• Membrane Journal
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• v.16 no.2
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• pp.153-158
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• 2006

The crosslinked poly(vinyl alcohol) (PVA) mwmbranes with poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA) were used to measure the water vapor and air permeabilities at 25 and $35^{\circ}C$. In addition, the contact angles of crosslinked PVA membranes were observed and increased with PSSA-MA contents. The water vapor permeability of 15300 Baller (1 Baller=$10^{-10}cm^3(STP){\cdot}cm/cm^2{\cdot}s{\cdot}cmHg$) was shown the maximum value at $35^{\circ}C$ when PSSA-MA=7 wt% membrane was used. The gas permeability of 146 Barrer was indicated the maximum at PSSA-MA=7 wt% at $35^{\circ}C$ and $P(H_2O)/P(Air)$ was the highest value 109.2 at $25^{\circ}C$.

• Membrane Journal
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• v.18 no.1
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• pp.44-52
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• 2008

Pervaporation separation for water-ethanol mixtures has been carried out using crosslinked poly(vinyl alcohol) (PVA) membranes with poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA) and at which tetraethylorthosilicate (TEOS) was introduced. The concentration of PSSA_MA was fixed 7 wt% over PVA and the TEOS contents, 3, 5, and 7 wt%, were varied against PVA. The composition of the feed mixtures were 10, 20, 30 and 50 wt% of water in it. PVA/PSSA_MA/5 wt% TEOS membrane showed the separation factor, 1730 and the permeability, $16.3g/m^2{\cdot}hr$ for water : ethanol = 10 : 90 at $50^{\circ}C$.

• Journal of the Korean Applied Science and Technology
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• v.20 no.1
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• pp.8-19
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• 2003

Environmental friendly acrylics/urea high-solid paints (BEHCU) were prepared through the curing reaction of acrylics resin(BEHC) containing 70wt% of solids content and butylated urea curing agent. BEHC was synthesized by addition copolymerization of caprolactone acrylate(CLA), 2-hydroxypropyl methacrylate(2-HPMA), ethyl methacrylate, and n-butyl acrylate. The addition polymerization of these monomers, especially including flexible CLA monomer and 2-HPMA monomer with OH funtional group, under appropriate reaction conditions resulted in polymers with controlled glass transition temperature($T_g$) and crosslinking density. The molecular weight($M_w$) of these polymers(BEHCs) was 2940${\sim}$3240 and polydispersity ($M_w/M_n$) was in the range of 1.61${\sim}$1.72. The viscosity and the molecular weight of these acrylic resins increased with increasing $T_g$. The coated films were prepared using curing reaction between BEHC resin and butylated urea curing agent at 100$^{\circ}C$ for 30 minutes. Our experimental resulted showed that enhancement of the coating properties such as adhesion, flexibility, impact resistance, water resistance, and abrasion resistance could be expected through introducing CLA component in acrylic resin for the high-solid content acrylics/urea coatings.

• Applied Chemistry for Engineering
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• v.4 no.2
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• pp.324-334
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• 1993

Chitin, the natural polymer has been known as harmless and innoxious material to human and has been also known to be biodegradable. Chitosan which was prepared by the deacetylation of chitin, was propionylated to obtain porous bead shaped propionyl chitosan and its possibility as a water-absorbant polymer was investigated. Propionyl chitosan porous bead was synthesized by acylation reaction using emulsion method of acetic acid solution and propionyl chitosan was partially crosslinked using ethyleneglycol diglycidyl ether. Through the experiment varying the moles of propionic anhydride, reaction time and reaction temperature, best results for water-absorption ability was obtained at reaction condition of 5 moles of propionic anhydride, 10 hours of reaction time and $22^{\circ}C$ of reaction temperature. The absorption ability to the distilled water, various salt solutions, artificial urine and artificial blood, absorption time and retention of water of synthesized porous bead were investigated and also mechanical strength after crosslinking was determined.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.450-455
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• 1999

Unsaturated diol (UD) was prepared from the esterification of maleic anhydride with diethylene glycol (DEG). Unsaturated polyesters modified with rosin (UPMR) or with rosin maleic anhydride adduct (RMA) from 2-hydroxyethylmethacrylate (HEMA) and rosin (UPMRH) were prepared by the reaction of UD with RMA or RMA-HEMA. After crosslinking of UPMR and UPMRH with styrene and methylmethacrylate (MMA), respectively, solvent resistance, tensile strength, and adhesion property of the resins were measured. UPMR crosslinked with styrene or MMA shows an excellent resistance to water and acid. Solvents resistance and tensile strength of UPMR using styrene as crosslinking agent were increased compared with those of UPMR using MMA as crosslinking agent. UPMRH showed better solvents resistance and tensile strength than UPMR. Adhesion strengths of UPMR crosslinked with styrene and MMA were 1.61 and 3.02 MPa, and those of UPMRH were 2.32 and 3.89 MPa, respectively.

