Poly(acrylamide-co-acrylate)/rice husk ash hydrogel composites. II. Temperature effect on rice husk ash obtention

Superabsorbent hydrogel composites based on poly(acrylamide-co-acrylate) and rice husk ash (RHA) were prepared by free-radical copolymerization in aqueous media, using N,N-methylenebisacrylamide (MBA), as crosslinker and potassium persulfate (K2S2O8), as initiator. The effect of calcination temperatures (400-900 °C) for obtaining RHA was evaluated. FTIR, WAXS, SEM-EDS and TGA were applied to characterize a series of hydrogels filled with RHA. The hydrogels composites were formed with constant amounts of RHA (10 wt.%) and crosslinking agent (0.1 mol-%) in relation to the relative to the total mass of acrylamide (AAm) and potassium acrylate (KAc) monomers (50-50 mol-%). A blank sample of poly(acrylamide-co-acrylate) hydrogel without RHA was used as control. A superabsorbent hydrogel composite, with a maximum absorption Weq > 1000 gwater/gabsorbent, was obtained with the RHA calcined at 900 °C. In addition, the hydrogel composite showed to be sensitive to the pH variation and to the presence of salts in the swelling media. From the results, it is possible to infer that the poly(acrylamide-co-acrylate)/RHA hydrogel composites presented good characteristics to be applied as soil conditioner for using in agriculture.