Homogeneous and Heterogeneous Grafting of 4-Vinyl-Pyridine onto Chitosan

Modification of chitosan by grafting with vinyl pyridine (VP) was carried out both in homogeneous and heterogeneous phases using potassium persulfate (K2S2O8) and sodium bisulfite (NaHSO3) as redox initiators. Values of grafting percentages up to 96 % were reached in heterogeneous conditions and up to 130 % in homogeneous conditions (in 5% acetic acid). The effect of monomer concentration on the extent of grafting (G %) was studied and was found to increase linearly with the monomer concentration. The grafting percentage reached maximum at 3 x 10-3 M concentration of the initiator mixture with a ratio 1:0.75 of K2S2O8:NaHSO3 respectively. Maximum grafting percentage was achieved at 55 degree C after about 3 hrs. The grafted chitosan samples were soluble with difficulty in warm acetic acid solution. Dye uptake of the grafted samples towards the different types of dyes (acidic, and basic) was investigated and was found to improve profoundly over the native chitosan with a higher uptake for the acidic dye. The grafted samples showed an increased swelling in water, which increased further upon quaternization of the graft copolymers. The extent of swelling is higher in acidic and basic media more than in neutral pH. The quaternized graft copolymer was found to be soluble in water. The quaternized graft copolymers (vinyl pyridine (G=130 and 80%) have an inhibition effect on both the Azotobacter fungus and the bacterium Fusarium-oxysporium. The effect on the micro organisms is proportional to the amount of VP in the graft copolymer