Preparation And Properties Of Cellulose-based Functional Slow-controlled Release Fertilizer

Fertilizer has a very important position in current agricultural production.However,today's application of chemical fertilizers has many problems such as low utilization rate and environmental pollution caused by irrational application.Therefore,how to reduce environmental pollution,increase fertilizer utilization rate,and develop sustainable Agriculture is a hot issue that researchers are paying close attention to.One of the effective ways to solve this problem is to develop slow and controlled release fertilizer.Cellulose is the most abundant natural polymer on the earth.Because it has the advantages of wide sources,low cost,non-toxicity,good biocompatibility and renewable,so the slow and controlled release fertilizer with cellulose as base material preparation will have broad prospect of application of coating materials.This paper used cellulose as a substrate to synthesize a superabsorbent resin by graft copolymerization with acrylic acid and acrylamide.A certain amount of modified bentonite was added during the synthesis to improve the gel strength of the resin and Adsorption.And a series of performance characterizations were performed on the resin,such as water absorption,water retention,gel strength,degradability,pH buffering effect,and adsorption on biochemical inhibitors.In order to improve the use efficiency of fertilizers and reduce the negative impact on the environment,a novel double-coated multifunctional slow-release fertilizer was developed using urea as the core,ethyl cellulose as inner coating and cellulose-based superabsorbent polymer adsorbing biochemical inhibitors as outer coating.The slow-release effect of the fertilizer and its inhibitory effect on nitrase were also studied.The specific research and conclusions are as follows:(1)First,the raw materials cellulose and natural bentonite were acidified and CTAB modified,and the products were characterized by infrared,X-ray diffraction and scanning electron microscopy.The results showed that the acidified modified cellulose was more prone to graft reaction,and the CTAB modification of bentonite increased the interlayer distance.The above-treated cellulose,acrylic acid,and acrylamide were graft-copolymerized by aqueous solution polymerization to form cellulose-g-P(AA-co-AM),and cellulose-g-P(AA-co-AM)was obtained by wet mixing with modified bentonite to obtain a superabsorbent resin,and its structure and properties were characterized.The results of infrared spectrum and nuclear magnetic resonance carbon spectrum proved that acrylic acid and acrylamide were successfully grafted onto cellulose.Thermogravimetric characterization results showed that after pretreatment of cellulose,the heat resistance was reduced due to the cleavage of hydrogen bonds of cellulose.Compared with cellulose,the super absorbent resin had significantly improved heat resistance;the scanning electron microscope characterization results showed that the three-dimensional network structure of the super absorbent resin,as well as the unevenness and grooves on the surface,made it have good water absorbency.The process and formula were optimized based on the water absorption ratio.Finally,the optimal water absorption rate was 486 g/g(2)The superabsorbent resin prepared by the optimal experimental scheme with the water absorption ratio as an index was used as a test material,and the properties of the superabsorbent resin were investigated.By measuring the repeated water absorption capacity of the resin,it was found that the water absorption rate of the resin gradually decreased with the increase of the number of times of desorption,and the fifth water absorption rate was 86%of the initial water absorption rate.By testing the water retention rate of the resin on the soil,the results showed that the resin can effectively improve the water retention of the soil.By testing the gel strength of the resin,it was found that the addition of modified bentonite can effectively improve the gel strength of the resin.By testing the degradability of the super absorbent resin,the results show that the degradation loss rate of the super absorbent resin increases rapidly with time,and the degradation loss rate reaches 77.2%on the 50th day,shows that it has good degradability.By testing the buffering effect of the resin on aqueous solutions of different pH,it was found that the resin can increase the pH of acidic solutions and decrease the pH of alkaline solutions.By studying the adsorption of the biochemical inhibitors dicyandiamide and thiourea by the superabsorbent resin,it was found that the kinetics process of the resin adsorbing dicyandiamide conforms to the quasi-second-order kinetic equation,and the thermodynamic processes conform to both the Langmuir model and the Freundlich model.The kinetics process of thiourea adsorption by the resin conforms to both the quasi-first-order kinetic model and the quasi-second-order kinetic equation fitting.The thermodynamic process conforms to the Langmuir equation.(3)Using ethyl cellulose as the membrane material,and adding polyvinylpyrrolidone as the porogen,the membrane was characterized by scanning electron microscopy and contact angle.The results showed that polyvinylpyrrolidone has good porosity,and the membrane had strong hydrophobicity.The film was used as the inner film of urea particles,and the superabsorbent resin adsorbing biochemical inhibitors was used as the outer film of the fertilizer to make a cellulose-based double-layer multifunctional slow-release fertilizer.The effects of PVP content,coating ratio,inner-outer film ratio and temperature on nutrient release were discussed.The soil release method was used to study the release of the slow and controlled release fertilizer in the soil,and the inhibitory effect of the biochemical inhibitor on the nitrogen nitrification was also explored.The results showed that a multifunctional fertilizer with water retention,nitrification resistance and adjustable release rate was obtained.