• Proceedings of the Membrane Society of Korea Conference
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• 2003.11a
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• pp.61-63
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• 2003

A major research objective related to proton exchange membrane(PEM) for DMFC is to achieve high proton conductivity over 10$^{-2}$ S/cm, high hydrolytic stability and low methanol permeability with low cost base materials. for the purpose, a lot of thermoplastic polymers such as polysulfones, polyethersulfone, polyetherketones, polyimides, polyoxadiazole, polyphosphazene and polybenzimidazol have been investigated. Amongst those polymers, polyimides have been suggested as a potential PEM due to their excellent thermal, chemical stability and good mechanical properties. Generally, polyimides are synthesized by polycondensation with numerious diamines and dianhydriedes. In our study, polyimide was prepared using non-sulfonated diamine, sulfonated diamine directly synthesized by fuming sulfuric acid, and naphthalenic dianhydride to improve the hydrolysis stability under acidic condition. Through monomer sulfonation-subsequent polymerization method, the high proton conducting capability and the desired sulfonation level were effectively controlled at the same time. To reduce severe methanol transport through the membrane, the chemical crosslinking among polymer chains was introduced using various crosslinking agents with different chain lengths. The crosslinked sulfonated polyimide membranes showed high proton conductivity up to 8.09$\times$10$^{-2}$ S/cm and from crosslinking effect methanol transport through the membranes was considerably reduced as compared with unmodified membranes. For increase of chain length of crosslinker, methanol permeability was adversely reduced to 10$^{-8}$ $\textrm{cm}^2$/s due to decrease of IEC and increase of crosslinking desity.

• Clean Technology
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• v.17 no.3
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• pp.209-214
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• 2011

The effects of inlet gas velocity (0.26-0.31 m/s), inlet gas temperature (315-353 K) and the mass ratio (0.1-0.4) of fine polymer (crosslinked poly methyl methacrylate beads) to inert medium particles on the drying rate of fine polymer in a 0.15 m-ID ${\times}$ 1.0 m-high inert medium fluidized bed dryer have been investigated. Crosslinked PMMA beads of 20 ${\mu}m$ (group C) were used as fine polymer, and glass beads of 590 ${\mu}m$ (group B) were used as the inert medium. The drying rate increases with increasing inlet gas temperature and velocity. However, the drying rate decreases slightly as the mass ratio of fine polymer to inert medium particles increases. The particle size distribution of dried fine polymers was mono distribution.

• Macromolecular Research
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• v.13 no.1
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• pp.45-53
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• 2005

In this study, a series of highly swelling hydrogels based on sodium alginate (NaAlg) and polymethacryl­amide (PMAM) was prepared through free radical polymerization. The graft copolymerization reaction was performed in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator and N,N'-methylenebis­acrylamide (MBA) as a crosslinker. The crosslinked graft copolymer, alginate-graft-polymethacrylamide (Alg-g­PMAM), was then partially hydrolyzed by NaOH solution to yield a hydrogel, hydrolyzed alginate-graft-poly­methacrylamide (H-Alg-g-PMAM). During alkaline hydrolysis, the carboxamide groups of Alg-g-PMAM were converted into hydrophilic carboxylate anions. Either the Alg-g-PMAM or the H-Alg-g-PMAM was characterized by FTIR spectroscopy. The effects of the grafting variables (i.e., concentration of MBA, MAM, and APS) and the alkaline hydrolysis conditions (i.e., NaOH concentration, hydrolysis time, and temperature) were optimized systematically to achieve a hydrogel having the maximum swelling capacity. Measurements of the absorbency in various aqueous salt solutions indicated that the swelling capacity decreased upon increasing the ionic strength of the swelling medium. This behavior could be attributed to a charge screening effect for monovalent cations, as well as ionic cross-linking for multivalent cations. Because of the high swelling capacity in salt solutions, however, the hydrogels might be considered as anti-salt superabsorbents. The swelling behavior of the superabsorbing hydrogels was also measured in solutions having values of pH ranging from 1 to 13. Furthermore, the pH reversibility and on/off switching behavior, measured at pH 2.0 and 8.0, suggested that the synthesized hydrogels were excellent candidates for the controlled delivery of bioactive agents. Finally, we performed preliminary investigations of the swelling kinetics of the synthesized hydrogels at various particle sizes.

• Restorative Dentistry and Endodontics
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• v.41 no.4
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• pp.296-303
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• 2016

Objectives: The purpose of the present study was to evaluate the effects of proanthocyanidin (PAC), a crosslinking agent, on the physical properties of a collagen hydrogel and the behavior of human periodontal ligament cells (hPDLCs) cultured in the scaffold. Materials and Methods: Viability of hPDLCs treated with PAC was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The physical properties of PAC treated collagen hydrogel scaffold were evaluated by the measurement of setting time, surface roughness, and differential scanning calorimetry (DSC). The behavior of the hPDLCs in the collagen scaffold was evaluated by cell morphology observation and cell numbers counting. Results: The setting time of the collagen scaffold was shortened in the presence of PAC (p < 0.05). The surface roughness of the PAC-treated collagen was higher compared to the untreated control group (p < 0.05). The thermogram of the crosslinked collagen exhibited a higher endothermic peak compared to the uncrosslinked one. Cells in the PAC-treated collagen were observed to attach in closer proximity to one another with more cytoplasmic extensions compared to cells in the untreated control group. The number of cells cultured in the PAC-treated collagen scaffolds was significantly increased compared to the untreated control (p < 0.05). Conclusions: Our results showed that PAC enhanced the physical properties of the collagen scaffold. Furthermore, the proliferation of hPDLCs cultured in the collagen scaffold crosslinked with PAC was facilitated. Conclusively, the application of PAC to the collagen scaffold may be beneficial for engineering-based periodontal ligament regeneration in delayed replantation.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.63-68
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• 2008

We investigated the recycling method to re-plasticize cross-linked polyethylene by using supercritical methanol. The cross-linked polyethylene is successfully fragmented to thermoplasticized polyethylene with little degradation reactions in supercritical fluids. The thermo-plasticization reaction was accelerated with increase in temperature in the range from $360^{\circ}C$ to $400^{\circ}C$, resulting in decrease in crosslinking density, molecular weight and mechanical properties. However, the thermoplasticized polyethylene at $360^{\circ}C$ showed comparable tensile strength and impact strength with a raw resin of crosslinked polyethylene. Chemical structure of main chain of polyethylene was not affected by reaction condition.