Crosslinked starch-urea formaldehyde (St-UF) as a hydrophilic matrix for encapsulation: studies in swelling and release of carbofuran

Abstract

St-UF, starch crosslinked by urea-formaldehyde prepolymer, has been previously established as an effective matrix for controlled release of the systemic pesticide carbofuran for broadcast application to soil against various pests in agriculture. The water uptake and carbofuran release of this system fits in with the generalized equation M_t/M_∞ = ktⁿ applicable to controlled release systems involving swelling. The St-UF matrix shows an inverse relationship between rate of release and extent of crosslinking. The release rate at a particular crosslinking value is not affected by the extent of loading at low levels (3-10%), but increases at higher loading levels (20%) due to increase in porosity. The release rates were studied in mixtures of water and methanol at 0, 50, 70 and 100% methanol levels, thereby varying the solubility of carbofuran in the medium from 1.2 × 10³ to 100 × 10³ ppm. The release rates increase with solubility in a linear manner, indicating the porous nature of the matrix. Single particle release studies were conducted by a novel procedure for the first time for a matrix dispersed system of irregular shape. The results establish that the mechanism of release is non-Fickian (anomalous).