Macromolecular slow-release coated fertilizer

Abstract

The invention relates to the technical field of fertilizers, and discloses a high-molecular slow-release coating fertilizer, and a preparation method of a high-molecular slow-release coating comprises the following steps: S1, dissolving polyamide in N, N-dimethylformamide, adding a polyacrylic acid solution, adding benzoyl peroxide as a free radical initiator, and carrying out a grafting reaction; and S2, adding long-chain alkyl bromide into the grafted polymer, carrying out hydrophobic modification, stirring for 0.5-1.5 hours, slowly adding polyethylene glycol, carrying out hydrophilic regulation and control, and continuously stirring for 2-4 hours. According to the invention, the interaction between the fertilizer components and the polymer is increased through a method of grafting and modifying polyamide with polyacrylic acid, and pollution caused by excessive use of the fertilizer is reduced while the release of the fertilizer is slowed down by controlling the proportion of hydrophobic and hydrophilic groups in the polymer.

Description

Technical Field

[0001] The invention relates to the technical field of fertilizers, in particular to a polymer slow-release coating fertilizer. Background Art

[0002] In modern agricultural production, the use of fertilizers is one of the key factors in increasing crop yields. However, traditional fertilizers, especially quick-release fertilizers, have certain problems, such as nutrient release too quickly, resulting in a large amount of nutrients not being absorbed by crops and being lost under rain, which not only reduces the efficiency of fertilizer use, but may also lead to environmental problems such as eutrophication of water bodies. Therefore, developing a fertilizer that can effectively control the nutrient release rate to adapt to the crop absorption rate is of great significance for promoting sustainable agricultural development.

[0003] In recent years, with the progress of materials science, polymer materials have been widely studied and applied in the field of slow-release fertilizers due to their unique physical and chemical properties. These polymer materials can be combined with fertilizer ingredients through physical or chemical methods to form a slow-release system to extend the time of nutrient release. Most slow-release coated fertilizers on the market currently use synthetic polymers or natural polymers as carriers. These materials can control the release rate of fertilizers to a certain extent and reduce nutrient loss.

[0004] However, although existing technologies have made certain progress, how to further optimize the performance of polymer materials to adapt to the needs of different crops and soil environments remains a key issue that needs to be addressed in the development of agricultural fertilizer technology. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a polymer slow-release coated fertilizer, which can effectively control the release rate of nutrients in agricultural fertilizers to improve the use efficiency of fertilizers, reduce environmental pollution, and enhance the economic benefits of agricultural production.

[0006] To achieve the above objectives, the present invention is implemented by the following technical scheme: A method for preparing a polymer sustained-release coating comprises the following steps:

[0007] S1. Grafting reaction

[0008] In this step, polyamide is dissolved in N,N-dimethylformamide (DMF) to form a solution. Then the polyacrylic acid solution is added and benzoyl peroxide is used as a free radical initiator to start the grafting reaction. The carboxyl groups (-COOH) of polyacrylic acid are grafted onto the polyamide chains through a free radical mechanism to form a new copolymer. This step increases the functional groups of the polymer, thereby improving its ability to interact with fertilizer components.

[0009] The increased carboxyl groups can form stronger ionic bonds with cations in fertilizers (such as ammonium, potassium, etc.), thereby reducing the dissolution rate of nutrients in the fertilizer and achieving a slow-release effect.

[0010] S2. Hydrophobicity and hydrophilicity regulation

[0011] After the polymer grafting reaction is completed, long-chain alkyl bromide is added for hydrophobic modification. This step adds hydrophobic groups to the polymer surface, reducing the affinity between water and the polymer. After stirring for 0.5 to 1.5 hours, polyethylene glycol is slowly added to regulate the hydrophilicity. Stirring is continued for 2 to 4 hours. Polyethylene glycol increases the hydrophilicity of the polymer, helping the polymer to absorb and retain more water, but due to the previous hydrophobic modification, this water is not easy to release.

