Chemically Induced Graft Copolymerization of Acrylonitrile onto Carboxymethyl Chitosan and its Modification to Amidoxime Derivative

Carboxymethyl chitosan (CMCh) was prepared and characterized by determinating its degree of substitution and elucidating its structure by elemental analyses and FTIR. Graft copolymerization of acrylonitrile (AN) onto CMCh was carried out in aqueous solution using potassium persulfate (KPS) initiator. Evidences of grafting were obtained via FTIR spectroscopy, elemental analyses, scanning electron microscopy, X-ray diffraction and the differences in swellability profiles before and after grafting. The effects of initiator concentration, monomer concentration, reaction time and temperature on the graft copolymerization were studied by determining the grafting percentage (%G), grafting efficiency (%GE) and the amount of homopolymer formed (%H). The optimum grafting conditions were determined as follows: [KPS]=5x10-2mol/L, [M]=3mol/L, reaction temperature=65 degrees C and reaction time=3h. The capacity of the graft copolymers to uptake metal ions from their aqueous solutions and to capture different types of dyes were also studied. The work was extended to include the amidoximation reaction of the -CN groups of the grafted PAN on CMCh chains and to elucidate its effect on metal uptake, dye uptake and swellability in different pH buffer solutions. Results show that the amidoxime derivatives adsorb more metal ions than both CMCh and the graft copolymers. Also it was shown that as the % graft increases, the ability of CMCh to attract more dye molecules increases and also the amidoxime derivatives attract more dye molecules than the graft copolymers.