A nanocellulose-based composite material with a slow-release function and a preparation method thereof

Abstract

The application provides a nanocellulose-based composite material with a slow-release function and a preparation method thereof, and comprises the following steps: adding beta-cyclodextrin into a silane coupling agent solution to obtain aminated cyclodextrin, and adding the aminated cyclodextrin into a polylactic acid solution to obtain grafted and modified cyclodextrin; adding a compound fertilizer, and freeze-drying to obtain a coated and modified compound fertilizer; soaking citric acid modified nanocellulose in ethanol and heating to form a suspension, adding L-cysteine and heating to obtain grafted and modified nanocellulose; adding the compound and modified solution drop by drop into a bentonite suspension to obtain a compound and modified bentonite; mixing chitosan, sodium alginate and deionized water to obtain a mixed solution; adding the coated and modified compound fertilizer, the grafted and modified nanocellulose and the compound and modified bentonite to obtain a composite sol; adding the composite sol drop by drop into a calcium salt solution to obtain a hydrogel microbead precursor; soaking the hydrogel microbead precursor in a sulfate solution to obtain a composite hydrogel microbead; and freeze-drying.

Description

Technical Field

[0001] This invention belongs to the field of crop yield enhancement technology, and relates to a nanocellulose-based composite material with slow-release function and its preparation method. Background Technology

[0002] The growth and development of plants can be broadly divided into three stages: the vegetative growth stage, the stage of simultaneous vegetative and reproductive growth, and the reproductive growth stage. In the third growth stage, after grain formation, the plant enters the grain-filling stage. The grain-filling stage refers to the period when starch, protein, and accumulated organic matter produced through photosynthesis are assimilated and stored in the grain. During this stage, foliar fertilization is the primary method. Applying foliar fertilizers to supplement phosphorus, potassium, and water-soluble micronutrients during the grain-filling stage can promote the smooth progress of the grain-filling process.

[0003] The main method of foliar fertilization is foliar application, which involves spraying nutrients onto the surface of plant leaves using liquid spray. The nutrients are then transported to the interior of the leaves through penetration, diffusion, and active absorption, where they can be absorbed and utilized by the plant. Its advantages are: (1) Since it does not require soil fertilization, it avoids the fixation and decomposition of certain mineral elements and physiological active factors in the soil, so foliar fertilization can improve the utilization efficiency of fertilizers; (2) Compared with soil fertilization, the amount of fertilizer used in foliar fertilization is only 1 / 10 to 1 / 4 of that in soil fertilization, which can reduce a large amount of soil fertilization and avoid the pollution of soil and water caused by excessive application of chemical fertilizers; (3) Foliar fertilization is more targeted, and can spray the nutrients needed for crop growth at different growth stages and different growth environments, quickly correct and improve the symptoms of crop deficiency, promote plant growth, and improve yield and quality; (4) Foliar fertilization is a liquid mist spray, which can form a protective film on the leaf surface while supplementing nutrients, inhibiting the reproduction and destruction of harmful microorganisms on the leaf surface, improving the function of active enzymes, etc., and achieving the effects of disease prevention and antibacterial, and promoting plant growth.

[0004] Currently, there are many types of foliar fertilizers on the market, mainly including inorganic nutrient type, hormone-regulating type, and biological type, etc. Their main function is to provide nutrients to crops and regulate crop growth. However, due to different raw material sources, different types of foliar fertilizers vary greatly in function. For example, inorganic nutrient foliar fertilizers, like chemical fertilizers, can cause environmental pollution if used excessively; hormone-regulating foliar fertilizers, if used in excess, can inhibit crop growth and require high concentrations.

[0005] Slow-release and controlled-release technology was first applied in drug therapy, using biological methods to encapsulate drugs and release them slowly within the body to adapt to individual absorption patterns and maximize efficacy. Slow-release / controlled-release fertilizers utilize this principle, coating fertilizer granules with a waterproof membrane to prevent liquid water from passing through, temporarily isolating the fertilizer granules from the external environment. This allows the fertilizer to be released slowly into the soil over a period of time, or its release rate to be controlled to match the crop's growth cycle. Slow-release / controlled-release fertilizers are characterized by low soil nitrogen loss and high utilization rate of fertilizer in a single application, reducing environmental pollution caused by excessive foliar fertilization. Compared to traditional chemical fertilizers, they have significant implications for sustainable agricultural development and environmental protection.

[0006] To address the environmental pollution and difficulty in controlling the concentration associated with foliar fertilizers, it is urgent to improve the existing foliar fertilizer preparation process. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a nano-cellulose-based composite material with slow-release function and its preparation method. This invention uses sodium alginate and chitosan as gel carriers to prepare composite hydrogel microspheres loaded with compound fertilizer via a gelation method. The slow-release function is achieved through compounding with β-cyclodextrin and bentonite. The nano-cellulose-based composite material prepared by this invention, when used as a foliar fertilizer, can produce different release rates and effects at different stages of crop growth and development, showing broad application prospects in actual production.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a nano-cellulose-based composite material with sustained-release function, the preparation method comprising:

[0010] (I) A compound fertilizer is obtained by ball milling a mixture of diammonium hydrogen phosphate, potassium sulfate, ammonium molybdate, calcium nitrate, zinc sulfate, magnesium sulfate, copper sulfate, protease, and cellulase; β-cyclodextrin is added to a silane coupling agent solution, mixed evenly, and then subjected to a reflux reaction. The reaction product is filtered, washed, and dried to obtain an amino-modified cyclodextrin; the amino-modified cyclodextrin is added to a polylactic acid solution, and after mixing and reaction, a graft-modified cyclodextrin is obtained; the graft-modified cyclodextrin is dispersed in N,N-dimethylformamide to obtain a cyclodextrin solution, the compound fertilizer is added to the cyclodextrin solution, mixed evenly, and then freeze-dried to obtain a coated modified compound fertilizer;

[0011] (II) Citric acid is added to the nanocellulose solution and mixed evenly to obtain a first reaction solution. The first reaction solution is transferred to a reaction vessel for reaction. The reaction product is filtered, washed and dried to obtain citric acid modified nanocellulose. The citric acid modified nanocellulose is immersed in ethanol and heated to allow the citric acid modified nanocellulose to fully swell in the ethanol to form a suspension. L-cysteine ​​is added to the suspension and mixed evenly to obtain a second reaction solution. The second reaction solution is heated to allow the reaction to occur. The reaction product is filtered, washed and dried to obtain grafted modified nanocellulose.

[0012] (III) Bentonite is added to a silane coupling agent solution, heated and stirred to react, and the reaction product is filtered, washed and dried to obtain amino-modified bentonite; hexadecyltrimethylammonium bromide, polycarboxylic acid metal chelating agent and aluminum hydroxide pillar agent are dispersed in deionized water and mixed evenly to obtain a composite modified solution; the amino-modified bentonite is dispersed in deionized water and mixed evenly to obtain a bentonite suspension, and the composite modified solution is added dropwise to the bentonite suspension, while stirring and heating are carried out continuously during the dropwise addition. After all the dropwise addition is completed, heating is continued for a period of time, and then the composite modified bentonite is obtained after filtration, washing and drying.

[0013] (IV) Chitosan, sodium alginate, and deionized water are mixed and stirred until homogeneous to obtain a mixture; the coated modified compound fertilizer, the grafted modified nanocellulose, and the composite modified bentonite are added to the mixture, and ultrasonic dispersion is performed to obtain a composite sol; the composite sol is added dropwise to a calcium salt solution and soaked for a period of time to obtain a hydrogel microsphere precursor; the hydrogel microsphere precursor is taken out and soaked in a sulfate solution to obtain composite hydrogel microspheres; the composite hydrogel microspheres are freeze-dried to obtain the nanocellulose-based composite material.

[0014] This invention uses sodium alginate and chitosan as gel carriers and achieves a staged slow-release function by combining them with β-cyclodextrin and bentonite. Composite hydrogel microspheres loaded with compound fertilizer were prepared by sol-gel method, and after freeze-drying, nanocellulose-based composite materials were formed. The nanocellulose-based composite materials prepared by this invention can produce different release rates and release effects at different stages of crop growth and development when used as foliar fertilizer, and have broad application prospects in actual production.

[0015] The early stage of crop growth and development is the vegetative growth stage, during which soil fertilization is the main method and foliar fertilization is the supplementary method. Therefore, the release rate of foliar fertilizer should not be too high during this stage, otherwise it will lead to fertilizer excess. The nanocellulose-based composite material prepared by this invention is mainly composed of a composite gel system in the early stage of fertilization. The composite gel system is structurally stable and does not easily absorb water. At the same time, there are three slow-release barriers of β-cyclodextrin, bentonite and gel system in addition to the compound fertilizer. At this time, it is difficult for the compound fertilizer to penetrate through these three slow-release barriers and seep into the external environment. Therefore, the release rate of the compound fertilizer is low at this time and can be carried out simultaneously with soil fertilization.

[0016] The middle stage of crop growth and development is characterized by the simultaneous occurrence of vegetative and reproductive growth. During this stage, soil fertilization and foliar fertilization are carried out concurrently. The release rate of foliar fertilizer during this stage is at a moderate level. The nanocellulose-based composite material prepared in this invention is dominated by the bentonite system during the middle stage of fertilization. At this time, the gel barrier decomposes due to prolonged water absorption, and the pore size on the gel surface gradually increases, thus losing its slow-release barrier function. At this time, the compound fertilizer is encapsulated and adsorbed by β-cyclodextrin into the bentonite layer. Therefore, there are two slow-release barriers, β-cyclodextrin and bentonite, in addition to the compound fertilizer. The compound fertilizer can then seep into the external environment by passing through the two slow-release barriers of β-cyclodextrin and bentonite. Therefore, the release rate of the compound fertilizer at this time is at a moderate level and gradually increases with the fertilization time.

[0017] The later stage of crop growth and development is the reproductive growth stage, during which foliar fertilization is the main method and soil fertilization is the supplementary method. The release rate of foliar fertilizer is relatively high during this stage. The nano-cellulose-based composite material prepared by this invention is mainly composed of β-cyclodextrin system in the later stage of fertilization. At this time, as the nano-cellulose-based composite material continues to absorb water and swell, the coated modified compound fertilizer is separated from the interlayer of boron nitride, and boron nitride also loses its slow-release barrier function. At this time, the compound fertilizer is only encapsulated by β-cyclodextrin. The compound fertilizer can seep into the external environment by passing through the slow-release barrier of β-cyclodextrin. Therefore, the release rate of compound fertilizer reaches the highest level at this time.

[0018] The hydroxyl groups on the cellulose molecular chain are active functional groups capable of undergoing chemical reactions such as oxidation, etherification, and esterification. This invention utilizes citric acid to induce an esterification reaction with nanocellulose. Citric acid, a polycarboxylic acid, contains three carboxylic acid functional groups, with a quaternary carbon as the core, and the three carboxylic acid functional groups surrounding the quaternary carbon, resulting in a tetragonal geometry for the small molecule. The close proximity of the active functional groups leads to stronger reactivity and higher accessibility. In the nanocellulose molecular chain, the secondary hydroxyl group at C6 exhibits high reactivity. Therefore, the carboxyl group on citric acid can react with the secondary hydroxyl group on nanocellulose under mild reaction conditions to form a more stable ester bond, thereby modifying the cellulose aggregate structure. During the esterification process, the two adjacent carboxyl groups in citric acid first dehydrate to form an anhydride, which then further cross-links with the hydroxyl groups on the cellulose molecular chain to form ester bonds, enhancing the internal framework structure of the nanocellulose molecule. The modified nanocellulose, when added to the composite gel system, can effectively improve the stability of the three-dimensional network structure of the composite gel system and, to a certain extent, improve the mechanical properties of the composite hydrogel microspheres.

