Preparation And Performance Study Of Urea-formaldehyde Biodegradable Controlled-release Materials Modified By Sodium Lignin Sulfonat

The excessive use of traditional quick acting fertilizers can cause problems such as soil degradation and environmental pollution in cultivated land.Urea formaldehyde is currently the most widely used slow-release fertilizer,which can meet the nutrient requirements of crops throughout the entire growth cycle with just one application.However,the nutrient slow-release period of urea formaldehyde fertilizer can be as long as 1-2 years,and the long slow-release period limits its application range,making it difficult to apply to short-term crops such as vegetables and grains grown on a large scale.Therefore,it is crucial to modify urea formaldehyde fertilizers to shorten their nutrient release cycle.Lignin is the precursor of soil humus,which can inhibit soil urease activity,thereby reducing the rate of nutrient release.It is an ideal material for preparing slow-release fertilizers.Sodium lignosulfonate is the main source of industrial lignin.Currently,about 95% of sodium lignosulfonate is discharged as waste.If it can be turned into treasure,it can not only fully utilize resources,but also solve related environmental pollution problems.In response to the above issues,the specific research content and results of this study are as follows:Hydroxymethyl sodium lignosulfonate was prepared by introducing more hydroxymethyl group into sodium lignosulfonate through addition reaction with formaldehyde as modifier.The preparation process parameters were studied through orthogonal experiments and single factor optimization experiments,and the results showed that: When the reaction system p H is 13,the molar ratio of formaldehyde to sodium lignosulfonate is 1.4:1,the reaction temperature is 50 ℃,and the reaction time is 80 minutes,the formaldehyde consumption rate in the system is the highest,which is the optimal process parameter for sodium lignosulfonate hydroxymethylation.The FTIR and TG results indicate that sodium lignosulfonate undergoes a hydroxymethylation reaction with formaldehyde,resulting in a higher hydroxyl content in the hydroxymethylated sodium lignosulfonate molecule and higher reactivity.Using hydroxymethylated sodium lignosulfonate,formaldehyde,and urea as raw materials,solution polymerization and reactive extrusion techniques were used to prepare sodium lignosulfonate modified urea formaldehyde fertilizer.The preparation process parameters were studied through orthogonal experiments and single factor optimization experiments,and the results showed that: When the molar ratio of urea to formaldehyde is1.1:1,the condensation reaction p H is 5,the condensation reaction temperature is 60 ℃,and the ratio of sodium lignosulfonate addition to the total mass of the fertilizer is 30:100,the initial nitrogen release rate of the prepared fertilizer is 13.45%,meeting the requirements of the national standard(GB/T 23348-2009).The results of FTIR,TG,XRD,and SEM showed that there was a dehydration condensation reaction between lignin and urea aldehyde molecules,resulting in a decrease of 27.85% in the crystallinity of the modified urea aldehyde fertilizer.The compressive strength test results indicate that the modified urea formaldehyde fertilizer has a more stable external structure.The results of the still water release experiment showed that the nutrient release cycle of the modified urea formaldehyde fertilizer was significantly shortened compared to the unmodified one.On the 84 th day,the nutrient release rate reached 67.61%.The nutrient release performance of different types of sodium lignosulfonate modified urea formaldehyde slow-release fertilizers in soil was studied through a small rapeseed pot experiment system.The soil physicochemical properties and growth status of small rapeseed were analyzed to evaluate the effects of different fertilization treatments.The results indicate that different sodium lignosulfonate modified urea formaldehyde fertilizers can regulate soil physicochemical properties and enhance soil nutrient supply capacity.Among them,the modified urea formaldehyde fertilizer with a molar ratio of urea to formaldehyde of 1.3:1 and a ratio of sodium lignosulfonate to total fertilizer mass of 30:100 resulted in the highest yield of 154.9 g,which was 47.52% higher than the unmodified urea formaldehyde fertilizer treatment.