Polyaspartic acid chelated zinc and a method for preparing the same

Abstract

This invention proposes a polyaspartic acid chelated zinc and its preparation method, belonging to the technical field of polyaspartic acid materials. The preparation method of the polyaspartic acid chelated zinc includes: polymerizing L-aspartic acid under a phosphoric acid catalyst to obtain a polysuccinimide intermediate; and mixing the polysuccinimide intermediate with... α‑ After undergoing a ring-opening grafting reaction with amino acids and aminolated oligosaccharides, polyaspartic acid derivatives are obtained. The polyaspartic acid derivatives are then chelated with zinc salts to obtain the polyaspartic acid chelated zinc. This invention obtains polyaspartic acid chelated zinc by grafting α-amino acids and aminolated oligosaccharides onto polyaspartic acid molecules as modifiers followed by zinc chelation. Compared to ordinary polyaspartic acid zinc, it has a higher molecular weight and stronger chelating functional groups, thus enabling effective chelation of zinc ions. When used as a fertilizer synergist, it can effectively improve crop yield and quality.

Description

Technical Field

[0001] This invention relates to the field of polyaspartic acid materials technology, and in particular to a polyaspartic acid chelated zinc and its preparation method. Background Technology

[0002] Polyaspartic acid (PASP) is a water-soluble polymer formed by the polymerization of aspartic acid monomers via amide bonds. Its molecular chain contains numerous active functional groups such as carboxyl and amide groups, making it phosphorus-free, non-toxic, and completely biodegradable, thus internationally recognized as a "green chemical." Polyaspartic acid and its salts (such as potassium polyaspartate and zinc polyaspartate) have been widely used in water treatment, detergents, cosmetics, agriculture, and other fields.

[0003] In agriculture, zinc is an essential micronutrient for crop growth, participating in key physiological processes such as the activation of various enzymes, auxin synthesis, protein metabolism, and photosynthesis. Zinc deficiency in crops can lead to typical symptoms such as stunted seedling disease in rice, white spot disease in corn, and little leaf disease in fruit trees, severely impacting crop yield and quality. Therefore, scientifically supplementing zinc is of great significance for ensuring high-yield and high-quality agriculture and human nutritional health.

[0004] Currently, commonly used zinc fertilizer additives in agricultural production mainly include zinc sulfate and zinc oxide. However, these traditional zinc fertilizer additives have the following prominent problems in practical applications: (1) Low utilization rate: Inorganic zinc fertilizers (such as zinc sulfate and zinc oxide) are easily adsorbed and fixed by soil particles after being applied to the soil, or form insoluble precipitates with phosphate and other substances, resulting in a utilization rate of less than 10% in the current season; (2) Short duration of effect: Existing zinc fertilizer products decompose quickly in the soil and release nutrients in a concentrated manner, which makes it difficult to meet the zinc requirements of crops throughout their entire growth period. Multiple applications are required, which increases production costs. (3) Environmental pollution risk: Excessive or improper application of zinc fertilizer can easily leach into water bodies with rainwater, causing soil and water pollution and affecting the ecological balance; (4) Antagonism with phosphate fertilizer: Zinc ions (Zn 2+ ) and phosphate (PO4) 3- There is a clear antagonistic effect between them, and traditional zinc fertilizers should not be mixed with phosphate fertilizers, which limits their application in compound fertilizers; To address the aforementioned issues, researchers have attempted to chelate zinc ions with organic ligands to improve zinc stability and bioavailability. Polyaspartic acid, due to its excellent biocompatibility, chelating ability, and biodegradability, has been used to prepare polyaspartic acid chelated zinc (polyaspartic acid zinc). Existing literature reports the application of polyaspartic acid zinc in fertilizers, such as as a zinc fertilizer additive or fertilizer synergist. However, current technologies and products still have the following significant shortcomings: (1) Low molecular weight: Currently, commercially available zinc polyaspartate salts generally have low molecular weight (usually in the range of 3000-10000 Da) and short molecular chains, resulting in limited chelation sites and insufficient chelation ability for zinc ions, making it difficult to form a stable chelation structure.

