Characterizing Vitrification by Thermal Analysis During Curing of an Epoxy–Amine System

ABSTRACT During curing, the glass transition temperature of thermosets increases with conversion. When the process is carried out isothermally or at very low heating rates, the glass transition temperature of the resin may rise faster than the material temperature, eventually reaching the latter. This leads to vitrification: The partially cured resin enters the glassy state. The reaction rate drops drastically because it is no longer chemically controlled, but diffusion controlled. As a result, the final product may not be completely cured, which has a severe impact on its mechanical and thermal quality and is therefore crucial for the process. The concept of diffusion‐controlled kinetics during the curing reaction has been widely reported and documented. However, the systematic study of the influence of vitrification on specific heat, dielectric properties, and/or thermal diffusivity during crosslinking under isothermal and dynamic conditions has never been performed so far. This work investigates the impact of vitrification on the specific heat, ionic conductivity, and thermal diffusivity during dynamic and isothermal curing of an epoxy–amine system.