Evaluating Dielectric Properties for Semicrystalline Thermoplastics to Analyze the Thermal and Rheological Properties in Laser-Based Powder Bed Fusion of Plastics

Understanding plastics’ thermal and rheological properties in laser-based powder bed fusion of plastics (PBF–LB/P) is a prerequisite for industrial applicability. During PBF–LB/P, prolonged exposure to elevated temperatures causes the aging of semicrystalline thermoplastics. Even though thermal aging can be revealed by material property changes, analyzed by melt flow rate (MVR) or differential scanning calorimetry, these techniques are limited to ex situ analyzes and do not provide insights into the plastic's property changes during the PBF–LB–/P process. Dielectric analysis (DEA) is a potential in situ measurement technique that can provide insights into the material changes during processing. However, DEA has been mainly used to analyze the curing behavior of thermosets, and the relation between the dielectric, thermal, and rheological properties of semicrystalline thermoplastics has not yet been fully studied. Therefore, a new methodology is introduced to determine the characteristic melting and crystallization temperatures for semicrystalline thermoplastics with DEA. The repeatability of the measurements and the influence of measurement frequency are investigated on the demonstrator material, polyamide 12 (PA12). Results show that DEA reliably characterizes melting and crystallization ranges, while the measurement frequency influences the absolute temperatures. In addition, DEA can monitor plastic aging, even at lower temperatures, without melting it.