Chitosan-graft-poly(acrylic acid)/rice husk ash based superabsorbent hydrogel composite: preparation and characterization

Rice husk ash (RHA), an industrial waste, was incorporated in the preparation of high performance chitosan (CTS) and poly(acrylic acid) (PAA) based superabsorbent hydrogel. Hydrogels filled with RHA previously calcinated at 900 °C (RHA₉₀₀) showed better water uptake (225 g_water/g_absorbent) than those with husk calcinated at 400 °C (RHA₄₀₀) (198 g_water/g_absorbent) due to the higher purity and crystallinity, at same composition. The hydrogel composite at 5 wt-% of RHA₉₀₀ showed the best water uptake (255 g_water/g_absorbent). A clear reduction in swelling degree is observed by increasing the amount of crosslinker from 1 to 3 wt-% due to the increase in the crosslinking density forming more rigid hydrogels. On the other hand, an increase in the initiator amount from 1 to 3 wt-% increased the water uptake due to the formation of greater numbers of active sites increasing the number of PAA chains grafted into CTS backbone. Furthermore, the hydrogel composites presented responsive behavior in relation to both pH and sat solution. The data shows it is possible to obtain high performance materials by incorporating an industrial waste, rice husk ash, in the preparation of hydrogel composites.