[0012] This combined regulation of hydrophobicity and hydrophilicity enables the fertilizer to exist stably in a humid environment after absorbing water, prolongs the release time of water and nutrients, and reduces nutrient loss due to too rapid release.

[0013] Through the above technical solution, precise controlled release of fertilizer nutrients can be achieved, effectively extending the nutrient supply cycle and reducing environmental pollution caused by fertilizer loss. The polymer slow-release coated fertilizer using this coating slow-release material is not only suitable for a variety of crops, but also has high environmental adaptability, especially in rainy or frequently irrigated areas. In addition, by controlling the release of nutrients, farmers can reduce the number of fertilizations, reduce labor costs and increase economic benefits, while also reducing the pressure of agricultural activities on the ecosystem, providing effective support for the development of sustainable agriculture.

[0014] Preferably, the polyamide is prepared by the polycondensation reaction of caprolactam and water, which involves reacting caprolactam with an appropriate amount of water at high temperature to form a polyamide polymer.

[0015] The polycondensation reaction temperature is 240-280℃, which is based on the consideration of achieving the optimal molecular weight and degree of polymerization. Too low a temperature may lead to incomplete reaction, low polymer molecular weight, and unfavorable for subsequent modification. Too high a temperature may lead to side reactions, such as cross-linking or degradation, affecting product quality.

[0016] The duration is 10 to 14 hours, which is determined based on the reaction kinetics of polyamide and actual operation experience. A longer reaction time is conducive to the completion of the polymerization reaction and ensures the uniformity and stability of the polymer chain.

[0017] After the polymerization reaction is completed, the polymer needs to be slowly cooled from the high temperature environment to room temperature to prevent physical structure mutations caused by too rapid temperature changes. The cooled polymer is usually in a blocky or viscous state.

[0018] Cut the cooled polymer into small particles to facilitate subsequent processing and application. The size of the particles directly affects the efficiency and uniformity of the grafting modification. The appropriate particle size can increase the surface area of ​​the grafting reaction, thereby enhancing the modification effect.

[0019] Through the above technical solution, the physical and chemical properties of polyamide can be systematically optimized, providing a high-quality substrate for subsequent grafting modification. The polyamide prepared in this way has better chemical stability and mechanical properties, so that it exhibits better nutrient controlled release ability and environmental adaptability in the application of polymer slow-release coating fertilizers.

[0020] Preferably, the molecular weight of the polyacrylic acid is 80,000 to 120,000.

[0021] The molecular weight of polyacrylic acid within the preferred range can ensure sufficient chain length to more effectively undergo grafting reaction with polyamide. A higher molecular weight helps to form a stable polymer network rather than simple physical mixing, thereby improving the slow-release ability of the fertilizer at the chemical level.

[0022] The network structure formed by higher molecular weight polyacrylic acid in the polyamide matrix is ​​more complex and stable, which can effectively control the release rate of nutrients in the fertilizer. This structure limits the rapid diffusion of water and nutrients, and achieves a slow release of nutrients, which meets the needs of crop growth.

[0023] Within this molecular weight range, polyacrylic acid can maintain good handling and rheological properties, making it easy to process and apply in industrial production. At the same time, it ensures the mechanical strength and durability of the polymer, making it suitable for use in a variety of soil and climatic conditions and not easily degraded by environmental factors.

[0024] Through the above technical solution, while ensuring the grafting reaction and sustained release effect, the cost of the product can also be properly controlled.

[0025] Preferably, in the polyacrylic acid grafting reaction, the weight ratio of polyamide to polyacrylic acid is 0.5:1 to 1:1.

