Study On The Physicochemical Properties Of A New Environment Friendly Slow-release Nitrogen Fertilizer Coating Material

Fertilizers are widely used in China.The disadvantages of rapid release and excessive application of traditional inorganic fertilizers lead to low fertilizer utilization rates in my country.The use of slow-release fertilizers can solve this problem.The composition of the coating material determines the performance of the slow-release fertilizer,and it is necessary to study the coating material with environmental protection,high efficiency,low price and strong applicability.In this paper,a new type of coating material with polyvinyl alcohol（PVA）,polyvinylpyrrolidone（PVP）and zeolite as the main raw materials is proposed.The experiment set up four levels of water-based copolymer ratios A₁,A₂,A₃ and A₄,namely PVA:PVP were 56:0,51.1:4.9,46.2:9.8,41.3:14.7,and zeolite additions B₁,B₂,B₃,B₄,which were 0g,1.75g,3.5g and 7g,and 16 groups of different combinations of coating materials were prepared through comprehensive experimental design,by measuring viscosity,water absorption,water permeability,fertilizer permeability,mechanical properties,infrared spectroscopy,microscopic morphology and other indicators,the water-based copolymer ratio was clarified.The influence of the amount of zeolite and its coupling effect on each index of the coating material,and based on the analytic hierarchy process,the combination of the membrane material with the best comprehensive performance was obtained.Then,the effects of different solution p H,temperature and urea concentration on the nutrient release characteristics of the coating materials were explored,and the nutrient release kinetic model of the coating materials under different factors was constructed.Finally,the mass loss,infrared spectrum changes,and micro-morphological changes of the coating materials under different soil hydrothermal conditions were studied,the response of their degradation characteristics to different soil hydrothermal conditions was clarified,and a hydrothermal coupling model of the membrane degradation rate was constructed.The main conclusions are as follows:1.Study on physicochemical properties of coating materials with different water-based copolymer ratio zeolite content（1）PVP,PVA and zeolite are combined with each other through hydrogen bonding,and the addition of zeolite has obvious modification effect on the PVA/PVP composite membrane.The addition of zeolite can cause bumps and slight cracks on the membrane surface.The addition of polyvinylpyrrolidone makes the surface of the membrane smooth and uniform,reduces cracks,and effectively improves the integrity of the coating.（2）Except of the ratio of water-based copolymer and their interaction had no significant effect on the elongation at break and the amount of zeolite had no significant effect on the water permeability of the membrane,other factors have a significant impact on each index of the membrane（p>0.05）.And different factors affect the water absorption,water permeability,fertilizer permeability,viscosity,tensile strength and elongation at break of the coating material in the following order:A>A*B>B,A>B>A*B,B>A>A*B.The increase of A has an inhibitory effect on the viscosity,elongation at break and the increase of B has an inhibitory effect on water absorption in the range of A₁～A₃;The increase of A increases the water permeability of membrane material,increases the water absorption and fertilizer penetration rate at B₃ and B₄,and The increase of B increases the fertilizer penetration rate of membrane material at A₄;A increases the tensile strength of the film,B increases the mechanical properties of the film,B increases the water permeability of A₃ and A₄ films,the A₁ fertilizer permeability rate,and the A₄ water absorption is increased first and then decreased;The effects of A increase on the water absorption and fertilizer penetration rate of membrane materials at B₁ and B₂,and B increase on the viscosity and water penetration rate of membrane materials at A₁ and A₂,and the fertilizer penetration rate at A₃ are first inhibited and then promoted;B increased the film viscosity at A₃ and A₄,and the fertilizer penetration rate at A₂ was promoted inhibited promoted.（3）The evaluation results of the analytic hierarchy process show that the weights of each index are ranked as follows:fertilizer permeability>water absorption>tensile strength>water permeability>viscosity>elongation at break,the treatment with the best comprehensive performance is A₂B₃,and the treatment with the worst performance for A₄B₄.2.Effects of different external conditions on the sustained-release properties of coating materialsThe nutrient dissolution curves of the coating materials under different p H,temperature and urea concentrations all showed a trend of rapid increase-slow increase-and tending to be stable.The Bertalanffy,Elovich,and Gompertz models are used to describe the cumulative process of fertilization permeation of the coating materials.The results show that the order of fitting accuracy of all treatment models is:Bertalanffy>Gompertz>Elovich.Take the physical significance of the parameters is clear and the accuracy of the model into account,the sustained release of nutrients under different solution p H and temperature conditions should be quantitatively described by the Bernalanffy model,and the sustained release of nutrients under different urea concentrations should be quantitatively described by the Elovich model.Temperature and urea concentration have a promoting effect on the permeation rate of membrane materials,and the difference between the permeability rate of the coating material under neutral and alkaline conditions is not obvious,but the sustained release rate of the coating material under acidic treatment is slightly higher than that of neutral and alkaline treatment.3.Study on degradation characteristics of coating materials under Different Soil Hydrothermal ConditionsAfter the coating material was degraded in the soil for 80 days,the overall transmittance of the infrared spectrum was improved,and the number of functional groups decreased,but the chemical bonds and main types of groups of the membrane did not change greatly,and the increase in soil hydrothermal heat led to a decrease in the-OH vibration peak and C-H bond telescopic vibration peak of the membrane.After 80 days of degradation,roughness,holes and even cracks appeared on the surface of the membrane compared with the initial moment,indicating that the membrane would degrade in the soil,and the quality loss of the membrane was between 13.7%and 17.3%.When the soil moisture content and temperature increase,the surface roughness of the membrane material,cracks,folds,holes,etc.are gradually obvious,the degradation rate is significantly improved（p?0.01）,and the temperature promotion effect is more significant than that of water.A hydrothermal coupling model of membrane degradation rate is established,and the relative error between the measured value of the degradation rate and the predicted value is 0.13%-3.48%,and the simulation accuracy is good.