The need to consider torsion in the design of members of a structure has recently been increasing; therefore, many studies on torsion have been carried out. Recent research was focused on the torsional performance of concrete according to the reinforcing materials used. Of particular interest, are torsion studies of beams made of SFRC(steel fiber reinforced concrete), and there has been increasing use of SFRC at construction sites. In contrast, research on the composite PVA-ECC (polyvinyl alcohol-engineered cementitious composite) has only covered its mechanical performance, though it exhibits excellent tensile-strain performance (better than SFRC). Therefore, research on the torsion of concrete beams retrofitted using PVA-ECC is lacking. In this study, the behavior characteristics and performance of reinforced-concrete beams retrofitted by PVA-ECC was investigated experimentally. The experimental results show that the resistance to torsional cracking is increased by PVA-ECC. In addition, the strain on the rebar of the specimen was found to be reduced.

고농도의 초산수용액을 분리⋅농축하기 위해 polyacrylonitrile (PAN) 중공사 복합막을 제조한 후 투과증발 분리실험을 통해 제조된 복합막의 분리성능을 확인하였다. 제조된 중공사 복합막의 코팅여부를 알아보고자 SEM 사진을 측정하였으며 코팅두께가 3.85 µm로 균일하게 코팅된 것을 확인할 수 있었다. 또한 막의 투과성능평가 실험을 수행한 결과 가교제의 농도와 가교온도가 증가함에 따라 투과도는 감소하고 선택도는 증가하는 경향을 나타내었고, 대표적인 결과로 가교제인 glutaraldehyde 농도 13 wt%, 가교온도 140°C에서 투과도 250 g/m2⋅hr, 선택도 13의 결과를 얻을 수 있었으며, 또 다른 가교제로서 poly (acrylic acid) 농도 9 wt%, 가교온도 140°C일 때 투과도 330 g/m2⋅hr, 선택도 9의 값을 얻을 수 있었다.

Poly (vinylidene fluoride) (PVDF)ㆍpoly (acrylonitrile) (PAN) 중공사막에 친수성 고분자인 poly (vinyl alcohol) (PVA)과 가교제인 poly (acrylic acid) (PAA)을 코팅하여 복합막을 제조하였다. 제조된 막의 투과특성평가를 위해 90 wt% 물- 에탄올 혼합액에 대한 투과증발실험을 수행하였으며, 반응온도, PAA용액의 농도, 공급액의 온도변화에 따른 투과도 및 선택도를 측정하였다. 일반적으로 반응온도, PAA용액의 농도가 증가할수록 투과도는 낮아지고 선택도는 증가하는 경향을 보였으며, 공급액의 온도가 증가할수록 투과도는 증가하고 선택도는 낮아지는 경향을 보였다. 대표적으로 PVDF중공사 막은 투과도는 PAA 3 wt%, 반응온도 60°C, 공급액 온도 70°C에서 502 g/m 2 hr, 선택도는 PAA 11 wt%, 반응온도 100°C, 공급액 온도 50°C일 때, 218의 결과를 얻을 수 있었다.

There is increasing interest in zirconia as a dental material due to its aesthetics, as well as the exceptionally high fracture toughness and high strength that are on offer when it is alloyed with certain oxides like yttria. In recent years, many solution based chemical synthesis methods have been reported for synthesis of zirconia, of which the sol-gel method is considered to be best. Here, we synthesize zirconia by a sol gel assisted precipitation method using either PEG or PVA as a stabilizing agent. Zirconia sol is first synthesized using the hydrothermal method. We used NaOH as the precipitating agent in this method because it is easy to remove from the final solution. Zirconium and yttrium salts are used as precursors and PEG or PVA are used as stabilizers to separate the metal ions. The resulting amorphous zirconia powder is calcined at 900˚C for 2 h to get crystallized zirconia. XRD analysis confirmed the partially stabilized zirconia synthesis in all the synthesized powders. SEM was taken to check the morphology of the powder synthesized using either PEG or PVA as a stabilizing agent and finally the transparency was calculated. The results confirmed that the powder synthesized with 10 % PVA as the stabilizing agent had highest percentage of transparency among all the synthesized powder.

