Synthesis and modification of salt-resistant superabsorbent polymers

A salt-resistant superabsorbent, poly(acrylamide-co-acrylic acid) was synthesized from solution polymerization. To improve the properties of swollen hydrogel such as strength, resilience and dispersion, the copolymer was surface-crosslinked with ethylene glycol diglycidyl ether, and then the surface-crosslinked copolymer was blended with aluminum sulphate (Al2(SO4)3) together with sodium carbonate (Na2CO3) to obtain the aim sample. The factors that influenced the aim sample's properties were investigated, and the optimum conditions were obtained as follows: the molar ratios of sodium hydroxide (NaOH) to acrylic acid, acrylamide to acrylic acid, initiator [denoted with hydrogen peroxide (H2O2)] to acrylic acid, and ethylene glycol diglycidyl ether to acrylic acid were 65-70%, 30%, (7-11) × 10−5, and (2.5-3.5) × 10−4, respectively, the mass ratio of Al2(SO4)3 to crosslinked copolymer was 4.25% and the reaction time was 0.5-2 h. The water absorbency of the sample prepared at the above conditions in 0.9 wt% NaCl aqueous solution under certain load (P ≈ 2 × 103 Pa) and at atmosphere pressure were 17 and 60 g g−1, respectively. Moreover, excellent strength, resilience and dispersion could be shown by this sample.