Environment-friendly embedding humic acid (salt) hydrogel slow-release fertilizer and preparation method thereof
An environmentally friendly slow-release fertilizer was prepared by reactive extrusion of starch-based hydrogel framework and encapsulated humic acid (salt). This method solved the polymerization reaction problem of humic acid (salt) hydrogel slow-release fertilizer, achieving high loading, long slow release and environmentally friendly production, and improving soil structure.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HENAN ACADEMY OF SCI CHEM RES INST CO LTD
- Filing Date
- 2023-12-21
- Publication Date
- 2026-07-07
Smart Images
Figure CN117776812B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of hydrogel slow-release fertilizers, specifically relating to an environmentally friendly hydrogel slow-release fertilizer containing humic acid (salt) and its preparation method. Background Technology
[0002] Humic acid (salts) is a widely available and inexpensive organic fertilizer for crops, offering significant advantages in improving soil structure, promoting nutrient absorption by plants, and fostering plant growth and development. However, the utilization rate of water-soluble humic acid (salts) as fertilizer is very low. To explore ways to improve the utilization rate of humic acid (salt) fertilizers, hydrogel slow-release fertilizers based on humic acid (salts) have emerged. However, due to the inherent structural properties of humic acid (salts), some problems exist in the preparation and application of these hydrogel slow-release fertilizers. First, the structure of humic acid (salt) contains quinone, phenolic, and free radical groups, which significantly inhibit or retard the free radical polymerization of olefin monomers. This makes it difficult for the system to undergo polymerization, thus hindering its direct confinement into a gel structure for sustained release. Second, the polymerization-inhibiting effect of humic acid (salt) hydrogels limits the strength and loading capacity of humic acid (salt) in sustained-release fertilizers, restricting their widespread application. Third, traditional methods for preparing hydrogels involve batch-intermittent organic solution or suspension polymerization, sometimes requiring large amounts of solvent for sedimentation, resulting in low production efficiency and significant waste pollutants. Therefore, a novel, environmentally friendly method for preparing humic acid (salt) hydrogel sustained-release fertilizers is needed. Summary of the Invention
[0003] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide an environmentally friendly, encapsulated humic acid (salt) hydrogel slow-release fertilizer. This material consists of a starch-based hydrogel framework and encapsulated humic acid (salt), exhibiting environmental friendliness, good mechanical properties, high humic acid (salt) loading, and excellent slow-release performance.
[0004] Another objective of this invention is to provide a method for preparing the aforementioned environmentally friendly encapsulated humic acid (salt) hydrogel slow-release fertilizer. This preparation method comprises a humic acid (salt) encapsulation method (a physical encapsulation method involving crushing and grinding) and a reactive extrusion method. The characteristics of this preparation method are: low solvent content, fast reaction rate, and a green and efficient reaction process.
[0005] The objective of this invention is achieved through the following technical solution:
[0006] An environmentally friendly encapsulated humic acid (salt) hydrogel slow-release fertilizer is obtained by using water as the reaction medium, and by subjecting native starch, monomers, encapsulated humic acid or its salts, dual initiators and crosslinking agents to a graft polymerization reaction in a reactive extruder to obtain the environmentally friendly encapsulated humic acid (salt) hydrogel slow-release fertilizer; wherein the dual initiators are cerium ammonium nitrate and persulfate; and the monomers are one or more of acrylamide and acrylic acid monomers.
[0007] Preferably, the mass-to-volume ratio of starch to water is 0.1-1.0 g / mL.
[0008] Preferably, the amount of the monomer used is 10-50% of the starch mass.
[0009] Preferably, the amount of the embedding material is 5-99% of the starch mass; more preferably 15-50%.
[0010] Preferably, the amounts of cerium ammonium nitrate and persulfate are both 0.1-1.0% of the starch mass.
[0011] Preferably, the embedding material is a mixture of humic acid or its salt and an embedding agent, which is then crushed and ground 2-3 times to ensure that the humic acid or its salt is fully encapsulated by the embedding agent; the embedding agent is one or more of stearic acid, stearate (potassium stearate, sodium stearate), liquid paraffin, and paraffin oil, preferably stearic acid and liquid paraffin; the amount of embedding agent used is 1-20% of the mass of humic acid or its salt.
[0012] Preferably, the humic acid or its salt comprises one or more of potassium humate, sodium humate, fulvic acid, potassium fulvic acid, sodium fulvic acid, nitrohumic acid, potassium nitrohumate, sodium nitrohumate, and biochemical humic acid.
