Effect of the Composition and Molecular Weights of Lignosulfonates and Chitosan on the Physical and Mechanical Properties of Polymer Films on their Basis

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UDС

661.185

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Abstract

Objects of our research were films for separation membranes, obtained from interpolyelectrolyte complexes based on lignosulfonate and chitosan with the introduction of pulp fibers into the composition. The paper studies the influence of the composition and molecular weight distribution of lignosulfonate and chitosan natural polymers on the mechanical properties of films obtained from them. The films were prepared by spreading the mixture of aqueous lignosulfonate (LS) solution and acetous chitosan (CT) solution at a ratio LS:CT=10:7 on the inert support, followed by drying at a constant humidity and room temperature. To improve the mechanical properties of the films in the composition, unbleached softwood pulp (15 or 25 %) in the form of an aqueous suspension was added. To assess the strength and deformation properties of the films, we carried out tensile tests and mathematically treated a stress-strain curve ("?–?") obtained by processing the indicator load-elongation diagram ("F–?l") during the static tensile testing at a load rate of 10 mm/min. The films without cellulose fibers have a minimum thickness and their amorphous structure can not provide sufficient strength and extensibility. Conversely, the sample with high content of cellulose in its composition shows a mechanical behaviour different from the other samples, which is reflected in the load-elongation curves and stress-strain curves. It has the best strength and deformation properties, which is associated with the formation of an independent network of cellulose fibers bearing the primary mechanical load. The tensile properties of the films improve with increasing molecular weight of lignosulfonate, whereas for chitosan this dependence is of an extreme nature. By increasing chitosan molecular weight to 1000 kDa, tensile stiffness of the films is reduced and their elongation increased. The use of chitosan with a molecular weight of 500 kDa in the composition does not improve the mechanical properties of the films. Thus, the mechanical behaviour of the composite materials under study was to a large extent determined by the presence of the main film-forming polymer: chitosan. The evaluation of mechanical properties helped determine that the highest and most stable strength and deformation properties are found in the film consisting of an interpolyelectrolyte complex based on lignosulfonate and chitosan with a molecular weight of 90 and 500 kDa respectively and with addition of 25 % unbleached softwood pulp.

Authors

O.S. Brovko, T.A. Boytsova, I.A. Palamarchuk, K.G. Bogolitsyn, Institute of Ecological Problems of the North, Ural Branch of the Russian Academy of Sciences Ya.V. Kazakov,  D.A. Tormosina, K.G. Bogolitsyn, Northern (Arctic) Federal University named after M.V. Lomonosov

Affiliation

1 Institute of Ecological Problems of the North, Ural Branch   of the Russian Academy of Sciences 2Northern (Arctic) Federal University named after M.V. Lomonosov

Keywords

lignosulfonate, chitosan, cellulose, film, mechanical properties.