• Biotechnology and Bioprocess Engineering:BBE
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• 제2권2호
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• pp.117-121
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• 1997

Glutamic acid can be crystallized inside cation exchange column when displacer NaOH concentration is high enough to concentrate displaced glutamic acid beyond its solubility limit. Resulting crystal layer of glutamic acid was moved with liquid phase through the column, and thus could be eluted from the column and recovered in fraction collector. For the purpose of enhancing crystal recovery, effects of operating parameters on the crystal formation were investigated. The increase in the degree of crosslinking of resin favored crystal recovery because of its low degree of swelling. Higher concentration of displacer NaOH was advantageous. If NaOH concentration is too high, however, crystal recovery was lowered due to the solubility-enhancing effects of high pH and ionic strength. The decrease of mobile phase flow rate enhanced crystal recovery because enough time to attain local equilibrium could be provided, but film diffusion would control the overall crystal formation with extremely low flow rate. Lower temperature reduced solubility of glutamic acid and thus favored crystal formation unless the rate of ion exchange was severely reduced. The ion exchange operated by displacement mode coupled with crystallization was advantageous in reducing the burden of further purification steps and in preventing purity-loss resulted from overlapping between adjacent bands.

• Fibers and Polymers
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• 제6권1호
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• pp.1-5
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• 2005

In this study, we attempted to evaluate a novel use of sericin-fixed silk fiber (SFx) as an immobilization support of enzyme. Sericin was fixed on the silk fiber using glutaraldehyde as a fixation reagent. After 6 hours of fixation, the degree of fixation increases linearly with linear decrease of the amount of bound $\alpha$-chymotrypsin (CT). This suggests that the increase of the degree of fixation is due to the further crosslinking of free aldehyde groups on the surface of sericin-fixed silk fiber (SFx). Even though perfect fixation was not achieved, sericin did not dissolve seriously and could be removed by further washing. The specific activity did not differ significantly after 6 hours of fixation. The activity of immobilized CT on SFx decreased to its half after 6 hours of incubation at 50$^{\circ}C$. However, it retained $78\%$ of initial activity even after 1 hour of treat­ment with $100\%$ ethanol. As a result, the SFx could be used as an immobilization support of enzyme in non-aqueous media at ambient temperature.

• Bulletin of the Korean Chemical Society
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• 제4권4호
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• pp.162-169
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• 1983

The swelling and stress-elongation experiments have been performed for two kinds of gels of tactic poly (2-hydroxyethyl methacrylate) (P-HEMA) with varying crosslinker concentrations. The gels of isotactic and syndiotactic P-HEMA were swollen in aqueous salt solutions upon varying molal concentrations. The solute used were NaCl, $MgCl_2$, $Na_2SO_4$, $MgSO_4$ and urea. The water content at equilibrium swelling and the salt partition coefficient were determined, and stress-elongation curves of the gels were obtained. From these results, the effective number of chain (${\nu}_e$) and the Flory-Huggins interaction parameter (${\chi}_1$) were also obtained. The swelling experiment was also performed under varying solvents, and the degree of swelling was determined. The solubility parameter of P-HEMA was obtained as 13.4 (cal/mole)$^{l/2}$ using the correlation between the degree of swelling and the solubility parameter (${\delta}_1$) of solvents. The mechanical properties of syndiotactic P-HEMA is stronger than that of isotactic P-HEMA, and the water content of both gels become smaller when the crosslinking increases. Isotactic P-HEMA contains more water content than syndiotactic P-HEMA does.

