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Modeling how thermoplastic composites are processed using thermoforming is a challenging task, and not only due to the heterogenic nature of the material. During the thermoforming processes, the polymeric matrix has to be heated above the softening temperature, enabling the composite to be formed into three‐dimensional parts. As the system mobility increases, thermal deconsolidation takes place, and voids are created or expand within the composite sheet. These voids alter the sheet's material properties and aesthetic characteristics. The formation of gas‐filled voids in the material hinders the heat transport, resulting in longer heating times and inefficient processes. Moreover, such voids invalidate models widely used for processing thermoplastic composites. This study resulted in a novel analytical model that can be applied to calculate the anisotropic thermal conductivity of thermoplastic composites depending on the deconsolidation temperature and the fiber orientation. The model was validated by running hot disk tests on polypropylene reinforced with glass fibers (PP/GF) and applying X‐ray computed tomography to the composite samples. The samples are first consolidated in a hot‐plate press and consecutively deconsolidated in a pressure‐free process. The study findings show that the model is highly accurate within the temperature range relevant to composite processing and will be a useful asset in process modeling.

X-ray Computed Tomography (CT) in combination with a tensile/compression stage can deliver great insights in the damage mechanisms of a material. As the material properties change at low and high temperatures, materials may perform differently as they do at room temperature. In this paper, a novel Mechanical In-situ Stage with Temperature control (MIST) for the usage in laboratory CT devices for high resolution - (3 μm)³ - acquisitions is presented. Since the specimen temperature is controlled by air flow, the MIST stage is suitable for testing polymers and allows cooling and heating in one test cycle (-10 °C to +100 °C). The MIST stage is a modification of the CT500 DEBEN tensile/compression stage. It enables mechanical tests that combine the application of force and temperature on a sample at the same time. A technical description of the developed stage is presented. Furthermore, its advantages compared to existing devices are explored and application fields of the MIST are shown.

Tribo-charging is often a root cause of mass flow deviations and powder adhesion during continuous feeding. Thus, it may critically impact product quality. In this study, we characterized the volumetric (split- and pre-blend) feeding behavior and process-induced charge of two direct compression grades of polyols, galenIQ™ 721 (G721) for isomalt and PEARLITOL® 200SD (P200SD) for mannitol, under different processing conditions. The feeding mass flow range and variability, hopper end fill level, and powder adhesion were profiled. The feeding-induced tribo-charging was measured using a Faraday cup. Both materials were comprehensively characterized for relevant powder properties, and their tribo-charging was investigated for its dependence on particle size and relative humidity. During split-feeding experiments, G721 showed a comparable feeding performance to P200SD with lower tribo-charging and adhesion to the screw outlet of the feeder. Depending on the processing condition, the charge density of G721 ranged from -0.01 up to -0.39 nC/g, and for P200SD from -3.19 up to -5.99 nC/g. Rather than differences in the particle size distribution of the two materials, their distinct surface and structural characteristics were found as the main factors affecting their tribo-charging. The good feeding performance of both polyol grades was also maintained during pre-blend feeding, where reduced tribo-charging and adhesion propensity was observed for P200SD (decreasing from -5.27 to -0.17 nC/g under the same feeding settings). Here, it is proposed that the mitigation of tribo-charging occurs due to a particle size-driven mechanism. Graphical abstract

X-ray Computed Tomography (CT) combined with mechanical testing can deliver great insights in the damage mechanisms of polymers. Depending on the application area of the polymer, temperatures can be very high or low – leading to a different performance compared to room temperature. In this study, the influence of the temperature on damage mechanisms of a single particle in a polymer matrix should be investigated. Thus, three polymer tensile test specimens (length 30 mm; width 10 mm) – each containing a single particle – were cut out of a tape with a thickness of 0.5 mm and tested at various inspection temperatures. CT measurements were performed with the RX Solutions Easytom 160 laboratory CT device with a voxel size of (3 µm)³. Each specimen was scanned twice, namely at 0% strain and 30% strain. As inspection temperatures 0 °C, 22 °C and 60 °C were chosen. It is shown that temperature can have a great impact on the performance and damage mechanisms of a polymer, especially if a particle is present in the polymer matrix.