• Journal of the Korean Society of Food Science and Nutrition
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• v.26 no.3
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• pp.436-442
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• 1997

Corn starch was extruded under relatively low shear, high moisture, and low temperature. Puffing of corn starch dough was induced by injecting $CO_2$gas in the range from 0MPa to 0.09MPa. Piece density and compressive modulus for puffed corn starch were decreased by increasing the injection pressure to 0.07MPa, and increased above 0.07MPa. the microstructure of corn starch puffed with $CO_2$gas showed thick cell size, compared with those puffed with steam. RVA paste viscosity curves of corn starch puffed with $CO_2$had different patterns from those puffed with steam, probably resulted from partial gelatinization of starch. Water absorption and solubility were not significantly changed by $CO_2$injection pressure, but the average degree of polymerization was reduced by higher $CO_2$injection. The water absorption, water solubility, and the average degree of polymerization for corn starch puffed with $CO_2$were significantly lower than those puffed with steam.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.2
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• pp.85-90
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• 2014

Ag paste has been used in the front electrode of the Si-solar cell. It is composed by Ag powder, glass frit, binder, solvent and dispersant. The role of the binder and the solvent is to make a flow and a printing property. However, it was not enough to report the printing properties with the variation of binder in the controled viscosity. In this study, we selected 3 kinds of typical binder which were used as binder for the paste in the industry, such as Ethyl cellulose, Hydroxypropyl cellulose and Acrylic. Ag pastes using these were prepared, controled viscosity and printed on the SiNx coated Si wafer. In the 'A paste' used Acrylic binder, printed hight was highest and 'H paste' used Hydroxypropyl cellulose binder was lowest. Because 'H paste' was high viscosity due to the molecular weight, the solvent was added in the paste to control the viscosity. Therefore, the content of solid was lower in 'H paste'. The relative pattern width which is related to the spreading of paste was the best in the case of 'H paste' and 'EH paste' at $30^{\circ}C$. It is thought that the optimization of the relative pattern width is possible for a paste by the controling shear thinning phenomenon. In the case of 'A paste', though printing hight was best, the pattern width was dependant on the temperature.

• Macromolecular Research
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• v.12 no.6
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• pp.559-563
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• 2004

Both the ultrasonic velocity at 3 MHz and the absorption coefficient in the frequency range from 0.2 to 2 MHz were measured for aqueous solutions of poly(sodium 4-styrenesulfonate) over the concentration range from 5 to $25\%$ (by weight). The pulse echo overlap method was employed to measure the ultrasonic velocity over the temperature range from 10 to $90^{\circ}C;$ the high-Q ultrasonic resonator method was used for the measurement of the absorption coefficient at $20^{\circ}C.$ The velocities exhibited their maximum values at ca. 55, 59, 63, 67, and $71^{\circ}C.$ for the 25, 20, 15, 10, and $5\%$ solutions, respectively. The velocity increased with respect to the poly(sodium 4-styrene-sulfonate) concentration at a given temperature. A study of the concentration dependence of the both the relaxation frequency and amplitude indicated that the relaxation at ca. 200 kHz is related to structural fluctuations of the polymer molecules, such as the segmental motions of the polymer chains and that the relaxation at ca. 1 MHz resulted from the proton transfer reactions of the oxygen sites of $SO_3.$ Both the absorption and the shear viscosity increase upon increasing the polymer concentration, but they decrease upon increasing the temperature.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1324-1331
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• 2023

In the present work, we carried out a molecular dynamics study of the kinetic properties of the FLiNaK molten salt, as well as a detailed study of the structure of this salt melt. The high value of the self-diffusion coefficient of fluorine ions is due to the large number of Coulomb repulsions between the most numerous negative ions. The calculated values of shear viscosity are in good agreement with the experimental data, as well as with the reference data obtained on the basis of finding the most reliable data. The total and partial functions of the radial distribution are calculated. According to the statistical analysis, fluorine ions have the greatest numerical diversity in the environment of similar ions, and sodium ions with the lowest representation in FLiNaK, have the least such diversity. For the subsystem of fluorine ions, the rotational symmetry of the fifth order is the most pronounced. Some of the fluorine ions form linear chains consisting of three atoms, which are not formed for positive ions. The results of the work give an understanding of the behavior molten FLiNaK under operating conditions in a molten salt reactor and will find application in future studies of this molten salt.

• Journal of the Korean Society of Food Science and Nutrition
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• v.19 no.6
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• pp.612-616
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• 1990

The addition of water into oil phase containing hydrophobic emulsifier while stirring forms W/O emulsions. When dispersed phase increase up to a certain extent, phase inversion into O/W emulsions occurs and just before phase inversion O/W/O emulsions exist in a mixed state with W/O emulsions. Thus this experiment was carried out to examine O/W/O emulsions formation in W/O emulsions. The viscosity of sample emulsions(water phase： $H_2O$, oil phase : TGCR-containing olive oil) was measured at the shear rate of 1.92 to 384 per second and at temperature of 25$\pm$0.1$^{\circ}C$, and the development of O/W/O emulsions evaluated from the difference between theoretical and measured values by substituting measured value for Mooney's equation. The formation of O/W/O emulsions tended to be high in sample emulsions just before phase inversion and increase with decreasing TGCR concentrations. This result suggests that high viscosity observed right before phase inversion may also be caused by the formation of O/W/O emulsions.

