• Elastomers and Composites
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• v.51 no.2
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• pp.106-112
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• 2016

Maleimidopropyltriethoxysilane grafted natural rubber (MISNR) was prepared by reaction of maleic anhydride grafted natural rubber and 3-aminopropyl triethoxysilane. MISNR was used as the compatibilizer of natural rubber/silica composites. The composites were prepared by two-step mixing procedures. The final mixtures were cured with optimum cure condition, which was established by a rheometer. Effects of the amounts of compatibilizer in the composites on the cure characteristics, morphology, thermal stability, and physical and mechanical behaviors were investigated. The composites having MISNR had shown cure characteristics and physical and mechanical properties superior to those without MISNR. Silica particles in the former appeared to be more uniform and reduced in size compared with the latter. The effects of the types of silica were also evaluated.

• Bulletin of the Korean Chemical Society
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• v.20 no.11
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• pp.1329-1334
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• 1999

The curing characteristics of diglycidyl ether of bisphenol A (DGEBA) with diaminodiphenylmethane (DDM) as a curing agent were studied using differential scanning calorimetry (DSC), rheometrics mechanical spectrometry (RMS), and dielectric analysis (DEA). The isothermal curing kinetics measured by DSC were well represented with the generalized auto-catalytic reaction model. With the temperature sweep, the inverse relationship between complex viscosity measured by RMS and ionic conductivity obtained from DEA was established indicating that the mobility of free ions represented by the ionic conductivity in DEA measurement and the chain segment motion as revealed by the complex viscosity measured from RMS are equivalent. From isothermal curing measurements at several different temperatures, the ionic conductivity contribution was shown to be dominant in the dielectric loss factor at the early stage of cure. The contribution of the dipole relaxation in dielectric loss factor became larger as the curing further proceeded. The critical degrees of cure, at which the dipolar contribution in the dielectric loss factor starts to appear, increases as isothermal curing temperature is increased. The dielectric relaxation time at the same degree of cure was shorter for a sample cured at higher curing temperature.

• Applied Chemistry for Engineering
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• v.5 no.6
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• pp.967-974
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• 1994

We studied the cure kinetics of the DGEBA(Diglycidyl ether of bisphenol A)/MDA(4, 4' -methylene dianiline)/MN(Malononitrile)/HQ(Hydroquinone) system by Barrett method and Integral method with dynamic runs of differential scanning calorimetry(DSC). Kinetic parameters such as activation energy and pre-exponential factor were obtained and reaction order was estimated roughly supposing that present system was adjusted to nth order reaction. The MN(Malononitrile) was introduced as a chain extender and HQ(Hydroquinone) as a reactive accelerator or catalyst.

• Korean Journal of Materials Research
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• v.11 no.9
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• pp.786-791
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• 2001

$\alpha$,$\omega$-Bis(4-glycidyloxybenzylidene-4-aminophenyl)methane (BGBAM) was synthesized from the initial materials, 4-hydroxylbenzaldehyde (HBA), 4,4'-methylenedianiline (MDA) and epichlorohydrin. The DSC trace for BGBAM shows two endotherms associated with the liquid crystalline phase transition around $104.2^{\circ}C$ and the isotropic transition around $171.2^{\circ}C$, and it also has a broad exotherm in the range of $178~300^{\circ}C$ due to the anionic homopolymerization of BGBAM. DSC curve for the curing of BGBAM with hexamethylene diamine (HMD) shows an endothermic peak around $93^{\circ}C$ attributed to the melting of BGBAM. It also has three exothermic peaks around $128.4^{\circ}C$ and $180.2^{\circ}C$ associated with the epoxide-amine reaction and weak peak in the range of $200~263^{\circ}C$ related to the anionic homopolymerization between the unreacted epoxide groups. The activation energy values of cure reaction by Kissinger method are 66.5, 67.3 and 90.6 kJ/mol for $T_{pl},\; T_{p2}\; and \;T_{p3},\; respectively$. The kinetic parameters by isoconverional method are similar value to those from Kissinger method.

