ALTERNATING DIFFERENTIAL SCANNING CALORIMETRY: ISOTHERMAL CURING OF THE EPOXY RESIN

Ida Poljanšek,* Matjaž Krajnc

Faculty of Chemistry and Chemical Technology, Aškerčeva 5, 1000 Ljubljana, Slovenia

Abstract

In this study the quasi-isothermal curing of diepoxide resin with triamine was investigated by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The complex heat capacity measurements were carried out to analyze the vitrification process at curing temperatures (T_c) below the maximum glass transition of the fully cured epoxy. The modulus of the complex heat capacity /c_p^*/ increases until a maximum and then an abrupt decay of /c_p^*/, due to the vitrification of the system was observed. The phase angle and out-of phase heat capacity show an asymmetric wide peak during the vitrification process. The abrupt decay of /c_p^*/ at vitrification decreases with the increase of T_c and disappears at temperature T_gµ. The decay of /c_p^*/ during vitrification may be normalized between unity and zero by defining a mobility factor. This mobility factor was used to simulate the reaction rate during the stage where the reaction is controlled by diffusion. The observed reaction rate was simulated by the product of the kinetic reaction rate, determined by the auto-catalytic model, and the mobility factor.