• Elastomers and Composites
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• v.37 no.1
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• pp.21-30
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• 2002

Core-shell polymers of methyl methacrylate/styrene pair were prepared by sequential emulsion polymerization in the presence of sodium dodecyl benzene sulfonate(SDBS) as an emulsifier using ammonium persulfate(APS) as an initiator. The characteristics of these core-shell polymers were evaluated. Core-shell composite latex has the both properties of core and shell components in a particle, where as polymer blonds or copolymers show a combined properties from the physical properties or two homopolymers. This unique behavior of core-shell composite latex can be used in many industrial fields. However, in preparation of core-shell composite latex, several unexpected phenomina are observed, such as, particle coagulation, low degree of polymerization, and formation of new particles during shell polymerization. To solve the disadvantages, we studied the effects of surfactant concentrations, initiator concentrations, and reaction temperature on the tore-shell structure or PMMA/PSt and PSt/PMMA. Particle size and particle size distribution were measured by using particle size analyzer, and the morphology of the core-shell composite latex was observed by using transmission electron microscope. Glass transition temperature($T_g$) was also measured by using differential scanning calorimeter. To identify the core-shell structure, pH of the composite latex solutions were measured.

• Journal of Sericultural and Entomological Science
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• v.45 no.1
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• pp.34-45
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• 2003

Silk was treated with calcium hydroxide for degumming at different treatment times, temperatures and Ca(OH)$_2$ concentration to optimize degumming conditions in this thesis. After degumming, soluble and insoluble sericin were seperated and then the soluble sericin was characterized by measuring the average degree of polymerization (D.P.), lysinoalanine (LAL) content, DSC, and by amino acid analysis. And degummed silk fibroin was characterized by measuring tenacity and SEM. Degumming loss was increased by increasing the treatment time and temperature until about 30 minutes. After then, a slight difference was found along with treatment times at the Ca(OH)$_2$ concentrations of 0.07% and 0.1% solutions. After degumming, insoluble sericin ratio on degumming solution was increased by increasing treatment temperature at Ca(OH)$_2$ 0.04% solution. At the concentration Ca(OH)$_2$ of 0.07%, a soluble ratio was almost 100% regardless of treatment time and temperature. At the beginning of treatment, insoluble ratio was high at Ca(OH)$_2$ 0.1% solution but it was decreased by increasing treatment time. At the Ca(OH)$_2$ concentration of 0.04%, D.P. of soluble sericin was maintained as a constant value of 10 at 100$^{\circ}C$ although treatment time was increased. However, at 80$^{\circ}C$ and 90$^{\circ}C$, it was hard to prepare a soluble sericin having a constant D.P. by increasing treatment time. At the Ca(OH)$_2$ concentration of 0.07%, D.P. was almost 10 irrespective of treatment temperature and time. Soluble sericins with high D.P. of 20∼30 were obtained at 0.1% and 100$^{\circ}C$. LAL was not detected in soluble sericin. As the results of amino acid analysis, it showed that Ca(OH)$_2$ degumming reduced the contents of hydroxy amino acids like Ser., Thr. and Tyr. In DSC analysis of soluble sericin, endothermic peak by thermal deformation and pyrolysis showed at 189$^{\circ}C$ and at 299$^{\circ}C$, respectively. The tenacities of degummed silk were 15∼30% lower than that of raw silk. And it was decreased with increasing treatment time. From the morphological study, the thickness of degummed silk fibroin became thinner by increasing degumming loss. The roughness of a silk fibroin surface was appeared as treatment concentration was increased.

• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.328-328
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• 2002

PET 絲의 특성은 중합단계나 방사, 연신 등의 원사제조공정의 공정조건뿐 아니라 사가공 공정을 거쳐 winding, 2-for-1 twisting, sizing등의 제직준비 공정과 제직 공정에 의해서 물리적인 특성이 크게 변화한다. 이러한 공정을 거치면서 품질과 성능변화에 절대적인 영향을 미치는 공정요소는 온도, 시간 그리고 장력이다(37). PET 絲는 공정을 거치면서 역학적 특성이나 열적 특성의 차이로 인해 공정관리 면에서 middle stream의 중소기업들이 시행착오에 의해 공정조건을 결정하는 현실에 처해있다. (중략)

• The korean journal of orthodontics
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• v.25 no.5 s.52
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• pp.605-611
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• 1995

The purpose of this study was to evaluate effects of time on shear bond strengths of a light-cured glass ionomer cement and chemically cured resin cement to enamel, and to observe the failure patterns of bracket bondings. Shear bond strength of a light-cured glass ionomer cement were compared with that of a resin cement. Metal brackets were bonded on the extracted human bicuspids. Specimens were subjected to a shear load(in an Instron machine) after storage at room temperature for 5 and 15 minutes; after storage in distilled water at $37^{\circ}C$ for 1 or 35 days. The deboned specimens were measured In respect of adhesive remnant index. The data were evaluated and tested by ANOVA, Duncan's multiple range test, and t-test, and those results were as follows. 1. The shear bond strength of light-cured glass ionomer cement is higher than that of resin cement at 5 and 15 minutes. 2. The shear bond strengths of both light-cured glass ionomer cement and resin cement increase with time. There was no significant difference in those of both 1 day group and 35 day group 3. Light-cured glass ionomer cement is suitable as orthodontic bracket adhesives

