The mixing quality in nanoparticulate systems plays a fundamental role in the functional enhancement of advanced materials. In this study, we evaluate the effectiveness of mixing TiO 2 (rutile) and ZrO 2 (monoclinic) nanopowders using Raman mapping and energy-dispersive X-ray (EDX) spectroscopy within a scanning electron microscope (SEM). Eighteen experiments were carried out in an opposed jet fluidized bed, varying process time, mass ratio, and Laval nozzle back pressure. Raman mapping enabled spatially resolved identification of phases, while SEM/EDX provided high-resolution elemental composition. Both techniques indicated good overall inter-aggregate mixing efficiency, especially at a mass ratio of 1:1, with average Ti atomic fractions close to 0.607. Quantitative comparison showed that Raman micro spectroscopy yielded lower relative deviations from the expected values and required simpler sample preparation, making it a practical choice for assessing mixing homogeneity. Deviations from the expected compositions were more pronounced at other mass ratios (especially 1:2), likely owing to differences in particle size, density, and aggregation tendencies. Finally, in contrast to previous intra-aggregate mixing studies, the current results suggest that inter-aggregate composition tends to stabilize near equimolar proportions regardless of the initial mass ratio, highlighting self-regulating behavior at the macro scale. (c) 2025 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Nanoparticle powders produced by mixing have applications in catalysis, coatings, and advanced materials, yet they remain challenging owing to the strong cohesive behavior of the constituents. Hetero-aggregates form through hetero-contacts at interfaces between chemically distinct materials, but achieving a uniform distribution of components requires an efficient mixing process. Opposed jet fluidized beds offer a promising approach for overcoming these limitations. In this study, the formulation of titania-zirconia hetero-aggregates was investigated by analyzing process parameters and their impact on the inter- and intra-aggregate mixing quality. The effects of feed composition mass ratios (1:1, 2:1, and 1:2), back pressures of the Laval nozzles (0.5, 2.5, and 5.0 bar), and processing times (1 and 5 min) were evaluated by mapping the Ti atomic fraction. The composition and shape of the hetero-aggregates were investigated. The hetero-aggregates exhibited compositions closely aligned with the expected values, based on the initial masses of the components. Shape analysis revealed star-like, elongated, and irregular structures, with circularity and roundness values of approximately 0.4 and 0.5, respectively. Most hetero-aggregates exhibited porosities between 0.971 and 0.991, indicating highly porous structures with significant void spaces. These findings demonstrate that opposed jet fluidized beds enable control over the composition and morphology of hetero-aggregates, leading to efficient nanoparticle mixing.

A major challenge in the powder bed fusion (PBF) process with polyamides, which are the most commonly used powders, is the handling of already used powder (aged powder). During PBF, polyamide powders undergo chemical ageing, resulting in altered thermal and rheological properties of the feedstock material. Components made from aged powder are of inferior quality. Therefore, aged powder is usually refreshed with new (virgin) powder. Although, a substantial amount of aged powder accumulates over the course of processing. These excess quantities are either employed in other plastic manufacturing processes (downcycling) or, more frequently, disposed. A combined process of solvolysis with subsequent thermally induced liquid-liquid phase separation and polymer crystallisation (TIPS+S) is used to restore the thermal properties and rheological properties of aged polyamide 12 (PA12) and thus to make the powders suitable for PBF again. The degree of solvolysis of the aged PA12 is tuned by reaction temperature or reaction time. A kinetic model allows to determine suitable process parameters for TIPS+S depending on the ageing condition of the feed to match the thermal properties of the recycled PA12 powders to those of PA12 virgin powder. The optimised recycled PA12 powder shows comparable zero shear viscosity, particle size distribution, particle shape and flowability to the virgin material. Specimen built from equally mixed recycled and aged PA12 powder achieved the same mechanical properties like those obtain by PBF of equally mixed virgin and aged powder. Therefore, a closed loop recycling approach is feasible, in which aged PA12 powders from the PBF process are recycled by the proposed TIPS+S process.

