• Polymer(Korea)
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• v.38 no.6
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• pp.760-766
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• 2014

Bead type super-absorbent resins to be used for release-control were prepared by modification of the inverse suspension polymerization, and their physical properties were characterized. Acrylic acid and acrylamide were used as monomers, and N,N-methylenebisacrylamide was used as crosslinker, controlling the viscosity of monomer solution by adding hydroxyethylcellulose (HEC). SEM studies of the synthesized beads verified that the bead surfaces had many pores with their diameters of several tens nm. The bead sizes were in the range of $500{\sim}3000{\mu}m$, depending on the viscosity of the monomer solution. Both absorbent amount and absorbent rate of the beads were inversely proportional to the bead size, and the maximum water absorbent amount of 1 g beads was determined to be ca. 170~200 g for 5 hrs. The absorbent rate was also dependent on pH change of the aqueous solution, exhibiting the maximum rate in pH ranging from 5 to 11. The absorbent rate decreased as the concentration of salt (NaCl and $MgCl_2$) or ethanol and ethylene glycol increased. Release time of the water absorbed into the bead resins was 700 hrs, confirming the usefulness of the resin for the good release-control materials.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.947-953
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• 2017

In this study, the regeneration efficiency of the amino acid salt absorbent which can be applied to carbon dioxide absorption / regeneration process was confirmed. The regeneration efficiency has a great influence on the economical judgment of the process. so, continuous regeneration experiment was conducted to establish economical process. The amino acid salts used in the experiments are Potassium L-lysinate and Potassium L-alaninate. Each amino acid and potassium hydroxide(KOH) were mixed at a 1: 2 molar ratio. In order to confirm the regeneration efficiency of the absorbent, carbon dioxide was absorbed in the two materials, and the carbon dioxide desorption experiment was carried out by heating. The initial reaction rate was L-alanine was faster. Over time, L-lysine, desorption higher concentrations of carbon dioxide. L-lysine showed higher regeneration efficiency than L-alanine, (L-alanine 47.26% and L-lysine 62.11%). As a result of the continuous regeneration experiment using the L-lysine having good absorption and regeneration efficiency, it was confirmed that the regeneration efficiency decreases as the number of regeneration increases.

• Journal of the Korean Chemical Society
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• v.24 no.6
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• pp.444-451
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• 1980

In order to further elucidate the process of electron solvation in liquids, the medium effect, as the difference between the free energy of $H^+$ in aqueous and non-aqueous states (${\Delta}{\Delta}G_0$), of THF-water mixtures has been investigated. (${\Delta}{\Delta}G_0$) were determined by electromotive force masurements of the cell Pt$H_2Q$, Q, HCI, THF, $H_2O$|KC1 | $Hg_2Cl_2$|Hg(Pt), where $H_2Q$ and Q are hydroquinone and quinone respectively. The effect of dielectric constant on the difference of free energy and the absorption energy of solvated electrons have been studied. For the consideration of these effect the polymerization of water in THF has been studied. Near infrared spectrum of O-H stetching energy has been used to measure the extent of water aggregates. The expermental results indicate that at least in some composition of binary mixtures the electrons or other ions are solvated preferentially with one component of solvents.

• Polymer(Korea)
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• v.30 no.4
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• pp.332-337
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• 2006

Monodisperse polymer particles were prepared via one-step seeded polymerization using PMMA seed particles and HDDA (or EGDMA) as crosslinking monomer. For the study, the effects of 1) the ratio of the absorbed monomer or monomer mixture to the seed polymer particles (swelling ratio), 2) the ratio of EGDMA in absorbed monomer mixture, 3) the dosage of initiator, and 4) electro less Ni plating on the variation of mechanical properties of monodisperse polymer particles, such as recovery rate, K-values, breaking strength and breaking displacement, were investigated by using MCT (micro compression test). It was observed that monomer swelling ratio influenced only breaking strength, but EGDMA ratio in monomer mixture, dosage of initiator and electroless Ni plating affected both K-values and breaking strength.

• Polymer(Korea)
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• v.34 no.5
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• pp.442-449
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• 2010

Polyurethane(PU) prepolymer was synthesized from ethylene oxide/propylene oxide(EO/PO) random polyether polyol, toluene diisocyanate and chain extender such as ethylene glycol and 1,4-butanediol. PU foams having various compositions were fabricated from PU prepolymers with different hard segment contents(%) and mixed foaming solution of different compositions. PU foam from chain extender-introduced PU prepolymer and mixed foaming solution containing glycerin showed better mechanical property than other groups. Various PU foams were tested on their mechanical property, moisture vapor transmission rate, absorption speed, absorptivity, morphology and cell culture test. According to the test, the PU foam fabricated from chain extender-introduced PU prepolymer and mixed foaming solution containing optimum composition of F-68, glycerin and CMC was found to have the best property for wound dressing materials. From in vivo animal study, it was confirmed that above PU foam showed rapid wound recovery.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.737-742
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• 2016

An elastomer (especially PDMS) sponge is considered to be a promising selective absorber in cleaning up oil spills. The performance of a PDMS sponge in capturing and separating oil from (sea) water depends on several parameters such as surface roughness, physicochemical treatments, and hydrostatic stability. Here, we first present a method of fabricating the PDMS sponges having numerous micro-sized pores that act as absorption and storage spaces for the target material, and then we report an experimental effort undertaken to control the surface physicochemistry (i.e., hydrophobicity or hydrophilicity) of the PDMS sponges by adjusting the size of the pores and the concentration of the surfactant (i.e., silwet L-77). From the experimental results, we develop an in-depth understanding of the mechanism for controlling the surface physicochemistry of PDMS using water-soluble micro-sized particles and a surfactant. The surface energy and absorbing behavior of the PDMS sponges are also extensively discussed.

