Water-retaining composite material and method for producing the same

Abstract

The application provides a water-retaining composite material and a preparation method thereof, and the water-retaining composite material is prepared by the following steps: firstly, a porous water-retaining framework is prepared by inverse suspension polymerization as a water storage carrier; then, a root-promoting functional coating is coated on the outer layer of the framework; then, a sodium alginate-xanthan gum gel system is used to wrap the composite microbial agent to independently form microspheres, so as to isolate the damage of the external harsh environment to the microorganisms; finally, the microbial agent microspheres are embedded and filled into the open pores inside the framework through three-dimensional mixing, so that the water-retaining carrier, the slow-release microbial unit and the root-promoting coating are integrated in three layers from the structural level. The porous embedded three-dimensional space structure seals the microorganisms in the pores inside the framework, which can realize long-acting water absorption and water storage, and the gel microspheres can slow release and protect the microbial population, the outer coating can directly contact the seedling roots to stimulate rapid rooting, and the industry pain points such as difficulty in maintaining the activity of the microorganisms, poor water-retaining and biological function synergy, easy loss of the microbial agent, inability of the product to be stored for a long time, slow seedling rooting and the like are solved from the source.

Description

Technical Field

[0001] This invention relates to the field of water-retaining materials and their preparation technology, and particularly to a water-retaining composite material and its preparation method. Background Technology

[0002] Vegetation degradation and ecological restoration in arid and semi-arid regions are common challenges worldwide. Most arid regions are characterized by long dry seasons and low annual precipitation. Prolonged water scarcity directly induces the continuous expansion of desertification and karst desertification, making ecological degradation difficult to reverse. In sandy arid areas, prolonged drought coupled with excessive land consumption creates a vicious cycle, leading to continuous decline in surface vegetation, widespread desertification and sandification, loose soil layers, lack of organic matter, and extremely poor natural water retention capacity. Karst arid regions have even more fragile ecological foundations, with shallow and infertile topsoil layers, weak water and fertilizer retention capacity, and extremely long recovery periods after vegetation degradation. Seedlings cultivated through artificial afforestation generally suffer from weak resilience and low survival rates after planting. The core limiting factor across all arid regions is water scarcity; drought and water shortage significantly increase the difficulty of vegetation restoration and artificial afforestation.

[0003] Existing publicly available water-retaining microbial composite improvement products (such as CN 114686398 A) simply mix water-retaining substrates and microbial agents without creating a dedicated stable microenvironment for the microorganisms. This has two major drawbacks: First, the microorganisms are directly exposed to the arid and acid-base fluctuating soil environment, making it difficult to maintain their activity in the long term, resulting in severe loss of live bacteria during storage and field application. Second, the water-retaining substrate and microbial agents are merely a simple physical mixture, with their functions being independent and unable to form a synergistic structure. The water retention and release process cannot match the needs of microbial survival and root growth, leading to a disconnect between soil and water regulation and biological growth promotion functions, making it difficult to adapt to afforestation scenarios with long-term and continuous drought.

[0004] In response to the common ecological challenges faced by various arid regions, such as water scarcity, soil infertility, difficulty in seedling survival, and easy inactivation of microorganisms, the industry urgently needs to develop an integrated composite material that can maintain microbial activity for a long time, simultaneously achieve multiple synergistic functions such as long-term water retention, root growth promotion, and soil improvement, and is suitable for various arid afforestation environments. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides a water-retaining composite material and its preparation method. The water-retaining composite material can maintain microbial activity for a long time and simultaneously achieve multiple synergistic functions such as long-term water retention, root growth promotion, and soil improvement.

[0006] The specific details of the invention are as follows: In a first aspect, the present invention provides a method for preparing a water-retaining composite material, the method comprising: mixing potassium humate, naphthaleneacetic acid, composite amino acids, sodium carboxymethyl cellulose, and deionized water to form a coating solution; mixing neutralized acrylic monomer, bentonite, and biochar with deionized water to form a dispersion, and then adding a crosslinking agent N,N'-methylenebisacrylamide to prepare an aqueous phase; adding cyclohexane and surfactant Span-60 to a reaction vessel and mixing under heating conditions to form an oil phase; slowly adding the aqueous phase to the oil phase and adding an initiator, reacting at a constant temperature for 2-5 hours, and then filtering, washing, drying, and pulverizing the reactants to obtain a porous water-retaining framework material with a particle size of 1-3 mm; mixing sodium alginate, xanthan gum, and deionized water to form a carrier solution, and adding a composite bacterial agent to the carrier solution to prepare a gel-bacterial mixture; using a drop bead curing process to form immobilized bacterial agent microspheres with a particle size of 0.5-1.2 mm; and immersing the porous water-retaining framework material in the coating solution for 30 hours. After filtration and drying, water-retaining skeleton particles coated with a root-promoting coating are obtained. The water-retaining skeleton particles coated with the root-promoting coating and the microspheres are placed in a three-dimensional mixer for three-dimensional mixing, so that the microspheres enter the open pores of the water-retaining skeleton particles coated with the root-promoting coating to obtain the water-retaining composite material.

