Influence of crosslinker amount on the microstructure and properties of starch-based superabsorbent polymers by one-step preparation at high starch concentration

This work concerns how crosslinker amount (N, N′-methylene-bisacrylamide) affects the microstructural, absorbent and rheological features of one-step prepared starch-based superabsorbent polymers at a high starch concentration (0.27:1 w/w starch-water). The increased crosslinker amount evidently altered the microstructure and the absorbent and rheological features. Then, the variations in starch-based superabsorbent polymer properties were discussed from a microstructure viewpoint. Particularly, the higher crosslinker quantity rose the crosslinking density and the ratio (GR) of grafted anhydroglucose unit on starch backbone (from 27% to 52%), but short the average polyacrylamide (PAM) chain length (L_PAM). These structural features suppressed the chain stretch within starch-based superabsorbent polymer fractal gels (confirmed by smaller R _g value) and promoted the formation of smaller chain networks, thus weakening the water absorption to the starch-based superabsorbent polymer chain networks. Also, the increased GR and reduced L_PAM , with lowered chain extension and elevated crosslinking density, probably decreased the flexibility and mobility of chain segments in starch-based superabsorbent polymer gel matrixes. This caused the enhanced robustness and storage modulus of the gels with reduced chain energy dissipation ability.