PREPARATION OF CATION-EXCHANGE STARCHES CONTAINING PHOSPHORIC-ACID GROUPS

Poly(glycidyl methacrylate)-starch graft copolymer was prepared using hydrogen peroxide/ferrous sulphate/thiourea dioxide redox system as initiator. The copolymer was treated with orthophosphoric acid (H3PO4) under a variety of conditions to discover appropriate conditions for synthesizing the copolymer that can serve as cation exchanger. Results obtained indicated that the cation-exchange capacity is enhanced by: (a) increasing the H3PO4/epoxy molar ratio up to 4; (b) using material-to-liquor ratio 1 : 2; (c) increasing duration (15-300 min) and temperature (60-90-degrees-C); (d) increasing the amount of epoxy groups of the copolymer; and (e) increasing the percent neutralization of H3PO4 up to 33.3%. Based upon the results obtained with these parameters, it was postulated that three reactions are involved during treatment of the copolymer with H3PO4. These reactions are phosphorylation, crosslinking, and hydrolysis. Conditions were established under which the phosphorylation reaction occurs exclusively. Studied also were the ion-exchange properties of the phosphorylated copolymer, namely, pK(a) values, capacity for heavy metal ions removal, moisture content, durability, swellability, and solubility.