• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.239-240
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• 2008

• Polymer(Korea)
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• v.36 no.6
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• pp.733-738
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• 2012

The effect of glass bead and glass fiber on the enhancement of dimensional stability in poly(ethylene naphthalate) (PEN) flexible substrate for photovoltaic devices has been studied. It was found that the coefficient of thermal expansion (CTE) and the optical transmittance decreased with increasing inorganic filler content. In addition to filler contents, the size and size distribution of fillers are the other important factors to improve CTE and optical transmittance of PEN film. Our results showed that the optimum filler content was found to be about 5 wt% to enhance the dimensional stability of PEN by more than 50% with maintaining the optical transmittance over 85% for the flexible substrate.

• Polymer(Korea)
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• v.33 no.6
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• pp.530-536
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• 2009

A cycloaliphatic epoxy/acidic anhydride system incorporating short carbon fibers (SCF) and short glass fibers (SGF) was fabricated and thermal/mechanical properties were characterized. At low filler content both SCF- and SGF-reinforced composites showed a similar decrease in coefficient of thermal expansion (CTE), measured by a thermomechanical analyzer, with increasing loadings, above which SCF became more effective than SGF at reducing the CTE. Experimental CTE data for the SCF-reinforced composites is best described by the rule of mixtures at lower SCF contents and by the Craft-Christensen model at higher SCF contents. Storage modulus (E') at $30^{\circ}C$ and $180^{\circ}C$ was greatly enhanced for short fiber-filled composites compared to unfilled specimens, Scanning electron microscopy of the fracture surfaces indicated that the decreased CTE and the increased E' of the short fiber-reinforced composites resulted from good interfacial adhesion between the fibers and epoxy matrix.

• Polymer(Korea)
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• v.35 no.6
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• pp.599-604
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• 2011

The PET-PEN copolymers have been synthesized and the effect of their morphology on the physical properties of polyester flexible substrate was investigated. It was found that the block sequence of synthesized copolymer was varied depending upon DMT/NDC ratio in polymerization. Higher PET-PEN and PEN block sequence in polyester copolymer resulted in the increase of glass transition temperature and it caused the enhancement of dimensional stability as a polyester flexible substrate. The highest coefficient of thermal expansion(CTE) was obtained when DMT/NDC ratio is 50/50. Synthesized PET-PEN copolymer seems to be acceptable as a flexible substrate since it shows that their optical transmittance at 550 nm is over 80% and thermal weight loss at $280^{\circ}C$ for 1 hr is less than 0.4 wt%.

• Polymer(Korea)
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• v.29 no.6
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• pp.605-612
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• 2005

This study investigates the isothermal crystallization behaviors of polypropylene-polyethylene-(1-butene) terpolymer and the adiabatically expanded polyolefin structured foams. For this purpose, butane gas was used as a physical blowing agent. Avrami equation has been used to interpret theoretically the experimental results obtained by either DSC or polarized optical microscope. It is believed that elongation induced crystallization occurring during the adiabatic expansion process has resulted in an increase in crystallization rate, eventually leading to a faster growth rate of spherulites and an increase in the nucleation density. An analysis of the foam by SEM images showed that the structure of foam is uniform (below diameter 30 $\mu$m closed cell) In addition, the thermal conductivity and the compressive strength of the polyolefin structured foams was measured. The thermal conductivity of foamed resin with excellent insulation characteristics is reduced compared with unfoamed resin. The compressive strength is decreased with increase in the expansion ratio.

