• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.46 no.4
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• pp.28-36
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• 2014

We studied the green synthesis and antibacterial activity of paper coated with chitosan-silver (Ag) green nanocomposites for packaging applications. Green synthesis of Ag nanoparticles (AgNPs) was achieved by a chemical reaction involving a mixture of chitosan-silver nitrate ($AgNO_3$) in an autoclave at 15 psi, $121^{\circ}C$, for 30 min. AgNPs and their formation in chitosan was confirmed by UV-Vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). As-prepared chitosan-AgNPs composite materials were coated on manila paper using Meyer rod. Surface morphology and Ag contents in coating layer were characterized by field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). The mechanical properties such as tensile strength and elongation were significantly affected by coating with chitosan-AgNPs. The antibacterial test of coated paper was performed qualitatively and quantitatively against Escherichia coli (E. coli). It was shown to be effective in suppressing the growth of E. coli with increasing Ag contents on the surface of coated paper and more than 95 R (%) of antimicrobial rate was obtained at chitosan-AgNPs coated papers.

• Elastomers and Composites
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• v.43 no.4
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• pp.241-252
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• 2008

ZnAl-LDH(layered double hydroxide) modified with oleic acid(SO-ZnAl LDH) was synthesized and added to the flame retardant ABS compounds containing brominated epoxy resin(BER) and antimony trioxide(${Sb_2}{O_3}$). Flame retardant ABS compounds were manufactured by using a twin-screw co-rotating extruder and subsequently injection molded into several specimen for flame retardancy and mechanical properties. The XRD patterns of ABS nanocomposites showed no peaks. The thermal stability of ABS nanocomposites was enhanced by the addition of SO-ZnAl LDH as shown in TGA results. However, these nanocomposites showed no rating in the UL 94 vertical test at 1.6 mm thickness. Only ABS nanocomposites with additional BER more than 1.5 wt% showed UL 94 V0 rating. Notched Izod impact strength, tensile modulus, and elongation at break of flame retardant ABS nanocomposites increased with the proportion of So-ZnAl LDH whereas their melt index decreased.

• International Journal of Highway Engineering
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• v.13 no.2
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• pp.1-8
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• 2011

The objective of this paper is to evaluate the performance of low $CO_2$ asphalt binder properties using LEADCAP$^{(R)}$(Low Energy and Carbon Asphalt Pavement) additive as function of various aging methods such as RTFO(Rolling thin film oven), Ultraviolet(UV) lay. In order to simulate the short-term aging of asphalt binder that occurs during the hot-mixing asphalt process, the Rolling Thin Film Oven(RTFO) was used. Asphalt binder using LEADCAP$^{(R)}$ is prepared by addition of a photoinitiator activated by ultraviolet lay. The mechanical and rheological properties of the asphalt binder were estimated using UTM(Universal Testing Machine) and DSR(Dynamic Shear Rheometer). The test results showed that the asphalt binder using LEADCAP$^{(R)}$ additive was improved the rutting resistance at testing temperature ($70^{\circ}C$) and increased tensile strength at low temperature. Also, Thermal analysis shows that the Melting Point(Tm) of asphalt binder using LEADCAP$^{(R)}$ additive was constant although the asphalt binder was aged by Ultraviolet.

• Journal of Korean Society of Steel Construction
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• v.24 no.1
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• pp.59-71
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• 2012

Results of the analysis of the structural behavior of axially loaded nodes in freeform structure were not fully understood due to certain difficulties, including the application of various welding and bolting types. In this study, a node of single layered freeform structure was tested to determine its structural behavior when subjected to axial loads. The tests were classified into node ball tests to evaluate the center of the node subjected to cyclic and monotonic loading. The node part tests were also conducted to evaluate the whole node subjected to monotonic loading. The test showed that the node ball is safe with the tensile force, but the node ball needs to increase its strength with the node loaded compressive force due to the additional bending moment of the node ball's asymmetric form.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.571-579
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• 2014

The steel braces are used to control the lateral drift of high rise buildings. The braces are designed as tensile members since the braces consisted of slender member can not resist compressive loads by elastic buckling. To resolve this problem, a lot of research were performed to develop the non-buckling member. The force limiting device (FLD.) is one of them. The purpose of this study is the development of FLD. to prevent a elastic buckling for a slender member. The folded plate type is proposed to induce the yielding before occurring elastic buckling. In this study, member test and FEM analysis for proposed type were performed. Further, It is verified that the structure with FLD member is stable by high energy absorption. The proposed folded plate type FLD could be effective to preserve the compressive member from the elastic buckling.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.41-46
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• 2016

