• Macromolecular Research
• /
• v.12 no.5
• /
• pp.459-465
• /
• 2004

We have synthesized poly(l,4-cyclohexylenedimethylene terephthalate-co-hexamethylene terephthalate) [P(CT-co-HT)] random copolymers having various comonomer contents, from 0 to 100 mol% HT, by melt-condensation and have investigated their crystallization behavior by using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). We observed that P(CT-co-HT)s exhibit clear melting and crystallization peaks in their DSC thermograms and sharp diffraction peaks in their WAXD patterns for all of their copolymer compositions as a result of cocrystallization of the CT and HT units, even though the copolymers are statistically random copolymers. When we plotted the melting and crystallization temperatures of P(CT-co-HT)s and the d-spacings of all the reflections against the copolymer composition, we observed a eutectic point at ca. 80 mol% HT, which suggests that a crystal transition occured from a PCT-type crystal to a PHT-type crystal. Both the DSC and WAXD results support the notion that P(CT-co-HT) copolymers undergo an isodimorphic cocrystallization.

• Journal of the Korean Electrochemical Society
• /
• v.6 no.3
• /
• pp.183-186
• /
• 2003

In a PEM fuel cell electrode, backing layer has tremendous impact on electrode performance. The backing layer provides structural support for the porous electrode, distributes the reactants to the other layers and acts as a current collector. It has major influence on the water management in a PEM fuel cell. Selection of suitable backing layer material for the fabrication of electrode is thus very important to achieve high performance. In this paper we have compared the performance of PEM fuel cell electrodes fabricated using carbon paper EC-TPI-060T, carbon cloth EC-CCI-060T, (ElectroChem Inc.USA) and Carbon cloth from Textron, USA (CPW 003 grade). Mass transport problem was observed under non-pressurized condition, at high current densities, in the caie of EC-CC1-060T carbon cloth electrode (at $50^{\circ}C$), due to its higher thickness. The performance of carbon paper electrode was higher than EC-CCI-060T carbon cloth electrode. The performance of Textron carbon cloth was comparable to EC-TPI -060T carbon paper.

• Advances in concrete construction
• /
• v.4 no.4
• /
• pp.319-332
• /
• 2016

In most cases strengthening reinforced concrete columns exposed to high strain rate is to be expected especially within weak designed structures. A special type of loading is instantaneous loading. Rapid loading can be observed in structural columns exposed to axial loads (e.g., caused by the weight of the upper floors during a vertical earthquake and loads caused by damage and collapse of upper floors and pillars of bridges).Subsequently, this study examines the behavior of reinforced concrete columns under rapid loading so as to understand patterns of failure mechanism, failure capacity and strain rate using finite element code. And examines the behavior of reinforced concrete columns at different support conditions and various loading rate, where the concrete columns were reinforced using various counts of FRP (Fiber Reinforcement Polymer) layers with different lengths. The results were compared against other experimental outcomes and the CEB-FIP formula code for considering the dynamic strength increasing factor for concrete materials. This study reveals that the finite element behavior and failure mode, where the results show that the bearing capacity increased with increasing the loading rate. CFRP layers increased the bearing capacity by 20% and also increased the strain capacity by 50% through confining the concrete.

• Korea-Australia Rheology Journal
• /
• v.17 no.4
• /
• pp.181-190
• /
• 2005

Rheological characterisation of flocculated kaolinite pulps has been undertaken to elucidate particle interactions underpinning the dewatering behaviour induced by flocculation with polyethylene oxide (PEO), anionic polyacrylamide (PAM A) and their blends. Shear yield stress $(\tau_y)$ analysis indicated that polymer mediated particle interactions were markedly amplified upon shear of PEG based pulps. In contrast, PAM A based pulps showed a significant decrease in yield values upon shear. Steady stress measurements analysed using a modified Ellis model indicated subtle differences between the respective linear viscoelastic plateaus of the pulps. Furthermore, modified shear thinning behaviour was evident in PEG based pulps. Estimation of elastic and viscous moduli (G', G') was made using dynamic stress analysis for comparison with values determined from vane measurements. Despite a noticeable difference in the magnitude of G' between the two methods, similar trends indicating sheared PEG-based pulps to be more elastic than PAM based pulps, were observed. Floc microstructural observations obtained in support of rheological properties indicate that PEG flocculant induces significantly more compact particle aggregation within the clay pulps under shear consistent with the yield stress data, in contrast to PAM A, or indeed unsheared PEG based pulps. Consequentially, sheared PEG based pulps show significantly improved dewatering behaviour. The implications of the results, potential benefits and drawbacks of flocculation with PEG and PAM A are discussed with respect to improvements in current dewatering processes used in the minerals industry.