[0026] When the weight ratio of polyamide to polyacrylic acid is close to 1:1, sufficient polyacrylic acid molecules are provided to graft with polyamide, increasing the chance of reaction, thereby forming a higher density graft network. This helps to enhance the structural stability of the polymer and improve the slow-release properties of the fertilizer. A higher polyacrylic acid ratio (close to 1:1) can form a stronger ion cross-linked network in the polymer. This network structure can more effectively control the release of nutrients in the fertilizer, avoid rapid nutrient loss, and thus extend the time of nutrient supply.

[0027] When the weight ratio is as low as 0.5:1, although the amount of polyacrylic acid is relatively small, it is still enough to achieve effective grafting and reduce the cost of use, which is suitable for cost-sensitive applications. Although the grafting density is slightly lower at a lower ratio (0.5:1), it can still provide an improved slow-release effect over conventional fertilizers while maintaining a low material cost.

[0028] Through the above technical solution, the method of the present invention can flexibly respond to different agricultural needs and environmental conditions to achieve the optimization of fertilizer performance. This ratio range allows manufacturers to select the most appropriate ratio according to specific application requirements and cost control requirements, ensuring that the fertilizer product provides excellent slow-release effect while maintaining the economy of production and application.

[0029] Preferably, the reaction temperature in the polyacrylic acid grafting reaction is 90-100° C. and the duration is 4-6 hours.

[0030] Reaction temperature (90~100℃):

[0031] This temperature range is considered ideal because it is above the glass transition temperature (Tg) of polyacrylic acid, allowing the polyacrylic acid segments to have sufficient mobility in solution to promote effective contact and chemical reaction of the polyamide chains.

[0032] The temperature is set within this range to prevent excessive heat from causing polymer degradation or premature reaction termination, while being sufficient to activate the benzoyl peroxide initiator, effectively generate free radicals, and promote the grafting reaction.

[0033] Duration (4-6 hours):

[0034] This time range is based on the need to achieve sufficient grafting of polyacrylic acid and polyamide. Too short a time may result in incomplete grafting, while too long a time may increase production costs or even cause unwanted side reactions such as cross-linking or degradation.

[0035] The 4 to 6 hour reaction time allows the polymer chains sufficient time to form stable chemical bonds while keeping the system energy and cost efficient.

[0036] Through the above technical solution, the prepared polymer slow-release coated fertilizer is not only technically feasible, but also has obvious advantages in economic and environmental benefits, which is helpful to promote its use in modern sustainable agricultural practices.

[0037] Preferably, in the hydrophobic modification, the long-chain alkyl bromide used is dodecyl bromide.

[0038] Dodecyl bromide (C12H25Br) is a commonly used hydrophobic surfactant. Its long hydrophobic chain can be effectively embedded into the polymer structure, enhancing the hydrophobicity of the entire polymer network through hydrophobic interactions.

[0039] This substance not only provides a hydrophobic effect in the polymer, but also interacts with other functional groups in the polymer due to the presence of bromide ions, further stabilizing the structure.

[0040] By introducing dodecyl bromide, the hydrophobicity of the polymer is enhanced, and water is not easy to penetrate the polymer matrix, thereby controlling the release rate of nutrients in the fertilizer. This controlled release mechanism is particularly suitable for crops that require long-term support and can provide continuous nutrient support throughout the growth cycle.

[0041] Through the above technical solution, the purpose of optimizing fertilizer release performance and enhancing environmental adaptability is achieved by changing the hydrophobic characteristics of the polymer.

[0042] Preferably, in the hydrophobic modification and hydrophilic regulation steps, the reaction temperature is 65-75°C.

[0043] In the temperature range of 65°C to 75°C, chemical reactions can be carried out effectively without being too rapid or intense, which helps control the reaction rate and ensures uniform hydrophobic and hydrophilic modification reactions. This temperature control helps avoid polymer degradation or undesirable side reactions that may occur due to excessively high temperatures.

[0044] Through the above technical scheme, the reaction temperature of hydrophobic modification and hydrophilic regulation is preferably set at 65°C to 75°C in order to ensure the effectiveness and safety of the chemical reaction, as well as the quality and performance of the obtained polymer slow-release coated fertilizer, to meet the needs of modern agriculture for efficient and environmentally friendly fertilizers.