[0013] Preferably, the crosslinking agent is N,N-methylenebisacrylamide; the persulfate is one or more of potassium persulfate, sodium persulfate, and ammonium persulfate.
[0014] The original starch is derived from one or more starch-containing plants, including cereals such as natural corn, wheat, and rice; tubers such as sweet potatoes, cassava, and potatoes; legumes such as soybeans, mung beans, and red beans; root vegetables such as lotus root, taro, and water chestnuts; and high-starch trees such as oak, sago palm, baobab, and sugar maple, with natural corn starch being preferred.
[0015] Preferably, the reaction temperature is 60~120 ℃; the reaction time is 2~20 min.
[0016] Preferably, the reaction temperature is 90±10 ℃ and the reaction time is 10±5 min.
[0017] Preferably, the reactive extruder includes a single-screw reactive extruder, a twin-screw reactive extruder, or a combined single / twin-screw reactive extruder system.
[0018] The preparation method of the hydrogel slow-release fertilizer is a reactive extrusion method combined with a dual initiation system. The original starch and monomer are first added to water for gelatinization, and then the encapsulating material, dual initiators and crosslinking agents are added to the gelatinization reaction system to initiate a polymerization reaction.
[0019] Preferably, the gelatinization temperature is 90±10 ℃; the order of addition of the dual initiators is cerium ammonium nitrate and persulfate.
[0020] This invention relates to an environmentally friendly humic acid-encapsulated hydrogel slow-release fertilizer, prepared from natural raw materials starch and humic acid or its salts encapsulated in a continuous reactive extrusion method combined with a dual-initiation system grafted with copolyacrylamide or acrylic monomers. With the addition of a small amount of water, this invention forms a high-viscosity gelatinized solution, which can be reacted directly in a reactive extruder. The reaction is rapid (requiring only about 10 minutes), and the resulting product requires no post-processing steps such as washing or drying. This achieves a green reaction throughout the entire process (raw materials, processing, and product).
[0021] Compared with the prior art, the present invention has the following advantages:
[0022] (1) The present invention is a reaction extrusion method combined with a dual initiation system. The reaction only takes about 10 minutes, which is continuous and efficient. At the same time, it improves the grafting efficiency and polymerization efficiency in the chemical reaction, which is conducive to the formation of a complete and dense three-dimensional network structure, laying the foundation for high loading and ultra-long sustained release of humic acid (salt).
[0023] (2) The environmentally friendly humic acid (salt) hydrogel slow-release fertilizer described in this invention has a higher humic acid (salt) loading, higher gel strength and better slow-release performance, with a slow-release period of more than 70 days.
[0024] (3) The humic acid (salt) loaded in the environmentally friendly humic acid (salt) hydrogel slow-release fertilizer described in this invention can be gradually dissolved and penetrated into the soil through a two-way permeation mechanism, which can improve the soil structure and texture, thereby improving the soil's permeability and water retention, and activating soil nutrients. It is a non-toxic and pollution-free fertilizer that avoids the negative impact on soil and crops caused by long-term use.
[0025] (4) The product process and quality of the present invention are easy to control, which is conducive to industrial production. The main raw materials are humic acid (salt) and starch, which are degradable, renewable, low-carbon and environmentally friendly, cheap and readily available. This not only controls the cost, but also allows the product to be degraded by microorganisms in the soil, thus avoiding environmental pollution and crop quality. Attached Figure Description
[0026] Figure 1The rheological curves are shown for the environmentally friendly potassium humate hydrogel slow-release fertilizers prepared in Examples 1-5 and the materials prepared in the comparative examples.
[0027] Figure 2 Scanning electron microscope (SEM) images of the microstructure of the environmentally friendly potassium humate hydrogel slow-release fertilizer prepared in Examples 1-5 and the materials prepared in the comparative examples.
[0028] Figure 3 The slow-release kinetic curves are shown for the environmentally friendly potassium humate hydrogel slow-release fertilizers prepared in Examples 1-5.
[0029] Figure 4 This is a comparison chart of the slow-release period of the environmentally friendly potassium humate hydrogel slow-release fertilizer prepared in Example 3 and three other reported slow-release fertilizers.
[0030] Figure 5 Images of the environmentally friendly potassium humate hydrogel slow-release fertilizers prepared in Examples 1-5 and the material samples prepared in the comparative examples. Detailed Implementation
[0031] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.
[0032] Unless otherwise specified in the embodiments and comparative examples of this invention, the conditions were performed under conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, were commercially available products.
