Effect of diprotic acids on grafting efficiency and water absorption of cassava starch-polyacrylamide via gamma-irradiation / Kanlaya Mongkolsawat = ผลของกรดสองโปรตอนต่อประสิทธิภาพการกราฟต์และการดูดซึมน้ำของแป้งมันสำปะหลัง-พอลิอะคริลาไมด์โดยการฉายรังสีแกมมา / กัลยา มงคลสวัสดิ์
Graft copolymerization of acrylamide onto cassava starch by a simultaneous irradiation technique using gamma-rays as initiator were studied via various important parameters: total dose (kGy), dose rate (kGy h-1), monomer-to-cassava starch ratio and maleic acid content. Graft copolymerization of acrylamide and/or acid onto cassava starch was also studied with the addition of sulfuric acid and maleic acid as acid additives. The graft copolymer was produced with the monomer-to-cassava starch ratio 2:1, acrylamide-to-acrylic acid ratio 1:1, total dose 6.0 kGy and dose rate 1.71 kGy h-1. Homopolymer and their free copolymer, which were the by-products of graft copolymerization, were removed 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 amide groups or carboxylic groups to carboxylate groups. Grafting parameters denoting the degree of graft copolymerization were determined in terms of the percentage of gel content, homopolymer, grafting efficiency, add-on relation to the water absorption. The graft copolymer produced with the total cose 4.0 kGy, dose rate 1.71 kGy h-1, the monomer-to-cassava starch ratio 2.5:1 and maleic acid content 2% w w-1 of monomer gave the saponified graft copolymer having the water absorption in distilled water as high as 2,256 g g-1 of its dried weight. The water absorptions of this saponified graft copolymer in salt solutions and buffer solutions were also carried out. The water absorption depends largely on type and concentration of salt solutions (lonic strength) and pH of buffer solutions. The presence of sulfuric acid of maleic acid in graft copolymerization of acrylamide and/or acrylic acid onto cassava starch increased the homopolymer, but decreased the grafting yield and the water absorption. This research explains the possible mechanism of polymerization reaction of maleic acid and acrylamide onto cassava starch. It also describes the influences that affect water absorption of graft copolymer newly synthesized.