Structure and characteristics of chitosan-based fibers containing chrysotile and halloysite

Abstract

With the use of the methods of X-ray diffraction and electron microscopy, chitosan fibers prepared by coagulation into an alcohol-alkali mixture are shown to possess a two-phase structure containing C- and O-type crystallites. These fibers and composite fibers containing halloysite and Mg chrysotile nanotubes are characterized by anisotropic structure, i.e., by the orientation of both chitosan crystallites and Mg chrysotile particles along the fiber axis. A comparison of the rates of shear induced by passing of a polymer solution through a die and the data of rheological studies allows the conclusion that the structuring of chitosan solution under the applied field of shear stresses and the orientation of polymer macromolecules and filler nanotubes occur. An increase in the draw ratio during fiber spinning does not assist orientation of polymer crystallites but, in contrast, increases surface defectiveness and leads to the nucleation of longitudinal cracks; as a result, the strength of fibers decreases. The introduction of 5 wt % Mg chrysotile into the chitosan matrix markedly increases the mechanical characteristics of the composite fibers owing to the reinforcing action of oriented filler nanotubes.