• Corrosion Science and Technology
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• v.6 no.6
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• pp.291-296
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• 2007

The corrosion of metals and alloys in flowing liquids can be classified into uniform corrosion and localized corrosion which may be categorized as follows. (1) Localized corrosion of the erosion-corrosion type: the protective oxide layer is assumed to be removed from the metal surface by shear stress or turbulence of the fluid flow. A macro-cell may be defined as a situation in which the bare surface is the macro-anode and the other surface covered with the oxide layer is the macro-cathode. (2) Localized corrosion of the differential flow-velocity corrosion type: at a location of lower fluid velocity, a thin and coarse oxide layer with poor protective qualities may be produced because of an insufficient supply of oxygen. A macro-cell may be defined as a situation in which this surface is the macro-anode and the other surface covered with a dense and stable oxide layer is the macro-cathode. (3) Localized corrosion of the active/passive-cell type: on a metal surface a macro-cell may be defined as a situation in which a part of it is in a passivation state and another in an active dissolution state. This situation may arise from differences in temperature as well as in the supply of the dissolved oxygen. Compared to uniform corrosion, localized corrosion tends to involve a higher wall thinning rate (corrosion rate) due to the macro-cell current as well as to the ratio of the surface area of the macro-anode to that of the macro-cathode, which may be rationalized using potential vs. current density diagrams. The three types of localized corrosion described above can be reproduced in a Jet-in-slit test by changing the flow direction of the test liquid and arranging environmental conditions in an appropriate manner.

• Biotechnology and Bioprocess Engineering:BBE
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• v.9 no.5
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• pp.405-413
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• 2004

The rheological properties of an exopolysaccharide, EPS-R, produced by the marine bacterium Hahella chejuensis strain 96CJ 10356 were investigated. The $E_{24}$ of $0.5\%$ EPS-R was $89.2\%$, which was higher than that observed in commercial polysaccharides such as xanthan gum ($67.8\%$), gellan gum ($2.01\%$) or sodium alginate ($1.02\%$). Glucose and galactose are the main Sugars in EPS-R, with a molar ratio of ${\~}1:6.8$, xylose and ribose are minor sugar components. The average molecular mass, as determined by gel filtration chromatography, was $2.2{\times}10^3$ KDa, The intrinsic viscosities of EPS-R were calculated to be 16.5 and 15.9 dL/g using the Huggins and Kraemer equations, respectively, with a 2.3 dL/g overlap. In terms of rigidity, the conformation of EPS-R was similar to that of caboxymethyl cellulose ($5.0{\times}10^{-2}$). The rheological behavior of EPS-R dispersion indicated that the formation of a structure intermediate between that of a random-coil polysaccharide and a weak gel. The aqueous dispersion of EPS-R at concentrations ranging from 0.25 to $1.0\%$ (w/w) showed a marked shear-thinning property in accordance with Power-law behavior. In aqueous dispersions of $1.0\%$ EPS-R, the consistency index (K) and flow behavior index (n) were 1,410 and 0.73, respectively. EPS-R was Stable to pH and salts.

• Food Science and Biotechnology
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• v.15 no.2
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• pp.207-213
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• 2006

The effects of gellan gum (from S. paucimobilis), EPS-CB (exopolysaccharide from S. chungbukensis), and a series of commercial gums (arabic gum, xanthan gum, guar gum, deacyl gellan gum), on the swelling, rheological, and pasting properties of non-waxy rice flour dispersions were investigated. The swelling properties of rice flours in gellan or guar gum dispersion after heating were found to have increased with increasing gum concentrations, but the swelling properties of rice flour/other gum systems decreased with increasing concentrations. The rice flour/gum mixtures showed high shear-thinning flow behavior (n=0.14-0.32), and consistency index (K) was higher in guar gum than other gum dispersions. The initial pasting temperatures and peak times increased along with increasing gum concentration. The peak viscosity of rice flour increased in guar gum and deacyl gellan dispersions, and the breakdown and setback viscosity of the rice flour paste was lowest in the xanthan gum system, but remained higher than those of the control. The apparent viscosities of the rice flour/gellan gum mixture pastes were the highest among the tested combinations.

• Journal of the Korean Society of Clothing and Textiles
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• v.38 no.3
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• pp.372-385
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• 2014

Lignin is an abundant natural polymer in the biosphere and second only to cellulose; however, it is under-utilized and considered a waste. In this study, lignin was fabricated into nanofibers via electrospinning. The critical parameters that affected the electrospinnability and morphology of the resulting fibers were examined with the aim to utilize lignin as a resource for a new textile material. Poly(vinyl alcohol) (PVA) was added as a carrier polymer to facilitate the fiber formation of lignin, and the electrospun fibers were deposited on polyester (PET) nonwoven substrate. Eleven lignin/PVA hybrid solutions with a different lignin to PVA mass ratio were prepared and then electrospun to find an optimum concentration. Lignin nano-fibers were electrospun under a variety of conditions such as various feed rates, needle gauges, electric voltage, and tip-to-collector distances in order to find an optimum spinning condition. We found that the optimum concentration for electrospinning was a 5wt% PVA precursor solution upon the addition of lignin with the mass ratio of PVA:lignin=1:5.6. The viscosity of the lignin/PVA hybrid solution was determined as an important parameter that affected the electrospinning process; in addition, the interrelation between the viscosity of hybrid solution and the electrospinnability was examined. The solution viscosity increased with lignin loading, but exhibited a shear thinning behavior beyond a certain concentration that resulted in needle clogging. A steep increase in viscosity was also noted when the electrospun system started to form fibers. Consequently, the viscosity range to produce bead-free lignin nanofibers was revealed. The energy dispersive X-ray analysis confirmed that lignin remained after being transformed into nanofibers. The results indicate the possibility of developing a new fiber material that utilizes biomass with resulting fibers that can be applied to various applications such as filtration to wound dressing.