[0005] (2) Weak adsorption capacity: Low molecular weight polyaspartic acid zinc salt has a weak adsorption capacity in soil and is easily lost with water migration, which reduces the retention of zinc additives.

[0006] (3) Limited water and fertilizer retention capacity: Existing products have insufficient water and fertilizer retention capacity, making it difficult to play an ideal role in enhancing efficiency in arid or semi-arid regions.

[0007] (4) Fast decomposition rate: Low molecular weight polyaspartic acid zinc salt degrades rapidly in the soil and has a short nutrient release cycle, which cannot meet the needs of crops throughout the growing season.

[0008] (5) Insufficient functional group content: High molecular weight means that the molecular chain contains more functional groups such as carboxyl groups and amide groups, which are active sites for chelating metal ions. Existing low molecular weight products have low functional group density and limited chelating ability.

[0009] Based on the current state of technology, existing polyaspartic zinc salts suffer from inherent defects such as low molecular weight and weak chelating ability, making it difficult to achieve effective zinc supply. Consequently, their effect on promoting crop yield is significantly limited. Therefore, developing an efficient method for preparing polyaspartic zinc salts is of great practical significance. It has important technical value and application prospects for solving the problem that existing polyaspartic zinc salts, as zinc fertilizer additives, have limited effects on crop yield due to their generally low molecular weight and weak chelating ability. Summary of the Invention

[0010] Based on the technical problems existing in the background art, the present invention proposes a polyaspartic acid chelated zinc and its preparation method. The polyaspartic acid chelated zinc is obtained by grafting α-amino acids and amino-modified oligosaccharides onto polyaspartic acid molecules as modifiers and then chelating zinc. Compared with ordinary polyaspartic acid zinc, it has a higher molecular weight and stronger chelating functional groups, thereby effectively chelating zinc ions. When used as a fertilizer synergist, it can effectively improve the yield and quality of crops.

[0011] The present invention proposes a method for preparing polyaspartic acid chelated zinc, comprising the following steps: S1. After L-aspartic acid is polymerized under phosphoric acid catalyst, polysuccinimide intermediate is obtained; S2. After performing a ring-opening grafting reaction between the polysuccinimide intermediate and α-amino acids and aminoized oligosaccharides, a polyaspartic acid derivative is obtained. S3. After chelating the polyaspartic acid derivative with zinc salt, the polyaspartic acid chelated zinc is obtained.

[0012] In this invention, the polysuccinimide intermediate obtained by polymerizing L-aspartic acid is subjected to ring-opening grafting reactions with α-amino acids and aminoated oligosaccharides, respectively, and then chelated with zinc to obtain polyaspartic acid chelated zinc. On the one hand, the molecular weight of this polyaspartic acid chelated zinc is greatly increased, which is beneficial for nutrient encapsulation and slow release, prolonging the crop utilization period of nitrogen, phosphorus, and potassium nutrients and improving fertilizer utilization. On the other hand, due to the large number of highly active free carboxyl and hydroxyl groups on the molecular chain, its hydrophilicity is enhanced, chelation sites are sufficient, and it also has high water absorption and water retention capacity. On the other hand, this polyaspartic acid chelated zinc has a strong zinc chelating ability, and the effective zinc content will also increase accordingly. It can provide active nutrients and can be absorbed and utilized in the form of a composite mosaic, determining the radicle dominance effect in the competition between the radicle and plumule during crop germination. The aminoated oligosaccharides can realize the functions of penetration, disease resistance, and biostimulation, thereby quickly opening the crop's nutrient absorption channels.

[0013] Preferably, in step S1, the polymerization reaction includes: first heating to 140-160°C, holding at that temperature for 0.5-2 hours, then heating to 180-200°C, evacuating to -80--15 kPa, holding at that temperature for 1-2 hours, and then heating to 210-220°C, holding at that temperature for 1-2 hours.

[0014] In this invention, the polymerization reaction is first heated to 140–160°C. During this stage, free water is mainly removed, and the polycondensation reaction begins. The rate of water removal is controlled. Then, the temperature is further increased to 180–200°C. This stage is the main polymerization period, during which the molecular chains grow rapidly. Viscosity is measured by sampling, and the intrinsic viscosity is controlled at 0.8–1.2 dL / g. Finally, the temperature is increased to 210–220°C. This stage promotes molecular chain extension and moderate cross-linking. Torque changes are monitored to prevent excessive cross-linking.

