Preparation And Properties Of Urea-Formaldehyde/Starch Biodegradable By In-Situ Extrusion

At present,slow and controlled release fertilizers play an increasingly important role in achieving grain production increase and protecting the environment.Controlled release fertilizers are rarely used due to their complex production processes,high costs,and difficulty in degradation.However,slow-release fertilizers are widely used in various countries,with urea formaldehyde(UF)fertilizers being the most widely used.However,there are still problems such as long nutrient release cycles and cumbersome industrial production processes,which limit the further promotion of UF.In this paper,tapioca(ST)modified UF biodegradable polymer ST/UF with excellent slow release performance and mechanical properties was successfully prepared by a twin screw reactive extruder.The optimal process parameters were obtained through orthogonal experiments and single factor optimization experiments;The structure and properties of the prepared ST/UF were systematically studied and analyzed using testing and characterization methods such as Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),and thermogravimetric analyzer(TG);The degradation performance and nutrient release characteristics of ST/UF biodegradable polymer in soil were studied through a small rapeseed pot experiment,and their effects on soil physicochemical properties and rapeseed growth were studied.The main research content and results are as follows:(1)The optimal process parameters for preparing ST/UF by reactive extrusion were obtained through orthogonal experiments and single factor optimization experiments.ST/UF polymers with excellent nitrogen nutrient slow and controlled release properties were successfully prepared.The initial nitrogen release rates of 8% ST/UF and 16% ST/UF with ST addition of 8 and 16 wt% were 15.82% and 21.25%,respectively.The test results of FT-IR indicate that the precursor of UF,hydroxymethylurea(MU),undergoes in situ polymerization with ST,generating ST/UF polycondensates based on UF.After normalization of FT-IR,a red shift of the secondary amide bond was observed,indicating that ST also interacts with the amide group of UF through hydrogen bonding.The XRD test results showed that both 8% ST/UF and16% ST/UF contained characteristic diffraction peaks of UF,indicating the occurrence of insitu reactions;In addition,the crystallinity of the two material systems decreased compared to the UF,ST,and UF physical mixture systems(ST+UF),indicating that the addition of starch changed the structure of the materials.The test results of TG and DTG showed a decrease in thermal stability of 8% ST/UF and 16% ST/UF compared to UF and(ST+UF),confirming the XRD results.The test results of the material particle strength using a universal testing machine show that the addition of ST can effectively improve the mechanical properties of the UF system.The particle strength of 8% ST/UF is 4.29 times higher than that of pure UF,and it is 9.31 times higher than that of 16% ST/UF;The test results of the torque rheometer indicate that both 8%ST/UF and 16% ST/UF have excellent forming and processing performance;The test results of the still water release experiment showed that the nitrogen release rates of 8% ST/UF and 16%ST/UF after 56 days were 42.21% and 50.28%,respectively,which were increased by 16.40%and 38.66% compared to 36.26% of UF.(2)The degradation rate and nitrogen nutrient release rate of the 8% ST/UF and 16%ST/UF systems are higher than those of UF and(ST+UF),indicating that 8% ST/UF and 16%ST/UF are not simple physical mixtures but undergo chemical reactions;In addition,the addition of ST can effectively improve the shortcomings of UF in plant growth,such as rapid release of nitrogen nutrients in the early stage and slow release in the later stage.It can ensure a good release of nitrogen nutrients during the growth cycle of small rapeseed,greatly improving the comprehensive utilization rate of fertilizers;At the same time,it also helps to improve soil physicochemical properties and urease activity.Therefore,treatment with 8%ST/UF and 16% ST/UF can significantly improve the yield and dry weight of small rapeseed.