Open Access

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.

To address the needs for increasing efficiency in power conversion, stratified structures like thermal barrier coatings, are used to increase operation temperature. Also advanced material processing like 3D laser printing of metals and ceramics are based on a layer-to-layer process at high temperatures, resulting in non-homogeneous components. Both systems require more and more detailed investigation methods to characterise the material properties of the resulting structures and to optimize the relevant processes. To address the required needs in advanced material characterisation recently an attempt was started to develop a unique measurement set-up for advanced material characterisation. This method is based on the well know laser flash principle, which was improved by adding supplementary heating sources and additional detection channels. Combining different heating mechanism and heating times with the two-dimensional measuring of the thermal flow across the sample enables the determination of different opto-thermal parameters and other material properties, e.g. mechanical contact, electrical conductivity or optical data, which also depend on or affect the flow of heat. In this paper we describe the implementation of the different optical methods to measure the thermal heat flow by point-like and two-dimensional temperature measurement and present first results on several samples.