• Elastomers and Composites
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• v.39 no.1
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• pp.12-22
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• 2004

The plasma surface modification of natural rubber vulcanizate was carried out using chlorodifluoromethane in a radio-frequency (13.56 MHz) electrodeless bell type plasma reactor. The modification was qualitatively assessed by Fourier transform infrared spectroscopy. The frictional force of the plasma-treated surface was found to decrease with the time of plasma treatment. An increase in the surface polarity, as evidenced by the decrease in contact angle of a sessile drop of water and ethylene glycol on the natural rubber vulcanizate surface, was noted with the plasma modification. In the case of similar plasma treatment of glass surface, only a reduction in the polarity was observed. The use of geometric and harmonic mean methods was found to be useful to evaluate the London dispersive and specific components of surface free energy. Irrespective of the method used for evaluation, an increasing trend in the surface free energy was noted with increasing plasma treatment time. However, the harmonic mean method yielded comparatively higher values of surface free energy than the geometric mean method. The plasma surface modification was found to vary the frictional coefficient by influencing the interfacial, hysteresis and viscous components of friction in opposing dual manners.

• KSBB Journal
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• v.31 no.4
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• pp.256-262
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• 2016

The need for natural cosmetic ingredients has been increasing over the world nowadays. Agarose, a natural polymer from red seaweeds, has high hydrophilic character and a function of scaffolder. As skin moisturizer, agarose is adequate for percutaneous absorption. While, blueberry fruits extract possesses rich procyanidins and anthocyanins which show health benefits, anti-oxidant effect, anti-aging and anti-melanogenesis. Stability, sensory preference, skin trouble of the emulsion formula are important for cosmetic product development. In this study, we manufactured an emulsion formula for skin moisturizers using the two ingredients and tested emulsion stability and skin trouble. Total phenolic contents of the blueberry fruits extract were evaluated as well as tyrosinase inhibitory and collagenase inhibitory activities. $IC_{50}$ values of blueberry fruits extract for anti-tyrosinase and anti-collagenase activities were 168 and $112{\mu}g/mL$, respectively using gallic acid as a control ($64.8{\mu}g/mL$). The stability (pH and viscosity) of the formula containing 2% blueberry fruits extracts and 0.1% agarose was measured at five different temperatures (room temp., $25^{\circ}C$, $55^{\circ}C$, $45^{\circ}C$, $55^{\circ}C$) under the sun light at 2 day intervals for 12 days. There has been little pH change at the different temperatures. According to the sensory evaluation, there was no significant flavor, discoloration and physical changes of the formula at $25-65^{\circ}C$. These results suggest that emulsion formula containing blueberry extract and agarose could be used as a candidate for lotion and essence products.

• Polymer(Korea)
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• v.33 no.4
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• pp.307-312
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• 2009

The fabrication of PHBV nanofibers containing various plant polyphenols by electrospinning has been examined. It has been found that the average diameters of fibers increased by the adding of polyphenols. The resulting fibers exhibited a uniform diameter ranging from 340 to 450 nm. As the concentration of polyphenols increased, the diameter of fibers increased due to the hydrogen bonding interaction between the ester groups of PHBV and hydroxyl groups of polyphenols. The interaction between PHBV and polyphenols, which forms a complex together in solution, was verifed by UV measurement. ATR-FTIR analysis confirmed the existence of the hydrogen bonding interaction. The semicrystalline structure of the PHBV nanofiber was observed from XRD pattern. The crystallinity of PHBV nanofibers was increased by the adding of polyphenols. PHBV nanofibers containing polyphenols showed superior antimicrobial activities.