[0045] Preferably, in the hydrophilicity regulating step, the molecular weight of the polyethylene glycol selected is 3,000 to 5,000.

[0046] The molecular weight of polyethylene glycol is 3,000 to 5,000 to provide sufficient hydrophilicity while avoiding the increase in viscosity or difficulty in handling that may be caused by too high a molecular weight. Polyethylene glycol in this molecular weight range can effectively increase the hydrophilicity of the polymer, helping the polymer to form a stable hydration layer after contacting soil moisture, thereby controlling the slow release of water and nutrients.

[0047] This molecular weight range of polyethylene glycol ensures its good dispersibility and compatibility in the polymer matrix, helping to maintain the overall mechanical strength and structural integrity of the polymer. This is because too low a molecular weight may result in insufficient formation of an effective hydration layer, while too high a molecular weight may make the polymer too viscous, affecting its subsequent handling and application.

[0048] Through the above technical scheme, polyethylene glycol with a molecular weight of 3,000 to 5,000 is selected for hydrophilicity regulation, which can not only effectively improve the water retention capacity and slow-release performance of the fertilizer, but also help to achieve the economic efficiency of the production process and the environmental protection goals of the product.

[0049] The present invention also provides a polymer slow-release coating fertilizer prepared by the method, wherein the polymer slow-release coating fertilizer comprises core NPK fertilizer particles and a polymer slow-release coating coated on the outside thereof.

[0050] Preferably, the preparation of the polymer slow-release coating fertilizer includes:

[0051] The modified polymer is mixed with NPK fertilizer at a mass ratio of 0.01:1 to 0.05:1, and granulated at a temperature of 70-90°C. The temperature is controlled to ensure the stability of the physical properties of the polymer and fertilizer, while optimizing the shape and size of the particles to meet the fertilization requirements of agricultural machinery.

[0052] The mixing and granulation steps ensure uniform distribution of polymers and fertilizer components, improving the mechanical application performance of the fertilizer and the nutrient absorption efficiency of the crop. Granulation also helps to reduce dust, avoid fertilizer agglomeration and reduce nutrient losses during storage.

[0053] The present invention provides a polymer slow-release coating fertilizer having the following beneficial effects:

[0054] 1. The present invention increases the interaction between fertilizer components and polymers by grafting polyacrylic acid to modify polyamide, and in particular, enhances the ionic bond with fertilizer components by introducing functional carboxyl groups. This modified polymer significantly improves the utilization rate of fertilizers because it can more effectively control the release rate of nutrients, so that nutrients are slowly and continuously provided throughout the growth cycle of plants, reducing the loss and waste caused by rapid release of nutrients.

[0055] 2. The present invention controls the ratio of hydrophobic and hydrophilic groups in the polymer, which slows down the release of fertilizer and reduces environmental pollution caused by excessive use of fertilizer. The combination of hydrophobic modification and hydrophilic modification optimizes the interaction between fertilizer and soil and water, reduces the risk of nutrients leaking into water bodies through surface runoff and deep infiltration, and thus protects the ecological safety of groundwater quality and nearby water bodies. DETAILED DESCRIPTION

[0056] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0057] Embodiment 1:

[0058] Materials and proportions:

[0059] Polyamide: prepared by polycondensation of caprolactam and water at a temperature of 250°C for 12 hours. The obtained polyamide is cooled and cut into pellets.

[0060] Polyacrylic acid (PAA): molecular weight 100,000, weight ratio with polyamide 1:1.

[0061] Benzoyl Peroxide: acts as a free radical initiator.

[0062] Dodecyl bromide: used for hydrophobic modification.

[0063] Polyethylene glycol (PEG): molecular weight 4,000, used for hydrophilicity regulation.

[0064] NPK fertilizer: The mass ratio to modified polyamide is 0.03:1.

