Preparation And Properties Of Carboxymethyl Starch Based Slow Release Fertilizers

Fertilizer plays an indispensable role in the growth of plant except normal conditions of light,heat,water and air.In recent years,with the continuous increase of population,how to apply fertilizer scientificly and sustainably seems very important.However,traditional fertilizer has low fertilizer efficiencies due to leaching,which leads to the frequency of fertilizer application increasing.Hence,a series of environment problems including soil hardening,water pollution and so on has been induced.Slow and controlled-released fertilizer(SRF/CRF)was prepared by researchers to solve the problem.SRF/CRF are fertilizers wrapped nutrient in other materials with slow release in a long period,which could meet the demand of crop in the whole growth period.This thesis focuses on the biodegradable,efficient,cheap and accessible slow release fertilizers.Starch is used widely in many fields due to wide source,low price,non-toxic and environment protection with plenty of easily modified hydroxyl.Caoboxymethyl starch is an important starch derivate,which is obtained when starch reacts with chloroacetic acid after alkalization.In this thesis,carboxymethyl starch which was used as the basic material to prepare a series of slow release fertilizers.The specific research contents and conclusions are as follows:1.Porous carboxymethyl starch was prepared by enzymatic hydrolysis to absorb iron nitrate,then getting a new adsorbent was obtained.A slow release phosphate fertilizer was synthesized by absorbing ammonium dihydrogen phosphate using the new absorbent,then coated by zein,which is low-price,biodegradable and accessible.The experiment results showed that the content of phosphorus was as high as 166 mg/g.The release experiments in water revealed the slow release behavior.Pot experiments showed utility efficiency of phosphorus was 67.99%,which was more than three times as much as ammonium dihydrogen phosphate.Additionally,iron could promote the synthesis of chlorophyll.2.Porous carboxymethyl starch microsphere was prepared by reverse suspension crosslinking polymerization(W/O),in which trimetaphosphate,polyethylene glycol 6000 and sorbitan oleate were used as cross-linker,porogen and emulsifier,respectively.A slow release znic fertilizer was prepared by absorbing znic sulfate using the porous carboxymethyl starch microsphere,then coated by graphene oxide.The release of nutrient behavior in different pH solution showed sustainable release behavior.3.A multielement compound fertilizer was fabricated using ammonium zinc phosphate as kernel nutrient element,polydopamine film as inner coating,and sodium carboxymethyl starch(SCS)as the outer coating.In addition,iron(Fe),the vital microelement for the growth of crops,was chelated by the carboxylate groups of SCS,contributing to make the outer coating compact.The release behavior showed that the cumulative release of nitrogen,phosphorus,zinc and Fe reached 75%,63%,59% and 51% in 30 days,respectively.Pot experiment showed the use efficiency of iron was 65.51%,which alleviated the leaf chlorosis.