• Elastomers and Composites
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• 제43권4호
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• pp.259-263
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• 2008

저밀도 폴리에틸렌에 대한 장시간 저온 열처리가 저밀도 폴리에틸렌 고분자의 결정화도에 미치는 효과를 고체 수소 핵자기공명을 이용하여 연구하였다. 장시간 열처리는 첫째, 저밀도 폴리에틸렌의 색깔을 엷은 노란색으로 변하게 하였고 둘째, 저밀도폴리에틸렌에서 수소 핵의 스핀-스핀 및 스핀-격자 완화시간을 증가시켰으며, 셋째, 결정화도를 줄어들게 하였다. 먼저, $T_1$의 증가를 저밀도폴리에틸렌의 전체 스핀-격자 완화시간을 결정하는 비정질 영역의 부피 감소에 의한 것이거나 분자간 가교나 수소결합에 의한 특정 분자 운동 성분의 느려짐에 의해 발생하는 것으로 고려하였다. 하지만 결정화도의 감소는 열처리에 의한 비정질 영역의 감소를 의미하므로 전자와는 배치되었다. 따라서 $T_1$의 증가는 후자에 의한 결과임을 알 수 있었다.

• 공업화학
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• 제7권5호
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• pp.843-848
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• 1996

현탁중합에 의하여 다공성 스티렌-디비닐벤젠 공중합 수지입자를 제조하였으며, 그 수지입자는 가교제인 디비닐벤젠과 세공형성제인 톨루엔 농도가 각각 30wt% 이상일 때만 다공성을 나타내었다. 다공성 수지입자의 비표면적은 디비닐벤젠과 톨루엔의 농도에 따라 증가하였으며, 진한 황산으로 황산화시켰을 때 비표면적은 감소하였다. 에틸아세테이트와 1-프로판올의 에스테르화 반응에서 황산화된 수지촉매의 활성은 가교도에 따라 증가하였다. 수용액 중 sodium dodecylbenzene sulfonate의 흡착에서 다공성 수지입자의 표면적에 따라 흡착량이 증가하였다.

• Journal of Pharmaceutical Investigation
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• 제23권3호
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• pp.145-153
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• 1993

Retaining a drug in the stomach by some means is sometimes necessary to extend the G1 absorption time of the drug more than 6-8 hrs. Hydrogel has often been examined for its feasibility as a dosage form, so called platform, that could be retained in the stomach due to its excellent swelling properties in the gastric fluid. In this study, polyvinylpyrrolidone (PVP) hydrogel crosslinked by albumin or acrylated albumin was synthesized in a tablet form and evaluated for its possibility as the platform. The synthesis of the hydrogel was performed by $^{60}Co\;{\gamma}-ray$ irradiation of N-vinyl-2-pyrrolidone (monomer) in the presence of a crosslinking agent: aqueous solution of albumin or acrylated albumin. Synthetic conditions such as radiation dose, dose rate and concentration of crosslinking agent were varied in order to optimize the swelling and mechanical properties of the hydrogels. Degree of swelling of albumin-crosslinked PVP (Al-PVP) was highly dependent on radiation dose, dose rate and albumin concentration: it was decreased as they increased. On the other hand, that of acrylated albumin-crosslinked PVP (Acryl-PVP) was almost independent on them except dose rate: it was decreased as the radiation dose rate increased. The compressive strength of the two hydrogels was decreased as the dose rate increased. Digestion of both PVP in artificial gastric fluid containing pepsin was delayed by the ${\gamma}-ray$ irradiation. In conclusion, Al-PVP and Acry-PVP with diverse swelling and mechanical properties could be obtained by controlling synthetic conditions, mainly the irradiation dose rate.

• 폴리머
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• 제25권4호
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• pp.545-557
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• 2001

Hydroxypropyl cellulose (HPC)를 이용하여 제조한 메탄올의 유방성 용액에 두 종류의 aliphatic dicarboxylic acid chlorides (succinyl chloride 와 suberoyl chloride)를 첨가하여 주형시킴에 의해 cholesteric 질서를 지닌 가교필름들을 제조하였다. 가교필름의 cholesteric pitch의 온도의존성과 물과 메탄올중에서의 가교필름의 팽윤거동을 검토하였다. 필름들은 cholesteric 액정상의 특징적인 지문조직을 나타내었으며 이들의 pitch는 HPC 자체와 동일하게 온도가 상승함에 따라 증가하였다. 그러나 모든 가교시료들은 주어진 온도하에서 HPC가 나타내는 pitch에 비해 대단히 크며 가교제의 농도 및 길이의 증가에 의해 증가하였다. 가교시료들은 두 용매중에서 이방성 팽윤을 나타냈다. 이방성 팽윤의 정도는 용매와 가교제의 종류에 다소 의존하나 검토된 가교제의 농도에는 거의 의존하지 않았다.

