• Polymer(Korea)
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• v.38 no.4
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• pp.491-495
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• 2014

Pressure sensitive adhesive (PSA) based on 2-ethylhexyl acrylate (2-EHA)/acrylic acid (AA) copolymer was synthesized using different photoinitiators. Results showed that PSA with Irgacure$^{(R)}$651 (benzyldimethylketal) and Irgacure$^{(R)}$184(1-hydroxy-cyclohexylphenyl ketone) proved to be good for adhesion properties. This may be attributed to strong absorption near 350 nm wavelength and also high solubility in monomer mixtures. The addition of Irgacure$^{(R)}$819, bisacylphosphine oxides as a photoinitiator caused cohesive failure with high loading in a peel test owing to the additional radical formation. It is assumed that the insoluble photoinitiator reacts with oxygene, which may act as a hydrogen donor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1087-1093
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• 2008

Regenerative cooling passage to guarantee the thermal survivability in high performance rocket engine combustors could have complex configurations of the branching/merging of channels and flow turning, etc. By applying the classical hydraulic coefficients which can be found in the literature according to the flow conditions, hydraulic characteristics in regenerative cooling passages can be obtained effectively through dividing the pressure loss into friction loss and local resistance loss. Satisfactory agreement has been obtained by comparing the present results with experimental measurement of water flow test. In addition, the present results were in good agreement with CFD results when the actual coolant, kerosene was used. Therefore, the application of the present method is expected to be useful to design regeneratively cooled combustors.

• Elastomers and Composites
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• v.48 no.4
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• pp.294-299
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• 2013

Solution polymerization was conducted with water-soluble methacrylic acid (MAA) as a monomer and potassium persulfate (KPS) as an initiator at a selected temperature between $70^{\circ}C$ and $90^{\circ}C$. When the ratio between MAA and water was reduced or initiator concentration increased, molecular weights decreased. Molecular weights of poly(methacrylic acid) (PMAA) showed nearly no dependence on reaction temperature. The Weissenberg effect was observed in most polymerization reactions, while its effect weakened at $90^{\circ}C$. The polydispersity index was less than 1.5 in most of the reactions. An increase in the stirring speed produced PMAAs with increasing molecular weights. When the stirring speed reached 800 rpm, we retrieved a monodisperse PMAA with both the number and weight average molecular weights of 791,000 g/mol. The glass transition temperature was found to be $162^{\circ}C$.

• Journal of Adhesion and Interface
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• v.6 no.3
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• pp.19-25
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• 2005

Synthetic rubber based pressure-sensitive adhesives (PSAs) usually containing SIS or SBS block copolymer, tackifier, plasticizer, and other additives are now widely used on various applications. As these PSAs are physically crosslinked and can be applied without the use of solvent, they are thermally processable and environmentally friendly. However these PSAs cannot be used in high temperature applications and in applications where solvent and chemical resistance properties are required. We developed the PSA adding UV curable system, such as thiol-ene system, to increase adhesion properties at elevated temperature. The adhesion properties such as probe tack, peel strength, shear adhesion failure temperature (SAFT) were evaluated. The probe tack test was conducted with varying probe materials and coating thickness of PSAs. Using the contact angle, the surface property of the cured PSAs was also observed.

• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.678-686
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• 2009

A trial run of locally-developed tilting train has been in process on Chungbuk line since the test vehicle was first produced. For the system stabilization, interface verification among the systems including track, structure, catenary and signaling system, not to mention the rolling stock, is very crucial. Therefore, in this study, the dynamic rail force of the tilting (Hanvit 200), high-speed (KTX) and general (Mugunghwa) vehicle caused by driving in transition curve track was measured. And, it compared the tilting response with the other by using the measured rail force data in transition curve track, and then evaluated probability the range of load fluctuation for the variable dynamic vertical and lateral wheel load. As a result, a range of rail force by occurred a change of cant from the high-speed and general vehicle which had fixed bogie structure was distributed throughout small deviation. Otherwise, in case of the tilting train which was consisted of the pendulum bogie structure was distributed wide range about large deviation by changed of cant.

