Showing papers by "Arno Kwade published in 2020"

Development of a New Procedure for Nail Penetration of Lithium-Ion Cells to Obtain Meaningful and Reproducible Results

Abstract: Internal short circuit tests of Lithium-Ion Batteries (LIBs) are used to test battery safety behavior in a custom made battery cell stressing chamber. However, systematic investigations regarding the test setup and test procedure are rare. In our research commercially available pouch cells (5 Ah) are employed for the method development and validation of nail penetration tests including measurement of gaseous reaction products. The effects of the thermal insulation material, the nail material (conductive and non-conductive), the influence of the penetration depth and the nail velocity were examined. It was observed that low penetration velocities (1 mm s−1) in combination with a conductive nail and a nail motion control, which is based on monitoring the temporal evaluation of the cell voltage change, provide the most promising results in terms of reproducibility at low standard deviation. By applying this method, only the energy required for a Thermal Runaway (TR) is released, which makes it possible to determine a novel key value for the assessment of battery safety. Based on this, a proposal has been made for a nail penetration test method which would allow the results to be compared between different test facilities.

Holistic calendar aging model parametrization concept for lifetime prediction of graphite/NMC lithium-ion cells

Abstract: Aging and life time prediction is most important for any usage of Li-ion cells, especially for battery electric vehicles (BEV). One main focus is on the calendric aging, as a BEV will be used for many years, often in parking mode for most of the time. In this work a model approach is chosen based on a simplified physical description of the main aging mechanisms. The presented calendric aging model is based on the main aging mechanisms anodic side reaction (ASR), cathodic side reaction (CSR) and passive anode effect (PAE). Considering these three aging mechanisms, as well as the half and full-cell open circuit voltage (OCV) characteristics, an aging model with the ability for extrapolation and interpolation between operational conditions is achieved. It does not require many parameters that need to be determined specifically for the used materials such as particle sizes or diffusivity. For parametrization, several calendric storage tests are necessary, evaluating usable and mobile Li capacity, internal resistance and self-discharge at varying states of charge (SoC) and temperatures. With the chosen set of main aging mechanisms, the aging model test matrix and the parametrization procedure, we were able to model the capacity increase in the beginning of the tests due to the PAE. Moreover, by including CSR in the model, the maximum capacity fading at 70% compared to 100% SoC is represented.

Along the Process Chain to Probiotic Tablets: Evaluation of Mechanical Impacts on Microbial Viability

Abstract: Today, probiotics are predominantly used in liquid or semi-solid functionalized foods, showing a rapid loss of cell viability. Due to the increasing spread of antibiotic resistance, probiotics are promising in pharmaceutical development because of their antimicrobial effects. This increases the formulation requirements, e.g., the need for an enhanced shelf life that is achieved by drying, mainly by lyophilization. For oral administration, the process chain for production of tablets containing microorganisms is of high interest and, thus, was investigated in this study. Lyophilization as an initial process step showed low cell survival of only 12.8%. However, the addition of cryoprotectants enabled survival rates up to 42.9%. Subsequently, the dried cells were gently milled. This powder was tableted directly or after mixing with excipients microcrystalline cellulose, dicalcium phosphate or lactose. Survival rates during tableting varied between 1.4% and 24.1%, depending on the formulation and the applied compaction stress. More detailed analysis of the tablet properties showed advantages of excipients in respect of cell survival and tablet mechanical strength. Maximum overall survival rate along the complete manufacturing process was >5%, enabling doses of 6 × 108 colony forming units per gram (CFU gtotal-1), including cryoprotectants and excipients.