• Elastomers and Composites
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• v.48 no.1
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• pp.39-45
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• 2013

Melt grafting of citraconic acid (CCA) onto an ethylene-propylene-diene terpolymer (EPDM) with various peroxide initiators was performed using a Haake Rheocorder. Finding the optimum running condition and concentration is critical for effective grafting and performance of grafted material. Therefore, this study focused on the effects of mixing (reaction) condition and monomer/initiator dosages on the grafting degree, grafting efficiency and crosslinking degree (gel content), melt flow index and mechanical properties of CCA-g-EPDM. As the grafting degree/crosslinking degrees increased, the tensile strength increased significantly, but elongation at break and melt flow index decreased. The initiator 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane (T-101) appeared to meet for the best grafting(2.31%). The grafting degree increased markedly with increasing monomer CCA/initiator T-101 contents. The grafting degree also increased with increasing mixing temperature/time, and then leveled off or decreased/increased a little. The optimum monomer/initiator dosages and reaction temperature/time were found to be about 5/0.05 wt% and $180^{\circ}C$/15min, respectively.

• Proceedings of the Korean Fiber Society Conference
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• 2000.04a
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• pp.253-256
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• 2000

• Journal of the Korean Chemical Society
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• v.24 no.1
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• pp.80-85
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• 1980

The free radical copolymeriaztion of N-vinylurea(VU) with vinyl acetate (VAc) was carried out at $60^{\circ}C$ in three solvents. VU-vinyl alcohol(VA) copolymers were prepared by the methanolysis of the VU-VAc copolymers. From the nitrogen content measurements of VU-VA copolymers, the monomer reactivity ratios for the VU-VAc copolymerization and the values of Alfrey-Price's Q and e for VU were determined. These Q and $\varrho$ values obtained in the cases of using methanol and methanol-dioxane as the polymerization solvents are comparable with those found for other monomers which have > NCO-pendent groups. The $\varrho$ value indicates that the urea group of VU is a electron-donating group. The copolymerization parameter of VU shows a strong effect of the solvents. These results are interpreted to be that VU is in equilibrium with its tautomer at the polymerization temperature.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.33-37
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• 2002

The phosphorescence powder, $SrA1_2O_4:Eu^{2+}$, synthesized by a Polymerized Complex Method(PCM), has been compared with that by a Solid-State Reaction(SSR), and their luminescence characteristics have been studied. The PCM powders were synthesized at $900^{\circ}C$ and the SSR powders at $1200^{\circ}C$. The size of PCM powders was about $0.1{\mu}m$ and one tenth of that of the SSR powders, which was due to the lower synthesized temperature. On the other hand, residual carbon in the PCM powders decreased with an increase in the crystallinity of host lattice, which was responsible for the non-white color of the powders. Both powders showed the maximum luminescence peaks around 520nm in the wave length at room temperature. However, the peak position for the PCM powders was shifted to a slightly lower wavelength and the value of half-width of the peak was broad comparing to that of the SSR powders, and the peak intensity decreased significantly. Such a change in the luminescence characteristics was due to the large difference in size for two types of powders and partly the residual carbon in the PCM powders.

• Applied Chemistry for Engineering
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• v.26 no.1
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• pp.86-91
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• 2015

The MPPO (3-methyl-1-phenyl-2-phospholene-1-oxide) was prepared by using various polymerization inhibitors such as BHT (2,6-di-tert-butyl-4-methylphenol), TBC (4-tert-butylcatechol), and copper stearate. The MPPO was confirmed by the analysis using FTIR, $^1H$-NMR, and GC/MS regardless of the type of inhibitors. The yield of MPPO increased with the increase of reaction time, whereas the purity of MPPO decreased slightly. The yield and purity of MPPO increased with temperature, but the MPPO prepared by using copper stearate as a polymerization inhibitor exhibited no changes in the purity. The amount of inhibitors had no effect on the yield of MPPO. The purity of MPPOs increased with the amount of inhibitors, but the MPPO prepared by using BHT showed no changes of the purity. We found that the MPPO prepared by using copper stearate exhibited the highest catalytic activity for diphenylcarbodiimide synthesis.

• Biomedical Science Letters
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• v.2 no.2
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• pp.241-247
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• 1996

Poor yields of amplified DNAs could be resulted in polymerase chain reaction(PCR) processes with G+C-rich DNA primers because of their high $T_m$ values. To maximize the yields of amplification in PCR processes with G+C-rich primers, we compared the yields of amplified DNA fragments according to the concentrations of specific denaturants added to the reaction mixture of PCR system. With addition of the mixture of 2.5% glycerol and 1.25% formamide, or 2.5% dimethyl sulfoxide to the reaction cocktail, respectively, remarkable increases in the yields of amplified DNA fragments were not observed in the PCR systems with G+C-low primers of Lyl chromosomal gene from Borrelia burgdorferi but observed in the PCR system with G+C- ich primers of Is900 gene from Mycobacterium parahberculosis. Although we were not practically able to discriminate the yields of PCR DNAs according to the concentrations used in this study, addition of the mixture of 5% glycerol and 2.5% formamide, or 5% DMSO tended to increase the production of extra bands.