• Journal of the Korean Applied Science and Technology
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• v.31 no.4
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• pp.595-601
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• 2014

The microstructures of NATM were examined by SEM, FT-IR spectra, tensile properties, mole % of [NCO/OH], and particle size analyzer. Growing concerns in the environment-friendly industries have led to the development of solvent-free formulations that can be cured. We had synthesized NATM(New Austria Tunnel Method) resin having the ability to protect stainless steel against corrosion. Comparing with general NATM resin and coatings, this resin that synthesized with polyurethane and epoxy was highly stronger in intensity and longer durability. Hybrid resin was composed of polyols, MDI, epoxy, silicone surfactant, catalyst and crosslink agent, and fillers. Moreover, fillers such as fume silica not only accelerated the curing rate but also improved the physical property as thermal barriers. The rigid segments of synthetic resin in mechanical properties were due to fume silica and the increase the mole% of [NCO/OH] for corrosion protection. In conclusion, the hybrid resin microstructure with crosslink agent and fume silica are good material for thermosetting coating of metal substrates such as stainless steel.

• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.73-79
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• 2017

Maleic anhydride (MAH) grafted polypropylene (PP-g-MAH) copolymers were prepared by changing MAH and styrene monomer (SM) content, using a twin screw extruder at $190^{\circ}C$. The grafting degree was measured by non-aqueous back titration method. The grafting degree of PP-g-MAH-SM copolymer was higher than that of PP-g-MAH at the same MAH content. PP-g-MAH-SM/kenaf fiber (KF) composites were also prepared by using a PP-g-MAH as a matrix at $200^{\circ}C$ and the KF content was fixed at 20 wt%. Based on the degradation temperature investigated by TGA, the thermal stability of PP-g-MAH-SM/KF composites was more enhanced than that of PP-g-MAH only. Mechanical properties of the composites were also improved when MAH and SM applied together. The adhesion degree between the copolymer and KF was confirmed by both SEM pictures of the fractured surface and contact angles.

• Journal of Adhesion and Interface
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• v.4 no.3
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• pp.33-40
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• 2003

In this work, diglycidyl ether of bisphenol A (DGEBA)/polyetherimide (PEI) blends were cured using 4,4-diaminodiphenyl methane (DDM). And the effects of addition of different PEI contents to neat DGEBA were investigated in the thermal properties and fracture toughness of the blends. The contents of contents of containing PEI were varied in 0, 2.5, 5, 7.5, and 10 phr. The cure activation energies ($E_a$) of the cured specimens were determined by Kissinger equation and the mechanical interfacial properties of the specimens were performed by critical stress intensity factor ($K_{IC}$). Also their surfaces were examined by using a scanning electron microscope (SEM) and the surface energetics of blends was determined by contact angles. As a result, $E_a$ and $K_{IC}$ showed maximum values in the 7.5 phr PEI. This result was interpreted in the increment of the network structure of DGEBA/PEI blends. Also, the surface energetics of the DGEBA/PEI blends showed a similar behavior with the results of $K_{IC}$. This was probably due to the improving of specific or polor component of the surface free energy of DGEBA/PEI blends, resulting in increasing the hydrogen bonding of the hydroxyl and imide groups of the blends.

• Clean Technology
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• v.18 no.1
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• pp.57-62
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• 2012

Aqueous poly (vinyl alcohol) (PVA) solution was modified by using hydrophobic vinyltriethoxysilane (VTEOS) and then adding different amounts of poly (acrylic acid) (PAA) to the resulting solution. Thermal and mechanical properties, contact angle, water vapor transmission rate (MVTR) and oxygen gas transmission rate ($O_2TR$) of the film samples fabricated by these solutions were investigated. The glass transition temperature (Tg) of the VTEOS-modified films was sightly increased and the value remained unchanged according to the amount of PAA. The tensile strength of the VTEOS-modified films was found to be 9.48~10.72 $kg/mm^2$ which showed no significant difference compared with that of PVA. The film prepared with VTEOS-modified PVA/PAA (= 90/10), of which the swelling and solubility were measured to be 198% and 0%, respectively, showed improved water-resistance. The MVTR and $O_2TR$ for the PET film (thickness 50 ${\mu}m$) coated with VTEOS-modified PVA/PAA (= 90/10) film (thickness 2.5 ${\mu}m$) were measured to be 11.04 $g/m^2/day$ and 3.1 $cc/m^2/day$, respectively.

