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Fukui-shi, Japan

Iijima M.,Nagasaki University | Hatakeyama T.,Lignocell Research | Hatakeyama H.,Fukui University of Technology
Thermochimica Acta | Year: 2012

Among various kinds of polysaccharides known to form hydrogels, locust bean gum (LBG) consisting of a mannose backbone and galactose side chains has unique characteristics, since LBG forms hydrogels by freezing and thawing. In this study, effect of thermal history on gelation was investigated by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). Gel/sol ratio calculated by weighing method was found to be affected by sol concentration, freezing rate and the number of freezing and thawing cycle (n). Once LBG hydrogels are formed, they are thermally stable, although syneresis was observed when n increased. Dynamic Young's modulus (E′) of hydrogels measured by TMA in water increased with increasing n and decreasing freezing rate. Non-freezing water calculated from DSC melting peak of ice in the gel decreased with increasing n and decreasing freezing rate. Morphological observation of freeze-dried gels was carried out by scanning electron microscopy (SEM). The above results indicate that weak hydrogel having large molecular network structure transformed into strong gel with densely packed network structure by increasing n and decreasing freezing rate. © 2011 Elsevier B.V. All rights reserved. Source


Iijima M.,Nagasaki University | Hatakeyama T.,Lignocell Research | Hatakeyama H.,Lignocell Research
Thermochimica Acta | Year: 2014

Kappa-carrageenan (κC) was mixed with methylcellulose (MC) with various mixing ratios. Phase transition behaviour of the above mixed solutions with 1 and 2% concentration was investigated by visual observation and differential scanning calorimetry (DSC). Three regimes showing unique transition behaviour were observed: Regime I which is an MC rich region where only sol-gel transition is found, Regime II an intermediate mixing range of κC and MC where sinusoidal change of gel-sol-gel transition was observed, and Regime III a κC rich region where only gel-sol transition was detected. A phase diagram of κC/MC binary systems was established based on transition temperatures obtained by visual observation and DSC. © 2014 Elsevier B.V. All rights reserved. Source


Iijima M.,Nagasaki University | Hatakeyama T.,Lignocell Research | Hatakeyama H.,Lignocell Research | Hatakeyama H.,Fukui University of Technology
Journal of Thermal Analysis and Calorimetry | Year: 2013

Aqueous solution of cassia gum (CG), which is categorized as a galactomannan polysaccharide having mannose/galactose ratio = 5/1, forms hydrogels by freezing and thawing. When frozen CG aqueous solution was thawed, transparent sol was separated from a turbid gel, i.e. syneresis occurred. Gel concentration ({(Mass of dry gel) / (Mass of gel)} × 100) increased with increasing CG concentration. Viscoelastic properties of CG hydrogels formed by freezing and thawing were investigated by thermomechanical analysis (TMA) in water using an oscillation mode at 0.05 Hz. Dynamic modulus (E′) increased from 3 kPa to ca. 5 kPa with increasing freezing rate. In contrast, E′ maintained a constant value regardless of repeating number of freezing and thawing. From TMA results, it is concluded that the density of cross-linking network structure depends on the size of ice formed by freezing. At the same time, the low E′ value of CG gels is ascribed to the fact that association of galactosyl side group is disturbed by the stiff chain attributed to the unsubstituted region of CG. © 2013 Akadémiai Kiadó, Budapest, Hungary. Source


Iijima M.,Nagasaki University | Iijima M.,Tokai University | Kosaka S.,Nagasaki University | Hatakeyama T.,Lignocell Research | Hatakeyama H.,Lignocell Research
Journal of Thermal Analysis and Calorimetry | Year: 2016

Aqueous solution of poly(vinyl alcohol) (PVA) forms hydrogels by freezing and thawing. In this study, micro-fibrillated cellulose (MFC) was mixed with PVA aqueous solution. Thermal properties of PVA-MFC composite hydrogels were investigated in a wide range of water content by differential scanning calorimetry (DSC). On DSC heating curves, glass transition, exothermic peak due to cold crystallization and endothermic peak attributed to melting of water were observed. Phase diagrams of PVA-MFC composite hydrogels were established based on transition temperatures. The amount of non-freezing water increased when MFC is introduced into hydrogels. Glass transition temperature of amorphous ice restrained by PVA-MFC composite hydrogel is restricted by the presence of MFC. Results obtained by DSC suggest that gelation occurs in adjacent PVA molecules due to compartmentalization in the presence of MFC molecules. © 2015 Akadémiai Kiadó, Budapest, Hungary. Source

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