• Macromolecular Research
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• 제14권5호
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• pp.552-558
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• 2006

Biodegradable nanofibrous poly(L-lactic acid) (PLLA) scaffold was prepared by an electrospinning process for use in tissue regeneration. The nanofiber scaffold was treated with oxygen plasma and then simultaneously in situ grafted with hydrophilic acrylic acid (AA) to obtain PLLA-g-PAA. The fiber diameter, pore size, and porosity of the electrospun nanofibrous PLLA scaffold were estimated as $250\sim750nm,\;\sim30{\mu}m$, and 95%, respectively. The ultimate tensile strength was 1.7 MPa and the percent elongation at break was 120%. Although the physical and mechanical properties of the PLLA-g-PAA scaffold were comparable to those of the PLLA control, a significantly lower contact angle and significantly higher ratio of oxygen to carbon were notable on the PLLA-g-PAA surface. After the fibroblasts were cultured for up to 6 days, cell adhesion and proliferation were much improved on the nanofibrous PLLA-g-PAA scaffold than on either PLLA film or unmodified nanofibrous PLLA scaffold. The present work demonstrated that the applications of plasma treatment and hydrophilic AA grafting were effective to modify the surface of electrospun nanofibrous polymer scaffolds and that the altered surface characteristics significantly improved cell adhesion and proliferation.

• 한국가정과학회지
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• 제5권1호
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• pp.48-61
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• 2002

This study was carried out to investigate the effects of four kinds of leavening agents on Jeung-Pyun fermantation. Milk-wine(M), fresh yeast(F), dry yeast(D), instant yeast(I) were used in Jeung-Pyun ingredients. The physicochemical properties, sensory evaluation were examined. The results of this study are summarized as follows: 1. Basic recipes for Jeung-Pyun by preliminary test were developed. 2. Specific volumes and expansion ratio of Jeung-Pyun was higher in the fresh yeast-added sample. 3. The pH of Jeung-Pyun was decreased significantly as the fermentation progressed 4. In the result comparing Jeung-Pyun extracting after 1st fermentation with Jeung-Pyun extracting 2nd fermentation by SEM, the former was widely distributed in stability of bubble and pore than the latter. 5. Standard recipe by Q.D.A. test added four kinds of leavening agents were as follows: (1)Jeung-Pyun added milk wine was 240min for 1st fermentation time, 60min for 2nd fermentation time, 35$^{\circ}C$ for fermentation temperature, 80% for fermentation humidity respectively. (2) Jeung-Pyun added fresh yeast was 90min for 1st fermentation time, 40min for 2nd fermentation time, 35$^{\circ}C$ for fermentation temperature, 80% for fermentation humidity respectively. (3)Jeung-Pyun added dry yeast was 90min for 1st fermentation time, 60min for 2nd fermentation time, 35$^{\circ}C$ for fermentation temperature, 60% for fermentation humidity respectively. (4)Jeung-Pyun added instant yeast was 90min for 1st fermentation time, 40min for 2nd fermentation time, 30$^{\circ}C$ for fermentation temperature, 60% for fermentation humidity respectively. 6.Based on sensory evaluation, Jeung-Pyun added fresh yeast was significantry higher than others in color, sweetness, moistness, softness, and overall quality. There was negative significance between milk wine flavor and astrigentness, and yeast flavor.

• 멤브레인
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• 제24권6호
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• pp.438-447
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• 2014

무정형의 괴상의 다공성 borosilicate는 trimethylborate (TMB)/ tetraethylorthosilicate (TEOS) 몰비 0.01~0.10 겔체를 $700{\sim}800^{\circ}C$ 온도범위에서 열처리 하였을 때 얻어졌다. BET와 SEM 관찰에 의하면 $700{\sim}800^{\circ}C$에서 얻어진 borosilicate의 표면적은 $251.12{\sim}355.62m^2/g$이고, 기공직경은 3.5~4.9 nm이며, 입자크기는 30~60 nm이었다. TGA측정에 의하면 borosilicate가 poly[1-(trimethylsilyl)propyne](PTMSP)에 첨가되었을 때 PTMSP-borosilicate 복합막의 열적 안정성은 향상 되었다. SEM관찰에 의하면 borosilicate는 $1{\mu}m$ 크기로 복합막 내에 분산되어 있었다. 기체투과실험에 의하면 PTMSP에 borosilicate 함량이 증가하면 자유부피, 공동, 기공률이 증가하여 기체투과가 용해확산에 의한 것보다 분자체거름, 표면확산, Knudsen 확산에 의해 일어나는 경우가 점차 증가함으로 해서 $H_2$와 $N_2$의 투과도는 증가하고 선택도($H_2/N_2$)는 감소하였다.

