Preparation of porous superabsorbent particles based on starch by supercritical CO2 drying and its water absorption mechanism

The slow water-absorption speed of starch-based superabsorbent resin (St-SAP) limits its application. In this study, porous St-SAP (P-St-SAP) was prepared by inverse suspension polymerization and supercritical CO2 drying, the aim is to provide a preparation method of fast absorbent resin. The P-St-SAP at 33 % starch content had an interpenetrating porous structure with macropores, mesopores and micropores, and the surface area, pore volume and average pore diameter were 32.06 m(2)center dot g(-1), 0.116 cm(3)center dot g(-1) and 21.6 nm, respectively. The water-absorption process included rapid-section, medium-section and slow-section, according with internal diffusion, double-constant and quasi second-order kinetic models, respectively. In the initial 30 s, a water-absorption speed of 262.6 g center dot g(-1)center dot min(-1) in distilled water was much higher than some previous research results, and the equilibrium absorption value of 517.9 g center dot g(-1) in distilled water and 72.9 g center dot g(-1) in 0.9 % saline was better than that of nonporous St-SAP at similar starch content. Moreover, at the same stage the percentage of saline absorption ratio to equilibrium absorption value was 1.0- 2.0 times higher than that of distilled water. These research results indicate that the P-St-SAP has fast water-absorption speed and good salt resistance, which will have greater application prospects in sanitary materials, building concrete pouring, and flood control blocking piping.