[0065] Preparation steps:

[0066] 1. Polyacrylic acid grafting reaction: Dissolve polyamide in N,N-dimethylformamide, add polyacrylic acid solution, and carry out grafting reaction at 95°C for 4 hours.

[0067] 2. Hydrophobic modification and hydrophilic regulation: Add 10% dodecyl bromide, stir for 1 hour, then gradually add 7% polyethylene glycol, the total stirring time is 4 hours, and the reaction temperature is 70°C.

[0068] 3. Mixing and granulation: The modified polymer was mixed with NPK fertilizer and granulated at 80°C using an extruder.

[0069] Embodiment 2:

[0070] Compared with Example 1, the difference is:

[0071] Materials and proportions:

[0072] Polyamide: reaction temperature 260°C, duration 14 hours.

[0073] Polyacrylic acid (PAA): molecular weight 120,000, weight ratio to polyamide 0.5:1.

[0074] NPK fertilizer: The mass ratio to modified polyamide is 0.05:1.

[0075] Preparation steps:

[0076] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 100°C for 6 hours.

[0077] 2. Hydrophobic modification and hydrophilic regulation: Add 5% dodecyl bromide and 3% polyethylene glycol, reaction temperature 75°C.

[0078] 3. Mixing and granulation: After mixing, granulation is carried out at 85°C to ensure good particle morphology.

[0079] Embodiment 3:

[0080] Compared with Example 1, the difference is:

[0081] Materials and proportions:

[0082] Polyamide: reaction temperature 280°C, duration 10 hours.

[0083] Polyacrylic acid (PAA): molecular weight 80,000, weight ratio with polyamide is 1:1.

[0084] NPK fertilizer: The mass ratio to modified polyamide is 0.01:1.

[0085] Preparation steps:

[0086] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 90°C for 5 hours.

[0087] 2. Hydrophobic modification and hydrophilic regulation: 15% dodecyl bromide and 7% polyethylene glycol were added, and the reaction temperature was 65°C.

[0088] 3. Mixing and granulation: Mixing and granulation are carried out at a temperature of 70°C.

[0089] Embodiment 4:

[0090] Compared with Example 1, the difference is:

[0091] Materials and proportions:

[0092] Polyamide: reaction temperature 240°C, duration 14 hours.

[0093] Polyacrylic acid (PAA): molecular weight 110,000, weight ratio with polyamide 1:1.

[0094] NPK fertilizer: The mass ratio to modified polyamide is 0.05:1.

[0095] Preparation steps:

[0096] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 100°C for 4 hours.

[0097] 2. Hydrophobic modification and hydrophilic regulation: Add 10% dodecyl bromide and 5% polyethylene glycol, reaction temperature 75°C.

[0098] 3. Mixing and granulation: Mixing and granulation were carried out at 85°C.

[0099] Embodiment 5:

[0100] Compared with Example 1, the difference is:

[0101] Materials and proportions:

[0102] Polyamide: reaction temperature 275°C, duration 12 hours.

[0103] Polyacrylic acid (PAA): molecular weight 95,000, weight ratio to polyamide 0.75:1.

[0104] NPK fertilizer: The mass ratio to modified polyamide is 0.04:1.

[0105] Preparation steps:

[0106] 1. Polyacrylic acid grafting reaction: The grafting reaction was carried out at 95°C for 5 hours.

[0107] 2. Hydrophobic modification and hydrophilic regulation: 12% dodecyl bromide and 6% polyethylene glycol were added, and the reaction temperature was 70°C.

[0108] 3. Mixing and granulation: The mixture was granulated at 80°C.

[0109] Comparative experiment 1:

[0110] Objective: To evaluate the effect of polyacrylic acid grafting modification on the slow-release properties of polyamide-based fertilizers.

[0111] Experimental group: five different ratios of polyamide and polyacrylic acid were used to graft-modify the polymer (Examples 1-5).

