• The Journal of Korean Academy of Prosthodontics
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• v.44 no.3
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• pp.333-342
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• 2006

Statement of problem. Although many studies have been carried out to investigate the correlation between the degree of conversion and the flexural strength of composite resins, there is minimal information in the literature attempting to compare degree of conversion, flexural strength and their correlation between restorative composite resins and flowable composite resins. Purpose. The purposes of this study were to measure the degree of conversion and flexural strength of composite resins with different rheological behavior and to correlate the two properties. Materials and methods. Four restorative (Vit-1-escence, Z-250, Tetric ceram, Esthet-X) and four flowable (Aeliteflo, Admiraflow, Permaflo, Revolution) light-curing composite resins were investigated. The degree of conversion(DC) was analyzed with Fourier transfer infra-red spectroscopy(FTIR) spectrum by a potassium bromide(KBr) pellet transmission method. The spectrum of the unpolymerized specimen had been measured before the specimen was irradiated for 60s with a visible light curing unit. The Poiymerized specimen was scanned for its in spectrum. The flexural strength(FS) was measured with 3-point bending test according to ISO 4049 after storage in water at $37^{\circ}C$ for 24 hours. The data were statistically analyzed by an independent sample t-test and one-way ANOVA at the significance level of 0.05. The dependence of flexural strength on the degree of conversion was also analyzed by regression analysis. Results. Mean DC and FS values ranged from 43% to 61% and from 84.7MPa to 156.7MPa respectively. DC values of the flowable composite resins were significantly higher than those of restorative composite resins (P < 0.05). The FS values of restorative composite resins were greater than those of flowable composite resins. No statistically significant correlation was observed between the DC and the FS tested in any of the composites. The dependence of FS on DC in restorative or flowable composite resins was not significant. Conclusion. It can be concluded that radical polymerization of the organic matrix is not a major factor in determining flexural strength of the commercially available composite resins.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.3
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• pp.47-55
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• 2013

Curved duct channel flow characteristics for non-Newtonian gel fluid is investigated. A simulant gel propellant mixed by Water, Carbopol 941 and NaOH solution has been chosen to analyze the gel propellant flow behavior. Rheological data have been measured prior to the flow analysis where water-gel propellant and water-gel propellant with $Al_2O_3$ nano particles are both used. The critical Dean number examined by the numerical simulation in the U-shape duct flow reveals that although water-gel-nano propellants have higher apparent viscosity, the critical Dean number do show no notable difference for both the two gel propellant. It is found that the power-law index may be a dominant parameter in determining the critical Dean number and that the gel with particles addition may be more vulnerable to Dean instability.

• Polymer(Korea)
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• v.39 no.2
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• pp.247-255
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• 2015

Poly(1,2-propylene glycol adipate) (PPA) was used as an environmentally friendly plasticizer in flexible poly(vinyl chloride) (PVC). Thermal, mechanical, and rheological properties of the PVC/PPA blends were characterized by differential scanning calorimetry, dynamic mechanical analysis, tensile test, scanning electron microscopy and small amplitude oscillatory shear rheometry. The results showed that PPA lowered the glass transition temperature of PVC. The introduction of PPA could decrease tensile strength and Young's modulus of the PVC/PPA blends; however, elongation-at-break was dramatically increased due to the plastic deformation. The plasticization effect of PPA was also manifested by the decrease of dynamic storage modulus and viscosity in the melt state of the blends. The results indicated that PPA had a good plasticizing effect on PVC.

• Macromolecular Research
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• v.16 no.8
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• pp.704-710
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• 2008

Injectable hydrogels are quite promising materials due to their potential to minimize invasive implantation and this provides versatile fitness irrespective of the damaged regions and facilitates the incorporation of bioactive agents or cells. In situ gel formation through stereocomplex formation is a promising candidate for injectable hydrogels. In this paper, a new series of enantiomeric, four-arm, PEG-PLA block copolymers and their stereocomplexed hydrogels were prepared by bulk ring-opening polymerization of D-lactide and L-lactide, respectively, with stannous octoate as a catalyst. The prepared polymers were characterized by $^1H$ nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FT IR) spectroscopy, gel permeation chromatography (GPC) and thermal gravitational analysis (TGA), confirming the tailored structure and chain lengths. The swelling and degradation behavior of the hydrogels formed from a selected copolymer series were observed in different concentrations. The degradation rate decreased with increasing polymer content in the solution. The rheological behavior indicated that the prepared hydrogel underwent in situ gelation and had favorable mechanical strength. In addition, its feasibility as an injectable scaffold was evaluated using a media dependence test for cell culture. A Tris solution was more favorable for in situ gel formation than PBS and DMEM solutions were. These results demonstrated the in situ formation of hydrogel through the construction of a stereocomplex with enantiomeric, 4-arm, PEG-PLA copolymers. Overall, enantiomeric, 4-arm, PEG-PLA copolymers are a new species of stereocomplexed hydrogels that are suitable for further research into injectable hydrogels.

