• Polymer(Korea)
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• v.24 no.3
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• pp.418-430
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• 2000

A new hydroxylpropyl chitosan (HPCTO) capable of forming both thermotropic and lyotropic liquid crystalline phases was synthesized by reaction of alkali chitosan with propylene oxide and its solid films cross-linked with glyoxal were prepared by casting the liquid crystalline solution in methanol. The thermal and swelling properties of the cross-linked films were investigated. The films displayed fingerprint patterns characteristic of cholesteric liquid-crystalline phase, and their pitches increased with increasing temperature and cross-linker concentration. The cross-linked samples exhibited an anisotropic swelling in both water and methanol, suggesting that the two-dimensional cross-linking preferentially performs between HPCTO molecules. The degree of anisotropy highly depended on the solvent, but hardly on the cross-linker concentration investigated.

• Elastomers and Composites
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• v.48 no.4
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• pp.288-293
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• 2013

Crosslink characteristics of maleic anhydride-grafted EPDM (MAH-g-EPDM)/zinc oxide composite were investigated by weight losses after dichloroacetic acid (DCA)/toluene cosolvent extraction at different temperatures and by measurement of crosslink densities. The chemical changes were analyzed using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The weight losses by extraction at high temperature ($90^{\circ}C$) were remarkably greater than those at room temperature and those by DCA/toluene cosolvent extraction were greater than those by toluene one by more than 5 times. The crosslink densities were measured after the solvent extraction, and the second crosslink densities were higher than the first ones. The first crosslink density was lower when the extraction temperature was high, and it was much lower for the toluene extraction than for the DCA/toluene cosolvent extraction. The second crosslink density of the sample extracted with DCA/toluene cosolvent was greater than that extracted with toluene. The extracted components were depending on the extraction solvents and temperatures, for example; only strong crosslinked networks were remained when extracting with DCA/toluene cosolvent at high temperature, while only uncrosslinked polymer chains were extracted when extracting with toluene at room temperature. Therefore, crosslink characteristics of the MAH-g-EPDM/zinc oxide composite can be analyzed by comparison of the extracted components according to the extraction solvents and temperatures and by measurement of successive crosslink densities.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.541-548
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• 2009

A theoretical prediction model of fiber bridging curve was established based on the assumption that fibers are uniformly distributed on the crack surface. However, the distance between fibers and their orientation with respect to crack surface can greatly affect the prediction of fiber bridging curve. Since, the shape of fiber bridging curve is a critical factor for predicting the tensile stress-strain relationship of ECC, it is expected that the assumption of uniform distribution of fiber may cause a significant error when predicting the tensile behavior of ECC. To overcome this shortcoming, a new prediction method of stress-strain relation of ECC is proposed based on the modified fiber bridging curve. Only effective fibers are taken into account considering the effects of their orientation and distance between them. Moreover, the approach for formulating the tensile stress-strain relation is discussed, where a procedure is presented for obtaining important parameters, such as the first crack strength, the peak stress, the displacement at peak stress, tensile strain capacity, and the crack spacing. Subsequent uniaxial tensile tests were performed to validate the proposed method. It was found that the predicted stress-strain relations obtained based on the proposed modified fiber bridging curve exhibited a good agreement with experimental results.

• 한국노년학
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• v.31 no.1
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• pp.15-31
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• 2011

The purpose of this study is to explore the transition to retirement of the middle-aged in Korea according to the notion of "the career job" and "the bridge job". In order to scrutinize basic elements for the transition, three aspects such as the job history of the middle-aged, the characteristics of the demographic and economic status were investigated through the one to three wave of Korean Retirement and Income Study(KReIS). In addition, the characteristics of the career job and the bridge job were analyzed by both descriptive statistics and the conditional transition probability. Moreover, the influential factors to the job status of the middle-aged were examined by the multi-nominal logistic regression. The results of the study are as followed: first, gradual retirement is increasing in the transition to retirement of the middle-aged in Korea. Over time, the career job is decreasing whilst bridge job is increasing. However, the quality of the bridge job is poorer than the career job in terms of wage, employment status, industry, and occupation. Lastly, the middle-aged who work in the bridge job have vulnerable characteristics, so they work in the bridge job to supplement their economic needs. The results can be influential in the adjustment of the labor policies for the middle-aged in Korea. Moreover, the partial pension system could be a good alternative since the pension system is needed to protect the vulnerable situation of the middle-aged in Korea.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.423-424
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• 2003

셀룰로스 직물은 easy care 성능을 부여하기 위하여 가교제로 처리된다. 현재 공업적으로 가장 많이 이용되고 있는 DMDHEU와 같은 N-methyol 가교제는 공정 중 또는 처리된 제품의 저장 중에 발암물질인 포름알데하이드를 유리시키는 경향이 있어 포름알데하이드를 유리시키지 않는 가교결합제의 개발이 활발하게 연구되고 있다. 이러한 비포르말린계 가교제 중 글리옥살은 그 성능은 매우 뛰어나지만 DP 처리시 사용되는 촉매인 aluminium sulfate는 처리직물의 강도저하와 황변을 일으키는 단점을 지니고 있다[1]. (중략)

