Nanoparticle-functionalized polymers for laser powder bed fusion

As one of the major additive manufacturing (AM) techniques, laser powder bed fusion (PBF-LB) of polymers is of great interest for prototyping and flexible small-scale production of geometrically complex parts. Since polymer powders have material-related limitations regarding their processability, the modification and control of their optical and thermal properties have become decisive factors in PBF-LB. In order to expand the material variety, nano-functionalization captures high interest and even small nanoparticle loadings (≤ 0.1 wt%) affect the processing behavior. One challenge of nanoparticle-functionalization is nanoparticle dispersion and therefore also avoiding aggregates with sizes of hundreds of nm up to the µm-range, which may influence laser absorption, heat conduction, melting, or resolidification behavior, and could negatively affect the properties of the final part. However, a deep understanding of the interplay between the PBF-LB process and small mass fractions of nanoparticulate additives in the ppm range is required in order to exploit the potential of nanoparticle additivation. In this thesis, colloidal additivation is introduced as an approach to create nanoparticle-functionalized polymer powder materials for PBF-LB. Since colloids used in this approach are synthesized by laser ablation and laser post-processing in liquids, this thesis also aims to develop a deeper understanding of these laser-based synthesis methods. Research was conducted on the process kinetics and determinants of colloidal additivation based on adjustment of electrostatic interactions between nanoparticles and polymer microparticles. The effects of the nanoparticle material, its optical properties, and degree of dispersion on PBF-LB were investigated for different polymer-nanoparticle systems based on polyamide 12 and thermoplastic polyurethane. This thesis emphasizes the extraordinary importance of nanoparticle dispersion rather than just considering their mass loading (wt%), and sets out for a new way to functionalize parts generated by PBF-LB.

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