A temperature-sensitive coating material and a smart controlled-release fertilizer

Abstract

This invention proposes a temperature-sensitive coating material and an intelligent controlled-release fertilizer. The temperature-sensitive coating material is obtained by grafting starch with isocyanate paraffin@SiO2 microcapsules, followed by ring-opening polymerization with caprolactone. The isocyanate paraffin@SiO2 microcapsules are obtained by emulsifying paraffin with hexadecyltrimethylammonium bromide, followed by hydrolysis with tetraethyl orthosilicate and propyltriethoxysilane isocyanate. This invention coats fertilizer granules with the temperature-sensitive coating material. When the temperature is below the melting point of paraffin, the coating material shows no significant change; the presence of hydrophobic paraffin slows down and hinders water from entering the coating core and dissolving fertilizer nutrients, resulting in minimal nutrient release. When the temperature is above the melting point of paraffin, the hydrophobic paraffin dissolves, allowing a large amount of fertilizer nutrients to be released. This forms a temperature-responsive controlled-release fertilizer with good biodegradability.

Description

Technical Field

[0001] This invention relates to the field of organic polymer technology, and in particular to a temperature-sensitive coating material and an intelligent slow-release fertilizer. Background Technology

[0002] Agricultural practice shows that chemical fertilizers contribute over 40% to my country's grain production increase. As a crucial sector supporting agriculture, the fertilizer industry is directly related to national food security and ecological environmental protection. Controlled-release fertilizers, which use various polymer materials to coat fast-acting fertilizers, utilize a thin film to quantitatively control nutrient release. In practical applications, this allows the fertilizer's nutrient release rate to synchronize with crop nutrient absorption, thereby significantly improving fertilizer utilization, reducing labor costs, and increasing economic benefits. This lays the foundation for precision fertilization technology and the promotion of sustainable agricultural development.

[0003] Currently, my country is promoting a new green fertilizer research and development program, with precise and intelligent fertilizer release becoming a new hot topic in controlled-release fertilizer research. Since crop growth is influenced by environmental factors such as soil, temperature, and microorganisms, developing environmentally responsive intelligent controlled-release fertilizers can enable nutrient release to adapt to changes in these environmental factors. It is known that crop root growth, biomass, and nitrogen uptake are positively correlated with surface temperature. If the nutrient release rate of controlled-release fertilizers can respond to the soil temperature during periods of rapid nutrient absorption by crops, achieving intelligent release, it can more precisely match the nutrient absorption rate of crops. Summary of the Invention

[0004] Based on the technical problems existing in the background art, this invention proposes a temperature-sensitive coating material and an intelligent controlled-release fertilizer. By coating the fertilizer granules with a temperature-sensitive coating material containing starch, isocyanate paraffin@SiO2 microcapsules and polycaprolactone, when the temperature is below the melting point of paraffin, the coating material does not change significantly. The presence of hydrophobic paraffin slows down and prevents water from entering the coating core and dissolving fertilizer nutrients, resulting in less fertilizer nutrient release. When the temperature is above the melting point of paraffin, as the hydrophobic paraffin dissolves, a large amount of fertilizer nutrients are released to the outside, forming a temperature-responsive controlled-release fertilizer that also has good biodegradability.

[0005] The present invention proposes a temperature-sensitive coating material, which is obtained by grafting and condensing starch with isocyanate paraffin@SiO2 microcapsules, followed by ring-opening polymerization with caprolactone.

[0006] Preferably, the isocyanate paraffin@SiO2 microcapsules are obtained by emulsifying paraffin with hexadecyltrimethylammonium bromide, followed by hydrolysis with tetraethyl orthosilicate and propyltriethoxysilane isocyanate.

[0007] In this invention, paraffin wax is emulsified with a cationic surfactant, hexadecyltrimethylammonium bromide, and then tetraethyl orthosilicate and propyltriethoxysilane isocyanate are added as silica precursor and isocyanation modifier, respectively. These form silica particles rich in hydroxyl groups, which can bind to the ionic bonds of hexadecyltrimethylammonium bromide, thus firmly fixing them to the surface of the paraffin wax. This successfully prepares isocyanated paraffin wax@SiO2 microcapsules with isocyanated silica as the shell and paraffin wax as the core. Subsequently, some hydroxyl groups present on the starch surface are utilized to react with the isocyanated silica... Paraffin@SiO2 microcapsules undergo graft condensation, and then the residual hydroxyl groups on the starch surface initiate the ring-opening polymerization of caprolactone, ultimately yielding a temperature-sensitive coating material containing starch, isocyanate paraffin@SiO2 microcapsules, and polycaprolactone. This material can adjust the temperature response performance of the fertilizer after coating according to the temperature at which crop nutrient absorption peaks, thereby achieving rapid nutrient release at the temperature required for peak crop nutrient release. This is of great significance for improving fertilizer utilization and synchronizing fertilizer nutrient release with crop demand patterns.

