Development of Urea Uptake and Release Studies Using N, N-dimethylacrylamide/Maleic Acid/Citric Acid Based Macrogel

Abstract

Recently, the use of polymers in agricultural and horticultural applications has been seen as a solution to reduce water consumption and excess fertilizer use in particularly. In this study, macrogels were synthesized to allow fertilizer species and water to be controlled and released in the soil. A natural macrogel derived from N,N-Dimethylacrylamide (DMAAm), Maleic Acid (MA) and Citric Acid (CA) was selected because of its ability to absorb/release a large amount of water and to have modifiable functional groups. Urea, which is an abundant source of nitrogen, was chosen to model the fertilizer. The macrogel was prepared using easily available, low-cost, modifiable starting materials by redox polymerization technique. p(DMAAm-co-MA-co-CA) (DMC1) surface was modified by hydrochloric acid (HCl) and sodium hydroxide (NaOH) to obtain p(DMAAm-co-MA-co-CA)/HCl (DMC2) and p(DMAAm-co-MA-co-CA)/NaOH (DMC3), which have positively and negatively charged, respectively. After being analyzed for intermolecular interactions (Fourier-Transform Infrared Spectroscopy,FT-IR) and thermal properties (Thermogravimetric Analysis,TGA), the macrogels were tested in terms of sorption isotherms and thermodynamic parameters. However, in order to examine the urea release mechanism, the macrogels were tested using four release models such as Zero Order Kinetic Model(Z-O), First Order Kinetic Model(F-O), Higuchi(H) and the Korsmeyer-Peppas(K-P) power law. Cumulative urea release values for DMC1, DMC2 and DMC3 macrogels were calculated as 100% at pH 4 and 10, 100% at pH 6, 8 and 10, 100% at pH 4, 6, 8 and 10, respectively. Analyzes confirmed that synthesized macrogels can be good water holder for soil and can be a slow release of urea.