[0019] Based on citric acid modified nanocellulose, this invention further adds L-cysteine, utilizing the condensation between the amino group in L-cysteine ​​and the carboxyl group in citric acid modified nanocellulose to form an amide bond, thereby grafting L-cysteine ​​onto the molecular chain of citric acid modified nanocellulose. This invention utilizes L-cysteine ​​grafting modification of citric acid-modified nanocellulose to significantly improve the water retention, swelling rate, and sustained-release capacity of the resulting grafted nanocellulose compared to unmodified nanocellulose. This is because, firstly, the sulfonic acid functional group of cysteine ​​is a hydrophilic functional group, which, together with the numerous hydroxyl and carboxyl groups in citric acid-modified nanocellulose, can form hydrophilic channels, resulting in high water retention and swelling rates for the composite hydrogel microspheres. Secondly, the thiol groups on the side chains of L-cysteine ​​molecules chelate with carboxyl groups, which can adsorb metal ions in compound fertilizers, thereby inhibiting the release of compound fertilizers to a certain extent. Furthermore, nanocellulose has excellent biodegradability and can also achieve a sustained-release effect through biodegradation, thus improving the utilization rate of compound fertilizers and meeting the concept of green and sustainable development.

[0020] This invention improves the mechanical properties of nanocellulose-based composite materials by grafting L-cysteine, preventing leakage of the compound fertilizer inside due to external force damage, thus avoiding the direct loss of the slow-release effect. This is because the thiol groups on the side chains of L-cysteine ​​molecules can be reversibly oxidized by air in neutral and weakly alkaline solutions to form covalent disulfide bonds. These disulfide bonds are used for cross-linking to form a tough gel network. In addition, grafting L-cysteine ​​onto the nanocellulose molecular chains increases the number of functional groups such as ester and amino groups. The covalent bonds and the reversible hydrogen bonds generated between molecules have a synergistic effect, which can act as sacrificial bonds to resist external forces, thereby enhancing the mechanical properties of the composite hydrogel microspheres.

[0021] It should be noted that before the amidation reaction is performed before adding L-cysteine, the citric acid-modified nanocellulose needs to be activated with N-hydroxysuccinimide (NHS) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC). The specific steps include: adding EDC to the suspension, stirring at 20-30℃ for 10-15 min, then adding NHS, and continuing stirring at 20-30℃ for 0.5-1 h; wherein the molar ratio of NHS to EDC is 1:1, and the mass ratio of the total mass of NHS and EDC to the mass of citric acid-modified nanocellulose is (0.01-0.1):1. Activating the carboxyl groups in the citric acid-modified nanocellulose with NHS and EDC allows the carboxyl groups in the citric acid-modified nanocellulose to undergo an amidation reaction with the amino group in L-cysteine, without causing the amino group in L-cysteine ​​to undergo an amidation reaction with its own carboxyl group, thus preventing grafting onto the molecular chain of the citric acid-modified nanocellulose.

[0022] This invention uses β-cyclodextrin as the main component to encapsulate the guest compound fertilizer, ultimately forming a coated and modified compound fertilizer. During the mixing process of the compound sol, the β-cyclodextrin on the coated and modified compound fertilizer interacts with the hydroxyl groups on the surface of the grafted and modified nanocellulose through hydrogen bonding, which greatly enhances the interfacial force between the grafted and modified nanocellulose and the coated and modified compound fertilizer, allowing the grafted and modified nanocellulose and the coated and modified compound fertilizer to be uniformly dispersed in the compound sol.

[0023] This invention employs hexadecyltrimethylammonium bromide, polycarboxylated metal chelators, and aluminum hydroxide pillars as multi-component composite modifiers to perform organic-inorganic composite modification of bentonite. The synergistic intercalation effect among these multi-component composite modifiers facilitates the simultaneous entry of different types of intercalating modifiers into the interlayer space of bentonite, thereby effectively increasing the interlayer spacing. On one hand, the polycarboxylated metal chelators, with their relatively small volume and numerous negatively charged branches, can be electrostatically incorporated into the larger, positively charged long-chain hexadecyltrimethylammonium bromide and polyaluminum hydroxide ions, allowing the multi-component composite modifiers to simultaneously insert into the interlayer domains of bentonite, thus increasing its interlayer spacing. On the other hand, both hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions are positively charged, while polycarboxylic acid metal chelators contain multiple carboxyl functional groups. Under certain conditions, these groups dissociate to form negatively charged carboxylate ions. These negatively charged anions can act as a link, bridging the positively charged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions together through electrostatic attraction. The bridged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions can then simultaneously enter the interlayer of bentonite, further increasing the interlayer spacing of the composite modified bentonite. Furthermore, polycarboxylic acid metal chelators contain multiple carboxyl functional groups, while polyhydroxyaluminum pillar agents contain multiple hydroxyl functional groups. A large number of hydrogen bonds easily form between the polycarboxylic acid metal chelators and polyhydroxyaluminum ions. These hydrogen bonds, acting as an auxiliary intermolecular force, can further promote the synergistic insertion of the multi-component composite modifier into the interlayer of bentonite, thus achieving the purpose of multi-component modification.

[0024] The modified composite bentonite of this invention combines the excellent properties of both pillared bentonite and organic bentonite. The aluminum hydroxyl pillar agent, which enters the interlayer, occupies some of the exchangeable ion sites. The positively charged aluminum hydroxyl pillar agent is stably maintained by electrostatic attraction and the excess negative charge between the bentonite layers, aligning along a direction perpendicular to the crystal layers. This expands the interlayer spacing of the bentonite, thereby increasing the adsorption capacity of the composite modified bentonite for coated modified compound fertilizers. This improves the adsorption performance of the composite modified bentonite, enabling it to accommodate more coated modified compound fertilizers. Simultaneously, after organic modification with hexadecyltrimethylammonium bromide, the hexadecyltrimethylammonium bromide and aluminum hydroxyl ions adsorbed between the composite modified bentonite layers exceed the cation exchange capacity of the bentonite. Therefore, the final composite modified bentonite carries a certain positive charge, which, under the effect of charge repulsion, significantly improves its dispersion performance in the composite sol.

[0025] This invention uses sodium alginate and chitosan as carriers for a composite gel system, resulting in a dense three-dimensional porous network structure within the prepared composite hydrogel microspheres. Due to the strong hydrophilicity of sodium alginate, the final composite hydrogel microspheres have a high water content, allowing the formation of large ice crystals during freeze-drying. The ice crystals within the composite hydrogel microspheres sublimate, and air replaces the ice crystals, preserving the original three-dimensional macroporous network structure of the composite hydrogel. This interconnected macroporous structure is beneficial for the dissolution and release of compound fertilizers.

[0026] This invention adds chitosan to sodium alginate, utilizing the electrostatic interaction between sodium alginate and chitosan to increase the cross-linking density of the hydrogel. This results in a denser three-dimensional porous network structure of the composite hydrogel microspheres, extending the release channels of the compound fertilizer within the microspheres and thus hindering its release and penetration, achieving a slow-release effect. Furthermore, the dense three-dimensional porous network structure significantly improves the mechanical strength compared to sodium alginate gel alone. This is because during the ionic cross-linking of sodium alginate and chitosan, both molecules possess numerous functional groups for reaction, leading to a more complete reaction and a greater number of opposite charges. This results in a denser cross-linked network, enhancing the mechanical properties of the composite hydrogel microspheres.

[0027] Sodium alginate exhibits instantaneous gelation upon contact with calcium ions, forming a hydrogel network. Chitosan, on the other hand, can crosslink with sulfate ions to form a stable gel network. Furthermore, the primary amino groups on the chitosan molecular chain and the carboxyl groups on the sodium alginate molecular chain can undergo a polyelectrolyte complexation reaction under electrostatic forces to form composite hydrogel microspheres. The composite hydrogel microspheres prepared through dual crosslinking with calcium and sulfate ions have a more stable structure and are less prone to disintegration, providing favorable conditions for the slow release of the compound fertilizer within them.

[0028] As a preferred technical solution of the present invention, in step (I), the compound fertilizer comprises the following components in parts by weight:

[0029] 20-30 parts of diammonium hydrogen phosphate;

[0030] 12-15 parts potassium sulfate;

[0031] 5-10 parts of ammonium molybdate;

[0032] Calcium nitrate 3-6 parts;

[0033] 1-3 parts zinc sulfate;

[0034] Magnesium sulfate 0.5~1.5 parts;

[0035] Copper sulfate 0.1~0.5 parts;

[0036] 3-5 parts of protease;

[0037] Cellulase 2-4 parts.

[0038] The diammonium hydrogen phosphate can be present in weight proportions of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 parts; the potassium sulfate can be present in weight proportions of 12.0, 12.2, 12.4, 12.6, 12.8, 13.0, 13.2, 13.4, 13.6, 13.8, 14.0, 14.2, 14.4, 14.6, or 14.8 parts. The weight of ammonium molybdate can be 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, or 10.0 parts; the weight of calcium nitrate can be 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, or 6.0 parts; the weight of zinc sulfate can be 1.0, 1.2, 1.4, 1.6, 1.8, or 2.0 parts. 1 part, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, or 3.0 parts by weight; magnesium sulfate can be 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, or 1.5 parts by weight; copper sulfate can be 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, or 0.5 parts by weight; protease weight The parts can be 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, or 5.0 parts; the weight parts of cellulase can be 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, or 4.0 parts, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0039] In some optional instances, the rotational speed of the mixing ball mill is 100 to 200 rpm, for example, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm or 200 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] In some optional instances, the mixing and milling time is 40 to 60 minutes, for example, 40 minutes, 42 minutes, 44 minutes, 46 minutes, 48 ​​minutes, 50 minutes, 52 minutes, 54 minutes, 56 minutes, 58 minutes or 60 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0041] In some optional instances, the ball-to-material ratio of the mixed ball mill is (5~7):1, for example, it can be 5:1, 5.2:1, 5.4:1, 5.6:1, 5.8:1, 6.0:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1 or 7.0:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] As a preferred technical solution of the present invention, in step (I), the silane coupling agent solution is composed of silane coupling agent and ethanol aqueous solution.

[0043] In some optional instances, the mass fraction of the silane coupling agent in the silane coupling agent solution is 10 to 20 wt%, for example, it can be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] In some alternative instances, the mass ratio of the β-cyclodextrin to the silane coupling agent in the silane coupling agent solution is 1:(0.1~0.5), for example, it can be 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45 or 1:0.5, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0045] In some alternative instances, the temperature of the heating reflux reaction is 50 to 60°C, for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0046] In some alternative instances, the heating reflux reaction time is 3 to 4 hours, for example, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, or 4.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0047] In some optional examples, the polylactic acid solution contains a polylactic acid mass fraction of 5 to 15 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0048] In some alternative examples, the mass ratio of the aminocyclodextrin to the polylactic acid in the polylactic acid solution is (10~15):1, for example, it can be 10.0:1, 10.5:1, 11.0:1, 11.5:1, 12.0:1, 12.5:1, 13.0:1, 13.5:1, 14.0:1, 14.5:1 or 15.0:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] In some alternative examples, the temperature for mixing the aminocyclodextrin with the polylactic acid solution is 70-80°C, for example, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0050] In some alternative examples, the reaction time of the aminocyclodextrin with the polylactic acid solution is 5 to 8 hours, for example, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, 6.0 hours, 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours, or 8.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] In some optional instances, the mass fraction of grafted modified cyclodextrin in the cyclodextrin solution is 5 to 10 wt%, for example, it can be 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, or 10.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0052] In some optional instances, the mass ratio of the compound fertilizer to the grafted modified cyclodextrin in the cyclodextrin solution is 1:(10~20), for example, it can be 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0053] This invention achieves a phased slow-release effect of nano-cellulose-based composite materials during foliar fertilization by forming a three-layer slow-release barrier of β-cyclodextrin, boron nitride, and composite gel. In the three stages of crop growth and development, the inclusion effect of grafted modified cyclodextrin has a significant impact on the dissolution rate of compound fertilizer in the reproductive growth stage.

