• 한국식품영양과학회지
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• 제40권7호
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• pp.1048-1052
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• 2011

각기 다른 치환도를 가진 초산 고구마전분 페이스트의 유동특성 및 투과도 그리고, 이들 전분 겔의 냉.해동안정성 및 강도가 치환도의 함수로 분석되었다. 유동특성 측정 결과 power law 모델식과 Casson 모델식에 잘 적용되었으며, 높은 shear-thinning 거동을 가지고 있는 것으로 나타났다. 특정한 온도 범위($25{\sim}70^{\circ}C$)에서 전분 페이스트의 겉보기 점도($\eta_{a,100}$)의 온도 의존성은 Arrhenius 모델식에 잘 적용되었으며 초산 고구마전분이 천연전분에 비해 더 낮은 온도 의존성을 나타내었다. 전분 페이스트 이수현상 측정에서는 초산화에 의해 이수현상이 감소하는 것으로 나타났으며, 치환도가 증가할수록 낮아지는 것으로 나타났다. 겔 강도 측정에서도 초산화에 의해 겔 강도가 감소하는 것으로 나타났으며, 치환도가 증가할수록 겔 강도는 감소하는 것으로 나타났다. 페이스트 투과도(% T) 측정에서 초산전분은 천연전분 보다 투과도가 높은 것으로 나타났다.

• 폴리머
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• 제24권1호
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• pp.38-47
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• 2000

본 논문은 선형 폴리카보네이트와 분지화된 폴리카보네이트를 블렌드한 시스템에 대해서 연구하였다. 여러가지 조성으로 두 성분을 블렌드하여 각 조성에 대해서 상용성, 기계적 성질 그리고 유동특성을 조사하였다. 본 블렌드 시스템에서 상분리는 관찰되지 않았고 상용성도 있었다. 기계적 성질은 블렌드의 각 조성에 대해서 인장강도, 굽힘강도 그리고 충격강도 등을 측정하여 검토하였으며, 흐름특성 역시 블렌드의 각 조성에 대해 용융점도, 저장탄성률 및 손실탄성률을 여러 온도에서 측정하여 검토하였다. 그리고 용융점도의 분자량에 대한 의존성을 조사하였다. 선형 폴리카보네이트와 분지화된 폴리카보네이트의 조성에 따라 기계적 물성은 거의 변화가 없었으나, 흐름특성은 큰 변화가 있었다. 본 블렌드 시스템에서 분지화된 폴리카보네이트 함량이 증가할수록 점도의 분자량에 대한 의존성이 컸으며, shear thinning 현상은 두드러지게 나타났다. 따라서 재료의 기계적 물성의 변화없이 흐름특성이 다른 블렌드 시스템을 설계할 수 있다.

• 한국식품조리과학회지
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• 제33권3호
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• pp.300-306
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• 2017

Purpose: This study aimed to prepare sea tangle vinegar and test its applicability as a vinegar-based functional salad dressing in terms of physicochemical properties. Methods: Sea tangle vinegar was prepared by mixing sea tangle with sugar and vinegar and fermenting the mixture at room temperature for 3 months. The resulting sea tangle vinegar was examined for its physicochemical properties and antioxidant activity with brewed vinegar and persimmon vinegar as controls. Results: The sea tangle vinegar showed significantly higher viscosity than control vinegars, and shear thinning behavior that is typical for salad dressing containing polymers. In addition, storage modulus (G′) of sea tangle vinegar was relatively high in dynamic viscosity measurement while that of control vinegars remained negligible. Together with the high soluble solids content of sea tangle vinegar, rheological behavior indicates that sea tangle vinegar had soluble polysaccharides extracted from sea tangle, consequently leading to an increase in viscosity. Titratable acidity (TA) and pH were 2.52% and 3.58, respectively, which satisfies the TA and pH requirements for microbiological safety of a salad dressing. Absorbance at 285 nm and Folin Ciocalteu's reagent method revealed that sea tangle vinegar contained antioxidative phenolic compounds. Conclusion: This study demonstrates that sea tangle vinegar could be potentially developed as a vinegar-based functional salad dressing when combined with sensory evaluation in the future.

