소방차가 수용할 수 있는 물의 양을 증가시켜 초기 소방 과정에서 물 분무 시간을 늘려 화재로 인한 재산과 인명 피해를 크게 줄일 수 있다. 본 연구에서는 탄소섬유강화폴리머(CFRP) 복합재료를 경량 소화전 탱크의 재료로 적용하는 것을 조사하였다. CFRP 소화전 탱크 제조를 위해 사용되는 수지는 우수한 기계적 물성, 성형성, 치수안정성 등 여러 조건들을 만족시켜야 한다. 위의 조건들을 만족시키는 수지를 찾기 위해 KFR-120V, G-650, HG-3689BT, LSP8020, KRF-1031 등 5가지 수지를 후보로 선정하고 테스트하여 CFRP 소화전 탱크 제조 적합성을 조사였다. 분석 결과 KRF-1031이 소화전 탱크에 가장 적합한 특성을 보였다. 특히, KRF-1031을 이용한 CFRP는 열안정성 및 용출 시험에서 성공적인 결과를 보였다.