Influence of injection volume rate–driven temperature evolution on the molecular and mechanical properties of PA6.6 in injection molding

This study investigates the influence of injection volume rate (IVR) on local temperature development in a narrow slit and its effects on the mechanical and molecular properties of unfilled polyamide 6.6 (PA 6.6). An in-situ measurement setup was developed to capture high-resolution temperature profiles across the melt flow path during injection molding. Increasing IVR resulted in a substantial rise in peak melt temperatures, exceeding 500 °C at high IVR in the center region of the slit. However, these extreme temperatures were sustained only for fractions of a second, and the 350 °C threshold was never maintained for more than 2.5 s under any condition. Based on these thermal profiles, significant thermo-oxidation degradation might be expected. Nevertheless, differential scanning calorimetry with oxidative induction time (DSC-OIT) and gel permeation chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR) revealed no measurable signs of chemical degradation. Mechanical properties showed only minor variations, most likely arising from physical effects such as molecular orientation and chain entanglement rather than chemical changes. These findings indicate that, within the investigated processing window, high IVR can induce extreme but short-lived thermal loads without compromising polymer integrity.