[0054] When the amount of grafted modified cyclodextrin added is below the lower limit of the range defined in this invention, the grafted modified cyclodextrin fails to completely encapsulate the compound fertilizer, resulting in a high dissolution rate of the compound fertilizer. As the amount of grafted modified cyclodextrin added gradually increases, the grafted modified cyclodextrin can completely encapsulate the compound fertilizer, and the slow-release control effect of the grafted modified cyclodextrin is fully utilized, further reducing the dissolution rate of the compound fertilizer. In addition, because the surface of the grafted modified cyclodextrin contains a large number of hydroxyl groups, it has the characteristics of being hydrophilic on the outside and hydrophobic on the inside. Introducing grafted modified cyclodextrin into the composite gel system can increase the water absorption of the composite hydrogel microspheres, improve the hydrophilicity of the nanocellulose-based composite material, and increase the swelling degree of the nanocellulose-based composite material. When the amount of grafted modified cyclodextrin added exceeds the upper limit of the range defined in this invention, it will lead to an increase in the cross-linking density of the gel system, and the grafted modified cyclodextrin will be more dense in the gel system, resulting in an increase in intermolecular hydrogen bonds and a decrease in the swelling degree of the nanocellulose-based composite material.

[0055] In some alternative instances, the freeze-drying temperature is -30 to -20°C, for example, -30°C, -29°C, -28°C, -27°C, -26°C, -25°C, -24°C, -23°C, -22°C, -21°C, or -20°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0056] In some optional instances, the freeze-drying time is 1 to 3 hours, for example, 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0057] As a preferred technical solution of the present invention, in step (II), the mass fraction of the nanocellulose solution is 0.5~1.5wt%, for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] In some alternative examples, the mass ratio of nanocellulose to citric acid in the nanocellulose solution is 1:(5~8), for example, it can be 1:5.0, 1:5.2, 1:5.4, 1:5.6, 1:5.8, 1:6.0, 1:6.2, 1:6.4, 1:6.6, 1:6.8, 1:7.0, 1:7.2, 1:7.4, 1:7.6, 1:7.8 or 1:8.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0059] This invention specifically limits the mass ratio of nanocellulose to citric acid to 1:(5~8). Within this range, as the amount of citric acid increases, the content of carboxyl functional groups in citric acid-modified nanocellulose increases significantly. This is because a large number of reaction sites on nanocellulose remain unreacted, resulting in incomplete modification. Adding more citric acid can increase the number of carboxyl functional groups on nanocellulose. When the mass ratio of nanocellulose to citric acid reaches 1:8, the hydroxyl active sites on nanocellulose are basically saturated during the esterification reaction, achieving the optimal modification effect. As the amount of citric acid added continues to increase, the content of carboxyl functional groups in citric acid-modified nanocellulose begins to decrease. This is because adding too much citric acid leads to significant dehydration, resulting in cross-linking with excess citric acid during the esterification reaction and reducing the content of carboxyl functional groups formed on the surface of nanocellulose. Therefore, during the esterification process, the amount of citric acid added must be strictly controlled. Adding too much citric acid will actually reduce the content of carboxyl functional groups, which is both uneconomical and reduces the modification effect.

[0060] In some optional examples, the stirring speed for mixing the nanocellulose solution with the citric acid is 500-600 r / min, for example, 500 r / min, 510 r / min, 520 r / min, 530 r / min, 540 r / min, 550 r / min, 560 r / min, 570 r / min, 580 r / min, 590 r / min or 600 r / min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0061] In some alternative examples, the mixing and stirring time of the nanocellulose solution and the citric acid is 1 to 2 hours, for example, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2.0 hours, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0062] This invention specifically limits the mixing and stirring time of the nanocellulose solution and citric acid to 1-2 hours. When the reaction time is controlled within the range of 1-2 hours, the content of carboxyl functional groups on the nanocellulose continues to increase. When the reaction time is less than 1 hour, the esterification reaction is not sufficient, and premature termination results in some active sites on the surface of the nanocellulose not participating in the reaction. When the reaction time exceeds 2 hours, the content of carboxyl functional groups begins to decrease. This is because the carboxyl functional groups on the surface of the nanocellulose undergo dehydration and cross-linking, which greatly weakens the reaction efficiency.

[0063] In some optional instances, the reaction temperature of the first reaction solution is 90~110°C, for example, it can be 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, 102°C, 104°C, 106°C, 108°C or 110°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0064] In some optional instances, the reaction time of the first reaction solution is 3 to 5 hours, for example, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, or 5.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0065] As a preferred technical solution of the present invention, in step (II), the soaking time of the citric acid modified nanocellulose in the ethanol is 2-3 hours, for example, it can be 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3.0 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0066] In some optional instances, the citric acid-modified nanocellulose is immersed in ethanol at a temperature of 40-50°C, for example, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, or 50°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0067] In some optional instances, the mass ratio of citric acid-modified nanocellulose to L-cysteine ​​in the suspension is 1:(10~12), for example, it can be 1:10.0, 1:10.2, 1:10.4, 1:10.6, 1:10.8, 1:11.0, 1:11.2, 1:11.4, 1:11.6, 1:11.8 or 1:12.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0068] In some optional instances, the reaction temperature of the second reaction solution is 100~120°C, for example, 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0069] In some optional instances, the reaction time of the second reaction solution is 4 to 6 hours, for example, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0070] As a preferred technical solution of the present invention, in step (III), the silane coupling agent solution is composed of silane coupling agent and ethanol aqueous solution.

[0071] In some optional instances, the mass fraction of the silane coupling agent in the silane coupling agent solution is 10 to 20 wt%, for example, it can be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0072] In some alternative examples, the mass ratio of the bentonite to the silane coupling agent in the silane coupling agent solution is 1:(1.2~1.3), for example, it can be 1:1.2, 1:1.21, 1:1.22, 1:1.23, 1:1.24, 1:1.25, 1:1.26, 1:1.27, 1:1.28, 1:1.29 or 1:1.3, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0073] In some alternative examples, the reaction temperature of the bentonite with the silane coupling agent solution is 100~110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0074] In some alternative examples, the reaction time of the bentonite with the silane coupling agent solution is 0.5 to 1.5 h, for example, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h or 1.5 h, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0075] As a preferred technical solution of the present invention, in step (III), the concentration of hexadecyltrimethylammonium bromide in the composite modified solution is 0.1~0.25 mol / L, for example, it can be 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, 0.2 mol / L, 0.21 mol / L, 0.22 mol / L, 0.23 mol / L, 0.24 mol / L or 0.25 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0076] In some optional instances, the mass ratio of the hexadecyltrimethylammonium bromide to the amino-modified bentonite in the bentonite suspension is (0.2-0.3):1, for example, it can be 0.2:1, 0.21:1, 0.22:1, 0.23:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1, 0.28:1, 0.29:1 or 0.3:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0077] The amount of hexadecyltrimethylammonium bromide added significantly affects the release rate of compound fertilizer. As the amount of hexadecyltrimethylammonium bromide added increases, the release rate of the compound fertilizer gradually decreases and tends to stabilize. When the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is in the range of (0.2-0.3):1, hexadecyltrimethylammonium bromide is adsorbed into the interlayer of bentonite via ion exchange. Its cation end combines with the negatively charged centers on the bentonite surface through electrostatic interaction, while its long carbon chains aggregate to form an organic phase. The compound fertilizer enters the interlayer organic phase of bentonite through partitioning. When the concentration of the compound fertilizer in the planting environment is lower than its equilibrium concentration, the compound fertilizer dissolves and leaches out under the action of the concentration gradient. Simultaneously, the slow-release effect is achieved by the hindrance of the long carbon chains of hexadecyltrimethylammonium bromide.

[0078] When the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is less than 0.2:1, the interlayer spacing of the bentonite is too small, preventing the compound fertilizer from effectively entering the interlayer organic phase of the bentonite. Consequently, the inhibitory effect on the release of the compound fertilizer is not significant, and the staged slow-release effect of β-cyclodextrin-bentonite-composite gel cannot be achieved. Increasing the amount of hexadecyltrimethylammonium bromide can improve the interlayer spacing of the bentonite, thereby increasing the interfacial area between the interlayer organic phase and the aqueous phase, which is beneficial for the release of the compound fertilizer. Furthermore, it can enhance the inhibitory effect on the diffusion of compound fertilizer molecules, thus slowing down its release rate.

[0079] When the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite exceeds 0.3:1, further increasing the amount of hexadecyltrimethylammonium bromide added does not significantly increase the interlayer spacing of the organic bentonite. This is because the amount of hexadecyltrimethylammonium bromide added is too high, exceeding the total amount of exchangeable cations. Excess hexadecyltrimethylammonium bromide is adsorbed into the interlayer domain of bentonite through hydrophobic interactions, competing with the adsorption of compound fertilizer. At the same time, since there is no stable binding between excess hexadecyltrimethylammonium bromide and bentonite, it will move and diffuse in the interlayer domain of bentonite and even be released into the environment, thus having a very limited inhibitory effect on the diffusion of compound fertilizer.

[0080] In some optional examples, the ratio of the polycarboxylated metal chelating agent to the amino-modified bentonite in the bentonite suspension is (0.3~0.8) mL:1g, for example, it can be 0.3mL:1g, 0.35mL:1g, 0.4mL:1g, 0.45mL:1g, 0.5mL:1g, 0.55mL:1g, 0.5mL:1g, 0.6mL:1g, 0.65mL:1g, 0.7mL:1g, 0.75mL:1g or 0.8mL:1g, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0081] In some optional examples, the polycarboxylated metal chelating agent includes any one or a combination of at least two of tetraethylenepentamine, triethylenetetramine, ethylenediamine, or diethylenetriamine.

[0082] In some optional examples, the ratio of the amount of aluminum ions in the aluminum hydroxyl pillar to the amino-modified bentonite in the bentonite suspension is (1.0~1.5) mmol:1g, for example, it can be 1.0 mmol:1g, 1.05 mmol:1g, 1.1 mmol:1g, 1.15 mmol:1g, 1.2 mmol:1g, 1.25 mmol:1g, 1.3 mmol:1g, 1.35 mmol:1g, 1.4 mmol:1g, 1.45 mmol:1g or 1.5 mmol:1g, but is not limited to the values ​​listed, other unlisted values ​​within this range are also applicable.

[0083] In some optional instances, the mass fraction of amino-modified bentonite in the bentonite suspension is 1-5 wt%, for example, it may be 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, or 5.0 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0084] In some alternative instances, the heating temperature is 50-60°C, for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0085] In some optional instances, after all the composite modified solution has been added dropwise, the heating continues for 1 to 2 hours, for example, 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, or 2.0 h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0086] As a preferred technical solution of the present invention, in step (IV), the concentration of chitosan in the mixture is 10~20 mg / mL, for example, it can be 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, 16 mg / mL, 17 mg / mL, 18 mg / mL, 19 mg / mL or 20 mg / mL, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0087] In some optional examples, the mass ratio of the chitosan, the sodium alginate, the coated modified compound fertilizer, the grafted modified nanocellulose, and the composite modified bentonite is (2~3):(0.4~0.5):10:(2~3):(0.5~0.6), for example, it can be 2:0.4:10:2:0.5, 2.1:0.41:10:2.1:0.51, 2.2:0.42:10:2.2:0.52, 2.3:0.43:10:2.3:0. 53, 2.4:0.44:10:2.4:0.54, 2.5:0.45:10:2.5:0.55, 2.6:0.46:10:2.6:0.56, 2.7:0.47:10:2.7:0.57, 2.8:0.48:10:2.8:0.58, 2.9:0.49100:2.9:0.59, or 3:0.5:10:3:0.6, but not limited to the listed values; other unlisted values ​​within this range also apply.

[0088] The swelling degree of the nanocellulose-based composite material is maximized when the amount of sodium alginate added is within the range specified in this invention. When the amount of sodium alginate added is below the lower limit of the range specified in this invention, the number of active sites for the reaction is too small, the degree of cross-linking of the generated polymer is poor, and the composite hydrogel microspheres cannot form a dense surface. Therefore, water cannot be retained in the three-dimensional porous network structure of the composite hydrogel microspheres for a long time, resulting in a decrease in the swelling degree and poor water retention performance of the final nanocellulose-based composite material. When the amount of sodium alginate added exceeds the upper limit of the range specified in this invention, the sodium alginate content in the gel system is too high, and the sodium alginate molecular chains entangle into clumps. During the gelation process, the graft copolymerization reaction can only occur on the surface of the clump of sodium alginate, while it is difficult for the reaction to occur inside the clump of sodium alginate. This leads to a reduction in the effective active sites for the reaction, a decrease in the grafting rate, and consequently a decrease in the swelling degree and poor water retention performance of the nanocellulose-based composite material.