• Korean Journal of Food Science and Technology
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• v.27 no.4
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• pp.593-597
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• 1995

To measure theological properties of the starch dough, an Extrusion Capillary Viscometer(ECV) cell was self-made and attached to Instron machine(Model 1140). Apparent viscosities of corn and waxy corn starch doughs were measured and their gelatinization degrees were determined by enzymatic analysis. The effects of heating temperature on the viscosity of starch dough with $36{\sim}52%$ moisture contents were examined in terms of Arrhenius equation. The activation emergy(Ea) of the dough viscosity from the effect of heating temperatures changed from negative(-) to positive(+), as the moisture content increased from 44% to 48% in the corn starch dough and from 44% to 44% in the waxy corn starch dough.

• Journal of the Korean Society of Food Science and Nutrition
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• v.29 no.1
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• pp.64-67
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• 2000

Jellies enhancing physiological functions were prepared with using 5 and 10% dietary fiber isolated from ascidian (Halocynthia roretzi) tunic collected from recycled seafood waste. The texture development of the samples was examined with two-bite compression test and analyzed using five sorts ofrheological parameters with texture profile analysis as follows; hardness, adhesiveness, springiness, cohesiveness and gumminess. All the rheological parameters decreased in the fiber enhanced jellies. However, the springiness and cohesiveness increased slightly in the fiber enhanced jellis. Hunter L' and d' values increased in the fiber enhanced jellies and accordingly the color was light yellow. a' value showed green with the addition of fiber. As a result of sensory evaluations, the color and overall acceptability of 10% fiber enhanced jelly were significantly different at p<0.05. The 10% fiber enhanced jelly was noted as having high sensory scores and peferable acceptability.

• Elastomers and Composites
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• v.44 no.1
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• pp.63-68
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• 2009

Recently, much attention has focused on the permanent deformation of roads in hot summer and cracks in cold winter, which are detrimental to safe driving. This leads to necessity of modification of asphalt to resist those deformation. In this study, a type of modified asphalt was prepared by addition of a photoinitiator which is activated by ultraviolet lay. The mechanical and rheololgical properties of photoinitiator-modified asphalt were examined using UTM and rheometer. Results showed that the modified asphalt was effected by ultraviolet and thus tensile strength and storage modulus increased, due to molecular attraction, with initiator content and irradiation dose. Thermal analysis showed less weight loss upon photoinitiator-modification and this indicated that the molecular attraction is the result of cross linking reaction between asphalt molecules induced by photoinitiator. According to long term ultraviolet curing test, properties of the photoinitiator-modified asphalt did not decrease or even increase for 20 years. This indicates that useful life of the asphalt could be extended by addition of photoinitiator.

• Elastomers and Composites
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• v.42 no.3
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• pp.151-158
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• 2007

MWNTs have been widely investigated due to unique properties of such as good electrical conductivity and thermal stability in polymer composites industries. This paper established the procedure to fabricate PMMA/MWNT composites by a modular intermeshing co-rotating twin screw extruder with L/D ratio of 42. The electrical properties of PMMA/MWNT composites with different content of MWNT have been investigated. A sheet resistance percolation was observed at 4 wt% of MWNT for the melt processed composites. Sheet resistance of PMMA/MWNT composite film containing 4 wt% of MWNT was nearby $10^4{\Omega}/sq$ and this shows the possibility of potential application to EMI (Electronic Magnetic Interference) shielding materials. The characteristics of composites were analyzed by TGA, DSC, and SEM. In addition, MFI (Melt Flow Index) has been measured to analyze the rheological property.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.377-382
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• 2010

The Present study uses non-Newtonian simulant gel propellant mixed by Water, Carbopol 941, and NaOH solution in order to analyze the gel propellant flow behavior. Rheological data have been measured and obtained prior to the analysis of flow characteristics where water-gel propellant as well as water-gel propellant with $Al_2O_3$ nano particles are both used. The critical Dean number were examined by numerical simulation of gel propellant in the U-shape duct flow. It is found that though gel-nano propellants have higher apparent viscosity, the critical Dean number did not showed notable difference with respect to the water-gel propellant. It is believe that this is due to the fact that the power law index of both propellants have close value, as was demonstrated by Fellouah et al.[1]

• Korean Journal of Food Science and Technology
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• v.37 no.5
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• pp.763-767
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• 2005

Effect of ${\alpha}-amylase$ and various emulsifiers on characteristics of bread dough were examined. Fungal or bacterial ${\alpha}-amylase$ and various emulsifiers including monoglyceride (MG), sodium stearoyl-2-lactylate (SSL), and diacetyltartaric acid ester of mono- and diglycerides (DATEM) were added to bread dough both individually and as mixtures. Rheological characteristics of various bread doughs were examined through falling number, farinograph, alveograph, and rapid visco analysis. Results obtained showed falling number decreased via degradation of starch by ${\alpha}-amylase$. In farinogram, addition of ${\alpha}-amylase$ and emulsifiers in dough decreased consistency, water absorption, mechanical tolerance index, and dough development time. Farinogram characteristic was improved by adding SSL+MG to dough formula. Similar to farinogram addition of ${\alpha}-amylase$ and emulsifiers in alveogram of dough decreased overpressure, extensibility, swelling index, and deformation energy. Whereas addition of ${\alpha}-amylase$ did not affect pasting temperature, viscosity of dough tended to decrease.