Herein, we demonstrate the preparation of magnetic polyamide 11 feedstock powders for powder bed fusion (PBF) using liquid-liquid phase separation and crystallization. By adding magnetic nanomaterials during the precipitation process, the particulate additive is incorporated into the polymer matrix. This enables the production of filled systems at single particle level, which is advantageous in terms of the adjustable magnetic strength and homogeneity of the powder. Thermogravimetric analysis is used to determine the additive content and onset temperature of decomposition of composite powders, where additive-enhancement of PA11 powders with magnetic iron oxide nanoparticles showed a positive influence on the thermal stability of the feedstock. Successive analysis of particle size distribution, shape, colour, crystal structure, magnetic properties and thermal properties of the composite powders are carried out and their properties are discussed with respect to the PBF process. A decrease in particle size, width of the thermal process window and isothermal crystallization time can be attributed to the nucleating effect of the magnetic additive. The PBF processability of the composite feedstock is demonstrated by the production of magnetic tensile bar specimens from additive-enhanced PA11 powders with 1wt.-% magnetic iron oxide.

Raw data of fragments and corresponding morphological descriptors of green peas after impact comminution in a hammer mill.

Substituting conventional doctor blade- or roller-based powder application methods for laser-based powder bed fusion of polymers (PBF-LB/P) by electrophotographic powder application (EPA) offers significant advantages. In particular, the selective powder deposition enabled by EPA allows high powder efficiency and the possibility to locally adjust part properties during their fabrication. However, defined charging of powder particles is decisive for achieving an accurate selective deposition of powder layers by means of electrophotography. This is the first comprehensive study on the specific triboelectric charge control of polymer particles for their subsequent use in electrophotographic powder application for PBF-LB/P. For this purpose, approaches for charge control of toner particles in the context of digital (2D) printing technologies are adapted and applied to polypropylene (PP) feedstocks for PBF-LB/P. In order to show transferability to other polymers, the charge control method developed in this paper is also applied to polyamide 12 (PA12) high density polyethylene (HDPE) and polystyrene (PS). For successful EPA, unipolar charging of polymer particles is decisive. However, non-functionalized PP shows a strongly bipolar triboelectric charging, which is unsuitable for EPA. The charge control method developed in this work shifts this strongly bipolar triboelectric charging to a unipolar charging. This is achieved by the synergy of both functionalizing the particle surface with charge control agents (CCAs) and choosing suitable carrier particles known from two-component toners. The developed method allows to control crucial parameters of triboelectric charging, namely polarity, amount of charge and resulting surface potential. Furthermore, the presented results provide new insights into the transfer behavior of charged PP particles in an external electric field. Finally, this enables the triboelectric charging mechanism to be used for electrophotographic powder application in PBF-LB/P.

Substituting conventional doctor blade-or roller-based powder application methods for laser-based powder bed fusion of polymers (PBF-LB/P) by electrophotographic powder application (EPA) offers significant advantages. In particular, the selective powder deposition enabled by EPA allows high powder efficiency and the possibility to locally adjust part properties during their fabrication. However, defined charging of powder particles is crucial for achieving an accurate selective deposition of powder layers by means of electrophotography. This is the first comprehensive study on the specific triboelectric charge control of polymer particles for their subsequent use in electrophotographic powder application for PBF-LB/P. For this purpose, approaches for charge control of toner particles in the context of digital (2D) printing technologies are adapted and applied to polypropylene (PP) feedstocks for PBF-LB/P. In order to show transferability to other polymers, the charge control method developed in this paper is also applied to polyamide 12 (PA12) high density polyethylene (HDPE) and polystyrene (PS). For successful EPA, unipolar charging of polymer particles is crucial. However, non-functionalized PP shows a strongly bipolar triboelectric charging, which is unsuitable for EPA. The charge control method developed in this work shifts this strongly bipolar triboelectric charging to a unipolar charging. This is achieved by the synergy of both functionalizing the particle surface with charge control agents (CCAs) and choosing suitable carrier particles known from two-component toners. The developed method allows to control crucial parameters of triboelectric charging, namely polarity, amount of charge and resulting surface potential. Furthermore, the presented results provide new insights into the transfer behavior of charged PP particles in an external electric field. Finally, this enables the triboelectric charging mechanism to be used for electrophotographic powder application in PBF-LB/ P.

