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1

Rheology of concentrated suspensions of plasma-processed fine alumina

Jakobsons E., Faitelson L., Palcevskis E.

International Journal of Applied Mechanics and Engineering

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2003

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Vol. 8, no spec.

251-258

EN

The rheological properties (flow curves and viscoelastic behavior) of the injection-moulded suspensions prepared from two nanosized plasma-processed Al2O3 powders and water were investigated on wide ranges of shear rates and frequencies . Tiron (disodium salt of 4,5-dihydroxy-1,3-benzene-disulfonic acid) was chosen as a surfactant for preparation of the concentrated alumina suspensions. It is stated that, at an optimal Tiron content in suspensions, their viscosity, yield stress, and complex shear modulus have minimal values. A correlation was shown to exist between the optimal concentration of the dispersant obtained by rheological tests on the alumina powder water suspensions and the mentioned optimal concentration determined by measuring the zeta potential.

2

Effect of electrolytes on the rheological properties of microcrystalline cellulose gels

Laka M., Chernyavskaya S., Faitelson L., Jakobsons E.

International Journal of Applied Mechanics and Engineering

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2003

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Vol. 8, no spec.

265-269

EN

The rheological properties of microcrystalline cellulose (MCC) gels, obtained by dispersing in different electrolyte (salt, hydroxide, acid) solutions the wood pulp destructed to the levelling-off degree of polymerization were investigated. It has been found that, in all electrolyte solutions at the cellulose concentration ł 8%, MCC gels with rheological properties characteristic for liquid crystalline polymers are obtained. The values of the rheological characteristics depend on the chosen electrolyte. When dispersing the destructed pulp in salt solutions, the rheological indices are affected by the presence of both cations and anions in the solution. Cations promote gel formation, which results in obtaining of MCC gels with greater viscosity and yield stress, but the effect of anions is opposite. In hydroxide solutions, the values of the rheological indices (viscosity, yield stress) grow as the pH value increases, while, in acid solutions, they change little and tend to grow with decreasing the pH value. The connection of the obtained relationships with the effect of the investigated electrolytes on the z-potential of the cellulose particles present in MCC gels is considered.

3

Rheology of injection moulding suspension prepared from nanosized plasma processed AlN powder

Palcevskis E., Jakobsons E., Faitelson L.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

375-380

EN

The rheological properties (flow curves and viscoelastic behavior) of injection moulding suspension prepared from nanosized plasma processed AlN powder and paraffin wax were investigated in the broad region of shear rates (0.07-1350 s-1). Two viscosity platoaux are observed on the flow curves and the values of two yield stresses are obtained. The linear viscoelastic region is not reached at the lowest deformation amplitude (0.66 %). Higher values of dynamic viscosity than those of effective viscosity at 'gamma'='omega' are observed in all the range of the used frequency and shear rate (0.1-80 s-1). The rebuilding of destroyed particle packing structure during ultrasound or shear treatment is observed. It results in the dependence of rheologic properties on the pretreatment history of suspensions.

4

Rheological peculiarities of microcrystalline cellulose gels

Laka M., Chernyavska S., Faitelson L., Jakobsons E.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

351-355

EN

Rheological properties of MCC hydro- and alcogels have been studied. MCC gels were obtained by way of dispersing in water, ethyl alcohol and propyl alcohol media the wood pulp destructed to the levelling-off degree of polymerization (LODP) of cellulose by a method developed by us. At a sufficiently high cellulose concentration which was dependent on the liquid medium, MCC gels with rheological properties typical for liquid crystalline polymers (flow curves with three characteristic regions, viscosity concentrations curves with a local maximum, etc.) were obtained. These properties are more pronounced for hydrogels. MCC hydrogels are characterized also by a higher liquid phase retention volume (~ 380%), which is an important characteristic of a stable gel. For MCC alcogels, it makes up 40-65%. Inferior properties of MCC alcogels are connected with the chemical structure of alcohol molecules which, as compared to water molecules, are less favourable for bonds formation among cellulose microcrystallites and the liquid medium.

5

A rheological constitutive equation for suspensions of microcrystalline cellulose

Jakobsons E., Faitelson L., Laka M., Chernyavska S.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

17-20

EN

The steady and oscillatory shear flow behaviors were investigated for the suspension of 8 wt.% microcrystalline cellulose in water. The values of dynamic viscosity higher than those of effective viscosity at 'gama'='omega' are observed in the range of the used frequency and shear rate (0.063-50 s-1). Modified Akay-Leslie anisotropic liquid model is proposed for quantitative account of the test data.