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Properties of chitosan and microcrystalline cellulose composite gels

Laka M., Chernyavska S., Jakobsons E.

International Journal of Applied Mechanics and Engineering

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2005

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Vol. 10, no spec

323-327

EN

The rheological properties of chitosan and microcrystalline cellulose (MCC) composite gels, as well as the mechanical properties, water vapour sorption and swelling of films prepared from them were investigated. It has been shown that, on addition of liquid crystalline 9% MCC gels to non-liquid crystalline 2% chitosan gels, composite gels at sufficiently great MCC contents acquire liquid crystalline rheological properties. The dependence of the viscosity of composite gels on the MCC content has an extreme character with a minimum. When the MCC content reaches the value at which a liquid crystalline structure is formed in the composite gel, viscosity decreases somewhat. A study of the properties of the films has shown that, with increasing MCC content up to 65%, the tensile stress and modulus of elasticity of the film samples increase, while elongation at break, water vapour sorption and swelling decrease. This can be explained mainly by the formation of bonds between the MCC carbonyl and carboxyl groups and chitosan amino groups.

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

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.

4

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.