[0015] Preferably, in step S2, the general structural formula of the α-amino acid is: R-CH(NH2)-COOH, where R is hydrogen, alkyl, substituted alkyl or aryl containing at least one functional group selected from N, S, O, and P; The α-amino acid is at least one of glycine, L-lysine, glycylglycine, or phenylalanine.

[0016] In this invention, compared to other amino acids, α-amino acids grafted onto polyaspartic acid can form a five-membered ring complex structure with zinc ions, which helps to obtain a stable multidentate chelate structure and solves the problem of weak chelating ability of existing polyaspartic acid zinc for zinc ions. The complex structure is shown below: Preferably, in step S2, the aminoated oligosaccharide is obtained by condensing the oligosaccharide with 2-bromoacetyl bromide and then subjecting it to a quaternization reaction with 3-dimethylaminopropylamine. The oligosaccharide is at least one of mannan oligosaccharide, chitosan oligosaccharide, or seaweed oligosaccharide.

[0017] The structure of the above-mentioned amino-modified oligosaccharide in this invention is shown below: Compared to simple oligosaccharides, aminoated oligosaccharides can utilize their amino functional groups to participate in the ring-opening grafting reaction of polysuccinimide intermediates. This allows oligosaccharides to be chemically grafted onto polyaspartic acid, providing the resulting polyaspartic acid chelate zinc with chelating functional groups such as hydroxyl groups, and endowing the resulting polyaspartic acid chelate zinc with the functions of oligosaccharides such as permeation, disease resistance, and biostimulation.

[0018] Preferably, in step S2, the mass ratio of the polysuccinimide intermediate to α-amino acid and aminolated oligosaccharide is 10:0.5-2:1-5.

[0019] Preferably, in step S2, the temperature of the ring-opening grafting reaction is 170–210°C, and the time is 1–3 hours.

[0020] Preferably, in step S3, the zinc salt is at least one of zinc oxide, zinc sulfate, or zinc hydroxide; Preferably, the mass ratio of the polyaspartic acid derivative to the zinc salt is 12:5-30.

[0021] Preferably, in step S3, the chelation reaction temperature is 50–65°C and the time is 4–6 hours.

[0022] The present invention also proposes a polyaspartic acid chelated zinc, which is prepared by the above preparation method.

[0023] The present invention also proposes a fertilizer synergist comprising the above-mentioned polyaspartic acid chelated zinc.

[0024] Compared with the prior art, the present invention has the following beneficial effects: The polysuccinimide intermediate obtained by polymerizing L-aspartic acid is subjected to ring-opening grafting reactions with α-amino acids and aminoized oligosaccharides, respectively, and then chelated with zinc to obtain the polyaspartic acid chelated zinc. This method has important technical value and application prospects for solving the problem that existing polyaspartic acid zinc as a zinc fertilizer additive has limited effect on increasing crop yield due to its generally low molecular weight and weak chelating ability. Attached Figure Description

[0025] Figure 1 The infrared spectrum of the polyaspartic acid chelated zinc described in Example 1 of this invention; Figure 2 This is the GPC spectrum of the polyaspartic acid chelated zinc described in Example 1 of the present invention. Detailed Implementation

[0026] 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.

