• 한국막학회:학술대회논문집
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• 한국막학회 2003년도 The 4th Korea-Italy Workshop
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• pp.133-135
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• 2003

The removal of dissolved oxygen(DO) from water was studied using a poly(vinyliene fluoride)(PVDF) hollow fiber membrane contactor(HFMC) with the vacuum degassing process(VDP), Asymmetric porous PVDF hollow fiber membranes (HFM) for membrane contactor were prepared by a wet phase inversion method. In spinning of these PVDF hollow fibers, dimethy lacetamide (DMAc), LiCl and pure water were used as a solvent, a pore-forming additive and internal/external coagulant, respectively. The characteristics of the structure(pore size, porosity etc.) of the prepared PVDF HFMs as a function of concentration of pore-forming additive in polymer dope solution were studied. Also, the removal efficiency of DO from water according to flow rates of water, using PVDF HFMC with VDP, was studied. The performance of the asymmetric porous PVDF HFMC and a symmetric porous PP HFMC commercialized were compared. As a result, the asymmetric porous PVDF HFMC showed higher removal efficiency of DO than that of a symmetric porous PP HFMC.

• Fibers and Polymers
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• 제5권4호
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• pp.264-269
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• 2004

The present paper deals with improvement in disperse dyeablility as well as imparting of cationic dyeablility to difficultly dyeable polypropylene by a melt blending technique. Isotactic polypropylene (PP) was blended with fibre grade polybutylene terephthalate (PBT), cationic dyeable polyethylene terephthalate (CDPET) and polystyrene (PS), individually. The resulting binary blends were spun and drawn into fibres at draw ratio 2, 2.5, and 3. The compatibility of blends, structural changes of fibres in terms of X-ray crystallinity, relative crystallinity, sonic modulus, birefringence and thermal stability were examined. The blended fibres were found to be disperse dyeable by the conventional method of high temperature and high pressure dyeing. And this dye ability increased with increase in the level of substitution. PP/CDPET blend also exhibited dyeablility with cationic dyes in addition to that with disperse dyes. The optimum level of blending was predicted keeping in view of tenacity and thermal stability of melt blend fibres. The wash fastness properties of the dyed fibres were found to be of high rate.

• Carbon letters
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• 제15권4호
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• pp.290-294
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• 2014

New precursors, poly(acrylonitrile-co-crotonic acid) (poly(AN-CA)) and poly(acrylonitrile-co-itaconic acid-co-crotonic acid) (poly(AN-IA-CA)) copolymers, for the preparation of carbon fibers, were explored in this study. The effects of comonomers with acidic groups, such as crotonic acid (CA) and/or itaconic acid (IA), on the stabilization of nanofibrous polyacrylonitrile (PAN) copolymers were studied. The extent of stabilization, evaluated by Fourier transform infrared spectroscopy, revealed that the CA comonomer could retard/control the stabilization rate of PAN, in contrast to the IA comonomer, which accelerated the stabilization process. Moreover, the synthesized PAN copolymers containing CA possessed higher Mv than those of the IA copolymers and also showed outstanding dimension stability of nanofibers during the stabilization, which may be a useful property for improving the dimensional stability of polymer composites during manufacturing.

• Structural Engineering and Mechanics
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• 제18권2호
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• pp.167-194
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• 2004

In this paper axial loading tests on low strength concrete members, which were confined with various thickness of carbon fiber reinforced polymer (CFRP) composite sheets are described. Totally 46 specimens with circular, square and rectangular cross-sections with unconfined concrete compressive strengths between 6 and 10 MPa were included in the test program. During the tests, a photogrammetrical deformation measurement technique was also used, as well as conventional measurement techniques. The contribution of external confinement with CFRP composite sheets to the compressive behavior of the specimens with low strength concrete is evaluated quantitatively, in terms of strength, longitudinal and lateral deformability and energy dissipation. The effects of width/depth ratios and the corner radius of the specimens with rectangular cross-section on the axial behavior were also examined. It was seen that the effectiveness of the external confinement with CFRP composite sheets is much more pronounced, when the unconfined concrete compressive strength is relatively lower. It was also found that the available analytical expressions proposed for normal or high strength concrete confined by CFRP sheets could not predict the strength and deformability of CFRP confined low strength concrete accurately. New expressions are proposed for the compressive strength and the ultimate axial strain of CFRP confined low strength concrete.

• Structural Engineering and Mechanics
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• 제72권3호
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• pp.305-312
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• 2019

This paper investigates the effect of utilizing vacuum bagging process to enhance the bond behavior between fiber reinforced polymer (FRP) composites and concrete substrate. Sixty specimens were prepared and tested using double-shear bond test. The effect of various parameters such as vacuum, fiber type, and FRP sheet length and width on the bond strength were investigated. The experimental results revealed that utilizing vacuum leads to improve the bond behavior between FRP composites and concrete. Both the ultimate bond forces and the maximum displacements were enhanced when applying the vacuum which leads to reduction in the amount of FRP materials needed to achieve the required bond strength compared with the un-vacuumed specimens. The efficiency of the enhancement in bond behavior due to vacuum highly depends on the fiber type; using carbon fiber showed higher enhancement in the bond strength compared to the glass fiber when vacuum was applied. On the contrary, specimens with glass fiber showed higher enhancement in the maximum slippage compared to specimens with carbon fibers. Utilizing vacuum does not affect the debonding failure modes but lead to increase in the amount of attached concrete on the surface of the debonded FRP sheet.

