Synthesis and Swelling Behavior of Super-Absorbent Soluble Starch-<i>g</i>-poly(AM-<i>co</i>-NaAMC₁₄S) Through Graft Copolymerization and Hydrolysis

Abstract

By introducing sodium 2-acrylamido-tetradecanesulfonate (NaAMC14S) to graft copolymerization of soluble starch and acrylamide (AM), a novel super absorbent resin (SAR) of soluble starch-g-poly(AM-co-NaAMC14S) (SR-14) is synthesized. Polymer gels are hydrolyzed with sodium hydroxide (NaOH) to convert the function group −CONH2 to −COO-. The structures and qualitative changes of the polymer gels are characterized through Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental analysis, and rheometer. Results show the polymer gels through the hydrolysis by NaOH increased the water absorbency of the final SR-14 resin from 31.71 to 1183.43 g g−1 as the degree of hydrolysis (DH) increased from 0 to 80%. Drastic increases in the storage and loss modulus of SR-14 reflected the intensive molecular structural changes induced by the addition of NaAMC14S. The changes in the molecular structures of SR-14 can be attributed to hydrophobic associations among long-chain alkane. Soluble starch-g-poly(AM-co-NaAMC14S) exhibits the maximum water absorbency of 2536.77 g g−1 in distilled water and 92.98 g g−1 in 0.9 wt.% NaCl solution. In the absence of NaAMC14S, however, the water absorbency of soluble starch-g-poly(AM) decreases to 1222.27 g g−1 in distilled water and to 62.29 g g−1 in 0.9 wt.% NaCl solution. Results indicate that NaAMC14S has potential applications as a material that can enhance the water absorbency of SAR.