Experimental and modeling investigation on the rheological behavior of collagen solution as a function of acetic acid concentration

Systematic analysis of the rheological behavior of collagen solution (10 mg/mL) as a function of acetic acid (AA) concentration (0.1-10 M) was performed to achieve a deeper understanding about the interaction between collagen molecules and acidic solvent. Steady shear tests showed that all samples exhibited pseudo-plasticity with shear-thinning behavior. Viscosity decreased from 236.448 to 0.792 Pa·s at 0.1 s−1 suggesting the flow ability of collagen solution improved with increasing AA concentration. Dynamic frequency sweep analysis revealed that the storage modulus, loss modulus, and complex viscosity decreased with the increased AA concentration due to the disentanglement of collagen molecules, while the loss tangent increased. Hysteresis loop areas of collagen solutions were determined by thixotropic measurement, which demonstrated that weaker thixotropic behavior was associated with higher AA concentrations. Furthermore, the ability to resist deformation and elasticity was lower at higher AA concentration. Maximum compliance values increased from 0.042 to 376.407 Pa−1, and the recovery percentage decreased from 97.670% to 0.315%. Finally, corresponding mathematical models were employed to simulate and quantitatively assess the experimental data.