Abstract
Konjac glucomannan acetate with high degree of substitution ( KGM acetate) was synthesized by reaction of konjac glucomannan (KGM) and acetic anhydride catalyzed with concentrated sulphuric acid.The influences of the reaction conditions on the degree of substitution ( DS) were investigated,and the optimum ratio of ethanol /water,reaction time,reaction temperature,concentration of catalyst and ratio of KGM /acetic anhydride were 5∶ 5,2 h,75℃ ,0.1 mol /L and 5∶ 40 (g /mL),respectively,under which the DS of product was as high as 2.93,and the molecular weight of KGM acetate was significantly lower than that of KGM.KGM and KGM acetate were characterized by means of FTIR,XRD,SEM,TGA,DSC and rotary rheometer.The results showed that the carbonyl (C O)characteristic absorption peak of KGM acetate was much higher than that of KGM.Most of the apparent morphology of KGM acetate was loose flocculent.KGM and its acetate both were amorphous structure.The thermal stability of KGM acetate was lower than that of KGM,and the decomposition temperature of KGM and KGM acetate was 261.1℃ and 204.6℃ ,respectively.Before undergoing thermal decomposition,KGM acetate showed a glass transition temperature (Tg)at about 128.49℃ ,but KGM did not.The shear viscosity was very sensitive to temperature,so that the processing flowability of KGM acetate can be regulated easily by changing temperature.
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