• Korean Chemical Engineering Research
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• v.43 no.6
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• pp.683-690
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• 2005

The microwave carbonization of rice chaff was performed, and their kinetics were compared to those of conventional thermal carbonization. Thermal carbonization was carried out at $300-600^{\circ}C$ for 30 minutes. The weight loss and C/H mole ratio remarkably increased as increase of temperature, while there was no carbonization by microwave dielectric heating in spite of increasing incident power and irradiation time. However, microwave carbonization was successfully performed by addition of 6 wt％ of thermal carbonized rice chaff, it's C/H mole ratio is larger than 3.0, as a catalytic initiator to uncarbonized rice chaff, and the kinetics was depended on the incident power and irradiation time, resulting in the coincide with thermal carbonization to the Arrhenius equation. The activation energy of microwave carbonization was quite low as compared to that of thermal carbonization, while the kinetic constant was large. This is due to the internal volumetric heating characteristics of carbonized rice chaff by microwave. The effect of ash, and C/H mole ratio and amount of carbonized rice chaff were investigated on microwave carbonization.

• Journal of the Korean Chemical Society
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• v.43 no.4
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• pp.418-422
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• 1999

A method is described for the selective determination of Cr(III) and Cr(VI) in aqueous solutios by flame atomic absorption spectrometry. Selective extraction of $Cr_2O_7^{2-}$ was performed by Aliquat 336/NIBK from the mixtures of $Cr^{3+}$ and $Cr_2O_7^{2-}$, and the extraction of $Cr^{3+}$ was followed after complex formation with citrate by using the same extractant. The concentraction of each analyte in the extract was determined by $N_2O-C_2H_2$ flame atomic absorption spectrometry. The recoveries of $Cr^{3+}$ and $Cr_2O_7^{2-}$ from 50mL of aqueous solution ranging 0.1~1.0 ${\mu}g/mL$ as Cr respectively by single extractions with 5 mL of 1%(V/V) Aliquat 336/MIBK were resulted as 98.8∼101.7%.

• Food Science and Preservation
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• v.23 no.3
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• pp.355-360
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• 2016

In this study, the quality characteristics of spray dried powders from unripe fig extract were investigated. The protease activities of unripe fig and peeled unripe fig extract were 0.11 unit/mL and 0.28 unit/mL, respectively. The spray dried powder of unripe fig extracts was analzed using different maltodextrin ratios (F-MD 5, 5% maltodextrin; F-MD 10, 10% maltodextrin; and F-MD 20, 20% maltodextrin). The spray-dried powder showed the highest protease activity with F-MD 10 (0.84 unit/g). The moisture content and L value of the spray-dried powder were higher than those of the freeze-dried powder. The particle diameter of the freeze-dried powder ($209.67{\mu}m$) was higher than that of the spray-dried powders ($22.18{\sim}37.33{\mu}m$). The water absorption index ranged from 0.18 to 0.40, while the water solubility index ranged from 94.40% to 98.80%. In the in vitro digestion study, spray-dried powders of the unripe fig showed a protease survival range of 16.47%~24.80%. In conclusion, it is considered appropriate to use the spray-dried powder (F-MD 10) of unripe fig as a meat tenderizer for processing food.

• Journal of the korean academy of Pediatric Dentistry
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• v.40 no.3
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• pp.177-184
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• 2013

Calcium hydroxide mixture medicaments can nearly be considered to be the ideal primary tooth filling material. However, long-term application of calcium hydroxide combinations as an intra canal medicament softens dentin. The aim of this study was to evaluate the effect of calcium hydroxide on the microhardness of root dentin of primary tooth. For the study, 60 extractedprimary incisors were divided into 3 groups (no medicament, calcium hydroxide/iodorform mixture, and calcium hydroxide/distilled water mixture). After the cleansing and shaping of canals, calcium hydroxide medicaments were applied and stored for different periods of time (1, 7, 30, 90 days). The root was horizontally sectioned into 2 mm thick specimens and the microhardness was measured using Vickers microhardness tester. The results were as follows : Root dentin microhardness of primary teeth decreased with long term exposure to calcium hydroxide medicaments according to the experimental period and showed statistically significance (p < 0.05). Root dentin microhardness of primary tooth filled with calcium hydroxide mixed with distilled water showed more decrease than filled with Vitapex and showed statistically significance (p < 0.05). Root dentin microhardness of a control group without exposure to calcium hydroxide decreased according to the experimental period and showed statistically significance (p < 0.05).