• Clean Technology
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• v.17 no.1
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• pp.1-12
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• 2011

Scientists and engineers have altered the properties of materials such as metals, alloys, polymers, ceramics, and so on, to suit the ever changing needs of our society. Man-made engineering materials generally demonstrate excellent mechanical properties, which often tar exceed those of natural materials. However, all such engineering materials lack the ability of self-healing, i.e. the ability to remove or neutralize microcracks without intentional human interaction. The damage management paradigm observed in nature can be reproduced successfully in man-made engineering materials, provided the intrinsic character of the various types of engineering materials is taken into account. Various self-healing ptotocols that can be applied for the organic materials such as polymers, ionomers and composites can be developed by utilizing suitable chemical reactions and physical intermolecular interactions.

• Polymer(Korea)
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• v.34 no.1
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• pp.63-68
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• 2010

In this study, we evaluated the effect of fibrin, a natural material, on the local inflammatory reaction of PLGA in vivo. PLGA degradation products can decrease the pH in the surrounding tissue, causing local inflammatory reaction. To solve this problem, fibrin/PLGA scaffolds were implanted in 5-week-old Wister rats. To evaluate the influence of fibrin content on inflammatory cytokine expression induced by PLGA, RT-PCR analysis was used. Fibrous wall thickness and macrophage infiltration were evaluated by H&E and ED-1 immunohistochemical staining, respectively. In this study, we showed that fibrin/PLGA scaffolds reduced inflammatory reaction as compared to PLGA scaffold. We concluded that fibrin could reduce inflammatory response of PLGA.

• Macromolecular Research
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• v.12 no.4
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• pp.422-426
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• 2004

Solid polymer electrolytes based on poly(ethylene glycol)-polyurethane (PEG-PU) complexed with LiClO$_4$ salt have been prepared by the solvent casting method. A PEG-PU material (PEG:4,4'-diphenylmethane diisocyanate: l,4-butanediol = 1:2:1) was synthesized through a typical two-step condensation reaction. We investigated the effects of the salt concentration on the ionic conductivity ($\sigma$) and the glass transition temperature (T$_{g}$ ) of the complex electrolytes by using alternating current impedance spectroscopy, differential scanning calorimetry, and dynamic mechanical thermal analysis. The measured values of both $\sigma$ and T$_{g}$ exhibited similar tendencies in that they had maxima within the range studied, probably because of two opposite effects, i.e., the increased number of carrier ions and the decreased chain mobility (or increased T$_{g}$ ) caused by the increase in the salt concentration. The highest conductivity, on the order of 2.43 ${\times}$ 10$^{6}$ S$cm^{-1}$ /, was obtained at an [O]/[Li$^{+}$] ratio of ca. 16 (0.92 ㏖ salt per kg of matrix polymer).

• Journal of Adhesion and Interface
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• v.10 no.1
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• pp.23-29
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• 2009

We investigated effects of a compatibilizer on the rheological properties during mixing and thermal properties of polypropylene (PP)-natural fiber composites. Two types of natural fibers (cotton fiber and wood fiber) were compared. maleic anhydride grafted PP was used for a compatibilizer. On increasing the amounts of the compatibilizer, the torque values of composites were increased, regardless of the kind of fibers. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results showed a slight increase in the degree of crystallinity with adding the compaibilizing agent, while the effects of the kind of fibers were marginal. It may be considered, however, the cotton fiber exhibits better interaction with PP-g-MAH than the natural fiber based on the rheographs, DSC, and XRD results.

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3676-3680
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• 2012

An Epstein-Barr virus (EBV)-based plasmid contains the EBV nuclear antigen 1 (EBNA1) gene and EBV replication origin (oriP) sequence. Since EBNA1 (the only EBV-encoded protein) is combined with oriP, it is replicated simultaneously with chromosomal DNA in human, primate, and canine cells and is faithfully segregated at a stable copy number upon cell division. Consequently, it can be used to stably express gene inserts over a prolonged time in target cells. We have previously shown that the polyamidoamine (PAMAM) dendrimer can be surface-modified with L-arginine. Arginine is present at a high frequency in the transactivator of transcription (Tat) sequences of human immunodeficiency virus (HIV). It presents high membrane permeability and permits effective transfer of DNA inside the cells. In this study, we constructed two kinds of recombinant DNA by inserting the luciferase gene and enhanced green fluorescence protein (eGFP) gene as reporter genes into the pCEP4 plasmid vector. We measured dynamic light scattering (DLS) and zeta potential after preparing PAMAM-based cationic polymer/EBV-based plasmid complexes. We performed transfection of HEK 293 cell lines with the polyplexes, and monitored luciferase activity and green fluorescence protein (GFP) expression. Our results show that PAMAM-based cationic polymer/EBV plasmid complexes provide enhanced and sustained gene expression.