[0008] Preferably, the mass ratio of the paraffin, hexadecyltrimethylammonium bromide, tetraethyl orthosilicate and propyltriethoxysilane is 1:0.01-0.1:0.5-1.5:0.05-0.1.

[0009] Preferably, the catalyst for the hydrolysis reaction is at least one of ammonia, formamide, or dodecylamine;

[0010] Preferably, the hydrolysis reaction temperature is 60-80℃ and the time is 4-8h.

[0011] Preferably, the mass ratio of starch to isocyanate paraffin@SiO2 microcapsules is 1:1-3.

[0012] Preferably, the grafting condensation reaction temperature is 60-80℃ and the time is 4-8h.

[0013] Preferably, the mass ratio of starch to caprolactone is 1:4-6.

[0014] Preferably, the catalyst for the ring-opening polymerization reaction is at least one of dibutyltin dilaurate, stannous octoate, di(dodecylthio)dibutyltin, or tetrabutyl titanate.

[0015] Preferably, the ring-opening polymerization reaction is carried out at a temperature of 100-120°C for 2-6 hours.

[0016] The present invention also proposes an intelligent controlled-release fertilizer, comprising fertilizer granules and a coating covering the fertilizer granules; the coating is obtained by spraying the above-mentioned temperature-sensitive coating material onto the surface of the fertilizer granules to form a coating.

[0017] Preferably, the fertilizer granules comprise, by weight: 30-40 parts biochar, 15-25 parts inorganic fertilizer, 5-15 parts modified mineral powder, 1-3 parts microbial inoculant, and 0.5-2 parts binder.

[0018] In this invention, biochar is used to provide organic matter and improve soil structure; inorganic fertilizer is used to provide core nutrients; modified mineral powder is used for nutrient adsorption and slow release and soil improvement; microbial agents are used to decompose organic matter and promote nutrient absorption; and binders are used to bind and provide carbon sources.

[0019] Preferably, the biochar is obtained by pyrolysis of crop straw; the inorganic fertilizer is at least one of urea, ammonium chloride, ammonium sulfate, monoammonium phosphate, diammonium phosphate, potassium chloride, potassium sulfate, or potassium dihydrogen phosphate; the microbial agent is at least one of Bacillus subtilis, Bacillus laterosporus, or Trichoderma harzianum; and the binder is gelatinized starch.

[0020] Preferably, the modified mineral powder is obtained by crushing and soaking attapulgite, centrifuging and purifying it, acidifying and activating it, and then freeze-drying it.

[0021] In this invention, the modified mineral powder is specifically made by crushing attapulgite clay, mixing it with a dispersant and water, using the dispersant to fully disperse the agglomerated mineral particles, soaking to remove soluble impurities adhering to the surface and between particles, and then using the density difference of different particles to achieve separation under centrifugal force. The attapulgite clay suspension is centrifuged, and the heavier, pure attapulgite clay settles to the bottom of the tube, while the smaller impurities and organic matter remain in the upper turbidity. The upper turbidity and impurities are removed to obtain pure attapulgite sediment; then it is activated with an acid solution. Under heating conditions, hydrochloric acid reacts with impurities in the mineral (such as calcium carbonate, iron oxide, etc.), dissolving and washing them away. Purifying attapulgite involved eroding its crystal structure, increasing surface roughness and internal porosity, and significantly improving its specific surface area and chemical activity. The centrifuged purified attapulgite sediment was then frozen. During freezing and crystallization, water expands, and the resulting ice crystals exert a "spreading" and "tearing" effect on the attapulgite's pore structure, helping to open closed channels. Microwave thawing followed. Microwaves cause the polar water molecules inside the material to vibrate and rub at high speed, generating heat and achieving rapid, inside-out thawing. This intense thermal stress further disrupts particle aggregation, creating microcracks, thereby significantly increasing pore volume and connectivity, and deeply activating mineral activity.

[0022] Preferably, the dispersant used in the pulverization and soaking is a copolymer of isopentenyl alcohol polyoxyethylene ether, methacrylamide and 2-acrylamide-2-methylpropanesulfonic acid.

