Preparation And Performance Study Of Slow-release Fertilizer Based On Biodegradable Polymer

With the increasing development of agriculture,the demand for fertilizers has gradually increased,and the production of fertilizers plays a vital role in promoting crop growth.However,the loss of fertilizer and the excessive release rate have always been problems that need to be solved urgently in agricultural production.The emergence of slow-release fertilizers slows down the release rate of urea,effectively reduces the loss of fertilizers,and has an important impact on preventing soil eutrophication and ensuring crop growth.In the current slow-release urea on the market,most of them are in the form of sulfur coating and urea-formaldehyde method.The slow-release time is short and the coating material will pollute the environment during the slow-release process.Therefore,a material is needed to extend the slow-release time and environmentally friendly.Because of its biodegradability and other characteristics,biodegradable polymers have gradually been widely used in the pharmaceutical field as drug slow-release materials and biomedical frameworks in recent years,but in the agricultural field,especially in the field of slow-release fertilizers.Extensive research.The key to ensuring the large-scale application of slow-release fertilizers prepared from biodegradable polymers lies in the preparation technology of coated urea,so that the prepared urea has a long slow-release time and is in line with the growth cycle and growth environment of various crops.Therefore,in this paper,using the characteristics of biodegradable polymers,two materials,polylactic acid(PLA)and polycaprolactone(PCL),were selected to prepare sustained release by coaxial electrospinning method and dip coating method.urea,the effect of different polymer and urea ratios on slowrelease properties was discussed,and the slow-release properties of PLA/PCL-coated urea slow-release fertilizers under different conditions were analyzed.The main contents are as follows:First,PLA@urea coaxial electrospinning nano slow-release fertilizer was prepared by encapsulating urea in PLA fibers by coaxial electrospinning.The study found that PLA@urea slow-release fertilizer has strong hydrophobicity,thermal stability and certain mechanical strength.There is no mutual reaction between PLA and urea,and there is a weak hydrogen bond.The measurement of the coverage rate proved that most of the urea was wrapped inside the fibers.In terms of sustained-release performance,8% PLA@10% urea,8% PLA@20% urea and 10% PLA@20% urea have good sustained-release ability,and the sustained-release time can last for 84 d at neutral 25 °C.At the same time,the slow-release measurement of acid-base and high-temperature environment showed that PLA@urea slow-release fertilizer has certain acid and alkali resistance and high temperature resistance.Secondly,in order to further reduce the coating cost,we chose to blend PCL and PLA,and use coaxial electrospinning to wrap urea to prepare PLA/PCL@urea coaxial electrospinning nano slow-release fertilizer.The study found that the addition of PCL improved the fiber morphology,enhanced the hydrophobicity and mechanical strength of the fiber membrane,and decreased the thermal stability.There is no reaction between PLA and PCL,and between PLA/PCL and urea,and there is only hydrogen bond interaction.In terms of coverage,PLA/PCL blended coaxial electrospinning coated slow-release fertilizers can well wrap urea inside the fibers.In the slow-release rate determination,when the urea concentration is 10% or 20%,the sustained-release time can last for 140 days under the condition of neutral 25 °C,which is in line with most crop growth cycles.At the same time,in different environmental tests,it was found that PLA/PCL@urea sustained-release urea could maintain continuous release in acid and alkali and high temperature environments,and had certain acid and alkali resistance and high temperature resistance.Finally,in order to further reduce the cost,we chose the dip coating method,and the granular urea was placed in PLA,PCL,and PLA/PCL solutions with a mass fraction of 10% for coating,and the PLA/PCL coated urea was coated.The times were one and three,respectively,and four kinds of particle-coated urea were prepared.The study found that the coated slow-release urea has good thermal stability,and there is no interaction force other than hydrogen bonds between polymers and between polymers and urea.In terms of sustained-release performance,only the three-layer PLA/PCL particle-coated urea meets the national standard and has good sustained-release ability,with a cumulative release of 77.2% in 28 d neutral 25°C water environment.At the same time,the results of acid-base and high-temperature slow-release tests show that the coated urea also has certain acid-base and high-temperature resistance capabilities,and the amount of polymer used is small,but the overall slow-release rate is faster.