• Archives of Pharmacal Research
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• 제26권1호
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• pp.76-82
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• 2003

Drug releasing porous poly($\varepsilon$-caprolactone) (PCL)-chitosan matrices were fabricated for bone regenerative therapy. Porous matrices made of biodegradable polymers have been playing a crucial role as bone substitutes and as tissue-engineered scaffolds in bone regenerative therapy. The matrices provided mechanical support for the developing tissue and enhanced tissue formation by releasing active agent in controlled manner. Chitosan was employed to enhance hydrophilicity and biocompatibility of the PCL matrices. PDGF-BB was incorporated into PCL-chitosan matrices to induce enhanced bone regeneration efficacy. PCL-chitosan matrices retained a porous structure with a 100-200 $\mu$m pore diameter that was suitable for cellular migration and osteoid ingrowth. $NaHCO_3$ as a porogen was incorporated 5% ratio to polymer weight to form highly porous scaffolds. PDGF-BB was released from PCL-chitosan matrices maintaining therapeutic concentration for 4 week. High osteoblasts attachment level and proliferation was observed from PCL-chitosan matrices. Scanning electron microscopic examination indicated that cultured osteoblasts showed round form and spread pseudopods after 1 day and showed broad cytoplasmic extension after 14 days. PCL-chitosan matrices promoted bone regeneration and PDGF-BB loaded matrices obtained enhanced bone formation in rat calvarial defect. These results suggested that the PDGF-BB releasing PCL-chitosan porous matrices may be potentially used as tissue engineering scaffolds or bone substitutes with high bone regenerative efficacy.

• 산업기술연구
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• 제23권A호
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• pp.199-206
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• 2003

The charcoal-encapsulated methyl silica microcapsules were prepared by a O/W microemulsion sol-gel method, and the adsorption properties on aquatic humic acid were investigated. The capsules prepared were spherical, $100{\sim}1000{\mu}m$ in size. The size distribution was controllable by adjusting the size of charcoal powder, charcoal/methyl silica ratio, and agitating speed in O/W sol-gel process. Adsorption efficiency of charcoal for aquatic humic acid was decreased after encapsulation by methyl silica shell. The decreased adsorption efficiency can be dependent on the decrease of the BET surface area and pore volume after encapsulation. Diffusion properties of humic acid through the capsule shell also played an important role on adsorption efficiency. Therefore, the reasonable target pollutants for the capsules can be VOC or odor molecules which can overcome diffusion barrier through shell of capsules in air condition. Functionalization methods for the charcoal-encapsulated $CH_3(SiO)_n$ microcapsules by incorporation of $TiO_3$ as a phtocatalytic function and by incorporation of inorganic pigment as a color function were also investigated. $TiO_2$ coating properties were controllable by adjusting pH, temperature, and the concentration of $TiOSO_4$. In XRD measurement, the crystal form of the coated $TiO_2$ was anatase. For the colorization of the capsules, inorganic pigments were more efficient than organic dyes, and various color was introduced to the capsules using inorganic pigments.

• 대한화학회지
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• 제25권2호
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• pp.97-102
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• 1981

$SiO_2$/$Al_2O_3$ 비가 높은 제올라이트 ZSM-5를 합성하여 메탄올의 탄화수소로의 전환반응을 조사하였다. 메탄올이 전환되어 올레핀, 파라핀, 시클로파라핀 및 방향족화합물이 생성되었으며 특히 방향족 화합물에 대한 큰 선택성을 보여 주었고 1,3,5-trimethylbenzene의 크기정도에 제한된 형상선택성 촉매작용임을 알 수 있었다. 수소형태(HZSM-5)가 활성이 커, 메탄올이 탈수되어 일어나는 잇단 복잡한 반응들이 산촉매반응이 주임을 보여 주었다. ZSM-5와 구조가 유사한 mordenite와 3차원구조를 지닌 faujasite 촉매에서의 메탄올의 반응으로 구조적 영향과 TPD실험에 의한 산점분포를 비교한 결과 메탄올로부터 방향족화합물에 이르기까지의 탄화수소 합성에서의 ZSM-5 제올라이트의 촉매작용은 높은 실리카함량에 기인한 강한 산성과 교차하는 세공관 구조에 의한 분자체 효과에 의한 것으로 볼 수 있다.

• 한국세라믹학회지
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• 제31권1호
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• pp.104-114
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• 1994

ZrO2 fibers were fabricated by means of the Sol-Gel process using Zr(O-nC3H7)4-H2O-C2H5OH-HNO3 solution as a starting material. The optimum experimental parameters such as molar ratio of starting materials, concentration, temperature, viscosity, the amounts of stabilizer and the pH of solution were determined. The experimentally determined optimum variables which produce good ZrO2 fibers were used to manufacture the Y2O3-and CaO-ZrO2 fibers. The amounts of Y2O3 and CaO were varied within the range from 1.5~5 mol% and 3~15 mol% respectively. The phase transformation and microstructural evolution of the fabricated ZrO2 gel fibers were investigated after heat treatments up to 120$0^{\circ}C$ by X-ray diffraction, Raman microprobe spectroscopy, SEM, and specific surface area and pore volume measurements. From the analysis of X-ray diffraction and Raman spectra, the phase of heat treated Y2O3-and CaO partially stabilized ZrO2 gel fibers(Y2O3:2.5~3 mol%, CaO:6~9 mol%) were identified as a tetragonal phase up to 100$0^{\circ}C$. The maximum tensile strength of 2.5Y2O3-97.5ZrO2 and 6CaO-94ZrO2 (in mol%) fibers heat treated at 100$0^{\circ}C$ for 1 hr was found be 1.3~2 GPa with diameters of 10~20 ${\mu}{\textrm}{m}$.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.565-568
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• 2008