Influence of Formulation Parameters on Redispersibility of Naproxen Nanoparticles from Granules Produced in a Fluidized Bed Process

Abstract: The particle size reduction of active pharmaceutical ingredients is an efficient method to overcome challenges associated with a poor aqueous solubility. With respect to stability and patient's convenience, the corresponding nanosuspensions are often further processed to solid dosage forms. In this regard, the influence of several formulation parameters (i.e., type of carrier material, type and amount of additional polymeric drying excipient in the nanosuspension) on the redispersibility of naproxen nanoparticle-loaded granules produced in a fluidized bed process was investigated. The dissolution rate of the carrier material (i.e., sucrose, mannitol, or lactose) was identified as a relevant material property, with higher dissolution rates (sucrose > mannitol > lactose) resulting in better redispersibility of the products. Additionally, the redispersibility of the product granules was observed to improve with increasing amounts of polymeric drying excipient in the nanosuspension. The redispersibility was observed to qualitatively correlate with the degree of nanoparticle embedding on the surface of the corresponding granules. This embedding was assumed to be either caused by a partial dissolution and subsequent resolidification of the carrier surface dependent on the dissolution rate of the carrier material or by resolidification of the dissolved polymeric drying excipient upon drying. As the correlation between the redispersibility and the morphology of the corresponding granules was observed for all investigated formulation parameters, it may be assumed that the redispersibility of the nanoparticles is determined by their distance in the dried state.

Morphological and physiological characterization of filamentous Lentzea aerocolonigenes: Comparison of biopellets by microscopy and flow cytometry.

Abstract: Cell morphology of filamentous microorganisms is highly interesting during cultivations as it is often linked to productivity and can be influenced by process conditions. Hence, the characterization of cell morphology is of major importance to improve the understanding of industrial processes with filamentous microorganisms. For this purpose, reliable and robust methods are necessary. In this study, pellet morphology and physiology of the rebeccamycin producing filamentous actinomycete Lentzea aerocolonigenes were investigated by microscopy and flow cytometry. Both methods were compared regarding their applicability. To achieve different morphologies, a cultivation with glass bead addition (O = 969 μm, 100 g L-1) was compared to an unsupplemented cultivation. This led to two different macro-morphologies. Furthermore, glass bead addition increased rebeccamycin titers after 10 days of cultivation (95 mg L-1 with glass beads, 38 mg L-1 without glass beads). Macro-morphology and viability were investigated through microscopy and flow cytometry. For viability assessment fluorescent staining was used additionally. Smaller, more regular pellets were found for glass bead addition. Pellet diameters resulting from microscopy followed by image analysis were 172 μm without and 106 μm with glass beads, diameters from flow cytometry were 170 and 100 μm, respectively. These results show excellent agreement of both methods, each considering several thousand pellets. Furthermore, the pellet viability obtained from both methods suggested an enhanced metabolic activity in glass bead treated pellets during the exponential production phase. However, total viability values differ for flow cytometry (0.32 without and 0.41 with glass beads) and confocal laser scanning microscopy of single stained pellet slices (life ratio in production phase of 0.10 without and 0.22 with glass beads), which is probably caused by the different numbers of investigated pellets. In confocal laser scanning microscopy only one pellet per sample could be investigated while flow cytometry considered at least 50 pellets per sample, resulting in an increased statistical reliability.

Numerical Simulation of the Rheological Behavior of Nanoparticulate Suspensions

Abstract: Nanoparticles significantly alter the rheological properties of a polymer or monomeric resin with major effect on the further processing of the materials. In this matter, especially the influence of particle material and disperse properties on the viscosity is not yet understood fully, but can only be modelled to some extent empirically after extensive experimental effort. In this paper, a numerical study on an uncured monomeric epoxy resin, which is filled with boehmite nanoparticles, is presented to elucidate the working principles, which govern the rheological behavior of nanoparticulate suspensions and to simulate the suspension viscosity based on assessable material and system properties. To account for the effect of particle surface forces and hydrodynamic interactions on the rheological behavior, a resolved CFD is coupled with DEM. It can be shown that the particle interactions caused by surface forces induce velocity differences between the particles and their surrounding fluid, which result in increased drag forces and cause the additional energy dissipation during shearing. The paper points out the limits of the used simulation method and presents a correction technique with respect to the Peclet number, which broadens the range of applicability. Valuable information is gained for a future mechanistic modelling of nanoparticulate suspension viscosity by elucidating the interdependency between surface forces, shear rate and resulting drag forces on the particles.