Rheological Characterization of a Low‐Concentration Water‐Based Collagen Dispersion Under Extensional, Shear, and Oscillatory Deformation

This study presents an investigation of the extensional, shear, and oscillatory rheological behavior of a 3 wt% native bovinecollagen dispersion using capillary rheometer and oscillatory shear testing. Extensional viscosity was determined from the en-trance pressure drop using Cogswell's analysis. The entrance pressure drop was obtained through both Bagley extrapolation andorifice die methods. The close agreement between Bagley and orifice die results confirms the reliability of the entrance pressuremeasurements and indicates that the fabricated orifice die can be used for direct entrance pressure drop determination withinthe investigated range. The collagen dispersion exhibited pronounced shear thinning and extensional thinning behavior. Theapparent shear viscosity (𝜂ₐₚₚ) decreased from approximately 𝜂ₐₚₚ = 250 Pa·s to 𝜂ₐₚₚ = 6.3 Pa·s while the extensional viscosity (𝜂E) decreased from approximately 𝜂E = 1.6 × 10⁶ Pa·s to 𝜂E = 3.4 × 10⁴ Pa·s over the investigated deformation rate range. Small andlarge amplitude oscillatory shear (SAOS and LAOS) measurements showed solid-like viscoelastic behavior in the linear regimeand nonlinear viscoelastic behavior at large strain amplitudes. Fourier transform (FT) rheology results showed a progressiveincrease in higher harmonic contributions with increasing strain amplitude. Results are relevant for the design and optimizationof collagen-based food, biomedical, and extrusion processes