(2e) Production of Spherical Polyamide Particles for Additive Manufacturing By Precipitation

The application of polymer-based technologies for additive manufacturing is one the rise. With technologies like fused deposition modeling, stereolithography or binder jetting, a wide variety of solid to flexible parts are becoming available [1]. However, if functional parts with excellent mechanical properties are needed, only few additive manufacturing technologies are feasible. Among these are mostly exclusively powder-based technologies like selective laser sintering (SLS) [2]. While filament-based technologies offer already a wide variety of different materials including blends and composites, powder materials are still mainly polyamides (PA) with only few available commercial products and even less commercial producers [3]. Although the main route of production for these powders, namely thermal induced precipitation processes, is known in principle [4], hardly any information on the process outside of the patent literature [5–7] is available.

In this contribution, we shed light on the formation process of spherical micron-sized polyamide particles via precipitation. Short-chained alcohols for polyamides are used in pressure resistant autoclaves at high temperatures to dissolve the polyamide and subsequently to precipitate spherical particles upon decreasing the temperature. This way, direct transformation of granular bulk material into spherical particles with narrow size distribution can be achieved. The precipitation products are thoroughly characterized regarding morphology and size, structural and thermal properties. Therefore analysis via electron microscopy, static laser scattering, X-ray diffraction and dynamic scanning calorimetry is conducted. Furthermore, the flowability of the powders is investigated and product properties are correlated to process parameters, especially to temperature-time dependencies.

References

[1] I. Gibson, D. Rosen, B. Stucker, Additive manufacturing technologies, 2. ed., Springer, New York, NY, 2015.

[2] B. Wendel, D. Rietzel, F. Kühnlein, R. Feulner, G. Hülder, E. Schmachtenberg, Additive processing of polymers, Macromol. Mater. Eng. 293 (2008) 799–809. doi:10.1002/mame.200800121.

[3] T.T. Wohlers, Wohlers Report 2016, Wohlers Associates, Fort Collins, Col., 2016.

[4] M. Schmid, Selektives Lasersintern (SLS) mit Kunststoffen: Technologie, Prozesse und Werkstoffe, Hanser, 2015.

[5] F.E. Baumann, N. Wilczok, DE19708946

[6] S. Mumcu, H.-J. Panoch, J. Rüter, EP0200852.

[7] K.-R. Meyer, K.-H. Hornung, R. Feldmann, H.-J. Smigerski, EP0014772.