Preparation of mechanically activated starch-based composite hydrogel for controlled release of urea

The starch based ionic and nonionic composite superabsorbent(SCSA)used for agriculture was synthesized from mechanically activated cassava starch(60 min ball milling),partially neutralized acrylic acid by KOH and acrylamide.The functional groups and granular morphology of the samples were characterized by FT-IR and SEM,respectively.The SCSA was swollen in urea solution(5.0 mol·L-1)until equilibrium swelling and then the hydrogel(SCH)was obtained.The SCH was used as the release material for urea in aqueous solution.The effects of synthesis conditions and release environment on the release process were investigated.It was found that the release of urea from SCH was controlled by Fickian diffusion mechanism,and the release rate decreased with increasing swelling ratio and increased with increasing temperature.The activation energy for releasing urea from the SCH prepared under the conditions of mAA∶mAM=3∶3 and dosage of N,N′-methylenebisacrylamide solution 1.0 ml(0.02 mol·L-1)was 17.28 kJ·mol-1.