Slow-release Fertilizers Based On Natural Polysaccharides

Fertilizers and water play an important role in food production.In order to improve the utilization of fertilizers and water resources,people have developed a series of water-retention and slow-release fertilizers.However,the environmental friendliness and cost of fertilizers are still important factors that constrain its widespread use.As the cellulose,starch and other natural polysaccharides with a wide range of sources,biodegradable and other characteristics,their application in the slow release fertilizers was particularly noted.In this dissertation,for increasing fertilizer utilization rate,reducing the pollution to the environment and food,saving water resources and economic costs,multi-functional slow-release fertilizers were prepared by using granular urea,sodium dihydrogen phosphate and potassium chloride as chemical fertilizer feedstock,using water-absorbing and containing and water-insoluble polymer macromolecule hydrogels as carriers.This dissertation mainly includes the following four aspects of the work.(1)A kind of interpenetrating network hydrogels was prepared.First,hydroxyethyl starch(HES)was modified by 3-[(furan-2-ylmethyl)carbamoyl] propanoic acid(SFA)and 2-maleimidopropioacid(AMI)respectively to synthesize hydroxypropyl methyl starch(HES)containing diene groups and dienophile groups,obtaining HES-SFA and HES-AMI,respectively.Afterwards,the monomer of N-isopropylacrylamide,the crosslinker of poly(ethyleneglycol)dimethacrylate and the photoinitiator were dissolved in water,and then form a first network through Diels-Alder reaction,and a second network was formed by UV photopolymeration.The hydrogels were characterized by FTIR,SEM,DSC,etc.The relationship of the composition,structure,properties and fertilizer release kinetics of hydrogels was studied,which provides theoretical foundation for further application.(2)Sodium hydroxide-urea system was used to dissolve cellulose short cotton fibers at low temperature,then different proportions of acrylamide,potassium chloride,crosslinking agent and redox initiator were added to cellulose solution,by free radical polymerization cellulose grafted polyacrylamide hydrogels were prepared and used as a hydrophilic fertilizer inner core.The ethyl cellulose powder was coated on the surface of the core with 30% rosin solution as the binder.The samples were characterized and their structures and properties were studied.(3)Using acrylic acid as monomer,N,N-dimethyl bis-acrylamide as cross-linking agent,ammonium persulfate and ascorbic acid as the redox initiation system,urea,sodium dihydrogen phosphate,potassium chloride as the plant elements,a new-structured fertilizer was fabricated.The nutrient elements were dissolved in water,and then the cellulose short fiber powder was added to the resulting aqueous solution.After dispersing uniformly,the mixture was heated to 50 ?and subjected to radical polymerization to form cellulose grafted polyacrylic hydrogels which used as hydrophilic fertilizer inner core.The hydrophobic outer coating was formed on the surface of the core by 30% rosin solution as the binder,and the ethyl cellulose powder was encapsulated on the surface of the core to prepare the sustained-release fertilizers.The structure was characterized and its slow release property was determined.(4)Using a certain proportion of acrylamide,acrylic acid as monomer,N,N-dimethyl bis-acrylamide as cross-linking agent,ammonium persulfate and ascorbic acid for the redox initiation system,urea,sodium dihydrogen phosphate,chlorine potassium as fertilizer elements,all the components were dissolved in water,mixed evenly then increased temperature,a free radical polymerization took place to get cellulose grafted polyacrylamide acrylic hydrogel,which used as a hydrophilic fertilizer core.In the same manner,the ethyl cellulose powder was coated on the surface of the hydrophilic fertilizer with 30% rosin solution as the binder,and the hydrophobic outer coating was prepared.Characterization was performed with different equipments,and its slow release properties were determined.