| Slow-release/controlled-release fertilizers are paid more attection because they can significantly improve the utilization rate of traditional fertilizers,reduce environmental pollution,and improve crop yield and quality.The production and application of slow/controlled release fertilizers have become one of the main trends in the development of fertilizer industry and the inevitable requirement for the development of green agriculture.The current commercial few slow/controlled release fertilizers are mainly urea-formaldehyde one.The nutrient release cycle of urea-formaldehyde slow/controlled release fertilizers is long,however,and the nutrient controlled release can not be realized.Degradable polymer slow/controlled release fertilizers not only can regulate the release rate of nutrients,but also do not cause secondary pollution in soil.This dissertation focuses on the development of efficient and environmentally friendly slow/controlled release fertilizers,and the preparation of coating materials with polylactic acid,starch and humic acid and other raw materials,the design of a new segmented fluidized bed coating device,and the preparation of polylactic acid coated slow/controlled release fertilizers;The permeability coefficient of coated materials was tested and calculated,and a Shaviv model based on the temperature difference subsection simulation was established to predict the release performance of coated slow/controlled release fertilizers in the field.The sustained release behavior of polylactic acid coated fertilizers in water and soil was studied.The details are as follows:(1)The preparations of PLA and PLA/PS,HA/PLA composite membrane at 288 K,298 K and 308 K were investigated respectively.The permeability coefficient of water vapour and NPK nutrients were measuredin the urea,sodium dihydrogen phosphate,potassium chloride saturated solutions under different temperatures and membrane materials,and it was also discussesed the influence of the thickness of membrane materials and membrane-forming temperature on the permeability coefficient of water vapor and nutrients.(2)Through the starch esterification reaction catalyzed by Novezyme435,it has been successfully synthesized oklenate starch,laurate starch and palmitate starch.It was found the he substitution degree of DES could be improved by adding PEG-400,and the optimum esterification temperature was 338 K.Compared with the original starch,the modified starch had less degree of dissolution,gelatinization,recrystallization and esterification.With the increase of the carbon chain length in the fatty acids,the aggregation rate of the starch particles increased and the crystallinity decreased.The membrane-forming properties of starch were also studied.(3)The fluidized envelop process and device for separating the membrane-covering segment from the membrane-forming segment were designed.The membrane covered section adopted Worcester fluidized bed with completely closed air circulation and operated at room temperature.The membrane forming section adopted boiling fluidized bed and operated at high temperature.The conveying of materials between the coated section and the membrane-forming section adopted the pneumatic conveying method,which coukld reduce the contact probability and contact time between the particles,thus reducing the adhesion between the coated particles.The efficiency of membrane material and the uniformity of membrane were also improved as well.(4)Poly-lactic acid coated urea particles were prepared,and the permeability coefficient of nitrogen and water vapor was measured and calculated.The simulation conditions of Shaviv mathematical model were optimized,and a piecewise mathematical simulation method based on temperature difference was established,which could better predict the nutrient accumulation and release performance of coated urea nitrogen.Compared with the field test results,the average absolute deviation and the average relative deviation were 1.74 and 3.01% respectively.Using the mathematical model proposed by Shaviv et al and the method of segmental simulation could predict the nutrient release characteristics of coated fertilizers.(5)According to the previous research results,in view of the cotton,choose the reasonable coating materials coated slow/controlled release urea,poly(lactic acid)(PLA)was prepared by means of polylactic acid coated slow/controlled release urea and common urea contrast test of two kinds of urea was studied on cotton yield,N utilization ratio and environmental results show that the influence of polylactic acid coated slow/controlled release urea can effectively improve the utilization rate of nitrogen,reduce non-point source pollution... |
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