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 (H 3 PO 4 ) 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 H 3 PO 4 /epoxy molar ratio up to 4; (b) using material‐to‐liquor ratio 1 : 2; (c) increasing duration (15–300 min) and temperature (60–90°C); (d) increasing the amount of epoxy groups of the copolymer; and (e) increasing the percent neutralization of H 3 PO 4 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 H 3 PO 4 . 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.