Gelation Behavior of Konjac Glucomannan

• Main Authors: Worasaung Klinthong, 詹木泉
• Other Authors: Mao, Ching-Feng
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/69647444952479443444

碩士 === 南台科技大學 === 化學工程與材枓工程系 === 97 === This research studies the gelation behavior of konjac glucomannan (KGM) gel and konjac glucomannan and xanthan (KGM/XG) mixed gels described by the cascade model to understand the mechanism of gelation and the nature of their junction zones. The KGM and XG with molecular weights of 4.75  105 g/mol and 9.80  105 g/mol, respectively, are used as samples. During pretest, there is some liquid phase separating from gel phase, which is called syneresis. Thus, the syneresis of KGM gel is studied on the effect of concentration and aging times. It is shown that the syneresis reduces with the increment of polymer concentrations, whereas aging time shows no effect. Subsequently, the transient KGM gelling process is investigated based on the cascade modeling for single-component polymer network. The equilibrium parameters contains equilibrium functionality fe = 213, front factor a = 27.44 and equilibrium constant K is 2.77. The experimental data of G′ vs. t obtained are converted to time-dependent functionality. The first order kinetics expression is conducted to explain the evolution of functionality with time. The result shows that the concentration-independent k = 0.081+0.008 min-1, relates to the formation of deacetylated segments. The gel properties of XG and KGM mixtures are investigated. The concentration dependence of gel modulus and the composition dependence of critical gelling concentration are analyzed using cascade model. The number of cross-linking sites per molecule for KGM and XG, fXG and fKGM, determined by fitting experimental data to model are 1000 and 3, respectively. The value of fXG = 1000 implies that a cross-linking is formed in every 1 repeating unit along XG backbone and fKGM = 3 suggests that the cross-linking site in KGM is occurred in every 880 monosaccharide units from overall 2640 units. The cascade analysis of composition dependence of critical gelling concentration results in values of fXG = 500 and fKGM = 5 for competitive self-association reaction and fXG = 50, fKGM = 3 and fXG′ = 1000 for noncompetitive self-association reaction, respectively. The van’t Hoff analysis reflects the enthalpic and entropic changes of the cross-linking reaction of cross- and self-associations.