• Elastomers and Composites
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• 제48권1호
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• pp.18-23
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• 2013

용융상태에서 nylon 12 elastomer에 소량의 dicumyl peroxide (DCP) 와 triallyl cyanuate (TAC)를 첨가하여 nylon 12 elastomer를 부분적으로 가교시켰으며, 이에 따른 nylon 12 elastomer의 기계적, 동적기계적 그리고 유변학적 특성을 tensile test, DMA, small amplitude oscillating rheometer를 이용하여 각각 알아보았다. TAC의 함량이 증가함에 따라 인장탄성률과 영률은 증가하고, 파단신율은 감소하였다. DMA 측정결과, DCP로 부분적으로 가교시킨 nylon 12 elastomer의 PTMG상의 유리전이온도는 순수한 nylon 12 elstomer에 비해 증가하였고, storage modulus는 nylon 12상의 용융온도 이상에서도 거의 일정한 값을 나타내었다. 부분적으로 가교시킴에 따른 유변학적 특성의 변화는 TAC의 함량이 증가함에 따라 solid like behavior와 shear thinning behavior가 점점 뚜렷하게 나타남을 알 수 있었다. 이로부터 nylon 12 elastomer를 용융상태에서 부분적으로 가교시킴으로써 용융가공성을 저하시키지 않으면서, 기계적 물성은 효과적으로 향상시킬 수 있었으며, 특히, nylon 12 elastomer의 사용가능 온도범위를 증가시킬 수 있었다.

• 한국식품과학회지
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• 제41권1호
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• pp.32-36
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• 2009

농축시킨 Aloe vera gel을 동결건조하였을 때 그 농축도 차이에 의한 최종 건조분말의 물성 변화를 비교분석하였다. 분말의 최종 수분함량은 거의 차이가 없었으며. 점성 측정에서는 높은 농축 조건의 경우 전형적인 shear thinning 현상과 non-Newtonian 유체의 속성을 나타냈다. 이에 비하여 낮은 농축 조건의 경우 Newtonian 액체의 성질과 고형분이 입자가 아닌 풀린 형태로 존재할 때 나타나는 현상을 보였다. 분말이 물에 용해되는 동안 전기전도도의 변화를 실시간으로 측정한 결과 평형상태에 도달하였을 때, 가장 높은 농축 조건에서 전기전도도가 가장 낮게 나타나, 비전해질성 물질의 용해도가 가장 큰 것으로 해석되었다. 분말의 등온흡습성에서는 농축이 증가할수록 수분 흡착과 결합수의 양이 작아지는 것으로 분석되었다. 결과적으로 Aloe vera gel을 농축하여 동결건조할 때는 그 농축도에 따라 점성, 현탁시 전기전도도에 따른 용해성, 등온흡습성이 변하는 것으로 나타나, 특정 품질의 동결건조제품을 얻기 위해서는 그에 대한 농축의 최적화가 필요한 것으로 생각된다.

• 한국산학기술학회논문지
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• 제12권9호
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• pp.4261-4266
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• 2011

폴리프로필렌(polypropylene, PP)/talc 컴파운드를 talc의 조성을 20wt%로 하여 마스터뱃취(master-batch, MB)와 사출기를 이용한 직접 제조법으로 각각 제조하였다. MB는 talc 함량을 50wt%로 하여 소형 혼합기(mini compounder)로 $200^{\circ}C$에서 제조하였다. SEM-EDS를 이용하여 PP/talc 컴파운드의 talc 분산정도를 평가하였다. MB를 이용하여 제조한 컴파운드의 talc 분산성이 우수하게 나타났다. PP/talc 컴파운드의 유변학적 특성을 동적유변측정기를 이용하여 측정하였다. MB를 이용한 MB-PP 컴파운드가 직접 제조한 컴파운드보다 shear thinning과 탄성특성이 증가하였다. G'-G" plot의 기울기 변화로부터 talc 분산성 정도를 확인하였고, 탄성특성 증가를 확인하기 위해 Van Gurp-Palmen 분석을 이용하였다.

• Journal of Pharmaceutical Investigation
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• 제37권3호
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• pp.137-148
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• 2007

