Laser powder bed fusion of highly reusable nanocomposite PA12 powder functionalised with MWCNTs

Polyamide-12 (PA12) dominates the Polymer Laser Powder Bed Fusion (P-LPBF) material market, with limited alternatives. Functionalising polymers, such as PA12, with nanomaterials to create nanocomposite powders can enhance and diversify part properties. Open-chain end PA12s are commonly used as the matrix polymer, however, the unfused powder is typically only ~50% reusable and their poor re-useability can be exacerbated when functionalised using nanomaterials. Unfused end-passivated (closed chain end) PA12s are ~90% reusable as they resist process-related degradation/ageing better than open-chain end PA12s, enabling a near zero wastage P-LPBF workstream. However, the relatively narrow parameter space of end-passivated PA12s is perceived to require precise and challenging process control. Nanomaterial-based functionalisation is known to alter P-LPBF processability of open-chain end PA12s. Such an alteration risks rendering the end-passivated PA12s unsuitable for P-LPBF; hence, despite their better reusability, nanomaterial functionalisation of end-passivated PA12s has generally been avoided until now. Using MWCNTs as an example, we demonstrate nanocomposite powder preparation and P-LPBF processing using ~90% reusable end-passivated PA12. An unconventional approach of setting the powder bed temperature above the melting onset temperature of the powder has been shown not to require any challenging process control as previously perceived. A comprehensive energy density calculation metric, Effective Mass Energy Density (EMED), has been proposed and used to explain the impact of material properties and process parameters on part properties. The drastic increase in reusability without compromising processability opens the doors to a larger material palette using more exotic nanomaterials while lowering cost, waste and carbon footprint.