[0027] Example 1 A polyaspartic acid chelated zinc is prepared by the following method: (1) Disperse the mannan oligosaccharide evenly in diethyl ether, then add 5 wt% of 2-bromoacetyl bromide of mannan oligosaccharide, heat to 40°C under nitrogen protection, stir for 6 h, centrifuge, wash with water to obtain mannan oligosaccharide containing bromomethyl; disperse the mannan oligosaccharide containing bromomethyl in ethanol evenly, add 5 wt% of 3-dimethylaminopropylamine of mannan oligosaccharide, heat to 60°C, stir for 6 h, centrifuge, wash with alcohol, dry to obtain aminoated oligosaccharide; (2) Add L-aspartic acid to the reaction vessel, add 5wt% phosphoric acid of L-aspartic acid, stir and mix well, raise the temperature to 150°C at a rate of 5°C / min, keep it at the temperature for 1 hour, raise the temperature to 190°C at a rate of 3°C / min, evacuate to -0.05MPa, keep it at the temperature for 1.5 hours, raise the temperature to 210°C at a rate of 2°C / min, evacuate to -0.08MPa, keep it at the temperature for 1.5 hours, lower the temperature to 150°C at a rate of 5°C / min, lower the temperature to 80°C at a rate of 10°C / min, and purge with nitrogen to break the vacuum to obtain polysuccinimide intermediate; Glycine and amino oligosaccharides were added according to the mass ratio of the polysuccinimide intermediate to glycine and amino oligosaccharides of 10:1:3. The temperature was increased to 190°C at a rate of 5°C / min, and held for 2 hours. Then the temperature was cooled to room temperature to obtain the polyaspartic acid derivative. (3) After adding pure water to the above-mentioned grafted polyaspartic acid derivative and stirring for 1 hour, a zinc oxide dispersion containing 15 wt% of the polyaspartic acid derivative was added. The mixture was heated to 60°C and stirred for 3 hours. Then, a zinc sulfate dispersion containing 5 wt% of the polyaspartic acid derivative was added dropwise. The mixture was heated to 70°C and stirred for 4 hours. After aging for 2 hours, the pH was adjusted to 7.0 ± 0.2 with a dilute sodium hydroxide solution (1 mol / L). The mixture was then filtered through a precision filter and vacuum concentrated to a solid content of 40-45 wt%, yielding a brownish-red transparent viscous liquid, which is the polyaspartic acid chelated zinc (determined by gel chromatography). W (32689).

[0028] The structural diagram of the polyaspartic acid chelated zinc is as follows: Its infrared spectrum is as follows Figure 1 As shown, refer to Figure 1 It can be known that 3426cm -1 The peak at 1716 cm⁻¹ is a superposition absorption peak of -OH and NH. -1 The peak of the stretching vibration at C=O is 1393 cm⁻¹. -1 The peak of the bending vibration of NH is located at 1292 cm⁻¹; fingerprint region. -1 1176cm -1 968cm -1 801cm -1 and 624cm -1 The values ​​at 1032 cm⁻¹ represent the bending absorption peaks of CH, the bending absorption peaks of OH, and their variation peaks, respectively. -1 A stretching vibration peak connected to -OH appeared at the point. The above peaks were attributed to the polyaspartic acid backbone and the grafted glycine and amino oligosaccharides in the product, respectively, which proved the successful synthesis of the target polyaspartic acid chelated zinc. Its GPC spectrum is as follows Figure 2 As shown, refer to Figure 2 It is known that the number-average molecular weight (Mn) of the polyaspartic acid chelate zinc compound is 17590, the weight-average molecular weight (Mw) is 32689, the molecular weight distribution index (PDI) is 1.86, and the peak molecular weight (Mp) is 31912.

[0029] Example 2 A polyaspartic acid chelated zinc (determination of M by gel chromatography) W The product is 29264, which is prepared by the method described in Example 1, except that chitosan oligosaccharide is used instead of mannan oligosaccharide in step (1).

[0030] Example 3 A polyaspartic acid chelated zinc (determination of M by gel chromatography) WThe formula is 30069, which is prepared by the method described in Example 1, except that L-lysine is used instead of glycine in step (2).

[0031] Example 4 A polyaspartic acid chelated zinc (determination of M by gel chromatography) W The value is 33750, which is prepared by the method described in Example 1, except that zinc hydroxide is used instead of zinc oxide in step (3).