• 접착 및 계면
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• 제9권3호
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• pp.14-19
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• 2008

본 연구는 Silicone rubber (SR40)과 Fluororubber (FKM)을 여러 가지 무게비로 하여 블렌드를 제조하였고 그 특성을 고찰하였다. 블렌드의 가교 거동은 SR40의 함량이 증가함에 따라 SR40 내의 가교제에 의해 가교 속도는 빨라졌다. 블렌드에서 FKM의 함량이 증가하면, 열분해 온도가 증가는 경향이 있고 SR40/FKM 블렌드 비율이 50/50일 때 순수한 SR40보다 높은 열안정성을 나타내었다. 표면 발수성의 척도인 접촉각을 측정한 결과, SR40의 함량이 증가할수록 블렌드의 접촉각은 증가하는 것을 확인하였다. 또한, 제조한 블렌드들은 모든 조성에서 전형적인 상분리의 모폴로지를 나타내는 것을 확인할 수 있었고, SR40의 비율이 증가할수록 상분리 정도가 증가하는 것을 확인할 수 있었다.

• Biomaterials and Biomechanics in Bioengineering
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• 제2권1호
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• pp.47-59
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• 2015

A bioactive and multifunctional elastin-like polymer (ELP) was produced by genetic engineering techniques to develop new artificial matrices with the ability to mimic the extracellular matrix (ECM). The basic composition of this ELP is a thermo- and pH-sensitive elastin pentapeptide which has been enriched with RGD-containing domains, the RGD loop of fibronectin, for recognition by integrin receptors on their sequence to promote efficient cell attachment. Hydrogels of this RGD-containing polymer were obtained by crosslinking with hexamethylene diisocyanate, a lysine-targeted crosslinker. These materials retain the "smart" nature and temperature-responsive character, and the desired mechanical behavior of the elastin-like polymer family. The influence of the degree of crosslinking on the morphology and properties of the matrices were tested by calorimetric techniques and scanning electron microscopy (SEM). Their mechanical behavior was studied by dynamical mechanical analysis (DMA). These results show the potential of these materials in biomedical applications, especially in the development of smart systems for tissue engineering.

• Elastomers and Composites
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• 제37권1호
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• pp.39-48
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• 2002

선형 수분간 폴리우레탄과 가교형 수분산 폴리우레탄을 2,4-톨루엔다이이소시아네이트, 다이메틸올프로피오닉에시드 및 폴리옥시프로필렌글리콜 또는 폴리옥시프로필렌글리세린를 사용하여 합성하였다. 합성된 중합체의 구조는 $^1H-NMR$ 및 FT-IR을 이용하여 분광학적 방법으로 측정하였고, 열적 성질은 DSC 및 TGA로 기계적 특성은 Instron, 입자의 형태는 AFM등으로 조사하였다. 수분산 폴리우레탄의 합성에서 폴리올의 분자량이 증가할수록 에멀젼의 입자 크기가 가교도가 증가할수록 에멀젼의 입자 크기, 점도 및 유리전이온도가 증가하였다. 폴리옥시프로필렌글리콜에 폴리옥시프로필렌글리세린을 혼합하여 합성하는 가교형 수분산 폴리우레탄에서는 폴리옥시프로필렌글리세린의 함량이 15% 이상부터는 수분산이 이루어지지 않았다. 따라서 본 연구에서는 폴리옥시프로필렌글리세린의 함량을 5%, 8%, 13% 및 15%로 한정하여 합성하였다.