[0112] Control group 1: pure polyamide without graft modification (100% polyamide).

[0113] Experimental steps:

[0114] 1. Sample preparation: Prepare graft-modified polymers and form fertilizer granules according to the description of Examples 1 to 5. Control group 1 uses the same method but does not undergo graft modification.

[0115] 2. Nutrient release test: Place each sample in standard test soil and maintain the same soil moisture and temperature conditions. Take samples at set time points (1 day, 3 days, 7 days, 14 days, 28 days) and analyze the nitrogen, phosphorus and potassium content in the soil solution.

[0116] 3. Data recording: Record the NPK concentration at each time point to evaluate the nutrient release rate.

[0117] The experimental results are shown in the following table:

[0118]

[0119] It can be observed from the data table that, compared with the control group, the graft-modified polyamides in Examples 1-5 significantly reduce the nitrogen release rate, and this phenomenon becomes more obvious with the increase of the polyacrylic acid content.

[0120] The higher molecular weight and lower ratio of polyacrylic acid in Example 1 (polyamide to polyacrylic acid ratio of 1:1) and Example 2 (ratio of 0.5:1) significantly affected the slow-release properties of the fertilizer, delaying the release of nutrients compared to the control group.

[0121] Examples 3, 4 and 5 also exhibited significant sustained-release effects, indicating that even if the molecular weight of the polyacrylic acid was low or the proportion was high, the graft modification was still effective.

[0122] From the experimental data, the carboxyl group (-COOH) introduced by grafted polyacrylic acid may form a stronger ionic bond with the ions in the fertilizer, making the fertilizer components more difficult to hydrolyze and elute. In addition, the increase in carboxyl groups may also enhance the water absorption of the polymer, thereby affecting the fertilizer release dynamics.

[0123] The release rate of fertilizer can be effectively controlled by grafting polyamide with polyacrylic acid, providing a continuous fertilizer solution for agriculture while reducing environmental pollution caused by excessive nutrient release. The innovation of this method is that it optimizes the performance of fertilizers through simple chemical modification, demonstrating the potential application of materials science in sustainable agricultural practices.

[0124] Comparative experiment 2:

[0125] Objective: To evaluate the effects of hydrophobicity and hydrophilicity modulation on the slow-release properties of fertilizers through dodecyl bromide and polyethylene glycol addition.

[0126] Experimental setup:

[0127] Experimental group: different ratios of dodecyl bromide and polyethylene glycol and use conditions in Examples 1-5.

[0128] Control group 2: Graft-modified polymer without hydrophobic or hydrophilic modification.

[0129] Experimental steps:

[0130] 1. Sample preparation: According to the description of Examples 1 to 5, polymers with different hydrophobic and hydrophilic modifications were prepared to form fertilizer particles. Control group 2 used the same grafted polymer but without subsequent hydrophobic or hydrophilic modification.

[0131] 2. Nutrient release test: Each sample was placed in a standardized test soil and maintained at the same soil moisture and temperature conditions. Samples were taken at set time points (1 day, 3 days, 7 days, 14 days, 28 days) to analyze the nitrogen, phosphorus, and potassium content in the soil solution.

[0132] 3. Data recording: Record the NPK concentration at each time point to evaluate the nutrient release rate.

[0133] The experimental results are shown in the following table:

[0134]

[0135] As can be seen from the data table, the hydrophobic and hydrophilic modified polymers in Examples 1 to 5 showed significantly reduced nutrient release rates compared to the control group. This phenomenon indicates that hydrophobic and hydrophilic regulation affects the release behavior of fertilizers by changing the physical and chemical properties of polymers.

[0136] The hydrophobic modification (addition of dodecyl bromide) increases the hydrophobicity of the polymer matrix, making it more difficult for water to penetrate the polymer, thereby slowing down the dissolution and release of the fertilizer components.