[0023] In this invention, compared to the traditional sodium polyacrylate as a dispersant, the copolymer of isopentenyl alcohol polyoxyethylene ether, methacrylamide and 2-acrylamide-2-methylpropanesulfonic acid is used as a dispersant. The ether bonds, amino groups and sulfonic acid groups contained therein give it good surface activity. It can activate the surface activity of attapulgite soil, improve the impurity removal effect, and enhance the adsorption and retention capacity of modified mineral powder for phosphate anions and ammonium cations in the soil.

[0024] Preferably, the mass of the temperature-sensitive coating material accounts for 2-10% of the mass of the fertilizer granules.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention proposes a temperature-sensitive coating material and an intelligent controlled-release fertilizer. The temperature-sensitive coating material can intelligently and flexibly respond to temperature changes when recognizing changes in soil temperature, realizing autonomous switching and controlling nutrient release, which is an important part of the intelligent control-release fertilizer. At the same time, its production process is simple, the production cost is low, the controlled-release period is long, it has temperature change response performance, and good biodegradability. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the temperature-sensitive coating material described in Example 1;

[0028] Figure 2 The infrared spectrum of the temperature-sensitive coating material described in Example 1 is shown. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0030] Example 1

[0031] This embodiment proposes a temperature-sensitive coating material, which is prepared by the following method:

[0032] Hexadecyltrimethylammonium bromide was dissolved in water by heating and stirring. Paraffin (melting point 40-50℃) was added and stirred at high speed to form a stable emulsion. Then, an ethanol solution containing tetraethyl orthosilicate and propyltriethoxysilane was added, followed by ammonia (26wt%). The mass ratio of paraffin, hexadecyltrimethylammonium bromide, tetraethyl orthosilicate, propyltriethoxysilane and ammonia was 1:0.05:1:0.08:2. The mixture was heated to 70℃ and stirred for 6 hours. After filtration, washing and drying, isocyanate paraffin@SiO2 microcapsules were obtained.

[0033] Corn starch (amylose content 28-30%, relative molecular mass Mw 1.3-1.4×10⁻⁶) was used. 6 After drying at 60℃ for 12h, the starch was dissolved in ethyl acetate and the isocyanate paraffin@SiO2 microcapsules were added. The mass ratio of corn starch to isocyanate paraffin@SiO2 microcapsules was 1:2. The mixture was heated to 70℃ and stirred for 6h. Ethyl acetate was removed by vacuum distillation to obtain the starch / isocyanate paraffin@SiO2 microcapsule graft product.

[0034] After caprolactone was vacuum-sealed at room temperature for 2 hours, it was added to the starch / isocyanate paraffin@SiO2 microcapsule graft product, followed by stannous octoate. The mass ratio of corn starch, caprolactone, and stannous octoate was 1:5:0.02. Under nitrogen protection, the mixture was heated to 110°C and stirred for 4 hours. After filtration, washing, and drying, the temperature-sensitive coating material was obtained. Its structural schematic and infrared spectrum are shown below. Figure 1 , 2 As shown.

[0035] This embodiment also proposes an intelligent slow-release fertilizer, including fertilizer granules and a coating covering the fertilizer granules, wherein the coating is made of the aforementioned temperature-sensitive coating material;

[0036] The fertilizer granules comprise, by weight, 35 parts biochar, 20 parts inorganic fertilizer, 10 parts modified mineral powder, 2 parts microbial inoculant, and 1 part binder.

[0037] The biochar is obtained by first drying rice straw at 80℃ for 24 hours, then heat-treating it at 550℃ for 2 hours in an oxygen-free atmosphere of ≤5%, and then pulverizing it through a 100-mesh sieve. The inorganic fertilizer includes monoammonium phosphate, potassium nitrate, and potassium sulfate in a mass ratio of 3:2:1. The microbial agent is Bacillus subtilis (effective viable count CFu greater than or equal to 200 million / g). The binder is gelatinized starch.

[0038] The modified mineral powder was prepared by the following method: attapulgite was crushed and passed through a 100-mesh sieve, then mixed with water, followed by the addition of a 5wt% (by weight of attapulgite) dispersant to form a suspension; the resulting suspension was centrifuged at 3000 rpm for 30 min; the resulting sediment was mixed with a 10wt% dilute hydrochloric acid solution, stirred at 50°C for 2 h, neutralized with sodium carbonate, washed with water until neutral, and dried; the resulting activated powder was frozen at -20°C for 12 h, and then subjected to 800W... The modified attapulgite was obtained by microwave thawing for 60 seconds, which is the modified mineral powder. The dispersant is a copolymer of isopentenyl alcohol polyoxyethylene ether, methacrylamide and 2-acrylamide-2-methylpropanesulfonic acid in a mass ratio of 1:0.5:1.5. It is obtained by adding isopentenyl alcohol polyoxyethylene ether, methacrylamide and 2-acrylamide-2-methylpropanesulfonic acid to xylene, then adding 2 wt% of azobisisobutyronitrile of isopentenyl alcohol polyoxyethylene ether, heating to 60°C and stirring for 3 hours.