• Food Science of Animal Resources
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• v.38 no.3
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• pp.476-486
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• 2018

In this study, the droplet size distribution, rheological properties, and stability of dairy cream-based emulsions homogenized with different sucrose fatty acid ester (SFAE, a non-ionic small-molecule emulsifier) concentrations (0.08%, 0.16%, and 0.24% w/w) at different homogenization pressures (10 MPa and 20 MPa) were examined. Homogenization at a high pressure resulted in a smaller droplet size and narrower droplet size distribution. The D[4,3] (volume-weighted mean) and D[3,2] (surface-weighted mean) values of the emulsions decreased with an increase in the SFAE concentration. The flow properties of the emulsions homogenized with SFAE showed shear-thinning (n=0.21-0.46) behavior. The apparent viscosity (${\eta}_{a,10}$) and consistency index (K) of the homogenized emulsions were lower than those of the control sample that is non-homogenized and without SFAE, and decreased with an increase in SFAE concentration. The storage modulus (G') and loss modulus (G") of all emulsions homogenized with SFAE were also lower than those of the control sample. The stability of all emulsions with SFAE did not show any significant change for 30 d at $5^{\circ}C$. However, the emulsions stored at $40^{\circ}C$ were unstable over the storage period. Therefore, the addition of SFAE enhanced the stability of dairy cream emulsions during storage at refrigeration temperature ($5^{\circ}C$).

• Textile Coloration and Finishing
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• v.28 no.3
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• pp.125-133
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• 2016

In this study, efforts were made to enhance the mechanical properties of the poly(vinyl alcohol) (PVA) fibers of medium molecular weight(number-average degree of polymerization=1735) varying the ratio in $DMSO/H_2O$ mixed solvent and spinning/drawing conditions. The gel fibers prepared from pure DMSO were opaquely frozen in the coagulating bath of $-20^{\circ}C$. However, transparent gel fibers were formed without freezing for the mixture to contain water less than 80wt%. As the amount of water in the mixture increased the residual solvent in the coagulated gel fibers decreased ranging from 85 to 42wt%. The complex viscosity increased with increasing PVA concentration in 80/20 $DMSO/H_2O$ exhibiting remarkable shear thinning at 18wt%. In the Cole-Cole plot, the 18wt% PVA solutions gave a deviated curve from 12 and 15wt% ones. Thus the optimum PVA concentration for the spinning processing of medium MW PVA solutions in 80/20 $DMSO/H_2O$ was determined to 18wt% with rheological concept. Low degree of drawing during hot drawing process in the dry state was available for high bath draft in the coagulation bath. The most improved mechanical properties were observed by applying the highest possible draw ratio attained by reducing bath draft over multi-step drawing process. In the given bath draft, linear relationship was observed between both tensile strength and modulus and draw ratio showing the inflection points at the draw ratio of 19.5 and 18.0 for tensile strength and modulus, respectively.

• 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.

• Polymer(Korea)
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• v.38 no.6
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• pp.735-743
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• 2014

The rheological measurement of polypropylene (PP) has been performed using a rheometer, an intrinsic viscometer, and an MI machine to predict the molecular weight and the molecular weight distribution. Also, GPC has been used for the determination of the molecular structure. The distribution broadness parameter using modified Carreau model has been used to make the correlation between the rheological parameter and the molecular structure instead of the rheological PI (polydispersity index) which is determined from the cross of modulus from the dynamic oscillatory measurement. Even though the rheological PI is useful to determine the molecular weight distribution of the PP using controlled rheology, which has narrow and uniform molecular weight distribution, but not suitable to determine the molecular weight distribution of the PP made from direct polymerization which has broad and various molecular weight distribution. However the distribution broadness parameter which determined from the index of the shear thinning of the PP melt well predicts the molecular weight distribution of PP.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.39 no.1
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• pp.47-54
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• 2013

Aloe gel microcapsule was prepared by dehydrating dispersed aloe gel droplets in the form of W/O emulsion using a vacuum evaporator. The microcapsules remained in stable suspensions after washing with mineral oil and had a homogeneous spherical structure with diameter less than 6.4 ${\mu}m$. The microcapsule suspension in mineral oil (> 41%) exhibited a step increase in viscosity and shear-thinning but not showed thixotropic behavior with a yield stress higher than 300 Pa. The dense suspension appeared to be semi-solid as the microcapsule fraction increases and to be stable after heat treatment at $105^{\circ}C$ for 15 min. In conclusion, the dense suspension composed of gel microcapsules is expected to provide a basic cosmetic formulation that can be applied to develop various types of aloe gel cosmetic products.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.1512-1518
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• 2013

Polycarbonates (PCs) with six different end capping agents were synthesized from melt polymerization. Chemical structure of the synthesized PC was determined by FT-IR spectroscopy. The average molecular weight and distribution, glass transition and thermal degradation temperatures were determined by GPC, DSC and TGA. 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 PCs decreased with the concentration of the agent, the number average molecular weight was observed as 20,000 - 30,000 when 0.05-0.15 mol% of 4-tert-butylphenol added in PCs. The melt viscosities and glass transition temperature of the PCs decreased with molecular weight. The change for adding method of the agent affected on both the molecular weight distribution and decrease in power law index.