Within this contribution, the incorporation of nanoparticles (SiO2, Al2O3, TiO2) into the matrix of precipitated polyamide particles during thermally induced phase separation (TIPS) is demonstrated. The obtained polymer composite powders are tailored for their application in powder bed fusion (PBF). The flexible process allows to tune and adapt the powder properties to meet specific challenges like narrow particle size distribution, spherical particles, high additive contents and good distribution of the additive within the powder. Thermogravimetric analysis and electron microscopy prove the incorporation of the nano-sized additive into the matrix of the polymer. The influence of the additive material during polymer precipitation on the particle size distribution and shape of the powders is discussed. Thermal properties of the composite powders were assessed by dynamic and isothermal DSC for subsequent Avrami analysis. The observed acceleration of the crystallization kinetics could be attributed to the nucleating effect of the additive. All powders showed an easy-flowing (flow index ffC > 4) behavior. This allowed the deposition of homogeneous powder layers during PBF experiments also at high temperatures. The processability of the composite powders in the PBF process was demonstrated by single layer experiments.

This study presents bulk material characterization, especially powder flowability, of eight food powders from six different plants (almond, chestnut, chickpea, coconut, hazelnut and rice). The characterization of the bulk powders includes the particle size distributions, true densities, bulk and tapped densities, as well as the powder porosity and moisture content. The flowability is determined by means of Hausner ratio, Carr's index, flow function by an annular shear cell and dynamic angle of repose. The flowability characteristics are discussed in regard to the bulk powder properties and evaluated for their applicability as some methods could give misleading results for the flowability.

Powder bed fusion of polymers with laser beam (PBF-LB/P) involves selectively melting plastic micro particles with a laser and building up the parts layer by layer, which offers great freedom of design. However, the choice of commercially available thermoplast feedstock powders is limited (90% polyamides). In order to extend the range of materials, this contribution presents the production of highly spherical micro particles by melt emulsification followed by spray agglomeration for ester wax. The effect of process parameters during emulsification (energy input, surfactant to polymer ratio) on the particle size distribution is demonstrated in detail for the ester wax system. In order to generate and tune particle sizes to a range suitable for PBF, melt emulsified ester wax dispersions are spray agglomerated. Agglomerated ester wax powders were used for the PBF process to manufacture tensile strength specimens type 5A.

In laser powder bed fusion, micro-particles are selectively fused by a laser to produce parts, layer-by-layer. While this process offers a high freedom of design, the variety of commercially available materials, especially composites are limited. Conductive polymers blends, are very interesting for many applications, especially as sensors with freely definable shape. First, the amount of carbon-black needed to make the composite electrically conductive has to be determined; this limit is called percolation threshold (PT). The PT depends on many properties, such as particle size and shape of both polymer and carbon-black and will be determined experimentally. In this work, polypropylene is dry mixed with different types of micron sized carbon blacks. The PT and the conductivity is determined by means of impedance spectroscopy.

The influence of process temperature on the triboelectric charge during dry coating of cohesive polymer powders is investigated. The purpose of heating is to decrease the surface moisture of the powder, which results in an increase of electrical charge of the powder. The effect of the hydrophilicity of the SiO2 guest particles on the quality of the dry coating of PP host particles was investigated with respect to the integral charge of the dry coated powder. Furthermore, the flowability, crystallization behavior and degree of coverage (DOC) were investigated to determine the influence of the increased charge on these topics. Increased process temperature increases the electrical charge of the powder, which leads to a higher DOC with guest particles and, thus, drastically improved flowability compared to dry coating at ambient temperature. Furthermore, changes in the crystallization behavior of polypropylene are observed, due to more nuclei.

Polybutylene terephthalate (PBT) – polycarbonate (PC) multi-materials with a PBT mass content of 25% to 75% were produced for the powder bed fusion process by the means of co-grinding and spray agglomeration. The influence of the PC content and the process parameters on the thermal properties of the obtained powders are discussed in detail. Compared to pure PBT powder, the PBT/PC multi-materials crystallize at lower temperatures, which improves the handling during the additive manufacturing process.