• Macromolecular Research
• /
• v.17 no.3
• /
• pp.192-196
• /
• 2009

Recently, the multi-screening of target materials has been made possible by the development of the surface plasmon resonance (SPR) imaging method. To adapt this method to biochemical analysis, the multi-patterning technology of protein microarrays is required. Among the different methods of fabricating protein microarrays, the microfluidic platform was selected due to its various advantages over other techniques. Microfluidic devices were designed and fabricated with polydimethylsiloxane (PDMS) by the replica molding method. These devices were designed to operate using only capillary force, without the need for additional flow control equipment. With these devices, multiple protein-patterned sensor surfaces were made, to support the two-dimensional detection of various protein-protein interactions with SPR. The fabrication technique of protein microarrays can be applied not only to SPR imaging, but also to other biochemical analyses.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.2
• /
• pp.44-51
• /
• 2019

With the goal of tissue regeneration for organs damaged through an accident or a disease, research on tissue engineering has been conducted to produce 3-D scaffolds that can support the cells in the attachment and growth for the cell proliferation and differentiation. A scaffold requires a suitable pore size and porosity to increase the nutrient circulation or oxygen supply for the attachment and growth of cells. The existing production methods such as solvent-casting particulate leaching, phase separation, and fiber bonding have certain disadvantages. With these methods, it is difficult to obtain a free desired shape. In addition, certain pore sizes and interconnectivities among the pores may not be guaranteed. To solve these problems, this study has fabricated a scaffold with a 3-D shaped nose using Alginate, which is a natural polymer obtained through Fused Deposition Modeling (FDM), one of the CAD/CAM-based Solid Freeform Fabrication (SFF) methods.

• Structural Engineering and Mechanics
• /
• v.76 no.6
• /
• pp.737-749
• /
• 2020

A hybrid bridge deck is proposed, which includes steel bars, concrete and glass-fiber-reinforced-polymer (GFRP) plates with channel sections. The steel bar in the negative moment region can increase the flexural stiffness, improve the ductility, and reduce the GFRP ratio. Three continuous decks with different steel bar ratios and a simply supported deck were fabricated and tested to study the mechanical performance. The failure mode, deflection, strain distribution, cracks and support reaction were tested and discussed. The steel bar improves the mechanical performance of continuous decks, and a theoretical method is proposed to predict the deformation and the shear capacity. The experimental results show that all specimens failed with shear failure in the positive moment region. The increase of steel bar ratio in the negative moment region can achieve an enhancement in the flexural stiffness and reduce the deflection without increasing GFRP. Moreover, the continuous deck can achieve a yield load, and the negative moment can be carried by GFRP plates after the steel bar yields. Finally, a nonlinear analytical method for the deflection calculation was proposed and verified, with considering the moment redistribution, non-cracked sections and nonlinearity of material. In addition, a simplified calculation method was proposed to predict the shear capacity of GFRP-concrete decks.

• Journal of Ceramic Processing Research
• /
• v.19 no.6
• /
• pp.492-498
• /
• 2018

In this study, a sea shell was converted into bioceramic phases at three different sintering temperatures ($450^{\circ}C$, $850^{\circ}C$, $1000^{\circ}C$). Among the obtained bioceramic phases, a valuable ${\beta}-TCP$ was produced via mechanochemical conversion method from sea snail Turritella terebra at $1000^{\circ}C$ sintering temperature. For this reason, only the bioceramic sintered at $1000^{\circ}C$ was concentrated on and FT-IR, SEM/EDX, BET, XRD, ICP-OES analyses were carried out for the complete characterization of ${\beta}-TCP$ phase. Biodegradation test in Tris-buffer solution, bioactivity tests in simulated body fluid (SBF) and cell studies were conducted. Bioactivity test results were promising and high rate of cell viability was observed in MTT assay after 24 hours and 7 days incubation. Results demonstrated that the produced ${\beta}-TCP$ bioceramic is qualified for further consideration and experimentation with its features of pore size and ability to support bone tissue growth and cell proliferation. This study suggests an easy, economic method of nanobioceramic production.

• Journal of the Korean Institute of Gas
• /
• v.26 no.2
• /
• pp.14-20
• /
• 2022

In this study, the catalytic reaction characteristics for producing hydrogen using methanol steam reforming were investigated. Nickel and copper are frequently used in steam reforming reaction and methanol synthesis, were used as main active metals. As a support, hydrotalcite has a high specific surface area, excellent porosity and thermal stability, and has weak Lewis acid sites and basic properties. Hydrotalcite was used to identify catalysts of methanol steam reforming with catalytic activity and their properties. In this research, high reactivity was shown in the catalyst of copper metal with high reducibility. And increasing of active metal loading showed the higher the methanol conversion and hydrogen selectivity.

• Structural Engineering and Mechanics
• /
• v.84 no.5
• /
• pp.605-618
• /
• 2022

Glass fiber reinforced polymer (GFRP) elastic gridshells consist of long continuous GFRP tubes that form elastic deformations. In this paper, a method for the form-finding of gridshell structures is presented based on the interpretable machine learning (ML) approaches. A comparative study is conducted on several ML algorithms, including support vector regression (SVR), K-nearest neighbors (KNN), decision tree (DT), random forest (RF), AdaBoost, XGBoost, category boosting (CatBoost), and light gradient boosting machine (LightGBM). A numerical example is presented using a standard double-hump gridshell considering two characteristics of deformation as objective functions. The combination of the grid search approach and k-fold cross-validation (CV) is implemented for fine-tuning the parameters of ML models. The results of the comparative study indicate that the LightGBM model presents the highest prediction accuracy. Finally, interpretable ML approaches, including Shapely additive explanations (SHAP), partial dependence plot (PDP), and accumulated local effects (ALE), are applied to explain the predictions of the ML model since it is essential to understand the effect of various values of input parameters on objective functions. As a result of interpretability approaches, an optimum gridshell structure is obtained and new opportunities are verified for form-finding investigation of GFRP elastic gridshells during lifting construction.