Preparation and characterization of slow-release fertilizer from semi-interpenetrating network hydrogel based on cassava starch

The development of eco-friendly hydrogels and super-absorbents for agricultural applications is an important challenge in the field of synthesis on account of the materials’ sources and biodegradability. The cassava starch-g-P (acrylic acid-co-AM) semi-IPN hydrogels were synthesized by the aqueous solution polymerization method. The synthesized semi-IPN hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo Gravimetric analysis (TGA), and X-ray diffraction (XRD). The properties of various cross-linking agents, initiators, monomers, and raw material contents in the CSt-g-P(AA-co-AM) semi-IPN hydrogel were investigated. The optimum of methylene bisacrylamide (MBA) contents to get the highest water absorbency and eco-friendliness for the environment contained MBA 0.015 g, potassium peroxydisulfate (KPS) 0.03 g, acrylic acid (AA) 10 g, acrylamide (m) 3 g, and cassava 7 g. The prepared semi-IPN hydrogel presented a maximum water absorbency or swelling behavior at 3,0945% in distilled water. In addition, the de-swelling, re-swelling, and biodegradation capacity were observed. Moreover, the application of the CSt-g-P(AA-co-AM) semi-IPN hydrogel for urea-loading and sustained-release behaviors were studied. The urea-loading percentage of CSt-g-P(AA-co-AM) semi-IPN hydrogel was modulated by the concentration of the urea. Results indicated that the release of urea in de-ionized water exhibited a typical slow release behavior. Water absorbency affected the release profile significantly and the release longevity reaching 168 h. A weight residue of 70.45 wt% was attained after being buried in soil for 45 d. These positive results strongly suggest that the synthesized hydrogels may significantly reduce the production cost and make the technique environmentally-friendly, factors that are crucial in regard to semi-IPN hydrogels for agricultural use.