用DSC测量葡萄糖溶液部分玻璃化转变温度的新方法

用差示扫描量热仪, 采用经过退火处理的连续扫描法, 以不同浓度(20%、45%)的葡萄糖溶液为研究对象, 研究了退火温度对Tgf(部分结晶的玻璃化转变温度)的影响, 给出了确定Tg′(部分玻璃化转变温度)的新方法. 研究发现, 不同退火温度下的Tgf不同. 在−50 ℃以上退火, Tgf随着退火温度的增大而减小; 在−50 ℃以下退火, Tgf随着退火温度的增大而增大, 都有很好的线性关系. 不同浓度的溶液具有相似的规律. 提出从Tgf确定Tg′的方法: Tgf在−50 ℃上下随退火温度变化线的交点所对应的部分结晶玻璃化转变温度即为Tg′. 使用该方法测得葡萄糖的Tg′为−55 ℃.

A New Method for Measuring the Glass Transition Temperature of the Maximally Freeze-Concentrated Glucose Solution by DSC

The new concept of the glass-transition temperature of the partially freeze-concentrated solution (Tgf) is brought forward and a new method is given for measuring Tgf of 20% and 45% glucose solution using differential scanning calorimetry (DSC), which is based on annealing samples for long periods of time at different temperatures. The influence of annealing temperature on Tgf is studied. It is found that the Tgf increases initially with annealing temperature up to −50 ℃, and decreases as the temperature continues to increase, and exhibiting a good linear relation in both cases. The same phenomenon was observed for glucose solutions of different concentrations. It is concluded that the Tg′ (glass transition temperature of the maximally freeze-concentrated solution) can be determined from the intersection of the two curves reflecting the Tgf change with annealing temperature. The optimal annealing temperature(−50 ℃) and accurate glass transition temperature(Tg′, −55 ℃） of glucose solution are obtained.