• Composites Research
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• v.29 no.5
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• pp.282-287
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• 2016

p-DCPD (poly dicyclopentadiene) is the resin that the versatile mechanical properties can be changeable via the control of inner monomer and catalysts. In this work, to improve the strength of composites, surface treated MGF (milled glass fiber) was used as an reinforcement in p-DCPD by molybdenum (Mo) catalyst matrix. The optimum concentration of surface treatment was obtained and the cohesion of MGF themselves increased with concentration. In case of 0.2 wt% silane concentration, the maximized mechanical properties of MGF/p-DCPD composite exhibited because of minimized MGF cohesion. When butyl silane showing minimizing cohesion was used as the optimized alkyl length, high tensile and flexure strength exhibited due to the steric hindrance effect among MGFs. Mechanical and their fractured surfaces of MGF/p-DCPD composites was compared for 4 different chemical functional groups. Norbornene functional groups containing similar chemical structure to DCPD matrix exhibited higher interfacial adhesion between MGFs and DCPD matrix.

• KSBB Journal
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• v.17 no.2
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• pp.153-157
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• 2002

A fusion protein, consisting of a human epidermal growth factor as the recognition domain and human angiogenin as the toxin domain, can be used as a targeted therapeutic against breast cancer cells among others. The fusion protein was expressed as an inclusion body in recombinant E. coli, yet when the conventional solution-phase refolding process was used the refolding yield was very low due to severe aggregation, probably because of the opposite surface charge resulting from the vastly different pl values of each domain. Accordingly the solid-phase refolding process, which exploits the ionic interactions between a solid matrix and the protein, was tried, however the ionic binding yield was also very low regardless of the resins and pH conditions used. Therefore, to provide a higher affinity toward the solid matrix, six Iysine residues were tagged to the N-terminus of the hEGF domain. When cation exchange resins, such as heparin- or CM-Sepharose, were used as the matrix, the adsorption capacity increased 2.5~3-fold and the subsequent refolding yield increased nearly 15-fold compared to the conventional process. A similat result was also obtained when an Ni-NTA metal affinity resin was used.

• Polymer(Korea)
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• v.33 no.3
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• pp.224-229
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• 2009

The dielectric properties of semi-IPN poly(phenylene oxide)(PPO) blend/$BaTiO_3$(BT) composites are investigated. The composites are fabricated via melt-mixing of crosslinker and peroxide in precursor PPO composite obtained by precipitating the suspension consisted of PPO, BT and toluene into methylethyl ketone, poor solvent of PPO. The permittivity of the precursor PPO composites shows higher value than that of integral-blended PPO composites by extruder and coincides with the theoretical value calculated by logarithmic rule of mixture. The blend of PPO and cross-linked triallyl isocyanurate is most effective for lowering the permittivity and loss tangent owing to the suppression of the orientation polarization of matrix. In contrast, 4,4'-(1,3-phenylene diisopropylidene) bisaniline, which has amine unit in its structure, increases the permittivity as well as loss tangent of the composite, but it has the ability to densify the matrix resin and the interfacial adhesion between the matrix and filler to improves flexural strength and modulus.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.46 no.1
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• pp.67-72
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• 2020

In this study, we attempted to obtain an active ingredient that inhibits the production of matrix metalloproteinase-1 (MMP-1) that breaks down collagen in human skin fibroblasts. More than 50 plant extracts were screened, and Lonicera japonica was selected for this study. The stem of L. japonica was extracted with 70% ethanol and fractions with solvents in the order of hexane, ethyl acetate, and butanol. MMP-1 production were significantly inhibited at the concentration of 50 ㎍/mL of the ethyl acetate layer and 200 ㎍/mL of the butanol layer. To get a fraction containing all of these effective components, 80% ethanol fraction (LJ F80) was obtained through HP20 resin column chromatography. The reference substance, loganin and LJ F80 inhibited dose-dependently MMP-1 production. At the same concentration, LJ F80 showed a higher inhibitory effect than loganin. The stability of this fraction was analyzed with HPLC while kept storing at 4 ℃, room temperature, and 40 ℃, for 16 week. The stability was maintained as ± 10% of initial value with reference loganin. Therefore, it is thought that LJ F80 of L. japonica may be used to improve wrinkles.

• Composites Research
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• v.36 no.3
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• pp.180-185
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• 2023

This paper investigates the impact of fiber dispersion on the internal structure and mechanical strength of SiC_f/SiC composites manufactured using spread SiC fibers. The fiber volume ratio of the specimen to which spread SiC fiber was applied decreased by 9%p compared to the non-spread specimen, and the resin slurry impregnated between the fibers more smoothly, resulting in minimal matrix porosity. In order to compare the fiber dispersion of each specimen, a method was proposed to quantify and evaluate the separation distance between fibers in composite materials. The results showed that the distance between fibers in the spread specimen increased by 2.23 ㎛ compared to the non-spread specimen, with a significant 42.6% increase in the distance between fiber surfaces. Furthermore, the 3pt bending test demonstrated a 49.3% higher flexural strength in the spread specimen, accompanied by a more uniform deviation in test data. These findings highlight the significant influence of SiC fiber dispersion on achieving uniform densification of the SiC_f/SiC matrix and increasing mechanical strength.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.530-539
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• 2003