우리나라의 경우 매년 전국적으로 일평균기온이 0$^{\circ}C$이하로 되는 경우가 대부분이므로 거의 모든 지역의 콘크리트가 반복되는 동결융해의 피해를 입고 있다고 볼 수 있다. 이러한 동결융해의 반복에 대한 콘크리트의 내구성은 콘크리트의 공기량과 매우 관계가 깊다. 따라서, 현재 콘크리트의 동결융해에 대한 저항성을 향상시키기 위해 AE제 등을 사용하고 있으며 콘크리트의 기포간극계수를 $250{\mu}m$ 이하로 권장하고 있다. 외국의 경우도 마찬가지로 AE제 및 감수제에 관한 품질규격에서 기포간극계수를 캐나다의 경우 각각 $200{\mu}m$ 이하 및 $230{\mu}m$ 이하로 규정하고 있으며 일본학회에서도 기포간극계수 $250{\mu}m$ 이하가 적당하다고 보고되고 있다. 또한, 융설제와 동결융해의 복합작용에 의해 콘크리트의 스켈링 저항성을 향상시키는 데에도 일반 동해와 마찬가지로 공기량이 상당히 중요하다고 알려져 있다. 따라서, 반복되는 동결융해에 의한 동해를 동시에 받는 복합열화 환경하에 있는 일반콘크리트의 내구성에 크게 영향을 미치는 인자로 알려져 있는 공기량에 따른 동결융해 내구성을 알아보고자 Non AE(공기량 1.5%), AE(공기량 4.5%, 7.2%) 콘크리트를 통해 동결융해에 따른 상대동탄성계수와 중량감소율, 스켈링 저항성 및 공극특성을 비교검토 하였다.

• 한국지반공학회지:지반
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• 제4권1호
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• pp.17-28
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• 1988

흙의 역학적거동을 파악하기 위한 요소시험중 공시체의 주응력방향을 회전시킬 수 있는 비틀림 전단시험기의 기능에 대하여 검토하였다. 본 연구에서는 이 비틀림전단시험기가 점토시료에 사용 될 수 있게 개량제작되었다. 이 시험기를 사용하여 반죽성형된 Ko-견밀점토시료에 대한 약간의 비배수 비틀림전단시험을 실시하여 혼의 거동에 미치는 주수력축의 회전영향이 조사되었다. 우선, torque없이 비틀림전단시험기를 사용하여 얻은 흙의 역학적 거동이 통상의 축대칭삼축압 축시험에 의한 결과와 비교검토됐다. 흙의 응력일변형거동, 문극수압및 주응력비는연직하중과 torque에 의한 응력경로에 크게 영향을 받았으며 전단변형률의 증가에 따라 주응력회전각과 주응력의 상대적 크기, b(=o2-o3)/(o1-o3)) 값토 점진적으로 커져 파괴시의 값에 수렴하였다.

• 한국지반공학회논문집
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• 제21권8호
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• pp.27-35
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• 2005

액상화에 따른 지반의 과도한 변형으로 인한 피해가 자주 발생되고 있다. 그에 따른 지반의 움직임을 예측하기 위해서는 유효응력 개념에 기초한 수치해석 기법이 요구되어 진다. 본 연구에서는 지진 및 유사한 반복 하중에 따른 수압의 상승을 예측할 수 있는 연성(fully coupled) 유효응력 구성모델인 UBCSAND를 제안하였다. 제안된 모델은 간단한 완전탄소성모델인 Mohr-Coulomb을 변형한 형태로 마찰각(friction angle)과 팽창각(dilation angle)을 점진적으로 증가시킴으로써, 기존의 파괴상태내에서도 연속적인 소성변형 발생을 표현할 수 있다. 항복함수는 전단응력과 평균응력의 비인 $(\sigma'_1-\sigma'_3)/(\sigma'_1-\sigma'_3)$로 나타내며, 응력도의 원점에서 시작하는 무한개의 방사선을 의미한다. 따라서, Mohr-Coulomb의 파괴면과 같은 형태의 무수한 항복면을 가진다. 소성 경화법칙은 등방경화(isotropic hardening)와 이동경화(kinematic hardening)를 혼합한 형태를 이루고 있다. 재하(loading) 및 재재하(reloading)시에는 연속적인 소성 변형이 일어나나, 제하(unloading)시에는 탄성변형을 가정하였다. 제안된 모델은 느슨한 Fraser River 모래를 이용한 직접단순전단시험(Direct simple shear test)결과와 비교하여 검증하였다.