With the recent increase in size of ships and offshore structures, there are more demand for thicker plates. As the thickness increases, it is known that fatigue life of the structures decrease. To improve the fatigue life, post weld treatments techniques, such as toe grinding, TIG dressing and hammer peening, are typically employed. However, these techniques require additional construction time and production cost. Therefore, it is of crucial interest steels with longer fatigue crack growth life compared to conventional steels. This study investigates fatigue crack growth rate (FCGR) behaviours of conventional EH36 steel and Ferrite-Bainite dual phase EH36 steel (F-B steel). F-B steel is known to have improved fatigue performance associated with the existence of two different phases. Ferrite-Bainite dual phase microstructures are obtained by special thermo mechanical control process (TMCP). FCGR behaviours are investigated by a series of constant stress-controlled FCGR tests. Considering all test conditions (ambient, low temperature, high stress ratio), it is shown that FCGR of F-B steel is slower than that of conventional EH36 steel. From the tensile tests and impact tests, F-B steel exhibits higher values of strength and impact energy leading to slower FCGR.

• Polymer(Korea)
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• v.31 no.1
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• pp.31-36
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• 2007

It has been reported that the surface properties of the plasma treated material were changed while maintaining its bulk properties. In this study, surface modification of nylon fiber by plasma treatment was tried to attain high water-repellency Nylon fiber was treated with RF plasma under a vacuum system using various parameters such as gas specious, processing time and processing power. Morphological changes by low pressure plasma treatment were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, the mechanical and inherent properties were analyzed by tensile strength, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The high water-repellency property of nylon fiber was evaluated by a water-drop standard test under various conditions in terms of aging effect. The results showed that the water-repellency of plasma-surface-treated nylon fiber was greatly improved compared to untreated nylon fiber.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.441-453
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• 2016

This study aimed to develop a two-component TSL suitable for reducing dust and guaranteeing homogeneous qualities during its spraying. Its performance was evaluated by a series of laboratory and field tests. High ductility of two-component TSL prototypes resulted in increasing their elongation at break even though their tensile strengths were slightly lower than those of one-component powder TSLs. One prototype of the two-component TSLs developed in this study was verified to satisfy every criterion specified by EFNARC (2008). Especially, it increased the average compressive strength of mortar specimens by 50% even when it coated them only with the thickness of 3 mm. From a preliminary spraying test, a spraying machine suitable for the developed TSL prototype was derived and modified. After its field application, dust and rebound generated during its spraying works were found to be very minimal. Its spraying rate was recorded to be approximately $60m^2/hr$. In addition, it showed a very rapid hardening characteristic compared with general sprayable waterproofing membranes.

• Journal of Korea Foundry Society
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• v.32 no.2
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• pp.104-108
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• 2012

The effect of heat treatment on mechanical properties of 0.4C-2.3Si(wt%) steel with bainitic ferrite matrix were investigated. This steel has been synthesized intergrating concepts from TRIP(Transformation Induced Plasticity) steel & Austempered Ductile Cast Iron(ADI) technology. The low alloy medium carbon (0.4 %C) steel with high silicon (2.3 %Si) was initially annealed for 60 min at $800^{\circ}C$, $820^{\circ}C$ and $840^{\circ}C$ respectively in the intercritical region and then subsequently austempered at various temperatures at $260^{\circ}C$, $320^{\circ}C$ and $380^{\circ}C$ for 30 min in a salt bath. The mechanical properties were measured by using a tensile test. A detailed study of the microstructure of this steel after heat treatment was carried out by means of electron back scattering diffraction (EBSD) technic. In this study, a new low alloy steel with high strength (780~1,050MPa) and exceptionally high ductility (20~40%) was obtained.

• Tunnel and Underground Space
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• v.14 no.5
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• pp.345-352
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• 2004

In a shotcrete support system, the cooperation of the ground and the shotcrete lining makes it possible to transfer the shear stress to the shotcrete lining, which is dedicated to form a stable structure. In this study, a homogeneous model ground with constant strength was produced by using gypsum and the tunnel was excavated with a top heading method under the definite initial stress. During the excavation, the stress in the ground around the tunnel and the deformation of shotcrete lining were measured, The tensile stress was generated in tangential direction in the ground near the tunnel and in the shotcrete lining due to tunnel excavation. This shows the unified behavior of the ground and shotcrete lining, which is the most typical characteristic of the shotcrete support. As a result, the rates of in-situ stress during the excavation at a top boundary line was 9% and at top arch heading 15%. It was 48% right after excavating the heading and 94% before cutting the bench.