[0039] The above-mentioned controlled-release fertilizer is prepared by the following method:

[0040] (1) Place biochar, inorganic fertilizer, modified mineral powder, microbial agent and binder in a mixing drum and add water to mix evenly to obtain a viscous compound fertilizer with a water content of 15wt%. Place the viscous compound fertilizer on a disc granulator to form granules. After screening, place it in a drying drum and dry at a controlled temperature of 40℃ to obtain fertilizer granules with a particle size of 3-6mm.

[0041] (2) The above-mentioned temperature-sensitive coating material is dispersed in ethanol to obtain a coating material solution. The coating material solution is sprayed into a mist using a spray atomizing device and enters the coating equipment to fully contact the above-mentioned fertilizer particles in the opposite direction. It is continuously dried at 70°C for 2 hours to form a coating on the surface of the fertilizer particles. The mass of the temperature-sensitive coating material accounts for 6wt% of the mass of the fertilizer particles. After cooling, the controlled-release fertilizer is obtained.

[0042] Comparative Example 1

[0043] This comparative example presents a coating material, which is prepared by the following method:

[0044] Corn starch (amylose content 28-30%, relative molecular mass Mw 1.3-1.4×10⁻⁶) was used. 6 After drying at 60℃ for 12 hours, dry starch was obtained. After evacuating caprolactone under vacuum at room temperature for 2 hours, the dry starch was added, followed by the addition of stannous octoate. The mass ratio of corn starch, caprolactone, and stannous octoate was 1:5:0.02. The mixture was heated to 110℃ under nitrogen protection and stirred for 4 hours. After filtration, washing, and drying, the coating material was obtained.

[0045] This comparative example also proposes a fertilizer, comprising fertilizer granules and a coating covering the fertilizer granules; the coating is made of the aforementioned temperature-sensitive coating material;

[0046] The fertilizer granules comprise, by weight, 35 parts biochar, 20 parts inorganic fertilizer, 10 parts modified mineral powder, 2 parts microbial inoculant, and 1 part binder.

[0047] The biochar is obtained by first drying rice straw at 80℃ for 24 hours, then heat-treating it at 550℃ for 2 hours in an oxygen-free atmosphere of ≤5%, and then pulverizing it through a 100-mesh sieve. The inorganic fertilizer includes monoammonium phosphate, potassium nitrate, and potassium sulfate in a mass ratio of 3:2:1. The microbial agent is Bacillus subtilis (effective viable count CFu greater than or equal to 200 million / g). The binder is gelatinized starch. The modified mineral powder is prepared by the method described in Example 1.

[0048] The above fertilizer is prepared by the following method:

[0049] (1) Place biochar, inorganic fertilizer, modified mineral powder, microbial agent and binder in a mixing drum and add water to mix evenly to obtain a viscous compound fertilizer with a water content of 15wt%. Place the viscous compound fertilizer on a disc granulator to form granules. After screening, place it in a drying drum and dry at a controlled temperature of 40℃ to obtain fertilizer granules with a particle size of 3-6mm.

[0050] (2) The above coating material is dispersed in ethanol to obtain a coating material solution. The coating material solution is sprayed into a mist using a spray atomizing device and enters the coating equipment to fully contact the above fertilizer particles in the opposite direction. It is continuously dried at 70°C for 2 hours to form a coating on the surface of the fertilizer particles. The mass of the coating material accounts for 6wt% of the mass of the fertilizer particles. After cooling, the fertilizer is obtained.

[0051] Comparative Example 2

[0052] This comparative example presents a coating material, which is prepared by the following method:

[0053] Corn starch (amylose content 28-30%, relative molecular mass Mw 1.3-1.4×10⁻⁶) was used. 6 After drying at 60℃ for 12 hours, dry starch was obtained. After evacuating caprolactone under vacuum at room temperature for 2 hours, the dry starch was added, followed by the addition of stannous octoate. The mass ratio of corn starch, caprolactone, and stannous octoate was 1:5:0.02. The mixture was heated to 110℃ under nitrogen protection and stirred for 4 hours. After filtration, washing, and drying, the coating material was obtained.