[0007] Compared with the prior art, the present invention has the following advantages: This invention constructs two functional units in stages: a porous water-retaining framework coated with a root-promoting coating and immobilized microbial agent microspheres. The immobilized microbial agent microspheres are then embedded into the water-retaining framework particles coated with the root-promoting coating, forming a water-retaining composite material. This method abandons the crude processing approach of simply mixing water-retaining agents and microbial agents in the traditional method. First, a high-porosity porous water-retaining framework is prepared through reverse-phase suspension polymerization, endowing the material with long-lasting water absorption and retention capabilities. The root-promoting coating on the outer layer of the framework directly stimulates rapid root growth in seedlings. Then, the composite microbial agent is encapsulated in a sodium alginate-xanthan gum gel system to form independent microspheres, which can isolate the microorganisms from damage caused by drought and high temperatures, effectively extending the survival period of the microbial community. The water-based skeleton particles, root-promoting coating, and immobilized microbial agent microspheres work synergistically to form an integrated structure that enhances water regulation, slow-release of microorganisms, and root growth. The entire preparation process encapsulates the microbial agent within the skeleton's pores, preventing significant loss during transportation vibrations and field irrigation. The finished product can be stored in a vacuum and protected from light for extended periods. When applied to soils in arid and rocky desertification areas, it provides a continuous and stable supply of water and beneficial microorganisms, improving the rhizosphere soil microenvironment and significantly increasing the survival rate of afforestation seedlings under extreme dry conditions. This effectively overcomes many technical shortcomings of existing technologies, such as rapid decline in microbial activity, poor matching between water retention and biological growth promotion functions, easy loss of microbial agents, the need for materials to be prepared and used immediately, and slow seedling rooting. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A flowchart illustrating the preparation method of the water-retaining composite material provided in an embodiment of the present invention is shown. Detailed Implementation

[0010] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by anyone under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0011] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0012] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of this specification.

[0013] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0014] Firstly, this invention provides a method for preparing a water-retaining composite material. The invention first prepares a high-porosity porous water-retaining framework through reverse-phase suspension polymerization, endowing the material with long-lasting water absorption and retention capabilities. A root-promoting coating on the outer layer of the framework directly stimulates rapid root growth in seedlings. Then, a sodium alginate-xanthan gum gel system is used to encapsulate a composite microbial agent to form independent microspheres, which can isolate the microorganisms from damage caused by drought and high temperatures, effectively extending the survival period of the microbial community. The water-retaining framework particles, the root-promoting coating, and the immobilized microbial agent microspheres work synergistically to form a system that regulates moisture, provides slow-release microbial activity, and promotes root growth. It is an integrated structure that promotes growth and enhances synergistic effects. The entire preparation process encapsulates the microbial agent within the pores of the framework, preventing significant loss of the agent during transportation vibrations and field irrigation. The finished product can be stored in a vacuum and protected from light for a long time. When applied to soils in arid and rocky desertification areas, it can continuously and stably supply water and beneficial microorganisms, improve the rhizosphere soil microenvironment, and significantly increase the survival rate of afforestation seedlings under extreme dry season conditions. It effectively overcomes many technical shortcomings of existing technologies, such as rapid decline in microbial activity, poor matching between water retention and biological growth promotion functions, easy loss of microbial agents, the need for materials to be prepared and used immediately, and slow rooting of seedlings. Figure 1 A flowchart illustrating the preparation method of the water-retaining composite material provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the preparation method includes: S1. Potassium humate, naphthaleneacetic acid, compound amino acids, sodium carboxymethyl cellulose and deionized water are mixed to form a coating solution; In this specific step, the composition of the coating solution is as follows: potassium humate 15 g / L~25 g / L, naphthaleneacetic acid 0.4 g / L~1.0 g / L, compound amino acids 4 g / L~6 g / L, and sodium carboxymethyl cellulose 8~12 g / L. Potassium humate can improve the organic matter structure of arid and infertile soils, naphthaleneacetic acid can directionally stimulate seedling rooting, compound amino acids can continuously supply biological nutrients, and sodium carboxymethyl cellulose can act as a binder to ensure that the coating is uniformly and firmly coated on the surface of the skeleton. The preferred compound amino acid is a combination of glycine + glutamic acid + arginine, with a total amino acid content ≥50%. When the coating solution meets the above concentration range, the solution has suitable fluidity, can completely coat the skeleton particles without clogging the internal pores, and the coating is not easy to fall off after drying. When the material comes into contact with the seedling roots, it can quickly promote root growth, improve the soil, and enhance the seedlings' early resistance to drought stress. The coating solution is used for subsequent coating of porous water-retaining skeleton materials.

