Flow properties of hydroxypropyl guar gum and its long-chain hydrophobic derivatives (original) (raw)
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The influence of concentration on the shear and extensional rheology properties of aqueous solutions of xanthan and guar gums was studied in this work. Shear rheology involved small amplitude oscillatory shear (SAOS), flow curves and transient flow, while the extensional rheology was analyzed using hyperbolic contraction flow. In addition, the mechanical properties during solutions manufacture were monitored in situ through the evolution of torque with processing time by mixing rheometry. The results showed that the hydrocolloids exert a great influence on the process rheokinetics and on the resulting rheological response. SAOS tests showed that the xanthan gum solutions behaved as weak gels, whereas guar gum solutions suggest the presence of entanglement and the formation of a viscoelastic, gel-like structure. All the systems exhibited shear-thinning behaviour. Guar gum solutions obeyed the Cox-Merz rule, with some divergence at high rates for the more concentrated solutions, while...
Rheological Characterization and Modeling of Aqueous Guar Gum Solutions
2003
The rheological properties of aqueous guar gum solutions have been investigated for different concentrations and temperatures in a cone-and-plate rheometer in the linear and in the non-linear viscoelastic regime. In the linear viscoelastic regime we performed low amplitude oscillato- ry shear experiments to measure the complex modulus. We adopted the time-temperature and the time-concentra- tion superposition principle to increase the
Linear Rheology of Guar Gum Solutions
Macromolecules, 2000
We have investigated the linear viscoelastic behavior of guar gum solutions as a function of frequency, temperature, polymer concentration, and molecular weight. This was done to sort out the importance of different relaxation mechanisms like reptation or the breakup of physical bonds. In the kilohertz regime, Rouse behavior is observed. At lower frequencies, two storage modulus plateau zones were found, indicating two additional relaxations. One is operative between 1 and 100 Hz and gives rise to a very broad relaxation spectrum, even for monodisperse guar. Describing the dependencies of the relaxation time and low-shear viscosity on concentration and molecular weight with power laws resulted in unusually high coefficients. The second relaxation becomes manifest below 0.01 Hz and has not been earlier reported. Here the temperature dependence is very strong whereas all other dependencies are weak. Analyzing the experiments with existing models for transient polymer networks revealed that at best a partial decription of the experimental dependencies can be obtained. It was concluded that at least two different relaxation mechanisms must play a role, classical reptation not being one of these. Best overall predictions were obtained with a model assuming two types of associations. However, also the picture of star polymer-like structures held together via bonds with a long lifetime could give comparable predictions. For a further distinction between these mechanisms, more information about the mesoscopic structure is needed.
Journal of Texture Studies, 2010
Rheological studies of tragacanth and guar gums dispersions were carried out by means of steady shear (3 to 1000/s) and small amplitude oscillatory shear experiments (0.1 to 10 rad/s) for concentrations up to 8.9 g/L for tragacanth and 7.6 g/L for guar gum at 25C using stress controlled rheometer. The dispersions exhibited shear‐thinning characteristics. A simplified Cross model was adequate to fit the shear‐dependent viscosity behavior for both gums. Model parameters for guar gum were correlated with concentration employing power functions (with flow index constant) and for tragacanth gum the dependence was linear for flow index, power for time constant and exponential for zero‐shear rate viscosity. Mechanical spectra revealed that dispersions behave as dilute systems of coil polymers with trend to entangled systems at the highest concentrations. Loss and storage moduli were correlated with frequency and the resulting parameters were correlated with concentration. Cox–Merz rule hol...
Structural, rheological and dynamics insights of hydroxypropyl guar gel-like systems
Colloids and surfaces. B, Biointerfaces, 2018
A dynamic, rheological, and structural characterization of aqueous gel-like systems containing hydroxypropyl guar gum (HPG), borax and glycerol is presented in this paper. The role of glycerol, which is introduced as a plasticizer in the formulation, is investigated by means of B NMR and H NMR PGSTE measurements in order to clarify its contribution to the gel network formation and its interaction with borax, with whom it forms a complex. The effect of gels components on the rheological behaviour and on the activation energy related to the relaxation process of the system was assessed by means of rheology. The results obtained suggest that the mechanical properties of these gels can be tuned and controlled by modulating the formulation in a wide range of compositions. Moreover, a structural characterisation has been also carried out by means of Small Angle X-ray Scattering (SAXS) to highlight the role of the various components on the mesh size of the network. The structural and mecha...
Rheological studies of concentrated guar gum
Rheologica Acta, 2003
Polymers and surfactants are essential ingredients of the printing paste. Polysaccharides are used commercially to thicken, suspend or stabilise aqueous systems. Also they are used to produce gels and to act as flocculates, binders, lubricants, to serve as modifiers of film properties, and have a function as adjusters of rheological parameters. Surfactants, on the other hand, perform numerous functions acting as dispersants, wetting agents, emulsifiers and antifoaming agents. The rheological properties of polysaccharide thickeners (guar gums with different substitution levels and different producers) at different concentrations and temperatures and, second, the effects produced by the addition of nonionic surfactants (polyoxyethylene stearyl alcohols with different numbers of EO groups) have been studied under linear and nonlinear shear conditions. Experimental data have been correlated with the different models: flow curves with the Cross, Carreau and Meter-Bird model, and mechanical spectra with the generalized Maxwell model and Friedrich-Braun model. The surface tensions of aqueous systems containing polysaccharide and/or surfactants have been determined over extended concentration ranges in order to detect the CMC conditions and to provide a better understanding about the polysaccharide-surfactant interactions.
Understanding the rheology of novel guar-gellan gum composite hydrogels
Materials Letters, 2019
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Certain Rheological Aspects of Functionalized Guar Gum
International Journal of Carbohydrate Chemistry, 2013
Guar gum and its derivatives are highly important industrial hydrocolloids as they find applications in various industrial sectors. Guar is a polymer of high molecular weight and its aqueous solutions exhibit unique rheological properties, which has led to its wide acceptance by the industry. In certain industrial applications low molecular weight guar and its derivatives are needed, and conventionally chemical depolymerisation of guar is carried out for this purpose. Radiation processing is a novel and green technology for carrying out depolymerization and can be an ideal substitute for chemical depolymerisation technique. In order to study the effect of radiation on guar derivatives, three types of derivatives have been taken in the present study: carboxymethyl, hydroxyethyl, and methyl guar. The effect of 1-50 KGy radiation dose on the rheological behavior of these derivatives has been studied, and the results have been described in the present paper. The effect on storage and loss modulus with respect to frequency and effect on viscosity with respect to shear rate have been discussed in detail.