[0032] Comparative Example 1 A polyaspartic acid chelated zinc is prepared by the following method: (1) Add L-aspartic acid to the reaction vessel, add 5wt% phosphoric acid of L-aspartic acid, stir and mix well, raise the temperature to 150°C at a rate of 5°C / min, keep it at the temperature for 1h, raise the temperature to 190°C at a rate of 3°C / min, evacuate to -0.05MPa, keep it at the temperature for 1.5h, raise the temperature to 210°C at a rate of 2°C / min, evacuate to -0.08MPa, keep it at the temperature for 1.5h, lower the temperature to 150°C at a rate of 5°C / min, lower the temperature to 80°C at a rate of 10°C / min, and after purging with nitrogen to break the vacuum, obtain polysuccinimide intermediate; (2) After adding pure water to the above polysuccinimide intermediate and stirring for 1 hour, add zinc oxide dispersion containing 15 wt% of the polysuccinimide intermediate. Heat to 60°C and stir for 3 hours. Then add zinc sulfate dispersion containing 5 wt% of the polysuccinimide intermediate. Heat to 70°C and stir for 4 hours. After aging for 2 hours, adjust the pH to 7.0 ± 0.2 with dilute sodium hydroxide solution (1 mol / L). Filter with a precision filter. Add glycine (10 wt% of the polysuccinimide intermediate) and mannan oligosaccharide (30 wt% of the polysuccinimide intermediate). Vacuum concentrate to a solid content of 40-45 wt% to obtain a viscous liquid, which is the polyaspartic acid chelated zinc (determined by gel chromatography). W (7214).

[0033] Comparative Example 2 A polyaspartic acid chelated zinc is prepared by the method described in Example 1, except that 3-aminopropionic acid (β-alanine) is used instead of glycine in step (2).

[0034] Comparative Example 3 A polyaspartic acid chelated zinc is prepared by the method described in Example 1, except that mannan oligosaccharide is used instead of amino oligosaccharide in step (2).

[0035] Application examples The polyaspartic acid chelated zinc prepared in the examples and comparative examples were used as fertilizer synergists. 5 wt% of each was added to a drum mixer along with 25 wt% urea, 25 wt% monoammonium phosphate, 20 wt% diammonium phosphate, and 25 wt% potassium sulfate. The mixture was stirred and mixed, and 5 wt% water (based on the total weight of the fertilizer) was sprayed in. The mixture was then granulated in a rotary drum granulator, with the particle size controlled to be about 3 mm. The mixture was first initially dried at 80°C for 30 minutes, then cooled to 60°C for 30 minutes, and finally cooled to room temperature with cold air. The qualified particles were then vibrated and sieved to obtain the fertilizers corresponding to the examples and comparative examples.

[0036] The fertilizers prepared according to the examples and comparative examples were used in field trials. Soil in the selected planting areas had the following basic fertility: organic matter 26.31 g / kg, total nitrogen 2.05 g / kg, available nitrogen 158.23 mg / kg, available phosphorus 8.02 mg / kg, and available potassium 147.23 mg / kg. The rice variety was Oryza sativa L. (Daohuaxiang No. 2). Eight treatments were set up, each with three replicates, using a randomized block design. Each plot was 20 m². 2 ; CK: Ordinary base fertilizer (N-P2O5-K2O: 15-15-15) (40g / m³) 2 ) + 0.2% potassium dihydrogen phosphate foliar fertilizer (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Experimental Group 1: Ordinary base fertilizer (N-P2O5-K2O: 15-15-15) (25g / m³) 2 Example 1: Fertilizer for spikelets (15g / m²) 2 ) + 0.2% potassium dihydrogen phosphate foliar fertilizer (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Experimental Group 2: Ordinary fertilizer base fertilizer (N-P2O5-K2O: 15-15-15) (25g / m³) 2 Example 2: Fertilizer for spikelets (15g / m²) 2 ) + 0.2% potassium dihydrogen phosphate foliar fertilizer (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Experimental Group 3: Ordinary base fertilizer (N-P2O5-K2O: 15-15-15) (25g / m³) 2 Example 3: Fertilizer for spikelets (15g / m²) 2 ) + 0.2% potassium dihydrogen phosphate foliar fertilizer (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Experimental Group 4: Ordinary base fertilizer (N-P2O5-K2O: 15-15-15) (25g / m³) 2 Example 4: Fertilizer for spikelets (15g / m²) 2 ) + 0.2% potassium dihydrogen phosphate foliar fertilizer (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Experimental Group 5: Ordinary base fertilizer (N-P2O5-K2O: 15-15-15) (25g / m³) 2 ) + Comparative Example 1 Fertilizer for spikelet growth (15g / m²) 2 ) + 0.2% potassium dihydrogen phosphate foliar fertilizer (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Experimental Group 6: Ordinary base fertilizer (N-P2O5-K2O: 15-15-15) (25g / m³) 2 ) + Comparative Example 2 Fertilizer for spikelet growth (15g / m²) 2 ) + 0.2% potassium dihydrogen phosphate foliar fertilizer (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Experimental Group 7: Ordinary base fertilizer (N-P2O5-K2O: 15-15-15) (25g / m³) 2 ) + Comparative Example 3 Fertilizer for spikelet growth (15g / m²) 2 ) + 0.2% potassium dihydrogen phosphate control foliar fertilizer spray (20mL / m 2 (Spray once each during the tillering stage and the heading stage); Basal fertilizer was evenly spread one day before transplanting and raked into the soil (0-10cm soil layer); panicle fertilizer was applied during the panicle differentiation stage (45 days after transplanting); foliar spraying was carried out evenly at 4 o'clock on sunny days during the tillering stage (25 days after transplanting) and the booting stage (55 days after transplanting), until both sides of the leaves were moist; data were analyzed for correlation using SPSS 18.0.