[0089] In some optional instances, the ultrasonic dispersion uses an ultrasonic power of 80 to 100 kW, such as 80 kW, 82 kW, 84 kW, 86 kW, 88 kW, 90 kW, 92 kW, 94 kW, 96 kW, 98 kW or 100 kW, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0090] In some optional instances, the ultrasonic dispersion treatment time is 1 to 3 hours, for example, 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0091] As a preferred technical solution of the present invention, in step (IV), the dropping rate of the composite sol is 0.1~0.2 mL / s, for example, it can be 0.1 mL / s, 0.11 mL / s, 0.12 mL / s, 0.13 mL / s, 0.14 mL / s, 0.15 mL / s, 0.16 mL / s, 0.17 mL / s, 0.18 mL / s, 0.19 mL / s or 0.2 mL / s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0092] In some optional instances, the mass fraction of the calcium salt solution is 2 to 3 wt%, for example, it may be 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0093] This invention specifically limits the mass fraction of the calcium salt solution to 2-3 wt%. Within this range, the swelling degree of the nanocellulose-based composite material is maximized. As the mass fraction of the calcium salt solution increases, the swelling degree of the nanocellulose-based composite material decreases. This is because when the mass fraction of the calcium salt solution is below 2 wt%, the degree of ionic cross-linking on the surface of the composite hydrogel microspheres is low, resulting in a loose and porous structure. Water entering the interior of the composite hydrogel microspheres will then seep out again through the pores on the surface, thus preventing water from being stored inside for an extended period, leading to low swelling degree and poor water retention. When the mass fraction of the calcium salt solution exceeds 2 wt%, the ionic cross-linking on the surface of the composite hydrogel microspheres is more dense, making it difficult for water to penetrate the surface and enter the interior, resulting in low swelling degree and poor water absorption.

[0094] In some optional instances, the immersion time of the droplets of the composite sol in the calcium salt solution is 10 to 20 minutes, for example, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0095] In some alternative examples, the sulfate solution has a mass fraction of 2 to 3 wt%, for example, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0096] In some optional instances, the immersion time of the hydrogel microbead precursor in the sulfate solution is 10-20 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0097] In some optional instances, the freeze-drying temperature of the composite hydrogel microspheres is -40 to -20°C, for example, -40°C, -38°C, -36°C, -34°C, -32°C, -30°C, -28°C, -26°C, -24°C, -22°C, or -20°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0098] In some optional examples, the freeze-drying time of the composite hydrogel microspheres is 6 to 12 hours, for example, 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours, 10.0 hours, 10.5 hours, 11.0 hours, 11.5 hours, or 12.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0099] By way of example, the present invention provides a method for preparing a nano-cellulose-based composite material with sustained-release function, the preparation method comprising:

[0100] (1) Mix 20-30 parts of diammonium hydrogen phosphate, 12-15 parts of potassium sulfate, 5-10 parts of ammonium molybdate, 3-6 parts of calcium nitrate, 1-3 parts of zinc sulfate, 0.5-1.5 parts of magnesium sulfate, 0.1-0.5 parts of copper sulfate, 3-5 parts of protease and 2-4 parts of cellulase and place them in a ball mill. The ball-to-material ratio is (5-7):1. The speed of the ball mill is 100-200 rpm. After mixing and ball milling in the ball mill for 40-60 minutes, a compound fertilizer is obtained.

[0101] β-Cyclodextrin was added to a 10-20 wt% silane coupling agent solution, with a mass ratio of β-cyclodextrin to silane coupling agent of 1:(0.1-0.5). After mixing evenly, the mixture was heated under reflux at a temperature of 50-60°C for 3-4 hours. The reaction product was filtered, washed, and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was then added to a 5-15 wt% polylactic acid solution, with a mass ratio of amino-modified cyclodextrin to polylactic acid of (10-15):1. The mixture was reacted at 70-80°C for 5-8 hours to obtain grafted modified cyclodextrin.

[0102] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 5-10 wt% cyclodextrin solution. Compound fertilizer was added to the cyclodextrin solution, with a mass ratio of compound fertilizer to grafted modified cyclodextrin of 1:(10-20). After mixing evenly, the mixture was freeze-dried at -30 to -20℃ for 1-3 hours to obtain the coated modified compound fertilizer.

[0103] (2) Add citric acid to a 0.5-1.5 wt% nanocellulose solution, with a mass ratio of nanocellulose to citric acid of 1:(5-8), and stir at a speed of 500-600 r / min for 1-2 h to obtain the first reaction solution; transfer the first reaction solution to a reaction vessel and react at 90-110℃ for 3-5 h; after filtration, washing and drying, the reaction product is obtained as citric acid modified nanocellulose.

[0104] Citric acid-modified nanocellulose was soaked in ethanol at 40-50°C for 2-3 hours to allow it to fully swell and form a suspension. EDC was added to the suspension, and the mixture was stirred at 20-30°C for 10-15 minutes. NHS was then added, and the mixture was stirred at 20-30°C for 0.5-1 hour. The molar ratio of NHS to EDC was 1:1, and the mass ratio of the total mass of NHS and EDC to the mass of citric acid-modified nanocellulose was (0.01-0.1):1.

[0105] Subsequently, L-cysteine ​​was added to the suspension. The mass ratio of citric acid modified nanocellulose to L-cysteine ​​was 1:(10~12). After mixing evenly, a second reaction solution was obtained. The second reaction solution was heated to 100~120℃ and kept at that temperature for 4~6h to allow the reaction to occur. The reaction product was filtered, washed and dried to obtain grafted modified nanocellulose.

[0106] (3) Add bentonite to a 10-20 wt% silane coupling agent solution, with a mass ratio of bentonite to silane coupling agent of 1:(1.2-1.3). Heat and stir at 100-110℃ for 0.5-1.5 h to allow the reaction to occur. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0107] Hexadecyltrimethylammonium bromide, a polycarboxylic acid metal chelating agent, and an aluminum hydroxide pillaring agent are dispersed in deionized water and mixed thoroughly to obtain a composite modified solution, wherein the concentration of hexadecyltrimethylammonium bromide in the composite modified solution is 0.1~0.25 mol / L; the amino-modified bentonite is dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 1-5 wt%; the composite modified solution is added dropwise to the bentonite suspension, wherein hexadecyltrimethylammonium bromide and ammonia... The mass ratio of the modified bentonite to the amino-modified bentonite is (0.2-0.3):1, the ratio of the polycarboxylated metal chelating agent to the amino-modified bentonite is (0.3-0.8) mL:1 g, and the ratio of the amount of aluminum ions in the aluminum hydroxide pillar agent to the amino-modified bentonite is (1.0-1.5) mmol:1 g. During the dropwise addition, the mixture is continuously stirred and heated in a water bath at 50-60℃. After all the addition is completed, the water bath heating is maintained for 1-2 hours. Then, the mixture is filtered, washed, and dried to obtain the composite modified bentonite.

[0108] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture. The concentration of chitosan in the mixture is 10~20mg / mL. The coated modified compound fertilizer obtained in step (1), the grafted modified nanocellulose obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is (2~3):(0.4~0.5):10:(2~3):(0.5~0.6). After mixing evenly, the mixture is ultrasonically dispersed at 80~100kW for 1~3h to obtain a composite sol.

[0109] The composite sol was added dropwise to a 2-3 wt% calcium salt solution at a dropping rate of 0.1-0.2 mL / s and soaked for 10-20 min to obtain a hydrogel microsphere precursor. The hydrogel microsphere precursor was then removed and soaked in a 2-3 wt% sulfate solution for 10-20 min to obtain composite hydrogel microspheres. The composite hydrogel microspheres were freeze-dried at -40 to -20℃ for 6-12 h to obtain the nanocellulose-based composite material.

[0110] Secondly, the present invention provides a nano-cellulose-based composite material with sustained-release function prepared by the preparation method described in the first aspect.

[0111] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0112] This invention uses sodium alginate and chitosan as gel carriers and achieves a staged slow-release function by combining them with β-cyclodextrin and bentonite. Composite hydrogel microspheres loaded with compound fertilizer were prepared by sol-gel method, and after freeze-drying, nanocellulose-based composite materials were formed. The nanocellulose-based composite materials prepared by this invention can produce different release rates and release effects at different stages of crop growth and development when used as foliar fertilizer, and have broad application prospects in actual production.

[0113] The early stage of crop growth and development is the vegetative growth stage, during which soil fertilization is the main method and foliar fertilization is the supplementary method. Therefore, the release rate of foliar fertilizer should not be too high during this stage, otherwise it will lead to fertilizer excess. The nanocellulose-based composite material prepared by this invention is mainly composed of a composite gel system in the early stage of fertilization. The composite gel system is structurally stable and does not easily absorb water. At the same time, there are three slow-release barriers of β-cyclodextrin, bentonite and gel system in addition to the compound fertilizer. At this time, it is difficult for the compound fertilizer to penetrate through these three slow-release barriers and seep into the external environment. Therefore, the release rate of the compound fertilizer is low at this time and can be carried out simultaneously with soil fertilization.

[0114] The middle stage of crop growth and development is characterized by the simultaneous occurrence of vegetative and reproductive growth. During this stage, soil fertilization and foliar fertilization are carried out concurrently. The release rate of foliar fertilizer during this stage is at a moderate level. The nanocellulose-based composite material prepared in this invention is dominated by the bentonite system during the middle stage of fertilization. At this time, the gel barrier decomposes due to prolonged water absorption, and the pore size on the gel surface gradually increases, thus losing its slow-release barrier function. At this time, the compound fertilizer is encapsulated and adsorbed by β-cyclodextrin into the bentonite layer. Therefore, there are two slow-release barriers, β-cyclodextrin and bentonite, in addition to the compound fertilizer. The compound fertilizer can then seep into the external environment by passing through the two slow-release barriers of β-cyclodextrin and bentonite. Therefore, the release rate of the compound fertilizer at this time is at a moderate level and gradually increases with the fertilization time.

[0115] The later stage of crop growth and development is the reproductive growth stage, during which foliar fertilization is the main method and soil fertilization is the supplementary method. The release rate of foliar fertilizer is relatively high during this stage. The nano-cellulose-based composite material prepared by this invention is mainly composed of β-cyclodextrin system in the later stage of fertilization. At this time, as the nano-cellulose-based composite material continues to absorb water and swell, the coated modified compound fertilizer is separated from the interlayer of boron nitride, and boron nitride also loses its slow-release barrier function. At this time, the compound fertilizer is only encapsulated by β-cyclodextrin. The compound fertilizer can seep into the external environment by passing through the slow-release barrier of β-cyclodextrin. Therefore, the release rate of compound fertilizer reaches the highest level at this time.

[0116] The hydroxyl groups on the cellulose molecular chain are active functional groups capable of undergoing chemical reactions such as oxidation, etherification, and esterification. This invention utilizes citric acid to induce an esterification reaction with nanocellulose. Citric acid, a polycarboxylic acid, contains three carboxylic acid functional groups, with a quaternary carbon as the core, and the three carboxylic acid functional groups surrounding the quaternary carbon, resulting in a tetragonal geometry for the small molecule. The close proximity of the active functional groups leads to stronger reactivity and higher accessibility. In the nanocellulose molecular chain, the secondary hydroxyl group at C6 exhibits high reactivity. Therefore, the carboxyl group on citric acid can react with the secondary hydroxyl group on nanocellulose under mild reaction conditions to form a more stable ester bond, thereby modifying the cellulose aggregate structure. During the esterification process, the two adjacent carboxyl groups in citric acid first dehydrate to form an anhydride, which then further cross-links with the hydroxyl groups on the cellulose molecular chain to form ester bonds, enhancing the internal framework structure of the nanocellulose molecule. The modified nanocellulose, when added to the composite gel system, can effectively improve the stability of the three-dimensional network structure of the composite gel system and, to a certain extent, improve the mechanical properties of the composite hydrogel microspheres.

