• Polymer(Korea)
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• v.25 no.2
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• pp.168-176
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• 2001

The effect of novel N-crotyl-N,N-dimethyl-4-methylanilinium hexafluoroantimonate (CMH) curing agent as a thermal latent initiator on thermal behaviors, rheological properties, and thermal stability of diglycidylether of bisphenol A (DGEBA) epoxy cationic system was investigated. From DSC measurements of DGEBA/CMH system, it was shown that this system exhibits an excellent thermal latent characteristic at a given temperature. The conversion and conversion rate of DGEBA/CMH system increased with increasing the concentration of initiator, due to high activity of CMH. Rheological properties of the system were investigated under isothermal condition using a rheometer The gelation time was obtained from the analysis of storage modulus (G'), loss modulus (G"), and damping factor (tan $\delta$). As a result, the reduction of gelation time was affected by high curing temperature and concentration of CMH, resulting in high degree of network formation in cationic polymerization, due to difference of activity. The thermal stability of the cured epoxy resin was discussed in terms of the activation energy for decomposition and thermal factors determined from TGA measurements.ents.

• Elastomers and Composites
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• v.33 no.3
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• pp.185-192
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• 1998

This study was investigated on the physical properties of synthetic rubber compounds containing silica and silane copuled silica. Surface area and pore volume of silane copuled silica appeared to be low compared with those of pure silica because silane coupling agent blocks the pore of silica surface during silanization reaction. Silica with large surface area and high structure showed the short scorch time$(t_5)$ and rapid cure rate. The silane coupled silica showed the shorter scorch time and more rapid cure rate than pure silica because of the of effect of sulfur in the silane coupling agent(Si 69), The high value of $N_2SA$ minus CTAB com-pared with surface area and structure of silica showed the high 300% modulus. Also, the surface area and structure of silica did not affected the amount of PICO loss that indicate the abrasion resistance but affected the amount of cut and chip loss.

• Korean Journal of Materials Research
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• v.7 no.3
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• pp.244-250
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• 1997

본 연구에서는 에폭시/산무수물계에 경화촉진제를 첨가한 시료를 몰드(mold)내에서 등온 경화시킬 때 시료 내부의 온도변화를 측정하여 얻어진 온도-시간 곡선(temperature-time profile)을 조사하였다. 실험에 사용한 경화촉진제의 종류는 1-cyanoethy1-2-ethy1-4-methy1 imidazole(1E4MZ-CN), N,N-dimethy1 benzy1 amine(BDMA), 2,4,6-tris(dimethy1-aminomethy1)-phenol(DMP-30)이며 그들의 농도(c)는 1.0,1.5,2.0,2.5,phr그리고 경화온도(T$_{cure}$ )는 65,70,85,95$^{\circ}C$로 하였다. 경화가 진행되는 동안 시료내부의 온도는 초기에 경화온도로 상승한 후 본격적인 경화 반응이 일어나기 시작하여 온도가 급격히 상승하였다가 다시 감소하는 양상을 보였다. 온도-시간 곡선상에 나타나는 온도가 최고로 상승되는 시점(t$_{peak}$ )과 그 때의 온도(T$_{peak}$ )는 촉진제의 종류와 농도 그리고 경화온도에 의하여 영향을 받았다. 사용한 경화촉진제중에 DMP-30이 가장 짧은 t$^{peak}$ 값을 가져 가장 우수한 촉진 효과를 갖는 것으로 나타났으며, T$_{peak}$ 는 촉진제의 농도와 경화온도가 증가할수록 상승하였다. 그리고 경화촉진제의 농도와 경화온도의 변화에 따른 t$_{peak}$ 과 T$_{peak}$ 의 변화를 보면 촉진제 농도와 경화온도가 낮을 때 그 변화가 민감하여 2E4MZ-CN 이 가장 민감한 촉진제로 나타났으며 또한 T$_{peak}$ 에 영향을 주는 여러가지 요소들을 본 연구에서 얻어진 결과로부터 자세히 살펴보았다.

• Elastomers and Composites
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• v.33 no.4
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• pp.274-280
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• 1998

Order of reaction, rate constant, activation energy for vulcanization reaction, crosslinking density, and elastic constant of the network produced by sulfur curing were investigated on the SBR/BR blends containing silica and carbon black under same cure system. The reaction order was shown to be first order regardless of filler types. The carbon black filled rubber compounds showed higher rate constant compared to silica filled compounds. But activation energy appeared to be same regardless of filler type and rubber blend ratio. The crosslinking density and elastic constant is higher in the carbon black filled compound compared to silica filled compounds because of strong interaction between rubber and carbon black. On the other hand, crosslinking density and elastic constant were decreased with increasing the butadine rubber content in rubber blends. From the comparison of combined sulfur content in the vulcanized rubber, sulfur content in the silica filled compound become constant 20min later after reaction initiates but sulfur content in the carbon black filled compound become constant 10min later after reaction starts. The silica compound has a longer induction time ($t_2$) and optimum cure time($t_{90}$) compared to those of the carbon black filled compound.

