Graft copolymerization of hydrolyzed cassava starch-acrylamide/acrylic acid by gamma irradiation

Abstract

Graft copolymerization of acrylamide and/or acrylic acid onto cassava starch by a simultaneous irradiation technique using gamma-rays as the initiator were studied via various parameters of importance: monomer-to-cassava starch ratio, total dose (kGy), dose rate (kGy hr-1), acrylamide-to-acrylic acid ratio, and the addition of nitric acid and maleic acid as the additives. Homopolymers of acrylamide and acrylic acid and their free copolymer were the by-products of graft copolymerization, which were removed later by water or methanol extraction. The purified graft copolymer was subsequently saponified with a 5% aqueous solution of potassium hydroxide at room temperature to convert the carboxylic group of acrylic acid to a carboxylate group. Grafting parameters denoting the degree of grafting copolymerization were determined in terms of the percentage of homopolymer, grafting efficiency, add-on, and grafting ratio in relation to the water absorption. he graft copolymer produced with monomer-to-cassava starch ratio 2:1, total dose 6.0 kGy, dose rate 2.24 kGy hr-1, and acrylamide-to-acrylic acid ratio 70:30 gave the saponified copolymer having the highest water absorption in distilled water, as high as 1142 g g-1 of its dry weight. The water absorption of this saponified graft copolymer in sodium chloride, magnesium chloride, calcium chloride, and buffer solutions was also measured. The water absorption depended largely on the type and concentration of salt solutions and pH of buffer solutions. FTIR was used to follow up the chemical changes of grafting and saponification, EA was used to investigate the optimum time for saponification by determining the elemental composition of the saponified products, and SEM was used to study the surface morphology.