(2a) Novel Approaches for the Production of Polymer Powders for Additive Manufacturing

Additive manufacturing (AM), often simply referred to as ‘3d printing’ allows the production of individualized and complex parts without the need of any tools or moulds. Especially powder and beam-based AM processes like selective laser sintering (SLS) of polymers are promising. SLS already is used to manufacture special parts, although, the opening of new fields of application is currently hindered by the limited availability of materials. To further extend the applications of SLS new and cheap materials with good processability must be supplied. Innovative and versatile processes being applicable to a wide variety of thermoplasts are desirable. Currently, the spectrum of commercial SLS powders is very limited, about 95 % of the total market share is made up of polyamide powders that are typically produced by bottom-up approaches like emulsion polymerization or precipitation processes.

Two innovative methods for production of spherical polymer micro particles for SLS will be discussed: The first approach is a process chain consisting of wet grinding of polymers in a stirred media mill followed by rounding of the obtained irregular-shaped particles in a heated downer reactor and subsequent dry coating of the spherical particles for improvement of powder flowability. The process chain is applicable to a various thermoplasts and will be discussed for pure polymers (polystyrene, polybutylene terephthalate) and for filled polymer systems. Bulk powder properties and polymer structures are thoroughly characterized along the process chain. The second approach, melt emulsification with subsequent dry coating, will be exemplified for polypropylene. In this process a polymer melt is emulsified by elongational and shear stresses in a rotor stator device.

Both approaches allow for production of spherical polymer micro particles of good flowability which are promising, novel powder materials for SLS.

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