Rheological Characterization of Low and High‐Solids‐Loaded Suspensions Using Capillary Rheometry

ABSTRACT Controlled extrusion of viscous liquids with suspended solids depends critically on rheology. The rheology of a binder (9:1 mass ratio of cellulose acetate butyrate (CAB) to triacetin with a 55 wt.% diethyl ketone balance) loaded with dilute (0–15 wt.%) and concentrated (≥50 wt.%) granulated sugar loadings from three particle size distributions (tenth to ninetieth percentile: 41–116, 95–228, and 173–492 µm) was investigated using capillary rheometry. Dilute suspensions were sheared across 10–150 s −1 at 20°C. Compared to the neat binder, suspensions with the smallest particles exhibited greater viscosity, while those with the two largest distributions exhibited lower viscosity. The viscosity increase in suspensions with the smallest particles is attributed to larger surface area and consequential particle‐particle interactions, while the viscosity reduction with the larger particles is attributed to the more complete coating of the larger sugar particles by triacetin, causing local viscosity reduction at the particle‐matrix interfacial boundaries. Concentrated suspensions were sheared across 1–100 s −1 at 20°C. Effects of solid content, filler modality (two or more different particle sizes in a well‐defined ratio), and binder molecular weight (70,000 and 30,000 g/mol) were evaluated. For monomodal loadings, the three largest distributions were evaluated. For bimodal loadings, coarse (95–228 µm) and fine (12–61 µm) particles were combined in a 7:3 ratio. Viscosity increased with solids content, monomodal (vs. bimodal) filler, and binder molecular weight. This study provides insight into the flow behavior and operational requirements for processing solids‐filled suspensions.