• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.438-439
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• 2006

Pure and stable YAG $(Y_3Al_5O_{12})$ powders were synthesized by a PVA (polyvinyl alcohol) polymer solution technique. PVA was used as an organic carrier for the precursor ceramic gel. The precursor gels were crystallized to YAG at relatively a low temperature of $900\;^{\circ}C$. The synthesized powders, which have nano-sized primary particles, were soft and porous, and the porous powders were ground to sub-micron size by a simple ball milling process. The ball-milled powders were densified to 94% relative density at $1500\;^{\circ}C$ for 1h. In this study, the characteristics of the synthesized YAG powders were examined.

• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.560-565
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• 2007

Copper fine particles, ranging from $0.11{\mu}m$ to $0.64{\mu}m$ in average size, were prepared by a chemical reduction method using hydrazine ($N_2H_4$) as a reduction agent in waste copper solutions. The effect of the amount of hydrazine addition was investigated on the properties of the obtained powders. Also, the effect of the addition of dispersing agents [Polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP)] during particle synthesis was studied. The powders, obtained from 1 M waste copper solutions, showed the mixtures of Cu and $Cu_2O$ crystals at low hydrazine addition amounts of 0.8 mol and 1.0 mol, while those exhibited pure Cu crystals at adequate hydrazine addition amount of 0.12 mol. The average size of the Cu powders decreased with increasing the concentrations of hydrazine and dispersing agents. The addition of PVA to the solutions as a dispersing agent was more effective than that of PVP in preventing the aggregation of particles.

• Journal of the Korea Institute of Building Construction
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• v.20 no.3
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• pp.213-221
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• 2020

The aim of the research is to provide thixotropy on cement-based materials. For this purpose, the linkage between polyvinyl alcohol (PVA) and borax was used. Namely, adding the suspensions of PVA and borax in cement paste, the thixotropy of cement paste was confirmed. The thixotropy of cement-based materials can have various advantages on construction process, especially, the placing method using pipe can have advantages. As a result of this research, the linkage between PVA and borax is valid inside of cement paste. Therefore, using PVA and borax, it is confirmed that the cement-based materials can have thixotropy with this method, and it can be expected to contribute on developing new method of placing cement-based materials with thixotropy.

• Journal of Pharmaceutical Investigation
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• v.26 no.4
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• pp.299-308
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• 1996

In order to develop the controlled release of a drug from the suppsitories, in vitro drug release and in vivo absorption in rabbits were investigated. Various suppository forms with hollow cavities, into which drugs in the form of fine powder or solid dispersion system(SDS) could be placed, were utilized. The polyvinyl alcohol(PVA) hydrogel as a base, and propranolol HCl(PPH) as a model drug were employed. In vitro drug dissolution studies showed that the dissolved amounts(%) of PPH from PPH-methylcellulose(MC)-SDS and PPH-ethylcellulose(EC)-SDS reached 100% and 63% in 4.5-hours, respectively. In the relative strength test for PVA hydrogel, PVA hydrogel became harder and more rigid when the number of freezing-thawing cycles and the ratio of PVA 2000 were increased. In vitro drug release profile revealed that the release rate(%) of PPH from PPH-EC-SDS and PPH-MC-SDS hollow type suppositories were sustained. The release amount(%) of PPH from PPH-EC-SDS hollow type suppositories was not affected by storage time, but since the use of hydrophilic MC made PPH diffuse into the hydrogel after it absorbed the water of base, the various release patterns were appeared as the storage time went by. In vivo absorption experiments with rabbits showed that PPH-EC-SDS(PPH : EC=1:3) hollow type suppository delayed the absorption of PPH, significantly. The $C_{max}$, $AUC_{0{\rightarrow}8}$ and MRT of PPH powder hollow type suppository were $196.37{\pm}5.63\;ng/ml$, 1105.26 ng/ml/min and 8.66 min, respectively. The $C_{max}$, $AUC_{0{\rightarrow}8}$ and MRT of PPH-EC-SDS(PPH : EC=1:3) were $91.30{\pm]14.14\;ng/ml$, 554.69 ng/ml/min, 235.99 min, respectively.

