• Polymer(Korea)
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• 제25권2호
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• pp.168-176
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• 2001

The effect of novel N-crotyl-N,N-dimethyl-4-methylanilinium hexafluoroantimonate (CMH) curing agent as a thermal latent initiator on thermal behaviors, rheological properties, and thermal stability of diglycidylether of bisphenol A (DGEBA) epoxy cationic system was investigated. From DSC measurements of DGEBA/CMH system, it was shown that this system exhibits an excellent thermal latent characteristic at a given temperature. The conversion and conversion rate of DGEBA/CMH system increased with increasing the concentration of initiator, due to high activity of CMH. Rheological properties of the system were investigated under isothermal condition using a rheometer The gelation time was obtained from the analysis of storage modulus (G'), loss modulus (G"), and damping factor (tan $\delta$). As a result, the reduction of gelation time was affected by high curing temperature and concentration of CMH, resulting in high degree of network formation in cationic polymerization, due to difference of activity. The thermal stability of the cured epoxy resin was discussed in terms of the activation energy for decomposition and thermal factors determined from TGA measurements.ents.

• Journal of the Korean Society for Railway
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• 제19권1호
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• pp.1-10
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• 2016

To improve the sound insulation performance of laminated glass in high speed trains, it is beneficial to study the relationship between the characteristics of interlayer films and the acoustical performance. In addition to those of conventional PVB (polyvinyl butyral), the dynamic mechanical properties of PVB derivatives and PC (polycarbonate), which are candidates for interlayer films, were analyzed. We assumed that PVB-HEMU, which has a glass transition temperature ($T_g$) around room temperature and a large tan ${\delta}$ (loss tangent) value, can be made to damp efficiently. The damping capability was tested utilizing sound transmission loss measurement and simulation under the identical structure of laminated glass in high speed trains. We also built a database for analysis of relations between interlayer film characteristics and acoustical performance; this was followed by the determination of sound transmission loss using the intensity technique and FEA.

• Elastomers and Composites
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• 제35권2호
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• pp.106-114
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• 2000

The foam of ethylene vinyl acetate (EVA)/styrene-vinyl isoprene-styrene triblock copolymer(SVIS) blend was prepared to improve the shock-absorption and compression set characteristics at room temperature. The effects of blowing agent and blend ratio of EVA/SVIS on expansion ratio, cell structure and mechanical properties of the foam were investigated. As the SVIS content increased, the viscosity of blends was increased but the crosslinking rate was slow down, the expansion ratio was decreased. and the specific gravity was increased. At room temperature, the resilience was not affected by increasing the amount of blowing agent. The value of tan ${\delta}$ was increased by increasing the amount of SVIS. As a result, the value of compression set was decreased. This is due to the increased values of specific gravity and crosslinking density of the EVA/SVIS foam.

• Elastomers and Composites
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• 제47권3호
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• pp.231-237
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• 2012

This study measured the mechanical and damping properties of EPDM compounds including fillers. Semi-reinforcing furnace black (SRF), high abrasion furnace black (HAF) and acetylene black were used as fillers. Dicumyl peroxide (DCP) were used as curing agents. The measurements were conducted using a moving die rheometer (MDR), durometer, universal testing machine (UTM), compression set and dynamic mechanical analysis (DMA). The tensile strength and elongation at break increased with increasing SRF contents in EPDM compounds. However, they decreased with increasing the amount of acetylene black. In the inspecting temperature range, EPDM compound filled acetylene black had stable storage modulus. Furthermore, the tan ${\delta}$ of the EPDM compounds obtained was enhanced by compounding with acetylene black.

• Polymer(Korea)
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• 제28권5호
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• pp.433-443
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• 2004

The membranes of the blends of chitosan and polycaprolactarn (PA6) were prepared in formic acid. FT-IR data revealed that hydrogen bonding between amide and hydroxyl groups of chitosan and PA6, respectively, was formed. Thermogravimetric analysis demonstrated that the blend samples contain water. DMA results showed that the dissipation of water in the samples significantly reduced the storage modulus (E'). The mechanical loss tangent (tan $\delta$) data of the blend samples showed the $\beta$d loss peak around $0^{\circ}C$. The blend samples were completely dried in a vacuum and then exposed to high moisture to absorb water which would cause, so called, w-bridges between the molecules. The E' data of these regained samples increased abnormally and additional loss peak appeared on the shoulder of the peak around $50^{\circ}C$. Under dry condition, the samples with a blend ratio of 40/60 for chitosan/PA6 displayed a better miscibility between two components.

• Polymer(Korea)
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• 제24권3호
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• pp.350-357
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• 2000

Curing behaviors of glass/epoxy prepreg for printed circuit boards (PCB) were studied by using dielectrometer and differential scanning calorimeter. This prepreg was showed the lowest ionic viscosity at about 115$^{\circ}C$, and then the ionic viscosity was gradully increased up to 15$0^{\circ}C$. This indicated that the curing reaction of this prepreg started at 115$^{\circ}C$ and the molecular weight was increased by the accelerated thermal cross-linking reaction. The loss factor and tan $\delta$ values were also measured and discussed. The dielectric behaviors of this prepreg system were also measured according to the cure cycle for PCB. This material was found to be thermally stable up to about 30$0^{\circ}C$ and then was showed an abrupt decomposition beyond this temperature.