[0033] The preparation process of the comparative examples and embodiments of this invention is as follows: Acrylamide and starch are first added to deionized water and gelatinized at 90 °C. Then, potassium humate encapsulation material, cerium ammonium nitrate, ammonium persulfate, and N,N-methylenebisacrylamide are sequentially added to the gelatinization reaction system (reactive extruder) to initiate the polymerization reaction. The specific raw material amounts and reaction conditions are as follows:
[0034] Comparative Example
[0035] Acrylamide (2.5 g), starch (5 g), cerium ammonium nitrate (0.0375 g), potassium persulfate (0.0375 g), and N,N-methylenebisacrylamide (2.5 mg) were dispersed in 25 ml of deionized water and reacted in an extruder at 90 °C for 10 min.
[0036] In Examples 1-3, the potassium humate embedding material was prepared by a pulverizing-mixing-grinding process using potassium humate and liquid paraffin (mass ratio 14:1), and samples with particle sizes (50-200 μm) were screened for later use.
[0037] Example 1
[0038] Acrylamide (2.5 g), starch (5 g), potassium humate encapsulation (0.375 g), cerium ammonium nitrate (0.0375 g), potassium persulfate (0.0375 g), and N,N-methylenebisacrylamide (2.5 mg) were dispersed in 25 ml of deionized water and reacted in an extruder at 90 °C for 10 min.
[0039] Example 2
[0040] Acrylamide (2.5 g), starch (5 g), potassium humate encapsulation (0.75 g), cerium ammonium nitrate (0.0375 g), potassium persulfate (0.0375 g), and N,N-methylenebisacrylamide (2.5 mg) were dispersed in 25 ml of deionized water and reacted in an extruder at 90 °C for 10 min.
[0041] Example 3
[0042] Acrylamide (2.5 g), starch (5 g), potassium humate encapsulation (1.5 g), cerium ammonium nitrate (0.0375 g), potassium persulfate (0.0375 g), and N,N-methylenebisacrylamide (2.5 mg) were dispersed in 25 ml of deionized water and reacted in an extruder at 90 °C for 10 min.
[0043] Example 4
[0044] Acrylamide (2.5 g), starch (5 g), potassium humate encapsulation (1.5 g), cerium ammonium nitrate (0.0375 g), and N,N-methylenebisacrylamide (2.5 mg) were dispersed in 25 ml of deionized water and reacted in an extruder at 90 °C for 10 min.
[0045] Example 5
[0046] Acrylamide (2.5 g), starch (5 g), potassium humate encapsulation (1.5 g), cerium ammonium nitrate (0.0375 g), potassium persulfate (0.0375 g), and N,N-methylenebisacrylamide (2.5 mg) were dispersed in 250 ml of deionized water and reacted at 90 °C for 2 h. The mixture was then washed with methanol-water solution.
[0047] The environmentally friendly potassium humate hydrogel slow-release fertilizers obtained in Examples 1-5 above are in black and brown gel states, while the comparative example is in white gel state.
[0048] Structural characterization and performance testing:
[0049] (a) Rheological properties test of the slow-release fertilizers prepared in Examples 1-5 of the present invention and the materials prepared in the comparative examples.
[0050] The rheological properties of the samples were investigated using a Discovery hybrid rheometer (TA Instruments, USA) with a stainless steel parallel plate geometry (d = 20 mm). For each measurement, a disc-shaped hydrogel sample with a diameter of 20 mm and a thickness of 2 mm was prepared. Prior to oscillation measurements, the linear viscoelastic region of the hydrogel samples was measured by strain scanning (0.1–100%) at 25 °C and 1 rad / s. Environmental frequency scanning was performed within the angular frequency range of 1–100 rad / s with a fixed strain of 0.1%.
[0051] Figure 1 The rheological property test curves are for the slow-release fertilizers prepared in Examples 1-5 and the materials prepared in the comparative examples.
[0052] Figure 1 It can be seen that the G' and G'' values of Examples 1-3 are comparable to those of the Comparative Example, indicating that Examples 1-3 and the Comparative Example have similar viscoelasticity, and the viscoelasticity of Examples 1-3 is not reduced by the addition of potassium humate, which has a polymerization inhibitory effect. This also demonstrates that the humic acid encapsulation method can effectively stabilize potassium humate. Furthermore, Examples 4 and 5 show the rheological test results of samples prepared by a single initiator combined with reactive extrusion and a dual initiator system combined with a water bath method, respectively. The values of G' and G" in Example 4 are significantly lower than those in the comparative example, and the difference between G' and G" is smaller. Therefore, Example 4 exhibits weaker viscoelasticity. This example demonstrates that the dual initiator system has a higher graft polymerization efficiency than the single initiator system. The values of G' and the difference between G' and G'" in Example 5 are both lower than those in Example 4. Example 5 exhibits weaker viscoelasticity than Example 4, indicating that the synthesis method in Example 5 has lower reaction efficiency. Example 5 also uses more reaction solvent (250 ml) and reaction time (2 h), and also generates a large amount of waste liquid. This shows that reactive extrusion is a more efficient and greener preparation method than solvothermal methods. In summary, Examples 1-5 and the comparative example show that reactive extrusion combined with a dual initiator system is a greener and more efficient preparation method.
