• Carbon letters
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• v.23
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• pp.55-62
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• 2017

We report on the dispersion state of partially reduced graphene oxide (PRGO) in organic solvents, namely methyl ethyl ketone, ethyl acetate, methylene chloride, toluene, and xylene, by controlling the carbon to oxygen (C/O) atomic ratio of the PRGOs. A two-phase solvent exchange method is also proposed to transfer PRGO from water to an aprotic solvent, such as methyl ethyl ketone. We achieve relatively good dispersion in aprotic and non-polar solvents by controlling the C/O atomic ratio of the PRGOs and applying the two-phase solvent exchange method. There is an increase in the glass transition temperatures with the dispersion of PRGOs into amorphous polymers, in particular a $4.4^{\circ}C$ increase for poly(methyl methacrylate) and $3.0^{\circ}C$ increase for polycarbonate. Good dispersion of PRGO in a nonpolar polymer, such as linear low density polyethylene, is also obtained.

• KSBB Journal
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• v.26 no.5
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• pp.453-458
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• 2011

In this study, two different extraction techniques, organic solvent extraction and supercritical carbon dioxide ($SCCO_2$) extraction, were employed to evaluate the extraction efficiency of oil from Chlorella vulgaris. In the organic solvent extraction, the effects of various organic solvent on the extraction yield were investigated. The $SCCO_2$ extraction was carried out while varying such operating parameters as temperature, pressure, $SCCO_2$ flow rate, and cosolvent. About 4.9 wt% of oil was extracted from ground Chrollera vulgaris for 18 h when dichloromethane/methanol (2：1, v/v) was used as an extraction solvent. The oil yield of the $SCCO_2$ extraction was found to be very low (0.53 wt%) and to increase up to about 0.86 wt% with the addition of cosolvent.

• Journal of Preventive Medicine and Public Health
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• v.31 no.4 s.63
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• pp.628-643
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• 1998

To investigate the exposure levels of organic solvents and subjective symptoms of dry-cleaning workers, 77 male and 52 female dry-cleaning workers who had been worked in a small city of Chungnam province, and a large city, Taejon were selected for the study group. Air concentrations of organic solvents in the working environment were analyzed, and subjective symptoms of dry-cleaning workers were surveyed, from July to August 1996. The results obtained were as follows : 1. The concentrations of organic solvents in the working environment were within permissible TLV-TWA limits. 2. For the 13 symptom clusters, the most frequently complained symptom clusters were fatigue as 71.3%, and followed by depression and urinary disturbances as 53.5% and 51.9%. Other symptom clusters complained were below 50%. 3. Positive response rates of subjective symptoms were significantly higher in worker groups such as lived in a large city, female, higher education level, more frequently alcohol drinking, higher concentration of organic solvent in working environment, work in alone. 4. Workers who had used solvent B showed 2.3 point higher scores of subjective symptoms than those of solvent A. Of the subjective symptoms scores, amnesia and nervousness were higher in solvent B user group than solvent B user group. 5. As a result of factor analysis, 3 factors such as depression, urinary disturbance and neurologic disturbance were selected. 6. As a result of the logistic regression analysis, sex, the number of fellow workers, working time, region, job tenure, smoking, alcohol drinking, ventilating system, concentration of organic solvent in working environment and place of residence were selected for the related variables. For the conclusion, even though the concentrations of organic solvents in the working environments of dry-cleaning workers were within permissible limit of TLV-TWA, many dry-cleaning workers complained symptoms, such as fatigue, depression, urinary disturbances and so on. And the factors affecting to the symptoms of dry-cleaning workers were the number of fellow workers, work hours, region, job tenure, smoking and alcohol drinking.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.342-342
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• 2006

Atomic force microscope (AFM) enables us to stretch a single polymer chain by picking it at its two modified termini. Using this method called "nanofishing," we have studied statistical properties of single polymer chains. A force-extention curve obtained for a polystyrene with thiol termini in a cyclohexane showed a good agreement with a worm-like chain (WLC) model, and thus gave microscopic information about entropic elasticity. In this report, the experiments were performed at wide-range temperatures, resulting in wide-range solvent qualities from poor to good solvent condition. The temperature dependence of statistical properties of polystyrene was examined. The coil-strand transformation realized in a poor solvent was also discussed.

• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.214-222
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• 1996

The effect of physicochemical properties of organic solvent and dispersant among organic solvent dispersant binder and plasticizer which are used as processing additives in MLCC fabrication process on the dispersion of BaTiO3 was studied. The steric and electrostatic stabilization mechanisms in dispersion of BaTiO3 in organic media were evaluated respectively. The sttability of BaTiO3 achieved bysteric stabilization was dependent on the fraction of surface coverage of dispersant adsorption on BaTiO3. The electrostatic repulsive forces of BaTiO3 particles dispersed in orgainc media was found to be appreciabley great and dependent mainly on the kinds of organic solvent used. The mechanism affecting the stability of BaTiO3 was studied by the method of rheologi-cal behaviors of BaTiO3 suspension.

• 한국생물공학회:학술대회논문집
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• 2003.10a
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• pp.490-493
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• 2003

Enzymatic synthesis of sugar fatty acid esters was investigated in organic solvent using Candida rugosa lipase. To overcome sugars insolubility in organic solvent, sugar absorption procedure was done on a silica gel. The product yield was determined by using ion Chromatography, with various factors such as reaction time, enzyme fatty acid molar ratio, number of carbon in fatty acid.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4167-4170
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• 2011

An inexpensive and efficient catalyst system has been developed for the N-arylation of phenylurea including a variety of aryl halides. This simple protocol uses $Cu_2O$ as the catalyst, microwave assisted, solvent- and ligand-free, $K_3PO_4{\cdot}H_2O$ as the base.

• Resources Recycling
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• v.11 no.6
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• pp.38-46
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• 2002

Fundamental investigations were conducted far the recovery process of waste organic solvent by fractional distillation in the aspects of equilibrium and kinetics. Mixture of toluene and xylene, which were both being used in the largest amount as industrial organic solvent, was taken as the artificial waste organic solvent and their distillation behaviors were studied. The purity of recovered solvent was investigated by Cir Chromatography and shown to be in the range of 94～98%. Based upon equilibrium calculations, the changes in the Gibbs free energy, standard enthalpy, and standard entropy for distillation reaction have been estimated. The standard enthalpy changes for toluene and xylene were shown to be 44.833 and 47.044 kJ $mol^{-1}$ respectively, which were similar to their molar heats of evaporation. The activation energies of distillation fur toluene and xylene obtained from kinetic studies were 3.281 and 2.699 kJ $mol^{-1}$ and they were about one tenths of the standard enthalpy changes of distillation reaction. The highness of the purity of recovered organic solvents suggested the possibility that the recovered waste organic sol-vent could partly replace the original solvent.

• Journal of Microbiology
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• v.44 no.6
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• pp.583-590
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• 2006

In this study, an organic solvent tolerant bacterial strain was isolated. This strain was identified as Pseudomonas sp. strain S5, and was shown to degrade BTEX (Benzene, Toluene, Ethyl-Benzene, and Xylene). Strain S5 generates an organic solvent-tolerant lipase in the late logarithmic phase of growth. Maximum lipase production was exhibited when peptone was utilized as the sole nitrogen source. Addition of any of the selected carbon sources to the medium resulted in a significant reduction of enzyme production. Lower lipase generation was noted when an inorganic nitrogen source was used as the sole nitrogen source. This bacterium hydrolyzed all tested triglycerides and the highest levels of pro-duction were observed when olive oil was used as a natural triglyceride. Basal medium containing Tween 60 enhanced lipase production to the most significant degree. The absence of magnesium ions ($Mg^{2+}$) in the basal medium was also shown to stimulate lipase production. Meanwhile, an alkaline earth metal ion, $Na^+$, was found to stimulate the production of S5 lipase.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.44 no.6
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• pp.50-57
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• 2012

In this study, the beeswax extraction methods using organic solvents were examined to develop a optimal dewaxing technology for beeswax-treated Hanji. Thermally-aged beeswax-treated Hanji was dewaxed using four types of extraction methods including dipping, Soxhlet extraction, ultrasonic washing and shaking methods. Then, the aging stability of the dewaxed Hanji was evaluated in terms of variations in paper strength and in the color of the printed area with muk. The experimental results suggested that the dewaxing methods allowing solvent to flow during extraction showed superior extraction efficiency. The dipping method in which the organic solvent does not flow showed the slowest extraction rate of beeswax compared to three other methods. In terms of variations in tensile strength and folding endurance, however, no obvious differences in the aging stability were observed amongst these four extraction methods. Regarding the aging stability in terms of the color of the printed area with muk, Soxhlet extraction method showed the best performance of dewaxing.