• Macromolecular Research
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• v.13 no.3
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• pp.206-211
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• 2005

Multi-walled carbon nanotubes (MWNTs) pre-treated by concentrated mixed acid or oxidized at high temperature were melt mixed with poly(methyl methacrylate) (PMMA) using a twin screw extruder. The morphologies and electrical properties of the MWNT/PMMA composites were investigated. The thermally treated MWNTs (t-MWNTs) were well dispersed, whereas the acid treated MWNTs (a-MWNTs) were highly entangled, forming large-sized clusters. The resulting electrical properties of the composites were analyzed in terms of the carbon nanotube (CNT) dispersion. The experimental percolation threshold was estimated to be $3 wt\%$ of t-MWNTs, but no percolation occurred at similar concentrations in the a-MWNT composites, due to the poor dispersion in the matrix.

• Macromolecular Research
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• v.10 no.4
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• pp.221-229
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• 2002

PET nanocomposites filled with fumed silicas were prepared via direct melt compounding method at various mixing conditions such as filler type and filler content. Some fumed silicas were pre-treated to improve the wettability and dispersibility, and principal characterizations were performed to investigate the effects of nano fumed silicas on polymer matrix. Hydrophobic fumed silica (M-FS), which has the similar contact angles of water with neat PET, acted as the best reinforcement for the thermal stability and mechanical properties of PET nanocomposite, and FE-SEM images also showed that M-FS was uniformly dispersed into matrix and had good wettability. But, some filler (O-FS) had low dispersibility and caused the deterioration of mechanical properties. Besides, the results of DSC revealed the nucleation effect of all fillers in polymer matrix, and PET nanocomposite filled with hydroptilic fumed silica (FS) showed markedly the characteristic dynamic rheological properties such as shear thinning behavior at very low frequencies and the decrease of viscosity.

• Macromolecular Research
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• v.11 no.1
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• pp.62-68
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• 2003

Thermotropic liquid crystalline polymer (TLCP)/poly(ethylene 2,6-naphthalate) (PEN)/poly(ethylene terephthalate) (PET) ternary blends were prepared by melt blending, and were melt-spun to fibers at various spinning speeds in an effort to improve fiber performance and processability. Structure and property relationship of TLCP/PEN/PET ternary blend fibers and effects of annealing on those were investigated. The mechanical properties of ternary blend fibers could be significantly improved by annealing, which were attributed to the development of more ordered crystallites and the formation of more perfect crystalline structures. TLCP/PEN/PET ternary blend fibers that annealed at 18$0^{\circ}C$ for 2 h, exhibited the highest values of tensile strength and modulus. The double melting behaviors observed in the annealed ternary blend fibers depended on annealing temperature and time, which might be caused by different lamellae thickness distribution as a result of the melting-reorganization process during the DSC scans.

• Macromolecular Research
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• v.16 no.3
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• pp.218-223
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• 2008

In order to obtain crosslinked poly(butylene succinate) (PBS) foams with a closed-cell structure, a commercial-grade PBS was first modified in the melt using two different branching agents to increase the melt viscosity. The rheological properties of the branched and crosslinked PBS were examined by varying the amount of the branching agents. The complex viscosity of the crosslinked PBS increased with increasing amount of the branching agent. However, it decreased with increasing frequency. When 2 phr of the branching agent was added to PBS, the storage modulus (G') was higher than the loss modulus (G") throughout the entire frequency range, showing that the addition of a branching agent increases the melt viscosity and elasticity of PBS effectively. Closed-cell PBS foams were prepared by mixing the chemical blowing agent with the crosslinked PBS. The effect of the foaming conditions such as temperature and time, and the amount of the crosslinking agent on the structure of the expanded PBS foams were also investigated.

