The influence of physical form and annealing conditions of dye sorption by chitosan.
Dye sorption behaviors of chitosan prepared in different physical forms are evaluated by an isothermal equilibrium method. Chitosans of moderate and high degrees of N- deacetylation are prepared as flakes, films, powders, and novel staple-length shear precipitated fibrids. Methods for solution processing chitosan films, blender powders, and shear precipitated fibrids are described. Preparation of translucent and opaque handsheets from chitosan fibrids is described. Precursor polymer and solution processed products are characterized according to their chemical, physical, and morphological properties by methods including titration, viscometry, FT-IR, SEM, WAXD, polarized light microscopy, and tensile testing. Chitosan flakes, powders, and fibrids are oriented and crystalline. Chitosan film crystal morphology depends on coagulant- annealing conditions. Hydrous annealing conditions cause complete conversion of chitosan-salt films to the free chitosan form while incomplete conversion is obtained with anhydrous annealing conditions. Extent of conversion to free chitosan influences the saturation dye sorption capacity of chitosan for C.I. Acid Red 33. High dye sorption capacity is associated with residual chitosan- salt in the parent flake or solution processed chitosan film. At pH 8, where chitosan-salt ionic interactions are suppressed, chitosans of different molecular weight and degree of deacetylation, prepared in flake, film, and fibrid form, have similar saturation dye sorption capacity.