[0117] Based on citric acid modified nanocellulose, this invention further adds L-cysteine, utilizing the condensation between the amino group in L-cysteine ​​and the carboxyl group in citric acid modified nanocellulose to form an amide bond, thereby grafting L-cysteine ​​onto the molecular chain of citric acid modified nanocellulose. This invention utilizes L-cysteine ​​grafting modification of citric acid-modified nanocellulose to significantly improve the water retention, swelling rate, and sustained-release capacity of the resulting grafted nanocellulose compared to unmodified nanocellulose. This is because, firstly, the sulfonic acid functional group of cysteine ​​is a hydrophilic functional group, which, together with the numerous hydroxyl and carboxyl groups in citric acid-modified nanocellulose, can form hydrophilic channels, resulting in high water retention and swelling rates for the composite hydrogel microspheres. Secondly, the thiol groups on the side chains of L-cysteine ​​molecules chelate with carboxyl groups, which can adsorb metal ions in compound fertilizers, thereby inhibiting the release of compound fertilizers to a certain extent. Furthermore, nanocellulose has excellent biodegradability and can also achieve a sustained-release effect through biodegradation, thus improving the utilization rate of compound fertilizers and meeting the concept of green and sustainable development.

[0118] This invention improves the mechanical properties of nanocellulose-based composite materials by grafting L-cysteine, preventing leakage of the compound fertilizer inside due to external force damage, thus avoiding the direct loss of the slow-release effect. This is because the thiol groups on the side chains of L-cysteine ​​molecules can be reversibly oxidized by air in neutral and weakly alkaline solutions to form covalent disulfide bonds. These disulfide bonds are used for cross-linking to form a tough gel network. In addition, grafting L-cysteine ​​onto the nanocellulose molecular chains increases the number of functional groups such as ester and amino groups. The covalent bonds and the reversible hydrogen bonds generated between molecules have a synergistic effect, which can act as sacrificial bonds to resist external forces, thereby enhancing the mechanical properties of the composite hydrogel microspheres.

[0119] This invention uses β-cyclodextrin as the main component to encapsulate the guest compound fertilizer, ultimately forming a coated and modified compound fertilizer. During the mixing process of the compound sol, the β-cyclodextrin on the coated and modified compound fertilizer interacts with the hydroxyl groups on the surface of the grafted and modified nanocellulose through hydrogen bonding, which greatly enhances the interfacial force between the grafted and modified nanocellulose and the coated and modified compound fertilizer, allowing the grafted and modified nanocellulose and the coated and modified compound fertilizer to be uniformly dispersed in the compound sol.

[0120] This invention employs hexadecyltrimethylammonium bromide, polycarboxylated metal chelators, and aluminum hydroxide pillars as multi-component composite modifiers to perform organic-inorganic composite modification of bentonite. This facilitates the simultaneous entry of different types of intercalation modifiers into the interlayer space of bentonite, thereby effectively increasing the interlayer spacing. On one hand, the polycarboxylated metal chelators have a relatively small volume and numerous negatively charged branches, which can be intercalated into the larger, positively charged long carbon chains of hexadecyltrimethylammonium bromide and polyaluminum hydroxide ions through electrostatic interactions. This allows the multi-component composite modifiers to simultaneously insert into the interlayer domains of bentonite, thereby increasing its interlayer spacing. On the other hand, both hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions are positively charged, while polycarboxylic acid metal chelators contain multiple carboxyl functional groups. Under certain conditions, these groups dissociate to form negatively charged carboxylate ions. These negatively charged anions can act as a link, bridging the positively charged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions together through electrostatic attraction. The bridged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions can then simultaneously enter the interlayer of bentonite, further increasing the interlayer spacing of the composite modified bentonite. Furthermore, polycarboxylic acid metal chelators contain multiple carboxyl functional groups, while polyhydroxyaluminum pillar agents contain multiple hydroxyl functional groups. A large number of hydrogen bonds easily form between the polycarboxylic acid metal chelators and polyhydroxyaluminum ions. These hydrogen bonds, acting as an auxiliary intermolecular force, can further promote the synergistic insertion of the multi-component composite modifier into the interlayer of bentonite, thus achieving the purpose of multi-component modification.

[0121] The modified composite bentonite of this invention combines the excellent properties of both pillared bentonite and organic bentonite. The aluminum hydroxyl pillar agent, which enters the interlayer, occupies some of the exchangeable ion sites. The positively charged aluminum hydroxyl pillar agent is stably maintained by electrostatic attraction and the excess negative charge between the bentonite layers, aligning along a direction perpendicular to the crystal layers. This expands the interlayer spacing of the bentonite, thereby increasing the adsorption capacity of the composite modified bentonite for coated modified compound fertilizers. This improves the adsorption performance of the composite modified bentonite, enabling it to accommodate more coated modified compound fertilizers. Simultaneously, after organic modification with hexadecyltrimethylammonium bromide, the hexadecyltrimethylammonium bromide and aluminum hydroxyl ions adsorbed between the composite modified bentonite layers exceed the cation exchange capacity of the bentonite. Therefore, the final composite modified bentonite carries a certain positive charge, which, under the effect of charge repulsion, significantly improves its dispersion performance in the composite sol.

[0122] This invention uses sodium alginate and chitosan as carriers for a composite gel system, resulting in a dense three-dimensional porous network structure within the prepared composite hydrogel microspheres. Due to the strong hydrophilicity of sodium alginate, the final composite hydrogel microspheres have a high water content, allowing the formation of large ice crystals during freeze-drying. The ice crystals within the composite hydrogel microspheres sublimate, and air replaces the ice crystals, preserving the original three-dimensional macroporous network structure of the composite hydrogel. This interconnected macroporous structure is beneficial for the dissolution and release of compound fertilizers.

[0123] This invention adds chitosan to sodium alginate, utilizing the electrostatic interaction between sodium alginate and chitosan to increase the cross-linking density of the hydrogel. This results in a denser three-dimensional porous network structure of the composite hydrogel microspheres, extending the release channels of the compound fertilizer within the microspheres and thus hindering its release and penetration, achieving a slow-release effect. Furthermore, the dense three-dimensional porous network structure significantly improves the mechanical strength compared to sodium alginate gel alone. This is because during the ionic cross-linking of sodium alginate and chitosan, both molecules possess numerous functional groups for reaction, leading to a more complete reaction and a greater number of opposite charges. This results in a denser cross-linked network, enhancing the mechanical properties of the composite hydrogel microspheres.

[0124] Sodium alginate exhibits instantaneous gelation upon contact with calcium ions, forming a hydrogel network. Chitosan, on the other hand, can crosslink with sulfate ions to form a stable gel network. Furthermore, the primary amino groups on the chitosan molecular chain and the carboxyl groups on the sodium alginate molecular chain can undergo a polyelectrolyte complexation reaction under electrostatic forces to form composite hydrogel microspheres. The composite hydrogel microspheres prepared through dual crosslinking with calcium and sulfate ions have a more stable structure and are less prone to disintegration, providing favorable conditions for the slow release of the compound fertilizer within them. Attached Figure Description

[0125] Figure 1 The following is a process flow diagram of the preparation process of the nano-cellulose-based composite materials provided in Examples 1-13 of this invention;

[0126] Figure 2 Infrared spectra of unmodified bentonite and the composite modified bentonite prepared in Example 1 of this invention;

[0127] Figure 3 XRD patterns of unmodified bentonite and composite modified bentonite prepared in Example 1 of this invention;

[0128] Figure 4 This is a scanning electron microscope image of the surface of the nano-cellulose-based composite material prepared in Example 1 of the present invention;

[0129] Figure 5 This is a scanning electron microscope image of the surface of the nano-cellulose-based composite material prepared in Example 1 of the present invention;

[0130] Figure 6 This is a cross-sectional scanning electron microscope image of the nanocellulose-based composite material prepared in Example 1 of the present invention;

[0131] Figure 7 This is a cross-sectional scanning electron microscope image of the nanocellulose-based composite material prepared in Example 1 of the present invention. Detailed Implementation

[0132] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0133] Example 1

[0134] This embodiment provides a method for preparing a nano-cellulose-based composite material with sustained-release function, such as... Figure 1 As shown, the preparation method includes:

[0135] (1) Mix 20 parts of diammonium hydrogen phosphate, 12 parts of potassium sulfate, 5 parts of ammonium molybdate, 3 parts of calcium nitrate, 1 part of zinc sulfate, 0.5 parts of magnesium sulfate, 0.1 parts of copper sulfate, 3 parts of protease and 2 parts of cellulase and place them in a ball mill with a ball-to-material ratio of 5:1 and a ball mill speed of 100 rpm. After mixing and ball milling in the ball mill for 60 min, a compound fertilizer is obtained.

[0136] β-Cyclodextrin was added to a 10 wt% solution of silane coupling agent KH550, with a mass ratio of β-cyclodextrin to silane coupling agent KH550 of 1:0.1. After mixing evenly, the mixture was heated under reflux at 50°C for 4 hours. The reaction product was filtered, washed, and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was then added to a 5 wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 10:1. The mixture was reacted at 70°C for 8 hours to obtain grafted modified cyclodextrin.

[0137] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 5wt% cyclodextrin solution. Compound fertilizer was added to the cyclodextrin solution at a mass ratio of 1:10 to the grafted modified cyclodextrin. After mixing evenly, the mixture was freeze-dried at -30℃ for 1 hour to obtain the coated modified compound fertilizer.

[0138] (2) Add citric acid to a 0.5 wt% nanocellulose solution, with a mass ratio of nanocellulose to citric acid of 1:5. Stir at 500 r / min for 2 h to obtain the first reaction solution. Transfer the first reaction solution to a reaction vessel and react at 90 °C for 5 h. After filtration, washing and drying, the reaction product is citric acid modified nanocellulose.

[0139] Citric acid-modified nanocellulose was soaked in ethanol at 40°C for 3 hours to allow it to fully swell and form a suspension. EDC was added to the suspension, and NHS was added after stirring at 20°C for 15 minutes. Stirring was continued at 20°C for 1 hour. The molar ratio of NHS to EDC was 1:1, and the mass ratio of the total mass of NHS and EDC to the mass of citric acid-modified nanocellulose was 0.01:1.

[0140] Subsequently, L-cysteine ​​was added to the suspension. The mass ratio of citric acid modified nanocellulose to L-cysteine ​​was 1:10. After mixing evenly, a second reaction solution was obtained. The second reaction solution was heated to 100°C and kept at that temperature for 6 hours to allow the reaction to occur. The reaction product was filtered, washed, and dried to obtain grafted modified nanocellulose.

[0141] (3) Add bentonite to a 10wt% solution of silane coupling agent KH550. The mass ratio of bentonite to silane coupling agent KH550 is 1:1.2. Heat and stir at 100℃ for 1.5h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0142] Hexadecyltrimethylammonium bromide, tetraethylenepentamine, and aluminum hydroxyl pillar agent were dispersed in deionized water and mixed evenly to obtain a composite modified solution, wherein the concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.1 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed evenly to obtain a bentonite suspension with a mass fraction of 1 wt%. The composite modified solution was added dropwise to the bentonite suspension, wherein the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.2:1, the ratio of tetraethylenepentamine to amino-modified bentonite was 0.3 mL:1 g, and the molar amount of aluminum ions in the aluminum hydroxyl pillar agent to amino-modified bentonite was 1 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 50°C. After all the addition was completed, the water bath heating was maintained for 1 hour. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0143] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 10 mg / mL. The coated modified compound fertilizer obtained in step (1), the grafted modified nanocellulose obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is 2:0.4:10:2:0.5. After mixing evenly, the mixture is ultrasonically dispersed at 80 kW for 3 h to obtain a composite sol.

[0144] The composite sol was added dropwise to a 2 wt% calcium chloride solution at a rate of 0.1 mL / s and soaked for 10 min to obtain a hydrogel microsphere precursor. The hydrogel microsphere precursor was then removed and soaked in a 2 wt% sodium sulfate solution for 10 min to obtain composite hydrogel microspheres. The composite hydrogel microspheres were freeze-dried at -40℃ for 6 h to obtain the nanocellulose-based composite material.

