Selection of Flow Aids: Model-based Prediction of Flow Properties Enhancement

Publication Reference: 
ARR-107-02
Author Last Name: 
Dave
Authors: 
Rajesh N. Davé
Report Type: 
ARR - Annual Report
Research Area: 
Powder Flow
Publication Year: 
2023
Country: 
United States

This annual report presents key advances made during year 2 moving towards year 3. Building upon the experimental study from the previous report period, comprehensive work was done towards validation of the contact mechanics based predictive models for the selection of flow aids (silica) type and amount. This significant component of the outcomes is reported as detailed in a recently published paper; “Selection of Silica Type and Amount for Flowability Enhancements via Dry Coating: Contact Mechanics Based Predictive Approach”, see Appendix A. In the area of modeling, the previous year’s report reviewed the available particle contact models for smooth and rough particles. During the current reporting period, advancement was made by accounting for the intrinsic macro-roughness of the particle on its cohesion and subsequent reduction after dry coating. A Manuscript, in preparation, will be submitted in Spring 2024. Another major accomplishment is a comprehensive study to account for the entire PSD of the powder sample via the size class dependent Bond number approach as a promising tool to account for different cohesion amongst fine powders with similar d50 but varying size distributions. That work can help develop a decision tool to identify which component of a powder blend to dry coat while minimizing cohesion yet using the lowest possible flow aid amounts in the blend. A manuscript in preparation will be ready and submitted by the end of Spring 2024. Another effort towards fulfilling a major deliverable examined four industry relevant silicas, including three hydrophilic and two hydrophobic, detailed in a published Manuscript, “On predicting the performance of different silicas on key property enhancements of fine APIs, blends, and tablets”; see (Appendix B). In this work, the predictability of the performance of different silica types on cohesion reduction is better explained by combining several models, some of which counter each other for more pragmatic understanding of the nuances involved: (1) the Multi-asperity contact model, (2) Deng’s stick and bounce model explain the aggregation tendency of nano flow aids (e.g., silica) on the host particle as a function of process intensity and guest-host sizes (Details in recently published paper is attached in Appendix C), and the interactive mixture model based on host-guest total surface energy differential (discussed in the paper included in Appendix B). The results convey that while silica size and its extent are important, silica aggregation is another key parameter governing the performance of dry coating indicating what role is played by the process intensity and time. Interestingly, a major take home message of this work is that while coating of nano-sized flow aids requires high-intensity processing, subsequent processing of the blends in a conventional low intensity mixer may be adequate since it leads to synergistic transfer of flow aids that greatly enhances the blend flowability. This outcome has significant industrial implications in designing of powder blends and processing and will be one major focus of the future work beyond year three. This synergy along with the effect of blend mixing time were further examined to uncover the effect of mixing time on blend bulk properties when a dry coated component is mixed; detailed in a published manuscript, see Appendix D. Current work, which will continue through 2024 and beyond will examine applicability of industry relevant, potentially scalable approaches to dry coating. This includes  assessing the dry coating performance from a batch device such as LabRAM against using low-intensity batch-mode V-Blender, as well as potentially continuous, higher intensity COMIL while varying the processing parameters. These outcomes will be included in a manuscript which will also form basis to propose additional work beyond year three. Last, these significant advancements during the current reporting period would not have been possible without regular IFPRI member interactions gained through regular update meetings and additional tutorial style meetings as needed. Such activities will continue and a workshop on this topic will be offered in Fall 2024.