Radiation synthesis of kappa-carrageenan/acrylamide graft copolymers as superabsorbents and their possible applications

Kappa-carrageenan (κC) was modified via graft copolymerization of acrylamide (AAm) using γ-irradiation and followed by alkaline hydrolysis to achieve a novel superabsorbent hydrogel. The effect of grafting variables and alkaline hydrolysis conditions such as κC/AAm compositions and irradiation doses, NaOH concentration, hydrolysis time and temperature were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Swelling properties and FT-IR of untreated κC-g-PAAm and hydrolyzed κC-g-PAAm (H-κC-g-PAAm) were determined. The swelling capacity of hydrolyzed κC-g-PAAm was about 10 times in distilled water and three times in NaCl solution higher than that for κC-g-PAAm. The swelling of superabsorbing hydrogels was examined in buffer solutions. The swelling capacity of hydrogels was also measured in various salt solutions (LiCl, NaCl, KCl, CaCl₂, and FeCl₃). Results indicated that the swelling ratios decreased with an increase in the ion radius, valence and ionic strength of the salt solutions. Due to their high swelling ability in salt solutions, the hydrogels may be referred to as ‘anti-salt superabsorbent’ polymers. Thus, the salinity of water treated with H-κC-g-PAAm hydrogels was determined. It was found that the H-κC-g-PAAm hydrogels have a capability to absorb and retain the fresh water from the saline solution. The results obtained suggested the possible used of such prepared superabsorbent in agricultural purposes as a material for sodic soil remediation.