Study of two chitosan derivatives phosphorylated at hydroxyl or amino groups for application as flocculants

Abstract Two phosphorylated chitosan derivatives with a similar degree of substitution of about 0.5 were synthesized via either the esterification of chitosan's hydroxyl groups by P 2 O 5 in methanesulfonic acid or the selective incorporation of methylene phosphonic groups on chitosan's amino groups by formaldehyde/H 3 PO 3 in water. The performances of the resulting O ‐phosphorylated chitosan (OPC) and N ‐methylene phosphonic chitosan (NMPC) as amphoteric flocculants were assessed in comparison with that of unmodified chitosan. In turbidity removal experiments using kaolin suspensions in water, OPC removed about 90% turbidity, but NMPC only removed 60%. The lower flocculation efficiency of NMPC was attributed to the decreased acid strength of the N ‐methylene phosphate groups in NMPC. These results revealed that the acidity of the phosphate groups introduced in the modified chitosans is an important factor with regard to the flocculation efficiency, and consequently that O‐phosphorylation is more suitable than N‐phosphorylation for preparing chitosan‐based amphoteric flocculants. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012