• Elastomers and Composites
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• v.34 no.1
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• pp.20-30
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• 1999

In this study, binary polyamide 6,6(PA 6,6)/ethylene-propylene rubber(EPM) or EPM-g-maleic anhydride(EPM-g-MA) blends and ternary PA 6,6/EPM/EPM-g-MA blends with various elastomer content were prepared in order to investigate the degree of influence of elastomer content and average particle size, morphology, and distribution of dispersed elastomer on mechanical and thermal properties of blends. According to the results, notched Izod impact strength and relative crystallinity of binary blends modified with EPM-g-MA as well as average particle size and distribution of dispersed elastomer in such blends were more improved than those of binary blends modified with EPM. Notched Izod impact strength of blend whose composition ratio(wt % ) was 70:30(PA 6,6 : EPM-g-MA) was the highest among the binary PA 6,6/EPM-g-MA blends. The impact strength was increased by 25 times and its relative crystallinity was increased by 7 times when compared with those of polyamide 6,6. In the case of ternary PA 6,6/EPM/EPM-g-MA blend of which composition ratio was 70:15:15(PA 6,6:EPM:EPM-g-MA), the elastomer was finely distributed with the average particle size of $0.56{\mu}m$. The Izod impact strength of this blend was the highest of all blends prepared with different elastomer content.

• Polymer(Korea)
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• v.38 no.1
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• pp.54-61
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• 2014

Water-soluble sulfobetaine chitosan (SCs) was prepared for a blending film with Bombyx mori silk fibroin (SF) by reacting chitosan with 1,3-propanesultone. A series of SF/SCs blended films were successfully prepared by mixing aqueous solutions of B. mori SF and SCs. The SF/SCs blended films were examined through spectroscopic and thermal analysis to determine the morphological changes of SF in the SCs. The effects of the SF/SCs blend ratios on physical and mechanical properties were investigated to discover the feasibility of using these films as biomedical materials such as artificial skin and wound dressing. X-ray analysis showed good compatibility between the two biopolymers. The in vitro degradation behavior of the SF/SCs blended films was systematically investigated for up to 8 weeks in phosphate buffered saline solution at $37^{\circ}C$ and showed a mass loss of 46.4% after 8 weeks. All films showed no cytotoxicity by MC3T3-E1 assay. After 3 days of culture, the relative cell number on all the SF/SCs films was slightly lower than that of an optimized tissue culture plastic.

• Journal of the Korea Convergence Society
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• v.12 no.12
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• pp.145-151
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• 2021

This study aimed to investigate the efficient conduct of HA coating on Ti Gr4 for the practical use of medical device. Ti Gr4 alloy specimens measuring 𝜱 25mm × 1mm were sprayed with hydroxyapatite using thermal spray according to ASTM F1185-88. The surface was evaluated at #120, #400, #1,000 sandpaper and barrel finishing. Each coating properties was analyzed using SEM, UTS 20,000psi cap. and in vitro cytotoxicity. Surface morphology consists of well molten particles with very little resolidified or unmolten areas. The average Ca/P ratio is 1.74 which is in good agreement with theoretical value of 1.67. The average roughness Ra is very representative of roughness of specimen. The coatings are dense and well adhered to the substrate. The average bond strength was 61.74 MPa with a standard deviation of 4.06 which indicates fairly reliable results for ASTM 633 type tests. Variations in results from jig design, epoxy used, crosshead speeds etc. in vitro cytotoxicity result had a Grade 3. The results of the study are expected to be helpful in osseointegration and plasma-spray HA coated Ti Gr4 are more satisfactory in HA coating thickness elevation which is preferable to any other system.