[0037] Table 1 Observation Indicators and Methods

[0038] Table 2. Characteristics and yield of harvested rice

[0039] Note: Different lowercase letters after the data in the same column in the table indicate that the differences between different treatments are significant at the 0.05 level.

[0040] Table 3. Effects on protein absorption and accumulation

[0041] Note: Different lowercase letters after the data in the same column in the table indicate that the differences between different treatments are significant at the 0.05 level.

[0042] Referring to Tables 2 and 3, it can be seen that the fertilizer treatment of the present invention significantly increases rice yield compared to ordinary fertilizer treatment, and also increases the protein content of rice grains. Among them, treatments 1-4 in the experimental groups not only showed the most significant yield increase, but also the most significant effect in promoting protein synthesis and accumulation. This indicates that after the polysuccinimide intermediate in the examples was ring-opened grafted with α-amino acids and aminoated oligosaccharides respectively, and then chelated with zinc to obtain polyaspartic acid chelated zinc, which is used as a fertilizer synergist, it has a higher molecular weight (M). W (29264-33750), with a stronger chelating functional group (a five-membered ring chelate structure formed after the α-amino acid ring is opened), and after chemically grafting aminoated oligosaccharides, it can also provide chelating functional groups of hydroxyl groups, exerting the functions of oligosaccharide biostimulation, etc. Therefore, it can not only increase the efficiency of nutrient absorption and utilization and improve photosynthetic efficiency to achieve increased yield, but also improve nitrogen utilization, enhance the activity of key enzymes in nitrogen metabolism (such as nitrate reductase and glutamine synthase) to promote protein synthesis and accumulation, and improve amino acid composition, including an increase in the proportion of essential amino acids and an increase in the proportion of gluten.

[0043] The experimental group 5 showed the worst yield increase and the worst effect in promoting protein synthesis and accumulation, indicating that the conventional polyaspartic acid zinc obtained by directly chelating zinc with the polysuccinimide intermediate without ring-opening grafting with α-amino acids and aminoated oligosaccharides in Comparative Example 1 has a low molecular weight (M W (7214), with weak chelating ability, cannot be grafted with oligosaccharides, which greatly reduces its efficiency in increasing nutrient absorption and utilization. At the same time, its effect on enhancing the activity of key enzymes in nitrogen metabolism is also limited. Therefore, its effect on increasing production and promoting protein synthesis and accumulation is not obvious.

[0044] The yield increase and the effect of promoting protein synthesis and accumulation after treatment in experimental group 6 were only average. This indicates that although polyaspartic acid chelated zinc was obtained by ring-opening grafting of polysuccinimide intermediate with amino acids and aminolated oligosaccharides and then chelating zinc in Comparative Example 2, the use of β-amino acids instead of α-amino acids resulted in a relatively weak chelating ability for zinc because the former could not form a stable five-membered ring chelate structure. Consequently, its ability to increase nutrient absorption and utilization efficiency was reduced, and its effect on enhancing the activity of key enzymes in nitrogen metabolism was also limited. Although the obtained polyaspartic acid chelated zinc could increase yield and promote protein synthesis and accumulation, the effect was only average.