• Journal of Adhesion and Interface
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• v.6 no.4
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• pp.12-17
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• 2005

Natural fiber/phenolic biocomposites with chopped henequen fibers treated at various levels of electron beam irradiation (EBI) were made by means of a matched-die compression molding method. The interfacial property was explored in terms of interfacial shear strength measured by a single fiber microbonding test. The thermal properties were studied in terms of storage modulus, tan ${\delta}$, thermal expansion and thermal stability measured by dynamic mechanical analysis, thermomechanical analysis and thermogravimetric analysis, respectively. The result showed that the interfacial and thermal properties depend on the treatment level of EBI done to the henequen fiber surfaces. The present result also demonstrates that 10 kGy EBI is most preferable to physically modify the henequen fiber surfaces and then to improve the interfacial property of the biocomposite, supporting earlier results studied with henequen/poly (butylene succinate) and henequen/unsaturated polyester biocomposites.

• Bulletin of the Korean Chemical Society
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• v.22 no.11
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• pp.1255-1260
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• 2001

The expansion of two different kinds of hydrodynamic size of polymethyl methacrylate (PMMA Mw: 1.56- 2.04 ${\times}$ 106 g/mol) has been measured by dynamic light scattering and viscometry above the Flory $\theta$ temperature of the variou s solvents such as n-butyl chloride, 3-heptanone, and 4-heptanone. The expansion of PMMA chains was analyzed in terms of universal temperature parameters and also compared with previous results of polystyrene (PS) system. First it was found that simple $\tau/{\tau}c$ parameter no longer had its universality for the expansion behavior of hydrodynamic size in the chemically different linear polymer chains. However after modifying ${\tau}/{\tau}c$ parameter into $(Mw/Ro2)3}2(\tau/\tauc)$, we observed a much better universality for both PMMA and PS systems. Here Mw, Ro, $\tau[=(T-{\theta}$)/${\theta}$]$, and ${\tau}c[=({\theta}-Tc)/Tc]$ are defined as the weight average molecular weight, the unperturbed end-to-end distance, the reduced temperature and the reduced critical temperature, respectively.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.75-78
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• 2007

The steel slag, a by-product which is produced by refining pig iron during the manufacture of steel, is mainly used as road materials after aging. It is necessary to age steel slag for long time in air because the reaction with water and free-CaO in steel slag could make the expansion of volume. This problem prevents steel slag from being used as aggregate for concrete. However, steel slag used in this study was controled by a air-jet method which rapidly cools substance melted at a high temperature. The rapidly-chilled method would prevent from generation of free-CaO in steel slag. Also, Molten steel slag rapidly-chilled by air in high speed becomes a fine aggregate of nearly spherical shape. This study dealt with the influence of the using rate of rapidly-chilled steel slag and polymer resin on fluidity of polymer concrete, as a results Since RCSS has spherical shape and high density, up to replacement ratio of 100%, increases concrete fluidity under same polymer content and decrease polymer content in order to secure the same fluidity

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.288-289
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• 2014

The purpose of this research is to examine strength properties of epoxy-modified mortar with expansive and swelling agent contents. The polymer-modified mortars (PMMs) using epoxy resin are prepared with various polymer-binder ratios, expansive and swelling agent contents. The PMMs using epoxy resin are tested for compressive, flexural and tensile strengths. As a result, the strength properties of the PMMs using epoxy resin are depending on the polymer-binder ratio rather than expansive and swelling agent content, and are remarkably improved over unmodified mortar (UMM).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1609-1618
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• 1997

Thermo-mechanical behaviors of polymer matrix composite(PMC) with continuous TiNi fiber are studied using theoretical analysis with 1-D analytical model and numerical analysis with 2-D multi-fiber finite element(FE) model. It is found that both compressive stress in matrix and tensile stress in TiNi fiber are the source of strengthening mechanisms and thermo-mechanical coupling. Thermal expansion of continuous TiNi fiber reinforced PMC has been compared with various mechanical behaviors as a function of fiber volume fraction, degree of pre-strain and modulus ratio between TiNi fiber and polymer matrix. Based on the concept of so-called shape memory composite(SMC) with a permanent shape memory effect, the critical modulus ratio is determined to obtain a smart composite with no or minimum thermal deformation. The critical modulus ratio should be a major factor for design and manufacturing of SMC.