• Elastomers and Composites
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• v.49 no.3
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• pp.232-238
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• 2014

Solution polymerization was conducted with water-soluble acrylic acid (AA) as a monomer and potassium persulfate (KPS) as an initiator at a selected temperature between $60^{\circ}C$ and $90^{\circ}C$ with water as a reaction medium. When the ratio between AA and water was reduced or initiator concentration increased, molecular weights decreased. An increase in the reaction temperature produced lower molecular weights. The polydispersity index was close to 1.5 in most of the reactions. An increase in the stirring speed up to 400 rpm led to a progressive increase in molecular weights. When the stirring speed reached 800 rpm, however, we found that both the number and weight average molecular weights decreased. The glass transition temperature was nearly independent of moelcular weights and determined to be between $113^{\circ}C$ and $116^{\circ}C$.

• Elastomers and Composites
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• v.45 no.3
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• pp.217-222
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• 2010

Paved roads are suffered from the permanent plastic deformation in hot summer and cracks in cold winter, which are detrimental to safe driving. This leads to necessity of modification of asphalt to resist those deformation. In this study, two kinds of modifiers were examined; organic polymers and a photoinitiator which is activated by ultraviolet lay. The mechanical and rheololgical properties of modified asphalts were examined using UTM and rheometer. Results showed that the properties were varied depending on the types of polymer and irradiation time. UV irradiation increased the tensile strength and storage modulus of thermoplastic polymer-modified asphalt, however UV was not effective on thermoset polymer. According to long term ultraviolet curing test, properties of the polymer/photoinitiator-modified asphalt did not decrease, but rather increase for 20 years. This indicates that the useful life of the asphalt could be extended by addition of photoinitiator.

• Journal of the Korean Chemical Society
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• v.20 no.2
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• pp.158-165
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• 1976

The anionic polymerization of ${\varepsilon}$-caprolactam with N,N'-adipyl-bis-${\varepsilon}$-caprolactam as an initiator and potassium hydroxide as a catalyst was studied under various conditions.It was found that concentration of catalyst and initiator was 4.2 and 1.6 mole %, and polymerization temperature of 130$^{\circ}C$C, polymerization time of 1.5 hours was the optimum condition. The intrinsic viscosity and molecular weight of the obtained polymer was over 0.9 dl/g and 12,000. The polymerization was carried out in the presence of N-acyl-${\varepsilon}$-caprolactam as an initiator, it was observed that the reactivity of N,N'-adipyl-bis-${\varepsilon}$-caprolactam was greater than both of the N-benzoyl-${\varepsilon}$-caprolactam and N-acetyl-${\varepsilon}$-caprolactam. In general it was also observed that the intrinsic viscosity and yield of conversion was increased as an increasing of concentration of catalyst and initiator and also highly depend on temperature.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.3
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• pp.283-289
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• 2011

As leisure boats become large-scaled and high value-added, their design requirements gradually get more complicated and accordingly their manufacturing processes get more complicated than those of existing ones. Leisure boat builders overseas make efforts to overcome this circumstance by establishing a 3-D model-based design system which is based on the concept of PLM. On the other hand, Korean shipbuilders still remain in the development process of traditional leisure boats which are mainly based on 2-D drawings. There have been some efforts made to have the 3-D model-based design system; however, they belong to a very early stage. This study carried out initial research to apply DMU technology to the development process of leisure boats. It established the design process based on a DMU model and proved its usefulness through a case study on the design of 40-ft class aluminum leisure boats.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1559-1565
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• 2013

This study aims to investigate the dynamic interaction characteristics between Maglev vehicles and an elevated guideway. A more detailed model for the dynamic interaction of the vehicle/guideway is proposed. The proposed model incorporates a 3D full vehicle model based on prototyping, flexible guideway by a modal superposition method, and levitation electromagnets including the feedback controller into an integrated model. The proposed model was applied to an urban transit Maglev developed for a commercial application to analyze the dynamic response of the vehicle and guideway, and the effect of the surface roughness of the rail, mid-span guideway deflections, and air gap variations are then investigated from the numerical simulation.