Poly vinylidene fluoride (PVDF) 중공사막을 polyethylenimine (PEI)와 p-xylylene dichloride (XDC)를 이용해 친 수화 시킨 후 poly(vinyl alcohol) (PVA)과 가교제인 poly(acrylic acid-co-maleic acid) (PAM) 혼합용액을 코팅하여 막을 제조 하였다. 중공사막 표면의 코팅여부는 scanning electron microscope (SEM)을 통해 관찰하였으며, 막의 특성평가를 위해 물/에 탄올 혼합액에 대한 투과증발 실험을 수행하였다. 공급액 조성은 90 wt% 에탄올 수용액을 사용하였으며, 가교제 농도, 공급 액과 반응온도 변화에 따른 투과도 및 선택도를 측정하였다. 투과도는 반응온도 100°C, PAM 농도 3 wt%, 공급액온도 70°C 에서 1,480 g/m 2 hr, 그리고 선택도는 반응온도 100°C, PAM 농도 15 wt%, 공급액온도 25°C에서 αW/E = 82의 결과를 얻을 수 있었다.

Poly(vinyl alcohol) (PVA)에 대하여 가교제로써 glutaraldehyde (GA), maleic anhydride (MA)를 이용하여 제조한 코팅용액을 알칼리로 가수분해 시킨 poly acrylonitrile (PAN) 중공사 막표면에 코팅하여 막을 제조하였다. 제조된 막의 투과 특성평가를 위해서 물/에탄올 혼합액에 대한 투과증발 실험을 수행하였다. 60°C의 90 wt%의 물/에탄올 혼합액에 대하여 반응온도 및 가교제의 농도변화에 따른 투과도 및 선택도를 측정하였다. 일반적으로 반응온도, 가교제 농도가 증가할 경우 투과 도는 낮아지고, 선택도는 증가하는 경향을 보여주었다. 가교제로 GA의 대표적 결과는 반응온도 120°C, GA 11 wt%로 투과 도는 165 g/m 2 hr 선택도는 81이고, MA는 반응온도 120°C, MA 11 wt%로 투과도는 174 g/m 2 hr 선택도는 73의 결과를 얻을 수 있었다.

지지체인 Polyacrylonitrile (PAN) 중공사에 Poly (vinyl alcohol) (PVA)과 가교제인 Glutaraldehyde (GA)를 코팅하 여 막을 제조하였으며, 특성평가를 위해 물/Isopropyl alcohol (IPA) 혼합액에 대한 투과증발 실험을 수행하였다. 코팅용액의 조성변화와 반응온도의 조건변화에 따른 투과도 및 선택도를 측정하였고, 공급액의 조성은 85 wt% IPA 수용액을 사용하였으며, 온도는 30, 50, 70, 90℃로 변화시켰다. 투과도는 PVA 3.5 wt%, 공급액 온도가 90℃일 때 1,870 g/m 2 ⋅hr, 선택도는 PVA 7 wt% 공급액 온도가 30℃일 때 804로 가장 높은 값을 얻을 수 있었다.

The Oriental White Stork (Ciconia boyciana) is a representative wetland species distributed across East Asia. The species has been declined to face the threat of species extinctions with estimation of at about 3000 individuals. In order to re-introduce the endangered storks in the field, we developed a baseline model using the program VORTEX, performed sensitivity test, and finally suggested an ideal model based on results of the sensitivity test. The baseline model predicted 12.5% extinction probability with mean time to first extinction of 82.0 year. Sensitivity test revealed that two demographic variables (first-year mortality and percent of adult female breeding) had the greatest impacts on population persistence. Thus, corrected model improved the population persistence, where the extinction probability decreased to 1.0% in 100 years by changing values of two variables within a range of applicable to the population. Our models for stork re-introduction suggest this population will be stable by improving first-year mortality and adult female fecundity.

A drug delivery system (DDS) was prepared with a temperature and pH-responsive hydrogel. Poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAAc)/poly(N-isopropylacrylamide) (PNIPAAm)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by radical polymerization for the temperature and pH-responsive hydrogels. MWCNTs were employed to improve both the thermal conductivity and mechanical properties of the PVA/PAAc/PNIPAAm/MWCNT nanocomposite hydrogels. Various amounts of MWCNTs (0, 0.5, 1 and 3 wt%) were added to the nanocomposite hydrogels. PVA/PAAc/PNIPAAm/MWCNT nanocomposite hydrogels were characterized with a scanning electron microscope. The mechanical properties were measured with a universal testing machine. Swelling and releasing properties of nanocomposite hydrogels were investigated at various temperatures and pHs. Temperature and pH-responsive release behavior was found to be dependent on the content of MWCNTs in nanocomposite hydrogels.

