Viscosity and rheological behaviour of carbon dioxide-expanded fish oil triglycerides: Measurement and modeling

Viscosity and rheological behaviour of carbon dioxide-expanded (CX) fish oil (FO) triglycerides (CXFO) were determined at 40, 55, and 70 °C at pressures of up to 12 MPa using a rotational rheometer equipped with a high pressure cell at shear rates of 100–500 s−1. The mass fraction of CO2 (wCO2wCO2) in CXFO was determined at 40 and 55 °C at pressures of up to 25 MPa. The viscosity of CXFO determined at a shear rate of 300 s−1 decreased substantially with pressure due to dissolution of CO2 in FO. Decrease in viscosity with pressure and hence wCO2wCO2 was temperature dependent. The viscosity of CXFO decreased with a pressure increase from 0.1 to 12.2 MPa by about 90% (25 to 2.65 mPa s) and 70% (11.6 to 3.38 mPa s) at 40 °C and 70 °C, respectively. A new empirical model correlating the viscosity of CXFO to temperature and pressure was developed. The viscosity decreased up to wCO2wCO2 levels of about 30% (w/w) then approaching a constant level. CXFO viscosity data were successfully correlated to wCO2wCO2 and pure component viscosities using the empirical Grunberg and Nissan model. Rheological measurements showed dilatant flow behaviour for CXFO at elevated pressures, with the flow behaviour index approaching 1.5 at 12.4 MPa. Novel process development and design of equipment will benefit from a better understanding of such rheological behaviour.

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► Viscosity of CO2-saturated fish oil (FO) decreased with CO2-pressure up to 90%.
► CO2-expanded FO showed shear thickening (dilatant) behaviour.
► Viscosity and dilatant behaviour are linked to solubility of CO2 in FO (XCO2XCO2).
► XCO2XCO2 in FO increased with pressure and decreased with temperature up to 20 MPa.
► Viscosity was modeled using pressure, temperature and XCO2XCO2.