[0145] Infrared spectroscopy analysis was performed on unmodified bentonite and the composite modified bentonite prepared in this embodiment, and the results were as follows: Figure 2 The infrared spectrum shown is from Figure 2 It can be seen that 1723cm -1 A new absorption peak appeared at 2851 cm⁻¹, which is attributed to the characteristic absorption peak of the Al-O stretching vibration in the aluminum hydroxyl pillar, indicating that aluminum hydroxyl ions have entered the interlayer of bentonite. Furthermore, at 2851 cm⁻¹...-1 and 2920cm -1 Two new absorption peaks appeared at 1474 cm⁻¹, attributed to the characteristic absorption peaks of the symmetric and antisymmetric stretching vibrations of HCH in the -CH₂ functional group of hexadecyltrimethylammonium bromide. Additionally, at 1474 cm⁻¹... -1 A new absorption peak appeared, which is attributed to the bending vibration absorption peak of the carboxyl group of tetraethylenepentamine, indicating that both CTAB and the metal chelating agent successfully entered the interlayer of bentonite.

[0146] X-ray diffraction (XRD) was used to perform XRD tests on unmodified bentonite and the composite modified bentonite prepared in this embodiment. The XRD tube was a Cu target, the voltage was set to 40 kV, the current to 30 mA, the scan rate to 1.5 / min, the scan range to 5-60°, and the scan wavelength to 0.15 nm. The XRD results are as follows: Figure 3 The XRD patterns shown are used to calculate the interlayer spacing of unmodified bentonite and composite modified bentonite. The calculated interlayer spacing of unmodified bentonite is 1.252 nm, while that of composite modified bentonite is 2.188 nm. This indicates that the interlayer spacing of bentonite is significantly improved after multi-component composite modification.

[0147] Figure 4 and Figure 5 This is a scanning electron microscope (SEM) image of the surface of the nanocellulose-based composite material prepared in this embodiment. Figure 4 and Figure 5 It can be seen that the nanocellulose-based composite material has a spherical morphology and a smooth and dense surface, which plays a key role in hindering the release of compound fertilizer. Figure 6 and Figure 7 This is a cross-sectional scanning electron microscope image of the nanocellulose-based composite material prepared in this embodiment. Figure 6 and Figure 7 It can be seen that it has a rich three-dimensional porous network structure with an average pore size of 10~100μm, which can effectively prevent the diffusion and dissolution of compound fertilizer inside it.

[0148] Example 2

[0149] This embodiment provides a method for preparing a nano-cellulose-based composite material with sustained-release function, such as... Figure 1 As shown, the preparation method includes:

[0150] (1) Mix 22 parts of diammonium hydrogen phosphate, 13 parts of potassium sulfate, 6 parts of ammonium molybdate, 4 parts of calcium nitrate, 1.5 parts of zinc sulfate, 0.8 parts of magnesium sulfate, 0.2 parts of copper sulfate, 3.5 parts of protease and 2.5 parts of cellulase and place them in a ball mill with a ball-to-material ratio of 5.5:1 and a ball mill speed of 120 rpm. After mixing and ball milling for 55 min, a compound fertilizer is obtained.

[0151] β-Cyclodextrin was added to a 12 wt% solution of silane coupling agent KH550, with a mass ratio of β-cyclodextrin to silane coupling agent KH550 of 1:0.2. After mixing thoroughly, the mixture was heated under reflux at 52 °C for 3.8 h. The reaction product was filtered, washed, and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was then added to an 8 wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 11:1. The mixture was reacted at 72 °C for 7 h to obtain grafted modified cyclodextrin.

[0152] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 6wt% cyclodextrin solution. Compound fertilizer was added to the cyclodextrin solution at a mass ratio of 1:12 to the grafted modified cyclodextrin. After mixing evenly, the mixture was freeze-dried at -28℃ for 1.5h to obtain the coated modified compound fertilizer.

[0153] (2) Add citric acid to a 0.8 wt% nanocellulose solution, the mass ratio of nanocellulose to citric acid is 1:6, stir at 520 r / min for 1.8 h to obtain the first reaction solution; transfer the first reaction solution to a reaction vessel and react at 95 °C for 4.5 h. After filtration, washing and drying, the reaction product is citric acid modified nanocellulose.

[0154] Citric acid-modified nanocellulose was soaked in ethanol at 42°C for 2.8 h to allow it to fully swell and form a suspension. EDC was added to the suspension, and NHS was added after stirring at 22°C for 14 min. Stirring was continued at 22°C for 0.8 h. The molar ratio of NHS to EDC was 1:1, and the mass ratio of the total mass of NHS and EDC to the mass of citric acid-modified nanocellulose was 0.03:1.

[0155] Subsequently, L-cysteine ​​was added to the suspension. The mass ratio of citric acid modified nanocellulose to L-cysteine ​​was 1:10.5. After mixing evenly, a second reaction solution was obtained. The second reaction solution was heated to 105°C and kept at that temperature for 5.5 h to allow the reaction to occur. The reaction product was filtered, washed and dried to obtain grafted modified nanocellulose.

[0156] (3) Add bentonite to a 12wt% solution of silane coupling agent KH550. The mass ratio of bentonite to silane coupling agent KH550 is 1:1.22. Heat and stir at 102℃ for 1.2h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0157] Hexadecyltrimethylammonium bromide, triethylenetetramine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution, wherein the concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.15 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 2 wt%. The composite modified solution was added dropwise to the bentonite suspension, wherein the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.22:1, the ratio of triethylenetetramine to amino-modified bentonite was 0.4 mL:1 g, and the molar ratio of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.1 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 52 °C. After all the addition was completed, the water bath heating was maintained for 1.2 h. The resulting product was then filtered, washed, and dried to obtain the composite modified bentonite.

[0158] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 12 mg / mL. The coated modified compound fertilizer obtained in step (1), the grafted modified nanocellulose obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is 2.2:0.42:10:2.2:0.52. After mixing evenly, the mixture is ultrasonically dispersed at 85 kW for 2.5 h to obtain a composite sol.

[0159] The composite sol was added dropwise to a 2.2 wt% calcium chloride solution at a rate of 0.12 mL / s and soaked for 12 min to obtain a hydrogel microsphere precursor. The hydrogel microsphere precursor was then removed and soaked in a 2.2 wt% sodium sulfate solution for 12 min to obtain composite hydrogel microspheres. The composite hydrogel microspheres were freeze-dried at -35℃ for 8 h to obtain the nanocellulose-based composite material.

[0160] Example 3

[0161] This embodiment provides a method for preparing a nano-cellulose-based composite material with sustained-release function, such as... Figure 1 As shown, the preparation method includes:

[0162] (1) Mix 25 parts of diammonium hydrogen phosphate, 14 parts of potassium sulfate, 7 parts of ammonium molybdate, 5 parts of calcium nitrate, 2 parts of zinc sulfate, 1 part of magnesium sulfate, 0.3 parts of copper sulfate, 4 parts of protease and 3 parts of cellulase and place them in a ball mill with a ball-to-material ratio of 6:1 and a ball mill speed of 150 rpm. After mixing and ball milling for 50 min, a compound fertilizer is obtained.

[0163] β-Cyclodextrin was added to a 15 wt% solution of silane coupling agent KH560, with a mass ratio of β-cyclodextrin to silane coupling agent KH560 of 1:0.3. After mixing thoroughly, the mixture was heated under reflux at 55 °C for 3.5 h. The reaction product was filtered, washed, and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was then added to a 10 wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 12:1. The mixture was reacted at 75 °C for 6 h to obtain grafted modified cyclodextrin.

[0164] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 7wt% cyclodextrin solution. Compound fertilizer was added to the cyclodextrin solution at a mass ratio of 1:15 between the compound fertilizer and the grafted modified cyclodextrin. After mixing evenly, the mixture was freeze-dried at -25℃ for 2 hours to obtain the coated modified compound fertilizer.

[0165] (2) Add citric acid to a 1 wt% nanocellulose solution, the mass ratio of nanocellulose to citric acid is 1:7, stir at 550 r / min for 1.5 h to obtain the first reaction solution; transfer the first reaction solution to a reaction vessel and react at 100 °C for 4 h; after filtration, washing and drying, the reaction product is obtained as citric acid modified nanocellulose.

[0166] Citric acid-modified nanocellulose was soaked in ethanol at 45°C for 2.5 h to allow it to fully swell and form a suspension. EDC was added to the suspension, and NHS was added after stirring at 25°C for 13 min. Stirring was continued at 25°C for 0.7 h. The molar ratio of NHS to EDC was 1:1, and the mass ratio of the total mass of NHS and EDC to the mass of citric acid-modified nanocellulose was 0.05:1.

[0167] Subsequently, L-cysteine ​​was added to the suspension. The mass ratio of citric acid modified nanocellulose to L-cysteine ​​was 1:11. After mixing evenly, a second reaction solution was obtained. The second reaction solution was heated to 110°C and kept at that temperature for 5 hours to allow the reaction to occur. The reaction product was filtered, washed, and dried to obtain grafted modified nanocellulose.

[0168] (3) Add bentonite to a 15wt% solution of silane coupling agent KH560. The mass ratio of bentonite to silane coupling agent KH560 is 1:1.25. Heat and stir at 105℃ for 1h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0169] Hexadecyltrimethylammonium bromide, ethylenediamine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution, wherein the concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.2 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 3 wt%. The composite modified solution was added dropwise to the bentonite suspension, wherein the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.25:1, the ratio of ethylenediamine to amino-modified bentonite was 0.5 mL:1 g, and the molar amount of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.2 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 55 °C. After all the addition was completed, the water bath heating was maintained for 1.5 h. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0170] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 15 mg / mL. The coated modified compound fertilizer obtained in step (1), the grafted modified nanocellulose obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is 2.5:0.45:10:2.5:0.55. After mixing evenly, the mixture is ultrasonically dispersed at 90 kW for 2 h to obtain a composite sol.

[0171] The composite sol was added dropwise to a 2.5 wt% calcium chloride solution at a rate of 0.15 mL / s and soaked for 15 min to obtain a hydrogel microsphere precursor. The hydrogel microsphere precursor was then removed and soaked in a 2.5 wt% sodium sulfate solution for 15 min to obtain composite hydrogel microspheres. The composite hydrogel microspheres were freeze-dried at -30℃ for 10 h to obtain the nanocellulose-based composite material.

[0172] Example 4

[0173] This embodiment provides a method for preparing a nano-cellulose-based composite material with sustained-release function, such as... Figure 1 As shown, the preparation method includes:

[0174] (1) Mix 28 parts of diammonium hydrogen phosphate, 14 parts of potassium sulfate, 8 parts of ammonium molybdate, 5 parts of calcium nitrate, 2.5 parts of zinc sulfate, 1.2 parts of magnesium sulfate, 0.4 parts of copper sulfate, 4.5 parts of protease and 3.5 parts of cellulase and place them in a ball mill with a ball-to-material ratio of 6.5:1 and a ball mill speed of 180 rpm. After mixing and ball milling for 45 min, a compound fertilizer is obtained.

[0175] β-Cyclodextrin was added to an 18 wt% solution of silane coupling agent KH560, with a mass ratio of β-cyclodextrin to silane coupling agent KH560 of 1:0.4. After mixing thoroughly, the mixture was heated under reflux at 58 °C for 3.2 h. The reaction product was filtered, washed, and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was then added to a 12 wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 13:1. The mixture was reacted at 78 °C for 6 h to obtain grafted modified cyclodextrin.

[0176] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain an 8wt% cyclodextrin solution. Compound fertilizer was added to the cyclodextrin solution at a mass ratio of 1:18 to the grafted modified cyclodextrin. After mixing evenly, the mixture was freeze-dried at -22℃ for 2.5h to obtain the coated modified compound fertilizer.

[0177] (2) Add citric acid to a 1.2 wt% nanocellulose solution, with a mass ratio of nanocellulose to citric acid of 1:7. Stir at 580 r / min for 1.2 h to obtain the first reaction solution. Transfer the first reaction solution to a reaction vessel and react at 105 °C for 3.5 h. After filtration, washing and drying, the reaction product is citric acid modified nanocellulose.