The aim of this study was to evaluate the resistance to degradation of four commercial composite resins in an alkaline solution. The brands studied were Charisma, Filtek P 60, Palpique Estelite, and Spectrum. Preweighed discs of each brand were exposed to 0.1N NaOH solution at $60^{\circ}C$. After 2 weeks they were removed, neutralized with HCl, washed with water and dried. Resistance to degradation was evaluated on the basis of following parameters: (a) mass loss(%) - determined from pre-and post-exposed specimen weights; (b) Si loss(ppm) - obtained from ICP-AE analysis of solution exposed to specimens; and (c) degradation depth(${\mu}m$) - measured SEM and CLSM from polished circular sections of exposed specimens. The results were as follows: 1. The sequence of mass loss was in descending order by Palpique Estelite, Filtek P 60, Charisma, and Spectrum. 2. The sequence of the degree of degradation layer depth was in descending order by Filtek P 60, Charisma, Palpique Estelita, and Spectrum. 3. The sequence of the Si loss was in descending order by Chrisma, Spectrum, Palpique Estelite, and Filtek P 60. 4. The correlation coefficient between mass loss and degradation layer depth was relatively high(r=0.704, p<0.05). 5. When observed with SEM, destruction of bonding was observed between resin matrix and filler. 6. When observed with CLSM, degradation layer depth of composite resin surface was observed.

• Composites Research
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• v.18 no.2
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• pp.20-29
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• 2005

To evaluate the flexural deformation and strength of composite motor case above the glass transition temperature$(T_g),\;170^{\circ}C$, of resin material, a finite element analysis(FEA) model in which material non-linearity and progressive failure mode were considered was proposed. The laminated flexural specimens which have the same lay-up and thickness as the composite motor case were tested by 4-point bending test to verify the validity of FEA model. Also. mechanical properties in high temperature were evaluated to obtain the input values for FEA. Because the material properties related to resin material were highly deteriorated in the temperature range beyond $T_g$, the flexural stiffness and strength of laminated flexural specimen in $200^{\circ}C$ were degraded by also $70\%\;and\;80\%$ in comparison with normal temperature results. Above $T_g$, the failure mode was changed from progressive failure mode initiated by matrix cracking at $90^{\circ}$ ply in bottom side and terminated by delamination at the center line of specimen to fiber compressive breakage mode at top side. From stress analysis, the progressive failure mechanism was well verified and the predicted bending stiffness and strength showed a good agreement with the test results.

• Korean Chemical Engineering Research
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• v.54 no.3
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• pp.410-418
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• 2016

In this study, we prepared electrically conducting composites using epoxy resin of diglycidyl ether of bisphenol A (DGEBA) as a matrix, triethylenetetramine (TETA) as a hardener and nickel powder or multi-walled carbon nanotubes (MWCNTs) grafted with $-NH_2$ groups (MWCNT-$NH_2$) as electrically conducting fillers. Electrical conductivity of composite films were measured by coating on the slide glass with a doctor blade. We measured modification reactions of MWCNT and reaction of MWCNT-$NH_2$ with DGEBA epoxy resin by fourier transform infrared spectrometer (FTIR), thermogravimetric analyzer (TGA) and elemental analyzer (EA). Morphology of composites was investigated by scanning electron microscope (SEM) and sheet resistances of composites were measured by 4-point probe. We found $(9.87{\pm}1.09){\times}10^4{\Omega}/sq$ of sheet resistance for epoxy composite containing both 40 wt% nickel powder and 0.5 wt% of MWCNT-$NH_2$ as fillers, equivalent to epoxy composite containing 53.3 wt% nickel powder only as a filler.

• Journal of the Korean Wood Science and Technology
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• v.44 no.3
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• pp.406-414
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• 2016

The lignin-based carbon nanofiber reinforced epoxy composite has been prepared by immersing carbon nanofiber mat in epoxy resin solution in order to evaluate the physical and mechanical properties. The thermal and mechanical properties of the carbon nanofiber reinforced epoxy composite were analyzed using thermogravimetric analysis (TGA), differential scanning calorimeter (DSC) and tensile tester. It was found that the thermal properties of the carbon nanofiber reinforced epoxy composite improved, with its glass-transition temperature ($T_g$) increased from $90.7^{\circ}C$ ($T_g$ of epoxy resin itself) to $106.9^{\circ}C$. The tensile strengths of carbon nanofiber mats made from both lignin-g-PAN copolymer and PAN were 7.2 MPa and 9.4 MPa, respectively. The resulting tensile strength of lignin-based carbon nanofiber reinforced epoxy composite became 43.0 MPa, the six times higher than that of lignin-based carbon nanofiber mats. The carbon nanofibers were pulled out after the tensile test of the carbon nanofiber reinforced epoxy composite due to high tensile strength (478.8 MPa) of an individual carbon nanofiber itself as well as low interfacial adhesion between fibers and matrices, confirmed by the SEM analysis.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.1
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• pp.118-128
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• 2001

This study was performed to evaluate the toothbrush abrasion characteristics of seven commercially available light-cured cervical restorative materials one resin-modified glass-ionomer material(Fuji II LC) three polyacid-modified composites(Compoglass, Dyract, F2000), and three light-cured composites(Heliomolar, Palpique Estelite, UniFil F). All samples were stored in distilled water at $37^{\circ}C$ for 10 days. 2.0N of weight was loaded during the test and the abraded surfaces were examined with profilometer and SEM after 100,000 cycles. The results obtained were summarized as follows; 1. The highest hardness value of 79.7 was observed in the FT group and the lowest value of 20.0 was observed in the HM group. Results of Tukey test showed that an overall significant difference was indicated except the CG and DR groups(p<0.05). 2. The highest surface roughness was observed in the FL group and the lowest was observed in the UF group. Results of Tukey test showed the significant difference between the FL or FT and UF groups(p<0.05). 3. Statistically higher abrasion and surface roughness were observed for the dentifrice of paste type, Perio A+, than for that of gel paste type, Tom & Jerry. 4. The surface roughness values increased on the abraded surfaces because of the protrusion of filler particles due to selective removal of matrix resin.