[0015] S2. Neutralized acrylic monomer, bentonite and biochar are mixed with deionized water to form a dispersion, and then crosslinking agent N,N'-methylenebisacrylamide is added to prepare an aqueous phase; cyclohexane and surfactant Span-60 are added to the reactor and heated to form an oil phase; In this step, when preparing the aqueous phase, based on 100 parts by weight of neutralized acrylic acid, the amounts of bentonite (12-18 parts), biochar (8-15 parts), and crosslinking agent N,N'-methylenebisacrylamide (0.06%-0.1% of the mass of neutralized acrylic acid) are limited. Appropriate amounts of bentonite enhance the ion exchange capacity and brine adsorption performance of the framework. Biochar acts as a controllable pore-forming agent to construct continuous porous channels, and the crosslinking agent is used to precisely control the density of the three-dimensional crosslinked network. Within the above ratio range, the aqueous dispersion system is uniform and stable. After polymerization, the framework has an open porosity of over 40%, and the water absorption ratio of deionized water and brine meets the standards. Even after 20 repeated water absorption cycles, it retains over 70% of its initial water retention capacity. The framework structure is not easily disintegrated, and the sufficient pores provide a stable embedding space for subsequent microbial agent microspheres. This approach balances water retention capacity, pore structure stability, and framework mechanical strength, providing a suitable carrier substrate for the embedded composite structure.

[0016] It should be noted that the neutralized acrylic acid monomer was obtained by adding sodium hydroxide solution dropwise to the acrylic acid monomer under ice-water bath for neutralization treatment, and the degree of neutralization was controlled at 65%~75%; the biochar used in this embodiment can preferably be coconut shell or rice husk biochar with a mesh size of 200-500 mesh.

[0017] When preparing the oil phase, the volume ratio of cyclohexane to the aqueous phase is 1.8:1 to 2.2:1; the mass ratio of surfactant Span-60 in the oil phase is 2% to 4%. This ratio forms a stable and uniform W / O water-in-oil suspension system, dispersing the aqueous phase into uniformly sized microdroplets. After polymerization, sieving yields stable 1-3 mm standard particle size skeleton particles with no large agglomerates and uniform pore distribution. When heated to 50℃-60℃, cyclohexane and surfactant Span-60 are thoroughly mixed after the surfactant Span-60 dissolves. An appropriate amount of Span-60 only plays an emulsifying and dispersing role and can be basically removed by washing after polymerization. It will not inhibit the subsequent embedding of microorganisms, thus ensuring the quality of skeleton formation while controlling the cost of emulsifiers and organic solvents.

[0018] S3. The aqueous phase is slowly added dropwise to the oil phase, and an initiator is added. The reaction is carried out at a constant temperature of 55 ℃-80 ℃ for 2h-5h. The reactants are then filtered, washed, dried and pulverized to obtain a porous water-retaining skeleton material with a particle size of 1~3 mm. In this step, a redox complex initiation system of ammonium persulfate and sodium bisulfite in a 1:1 molar ratio is used. This complex system can stably release free radicals at medium and low temperatures of around 60 °C, resulting in a uniform and controllable polymerization rate and avoiding localized explosive agglomeration. The total addition amount is controlled to be 0.4%~0.6% of the total mass of neutralized acrylic acid monomers to ensure full polymerization of acrylic acid monomers, significantly reduce toxic monomer residues, eliminate the killing effect of residual monomers on the composite microbial agent, and at the same time avoid excessive cross-linking and blocking of the framework pores, ensuring that the porous water-retaining framework has a uniform and interconnected pore structure, thus balancing polymerization integrity, pore formation effect, and microbial safety.

[0019] S4. Sodium alginate, xanthan gum, and deionized water are mixed to form a carrier solution, and the composite bacterial agent is added to the carrier solution to prepare a gel-bacterial mixture; the gel-bacterial mixture is solidified by a drop bead curing process to form immobilized bacterial agent microspheres with a particle size of 0.5~1.2 mm; In this specific implementation step, the total mass-volume concentration of sodium alginate and xanthan gum in the carrier solution is 2.0%~3.0%; the mass ratio of sodium alginate to xanthan gum is 3:1~4:1. Xanthan gum can form a composite cross-linked gel network with sodium alginate, significantly improving the mechanical resistance to breakage of microspheres and reducing stirring losses. The flowability of the carrier solution in this concentration range is suitable for peristaltic pump droplet technology, which can stably form standard microspheres of 0.5~1.2 mm. The composite gel network has a controllable slow-release channel, which can both solidify and encapsulate microorganisms to prevent large-scale loss in a short period of time, and slowly decompose and release beneficial bacteria in the soil environment, so as to achieve a long-term continuous supply of rhizosphere microorganisms during the dry season. In this specific implementation step, the compound microbial agent is obtained by mixing arbuscular mycorrhizal (AM) fungal spore suspension, Bacillus subtilis bacterial solution, and yeast bacterial solution in a volume ratio of 1:1.5:1 to 1:2.5:1. AM fungi are used to promote the extension of seedling roots, Bacillus subtilis has the function of phosphorus solubilization and nitrogen fixation to improve soil, and yeast optimizes the rhizosphere microenvironment to enhance the overall stress resistance of the microbial community. The three work synergistically to significantly improve the drought resistance of seedlings. At the same time, the volume ratio of compound microbial agent to carrier solution in gel-bacteria mixture is limited to 1:3 to 1:5. Without compromising the gel droplet forming performance, this ensures that the microspheres have a sufficient live bacteria load, taking into account both gel forming stability and effective microbial addition, so that the finished product can maintain a high concentration of live bacteria in the rhizosphere even in long-term drought soil.

