Rheological Properties of Aqueous Acid Solutions of Chitosan: Experiment and Calculations of the Viscometric Functions on the Basis of a Mesoscopic Model

Abstract

The rheological properties of chitosan solutions in acetic acid at 20 o C in the range of polymer concentrations from 0.5 to 8 mass% and acid concentrations from 2 to 70% have been investigated. With the use of a modifi ed Vinogradov-Pokrovskii model based on the microstructural approach to the description of polymer fl uid dynamics, numerical solutions of gradient dependences of viscometric functions of aqueous acid solutions of chitosan have been obtained. It has been established that the numerical solution describes with good accuracy the experimental viscosity rheograms. The values of the highest Newton viscosity η max have been calculated. The concentration modes of semidiluted and concentrated solutions have been determined by the dependence of η max on the polymer concentration, and the range of concentrations in which the mass transfer mechanism changes and a fl uctuation network is formed has been found. It has been shown that the concentration of acetic acid practically does not infl uence the structure and character of fl ow of chitosan solutions, the formation concentration of a network, and the effi ciency of its labile nodes.Introduction. Chitosan -a product of partial or complete deacetylation of chitin -is an aminopolysaccharide of linear structure exhibiting in an acid medium the properties of an ionogenic polymer. It shows promise as a substance that can be used in a wide variety of spheres of human life due to a complex of practically valuable properties, as well as a practically inexhaustible (annually renewable) source of raw materials [1][2][3][4][5]. Because of the high adhesion energy, the thermal decomposition temperature of chitosan is lower that its melting temperature. Therefore, processing the given polymer into fi nished articles involves the stage of dissolution in organic or inorganic acids.It is known that the concentration mode is one of the major factors infl uencing many properties of polymer solutions and, consequently, determining the conditions of their processing into a fi nished product [6][7][8]. Such polymer materials as fi lms, fi bers, capsules, etc. are obtained mainly from concentrated solutions. For inorganic polymers, chitosan among them, the diagnostic variable of going from the mode of diluted solutions to the mode of concentrated solutions is the formation concentration of a network C e which in absolute value can exceed several times the crossover concentration C * -overlap of coiled molecules [9][10][11][12][13]. The parameter C e in combination with the concentration and gradient dependences of viscosity η permits not only estimating the features of the structure formation of solutions of polyelectrolytes, but also predicting the conditions for the formation of a polymer material, as well as its structure and properties [14][15][16]. Therefore, the investigation of the rheological characteristics of a chitosan-containing system is of interest both for analysis of the structure of chitosan solutions in various concentration modes and for the technology of obta...

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Photo-Curing Chitosan-g-N-Methylolacrylamide Compositions: Synthesis and Characterization

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Structural and Morphological Features of Anisotropic Chitosan Hydrogels Obtained by Ion-Induced Neutralization in a Triethanolamine Medium

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