• Elastomers and Composites
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• v.37 no.4
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• pp.244-257
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• 2002

A thermotropic liquid crystalline polymer(TLCP) which has flexible butylene/hexylene spacers in the main chain and a triad aromatic ester type mesogenic unit containing a naphthyl group was prepared by solution polycondensation. The in-situ composites based on poly(ethylene 2,6-naphthalate) (PEN) and a thermotropic liquid crystalline polymer(TLCP) were prepared and melt spun at different TLCP contents and different draw ratios to produce monofilaments. Blends of the TLCP with PEN were investigated in terms of thermal, mechanical properties and morphology. The TLCP synthesized showed nematic mesophasic behavior and its transition temperature to isotropic melt from mesophase was 249℃. The blends showed well dispersed TLCP phases in the PEN matrix without macroscopic phase separation. Inclusion of TLCP in the blends decreased the cold crystallization temperature of PEN in the blend, therefore, the TLCP acts as a nucleating agent in the blend and showed good interfacial adhesion between the dispersed LCP phases and PEN matrix with domain sizes 40~50 nm in diameter and well developed fibrillation in the monofilaments. The TLCP acted effectively as a reinforcing material in the PEN matrix at the 10wt% level, it led to an increase of initial modulus up to 270% and tensile strength by 235%, while the elongation rate increasing with higher draw ratios.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.3
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• pp.111-118
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• 2023

MXene, a two-dimensional transition metal carbide or nitride, has recently attracted much attention as a lightweight and flexible electromagnetic shielding material due to its high electrical conductivity, good mechanical strength and thermal stability. In particular, the Ti-based MXene, Ti₃C₂T_x and Ti₂CT_x are reported to have the best electrical conductivity and electromagnetic shielding properties in the vast MXene family. Therefore, in this study, Ti₃C₂T_x and Ti₂CT_x films were prepared by vacuum filtration using Ti₃C₂T_x and Ti₂CT_x dispersions synthesized by interlayer metal etching and centrifugation of Ti₃AlC₂ and Ti₂AlC. The electrical conductivity and electromagnetic shielding efficiency of the films were measured after heat treatment at high temperature. Then, X-ray diffraction and photoelectron spectroscopy were performed to analyze the structural changes of Ti₃C₂T_x and Ti₂CT_x films after heat treatment and their effects on electromagnetic shielding. Based on the results of this study, we propose an optimal structure for an ultra-thin, lightweight, and high performance MXene-based electromagnetic shielding film for future applications in small and wearable electronics.

• Journal of Korea Foundry Society
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• v.38 no.5
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• pp.103-110
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• 2018

The effects of a heat treatment on the carbide formation behavior and mechanical properties of the cobalt-based superalloy X-45 were investigated here. Coarse primary carbides formed in the interdendritic region in the as-cast specimen, along with the precipitation of fine secondary carbides in the vicinity of the primary carbides. Most of the carbides formed in the interdendritic region were dissolved into the matrix by a solution treatment at $1274^{\circ}C$. Solutionizing at $1150^{\circ}C$ led to the dissolution of some carbides at the grain boundaries, though this also caused the precipitation of fine carbides in the vicinity of coarse primary carbides. A solution treatment followed by an aging treatment at $927^{\circ}C$ led to the precipitation of fine secondary carbides in the interdendritic region. Very fine carbides were precipitated in the dendritic region by an aging heat treatment at $927^{\circ}C$ and $982^{\circ}C$ without a solution treatment. The hardness value of the alloy solutionized at $1150^{\circ}C$ was somewhat higher than that in the as-cast condition; however, various aging treatments did not strongly influence the hardness value. The specimens as-cast and aged at $927^{\circ}C$ showed the highest hardness values, though they were not significantly affected by the aging time. The specimens aged only at $982^{\circ}C$ showed outstanding tensile and creep properties. Thermal exposure at high temperatures for 8000 hours led to the precipitation of carbide at the center of the dendrite region and an improvement of the creep rupture lifetimes.