[0137] Hydrophilicity regulation (addition of polyethylene glycol) increases the hydrophilicity of the polymer matrix, allowing water to enter more easily but by increasing the gel properties of the polymer, a more uniform hydration environment is formed, thereby controlling the diffusion and release of the fertilizer to a certain extent.

[0138] Example 5 showed the lowest nutrient release rate, which may be because the higher proportion of polyethylene glycol enhanced the gel property of the polymer and effectively controlled the diffusion of nutrients. In addition, Example 2 and Example 4 also showed good sustained release performance after adding lower proportions of polyethylene glycol and dodecyl bromide.

[0139] The effectiveness of optimizing the release performance of fertilizers by chemically regulating the hydrophobicity and hydrophilicity of polymers provides a method for agricultural production to optimize crop nutrient utilization by controlling the fertilizer release rate, which can not only improve the economic benefits of fertilizers but also reduce the potential impact of fertilizer use on the environment.

[0140] Comparative experiment 3:

[0141] Objective: To evaluate the effects of different mixing ratios of NPK fertilizer and modified polymer on the slow-release properties of the fertilizer.

[0142] Experimental setup:

[0143] Experimental group: different mixing ratios of NPK fertilizer and polymer according to Examples 1-5 (from 0.01:1 to 0.05:1).

[0144] Control group 3: unmodified pure NPK fertilizer.

[0145] Experimental steps:

[0146] 1. Sample preparation: Fertilizer granules with NPK fertilizer and polymer mixed in different ratios were prepared according to the description of Examples 1 to 5. The control group used unmodified pure NPK fertilizer.

[0147] 2. Nutrient release test: Each sample was placed in a standardized test soil and maintained at the same soil moisture and temperature conditions. Samples were taken at set time points (1 day, 3 days, 7 days, 14 days, 28 days) to analyze the nitrogen, phosphorus, and potassium content in the soil solution.

[0148] 3. Data Recording:

[0149] The NPK concentration was recorded at each time point to assess the nutrient release rate.

[0150] The experimental results are shown in the following table:

[0151]

[0152] It can be seen from the experimental data that the different mixing ratios of the modified polymer and the NPK fertilizer in Examples 1-5 significantly reduced the nitrogen release rate, showing a significant slow-release effect compared to the control group.

[0153] Example 1 (polymer to NPK ratio of 0.03:1) showed the slowest nutrient release rate, indicating that higher polymer content significantly slowed nutrient release, probably because the high concentration of polymer physically hindered nutrient dissolution.

[0154] Example 5 (polymer to NPK ratio of 0.04:1) showed a release rate close to that of the control group, but still had a certain degree of slow release effect. This shows that even at a high fertilizer ratio, the modified polymer can still effectively control nutrient release.

[0155] Examples 2 to 4 respectively show a gradually increasing release rate, which is proportional to the respective fertilizer ratios, indicating that adjusting the ratio of fertilizer to polymer can be used as an effective means to regulate the release rate.

[0156] By adjusting the mixing ratio of fertilizer and modified polymer, the release rate of fertilizer can be effectively controlled, providing a refined nutrient management method for agricultural production, which not only improves the economic benefits of fertilizers but also reduces the potential impact on the environment. In this way, the innovative slow-release technology demonstrates the practical application potential of materials science in agricultural practice.

[0157] Comparative experiment 4:

[0158] Objective: To evaluate the comprehensive performance of modified polymer slow-release coating fertilizer in practical agricultural applications, including the economic benefits of fertilizers, crop yields and environmental impacts.

[0159] Experimental setup:

[0160] Experimental group: macromolecular slow-release coating fertilizers with different modified polymers described in Examples 1-5.

[0161] Control group: slow-release fertilizer commonly used in the market.

[0162] Experimental steps:

[0163] 1. Prepare samples: Use the modified polymer formula described in Examples 1-5 to prepare high molecular weight slow-release coated fertilizers, and use conventional slow-release fertilizers purchased on the market as a control group.