[0054] This comparative example also proposes a fertilizer, comprising fertilizer granules and a temperature-sensitive coating covering the fertilizer granules, wherein the temperature-sensitive coating is made by sequentially coating paraffin and the aforementioned coating material;

[0055] The fertilizer granules comprise, by weight, 35 parts biochar, 20 parts inorganic fertilizer, 10 parts modified mineral powder, 2 parts microbial inoculant, and 1 part binder.

[0056] The biochar is obtained by first drying rice straw at 80℃ for 24 hours, then heat-treating it at 550℃ for 2 hours in an oxygen-free atmosphere of ≤5%, and then pulverizing it through a 100-mesh sieve. The inorganic fertilizer includes monoammonium phosphate, potassium nitrate, and potassium sulfate in a mass ratio of 3:2:1. The microbial agent is Bacillus subtilis (effective viable count CFu greater than or equal to 200 million / g). The binder is gelatinized starch. The modified mineral powder is prepared by the method described in Example 1.

[0057] The above fertilizer is prepared by the following method:

[0058] (1) Place biochar, inorganic fertilizer, modified mineral powder, microbial agent and binder in a mixing drum and add water to mix evenly to obtain a viscous compound fertilizer with a water content of 15wt%. Place the viscous compound fertilizer on a disc granulator to form granules. After screening, place it in a drying drum and dry at a controlled temperature of 40℃ to obtain fertilizer granules with a particle size of 3-6mm.

[0059] (2) First, paraffin wax is sprayed into a mist using a spray atomizing device and enters the coating equipment to fully contact the fertilizer particles in the opposite direction. After cooling, a paraffin wax layer is formed on the surface of the fertilizer particles. The mass of the paraffin wax accounts for 1.5 wt% of the mass of the fertilizer particles. Then, the coating material is dispersed in ethanol to obtain a coating material solution. The coating material solution is sprayed into a mist using a spray atomizing device and enters the coating equipment to fully contact the fertilizer particles coated with the paraffin wax layer in the opposite direction. The mixture is dried continuously at 70°C for 2 hours to form a coating layer on the surface of the fertilizer particles. The mass of the coating material accounts for 4.5 wt% of the mass of the fertilizer particles. After cooling, the fertilizer is obtained.

[0060] Test Example 1

[0061] (1) Experimental objective:

[0062] By simulating a fertilizer solution environment, the effects of attapulgite, sodium polyacrylate-modified attapulgite, and the modified attapulgite described in Example 1 on phosphate ions (PO4) in fertilizer were compared. 3- The adsorption capacity of sodium polyacrylate was used to evaluate its synergistic effect on fertilizers; the sodium polyacrylate modified attapulgite was modified according to the method described in Example 1, except that sodium polyacrylate was used as a dispersant.

[0063] (2) Equipment and reagents:

[0064] Equipment: conductivity meter, spectrophotometer, analytical balance, constant temperature shaker, centrifuge, pipette, volumetric flask, conical flask (250mL);

[0065] Reagents: Attapulgite (Group A), sodium polyacrylate modified attapulgite (Group B), modified attapulgite of this invention (Group C), potassium dihydrogen phosphate (KH2PO4), ammonium molybdate, potassium antimony tartrate, ascorbic acid.

[0066] (3) Experimental methods:

[0067] Preparation of standard stock solution: Accurately weigh 0.4394 g of dried KH2PO4, dissolve it in deionized water, and make up to 1 L to obtain a standard stock solution with a concentration of 100 mg / L (calculated as P);

[0068] Preparation of standard series solutions: Accurately measure the stock solution with a pipette and dilute it to prepare a series of phosphate standard solutions with concentrations of 0, 0.5, 1.0, 2.0, 4.0, and 6.0 mg / L.

[0069] Plotting the standard curve: Take 10 mL of the above standard solution into colorimetric tubes, add an appropriate amount of molybdenum antimony colorimetric reagent, dilute to volume, shake well, and let stand for 15 min to develop color; use a spectrophotometer at a wavelength of 700 nm, zeroing with a blank solution (0 mg / L), and measure the absorbance of each solution to plot the standard curve; under acidic conditions, phosphate ions react with ammonium molybdate to form phosphomolybdic heteropolyacid, which is then reduced by ascorbic acid to form a stable blue complex (phosphomolybdic blue). The absorbance of this blue solution is directly proportional to the phosphate concentration within a certain range (Lambert-Beer Law).

