Multilayer-Coated NPK Compound Fertilizer Hydrogel with Controlled Nutrient Release and Water Absorbency

A novel trilayered controlled-release nitrogen, phosphorous, and potassium (NPK) fertilizer hydrogel was prepared by dipping the NPK fertilizer granules sequentially in 7% w v(-1) poly(vinyl alcohol) (PVA) and 2% w v(-1) chitosan (CS) solutions and then cross-linking the CS layer (cross-CS) via glutaraldehyde vapor deposition. Different NPK fertilizer hydrogels were then synthesized by inverse suspension polymerization of the dried PVA/cross-CS bilayer-coated fertilizer granules in various molar ratios of acrylamide (AM) and acrylic acid (AA) monomers, and polymerization with varying molar ratios of ammonium persulfate, N,N,N,N-tetramethylethylenediamine and N,N-methylenebisacrylamide (N-MBA). The water dissolution time of the obtained PVA/cross-CS/poly (AA-co-AM) trilayer-coated NPK fertilizer hydrogel granules was prolonged, while the water absorbency increased with increasing AA contents, and decreased with increasing N-MBA contents in the outer poly(AA-co-AM) coating. The optimal trilayer-coated NPK fertilizer hydrogel obtained released 84 +/- 18, 63 +/- 12, and 36 +/- 15% of the N, P, and K nutrients, respectively, after a 30-day immersion in water. The release phenomena of the N, P, and K nutrients of the fertilizer hydrogel obeyed both the Korsmeyer-Peppas and Ritger-Peppas models with a pseudo-Fickian diffusion mechanism. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41249.