본 연구는 고내구성을 가진 고분자 전해질 막을 제조하는 것으로 연료전지에 적용하기 위하여 poly(vinyl alcohol)를 주쇄부로 하여 poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA)와 3-(trihydroxysilyl)-1-propanesulfonic acid (THS-PSA)를 polyethylene막에 함침시켜 막을 제조하였다. 제조된 막을 함수율, 접촉각, FT-IR, 수소이온전도도, 탄성계수 등의 측정을 통해 친수성 고분자가 함침된 막의 특성평가를 실시하였다. FT-IR 분석과 접촉각 측정을 통해 PE막에 함친된 막에서 친수성기의 유무를 확인하였다. 수소이온전도도를 측정한 결과 30% THS-PSA의 막이 55℃에서 1.27×10 ­1S/㎝의 값을 나타내어 우수한 수소이온전도도를 나타내었으며, 탄성계수의 측정을 통해 polyethylene막에 비하여 THS-PSA가 함침된 막의 기계적 강도가 15%까지는 최대 7배까지 향상되어 막의 내구성이 향상되었음을 확인하였다.

Multi-walled carbon nanotube (MWCNT)/poly(vinyl alcohol) (PVA) nanocomposite hydrogels were prepared by freezingthawing method for the electro-responsive transdermal drug delivery. MWCNTs were used as the functional ingredient to improve both mechanical and electrical properties of MWCNT/PVA nanocomposite hydrogels. The morphology of nanocomposites revealed the uniform distribution of MWCNTs and the good interfacial contact. The compression moduli of hydrogel matrices increased greatly from 40 to 1500 kPa by forming MWCNT/PVA nanocomposites. The swelling ratio of MWCNT/PVA nanocomposites decreased as the content of MWCNTs increased under no electric voltage applied. However, the swelling ratio of MWCNT/PVA nanocomposites increased as the content of MWCNTs increased under electric voltage applied and the applied electric voltage increased. The drug was released in the electro-responsive manner through the skin due to the electro-sensitive swelling characteristics of MWCNT/PVA nanocomposite hydrogels.

Multilayer Poly methyl methacrylate (PMMA)/ Poly vinyl alcohol (PVA) bone plates were fabricated using electrospinning and in vitro investigations were carried out for pre-clinical biocompatibility studies. The initial cellular cytotoxicity of the methacrylate (PMMA)/ Poly vinyl alcohol (PVA) bone plates was measured by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay using fibroblast-like L-929 cells. Cellular adhesion and differentiation studies were carried out using osteoblast-like MG-63 cells. As simulated body fluid (SBF) contains the same ionic concentration of body fluid and any bioactive material tends to deposit bone-like apatite on the samples surfaces into the SBF, in vitro bioactivity of the multilayer bone plates were investigated using SBF. We also studied the internal organization and tensile strength of the multilayer PMMA/PVA bone plates using micro-computed topography (μ-CT) and universal testing instrument (UTI, Korea) respectively. The cellular cytotoxicity study with MTT confirmed that the cellular viability was 78 to 90% which indicates good cyto-compatibility. Scanning electron microscopic findings revealed a good attachment and adhesion phenomenon of MG-63 cells onto the surfaces of the samples. Cellular differentiation studies also showed that osteogenic differentiation was switched on in a timely manner and affirmed along with that of the control group. Bone-like apatite formation on the surfaces was confirmed within 14 days of SBF incubation. Initial organizations of the multilayer PMMA/PVA bone plates were characterized as dense and uniform. The tensile strength of the post-pressing electronspun mat was higher than that of the pre-electronspun mat. These results suggest that a multilayer PMMA/PVA bone plate system is biocompatible, bioactive and a very good alternative bone plate system.

