Within this contribution liquid-liquid phase separation (LLPS) and precipitation from ethanol was studied as an approach to produce polyamide 11 (PA11) powders for selective laser sintering (SLS). To this end, the cloud point and solution temperature curve of the PA11ethanol was determined experimentally via turbidity measurements. The proper range of system composition and temperature for particle formation was deduced. The dependence of particle characteristics on process parameters (polymer concentration, stirring conditions and temperature regime) during LLPS and precipitation was assessed and the products were characterized with respect to their size and morphology. Furthermore, structural, rheological (c.f. viscosity number) and thermal characteristics were analyzed and correlated with process parameters. Rheological characteristics and molecular weight distributions were determined.After removal of fines and dry coating with hydrophobic fumed silica, an optimized PA11 powder with mean particle of several 10 microns showing good flowability for SLS was obtained. SLS processability of this optimized PA11 powder was demonstrated by building multi-layered test specimens in a laser sintering machine. With this contribution, we present a comprehensive workflow for the process development, product characterization and product application of a SLS powder manufactured via precipitation.

The crystallinity determination of polymers using differential scanning calorimetry (DSC) is a standard procedure in industrial and university research. Its value strongly depends on the enthalpy of fusion, which cannot be determined directly using DSC, but must be calibrated using external methods such as X‐ray diffraction (XRD) or density measurements. In addition, the determination of the enthalpy or heat of fusion is not trivial and thus error‐prone; hence, values from 60 to 260 J g−1 are quoted for polypropylene in the literature. It is therefore of great relevance to devise a consistent method to determine the heat of fusion. To determine the heat of fusion for polypropylene, a sample set with a broad range of crystallinities is produced using cooling rates between 1 and ≈3500 K min−1. The melting enthalpy of the samples is determined using DSC measurements. The determination of the melting enthalpy based on XRD measurements is discussed in detail, validated using Fourier‐transform infrared spectroscopy (FTIR), and compared with values quoted in the open literature. Although two different approaches are used to determine the enthalpy of fusion, a value of 170 ± 3 J g−1 is determined.

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Polypropylene (PP) powders are coated with silica nanoparticles in a fluidized bed to improve the flow behavior of the powders and the processability in powder bed fusion. The nanoparticles are produced in situ via dusty plasma‐enhanced chemical vapor deposition (PECVD) in an atmospheric‐pressure Ar/O2 plasma jet fixed at the distributor plate of the fluidized bed. Hexamethyldisiloxane is used as a precursor of the nanoparticles. The influence of the oxygen concentration in the plasma gas and the number of treatment cycles on the chemical composition of the nanoparticles, the amount of nanoparticles deposited, and the flow properties of the coated PP powders is investigated. The chemical composition of the formed silica particles is determined by X‐ray photon spectroscopy and infrared spectroscopy. The results reveal that the composition of the nanoparticles is SiOxCy, that is, the portion of organic residues introduced by the precursor can be controlled by changing the oxygen concentration in the plasma gas. The mass of nanoparticles deposited on the polymer powder's surface, as determined by inductively coupled optical emission spectroscopy, shows a linear dependence of the number of cycles and the oxygen concentration in the plasma gas. A considerable improvement of the flow behavior of the PP powders is observed after PECVD treatment.