• Macromolecular Research
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• v.10 no.3
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• pp.158-167
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• 2002

In order to endow with new bioactive functionality from small intestine submucosa (SIS) powder as natural source to poly (L-lactide) (PLA) and poly (lactide-co-glycolide) (PLGA) synthetic biodegradable polymer, porous SIS/PLA and SIS/PLGA as natural/synthetic composite scaffolds were prepared by means of the solvent casting/salt leaching methods for the possibility of the application of tissue engineered bone and cartilage. A uniform distribution of good interconnected pores from the surface to core region was observed the pore size of 40~500 ${\mu}{\textrm}{m}$ independent with SIS amount using the solvent casting/salt leaching method. Porosities, specific pore areas as well as pore size distribution also were almost same. After the fabrication of SIS/PLA hybrid scaffolds, the wetting properties was greatly enhanced resulting in more uniform cell seeding and distribution. Five groups as PGA non-woven mesh without glutaraldehyde (GA) treatment, PLA scaffold without or with GA treatment, and SIS/PLA (Code No.3 ; 1 : 12 of salt content, (0.4 : 1 of SIS content, and 144 ${\mu}{\textrm}{m}$ of median pore size) without or with GA treatment were implanted into the back of nude mouse to observe the effect of SIS on the induction of cells proliferation by hematoxylin and eosin, and von Kossa staining for 8 weeks. It was observed that the effect of SIS/PLA scaffolds with GA treatment on bone induction are stronger than PLA scaffolds, that is to say, in the order of PLA/SIS scaffolds with GA treatment > PLA/SIS scaffolds without GA treatment > PGA nonwoven > PLA scaffolds only with GA treatment = PLA scaffolds only without GA treatment for the osteoinduction activity. The possible explanations are (1) many kinds of secreted, circulating, and extracellular matrix-bound growth factors from SIS to significantly affect critical processes of tissue development and differentiation, (2) the exposure of SIS to GA resulted in significantly calcification, and (3) peri-implant fibrosis due to covalent bonding between collagen molecule by crosslinking reaction. In conclusion, it seems that SIS plays an important role for bone induction in SIS/PLA scaffolds for the application of tissue engineering area.

• Macromolecular Research
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• v.13 no.1
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• pp.30-38
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• 2005

Sulfur-cured gum natural rubber vulcanizates were devulcanized using two different concentrations of diallyl disulfide. The devulcanization process was performed at $110^{\circ}C$ min in an open two-roll cracker-cum-mixing mill. Natural rubber vulcanizates having various sulfur/accelerator ratios were used to study the cleavage of monosulfide, disulfide, and polysulfide bonds. The properties of devulcanized natural rubber increased upon increasing the disulfide concentration and the mechanical properties of the revulcanized natural rubber increased upon decreasing the sulfur content in the original rubber vulcanizates. The scorch time and the maximum state of cure both increased when the ground vulcanizates were treated with higher amounts of disulfide. TGA and DMA were conducted to study the effects of the devulcanization on the thermal stability and the $T_g$ behavior of the vulcanizates. SEM analysis was conducted to study how the failure mechanism was affected by the devulcanization process. It was possible to recover $70-80\%$ of the original gum rubber properties by using this process. From IR spectroscopic analysis, we observed that the oxidation of the main chains did not occur during high-temperature milling.