• Journal of Bio-Environment Control
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• v.16 no.1
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• pp.21-26
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• 2007

This study was carried out to investigate the effects of tree-spray of calcium formate compound extracted from oyster shell with several active agents on the calcium concentration, fruit skin shape and quality of 'Fuji' apple. The tree-spray of calcium formate compound extracted from oyster shell (Os-CaF, $52.4\;mg{\cdot}kg^{-1}$) appeared to have more effectiveness on the calcium translocation into leaves, fruit skin and flesh than control. Addition of adjuvants to Os-CaF increased calcium concentration of 'Fuji' apple when sprayed three times before harvest. Among the active agents examined, the treatment ascorbic acid and poly-vinyl alcohol (PVA) in leaves, Ag-colloidal and PVA in fruit skin, ascorbic acid, Ag-colloidal, and PVA in fruit flesh exhibited highest effectiveness. Fruit qualities (fruit weight, firmness, soluble solids, acidity and Hunter value) were not affect by Os-CaF on different concentrations and solutions of active agents.

• Journal of the Korea Institute of Building Construction
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• v.8 no.5
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• pp.101-107
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• 2008

This study investigated fundamental characters of the concrete according to various fiber types and contents and their properties of spatting resistance and residual compressive strength after fire test corresponding to ISO and RABT heating corves. The results were summarized as following. The Flowability was gradually declined as the increase of fiber contents, and it was the most favorable with nylon(NY) fibers. The decrease of air contents due to increasing fiber contents was in order by polypropylene(PP), polyvinyl alcohol(PVA) and NY fibers. The compressive strengths were over 40 MPa at 7 days and 50 MPa at 28 days. It was in order by PVA, PP and NY fibers. For the spatting properties, all specimens were prevented at ISO heating curve. In the other hand, the partial spatting at the surface occurred on the plain without fibers, but it was prevented over 0.10 % of PVA and 0.05 % of PP and NY fibers at the RABT heating curve.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.148-156
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• 2007

The fiber dispersion in fiber-reinferced cementitious composites is a crucial factor with respect to achieving desired mechanical performance. However, evaluation of the fiber dispersion in the composite PVA-ECC (polyvinyl alcohol-engineered cementitious composite) is extremely challenging because of the low contrast of PVA fibers with the cement-based matrix. In the present work, a new evaluation method is developed and demonstrated. Using a fluorescence technique on the PVA-ECC, PVA fibers are observed as green dots in the cross-section of the composite. After capturing the fluorescence image with a charged couple device (CCD) camera through a microscope, the fiber dispersion is evaluated using an image processing technique and statistical tools. In this image processing technique, the fibers are more accurately detected by employing an enhanced algorithm developed based on a discriminant method and watershed segmentation. The influence of fiber orientation on the fiber dispersion evaluation was also investigated via shape analyses of fiber images.

• Korean Chemical Engineering Research
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• v.49 no.4
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• pp.449-455
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• 2011

This study was performed to develop antimicrobial films using polyvinyl alcohol and methyl cellulose. Methyl cellulose and polyvinyl alcohol films plasticized with PEG(polyethylene glycol) were prepared by solvent casting process under addition of 0.025~1.0 wt% ampicillin and 0.1~1.0 wt% streptomycin as an antimicrobial agent. The mechanical properties of prepared films were examined by universal testing machine(UTM). Tensile strength of methyl cellulose films was 15.44~21.70 $N/mm^2$. Tensile strength of PVA(15 wt%) film was 20.2~51.5 $N/mm^2$, and the tensile strength of the antimicrobial films were decreased linearly with increasing the antibiotic loading amount up to 1 wt%. Antimicrobial activities of PVA and methyl cellulose films containing ampicillin and streptomycin through the disc diffusion test for the Staphylococcus aureus and Escherichia coli. The antimicrobial activity of methyl cellulose films and PVA containing ampicillin were higher than that of containing streptomycin methyl cellulose films. The results indicate the films may be a proper materials for antimicrobial packing applications.

