Drying process optimization for the recycling of polyamide 6

The recycling of polyamide 6 (PA6) is a major challenge within circular manufacturing, particularly in high-throughput industrial extrusion processes. One of the main limiting factors in the reprocessing of recycled PA6 is its sensitivity to moisture, which leads to significant losses in mechanical performance and poor process stability if not adequately removed before extrusion. At Habasit AG, the currently installed desiccant drying systems are unable to meet the required production rates and contribute to operational inefficiencies. This thesis investigates the optimization of drying strategies for recycled PA6 under industrial conditions. The effects of moisture, thermal degradation, and oxidation were studied through an extensive experimental program including Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), oxidation induction time (OIT), melt volume rate (MVR), and rheological measurements. Several alternative drying technologies, fluidized bed dryers, advanced vacuum systems, and microwave-assisted drying, were reviewed and assessed against the technical and operational requirements of the extrusion line. The results indicate that microwave drying provides more uniform and controllable moisture removal than the existing equipment, while also significantly reducing energy consumption and material losses. A techno-economic assessment was carried out, considering capital investment, operating costs, labor implications, and the indirect benefits associated with improved product quality and process reliability. The study highlights the importance of pilot-scale trials in reducing implementation risk, supported by industrial data showing substantially higher success rates when pilot testing is performed prior to full-scale deployment. Beyond quantitative metrics, factors such as product consistency, production robustness, and long-term capacity expansion further strengthen the case for investment. Overall, this work delivers practical engineering guidance for improving industrial PA6 recycling processes and demonstrates the value of combining technical analysis with economic evaluation in the development of sustainable manufacturing solutions.