• Polymer(Korea)
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• v.28 no.5
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• pp.391-396
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• 2004

In order to overcome drawbacks in the conventional preparation of epoxy/silica nanocomposites, such as formation of micro voids and dimensional instability caused by evolution of volatile by-products during curing reaction, a novel preparation method using Si-N precursor has been proposed. When prepared through in-situ reaction of epoxy curing reaction with sol-gel reaction of Si-N precursor, methyltripiperidinylsilane (MTPS) which does not produce by-products during reaction, epoxy/silica nanocomposites of extremely even dispersion of inorganic phase could be successfully prepared, resulting in high enhancement of mechanical and thermal properties as well as outstanding transparency.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1041-1046
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• 2012

In this study, we performed experimental tests on five SP-100 aluminum powder epoxy specimens with several after-curing conditions in order to estimate their hardness with temperature and compressive strength. In the surface hardness test, it was found that the higher the after-curing temperature, the higher was the hardness. In particular, it was found that the hardness of the specimens in cases 3 and 4 was much higher than in the other cases. In addition, in the compression tests carried out to evaluate the compressive strength, it was found that the specimens showed relatively similar stiffness and strength with after-curing, and specimens with no after-curing showed compression stress-strain curves similar to those of thermoplastic resins.

• Composites Research
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• v.35 no.6
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• pp.412-418
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• 2022

Flame-retardant vinyl ester (VE) resin films were developed from the mixtures of brominated and non-brominated epoxy resins via esterification with methacrylic acid without reactive diluents. The films were used to fabricate carbon fiber (CF) prepregs via a hot melt impregnation process. The viscosity of VE resins suitable for film production was optimized by mixing low-viscosity bisphenol-A and high-viscosity brominated bisphenol-A epoxy precursors. Increasing the bromine content of the cured VE resin further increased the limited oxygen index (LOI) (39%), storage modulus (2.4 GPa) at 25℃ and residual carbonization (16.1%) values compared to non-brominated VE. Manual layup of as-prepared VE prepregs with subsequent curing led to the successful fabrication of CF-reinforced composites with high tensile and flexural strength. The results from the study hold high promise for a styrene-free, environmentally friendly VE composite process in the future.

• Composites Research
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• v.15 no.3
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• pp.39-44
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• 2002

Interfacial properties and microfailure modes or electrodeposition(ED) treated carbon fiber reinforced polyetherimide(PEI) toughened epoxy composites were investigated using microdroplet test. ED was performed to improve the interfacial shear strength(IFSS). As PEI content increased, IFSS increased due to enhanced toughness and plastic deformation of PEI. In the untreated cafe, IFSS Increased with adding PEI content, and IFSS of pure PEI matrix showed the highest. On the other hand, thor ED-treated case IFSS increased with PEI content with rather low improvement rate. In the untreated case, neat epoxy resin appeared brittle microfailure mode, whereas pure PEI matrix exhibited more likely ductile microfailure mode. In the ED-treated case, neat epoxy exhibited more ductile fracture compared to the untreated case. Interfacial properties of epoxy-PEI composite can be affected efficiently by both the control of matrix toughness and ED treatment.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.1
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• pp.130-135
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• 2010

In this study, the performance improvement of epoxy resin system had been tried by the improvement of particle size distribution and globularization of filler using polymerization method. From the results of particle size distribution measurement, the polydispersity value of reformed filler was 1.04 and that of silica flour before reformation was 2.6, it could be confirmed that the particle size uniformity of reformed filler had been improved greatly and the shape of particle was globular. Compatibility between monomer and silica was improved remarkably with the silanization pretreatment of silica flour. From the results of degree of crosslinking test, it could be confirmed that the binding structure of reformed filler was 3-dimensional net structure. And it could be also confirmed that the fluidness was improved at the casting of epoxy resin with reformed filler. From the above results, it could be concluded that the reformation of filler with the improvement of particle size distribution and globularization was very successful method to improve the performance of cast epoxy resin system.