[0070] Adsorption kinetics experiment: A simulated fertilizer solution with a concentration of 50 mg / L (calculated as P) was prepared using KH2PO4; 12 clean 250 mL Erlenmeyer flasks were divided into 3 groups (A, B, C), with 3 parallel samples in each group; 200 mL of simulated fertilizer solution was added to each Erlenmeyer flask, and then 1.00 g of the three mineral powders A, B, and C were accurately weighed and added to the corresponding Erlenmeyer flasks. A blank control was also set up (only fertilizer solution was added, without mineral powder).

[0071] Timed sampling and determination: The conical flasks were placed in a constant-temperature shaker (25℃, 150 rpm) and shaken. At 0, 5, 15, 30, 60, 120, 240, and 480 min, approximately 10 mL of the supernatant was drawn from each flask using a syringe. The supernatant was immediately filtered through a 0.45 μm filter membrane to remove solid particles, and the conductivity of the filtrate was measured. The total number of ions in the solution was positively correlated with the conductivity; as the ore adsorbed PO4... 3- (and the accompanying H2PO4) - / HPO42- The equilibrium shifts, and the total ion concentration in the solution decreases, leading to a decrease in conductivity. Changes in conductivity can quickly and indirectly reflect the overall trend of the adsorption process. Take an appropriate amount of the filtered clear liquid, and perform color development and absorbance measurement according to the method of plotting a standard curve. Substitute the measured absorbance into the standard curve equation to calculate the concentration of phosphate ions (Ct) remaining in the solution at that time point.

[0072] (4) Data processing and calculation:

[0073] Adsorption capacity calculation: Based on the data measured by spectrophotometry, the adsorption capacity per unit mass of ore at time t is calculated according to the following formula. (mg / g):

[0074]

[0075] in, This is the initial concentration (50 mg / L). Let t be the concentration (mg / L) measured at time t. m represents the solution volume (0.2 L) and m represents the ore dosage (1.00 g).

[0076]

[0077] (5) Experimental results:

[0078] Standard curve:

[0079] Table 1. Phosphate Standard Curve

[0080]

[0081] The fitted standard curve equation is: y = 0.0905x + 0.001 (R² = 0.9998).

[0082] Results of key time points in the adsorption experiment (average value):

[0083] Table 2 Adsorption Experiment Results

[0084]

[0085] As can be seen from Table 2 above, the conductivity of the solution in group C decreased the fastest and the final value was the lowest, followed by group B, while group A (unmodified) changed the slowest. This intuitively shows that group C, i.e. the modified attapulgite of this invention, adsorbed the most ions and had the highest efficiency.

[0086] Adsorption rate and adsorption capacity:

[0087] The calculation results show that at the end of the experiment (480 min), the adsorption rate of group C was as high as 67%, significantly higher than that of group B (44%) and group A (27%); the adsorption capacity Q was calculated. t Group C has a range of 50-16.5. 0.2 / 1 = 6.7 mg / g, which is much higher than the other two groups. Within the initial 30 minutes of the experiment, the adsorption rate of group C reached 30%, indicating that it has faster adsorption kinetics, can quickly fix nutrients, and reduce initial loss, while groups A and B are relatively slower.

[0088] As can be seen from the above, the present invention significantly improves the specific surface area, pore structure and surface activity of attapulgite through the synergistic effect of "dispersion + acid activation + freezing-microwave". This makes its adsorption capacity and adsorption rate for fertilizer nutrient molecules (such as phosphate) significantly better than those of unmodified products and ordinary modified attapulgite, indicating that the modified attapulgite using the present invention may have better nutrient slow release and fertilizer retention capabilities.

[0089] Test Example 2

[0090] (1) Experimental objective:

[0091] By simulating different soil temperature conditions, the dual advantages of the slow-release fertilizer of this invention in nutrient release compared to ordinary fertilizers were verified:

[0092] Temperature control capability: The nutrient release rate of slow-release fertilizers can respond to temperature changes, and the nutrient release rate is significantly higher at high temperatures than at low temperatures;

[0093] Advantages of slow-release fertilizers: Under variable temperature conditions, slow-release fertilizers can achieve an intelligent mode of "accelerated release at high temperatures to meet crop needs and slowed release at low temperatures to reduce losses", and their cumulative release curve is better than that of ordinary fertilizers.

