Enzyme-based green approach for the synthesis of gum tragacanth and acrylic acid cross-linked hydrogel: its utilization in controlled fertilizer release and enhancement of water-holding capacity of soil

Abstract

Enzyme lipase catalyzed graft copolymerization of acrylic acid onto gum tragacanth was carried out in an aqueous medium using glutaraldehyde as a cross-linker, one more step towards green chemistry. Various reaction variables such as time, amount of solvent, temperature, pH, lipase concentration, and monomer and cross-linker concentrations were optimized to achieve a cross-linked candidate polymer with maximum fluid absorbance capacity. The structure and morphology were confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. The synthesized hydrogel held a large amount of water and was used as a device for controlled release of urea. A 10 % (w/w) of swelled hydrogel was found to enhance the water-holding capacity of the soil. The synthesized device could increase the moisture content up to 52 % in sandy loam soil and 72 % in clay soil and was found to enhance the water-holding capability of the soil. Further, the candidate polymer was studied for the controlled release of urea under eco-friendly conditions and showed case-II type urea release. The initial diffusion coefficient was found to be higher than the later diffusion coefficient indicating a higher urea release rate during the early stage. Thus, the synthesized polymer is important from technological point of view.