[0053] (ii) Scanning electron microscope (SEM) images of the gel microstructure of the slow-release fertilizers prepared in Examples 1-5 of this invention and the materials prepared in the comparative examples.
[0054] Cross-sectional imaging of untreated embedded potassium humate hydrogels was performed using scanning electron microscopy (SEM). A Phenom ProX G6 benchtop SEM (Thermo Fisher Scientific, America) with a cryo-grade filter was used for this characterization. Scanning was performed at 15 kV and a high vacuum of -25 °C. The embedded potassium humate hydrogels were frozen to -25 °C before scanning and maintained at a stable temperature (-25 °C) throughout the process for SEM imaging.
[0055] Figure 2 Scanning electron microscope (SEM) images of the microstructure of the environmentally friendly potassium humate hydrogel slow-release fertilizer prepared in Examples 1-5 and the materials prepared in the comparative examples.
[0056] Figure 2 It can be seen that the slow-release fertilizers prepared in Examples 1-3 and the comparative materials possess a dense, porous three-dimensional network structure. Compared with the comparative example, the three-dimensional network structure of Examples 1-3 has no obvious defects. This characterization explains why the comparative example and Examples 1-3 exhibit comparable viscoelasticity. It also further proves that the humic acid encapsulation method can effectively stabilize potassium humate, and the addition of potassium humate, which has a polymerization inhibitory effect, did not affect the polymerization reaction. In addition, the porous three-dimensional network structure of the environmentally friendly potassium humate encapsulated hydrogel slow-release fertilizer prepared in Examples 1-3 provides conditions for the slow release of humic acid. Furthermore, the three-dimensional network structure of the material prepared in Example 4 has obvious defects (the network structure is not dense, and there is obvious separation and discontinuity between the networks), which is also the reason for its poor viscoelasticity. The three-dimensional network structure of the material prepared in Example 5 is coarse, with a large number of unreacted starch chains, exhibiting poor viscoelasticity.
[0057] (III) Potassium humate release kinetic curves of the slow-release fertilizers prepared in Examples 1-3 of this invention.
[0058] The experimental method used in this test was based on the method described in published literature (Wei H, Wang H, et al. Preparation and characterization of slow-release and water-retention fertilizer based on starch and halloysite[J]. International journal of biological macromolecules, 2019, 133: 1210-1218). An improved method was used to study the potassium humate release rate in water from the embedded potassium humate hydrogel. For each measurement, 0.5 g of sample and 5 mL of water were added to the activated dialysis bag. The dialysis bag was then transferred to an Erlenmeyer flask containing 500 mL of distilled water. At regular intervals (0.5 h, 1 h, 2 h, 4 h, 8 h, 1 day, 2 days, 3 days, 5 days, 12 days, 14 days, 21 days, 28 days, 35 days, 42 days, 49 days, 56 days, 63 days, 70 days), 5 mL of the leachate was taken from the flask for potassium humate content determination. Simultaneously, an equal volume of distilled water was immediately added to the culture system to maintain a constant solvent (stirring for 30 seconds before sampling to ensure homogeneous mixing). The concentration of potassium humate in the solution was determined using UV spectrophotometry according to standard operating procedures. Each release experiment was repeated three times, and the results given are based on the average value.
[0059] Figure 3 The slow-release kinetic curves are shown for the environmentally friendly potassium humate hydrogel slow-release fertilizers prepared in Examples 1-5.
[0060] Figure 3 It can be seen that the potassium humate in Examples 1-5 initially exhibits an explosive release, mainly originating from the release of potassium humate from the shallow layer and surface of the potassium humate-encapsulated gel. It then enters a slow release phase. The gel network structures of Examples 4 and 5 are discontinuous and coarse, with release periods of 14 days and 28 days, respectively. In contrast, the gel network structures of Examples 1-3 are complete and dense, with a release period reaching up to 70 days, demonstrating excellent slow-release kinetics.
