Rheological behaviour of aqueous methylcellulose systems: Effect of concentration, temperature and presence of tragacanth

- Methylcellulose (MC) w/o tragacanth (T) systems were rheologically characterized.
- MC solutions showed a predominantly viscous behaviour at tested temperatures.
- MC solutions exhibited high stability in a wide range of pH and ionic strength.
- MC-T dispersions displayed a predominant MC impact on viscosity at low shear rates.
- Flow curves (Cross-Williamson) and mechanical spectra (Maxwell) were modelled.

Rheology of aqueous methylcellulose (MC) solutions affected by polymer concentration, temperature, pH, ionic strength (by adding NaCl) and the presence of tragacanth (T) at different polymer ratios (MC:T, 0.25:0.75-0:75:0.25) was studied. Steady-shear and dynamic rheological measurements in a wide range of shear rates and angular frequencies, respectively, were conducted on a controlled stress rheometer. The viscosity exhibited a clear Newtonian plateau for all MC solutions dependent on polymer concentration and temperature. Mechanical spectra indicated the predominance of viscous behaviour for all MC solutions. Experimental data sets were successfully modelled using Cross-Williamson and Maxwell models, being the dependence with temperature established by Arrhenius functions. MC solutions were stable at the tested pH and ionic strengths ranges. MC-T dispersions exhibited a predominant MC effect on viscosity at low shear rates, decreasing the strong shear thinning behaviour of T samples. Cox-Merz rule was evaluated for all samples systems.