• Journal of Veterinary Science
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• v.22 no.6
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• pp.78.1-78.10
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• 2021

Background: Recurrent subclinical mastitis (RScM) due to resistant bacteria has low clinical and bacteriological cure rates, often requiring the culling of cows. The sequential intramammary administration of enrofloxacin hydrochloride-dihydrate (enro-C) followed by ceftiofur HCl may be useful for treating these cases. Objectives: This study assessed the bacteriological and clinical cure-efficacies of the sequentially intramammary administration of enro-C, followed by ceftiofur HCl to treat RScM in Holstein/Friesian cows. Methods: This trial was conducted in a herd with a high prevalence of RScM, and 20 Holstein/Friesian cows were included: 45% suffering subclinical mastitis and 38.9% of the mammary quarters affected. Twenty-nine bacterial isolates in vitro resistant to enro-C were obtained (coagulase-negative Staphylococcus spp, 55.2%; Staphylococcus aureus, 27.6%; Escherichia coli, 6.9%; Streptococcus uberis, 6.9%; Corynebacterium bovis, 3.4%). Polymerase chain reaction-isolated the following genes linked to enro-C resistance: chromosomal (gyrA) and plasmid (aac(6')-lb-cr). The treatments were as follows: twice-daily intramammary infusions of enro-C (300 mg/10 mL) for 5 days. Cows clinically considered treatment failures were also treated with intramammary ceftiofur (125 mg/10 mL, twice daily for 5 days. The clinical and bacteriological cure rates were carried out when completing each treatment phase and at 14 and 21 days, aided by a California mastitis test, somatic cell count, and failure to identify the initially causative bacteria. Results: Enro-C achieved 65% clinical and bacteriological cure rates, and 100% cure rates were obtained after the rescue treatment with ceftiofur HCl. Conclusions: Outstanding clinical and bacteriological cure rates in cows affected by RScM were achieved with the consecutive intramammary infusions of enro-C, followed by ceftiofur HCl.

• 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.

• Korea-Australia Rheology Journal
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• v.19 no.1
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• pp.7-16
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• 2007

A dynamic Monte Carlo percolation grid simulation is used to predict the cure behaviour of thermoset materials. Molecules are distributed in a fixed grid and a probability of reaction is assigned to each pair of neighbouring units considering both reaction rates and diffusion. The concentration and network characteristics are predicted throughout the whole curing process and compared to experimental data for an epoxy-amine matrix.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.179-179
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• 1994

• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.1046-1051
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• 1999

Cure behavior and thermal stability of the different ratio of diglycidylether of bisphenol A(DGEBA)/trimethylolpropane triglycidylether(TMP) epoxy blends initiated by 1 wt % N-benzylpyrazinium hexafluoroantimonate (BPH) as a cationic latent catalyst were studied using DSC and TGA, respectively. Latent properties were performed by measurement of the conversion as a function of temperature using dynamic DSC. Dynamic DSC thermograms of DGEBA/TMP blends revealed that the weak peak was formed by complex formation between the hydroxyl groups in DGEBA and BPH, and between epoxides and BPH in low temperature ranges. The strong peak was considered as an exothermic reaction by the formation of three-dimensional network in high temperature ranges. Isothermal DSC revealed that the reaction rate of the blends was found to be higher than that of the neat TMP. The thermal stabilities in the cured resins were increased with increasing the DGEBA content. These results could be interpreted in terms of the stable aromatic structure, existence of hydroxyl group and high molecular weight of DGEBA.

• Composites Research
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• v.21 no.1
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• pp.16-21
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• 2008

The cure behavior of epoxy resin with a conventional amide-type hardener(HD) was investigated in the presence of castor oil(CO), cashew nut shell liquid(CNSL) and CNSL-formaldehyde resin(CFR) by using a dynamic differential scanning calorimetry(DSC). The activation energy of curing reaction was also calculated based on the non-isothermal DSC thermograms at various heating rates. An one-stage curing was noted in the case of epoxy resin filled with CO, while the epoxy resin with CNSL and CFR showed a two-stage curing process. A competitive cure reaction was noted for the epoxy resin/CNSL(or CFR)/HD blends. In the absence of HD, the CFR showed lower values of curing enthalpy than that of CNSL. The activation energy of epoxy resin curing increased with increasing the CNSL and CFR loading.