[0178] Citric acid-modified nanocellulose was soaked in ethanol at 48°C for 2.2 h to allow it to fully swell and form a suspension. EDC was added to the suspension, and NHS was added after stirring at 30°C for 12 min. Stirring was continued at 28°C for 0.6 h. The molar ratio of NHS to EDC was 1:1, and the mass ratio of the total mass of NHS and EDC to the mass of citric acid-modified nanocellulose was 0.08:1.

[0179] Subsequently, L-cysteine ​​was added to the suspension. The mass ratio of citric acid modified nanocellulose to L-cysteine ​​was 1:11.5. After mixing evenly, a second reaction solution was obtained. The second reaction solution was heated to 115°C and kept at that temperature for 4.5 h to allow the reaction to occur. The reaction product was filtered, washed and dried to obtain grafted modified nanocellulose.

[0180] (3) Add bentonite to a 18wt% solution of silane coupling agent KH560. The mass ratio of bentonite to silane coupling agent KH560 is 1:1.28. Heat and stir at 108℃ for 0.8h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0181] Hexadecyltrimethylammonium bromide, diethylenetriamine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution, wherein the concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.2 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 4 wt%. The composite modified solution was added dropwise to the bentonite suspension, wherein the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.28:1, the ratio of diethylenetriamine to amino-modified bentonite was 0.6 mL:1 g, and the molar amount of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.3 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 58 °C. After all the addition was completed, the water bath heating was maintained for 1.8 h. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0182] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 18 mg / mL. The coated modified compound fertilizer obtained in step (1), the grafted modified nanocellulose obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is 2.8:0.48:10:2.8:0.58. After mixing evenly, the mixture is ultrasonically dispersed at 95 kW for 1.5 h to obtain a composite sol.

[0183] The composite sol was added dropwise to a 2.8 wt% calcium chloride solution at a rate of 0.18 mL / s and soaked for 18 min to obtain a hydrogel microsphere precursor. The hydrogel microsphere precursor was then removed and soaked in a 2.8 wt% sodium sulfate solution for 18 min to obtain composite hydrogel microspheres. The composite hydrogel microspheres were freeze-dried at -25℃ for 11 h to obtain the nanocellulose-based composite material.

[0184] Example 5

[0185] This embodiment provides a method for preparing a nano-cellulose-based composite material with sustained-release function, such as... Figure 1 As shown, the preparation method includes:

[0186] (1) Mix 30 parts of diammonium hydrogen phosphate, 15 parts of potassium sulfate, 10 parts of ammonium molybdate, 6 parts of calcium nitrate, 3 parts of zinc sulfate, 1.5 parts of magnesium sulfate, 0.5 parts of copper sulfate, 5 parts of protease and 4 parts of cellulase and place them in a ball mill with a ball-to-material ratio of 7:1 and a ball mill speed of 200 rpm. After mixing and ball milling in the ball mill for 40 min, a compound fertilizer is obtained.

[0187] β-Cyclodextrin was added to a 20 wt% solution of silane coupling agent KH570, with a mass ratio of β-cyclodextrin to silane coupling agent KH570 of 1:0.5. After mixing evenly, the mixture was heated under reflux at 60°C for 3 hours. The reaction product was filtered, washed, and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was then added to a 15 wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 15:1. The mixture was reacted at 80°C for 5 hours to obtain grafted modified cyclodextrin.

[0188] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 10wt% cyclodextrin solution. Compound fertilizer was added to the cyclodextrin solution at a mass ratio of 1:20 to the grafted modified cyclodextrin. After mixing evenly, the mixture was freeze-dried at -20℃ for 3 hours to obtain the coated modified compound fertilizer.

[0189] (2) Add citric acid to a 1.5 wt% nanocellulose solution, with a mass ratio of nanocellulose to citric acid of 1:8. Stir at 600 r / min for 1 h to obtain the first reaction solution. Transfer the first reaction solution to a reaction vessel and react at 110 °C for 3 h. After filtration, washing and drying, the reaction product is obtained as citric acid modified nanocellulose.

[0190] Citric acid-modified nanocellulose was soaked in ethanol at 50°C for 2 hours to allow it to fully swell and form a suspension. EDC was added to the suspension, and NHS was added after stirring at 30°C for 10 minutes. Stirring was continued at 30°C for 0.5 hours. The molar ratio of NHS to EDC was 1:1, and the mass ratio of the total mass of NHS and EDC to the mass of citric acid-modified nanocellulose was 0.1:1.

[0191] Subsequently, L-cysteine ​​was added to the suspension. The mass ratio of citric acid modified nanocellulose to L-cysteine ​​was 1:12. After mixing evenly, a second reaction solution was obtained. The second reaction solution was heated to 120°C and kept at that temperature for 4 hours to allow the reaction to occur. The reaction product was filtered, washed, and dried to obtain grafted modified nanocellulose.

[0192] (3) Add bentonite to a 20wt% solution of silane coupling agent KH570. The mass ratio of bentonite to silane coupling agent KH570 is 1:1.3. Heat and stir at 110℃ for 0.5h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0193] Hexadecyltrimethylammonium bromide, diethylenetriamine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution, wherein the concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.25 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 5 wt%. The composite modified solution was added dropwise to the bentonite suspension, wherein the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.3:1, the ratio of diethylenetriamine to amino-modified bentonite was 0.8 mL:1 g, and the molar amount of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.5 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 60 °C. After all the addition was completed, the water bath heating was maintained for 2 hours. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0194] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 20 mg / mL. The coated modified compound fertilizer obtained in step (1), the grafted modified nanocellulose obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is 3:0.5:10:3:0.6. After mixing evenly, the mixture is ultrasonically dispersed at 100 kW for 1 h to obtain a composite sol.

[0195] The composite sol was added dropwise to a 3 wt% calcium chloride solution at a rate of 0.2 mL / s and soaked for 20 min to obtain a hydrogel microsphere precursor. The hydrogel microsphere precursor was then removed and soaked in a 3 wt% sodium sulfate solution for 20 min to obtain composite hydrogel microspheres. The composite hydrogel microspheres were freeze-dried at -20℃ for 12 h to obtain the nanocellulose-based composite material.

[0196] Example 6

[0197] This embodiment provides a method for preparing a nano-cellulose-based composite material with a slow-release function. The difference from Example 1 is that in step (1), the mass ratio of compound fertilizer to grafted modified cyclodextrin is adjusted to 1:8, while other process parameters and operation steps are exactly the same as in Example 1.

[0198] Example 7

[0199] This embodiment provides a method for preparing a nano-cellulose-based composite material with a slow-release function. The difference from Embodiment 1 is that in step (1), the mass ratio of compound fertilizer to grafted modified cyclodextrin is adjusted to 1:23, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0200] Example 8

[0201] This embodiment provides a method for preparing a nanocellulose-based composite material with sustained-release function. The difference from Embodiment 1 is that in step (2), the mass ratio of nanocellulose to citric acid is adjusted to 1:3, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0202] Example 9

[0203] This embodiment provides a method for preparing a nanocellulose-based composite material with sustained-release function. The difference from Embodiment 1 is that in step (2), the mass ratio of nanocellulose to citric acid is adjusted to 1:10, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0204] Example 10

[0205] This embodiment provides a method for preparing a nanocellulose-based composite material with sustained-release function. The difference from Example 1 is that in step (3), the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is adjusted to 0.1:1. Other process parameters and operation steps are exactly the same as in Example 1.

[0206] Example 11

[0207] This embodiment provides a method for preparing a nanocellulose-based composite material with sustained-release function. The difference from Example 1 is that in step (3), the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is adjusted to 0.4:1. Other process parameters and operation steps are exactly the same as in Example 1.

[0208] Example 12

[0209] This embodiment provides a method for preparing a nanocellulose-based composite material with a slow-release function. The difference from Embodiment 1 is that in step (4), the mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is adjusted to 2:0.3:10:2:0.5. Other process parameters and operation steps are exactly the same as in Embodiment 1.

[0210] Example 13

[0211] This embodiment provides a method for preparing a nanocellulose-based composite material with a slow-release function. The difference from Embodiment 1 is that in step (4), the mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose and composite modified bentonite is adjusted to 2:0.6:10:2:0.5. Other process parameters and operation steps are exactly the same as in Embodiment 1.

[0212] Application examples

[0213] The nanocellulose-based composite material prepared in Example 1 of this invention was used in the potato planting process. The specific operation steps are as follows:

[0214] An experimental area was set up, with a planting area of ​​200m². 2 On level ground, create raised beds with a row spacing of 70-80cm, plant in single rows with a plant spacing of 15-18cm, cover with soil to a thickness of 10-13cm, and maintain 4000-4500 seedlings per mu (approximately 667 square meters). Prepare a 500-fold dilution (concentration 2.0 × 10⁻⁶) using the nano-cellulose-based composite material obtained in Example 1 above. 5 (cfu / mL, hereinafter referred to as this product), apply as a foliar spray once on the 30th, 45th and 60th day after the potatoes emerge, with a spraying amount of 40mL / acre each time;

[0215] Control area 1 was set up with a planting area of ​​200m². 2 Prepare raised beds on level ground, with a row spacing of 70-80cm. Plant in single rows with a plant spacing of 15-18cm. Cover with 10-13cm of soil, maintaining 4000-4500 seedlings per mu (approximately 667 square meters). Prepare a 500-fold dilution (2.0 × 10⁻⁶) of commercially available Stanley controlled-release fertilizer. 5 (cfu / mL, hereinafter referred to as commercially available product), apply as a foliar spray once each on the 30th, 45th and 60th day after the potatoes emerge, with a spraying amount of 40mL / acre each time;

[0216] Control area 2 was set up with a planting area of ​​200m². 2 Prepare raised beds on flat ground with a row spacing of 70-80cm. Plant in single rows with a plant spacing of 15-18cm. Cover the plants with 10-13cm of soil and maintain 4000-4500 seedlings per mu. Apply foliar spray with clean water on the 30th, 45th, and 60th days after the potatoes emerge, with each application being 40mL / mu.

[0217] The results showed that, compared with control area 2, the symptoms of leaf wrinkling and stunting were partially alleviated after spraying the commercially available product in control area 1, and the average yield per mu increased by 13.5%. Compared with control area 2, the symptoms of leaf wrinkling and stunting were significantly alleviated after spraying the product in the experimental area, and the average yield per mu increased by 25.8%. After spraying the product, potatoes grew well, had a low incidence of pests and diseases, and high foliar fertilizer utilization, which helped to enhance photosynthesis, improve potato yield and quality, and had good economic benefits and market promotion value.

[0218] The swelling rate, water retention rate, and sustained-release performance of the nanocellulose-based composite materials prepared in Examples 1-13 were tested. The specific test steps are as follows:

[0219] (1) Swelling rate

[0220] A certain mass of sample was placed in an 80℃ oven for vacuum drying for 1 hour. The dried sample was weighed and recorded as M2 (g). At room temperature, the dried sample was completely immersed in deionized water for 48 hours to allow it to fully swell. The swollen sample was then removed, and the surface moisture was blotted dry with filter paper. The swollen sample was weighed and recorded as M1 (g). The swelling rate (SR, %) of the sample was calculated using the following formula:

[0221] .

[0222] (2) Water retention rate

[0223] A certain mass of sample was placed in an 80℃ oven for vacuum drying for 1 hour. The dried sample was then completely immersed in deionized water for 48 hours to reach swelling equilibrium at room temperature. The swollen sample was weighed and recorded as W (g). It was then placed in a constant temperature and humidity environment of 25°C and 30% for 12 hours, and then weighed again and recorded as W. p (g) The water retention rate (WH, %) of the sample is calculated using the following formula:

[0224] .

[0225] (3) Sustained-release performance

[0226] According to the requirements of standard GB / T23348-2009 "Slow-Release Fertilizer Standard", the cumulative release rate of the nanocellulose-based composite materials prepared in Examples 1-13 was tested in still water at 25°C on the 15th and 30th days.

