物理化学学报 >> 2010, Vol. 26 >> Issue (01): 7-12.doi: 10.3866/PKU.WHXB20100120

热力学、热化学和溶液化学 上一篇    下一篇

木糖醇玻璃焓松弛的量热分析

高才, 杨锁, 刘向农, 王铁军, 江斌   

  1. 合肥工业大学机械与汽车工程学院, 合肥 230009
  • 收稿日期:2009-08-28 修回日期:2009-10-21 发布日期:2009-12-29
  • 通讯作者: 高才 E-mail:gao_cai@hotmail.com

Calorimetric Analysis on Enthalpy Relaxation in Xylitol Glass

GAO Cai, YANG Suo, LIU Xiang-Nong, WANG Tie-Jun, JIANG Bin   

  1. School of Mechanical and Automotive Engineering, Hefei University of Technology, Hefei 230009, P. R. China
  • Received:2009-08-28 Revised:2009-10-21 Published:2009-12-29
  • Contact: GAO Cai E-mail:gao_cai@hotmail.com

摘要:

为了考察木糖醇的玻璃化转变和焓松弛行为, 寻求碳链长度对线性多元醇玻璃化转变和焓松弛行为的影响, 利用差示扫描量热(DSC)技术测定了不同降温速率下木糖醇在玻璃化转变温度(Tg)前后的比热容(Cp), 通过曲线拟合获得了TNM(Tool-Narayanaswamy-Moynihan)模型参数, 并和其他多元醇类已有研究结果进行对照. 结果表明, 尽管TNM模型可以很好地重现不同降温速率体系的实验比热容数据, 但模型参数并不是材料常数, 而是和热历史有关, 不同的降温速率对应不同的模型参数. 指前因子(A)、非线性参数(x)和非指数参数(β)均随着降温速率的增加而降低, 松弛活化焓(△h*)的变化趋势刚好相反. 几种线性多元醇玻璃化转变和TNM模型参数的对照表明, 玻璃化转变温度, 松弛活化焓和动力学脆度(m)都随着烷基碳链长度的增加而增加. 虽然非线性参数、非指数参数随碳链长度的增加有降低的趋势, 但木糖醇展现出反常变化的情形.

关键词: 差示扫描量热法, 木糖醇, 玻璃化转变, 焓松弛, Tool-Narayanaswamy-Moynihan模型

Abstract:

To investigate the enthalpy relaxation behavior of xylitol glass and the influence of carbon chain length on the glass transition and relaxation of polyalcohols, differential scanning calorimetry (DSC) was employed to obtain the specific heat capacity (Cp) near the glass transition temperature (Tg) at different cooling rates. A curve-fitting method was used to obtain the TNM (Tool-Narayanaswamy-Moynihan) model parameters and the results were compared to the published data of other polyalcohols. Although the TNM model can be used to reproduce the experimentally normalized Cp curves of xylitol, different model parameters were found at different cooling rates, indicating that the TNM model parameters are not material constants but are sensitive to the thermal history. The pre-exponential parameter (A), non-linear parameter (x), and non-exponential parameter (β) decreased as the cooling rate increased while the apparent relaxation activation enthalpy (△h*) changed inversely. We found that Tg, △h*, and the dynamic fragility (m) increased as the alkyl carbon chain increased while x and β showed an approximate decrease except for the case of xylitol.

Key words: Differential scanning calorimetry, Xylitol, Glass transition, Enthalpy relaxation, Tool-Narayanaswamy-Moynihan model

MSC2000: 

  • O642