• Proceedings of the Korean Fiber Society Conference
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• 1998.10a
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• pp.133-136
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• 1998

DP가공은 면직물을 구성하고 있는 셀룰로오스 분자사이에 가교결합을 형성시켜 그 탄성한계를 높임으로써 구김을 방지할 목적으로 행해지는 가공이다. 현재 공업적으로 가장 많이 사용하고 있는 가교제는 셀룰로오스의 히드록시기와 ether형 가교를 형성하는 DMDHEU(dimethyloldihydroxyethylene urea) [1]이며 이와같은 ether형 가교제는 내가수 분해성이 높고 여러번의 세탁에도 견딜 수 있는 우수한 내구성을 지니고 있는 장점이 있으나 인체에 유해한 포름알데히드가 발생되는 단점이 있다. (중략)

• Proceedings of the Korean Fiber Society Conference
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• 2003.10b
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• pp.84-87
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• 2003

셀룰로즈 직물은 easy care 성능을 부여하기 위하여 가교제로 처리된다. 현재 공업적으로 가장 많이 이용되고 있는 DMDHEU와 같은 N-methyol계 가교제는 공정 중 또는 처리된 제품의 저장 중에 발암물질인 포름알데하이드를 유리시키는 경향이 있어 포름알데하이드를 유리시키지 않는 가교결합제의 개발이 활발하게 연구되고 있다. 이러한 비포르말린계 가교제 중 글리옥살은 그 성능은 매우 뛰어나지만 DP 처리시 사용되는 촉매인 aluminium sulfate는 처리직물의 강도저하와 항변을 일으키는 단점을 지니고 있다[1]. (중략)

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.10
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• pp.1525-1531
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• 2016

The objective of the present study was to investigate the rheological properties of potato starch cross-linked with different concentrations (0, 0.125, 0.25, and 0.5%, w/v) of cross-linking agents (10 g of adipic acid and 40 g of acetic anhydride). Cross-linked potato starch dispersions showed shear-thinning behaviors (n=0.43~0.63) at $25^{\circ}C$. Apparent viscosity (${\eta}_{a,100}$), consistency index (K), and yield stress (${\sigma}_{oc}$) significantly increased with an increase in the concentrations of cross-linking agents from 0.125 to 0.5% (w/v). Storage modulus (G') and loss modulus (G'') increased, whereas complex viscosity (${\eta}^*$) was reduced with increasing frequency (${\omega}$) from 0.63 to 62.8 rad/s. Magnitudes of G' and G'' for cross-linked potato starch were significantly increased with an elevation in the concentrations of cross-linking agents. G' values of cross-linked potato starches were significantly higher than G'', indicating that the starches had more elastic properties than viscous properties. Cox-Merz rule was not applicable to potato starch dispersions.

• 한국노년학
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• v.36 no.3
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• pp.541-562
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• 2016

The current study investigates the relationship and the mechanisms between bridge employment and change in marital satisfaction during midlife, using a three-wave panel dataset obtained from the Korean Baby Boomer Panel Study. A multivariate latent growth analysis reveals that the transition from career employment to bridge employment, compared to maintaining career employment, has an indirect negative effect on increase rate of marital satisfaction through the wage decrease. A steep decrease in wage following transition to bridge employment causes a lower increase in marital satisfaction. On the other hand, continuously engaging in bridge employment rather than career employment is associated with a higher increase in marital satisfaction via a higher increase in job commitment. This result implies that Baby Boomers adapt to bridge employment over time. Overall, the present study finds that the effect of bridge employment on the change in marital satisfaction during midlife varies with the duration of bridge employment. A future research needs to explore which factors can buffer the negative effect of decrease in wage during transition to the bridge employment on the change in marital satisfaction.

• Polymer(Korea)
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• v.29 no.6
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• pp.599-604
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• 2005

The hyaluronic acid (HA) with excellent biocompatibility has been combined with lactide, the ester dimer of polylactide, with good biodegradability to produce biocompatible materials which can control the period of degradation in a human body. By freeze frying method, HA and lactide were crosslinked with crosslinking agent, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC). Degree of lactide and EDC reaction was determined by the analysis of nuclear magnetic resonance spectroscopy. Both lactyl group and EDC conversion increased as the mole ratio of lactide to HA increased from 5 to 13. The membrane swelled less and became more brittle with the more addition of lactyl group resulting from the higher mole ratio of lactide to HA. Swelling ratio decreased and tensile modulus increased due to the more addition of lactyl group as the EDC concentration increased or reaction temperature decreased. Drug release experiment from various membranes with different degree of crosslinking showed that permeability decreased with increasing degree of crosslinking. The degradation became slower with the more addition of lactyl group. Mechanical property and degradation rate of the synthesized membrane were shown to be controlled through adjusting operation parameters such as mole ratio, temperature, and crosslinking agent concentration.