Formulation and Process Considerations for the Manufacturing of Dense Pastes
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Dobbs, Alexandra A.
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Abstract
Achieving high-quality functional composites with reproducible properties is a challenge as dense pastes are highly sensitive to formulation factors and processing conditions. These challenges can be mitigated through the implementation of quality by design (QbD) principles, including the development of formulation–process–property relationships and process analytical technologies (PATs). In this dissertation, challenges associated with dense paste mixing and shaping are addressed through the development of PATs and quantitative formulation–process–property relationships that enhance process understanding and material knowledge. Central to this work is the use of Resonant Acoustic® Mixers that employ resonant vibrations and are well suited for mixing highly viscous dense pastes. I demonstrate that motor data can be leveraged as an in-situ PAT capable of detecting changes in mixing behavior arising from both formulation and processing effects, including variations in total solids content and lot to lot material variability. I further show that transitions between coupled mixing and splashing behavior depend directly on paste viscosity and adhesion to the mixing vessel. I characterize these dependencies using a novel dimensionless adhesion number, AD, which captures the balance between kinetic input, viscous dissipation, and adhesive interactions. I also evaluate mixer diagnostics from a simplified model system of rubber bouncy balls to validate these measurements and establish clear guidelines for data interpretation and post-processing. Finally, I investigate the effects of polymer molar mass in the binder on heterogeneity formation during processing. I show that low molar mass binders at high concentrations provide improved stability against settling and shear-induced migration, which is attributed to balanced viscous dissipation and elasticity. Collectively, the findings presented in this dissertation establish a framework for improving process understanding and material knowledge to overcome critical challenges in the manufacturing of dense paste composites.
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2025-12
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Dissertation (PhD)