Amylose Modified Starches as Superabsorbent Systems for Release of Potassium Fertilizers

Abstract

High-amylose maize starch (AS) was modified by graft copolymerization with sodium acid maleate and disodium maleate, using the KMnO-NaHSO redox system, and covalently crosslinked with N,N'-bismethylene acrylamide in inverse suspension polymerization process. The resulting modified starches were evaluated as absorbent materials for release fertilizers. Firstly, AS was obtained by leaching from native maize starch and posterior precipitation in ethanol. The gelatinized AS, comonomers, redox pair and crosslinker were dissolved in distilled water, which was used as dispersed phase; while paraffin oil was used as the continuous phase and sorbitan esters as stabilizers. In the reacions, parameters such as the AS amount of 10 wt%/v with respect to the dispersed phase; the degree of neutralization of maleic acid of 80%; the ratio [NaHSO]/[KMnO] of 2.6; the ratio between crosslinker and comonomers of 8.9 × 10; the stirring speed of 250 rpm; the reaction temperature at 60 °C; and a reaction time of 3 h, were kept constant. All the resulting amylose modified starches were characterized by potenciometric titration, X-ray diffraction and scanning electronic microscopy. The absorption capacity of these materials was studied by analyzing their swelling in various media and different pHs. Finally, the amylose modified starches were evaluated as systems for release fertilizers by measuring the loaded and released amount of fertilizer by gravimetry and conductimetry, respectively.