Phase change detection in neat and fiber reinforced polyamide 6 using dielectric analysis

In this study online-capable dielectric analysis techniques were investigated to show its potential on the example of detecting phase transitions of polyamide 6 (PA6) and its composites. The differential scanning calorimetry (DSC), a standard testing method commonly applied in thermophysical analysis, is used as a reference method throughout this work. Dielectric measurement techniques are introduced as a means for providing an online measuring concept that is able to monitor phase changes in both neat, as well as glass and carbon reinforced PA6. Whereas a simple sensor setup has proven to be adequate for dielectric measurements of pure and glass reinforced PA6, the insertion of an additional insulation layer between sample and sensor was necessary to overcome short circuit problems induced through the conductive nature of carbon in carbon fiber reinforced PA6. Results show that crystallization and melting can be successfully identified using dielectric analysis and can be compared directly with results from the DSC. Analysis in the dielectric method is based on relative permittivity ϵʹ, loss factor ϵʺ and ion viscosity ρ. Here phase changes can be observed as a frequency dependent step in the measurement signal, which becomes increasingly apparent with increasing frequency. Plotting the first derivative of ϵʹ, ϵʺ and ρ relative to the temperature the phase change can be depicted in form of a peak, similar to the case of DSC. The derivative signals can be used as a direct means for monitoring in manufacturing processes.