Recycling Potential of SLS-Degraded PA12 Powder for Melt-Based Manufacturing: Insights Resulting from the Advanced Crystallization Modeling.

Selective laser sintering (SLS) of polyamide 12 (PA12) generates large quantities of thermally aged powder whose altered crystallization behavior limits its complete reuse in additive manufacturing. In the present study, the feasibility of repurposing SLS-degraded PA12 powder in conventional melt-processing techniques is investigated. Thermo-analytical, diffraction, spectroscopic, and microscopic techniques were employed to investigate the crystallization kinetics, crystal morphology, and mechanical properties of PA12 materials prepared from different SLS-processed powder grades, namely nondegraded (as purchased), degraded (recycled), and mixed (blended) PA12 powders. The mixed material (made from nondegraded and degraded powders in the weight ratio of 25/75) exhibited markedly slower crystallization, especially during isothermal and slow-cooling conditions, attributed to molecular incompatibility and impaired cocrystallization between long, irregular degraded chains and shorter nondegraded chains. Advanced kinetic modeling using the temperature-dependent M-catalytic Hoffman-Lauritzen framework confirmed increased nucleation barriers and distinct shifts in autocatalytic and growth-related kinetic parameters. Hot-stage microscopy further revealed distinct differences in the crystal growth kinetics, explaining the variable lamellae packing within forming spherulites. Mechanical properties of the melt-processed PA12 materials significantly differed below the glass transition temperature (T g) - stiffness of the degraded material increased, while it decreased for the mixture. On the contrary, above T g, the mechanical behavior was practically identical for the nondegraded material and for the blend with 75% of degraded material, which introduces an interesting alternative utilizing the SLS-processed PA12 powders in melting-based technologies, and provides guidance for optimizing compositions to balance processability, cost-effectiveness, and performance of the corresponding recycling.