• The Korean journal of helicobacter and upper gastrointestinal research
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• v.18 no.4
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• pp.264-270
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• 2018

Gastrointestinal stromal tumor (GIST) is a mesenchymal tumor derived from Cajal cells originating from the myotonic plexus. The expression of tyrosine kinase (KIT) membrane receptors that are active on KIT is inhibited by the KIT inhibitor imatinib mesylate. GISTs are resistant to conventional chemotherapy, and radiation therapy is not significantly beneficial for GISTs. With the development of imatinib mesylate, approximately 81.6% of patients with advanced and metastatic GIST exhibit an effect above the stabilization response, thereby increasing the survival time. However, imatinib mesylate alone is unlikely to cure metastatic GISTs. Even with a partial or stable response, imatinib mesylate may be used for a longer time period. However, resection of grossly visible lesions should be considered for patients with a stable response during surgical treatment. In this study, we present a case of GIST with liver metastasis after imatinib mesylate treatment, which was followed up without recurrence after partial resection.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.17-40
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• 2000

Resin cements are used for cementing indirect esthetic restorations such as resin or porcelain inlays. Because of its limitations in curing of purely light cured resin cements due to attenuation of the curing light by intervening materials, dual cured resin cements are recommended for cementing restorations. The physical properties of resin cements are greatly influenced by the extent to which a resin cures and the degree of cure is an important factor in the success of the inlay. The purpose of this study was to evaluate the influence of porcelain thickness and exposure time on the polymerization of resin cements by measuring the microhardness and the degree of conversion, to investigate the nature of the correlation between two methods mentioned above, and to determine the exposure time needed to harden resin cements through various thickness of porcelain. The degree of resin cure was evaluated by the measurements of microhardness [Vickers Hardness Number(VHN)] and degree of conversion(DC), as determined by Fourier Transform Infrared Spectroscopy(FTIR) on one light cured composite resin [Z-100(Z)] and three dual cured resin cements [Duo cement(D), 3M Resin cement(R), and Dual cement(DA)] which were cured under porcelain discs thickness of 0mm, 1mm, 2mm, 3mm with light exposure time of 40sec, 80sec, 120sec, and regression analysis was performed to determine the correlation between VHN and DC. In addition, to determine the exposure time needed to harden resin cements under various thickness of porcelain discs, the changes of the intensity of light attenuated by 1mm, 2mm, and 3mm thickness of porcelain discs were measured using the curing radiometer. The results were obtained as follows ; 1. The values of microhardness and the degree of conversion of resin cements without intervening porcelain discs were 31~109VHN and 51~63%, respectively. In the microhardness Z was the highest, followed by R, D, DA. In the degree of conversion, D and DA was significantly greater than Z and R(p<0.05). 2. The microhardness and the degree of conversion of the resin cements decreased with increasing thickness of porcelain discs, and increased with increasing exposure time, D and R showed great variation with inlay thickness and exposure time, whereas, DA showed a little variation. 3. The intensity of light through 1mm, 2mm, and 3mm porcelain inlays decreased by 0.43, 0.25, and 0.14 times compared to direct illumination, and the respective needed exposure times are 53 sec, 70 sec, and 93 sec. In D and R, 40 sec of light irradiation through 2mm porcelain disc and 80 sec of light irradiation through 3mm porcelain disc were not enough to complete curing. 4. The microhardness and the degree of conversion of the resin cements showed a positive correlationship(R=0.791~0.965) in the order of R, D, Z, DA. As the thickness of porcelain discs increased, the decreasing pattern of microhardness was different from that of the degree of conversion, however.

• Computational Structural Engineering
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• v.9 no.4
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• pp.181-187
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• 1996

This paper concerns the singular thermal stresses at the interface corner between the elastic fiber and the viscoelastic matrix of a two-dimensional unidirectional laminate model induced during cooling from cure temperature down to room temperature. Time-domain boundary element method is employed to investigate the nature of residual thermal stresses at the interface. Numerical results show that very large stress gradients are present at the interface corner and such stress singularity might lead to local yielding or fiber-matrix debonding.

• Elastomers and Composites
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• v.17 no.4
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• pp.215-225
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• 1982

The purpose of this study is to get comparitive results on the combined accelerator systems comprised of MBT, MBTS, DPG and CBS with TMTD, TMTM and Zn-MDC to SBR compound. Vulcanization characterstics and physical properties of the combined accelerators have been studied by means of the Mooney viscometer, the Monsanto disc rheometer, tensile testing machine, aging chamber and so on. According to the test results, DPG, MBT and Zn-MDC system have show faster Mooney scorch time and optimum cure time than other systems. The Vulcanizate comprise of DPG, MBT and TMTD accelerator system has taken adventage of tensile strength, elongation, 100% modulus, resilience, compresion set.

• Elastomers and Composites
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• v.32 no.1
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• pp.20-28
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• 1997

This study have Investigated the effect of various factors related to the physical properties of vulcanizated rubber compounds. rubber type, carbon black type and carbon black loading were selected as main factors and evaluation were tested by tables of orthogonal arrays with 3 factors and 3 levels. rubber types have affected cure time, tensile strength, and $T_g$ as main factor and carbon black loading have affected viscosity, scorch time, maximum torque, hardness, 300% modulus, rebound, heat build-up, $0\;&\;60^{\circ}C$ tangent delta, PICO and CUT/CHIP loss as main factor but the effects of carbon black type have affected only bound rubber content.

• Elastomers and Composites
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• v.23 no.3
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• pp.223-229
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• 1988

The effect of triazine thiol derivative on the physical properties of silica-polychloroprene(CR) composites and glass fiber(MGF)-CR composites was investigated. Optimum cure time of the MGF composites filled with 2-dibuthylamino-4, 6-dithiol-s-triazine(DBT) was the fastest one, while maximum torque was the best in case of the silica composites filled with s-triazine-2,4,6-trithiol(TAT) on the Oscillating Disk Rheometer(ODR) test. Stress-strain curves of the composites showed that the physical properties such as 100% modulus, 300% modulus, tensile strength of the silica composites filled with DBT was very satisfactory and the silica composites filled with TAT was higher density of crosslinking than other crosslinked elastomer. In aging properties, elastomer filled DBT and TAT were progress post-curing reaction with increasing of aging time and it have been improved the tensile strength and crosslinking density.