Using a strain-controlled rheometer [Rheometrics Dynamic Analyzer (RDA II)], the steady shear flow properties of a semi-solid ointment base (vaseline) have been measured over a wide range of shear rates at temperature range of $25{\sim}60^{\circ}C$. In this article, the steady shear flow properties (shear stress, steady shear viscosity and yield stress) were reported from the experimentally obtained data and the effects of shear rate as well as temperature on these properties were discussed in detail. In addition, several inelastic-viscoplastic flow models including a yield stress parameter were employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models was examined by calculating the various material parameters (yield stress, consistency index and flow behavior index). Main findings obtained from this study can be summarized as follows : (1) At temperature range lower than $40^{\circ}C$, vaseline is regarded as a viscoplastic material having a finite magnitude of yield stress and its flow behavior beyond a yield stress shows a shear-thinning (or pseudo-plastic) feature, indicating a decrease in steady shear viscosity as an increase in shear rate. At this temperature range, the flow curve of vaseline has two inflection points and the first inflection point occurring at relatively lower shear rate corresponds to a static yield stress. The static yield stress of vaseline is decreased with increasing temperature and takes place at a lower shear rate, due to a progressive breakdown of three dimensional network structure. (2) At temperature range higher than $45^{\circ}C$, vaseline becomes a viscous liquid with no yield stress and its flow character exhibits a Newtonian behavior, demonstrating a constant steady shear viscosity regardless of an increase in shear rate. With increasing temperature, vaseline begins to show a Newtonian behavior at a lower shear rate range, indicating that the microcrystalline structure is completely destroyed due to a synergic effect of high temperature and shear deformation. (3) Over a whole range of temperatures tested, the Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable and have an almostly equivalent ability to quantitatively describe the steady shear flow behavior of vaseline, whereas the Bingham, Casson,and Vocadlo models do not give a good ability.

• Nuclear Engineering and Technology
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• 제40권1호
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• pp.37-48
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• 2008

Flow fields inside feeder pipes have been simulated numerically using a CFD (computational fluid dynamics) code to calculate the shear stress distribution, which is the most important factor in predicting the local regions of feeder pipes highly susceptible to FAC (flow-accelerated corrosion)-induced wall thinning. The CFD approach, with schemes used in this study, to simulate the flow situations inside the CANDU feeder pipes has been verified as it showed a good agreement between the investigation results for the failed feedwater pipe at Surry unit 2 plant in the U.S. and the CFD calculation. Sensitivity studies of the three geometrical parameters, such as angle of the first and second bends, length of the first span between the grayloc hub and the first bend, and length of the second span between the first and the second bends have been performed. CFD analysis reveals that the local regions of feeder pipes of Wolsung unit 1 in Korea, on which wall thickness measurements have been performed so far, are not coincident with the worst regions predicted by the present CFD analysis located in the connection region of straight and bend pipe near the inlet part of the bend intrados. Finally, based on the results of the present CFD analysis, a guide to the selection of the weakest local positions where the measurement of wall thickness should be performed with higher priority has been provided.

• 한국전산유체공학회지
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• 제16권2호
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• pp.81-87
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• 2011

The importance of shear thinning non-Newtonian blood rheology on the hemodynamic characteristics of idealized cerebral saccular aneurysms were investigated by carrying out CFD simulations assuming two different non-Newtonian rheology models (Carreau and Ballyk models). To explore effects of vessel curvature, a straight and a curved vessel geometry were considered. The wall shear stress(WSS), relative residence time(RRT) and velocity distribution were compared at the different phases of cardiac cycle. As expected, blood entered the aneurysm at the distal neck and created large vortex in both aneurysms, but with higher momentum on the curved vessel. Hemodynamic characteristics such as WSS, and RRT exhibited only minor effects by choice of different rheological models although Ballyk model produced relatively higher effects. We conclude that the assumption of Newtonian fluid is reasonable for studies aimed at quantifying the hemodynamic characteristics, in particular, WSS-based parameters, considering the current accuracy level of medical image of cerebral aneurysm.

• Korea-Australia Rheology Journal
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• 제14권1호
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• pp.1-9
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• 2002

Steady and dynamic shear properties of two hydrophobically modified alkali soluble emulsions (HASE), NPJI and NPJ2, were experimentally investigated. At the same polymer concentration, NPJ1 is appreciably more viscous and elastic than NPJ2. The high hydrophobicity of NPJ1 allows hydrophobic associations and more junction sites to be created, leading to the formation of a network structure. Under shear deformation, NPJ1 exhibits shear-thinning behaviour as compared with Newtonian characteristics of NPJ2. NPJ1 and NPJ2 exhibit a very high and a low level of elasticity respectively over the frequency range tested. For NPJ1, a crossover frequency appears, which is shifted to lower frequencies and hence, longer relaxation times, as concentration increases. Three different surfactants anionic SDS, cationic CTAB, and non-ionic TX-100 were employed to examine the effects of surfactants on the rheology of HASE. Due to the different ionic behaviour of the surfactant, each type of surfactant imposed different electrostatic interactions on the two HASE polymers. In general, at low surfactant concentration, a gradual increase in viscosity is observed until a maximum is reached, beyond which a continuous reduction of viscosity ensues. Viscosity development is a combined result of HASE-surfactant interactions, accompanied by constant rearrangement of the hydrophobic associative junctions, and electrostatic interactions.