Preparation And Application In Peanut Planting Of A New Large Granular Slow Controlled Release Fertilizer For Peanut

Peanut is a major oilseed and cash crop in the world,and fertilizer is the key to improve peanut yield because it is sensitive to the availability and supply cycle of nutrients.Large granular slow controlled release fertilizer is a new type of fertilizer with slow controlled release nutrient capacity.It has become a hot research topic in the field of fertilizer because of the advantages of easy application,high nutrient utilization and environmental friendliness.Large granular slow controlled release fertilizer is a new type of fertilizer with the ability of slow controlled release of nutrients.It has become a hot spot for research in the field of fertilizer because of its advantages of easy application,high nutrient utilization and environmental friendliness.As a polymeric material with excellent performance,polyurethane is widely used in fertilizer coating.However,most polyurethane products are made of petroleum-based raw materials,which are expensive and environmentally unfriendly,limiting the commercial application of slow and controlled release coated fertilizers to a certain extent.This project addresses this problem by using castor plant oil,which is large in quantity and low in price and environmentally friendly,as the raw material for polyurethane synthesis.in addition,the synthesized polyurethane is used for the preparation of large particle slow controlled release fertilizer to promote the sustainable development of peanut slow controlled release fertilizer.In this study,castor oil and isoflurone diisocyanate were used as raw materials,1,4-butanediol was used as chain extender,and dibutyltin laurate was used as catalyst to prepare castor oil-based polyurethane for slow controlled release fertilizer coating material by prepolymerization method.In view of the poor water resistance of polyurethane,hydroxyl-polydimethylsiloxane was used to modify it,and the effect of modification on the performance of polyurethane was investigated.The castor oil-based polyurethane was used as coating material to prepare large particle slow controlled release fertilizer,to clarify the conformational relationship between coating structure and nutrient release performance,and to investigate the nutrient release mechanism:(1)Polyurethanes were prepared by the prepolymerization method using castor oil and isoflurone diisocyanate as raw materials and 1,4-butanediol as chain extender to study the effect of castor oil content on polyurethane properties.The results show that the viscosity of castor oil-based polyurethane decreases,the contact angle gradually decreases and the water absorption gradually increases as the castor oil content decreases.The mechanical test results show that the tensile strength gradually increases and the elongation at break gradually decreases.Thermogravimetric analysis showed that the thermal decomposition process of polyurethane materials was completed in two stages,and the overall differences between the thermomechanical properties of different ratios were not significant.When the molar ratio of isoflurone diisocyanate to castor oil was3.5:1,the viscosity of PU3 was 410 m Pa·s,the water absorption rate was 3.02%,the tensile strength was 10.04 MPa,and the elongation at break was 601.71%.(2)Castor oil-based polyurethanes were modified with hydroxyl-terminated polydimethylsiloxane,and the molecular structures of castor oil-based polyurethanes before and after modification were investigated by FTIR and XPS.The water resistance,viscosity,mechanical properties and thermal stability of the modified polyurethanes were tested to analyze and investigate the conformational relationships between molecular structure-polymer composition-material properties.The results showed that the contact angle of the unmodified polyurethane was 63.39°,and the contact angle of the modified polyurethane increased significantly,approaching and exceeding 90° with the increase of organosilane content.At the same time,the water absorption of the modified polyurethane decreased significantly.In addition,the viscosity of the modified polyurethane increased significantly due to the increase of cross-linking degree.From the thermal weight loss and DSC analysis,it can be seen that the introduction of organosilane improves the thermal stability of polyurethane.The SEM test results show that due to the low surface energy of the introduced organosilane chain segments,they will migrate and aggregate to the surface during film formation,which reduces the flatness of the adhesive film surface.When the organosilane was added at 6%,the prepared PU-Si3,with a viscosity of 605 m Pa·s,water absorption of 0.81%,contact angle of 96.15°,tensile strength of 21.3 MPa and elongation at break of 804.4%.And it was used as the subsequent coating material for the new large particle slow controlled release fertilizer for peanut.(3)Modified castor oil-based polyurethane was used for the preparation of slow and controlled release fertilizers and new large granular slow and controlled release fertilizers for peanuts.The nitrogen release rate of the fertilizers was determined by hydrostatic leaching method at 25°C,and the fertilizer samples were evaluated according to the indexes specified in the national standard of “slow release fertilizer”(GB/T 23348-2009): they all met the national standard of slow release fertilizer.The slow release cycle of the prepared modified polyurethane slow controlled release fertilizer was around 42 days.And the new large granular slow controlled release fertilizer for peanut has extended the slow release cycle to 56 days due to its larger specific surface area and double-layer structure.Meanwhile,the results of peanut pot experiments showed that the root vigor of peanut was improved under the action of the slow controlled release fertilizer due to the stable nutrient release rate.And it not only increased the nitrogen uptake of peanut and improved nitrogen utilization,but also further increased the chlorophyll content and thus promoted the growth of peanut.The study provided a theoretical basis for the preparation of high-performance peanut slow controlled release fertilizer.