• Coupled systems mechanics
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• 제10권2호
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• pp.161-184
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• 2021

Strengthening of reinforced concrete beams with externally bonded fiber reinforced polymer plates/sheets technique has become widespread in the last two decades. Although a great deal of research has been conducted on simply supported RC beams, a few studies have been carried out on continuous beams strengthened with FRP composites. This paper presents a simple uniaxial nonlinear analytical model that is able to accurately estimate the load carrying capacity and the behaviour of damaged RC continuous beams flexural strengthened with externally bonded prestressed composite plates on both of the upper and lower fibers, taking into account the thermal load. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the damaged concrete beam, the FRP plate and the adhesive layer. The flexural analysis results and analytical predictions for the prestressed composite strengthened damaged RC continuous beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The use of composite materials increased the ultimate load capacity compared with the non strengthened beams. The major objective of the current model is to help engineers' model FRP strengthened RC continuous beams in a simple manner. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the FRP-damaged RC hybrid structures.

• 한국염색가공학회지
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• 제35권2호
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• pp.121-127
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• 2023

In this study, a comprehensive investigation was conducted on the morphological and property changes of laser-induced nanocarbon (LINC) as a function of laser process parameters. LINC was formed on the surfaces of polyimide films with different backbone structures under various process conditions, including laser power, scan speed, and resolution. Three different forms of LINC electrodes (i.e., continuous 3D porous graphene, wooly nanocarbon fibers, line cut) were formed depending on the laser power and scan speed. Furthermore, heteroatom doping induced from the chemical structure of the polyimide during laser patterning was found to be effective in modifying the electrical properties of LINC electrodes. The LINC surfaces exhibited different microstructures depending on the laser beam resolution under constant laser power and scan speed, allowing for controllable surface wettability. The correlation between the chemical structure of the polymer substrate, laser process parameters, and carbonized surface properties in this study is expected to be utilized as fundamental understanding for the manufacturing of next-generation carbon-based electronic devices.

• Steel and Composite Structures
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• 제49권4호
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• pp.393-405
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• 2023

In this paper, the energy absorption capability of a novel cruciform composite lattice structure was evaluated through the simulation of compression tests. For this purpose, several test samples of Polylactic acid cellular reinforced with continuous glass fibers were prepared for compression testing using the additive manufacturing method of material extrusion. Using a conventional path design for material extrusion, multiple debonding is probable to be occurred at the joint regions of adjacent cells. Therefore, an innovative printing path design was proposed for the cruciform lattice structure. Afterwards, quasistatic compression tests were performed to evaluate the energy absorption behaviour of this structure. A finite element model based on local material property degradation was then developed to verify the experimental test and extend the virtual test method. Accordingly, different combinations of unit cells' dimensions using the design of the experiment were numerically proposed to obtain the optimal configuration in terms of the total absorbed energy. Having brilliant energy absorption properties, the studied cruciform lattice with its optimized unit cell dimensions can be used as an energy absorber in crashworthiness applications. Finally, a cellular structure will be suitable with optimal behavior in crush load efficiency and high energy absorption.

• 한국표면공학회지
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• 제56권5호
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• pp.309-319
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• 2023

Non-woven fabric is a textile product made by spinning thermoplastic polymers without manufacturing processes such as stretching, doubling, twisting, weaving, and knitting to form a sheet-shaped web in which fibers are tangled with each other, and then combining them by mechanical and physical methods. In addition, the non-woven fabric manufacturing process has various raw material choices, high productivity, so it is a textile manufacturing technology that can have various uses and increase added value. This study was conducted to control the shape and physical properties of products by improving the manufacturing method of melt-blown non-woven fabrics using process technology that easily changes the shape of non-woven fabrics and improves mechanical properties. In particular, it is considered that a non-woven fabric with a thin material shape and improved mechanical properties will be easily applied to a continuous secondary battery manufacturing industry such as roll to roll operation.

• Korean Chemical Engineering Research
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• 제47권5호
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• pp.558-564
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• 2009

고분자 광섬유(POF)는 유리광섬유에 비하여 경량성, 저가 그리고 다루기 쉬운 장점을 가지고 있다. 그러나 상대적으로 높은 전송손실과 낮은 대역특성으로 인하여 랜과 같은 단거리 네트워킹에 대한 사용이 적합하다. 전송손실을 낮게 하기 위한 고분자물질의 합성공정과 유연한 고분자광섬유의 활용을 보다 넓히기 위한 다양한 연구들이 진행되고 있다. 본 연구에서는 저잡음의 POF 모듈들이 개발되었으며, 이를 위하여 저잡음 증폭기와 저가의 650 nm의 발광다이오드(LED: Light Emitting Diode)가 최적화되었다. 광통신과 센서용 POF 모듈의 동적특성을 나타내기 위하여, 화상전송모듈, 광전송 속도측정모듈, RS-232용 광전송기와 음성전송모듈을 제작하여 그들의 신호특성을 평가하였다. 광전송속도의 측정에 있어서는 빠르고 간단한 측정으로서 모듈이 바로 사용될 수 있는 것으로 보여진다. 또한, 아날로그 증폭기, LED와 포토다이오드(PD: Photo Diode) 등을 활용하여, 소리와 화상의 전송은 POF를 통하여 최대 60 m까지 가능한 것으로 확인되었다. 또한 비례적분미분제어에서 확인한 실시간 데이터 전송효과는 산업용 공장의 설계와 제어에 있어서 매우 가치가 있을 것으로 고려된다.