• Applied Chemistry for Engineering
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• v.23 no.4
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• pp.388-393
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• 2012

Branched polycarbonates (B-PCs) were synthesized using melt polymerization method with four different end capping agents and vaying concentrations. The chemical structure of the synthesized PC was determined by FT-IR and $^{1}H-NMR$ spectroscopy, and the reaction of the end capping agent was confirmed by the existence of hydroxy group in FT-IR spectrum. The average molecular weight and distribution, glass transition and degradation temperatures were determined by GPC, DSC and TGA. The average molecular weight changed with the chemical structure of end capping agent, and 4-tert-butylphenol was estimated as the optimum end capping agent. The average molecular weights of B-PCs decreased with the increase of the concentration of the agent, the number average molecular weight represented 20000 when 0.05 mol% of 4-tert-butylphenol was added to B-PCs. The melt viscosities of the B-PCs decreased with the decrease of the molecular weight of B-PCs, and adding of the agent was not effected to shear thinning tendency.

• Polymer(Korea)
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• v.26 no.4
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• pp.508-515
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• 2002

The effects of the crosslinking caused by irradiation dose, molecular weights of the foaming materials, and various foaming processes on the foam structure of the polypropylene (PP) were investigated. The maximum gel content of the PP was 48% when the sheet was irradiated with 3.2 Mrad. This high gel content improved the cell structures by providing high thermal stability. The increase of both the gel content and structural development were stopped at the irradiation dose exceeding 3.2 Mrad. The increase of the molecular weights served to help produce a foam with particularly fine and even cell structures, along with improved thermal stability as well.

• Journal of Biomedical Engineering Research
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• v.22 no.6
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• pp.519-526
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• 2001

At present. about 0.3 million and more THRs (Total Hip Replacement) in a rear are being done worldwide. The increase in mechanical failure with the increase in THR, required more revisions. Revisions compensate mainly the wear of the artificial joint frictional surface and the loosening of the cup and stem. According to recent researches, loosening is mainly due to wear debris UHMWPE (Ultra High Molecular Weight Polyethylene) from frictional surfaces . To overcome the wear problems associated with artificial joint materials , new surface structures with regular Patterns were designed and fabricated The lubrication Properties were examined to evaluate the wear of the frictional surfaces. The surface structure manifested a Pattern of "dents" with a 0.2-1.0 mm of diameter and 0.6-2.0 mm of Pitch. From the friction test of the SUS316L vs UHMWPE using the frictional tester, we found that the lubrication Performance was improved due to of drastically reduced amount of abrasion. There were optimum sizes for the diameter and the pitch of the Pattern. The results demonstrated that the lubrication properties could be improved by Patterning of the frictional surfaces. The surface Patterning was effective in preventing wear of the frictional surfaces, and the life of an artificial joint could be extended with such Patterning.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.4
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• pp.226-231
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• 2005

To investigate the physical properties of sea tangle (Laminaria japonica) alginates, extracted by the Mexican process, the effects of extracting time and drying methods on intrinsic viscosities, MWs and DPs of alginates were examined. The MWs of alginates before and after dialysis decreased with increase of extracting time. The MW s before dialysis were lower than those after dialysis. The ash contents before dialysis decreased with increase of extracting time. After dialysis the ash contents of the alginates showed 10.4-10.9% of those, which were little affected by extracting time. In the ash composition after dialysis, the sodium content was 4.4 g/100 g, $90\%$ of total ash content. The ash contents, the intrinsic viscosities, the average molecular weight and the DPs of the alginates dried by AD before dialysis were higher than those by VF. The ash and uronic acid contents of alginates after dialysis showed $10.6-10.9\%\;and\l88.1-88.9\%$, respectively. But the intrinsic viscosities, the MWs and DPs of the alginates after dialysis gradually decreased by following dry methods. The decreased order was ADAD, ADVF, VFAD, VFVF. The coefficient of determination between MWs and DPs in the alginates having more than 300 kDa was 0.999.

• Food Science and Biotechnology
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• v.18 no.1
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• pp.157-161
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• 2009

Resveratrol-loaded poly($\varepsilon$-caprolactone) (PCL) nanoparticles were prepared by oil in water (O/W) emulsion solvent evaporation method. The morphology of the nanoparticles was evaluated using atomic force microscope (AFM), in which well-shaped and rigid nanoparticles were prepared. The mean particle size of nanoparticles prepared using only dichloromethane (DCM) ($523.5{\pm}36.7\;nm$) was larger than that prepared with a mixture of DCM and either ethanol (EtOH) ($494.5{\pm}29.2\;nm$) or acetone ($493.5{\pm}6.9\;nm$). The encapsulation efficiency of nanoparticles prepared only with DCM as dispersed phase ($78.3{\pm}7.7%$) was the highest of those prepared with solvent mixtures. An increase in the molecular weight of PCL led to an increase in encapsulation efficiency (from $78.3{\pm}7.7$ to $91.4{\pm}3.2%$). Pluronic F-127 produced the smallest mean size ($523.5{\pm}36.7\;nm$) with the narrowest particle size distribution. These results show that dispersed phase, molecular weight of wall materials, emulsion stabilizer could be important factors to affect the properties of nanoparticles.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.05
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• pp.223-225
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• 1996

