Synthesis and swelling property of the starch-based macroporous superabsorbent

ABSTRACT The starch‐based macroporous superabsorbent polymer (St‐MP SAP) was synthesized by graft copolymerization of acrylic acid (AA)/2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) onto cassava starch through free radical polymerization method by using sodium bicarbonate (SHC) as porogen. The monomer conversion kinetics was investigated to determine the suitable time of adding SHC so as to produce large numbers of stable and uniform pores inside the SAP. Introduction of SHC led to the formation of increasing pores and loose structure in St‐MP SAP, the decrease of shear storage modulus ( G ′). With increasing SHC content, the size of the macro pores increased and the wall thickness decreased, and a large number of micropores can be observed on the pore walls. Meanwhile the equilibrium swelling ratio of St‐MP SAP first increased and then decreased, and reached maximum as high as 1878 g/g and 119 g/g in distilled water and NaCl aqueous solution respectively for the sample with presence of 0.8 wt % SHC. Furthermore, the swelling rate constant ( k ) increased monotonously and fast swelling was presented. The macro and micropore structure in St‐MP SAP enabled water to flow by capillary effect with much fewer obstructions, and the specific surface area increased, with the result that more hydrophilic groups can get in touch with water molecules rapidly. By introduction of SHC, the water molecules which can form hydrogen bonds with St‐MP SAP molecules decreased, resulting in the decrease of the binding capacity of water molecules and water retention property. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44855.