[0164] 2. Grow the same variety of corn in a standardized farmland environment and apply different groups of fertilizers at recommended rates. Record the health status, growth rate and final yield of the crop throughout its growth cycle.

[0165] 3. Environmental impact assessment: Measure the residual rate of fertilizer components in the soil and the nutrient loss to surrounding water bodies. Evaluate the long-term impact of fertilizer use on soil quality.

[0166] The experimental results are shown in the following table:

[0167]

[0168] From the provided data, it can be seen that the modified polymer macromolecular slow-release coating fertilizers in Examples 1-5 show the following advantages compared to the control group:

[0169] Crop yield: The yield of all examples was higher than that of the control, with Example 5 showing the highest yield increase, indicating that the slow-release properties of the modified polymer may help crops absorb nutrients more efficiently, especially during critical growth periods. Example 4 also showed a significant increase in yield, which may be related to the nutrient release dynamics in the polymer formulation that better matches crop needs.

[0170] Soil residue and water nutrient loss: The use of modified polymer high molecular slow-release coated fertilizer reduces soil residue rate and water nutrient loss rate, especially Example 5, which shows the lowest residue and loss, which reduces the risk of nutrient waste and environmental pollution. This may be attributed to the polymer improving the adsorption and retention capacity of fertilizers, thereby reducing the loss of nutrients through surface runoff and leaching.

[0171] Growth cycle: The use of modified polymers also slightly shortened the crop growth cycle, probably due to more efficient nutrient supply that promoted crop growth.

[0172] These results show that the modified polymer slow-release coating fertilizer not only improves crop yield and growth efficiency, but also reduces nutrient loss and is environmentally friendly, demonstrating its potential application value in modern agricultural production. By optimizing fertilizer formulation, economic benefits and environmental sustainability can be further improved. The introduction of this innovative technology provides strong support for sustainable agricultural practices.

[0173] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polymer sustained-release coating, characterized in that: The following steps are involved: The polyamide is dissolved in N,N-dimethylformamide, a polyacrylic acid solution is added, and benzoyl peroxide is added as a free radical initiator to carry out a grafting reaction; Long-chain alkyl bromide is added to the grafted polymer to modify the hydrophobicity. After stirring for 0.5 to 1.5 hours, polyethylene glycol is slowly added to adjust the hydrophilicity. Stirring is continued for 2 to 4 hours.

2. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: The polyamide is prepared by polycondensation of caprolactam and water, and is cooled and cut into small particles. The polycondensation reaction temperature is 240-280° C. and the duration is 10-14 hours.

3. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: The molecular weight of the polyacrylic acid is 80,000 to 120,000.

4. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the polyacrylic acid grafting reaction, the weight ratio of polyamide to polyacrylic acid is 0.5:1 to 1:

1.

5. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the polyacrylic acid grafting reaction, the reaction temperature is 90-100° C. and the duration is 4-6 hours.

6. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the hydrophobic modification, the long-chain alkyl bromide used is dodecyl bromide.

7. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the hydrophobic modification and hydrophilic regulation steps, the reaction temperature is 65-75°C.

8. The method for preparing a polymer sustained-release coating according to claim 1, characterized in that: In the hydrophilicity regulating step, the molecular weight of the polyethylene glycol selected is 3,000 to 5,000.

9. A polymer slow-release coating fertilizer, characterized in that: The polymer slow-release coating fertilizer comprises a core NPK fertilizer particle and a polymer slow-release coating coated on the outside thereof, and the polymer slow-release coating is prepared by the preparation method according to any one of claims 1 to 8.

10. The polymer slow-release coating fertilizer according to claim 9, characterized in that: The preparation of the polymer slow-release coating fertilizer comprises: mixing the modified polymer and the NPK fertilizer at a mass ratio of 0.01:1 to 0.05:1 for granulation, and controlling the temperature at 70-90°C.

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