Sustained-release nitrogen fertilizer delivery systems based on carboxymethyl cellulose-grafted polyacrylamide: Swelling and release kinetics

Abstract

Sustained or controlled-release delivery systems can enhance functions such as nutrient usage; minimize soil contamination, and reduce the required fertilizer dose. This paper reports the development of a carboxymethyl cellulose-g-polyacrylamide copolymer (CMC-g-PAM) as a sustained and slow-release fertilizer carrier for urea. The developed copolymer was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and thermo gravimetric analysis (TG). The grafting process increased the activation energy of CMC from 0.1521 to 0.5952 J/mol with a higher loading percentage of 72.140.85% using a 15% urea solution. The swelling ratio is significantly dependent on the pH. The maximum swelling ratio of 1199.58% at pH 9. However, Swelling follows a pseudo-first-order reaction with the maximum swelling ratio in a saline of 349.76%.The CMC-g-PAM copolymer loaded with urea exhibited sustained and slow release, with the maximum cumulative percentage of 69.12% at pH 9 and 38.94% in saline. Urea release from the CMC-g-PAM copolymer followed the first-order, Fickian, and biexponential biphasic release mechanisms. The release of the CMC-g-PAM copolymer loaded with urea is a complicated process governed by diffusion and a biphasic releasing profile.