• International Journal of Highway Engineering
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• v.1 no.2
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• pp.121-133
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• 1999

This study was based on the evaluation of 9 asphalts that were produced in five major Korean refineries. The study was concentrated to identify the problems of the current asphalt specification (KS M 2201) and to determine the ranges of visco-elastic asphalt behavior. As a conventional asphalt property. asphalt penetration, ring and ball(R&B) softening point, asphalt viscosity, and flash point of asphalt were measured. Also Dynamic Shear Rheometer (DSR) were used to evaluate visco-elastic properties of asphalts in the $-20^{\circ}C$ through $30^{\circ}C$ temperature range. These properties before and after the short-term (RTFO) and long-term (PAV) aging were compared and analyzed to achieve the research objectives. The conclusion from this study can be summarized by the followings. The low temperature rheological behavior of all the straight asphalt from five major Korean refineries is similar regardless of asphalt grade. In the mean while, the rheological behavior at high and intermediate temperature of Korean straight asphalt varies depending on asphalt grade.

• Design & Manufacturing
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• v.14 no.4
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• pp.11-16
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• 2020

In this study, forming of carbon composite parts was performed using an injection/compression molding process. An impregnation of matrix is determined by ability of wet and flow rate between the matrix and reinforcement. The flow rate of matrix passing through the reinforcements is a function of permeability of reinforcement, a viscosity of matrix and pressure gradient on molding, and the viscosity of the matrix depends on the mold temperature, molding pressure and shear strain of matrix. Therefore, compression molding experiment was conducted using a heating mold in order to confirm the possibility of matrix impregnation. The impregnation of the matrix through the porosities between the woven yarns was confirmed by the cross-sectional SEM image of compression molded parts. An injection molding process was also performed at a short cycle time, high molding pressure and low mold temperature than those of compression experiment conditions. Deterioration of impregnation on the surface of molded parts were caused by these injection conditions and it could be the reason of decreasing the maximum tensile strength. In order to improve impregnation of matrix on the surface, injection/compression molding and insert-over molding were applied. As a result of applying injection/compression molding and insert-over molding, it was shown that the improvement of impregnation on the surface and the maximum tensile strength was increased about 2.8 times than the virgin matrix.

• Korean Journal of Agricultural Science
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• v.22 no.1
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• pp.103-109
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• 1995

The model foods were prepared by simulating mositure, protein and starch, and they were heated for 30 mins, at $80^{\circ}C$ and then cooled at $25^{\circ}C$ in water bath. Their rheological properties were investigated by the use of Brookfield wide-gap rotational viscometer at $30{\sim}60^{\circ}C$, and the rotation speed ranged from 0.6 to 6 rpm and solid content ranged from 8% to 11%, the results obtained were as follows. 1. All the model foods ($P_1S_3$, $P_2S_2$, $P_1S_1$, $P_2S_1$, $P_3S_1$, $P_4S_0$) exhibited pseudoplastic behaviors with yeild stress and were thixotropic foods which showed time - dependent structural decays, but the starch food of 8 ~ 11 % solid content did not show the flow behavior. 2. The correlation between the rheological parameters and the protein content of model foods in various moisture content did not appeared a constant relationship. 3. The change of shear stress against shear rate in high starch foods was larger than that in high protein foods and the structure at initial shear time was decayed with a quatic equation according to the Tiu's Model and structural decay was in parallel with the increase of shear rate. 4. The temperature dependency of the apparent viscosity of $P_1S_2$, and $P_2S_1$ was fully expressed by Arrhenius equation and activation energies of their food were 2.35 and $1.34Kcal/g{\cdot}mol$, respectively.

• Macromolecular Research
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• v.11 no.6
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• pp.410-417
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• 2003

Poly(methyl methacrylate-co-acrylonitrile) [P(MMA-co-AN)]/Na-MMT nanocomposites were synthesized through emulsion polymerization with pristine Na-MMT. The nanocomposites were exfoliated up to 20 wt% content of pristine Na-MMT relative to the amount of MMA and AN, and exhibited enhanced storage moduli, E', relative to the neat copolymer. The exfoliated morphology of the nanocomposite was confirmed by XRD and TEM. 2-Acryla-mido-2-methyl-1-propane sulfonic acid (AMPS) widened the galleries between the clay layers before polymerization and facilitated the comonomers, penetration into the clay to create the exfoliated nanocomposites. The onset of the thermal decomposition of the nanocomposites shifted to a higher temperature as the clay content increased. By calculating areas of tan$\delta$ of the nanocomposites, we observed that the nanocomposites show more solid-like behavior as the clay content increases. The dynamic storage modulus and complex viscosity increased with clay content. The complex viscosity showed shear-thinning behavior as the clay content increased. The Young's moduli of the nano-composites are higher than that of the neat copolymer and they increase steadily as the silicate content increases, as a result of the exfoliated structure at high clay content.

• Polymer(Korea)
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• v.37 no.4
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• pp.494-499
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• 2013

Modified polypropylene (m-PP) was fabricated by furfuryl sulphide (FS) as branching agent and m-PP/nano-filler composites were prepared with silicate and multi-walled carbon nanotube (MWCNT), using a twin screw extruder. The chemical structures and thermal properties of the m-PP were investigated by FTIR and DSC. The chemical structure of the m-PP was confirmed by the existence of =C-H stretching peak of the branching agent at 3100 $cm^{-1}$. There was no district change in melting temperature in case of m-PP, but a certain increase in crystallization temperature was notified and the increase was in the range of $10-20^{\circ}C$. The rheological properties, filler dispersion and foaming behaviors of the m-PP/nano-filler composites were investigated by dynamic rheometer, X-ray diffractometer (XRD) and scanning/transmission electron microscope (SEM/TEM). m-PP/nano-filler composites showed a high complex viscosity at a low frequency, an increase in melt elasticity, and a high shear thinning effect. Compared to pure PP, m-PP and m-PP/nano-filler composites were sufficient to enhance the foaming behavior.