• Korean Journal of Materials Research
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• 제22권7호
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• pp.368-373
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• 2012

Glasses were prepared with compositions of $(13-x)BaO-80B2_O_3-7Li_2O{\cdot}xSm_2O_3$, BBLSx(x=0.5, 0.4, 0.3) by melting the starting materials of boron oxide(99.9%), lithium oxide(99.9%), barium carbon oxide(99.9%), and samarium oxide(99.9%) and then quenching the melt at $1350^{\circ}C$. This led to good-quality BBLSx(x=0.4, 0.3) and poor-quality BBLSx(x=0.5) glasses. The physical and structural properties of the BBLSx glasses were studied by means x-ray diffraction, scanning electron microscopy(SEM), differential scanning calorimetry(DSC), and dielectric spectroscopy. From the x-ray diffraction and SEM results, the quality of the BBLSx glasses significantly depends on the $Sm_2O_3$ concentration. The x-ray diffraction pattern showed that the crystallites in the BBLSx glasses after heat treatment at $700^{\circ}C$ may be $LiBaB_9O_{15}$. From the DSC results, the glass transition temperatures($T_g$), crystallization temperatures($T_c$), and the maximum temperatures of the crystallized($T_p$) BBLSx glasses all changed with the $Sm_2O_3$ concentration. According to the dielectric spectroscopy results, the values of the real dielectric constant and Tan ${\delta}$ of the BBLSx glasses depended on the $Sm_2O_3$ concentration. The values of the real dielectric constant and Tan ${\delta}$ were also shown to depend on the measuring temperature, possibly due to the ion migration in the bulk of the BBLSx glasses.

• Korean Journal of Optics and Photonics
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• 제30권4호
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• pp.159-166
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• 2019

The trajectory of the transmission ellipsometric pseudoconstant ${\rho}=tan{\psi}_{\mu}e^{i{\Delta}_{\mu}}$ of a uniaxially anisotropic substrate like PET forms a circle in polar coordinates, as the phase-retardation angle is varied at a fixed azimuthal angle. The radius as well as the center's position of this circle are functions of the azimuthal angle only. This circle passes through the point (1,0), and the center of this circle is located on the real axis. These characteristics of the circle are examined analytically, and are utilized to derive simple expressions for the azimuthal angle and the phase-retardation angle of the uniaxially anisotropic substrate using the measured transmission ellipsometric constant. Finally, we confirm that the derived expressions are well applied to the analysis of the optical anisotropy of a PET film.

• Composites Research
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• 제32권1호
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• pp.71-77
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• 2019

In this study, the structural and rheological characterizations of polyacrylonitrile(PAN)/dimethyl sulfoxide(DMSO) solutions for PAN fiber were investigated according to the change of storage times and temperatures. As a result, PAN/DMSO solutions exhibited a very characteristic rheological behavior with variation of temperature. The solutions showed an increase of complex viscosity and a decrease of loss tangent($tan{\delta}$) as temperature was increased over the temperature range of 40 and $70^{\circ}C$ and it could be seen that the viscosity rapidly increased at low frequency. These results indicated that the gel polymer and denser gel structure were formed due to the intermolecular hydrogen bonding of water in the polymer solution depending on the storage time.

• Journal of Ceramic Processing Research
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• 제19권6호
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• pp.461-466
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• 2018

The effects of Ca/Sr ratio and the sintering temperature on the properties of $(Ca_xSr_{(1-x)})ZrO_3$ (CSZ) ceramics were investigated in this study. CSZ ceramics were prepared using solid-state reaction process, which were sintered in air at temperatures ranging from $1350^{\circ}C$ to $1450^{\circ}C$. Their structures were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The change in Ca/Sr ratio significantly affected the crystalline phase and the dielectric properties of the $(Ca_xSr_{(1-x)})ZrO_3$ ceramics. The secondary phase, $Ca_{0.15}Zr_{0.85}O_{1.85}$, was observed and increased correspondingly with the rising of sintering temperatures. In order to understand the effects of secondary phase on the dielectric properties of CSZ ceramics, the $Ca_{0.15}Zr_{0.85}O_{1.85}$ phase was prepared individually using solidstate method. The $Ca_{0.15}Zr_{0.85}O_{1.85}$ ceramics sintered at $1500^{\circ}C$ for 2 hours possessed a dielectric constant (${\varepsilon}_r$) of 21.7, a dielectric loss ($tan{\delta}$) of $49.510^{-4}$ and an Insulation Resistance (IR) of $2.1{\times}10^{10}{\Omega}$. The ($Ca_{0.7}Sr_{0.3})ZrO_3$ ceramics exhibited the best dielectric properties, with a permittivity of 29, a dielectric loss ($tan{\delta}$) of $2.7{\times}10^{-4}$, and an Insulation Resistance (IR) of $2.6{\times}10^{12}{\Omega}$.