Effects Of Multi-modification On Coating Structure And Nitrogen Release Characteristics Of Bio-based Polyurethane-coated Urea

In order to solve the problems of hydrophilicity and porosity of liquefied bio-based polyurethane coating materials and improve the degradability of coating materials,in this study,liquefied lignin-based polyurethane coated urea（LGPCU）was used as a control,the bio-based cross-linked modified polyurethane-coated urea（BCPCU）was prepared by mutual modification with castor oil and liquefied lignin,which improved the hydrophobicity of the fertilizer and prolonged its nitrogen-controlled release period.On the basis of the mutual modification,adding bis（2-hydroxyethyl）disulfide to the coating material endows the material with the ability to self-healing during the coating process,repairs the micropores in the membrane layer,and fixes the non-film-forming substances.By adding photosensitizer-iron stearate（Fe St₃）to the coating,the photodegradation of the coating was significantly promoted while regulating the release of nutrients.The main results of this study are as follows:（1）Under the same circumstances,the nitrogen-controlled release performance of BCPCU is significantly better than that of LGPCU.The release period was significantly extended by77.3%.Bis（2-hydroxyethyl）disulfide modified bio-based cross-linked modified polyurethane-coated urea（BCSPCU）has significantly better nitrogen-controlled release ability than BCPCU,and the nitrogen release period is further extended by 61.5%.（2）Mutual modification and self-healing modification effectively improved the structure of the surface and section of the fertilizer coating,the SEM results showed that the surface of the LGPCU coating had obvious roughness,and there were also many irregular hole structures in the cross-section.These structures would increase the rate at which water can enter the interior of the fertilizer,thereby accelerating nitrogen release.In contrast,the surface and cross-section of BCPCU are relatively smooth,but the surface is still rough due to non-film-forming substances in the LG.These rough structures will rub against each other during the transportation of fertilizers,thereby destroying the coating layer and affecting the nitrogen release of fertilizers.After the self-healing modification of the mutually modified coating material,the surface and cross-section of the BCSPCU fertilizer became smoother and more compact,which indicated that the self-healing modification could endow the coating material with self-healing ability,and effectively repair the micropores in the coating layer,making the coating layer denser and effectively control the nitrogen release of fertilizers.The experiment proved the self-healing effect of disulfide bonds in the film coating process by means of molecular dynamics,and through the dissolution test of inorganic ions and water-soluble organic matter,it is proved that the repair process effectively reduced the micropores in the coating and reduced the dissolution of inorganic ions and water-soluble organics.（3）The results of photosensitivity material modification experiments showed that the photodegradability of the coating was significantly improved by adding the photosensitizer to the coating material,and the intermediate products produced by the photodegradation of the coating did not adversely affect the germination and growth of rice seeds.Soil culture experiments with 1%photodegraded caoting added to different soils showed that the intermediate products of photodegradation did not adversely affect soil microorganisms.