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The addition of an increased amount of soluble fibre pectin in foods is desired due to its proven positive health benefits to human. The aim of this research was to explore the synergies between the commonly used food additives, carboxymethyl cellulose (CMC) and two types of pectin (high or low methoxyl, HM or LM) using rheological methods. The rheological properties of the reconstituted water solutions of the food additive powder were investigated, at different mass concentrations (0.05%–3.00%) and temperatures (4 °C, 20 °C, 37 °C and 60 °C), reflecting those of food storage and food consumption, using small and large deformation rheological measurements. Dynamic tests showed that CMC alone, HM and LM pectin alone and their combinations exhibit strong viscoelastic behaviour, under the conditions used in this study. For CMC solutions, the Cox–Merz rule was found to be obeyed to a reasonable degree at temperatures lower than the cloud point temperature. However, divergence from the Cox–Metz rule is observed when phase separation takes place. The current rheological methods are feasible to examine the synergy in viscosity and elasticity of mixed gel dispersion, which was determined by the polymer interactions via hydrophobic effects and hydrogen bonds depending on variables such as polymer substitution degree, polymer proportions and applied temperature.

Dispersions of clay particles in aqueous polymer solutions generally exhibit complex rheological behaviours depending on the mechanical history of the material. In this paper, the effect of the temperature on the rheological properties of bentonite dispersions in aqueous carboxymethylcellulose solutions is examined. The bentonite concentration was fixed to 5% w/w while the polymer is 0.5 or 1% w/w. For stresses lower than a yield stress, the systems behaved as a gel and, above the yield stress, they flowed as liquids. The samples were characterized both in permanent and oscillatory shear flow. In the liquid like regime, the viscosity of the fluids decreased as the temperature increased. In the solid like regime, when the temperature increased, the experimental results displayed unusual behaviours of the viscosity and of the shear moduli. The increase of the chain mobility induced by the Brownian motion combined with a dissociation of the aggregates of particles could result in the formation of an elastic network with more crosslinks. This could explain why a dramatic increase of the solid-like character of the dispersions was observed.

The rheological properties of aqueous solutions of poly(ethylene oxide) (PEO) of different molecular weights (1x10(5), 4x10(5), 1x10(6) and 4x10(6) g mol(-1)) and concentrations were investigated using shear viscosity and dynamic rheological measurements. It was found that the aqueous solutions of PEO do not exhibit a yield stress and that, above a critical shear rate, all PEO solutions exhibit shear-thinning behavior, well described by the Cross model, except for the solutions made by the lowest molecular weight (1x10(5) g mol(-1)) which were almost Newtonian. The parameters of the Cross model, namely the zero-shear rate viscosity and reciprocal of the time constant, allowed the determination of the critical concentrations c(*) and c(**) (respectively, the transition to semi-dilute network solution and concentrated solution). At concentrations higher than c(**) and below a critical shear rate, solutions made of PEO of high molecular weight exhibited a clearly shear-thickening behavior at very low shear rates. In addition, the dynamic tests showed that PEO solutions exhibit concentration-dependent viscoelastic properties, with a dominant viscous behavior at PEO concentrations lower than c(**) and a dominant elastic behavior at PEO concentrations greater than c(**).

Three different experimental measurements, namely, rheology, particle sizing, and x-ray diffraction (XRD), were used to study the effect of anionic additives on the properties of bentonite suspensions. The three additives were sodium carboxymethylcellulose, xanthan gum, and sodium dodecyl sulfate. Flow curves were obtained from shear stress–shear rate measurements, and the viscoelastic properties were determined from oscillatory and transient measurements. Mineralogical data were evaluated by XRD and the particle size analysis performed by light scattering technique. The presence of the surfactant modifies the face-to-face interactions and yields changes of the mixtures rheological behavior at low deformation rates. Polymers act by coating each clay particle and prevent their agglomeration. Therefore, the additives are responsible for the mechanisms of destructuration and structure reorganization as well as the mixtures viscous and viscoelastic behavior.

Bentonite are extensively used materials in a wide range of applications. Creep and oscillatory shear experiments in the linear viscoelastic domain were carried out on bentonite-water suspensions at different solid fractions. It was found that bentonite dispersions exhibit important viscoelastic behavior which could be represented by the generalized Kelvin-Voigt mechanical model. It is well known that an exhaustive study of colloidal dispersions may require the determination of its viscoelastic properties over a wide frequency scale. Unfortunately, due to microstructure changes, the experiments are limited in time. In order to avoid such limitation, oscillatory data were deduced from creep curves - without actually vibrating the clay dispersions - because a periodic experiment at frequency ω is qualitatively equivalent to a creep test at time 1/ω. That is, it was possible to complete the dynamic response in the low-frequency range using data obtained from the transient response in creep.

In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure–properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.