Study On Non-isocyanate Polyurethane Coated Urea

Urea is an important nitrogen fertilizer because of its high nitrogen content（47%）and good storage performance.However,the low utilization rate of urea in China has caused huge economic loss and serious environmental harm.The development of slow/controlled release urea fertilizer can improve the utilization rate of nitrogen,meet the nutritional needs of plants and protect the environment.Coated fertilizer is developing rapidly in recent years as a slow/controlled-release fertilizer,the current development of coated slow-release fertilizer mainly concentrated on the choice of coating materials,the ideal coated slow-release materials must have the following characteristics,namely the non-toxic harmless,good stability,mechanical properties and physical properties of raw material sources,low cost,simple operation,good for mass production.The most commonly used membrane material is polyurethane,which has foamability,high elasticity,wear resistance,high adhesion,low-temperature resistance,solvent resistance,and good insulation resistance,etc.,and has a very important application in the preparation of slow/controlled-release fertilizers.The synthesis of polyurethane is mainly based on the reaction between isocyanate and active hydride,but there are some problems in the preparation process,such as the use of toxic polyisocyanate,etc.With the requirements of environmental protection and the development of technology,the research on non-isocyanate route polyurethane（PU）has attracted more and more attention recently.In other words,non-isocyanate polyurethane（NIPU）was produced by the reaction of primary amine and polycyclic carbonate compounds.NIPU has become an important development direction of polyurethane.NIPU is used in the study of coated urea.It is very important to design and optimize the preparation conditions of coated urea,evaluate the slow release performance,and design and screen the catalysts used in the reaction process.In this paper,the reaction conditions and catalysts in the preparation process of NIPU coated urea was studied.Combined with the structural and property characterization of the catalyst and the evaluation results of the sustained release performance of coated urea,the relationship between the process conditions and the sustained release performance of coated urea was studied.The main work contents of this paper are as follows:1、In this paper,NIPU coated urea was prepared in two steps,namely alcoholysis reaction and polymerization reaction.The alcoholysis reaction is the reaction of grease and urea to produce cyclocarbonate.This step is an endothermic reaction and requires a catalyst.The polymerization reaction is cyclocarbonate and organic amine to produce NIPU.The reaction conditions were designed and optimized,and the coated urea with the best slow-release performance was discussed.Finally,the optimal reaction conditions are determined as follows:25 g urea,1.5 g MO catalyst,and 25 m L grease were placed in a flask,mixed and condensed in nitrogen atmosphere（flow rate is 100m L/min）,reacted at 70°C for 5 h,and the excess reactants were filtered out.12.5 m L organic amine was added,and the excess reactants were filtered out after being sealed and standing.Natural air drying for 12 h,and finally drying in a 40°C oven for 24 h,to get the desired product.The NIPU coated urea obtained by using this reaction condition has the advantages of a simple preparation process,good slow-release effect,and the slow release period can reach the national standard.2、In this paper,the water dissolution rate method was used to test the slow-release performance of NIPU coated urea,and the concentration of urea in water was tested by p-dimethylamino benzene formaldehyde spectrophotometry.The test conditions were optimized,and the best test conditions were obtained:0.1 m L of the sample,1 m L of PDAB color reagent,0.2 m L of 2 mol/L sulfuric acid solution,and 3.7 m L of deionized water were mixed and shaken,and its spectrophotometry was measured immediately at370 nm wavelength.The determination of urea content by this method has the advantages of high precision,high accuracy,good stability,strong operability,and simple procedure.In this paper,the release period of NIPU coated urea was tested by a25°C water immersion method,which could meet the nutrient release standard of the national slow-release fertilizer.3、In this paper,MO was selected as the catalyst for the alcoholysis reaction,and the effects of various methods on this reaction were studied,including urea precipitation method,reagent drying method,carbonate decomposition,nitrate decomposition,and oxalate separation method.And combined with N₂-adsorption,XRD,TPR,NH₃-TPD,and CO₂-TPD characterization methods,Finally,it is concluded that the acid-base balance and weak acid and weak base catalyst have the best effect on alcoholysis reaction,while the acid-base imbalance and strong acid and strong base catalyst have a poor effect on alcoholysis reaction.