Designing Starch–Alginate Hydrogels for Controlled Delivery of Fungicide for the Alleviation of Environmental Pollution

Abstract

In this work, a controlled delivery system for the fungicide thiophanate-methyl (TM) was developed for the alleviation of environmental pollution using starch–alginate–polyacrylamide hydrogels as a sustainable agricultural development approach. The polymer hydrogel was synthesized by grafting poly(acrylamide) onto starch–alginate using N,N-methylenebisacrylamide (NNMBA) as the cross-linker. The copolymers were confirmed by characterization techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared analysis, X-ray diffraction, 13C NMR, TGA-DTG, and differential scanning calorimetry. SEM confirmed the heterogeneity, and AFM showed the rough surface morphology of the copolymeric hydrogels. The thermogravimetric analysis results indicated the increase in the thermal stability of the cross-linked polymers after modification. Evaluation was carried out on the water absorption capacity of the polymer and the release of the encapsulated fungicide. The swelling of the hydrogel decreased with the increment in cross-linking density with a rise in [NNMBA]. It also influenced the diffusion of the fungicide from the encapsulated copolymer, wherein the increase in the cross-linker content decreased the fungicide release from the copolymer. Hydrogels absorbed 18.30 ± 1.40 (g/g of gel) water, indicating the water retention capacity of the hydrogel material which could be useful for plant growth in the arid regions. The release profile followed the non-Fickian diffusion mechanism with a sustained delivery of TM. Water retention and the controlled release properties of the hydrogel indicated its usefulness in sustainable agricultural development and alleviation of environmental pollution caused by the fungicide use. Overall, the formation of a controlled pesticide delivery system based on natural polysaccharides with polyacrylamide-based hydrogels which act as nutrients for plants on degradation is a unique approach, implying that the slow release of the pesticide will reduce environmental pollution and pesticide cost.