[0061] (III) Comparison of potassium humate release kinetics in Example 3 of the present invention with the slow-release kinetics of previously reported slow-release fertilizers.
[0062] Figure 4 The diagram shows a comparison of the slow-release cycles of the environmentally friendly potassium humate hydrogel slow-release fertilizer prepared in Example 3, three other reported urea slow-release fertilizers (U-2, U-6), and sodium humate slow-release fertilizer (SAR).
[0063] Figure 4It can be seen that U-2 and U-6 exhibit very fast release cycles. The release rate of urea reaches more than 90% on days 3 and 3.5, the release rate of sodium humate in SAR reaches more than 90% on day 30, and the release rate of potassium humate in Example 3 reaches more than 90% on day 70. They have better slow-release kinetics and provide the necessary conditions for continuously providing nutrients to crops. The slow-release period data for U-2 and U-6 are referenced from published literature (Chen F, Miao C, Duan Q, et al. Developing slowrelease fertilizer through in-situ radiation-synthesis of urea-embeddedstarch-based hydrogels[J]. Industrial Crops and Products, 2023, 191:115971.), and the slow-release period data for SAR are referenced from published literature (Yu X, Wang Z, Liu J, et al. Preparation, swelling behaviors and fertilizer-release properties of sodiumhumate modified superabsorbent resin[J]. Materials Today Communications, 2019, 19: 124-130.).
Claims
1. An environmentally friendly hydrogel slow-release fertilizer encapsulating humic acid or its salt, characterized in that, Using water as the reaction medium, native starch, monomers, humic acid or its salt encapsulated material, dual initiators, and crosslinking agents undergo a graft polymerization reaction in a reactive extruder to obtain an environmentally friendly hydrogel slow-release fertilizer encapsulated with humic acid or its salt; the dual initiators are cerium ammonium nitrate and persulfate; the monomers are one or more of acrylamide and acrylic acid monomers; The embedding material is prepared by mixing humic acid or its salt with an embedding agent, followed by crushing and grinding. The embedding agent is one or more of stearic acid, stearate, and liquid paraffin; The amount of the encapsulating agent used is 1 to 20% of the mass of humic acid or its salt.
2. The hydrogel slow-release fertilizer according to claim 1, characterized in that, The mass-to-volume ratio of the original starch to water is 0.1-1.0 g / mL; The amount of the monomer used is 10-50% of the starch mass; The amount of the embedding material used is 5-99% of the starch mass; The amounts of cerium ammonium nitrate and persulfate used are both 0.1-1.0% of the starch mass.
3. The hydrogel slow-release fertilizer according to claim 2, characterized in that, The humic acid or its salts include one or more of potassium humate, sodium humate, nitrohumic acid, potassium nitrohumate, sodium nitrohumate, and biochemical humic acid; the crosslinking agent is an organic dicarboxylic acid, a polyol, or a compound containing multiple unsaturated double bonds within its molecule.
4. The hydrogel slow-release fertilizer according to claim 2, characterized in that, The humic acid or its salt is one or more of fulvic acid, potassium fulvicate, and sodium fulvicate; the crosslinking agent is an organic dicarboxylic acid, a polyol, or a compound containing multiple unsaturated double bonds within its molecule.
5. The hydrogel slow-release fertilizer according to claim 3, characterized in that, The crosslinking agent is N,N-methylenebisacrylamide; the persulfate is one or more of potassium persulfate, sodium persulfate, and ammonium persulfate; and the native starch is natural corn starch.
6. The hydrogel slow-release fertilizer according to any one of claims 1-5, characterized in that, The reaction temperature is 60~120℃; the reaction time is 2~20 min.
7. The hydrogel slow-release fertilizer according to claim 6, characterized in that, The reaction temperature was 90±10 ℃; the reaction time was 10±5 min.
8. The hydrogel slow-release fertilizer according to claim 7, characterized in that, The reactive extruder includes a single-screw reactive extruder, a twin-screw reactive extruder, and a combined single / twin-screw reactive extruder system.
9. A method for preparing the hydrogel slow-release fertilizer according to any one of claims 1-8, characterized in that, The original starch and monomers are first added to water for gelatinization, and then the encapsulating agent, dual initiators and crosslinking agent are added to the gelatinization reaction system to initiate the polymerization reaction.
10. The preparation method according to claim 9, characterized in that, The gelatinization temperature is 90±10 ℃; the order of addition of the dual initiators is cerium ammonium nitrate and persulfate.