[0094] Principle of conductivity method: Fertilizer nutrients (such as K) + NH4 + NO3 - H2PO4 - (e.g., ions) dissociate into ions in deionized water, making the solution conductive; within a certain concentration range, the conductivity of the solution shows a good positive correlation with the total ion concentration (i.e., the amount of nutrients released);

[0095] Spectrophotometric principle: Determination of ammonium nitrogen (NH4) using indophenol blue spectrophotometry. + -N), and the available phosphorus was determined by vanadium molybdenum yellow spectrophotometry;

[0096] Temperature control mechanism: The temperature-sensitive coating material of this invention is temperature sensitive; when the ambient temperature is below the critical transition temperature, the membrane material does not change significantly, the membrane structure is dense, the permeability is low, and the nutrient release is slow; when the temperature approaches or exceeds its melting point, the hydrophobic paraffin dissolves, which slows down and hinders the water from entering the coating core to dissolve fertilizer nutrients, resulting in faster nutrient release.

[0097] (2) Equipment and reagents:

[0098] Equipment: conductivity meter, spectrophotometer, constant temperature shaking incubator (2 units, which can be set to 25℃ and 40℃ respectively), conical flask (250mL, with stopper), pipette, quantitative filter paper, volumetric flask, beaker;

[0099] Materials: Controlled-release fertilizer of Example 1, fertilizer of Comparative Example 1, fertilizer of Comparative Example 2, deionized water;

[0100] (3) Test method:

[0101] Nitrogen (N) standard curve (indophenol blue method): Accurately prepare 0, 10, 20, 40, 60, and 80 mg / L of NH4. + -N standard solution series; take appropriate amounts of each solution, add indophenol blue colorimetric reagent sequentially, and after a certain development time, measure the absorbance value at a wavelength of 625 nm using a spectrophotometer; NH4 + In an alkaline medium, it reacts with hypochlorite and phenol to produce water-soluble indigo blue dye, the intensity of which is directly proportional to the concentration of ammonium nitrogen.

[0102] Table 3 Standard Curve of Ammonium Nitrogen

[0103]

[0104] The fitted standard curve equation is: y = 0.0124x + 0.002 (R² = 0.999).

[0105] Phosphorus (P2O5) standard curve (vanadium molybdenum yellow method):

[0106] Precisely prepare a series of P2O5 standard solutions with concentrations of 0, 5, 10, 20, 30, and 40 mg / L; add ammonium vanadate as a colorimetric reagent, and measure the absorbance at a wavelength of 420 nm after color development. Under acidic conditions, phosphate ions react with ammonium vanadate and ammonium molybdate to form a yellow vanadium-molybdenum-phosphorus heteropolyacid, the intensity of which is directly proportional to the phosphorus concentration.

[0107] Table 4 Phosphorus Standard Curve

[0108]

[0109] The fitted standard curve equation is: y = 0.0177x + 0.005 (R² = 0.998).

[0110] Standard curve of electrical conductivity and total nutrient concentration:

[0111] The controlled-release fertilizer of Example 1, the fertilizer of Comparative Example 1, and the fertilizer of Comparative Example 2 were prepared into a series of solutions with known total nutrient concentrations (0, 100, 200, 500, 1000 mg / L) using deionized water. The conductivity values ​​of each solution were measured, and the conversion relationship between conductivity and total nutrient concentration was established for rapid estimation of release amount.

[0112] Table 5 Standard Curve of Electrical Conductivity and Total Nutrient Concentration

[0113]

[0114] The fitted standard curve equation is: y = 2.08x + 3.5 (R² = 0.999), where y is the conductivity value and x is the total nutrient concentration.

[0115] Nutrient release kinetics experiment:

[0116] The following six experimental groups were set up, with three replicates in each group: Example 1: Slow-release fertilizer released at 25°C; Example 2: Slow-release fertilizer released at 40°C; Comparative Example 1: Fertilizer released at 25°C; Comparative Example 2: Fertilizer released at 40°C; Comparative Example 2: Fertilizer released at 25°C; Comparative Example 2: Fertilizer released at 40°C.

[0117] Intelligent fertilizer temperature variation: Example 1 shows that the slow-release fertilizer is released under varying temperature conditions (0-24h at 25℃; 24-48h to 40℃; 48-72h to 25℃; 72-120h to maintain 25℃) to simulate temperature fluctuations caused by day and night or weather, and to verify its responsiveness.

[0118] Sampling: Accurately add 1.00g of fertilizer sample and 200mL of deionized water to each conical flask, place them in a pre-set constant temperature incubator, and shake continuously (100 rpm).