Mechanical coating process was applied to form 89 %-hydrolyzed poly vinyl alcohol (PVA) onto boron carbide (B4C) nanopowder using one step high energy ball mill method. The polymer layer coated on the surface of B4C was changed to glass-like phase. The average particle size of core/shell structured B4C/PVA was about 50 nm. The core/shell structured B4C/PVA was formed by dry milling. However, the hydrolyzed PVA of 98~99% with high glass transition temperature (Tg) was rarely coated on the powder. The Tg of polymer materials was one of keys for guest polymer coating on to the host powder by solvent free milling.

본 연구에서는 Poly(vinyl alcohol) (PVA)을 주쇄부(base polymer)로 하여 화학적 가교를 실시하기 위하여 Poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA)를 첨가하고, 실리카와 술폰산기를 함유한 3-(trihydroxysilyl)-1-propanesulfonic acid (THS-PSA)의 함량변화와 열 가교온도 변화를 통하여 직접 메탄을 연료전지(DMFC)에 적용하기 위한 고분자 전해질 막 소재에 관한 연구를 실시하였다. 제조된 막을 Nafion 115와 함께 비교하기 위하여 동일한 조건에서 함수율, 열 중량 분석(TGA), 이온교환용량, 이온전도도 및 메탄올 투과도를 실시하였다. 실험을 통하여 THS-PSA의 함량과 열 가교 온도변화에 따라서 메탄올 투과도가 10 -6에서 10 -8 cm 2 /s로 감소된 결과를 얻었으며, 이온전도도는 10 -3에서 10 -2 S·cm -1으로 향상되어 Nafion 115보다 우수한 결과를 나타내었다.

Cellulose nanofibers from microfibril cellulose (MFC) was prepared by hydrobromic acid (HBr) treatment at different concentrations. Polyvinyl alcohol (PVA) composite films at various loading level of nanofibers were manufactured by a film casting method. The analysis of degree of polymerization (DP), crystallinity (Xc) and molecular weight (Mw) of cellulose after acid treatment was conducted. The mechanical and thermal properties of the cellulose nanofibers reinforced PVA films were characterized using tensile tests and thermogravimetric analysis (TGA). The DP and Mw of MFC by HBr hydrolysis considerably decreased, but Xc showed no significant change. After acid hydrolysis, the diameter of cellulose nanofibers was in the range of 100 to 200 nm. The thermal stability of the films was steadily improved with the increase of nanofiber loading. There was a significant increase in the tensile strength of PVA composite films with the increase in MFC loading. Finally, 5 wt.% nanofiber loading exhibited the highest tensile strength and thermal stability of PVA composite films.

본 연구는 poly(vinyl alcohol) (PVA)와 가교제 poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA)을 이용하여 제조된 막에 tetraethylorthosilicate (TEOS)를 도입하여 물-에탄올 계에 대한 투과증발 실험을 다양한 가교온도별(120~140℃), 조업온도별(25~70℃)로 수행하였다. TEOS의 함량은 PVA 대비 3, 5, 7 wt%를 사용하였으며, 원액의 조성은 무게비로 물 10, 20, 30 및 50%에 대하여 조사하였다. 물 에탄올 = 10 : 90 조성, 조업온도 50℃에서 선택도 1730과 투과도 16.3g/m2·hr를 PVA/7 wt% PSSA_MA/5 wt% TEOS 막이 보여 주었다.

본 연구에서는 공기 중의 수분을 선택적으로 제거하기 위해 poly(vinyl alcohol) (PVA) 에 가교제로서 poly(styrene sulfonic acid-eo-maleic acid) (PSSA-MA)와 막의 물에 대한 선택적 분리 특성을 향상시키기 위해 3-(trihydroxysilyl)-1-propanesulfonic acid (THS-PSA) 를 첨가하여 막을 제조하였다. PSSA_MA 와 THS-PSA의 양과 가교온도를 변화시켜 가며 막을 제조하였다. 또한 제조된 막의 분리특성을 살펴보기 위해 동적증기용해도와 증기투과 실험을 수행하였다. 동적증기용해도 실험으로부터 가교온도의 증가는 평형 용해 상태에 도달하는데 더 오래 걸리는 것을 알 수 있었다. 120℃에서 제조 된 PVA/PSSA_MA (3%)/THA-PSA(7%) 막이 35℃에서 가장 투과도가 높은 480 barrer를 나타내었다.