[0227] The test results are shown in Table 1.

[0228] Table 1

[0229] Swelling rate % Water retention rate % 15-day cumulative release rate % 30-day cumulative release rate % Example 1 85.2 90.3 53.2 77.5 Example 2 88.4 93.5 50.3 73.4 Example 3 93.8 94.2 49.6 72.7 Example 4 95.5 95.8 47.5 70.3 Example 5 96.7 97.2 46.8 68.0 Example 6 66.0 80.4 84.5 90.3 Example 7 70.4 82.6 82.4 88.5 Example 8 72.7 83.3 78.2 86.1 Example 9 75.6 85.5 77.3 84.7 Example 10 78.1 86.7 75.8 82.6 Example 11 80.3 87.0 72.6 80.3 Example 12 56.9 74.6 88.4 95.8 Example 13 64.7 76.1 85.7 93.0

[0230] As can be seen from the test data of Examples 1-5, the nanocellulose-based composite material prepared by the present invention has excellent water retention capacity and slow release capacity. When used as a foliar fertilizer, it can produce different release rates and effects at different stages of crop growth and development, which is conducive to improving the utilization rate of compound fertilizer and also meets the concept of green and sustainable development. It has broad application prospects in actual production.

[0231] The test data from Examples 1, 6, and 7 show that the swelling rate and water retention rate of the nano-cellulose-based composite materials prepared in Examples 6 and 7 are lower than those in Example 1, and the cumulative release on days 15 and 30 are significantly higher than those in Example 1. This indicates that the compound fertilizer in the nano-cellulose-based composite materials prepared in Examples 6 and 7 is released in large quantities in the early stage of the slow-release performance test, and almost all of it is released by day 30, resulting in a poor slow-release effect. This is because the amount of grafted modified cyclodextrin added directly affects the encapsulation effect on the compound fertilizer, thereby affecting the swelling rate, water retention rate, and slow-release capacity of the final nano-cellulose-based composite material.

[0232] The test data from Examples 1, 8, and 9 show that the swelling rate and water retention rate of the nanocellulose-based composite materials prepared in Examples 8 and 9 are lower than those in Example 1. Furthermore, the cumulative release on days 15 and 30 are significantly higher than that in Example 1. This indicates that the compound fertilizer in the nanocellulose-based composite materials prepared in Examples 8 and 9 is released in large quantities in the early stages of the slow-release performance test, and is almost completely released by day 30, resulting in a poor slow-release effect. This is because the mass ratio of nanocellulose to citric acid directly affects the esterification effect of nanocellulose, reducing the carboxyl group content on the nanocellulose, thus affecting the swelling rate, water retention rate, and slow-release capacity of the final nanocellulose-based composite material.

[0233] The test data from Examples 1, 10, and 11 show that the cumulative release amounts of the nano-cellulose-based composite materials prepared in Examples 10 and 11 on days 15 and 30 were significantly higher than those in Example 1. This indicates that the compound fertilizer in the nano-cellulose-based composite materials prepared in Examples 10 and 11 was released in large quantities in the early stages of the slow-release performance test, and by day 30, it had been almost completely released, resulting in a poor slow-release effect. This is because the amount of hexadecyltrimethylammonium bromide added directly affects the intercalation effect on bentonite, thereby affecting the interlayer spacing of bentonite, and thus the inhibitory effect of the composite modified bentonite on the diffusion of compound fertilizer cannot be fully exerted.

[0234] The test data from Examples 1, 12, and 13 show that the swelling rate and water retention rate of the nanocellulose-based composite materials prepared in Examples 12 and 13 are lower than those in Example 1, and the cumulative release on days 15 and 30 are significantly higher than that in Example 1. This indicates that the compound fertilizer in the nanocellulose-based composite materials prepared in Examples 12 and 13 is released in large quantities in the early stage of the slow-release performance test, and by day 30, it has been almost completely released, resulting in a poor slow-release effect. This is because the amount of sodium alginate added directly affects the swelling rate and water retention rate of the nanocellulose-based composite material, thus affecting its slow-release capacity.

[0235] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a nano-cellulose-based composite material with sustained-release function, characterized in that, The preparation method includes: (I) A compound fertilizer is obtained by ball milling a mixture of diammonium hydrogen phosphate, potassium sulfate, ammonium molybdate, calcium nitrate, zinc sulfate, magnesium sulfate, copper sulfate, protease, and cellulase; β-cyclodextrin is added to a silane coupling agent solution, mixed evenly, and then subjected to a reflux reaction. The reaction product is filtered, washed, and dried to obtain an amino-modified cyclodextrin; the amino-modified cyclodextrin is added to a polylactic acid solution, and after mixing and reaction, a graft-modified cyclodextrin is obtained; the graft-modified cyclodextrin is dispersed in N,N-dimethylformamide to obtain a cyclodextrin solution, the compound fertilizer is added to the cyclodextrin solution, mixed evenly, and then freeze-dried to obtain a coated modified compound fertilizer; (II) Citric acid is added to the nanocellulose solution and mixed evenly to obtain a first reaction solution. The first reaction solution is transferred to a reaction vessel for reaction. The reaction product is filtered, washed and dried to obtain citric acid modified nanocellulose. The citric acid modified nanocellulose is immersed in ethanol and heated to allow the citric acid modified nanocellulose to fully swell in the ethanol to form a suspension. L-cysteine ​​is added to the suspension and mixed evenly to obtain a second reaction solution. The second reaction solution is heated to allow the reaction to occur. The reaction product is filtered, washed and dried to obtain grafted modified nanocellulose. (III) Bentonite is added to a silane coupling agent solution, heated and stirred to react, and the reaction product is filtered, washed and dried to obtain amino-modified bentonite; hexadecyltrimethylammonium bromide, polycarboxylic acid metal chelating agent and aluminum hydroxide pillar agent are dispersed in deionized water and mixed evenly to obtain a composite modified solution; the amino-modified bentonite is dispersed in deionized water and mixed evenly to obtain a bentonite suspension, and the composite modified solution is added dropwise to the bentonite suspension, while stirring and heating are carried out continuously during the dropwise addition. After all the dropwise addition is completed, heating is continued for a period of time, and then the composite modified bentonite is obtained after filtration, washing and drying. (IV) Chitosan, sodium alginate, and deionized water are mixed and stirred until homogeneous to obtain a mixture; the coated modified compound fertilizer, the grafted modified nanocellulose, and the composite modified bentonite are added to the mixture, and ultrasonic dispersion is performed to obtain a composite sol; the composite sol is added dropwise to a calcium salt solution and soaked for a period of time to obtain a hydrogel microsphere precursor; the hydrogel microsphere precursor is taken out and soaked in a sulfate solution to obtain composite hydrogel microspheres; the composite hydrogel microspheres are freeze-dried to obtain the nanocellulose-based composite material.

2. The preparation method according to claim 1, characterized in that, In step (I), the compound fertilizer comprises the following components in parts by weight: 20-30 parts of diammonium hydrogen phosphate; 12-15 parts potassium sulfate; 5-10 parts of ammonium molybdate; Calcium nitrate 3-6 parts; 1-3 parts zinc sulfate; Magnesium sulfate 0.5~1.5 parts; Copper sulfate 0.1~0.5 parts; 3-5 parts of protease; 2-4 parts cellulase; The rotation speed of the mixing ball mill is 100~200 rpm; The mixing and ball milling time is 40-60 minutes; The ball-to-material ratio of the mixed ball mill is (5~7):

1.

3. The preparation method according to claim 1, characterized in that, In step (I), the silane coupling agent solution is composed of a silane coupling agent and an aqueous ethanol solution; The mass fraction of the silane coupling agent in the silane coupling agent solution is 10~20 wt%; The mass ratio of the β-cyclodextrin to the silane coupling agent in the silane coupling agent solution is 1:(0.1~0.5); The temperature of the heating reflux reaction is 50~60℃; The heating and reflux reaction time is 3-4 hours; The polylactic acid solution contains 5-15 wt% polylactic acid. The mass ratio of the amino-enhanced cyclodextrin to the polylactic acid in the polylactic acid solution is (10~15):1; The mixing reaction temperature of the amino-substituted cyclodextrin and the polylactic acid solution is 70~80℃; The reaction time for the amino-modified cyclodextrin and the polylactic acid solution is 5-8 hours. The grafted modified cyclodextrin in the cyclodextrin solution has a mass fraction of 5-10 wt%. The mass ratio of the compound fertilizer to the grafted modified cyclodextrin in the cyclodextrin solution is 1:(10~20); The freeze-drying temperature is -30~-20℃; The freeze-drying time is 1 to 3 hours.

4. The preparation method according to claim 1, characterized in that, In step (II), the mass fraction of the nanocellulose solution is 0.5~1.5 wt%. The mass ratio of nanocellulose to citric acid in the nanocellulose solution is 1:(5~8); The mixing speed of the nanocellulose solution and the citric acid is 500~600 r / min; The mixing and stirring time for the nanocellulose solution and the citric acid is 1-2 hours; The reaction temperature of the first reaction solution is 90~110℃; The reaction time of the first reaction solution is 3-5 hours.

5. The preparation method according to claim 1, characterized in that, In step (II), the citric acid modified nanocellulose is soaked in ethanol for 2-3 hours; The citric acid-modified nanocellulose was soaked in ethanol at a temperature of 40-50°C. The mass ratio of citric acid-modified nanocellulose to L-cysteine ​​in the suspension is 1:(10~12); The reaction temperature of the second reaction solution is 100~120℃; The reaction time for the second reaction solution is 4-6 hours.

6. The preparation method according to claim 1, characterized in that, In step (III), the silane coupling agent solution is composed of a silane coupling agent and an aqueous ethanol solution; The mass fraction of the silane coupling agent in the silane coupling agent solution is 10~20 wt%; The mass ratio of the bentonite to the silane coupling agent in the silane coupling agent solution is 1:(1.2~1.3); The reaction temperature between the bentonite and the silane coupling agent solution is 100~110℃; The reaction time between the bentonite and the silane coupling agent solution is 0.5~1.5h.

7. The preparation method according to claim 1, characterized in that, In step (III), the concentration of hexadecyltrimethylammonium bromide in the composite modified solution is 0.1~0.25 mol / L; The mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite in the bentonite suspension is (0.2-0.3):1; The ratio of the polycarboxylated metal chelating agent to the amino-modified bentonite in the bentonite suspension is (0.3~0.8) mL:1 g; The polycarboxylated metal chelating agent includes any one or a combination of at least two of tetraethylenepentamine, triethylenetetramine, ethylenediamine or diethylenetriamine; The ratio of aluminum ions in the hydroxyaluminum pillar agent to amino-modified bentonite in the bentonite suspension is (1.0~1.5) mmol:1g. The mass fraction of amino-modified bentonite in the bentonite suspension is 1-5 wt%. The heating temperature is 50-60℃; After all the composite modified solution has been added dropwise, continue heating for 1-2 hours.

8. The preparation method according to claim 1, characterized in that, In step (IV), the concentration of chitosan in the mixture is 10~20 mg / mL; The mass ratio of the chitosan, sodium alginate, coated modified compound fertilizer, grafted modified nanocellulose, and composite modified bentonite is (2~3):(0.4~0.5):10:(2~3):(0.5~0.6); The ultrasonic power used for ultrasonic dispersion is 80~100kW; The ultrasonic dispersion process takes 1 to 3 hours.

9. The preparation method according to claim 1, characterized in that, In step (IV), the dropping rate of the composite sol is 0.1~0.2 mL / s; The calcium salt solution has a mass fraction of 2-3 wt%; The immersion time of the composite sol droplets in the calcium salt solution is 10-20 minutes; The sulfate solution has a mass fraction of 2-3 wt%. The hydrogel microbead precursor was soaked in the sulfate solution for 10-20 minutes. The freeze-drying temperature of the composite hydrogel microspheres is -40~-20℃; The freeze-drying time for the composite hydrogel microspheres is 6-12 hours.

10. A nanocellulose-based composite material with sustained-release function prepared by the preparation method according to any one of claims 1 to 9.

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