[0045] The yield increase and protein synthesis and accumulation promotion effects of the treatment in experimental group 7 were also mediocre. This indicates that although polyaspartic acid chelated zinc was obtained by ring-opening grafting of polysuccinimide intermediate with amino acids and mannooligosaccharides and then chelating zinc in Comparative Example 3, the use of mannooligosaccharides instead of aminated mannooligosaccharides meant that the former could not achieve chemical bonding with polyaspartic acid because it lacked amino functional groups to participate in the grafting and ring-opening reaction. At most, it could only form a certain adsorption through hydrogen bonds. Therefore, the oligosaccharide content on the grafted polyaspartic acid chelated zinc was relatively low, and its chelating ability for zinc was relatively weak. Similarly, its efficiency in increasing nutrient absorption and utilization was reduced, and its effect on enhancing the activity of key enzymes in nitrogen metabolism was also limited. Although the obtained polyaspartic acid chelated zinc could increase yield and promote protein synthesis and accumulation, the effect was only mediocre.

[0046] 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 method for preparing polyaspartic acid chelated zinc, characterized in that, Includes the following steps: S1. After L-aspartic acid is polymerized under phosphoric acid catalyst, polysuccinimide intermediate is obtained; S2. After performing a ring-opening grafting reaction between the polysuccinimide intermediate and α-amino acids and aminoized oligosaccharides, a polyaspartic acid derivative is obtained. S3. After chelating the polyaspartic acid derivative with zinc salt, the polyaspartic acid chelated zinc is obtained.

2. The method for preparing polyaspartic acid chelated zinc according to claim 1, characterized in that, In step S1, the polymerization reaction includes: first heating to 140-160°C, holding at that temperature for 0.5-2 hours, then heating to 180-200°C, evacuating to -80--15 kPa, holding at that temperature for 1-2 hours, and then heating to 210-220°C, holding at that temperature for 1-2 hours.

3. The method for preparing polyaspartic acid chelated zinc according to claim 1 or 2, characterized in that, In step S2, the general structural formula of the α-amino acid is: R-CH(NH2)-COOH, where R is hydrogen, alkyl, substituted alkyl or aryl containing at least one functional group of N, S, O, and P; The α-amino acid is at least one of glycine, L-lysine, glycylglycine, or phenylalanine.

4. The method for preparing polyaspartic acid chelated zinc according to claim 1 or 2, characterized in that, In step S2, the aminoated oligosaccharide is obtained by condensing the oligosaccharide with 2-bromoacetyl bromide and then subjecting it to a quaternization reaction with 3-dimethylaminopropylamine. The oligosaccharide is at least one of mannan oligosaccharide, chitosan oligosaccharide, or seaweed oligosaccharide.

5. The method for preparing polyaspartic acid chelated zinc according to claim 1 or 2, characterized in that, In step S2, the mass ratio of the polysuccinimide intermediate to α-amino acid and aminolated oligosaccharide is 10:0.5-2:1-5.

6. The method for preparing polyaspartic acid chelated zinc according to claim 1 or 2, characterized in that, In step S2, the temperature of the ring-opening grafting reaction is 170–210°C, and the time is 1–3 hours.

7. The method for preparing polyaspartic acid chelated zinc according to claim 1 or 2, characterized in that, In step S3, the zinc salt is at least one of zinc oxide, zinc sulfate, or zinc hydroxide; The mass ratio of the polyaspartic acid derivative to the zinc salt is 12:5-30.

8. The method for preparing polyaspartic acid chelated zinc according to claim 1 or 2, characterized in that, In step S3, the chelation reaction temperature is 50–65°C and the time is 4–6 hours.

9. A polyaspartic acid chelated zinc, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. A fertilizer synergist, characterized in that, Includes the polyaspartic acid chelated zinc as described in claim 9.

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