• Applied Chemistry for Engineering
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• v.7 no.1
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• pp.194-202
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• 1996

Hot melt adhesive based on the polyamide resin was studied to improve the conventional hot melt adhesives such as ethylene-vinyl acetate which have inherent problems against creep and heat resistance. It was found that the terpolymer of nylons6, nylon66, and nylon12 or the nylon blend instead of nylon homopolymer was suitable base resin for hot melt adhesives, since the disruption of regularity in the polymer chains reduced the crystallinity, resulting in lower melting point and melt viscosity. Also, the rheological properties of the polyamide based hot melt adhesive could be controlled by the incorporation of terpene resin, butyl benzyl phthalate, and paraffin wax. The results of melt viscosities and tensile properties of adhesive itself indicated that the optimum adhesion properties could be obtained through the blending of CM831/843P resins with weight ratio 75/25~50/50. The adhesion between steel and steel was tested by using lap shear geometry. It was found that the surface roughness of steel affected the adhesion strength.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.3
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• pp.291-298
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• 2014

This study uses two numerical approaches to analyze the filling behavior of micro patterns on micro-injection molding for V-grooves pattern which cannot be simulated with conventional CAE packages. The parametric studies have been performed to examine the fidelity of micro patterns with respect to temperature, pressure, inlet velocity and pattern location on the mold according to the boundary condition from the macro pressure and velocity data which can be obtained by conventional CAE packages. Through these numerical approaches, the filling behavior of polymer melt in micro patterns can be understood, the quality of replication can be predicted, and the V-groove pattern can be shaped uniformly during the process of injection molding.

• Polymer(Korea)
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• v.29 no.4
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• pp.385-391
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• 2005

Reactive melt processing has been carried out to investigate crosslinking characteristics of high density polyethylene OTDPE) with dicummyl peroxide (DCP) and perbutyle peroxide (PBP). The increase of torque in the internal mixer indicated that the crosslinking in HDPE has been occurred by peroxides. As a result, the substantial decrease of density, melting temperature, and melt enthalpy were found while the melt viscosity increased in partially crosslinked HDPE. In the mechanical properties of partially crosslinked HDPE, the increase of maximum strength and the decrease in elongation at break were clearly noticed and these were more pronounced when PBP was applied as a crosslinking agent. It seems that the maximum strength was obtained with reactive processing temperature at $150^{circ}C$, however, the mixing time did not affect to the strength of partially crosslinked HDPE.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.223-226
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• 2003

Due to the potential application to ultra-high strength fibers and excellent properties such as high mechanical properties, excellent thermal endurance and chemical stability, thermotropic liquid crystal polymers (TLCPS) are attractive in recent years [1, 2]. Furthermore, the melt blends of TLCPS and conventional thermoplastics have been extensively investigated because of their easy processing and high performance [3-6]. Since high performance polymers generally has high melt viscosity, introduction of the relatively low viscosity components may be one of the more effective techniques to improve processability through the decrement of melt viscosity in melt processing. (omitted)

• Polymer(Korea)
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• v.30 no.1
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• pp.22-27
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• 2006

The effect of transesterification on the rheological property of poly(ethylene naphthalate)/poly(butylene tore-phthalate) (PEN/PBT) blends has been investigated. The melt viscosity of PEN/PBT blends decreased with increasing PBT content due to the relatively low melt viscosity of PBT as well as introducing ransesterification between PEN and PBT Further melt viscosity decrease was achieved by the thermal annealing which caused both the chain scission and the acceleration of transesterfication. Calcium stearate (CaST) was applied as a lubricant in order to lower the melt viscosity of PEN and it was found that CaST was acting as the catalyst of transesterification as well. In general, reactive melt blending of PEN and PBT by transesterification resulted in the decrease of molecular weight of PEN and PBT, as a result, the loss of mechanical properties in PEN/PET blend was inevitable.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.26-30
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• 2005

Stamper surface temperature is very critical in replicating the high density optical disc substrates using injection molding as the pit or land/groove patterns on the optical disc substrate have decreased due to the rapid increase of areal density. During the filling stage, the polymer melt in the vicinity of the stamper surfaces rapidly solidifies and the solidified layer generated during polymer filling greatly deteriorates transcribability and fluidity of polymer melt. To improve transcribability and fluidity of polymer melt, stamper surface temperature should be controlled such that the growth of the solidified layer is delayed during the filling stage. In this study, the effect of heating on replication process was simulated numerically. Then, an injection mold equipped with instant active heating system was designed and constructed to raise the stamper surface temperature over the glass transition temperature during filling stage of the injection molding. Also, the closed loop controller using the Kalman filter and the linear quadratic Gaussian regulator was designed. As a result, the stamper surface temperature was controlled according to the desired reference stamper surface temperature.