Process parameter optimization for 3D printing of post-industrial recycled PP through in-situ thermal analysis

Abstract Fused filament fabrication (FFF) is commonly used to manufacture polymer components and has emerged as a sustainable manufacturing method when recycled materials are utilized. However, achieving consistent mechanical performance of recycled polymers remains challenging as semicrystalline polymers are highly sensitive to thermal history from prior manufacturing. This study investigates the effect of printing parameters on cooling behavior, crystallinity, and tensile performance of post-industrial recycled polypropylene (rPP). Additionally, an in-situ infrared thermal imaging approach was introduced to directly monitor temperature changes during the FFF process. A systematic experimental design was implemented by varying the wall thickness of the printed samples and the nozzle temperature, and their effects were correlated with real-time cooling rates, crystallinity measured by differential scanning calorimetry and Raman spectroscopy, and tensile properties. The results demonstrate that the cooling rate acts as a unifying parameter linking process conditions to crystallization behavior and mechanical response. The printed sample fabricated at a nozzle temperature of 190 ℃ and a wall thickness of 2.4 mm achieved an optimal balance between ordered and disordered crystalline regions, a good surface finish, uniform pigment dispersion, and a tensile strength of 20.95 MPa, which is comparable to previously reported values for rPP. This study presents a new experimentally validated method to predict and optimize printing parameters through real-time process-structure–property relationships for recycled semicrystalline polymers during material extrusion, thereby supporting sustainable manufacturing processes.