• Polymer(Korea)
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• v.30 no.6
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• pp.492-497
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• 2006

The epoxy composites are prepared with mixing temperature of epoxy/montmorillonite (MMT) melt master batch and the dielectric properties of the composites are also compared with intercalation of MMT. The exfoliation mainly occurrs iii the low content of MMT composites, while in the composites with high content of MMT the interspacing distance increases as the mixing temperature of epoxy/MMT master batch is increased. Class transition temperature of the composite which the MMT are effectively exfoliated is increased with the appropriate postcuring condition. Since the orientation polarization of dipoles in the epoxy molecules is restricted by the clay nanolayers exfoliated, the dielectric constant and dielectric loss of the composites are reduced. Furthermore, the dielectric properties could be improved by controling the mixing temperature and time of epoxy/MMT master batch as well as postcuring condition.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.142-146
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• 2008

Titanium silicalite-1 catalyst was prepared using a $SiO_2-TiO_2$ xerogel and applied to allylchloride (ALC) epoxidation by $H_2O_2$ as oxidant in a batch reactor. The reaction temperature was varied from 25 to $55^{\circ}C$, and the concentrations of ALC and $H_2O_2$ were changed from 0.2 to 3 M and from 0.2 to 1.5 M, respectively. The kinetic data obtained were applied to the power rate law, Eley-Rideal, and a Langmuir-Hinshelwood model, and power rate law fits the experimental data best. Activation energy was 27.9 kJ/mol, and the reaction orders with respect to $H_2O_2$ and ALC were determined to be 0.41 and 0.52, respectively.

• Elastomers and Composites
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• v.49 no.4
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• pp.267-274
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• 2014

Self vulcanizable blend system for magnetorheological elastomer (MRE) has been studied by dispersing magneto responsible particle (MRP) on elastomeric matrix. Chloroprene rubber was modified with maleic anhydride (MAH) using heat and pressure which is called dynamic maleation process. The optimum graft ratio of MAH was found at 10 phr contents and reaction temperature of $100^{\circ}C$. This could be confirmed by FT-IR analysis. Epoxided natural rubber (ENR) was blended with modified CR-g-MAH for self vulcanization. The optimum amounts of ENR was 30 wt% in terms of scorch time and curing rate. MRE was manufactured by electromagnetic equipment and orientation of MRE was confirmed by SEM. Finally, it was found that the tensile strength of anisotropic-MRE was higher than that of isotropic-MRE and the hardness was reverse.

• Composites Research
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• v.36 no.3
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• pp.154-161
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• 2023

This study explored the feasibility of replacing a metal link with a carbon fiber/epoxy composite link and assessed its capacity to withstand a given load condition using failure criteria. The micromechanics of failure (MMF) criterion was employed to predict the failure mode of the composite material, and mechanical tests were conducted to obtain reference strength parameters for MMF. The findings revealed that the stress distribution was concentrated near the hole, and weaknesses were found around the hole and at the end of the link under bending conditions. Based on the failure index, matrix tensile failure was predicted at the end of the link, and fiber compression failure occurred near the hole. The methods and results obtained from this study can provide valuable guidelines for assessing the safety of composite materials under specific load conditions when replacing metal parts with carbon fiber/epoxy composites to achieve weight reduction.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.37-37
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• 2000

복합재료는 높은 무게비 강도 및 강성뿐만 아니라 우수한 재료 특성 때문에 경량화와 구조적 안전성이 요구되는 항공기의 구조재로서 사용이 증대되고 있다. 소형 민용항공기는 구조적 안전성과 함께 제작과 정비, 유지보수의 용이성이 중요시된다. 본 연구에서는 복합재료를 구조재로 사용하였을 때의 성능변화와 경량화 등을 검토하기 위하여 기존의 알루미늄 합금을 이용하여 설계된 소형 프로펠러 경항공기 날개의 구조재로서 복합재료를 사용하여 재설계하였다. 날개의 기본 구조는 스킨, 스파, 웹으로 구성된 상자형 단면으로 설계하였으며 날개의 구조재로서 탄소/에폭시를 사용하여 상용 유한요소해석코드인 NISAII를 이용하여 굽힘, 좌굴 등의 응력해석을 수행하였고 기존 설계된 날개와의 성능비교를 위하여 알루미늄 합금으로 설계된 날개를 모델링하여 해석한 결과와 비교하였다. 비교결과 구조재로 탄소/에폭시를 사용하여 설계된 날개가 무게비 성능면에서 더 우수함을 확인하였다.