• Microbiology and Biotechnology Letters
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• v.25 no.1
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• pp.89-95
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• 1997

The current processer of the textile wastewater treatment are mostly consisted of a combination of a physico-chemical and a biological treatment. The overall efficiency of these processes is, however, assessed to be fairly low. It is even worse during the summer season when temperature of the wastewater rises above 40$\circ $C. Therefore, a feasible process of the textile wastewater treatment which can work efficiently at higher temperatures was investigated in this work. We used a bench scale reactor consisted of one 4 liter anaerobic and one 8 liter aerobic tank, and the thermophilic symbiotic PVA degraders, Pasteruella hemolytica KMG1 and Pseudomonas sp. KMG6 that had been isolated in our laboratory. In the preliminary flask experiments, we observed that the thermophilic symbiotic PVA degraders could not grow in the wastewater substrate. Then, we isolated the mutant strains by acclimating the KMG1and KMG6 strains to the wastewater medium. The mutant symbionts (KMG1-1 and KMG6-1) were isolated through 6 times successive transfers into the fresh wastewater medium after 5 days culture for each. The mutant strains obtained grew well in the mixed medium composed of 75% wastewater and 25% synthetic medium, and supplemented with 0.5% PVA as a sole carbon source. During the culture for 14 days at pH 7.0 and 40$\CIRC $C, the bacteria assimilated about 89% of the added PVA. The symbionts degraded equally well all the PVA substrates of different molecular weight (nd=500~30000). In contrast to the flask experiments, in the reactor system the mutant strains showed very low levels of the PVA and COD removal rates. However, the new reactor system with an additional aerobic tank attained 82% removal rate of COD, 94% of PVA degradation and 71% of color index under the conditions of 5% inoculm on the tank 2, incubation temperature of 40$\circ $C, dissolved oxygen level of 2~3 mg/l and retention time of 30 hours. This result ensures that the process described above could be an efficient and feasible treatment for the PVA contained textile wastewater at higher temperatures.

• Journal of the Korean Ceramic Society
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• v.37 no.9
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• pp.921-926
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• 2000

에틸렌과 프로판가스로부터 Ni 및 Ni-Cu의 합금촉매를 사용하는 화학증착반응에 의해 제조한 나노탄소섬유에 충전재로 하고, 환경 친화적인 폴리비닐알코올을 매트릭스로 이용하여 복합재를 제조하여 전자파 차폐효능을 조사해 보았다. 전자파 차폐용 충전재의 중요한 물성치인 전기전도도는 나노탄소섬유의 반응조건에 따라 매우 민감하게 변했는데, 전체적으로 10000 psi 압력에서 4.2~29 S/cm 사이에 분포하였고 합금촉매보다도 순수한 Ni로 제조된 나노탄소섬유의 전기전도도 값이 높았다. 한편, 나노탄소섬유/폴리비닐알코올 복합재의 전기전도도는 Ni:Cu(7:3) 합금촉매에서 제조된 나노탄소섬유를 충전시켰을 때, 가장 높게 얻어져서 충전재의 전기전도도 외에도 비표면적이 중요한 변수임을 알 수 있었다. PVA 양에 대한 나노탄소섬유의 함량이 증가할수록 나노탄소섬유 복합재의 전기전도도는 기하급수적으로 증가했고, 110$0^{\circ}C$에서 1시간 동안 나노탄소섬유의 열처리를 통하여 복합재의 전기전도도는 5~7배 증가하였으며, 전자파 차폐율은 2~3 dB 정도 향상시킬 수 있었다.