Poly (ethylene glycol) (PEG)macromers terminated with acrylate groups and interpenetrating polymer networks(IPN) composed of poly(hydroxyethyl methacrylate)(PHEMA) or poly(hydroxyethyl methacrylate-co-hydropropyl methacrylate-co-N-vinyl pyrrolidone) [P(HEMA-co-HPMA-co-NVP)] and PEG macromer were synthesized with the aim of obtaining protein adsorption resisatnt soft contact lens. Polymerization of PEG macromer resulted in the formation of cross-linked gels due to the multifunctionality of macromer. Crosslinked P(HEMA) or P(HEMA-co-HPMA-co-NVP) chains were interpenetrated into the cross-linked three-dimensional networks of PEG. It was found that albumin adsorption onto the contact lens prepared by P(HWMA)/PEG IPN decreases with a decrease of molecular weight of PEG whereas its adsorption onto the contact lens prepared by P(HEMA-co-HPMA-co-NVP)/PEG IPN decreases with an increase of molecular weight of PEG. Also, it was found that albumin adsorption onto the both contact lens decreases with an increase of concentration of PEG macromer in the IPN preparation. There are also more adequate in the bioinertness and bioadhesion for the contact lens by P(HEMA)/PEG IPN or P(HEMA-co-HPMA-co-NVP)/PEG IPN than that by P(HEMA) or P(HEMA-co-HPMA-co-NVP).

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.648-653
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• 1998

This study examines the effects of cell size and structure on the oil adsorption by polyurethane (PU) foam. A series of oil-adsorptive PU foam has been prepared, using various molecular weight of polyether polyol (GP-1000, GP-3000, GP-4000, GP-5000), together with TDI-80, water and additives. It was found that the cell size of PU foam decreased with increasing the agitation speed and surfactant content. Oil-adsotption of PU foam increased over 2000% with the increase of molecular weight of polyol and with the decrease of cell size. Increase in the surfactant content and the viscosity of adsorbed oil also give a remarkable decrease in oil adsorption.

• Journal of Environmental Science International
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• v.12 no.12
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• pp.1269-1276
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• 2003

In order to know the effect of atuoclaving on the heavy metal removal using chitosan, lead removal capacities and removal rates by various chitosans in aqueous solution were compared according to the various autoclaving time. The lead removal efficiencies and removal rates by the autoclaved chitosan were found to be on the order of 15 min(98％) ＞ 10 min(95％) ＞ 30 min(83％) ＞ 5 min(53％) ＞ 60 min(47％) ＞ 0 min(22％) chitosan. The molecular weight of chitosan was decreased by the increase of autoclaving time. Therefore, the heavy metal removal capacity was not well correlated to the molecular weight. Langmuir isotherm was well fitted to experimental results of equilibrium adsorption on chitosan. In order to examine the process of lead removal by the autoclaved chitosan, TEMs, SEMs and FT-IR analyses were used. The surface of autoclaved chitosan was much more porous and the lead removal was mainly occurred on the surface of chitosan. The structure of autoclaved chitosan was same as that of controlled chitosan.

• Biomolecules & Therapeutics
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• v.3 no.1
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• pp.80-84
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• 1995

Effects of titrated extract of Centella asiatica (TECA) and epidermal growth factor (EGF) isolated from the urine of pregnant horse on the proliferation of human epidermal keratinocyte in culture were studied. An increase in the number of keratinocyte was observed with the treatment of TECA at the concentration ranges from 1 $\mu\textrm{g}$/mι to 100 $\mu\textrm{g}$/mι. Effects of low molecular weight EGF (LEGF) and high molecular weight EGF (HEGF) on the proliferation of keratinocyte in culture were also studied. The number of keratinocyte in culture was significantly increased with LEGF and HEGF respectively at the concentration of 10 ng/mι. Simultaneous treatment of the keratinocyte with LEGF, HEGF and TECA led to the increased proliferation of keratinocytes resulting 96% of the effect of a positive control, EGF isolated from mouse submaxillary glands.

• Journal of the Korean Graphic Arts Communication Society
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• v.20 no.1
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• pp.65-78
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• 2002

The suspension polymerization of styrene was carried out to obtain the narrow-size distribution of particle by using poly(vinyl alcohol) (PVA) as suspension stabilizer according to the degree of hydrolysis and the molecular weight. The stabilizing properties of suspension are also dependent on the interfacial tension of aqueous solution when PVA is added. When the polymerization process was carried out with low hydrolyzed PVA, it gave single, well-defined particles, while high hydrolyzed PVA gave clusters. The size of particle produced in this study ranged between 5${\mu}{\textrm}{m}$ and 10${\mu}{\textrm}{m}$. The suspending agent, PVA, influences on the drop size and drop stability, When the molecular weight of PVA is increased, the drop size decreases and the drops become more stable toward coalescence. An increase in the PVA concentration decreases the mean drop size and narrows the drop size distribution.