Acta Phys. -Chim. Sin. ›› 2010, Vol. 26 ›› Issue (01): 7-12.

• THERMODYNAMICS,THERMOCHEMISTRY AND SOLUTION CHEMISTRY •

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

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.

MSC2000:

• O642