Synthesis Of Biomimetic Polymers And Their Applications In Controlled/Slow Release Fertilizer

Spectacular changes in agriculture have been observed to satisfy the expansion of the global population since the food demand is increasing rapidly in the last 40 years. For this purpose, large amounts of nutrient inputs, pesticides and water were utilized which result in a great increase in cereal production on a worldwide basis. However, high nutrient loss viavolatilization and leaching and the low nutrient utilization efficiency contribute to a serious waste of resource and severe environmental pollution, such as eutrophication, global greenhouse gas, and acidic rain. To alleviate these problems, controlled/slow-release fertilizers(CSRFs) have been widely produced to enhance nutrient utilization efficiency and the effective nutrients uptake in the modern agriculture.Biomimetic materials refer to materials which mimic features and characteristics of the organism, such as superhydrophobic material, polyamine acid and mussel chemistry. In recent years, biomimetic materials have drawn lots of attentions because of its excellent physical and chemical properties, such as high chemical activity, good biodegradability and biocompatibility. Therefore, it is important that the biomimetic materials was used in controlled/slow-release fertilizers systems.On the basis of poly(aspartic acid) and dopamine, three kinds of slow/controlled release fertilizer were synthesized, and the release behaviors of the fertilizers were investigated in detail. The main contents and results are shown as follows:1. The conventional fertilizer core urea was coated by deacetylated konjac glucomannan film that used as the inner coating, and a novel superabsorbent composition that used as the outer coating. Poly(aspartic acid) and a degradable macrocross-linker based on L-aspartic acid were synthesized and introduced into the superabsorbent composition to improve the fertilizer degradability and soil moisture-retention capacity. The water-holding and water-retention capacity of soil with the superabsorbent are obviously higher than the control soil without the superabsorbent. More importantly, the degradation experiment indicate that the novel superabsorbent has an excellent degradable performance. In addition, the slow release behaviors of the fertilizer were characterized in soil.2. A semi-IPN hydrogel was prepared on the basis of sodium polyaspartate, furfurylamine-functionalized sodium polyaspartate and bis-maleimido-poly(ethylene glycol), and the Diels-Alder reaction was used to synthesized the hydrogel. Meanwhile, a double cross-linked hydrogel was prepared by immersing the semi-IPN hydrogel into a Ca2+ solution. These two kinds of hydrogels were employed to load urea, which were used as the slow release fertilizer. The structure and morphology of the fertilizers were measured by scanning electron microscope(SEM), and water absorbency capacity in deionized water was carefully examined. The slow-release behaviors of the fertilizers were characterized in soil, and the results demonstrate that the fertilizers have an excellent slow-release performance. In addition, both of the hydrogels reveal predominantly degradable properties.3. A “smart” fertilizer with polymer brushes of poly(N,N-dimethylaminoethyl methacrylate) grafting from polydopamine-coated ammonium zinc phosphate via surfaceinitiated atom-transfer radical polymerization is prepared. The structure and morphology of the fertilizer were measured by transmission electron microscopy(TEM); the composition of the product was determined with Fourier transform infrared(FTIR) spectroscopy, thermogravimetric analysis(TGA), and inductively coupled plasma(ICP) emission spectrometer. Dual responsive controlled-release behaviors were characterized in water, and results demonstrate the “smart” fertilizer shows excellent temperature- and pH-responsive behavior to release nutrients according to the ambient environment.