[0119] Conductivity monitoring: On days 1, 3, 5, 7, 10, 14, 21, and 28, 10 mL of extract was pipetted from each conical flask (10 mL of fresh deionized water was added simultaneously to maintain a constant volume), and the conductivity of the extract was immediately measured using a conductivity meter.

[0120] Spectrophotometric verification: The extract sampled for conductivity monitoring was filtered using quantitative filter paper. A portion of the filtrate was taken, and the concentrations of ammonium nitrogen and phosphorus were accurately determined using the spectrophotometric method described above. The data obtained by this method were used to verify the accuracy of the conductivity method and to obtain precise nutrient concentrations at key time points. The cumulative nutrient release rate (taking nitrogen as an example) under different treatments changes over time as shown in the table below:

[0121] Table 6 Nutrient Cumulative Release Curve

[0122]

[0123] As shown in Table 6 above, at 40℃, the cumulative release rate of the controlled-release fertilizer on the 7th day (55.1%) was much higher than that at 25℃ (20.8%), with the release rate per unit hour increasing by about 2.2 times. In contrast, the release rates of fertilizers 1 and 2 at the two temperatures were relatively small (28.9% vs 58.6%) and (24.7% vs 56.7%), indicating that their temperature response was not sensitive.

[0124] Table 7 Cumulative Nutrient Release Curve of Controlled-Release Fertilizer in Example 1

[0125]

[0126] As shown in Table 7 above, at a constant temperature of 40℃, the release curve of the controlled-release fertilizer in Example 1 is smoother, avoiding the waste and potential seedling burn risk caused by the "explosive" release of ordinary fertilizer in the early stage. After the temperature of the controlled-release fertilizer in Example 1 was raised to 40℃ (days 3-5), the release rate jumped rapidly from 11.5% to 58.0%. After the temperature dropped back to 25℃, the release rate immediately slowed down, proving that its release rate can intelligently adjust according to temperature changes. Throughout the cycle, the controlled-release fertilizer in Example 1 released more slowly and persistently at 25℃ than the fertilizer, while it could reach the effective release level more quickly at 40℃, indicating that it can automatically adjust the nutrient supply intensity according to the ambient temperature and has a higher degree of matching with crop needs.

[0127] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A controlled-release fertilizer, characterized in that, The product includes fertilizer granules and a coating covering the fertilizer granules; the coating is obtained by spraying a temperature-sensitive coating material onto the surface of the fertilizer granules to form a coating; the temperature-sensitive coating material is obtained by grafting and condensing starch with isocyanate paraffin@SiO2 microcapsules, followed by ring-opening polymerization with caprolactone; The isocyanate paraffin@SiO2 microcapsules are obtained by emulsifying paraffin with hexadecyltrimethylammonium bromide and then hydrolyzing it with tetraethyl orthosilicate and propyltriethoxysilane. The fertilizer granules include modified mineral powder; The modified mineral powder is obtained by crushing and soaking attapulgite, centrifuging and purifying it, acidifying and activating it, and then freeze-drying it. The dispersant used in the crushing and soaking is a copolymer of isopentenyl alcohol polyoxyethylene ether, methacrylamide and 2-acrylamide-2-methylpropanesulfonic acid.

2. The controlled-release fertilizer according to claim 1, characterized in that, The mass ratio of paraffin, hexadecyltrimethylammonium bromide, tetraethyl orthosilicate and propyltriethoxysilane is 1:(0.01-0.1):(0.5-1.5):(0.05-0.1).

3. The controlled-release fertilizer according to claim 1, characterized in that, The catalyst for the hydrolysis reaction is at least one of ammonia, formamide, or dodecylamine; the hydrolysis reaction temperature is 60-80℃ and the time is 4-8h.

4. The controlled-release fertilizer according to any one of claims 1-3, characterized in that, The mass ratio of starch to isocyanate paraffin@SiO2 microcapsules is 1:(1-3).

5. The controlled-release fertilizer according to claim 1, characterized in that, The grafting condensation reaction is carried out at a temperature of 60-80℃ for 4-8 hours.

6. The controlled-release fertilizer according to any one of claims 1-3, characterized in that, The mass ratio of starch to caprolactone is 1:(4-6).

7. The controlled-release fertilizer according to claim 1, characterized in that, The catalyst for the ring-opening polymerization reaction is at least one of dibutyltin dilaurate, stannous octoate, di(dodecylthio)dibutyltin, or tetrabutyl titanate; the ring-opening polymerization reaction temperature is 100-120℃ and the time is 2-6h.

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