Preparation of anionic starch containing carboxyl groups and its utilization as chelating agent

Poly(methyl acrylate)-starch graft copolymer was treated with sodium hydroxide. The influence of sodium hydroxide concentration, reaction temperature and duration of treatment were studied. The extent of hydrolysis was assessed by estimating acrylic acid, methyl acrylate and total polymer content before and after treatment. It was found that the increase in acrylic acid content is equal to the decrease in the methyl acrylate content on using sodium hydroxide concentration up to 1 N, while using higher concentration leads to a difference in amount of acrylic groups formed and decrease in methyl acrylate content. This difference depended on sodium hydroxide concentration, on treatment temperature and duration. The optimum condition gave a release of 455 mmol acrylic group/100g sample using 1 N sodium hydroxide at 100°C for 150 min, showing 94.8% conversion of the poly (methyl acrylate) content of the treated copolymer. The alkali treated samples were evaluated for use as chelating agent. The sorption values for different heavy metals depended on the metal ion and follow the order Hg2+ > Cu2+ > Zn2+ > Pb2+. Sorption efficiency of the alkali treated samples increased with increasing the acrylic content. The sorption values of alkali treated copolymer was compared with that of carboxymethylated starch (having the same carboxy group content) to clarify the effect of the chemical structure of both starch derivatives on heavy metal sorption. It was found that the sorption value of Cu2+ on carboxymethylated starch was twice the value on alkali treated copolymer.