[0020] In this step, the droplet solidification process was carried out using a peristaltic pump (flow rate 2 mL / min). The gel-bacterial mixture was dropped into a sterile 3% (w / v) calcium chloride solution (containing 0.5% Tween-80) through a 0.8 mm inner diameter needle, with the needle 8 cm above the liquid surface. The mixture was allowed to solidify in the calcium chloride solution for 30 min, with gentle stirring to prevent adhesion. Finally, the collected microspheres were washed three times with sterile physiological saline (0.9% NaCl) to remove unfixed bacteria and residual calcium ions. Immobilized microspheres with a particle size range of 0.5–1.2 mm were collected by sieving. Plate count analysis showed that the viable Bacillus subtilis count within the microspheres was ≥1.2 × 10⁻⁶. 8 CFU / g, yeast ≥6×10 6 CFU / g, AM fungal spore density ≥10 spores / g, immobilization rate ≥97%.

[0021] S5. Immerse the porous water-retaining skeleton material in the coating solution for 30 min-120 min, and after filtration and drying, obtain water-retaining skeleton particles coated with a root-promoting coating. In this step, the solid-liquid ratio of the porous water-retaining skeleton material to the coating solution is 1:5-10, preferably 1:5. The filtered wet particles are spread evenly on a stainless steel mesh tray and dried in a 40 ℃ hot air drying oven until the surface is no longer sticky (about 2~3 hours), thus obtaining water-retaining skeleton particles coated with a root-promoting coating.

[0022] S6. The water-retaining skeleton particles coated with the root-promoting coating and the microspheres are placed in a three-dimensional mixer for three-dimensional mixing, so that the microspheres enter the open pores of the water-retaining skeleton particles coated with the root-promoting coating to obtain the water-retaining composite material.

[0023] In this specific step, the mixing volume ratio of the coated water-retaining skeleton particles to the immobilized microbeads is 35:1 to 45:1. Under this ratio, the number of microbeads matches the total volume of open pores inside the skeleton. During the three-dimensional mixing process, the vast majority of microbeads can be uniformly embedded inside the pores, and the number of free microbeads is extremely small. This ensures that the finished product has sufficient functional microorganisms, while significantly reducing the loss of microbeads during storage, transportation, and application. It balances the product's biological efficacy with the production cost, avoiding the two extreme problems of waste of microbeads and insufficient function. During the three-dimensional mixing process, the speed of the three-dimensional mixer is controlled at 20-50 rpm, and the mixing time is 10 min-30 min, so that the microbeads are uniformly embedded in the open pores of the water-retaining skeleton.

[0024] In some embodiments, after the three-dimensional mixing is completed, the preparation method further includes: laying the obtained material in a thin layer for maturation in a sterile environment, with a maturation temperature of 28℃~30℃, an ambient relative humidity of 50%~60%, and a maturation time of 10 h~14 h.

[0025] In the specific implementation of this step, after the three-dimensional mixing process, a sterile thin-layer curing step is added. Under a sterile, light-proof, and mild environment, relying on the residual trace moisture inside the system, the surface of the microsphere gel and the inner wall of the skeleton pores slightly adhere, forming weak bonding sites. After curing, the stability of the microspheres fixed in the pores is greatly improved, and the shedding rate under vibration and water flow is significantly reduced. The finished product can be vacuum-sealed and stored in the dark for a long time without the need for on-site preparation and use. This greatly expands the application scenarios for product transportation and warehousing, and solves the defects of existing biological water-retaining materials such as short storage period and easy loss of bacterial agents.

[0026] In a second aspect, the present invention provides a water-retaining composite material obtained by the preparation method described in the first aspect above.

[0027] To enable those skilled in the art to more clearly understand the present invention, the following embodiments will be used to provide a detailed description of the water-retaining composite material and its preparation method.

[0028] Example 1 (1) Preparation of root-promoting coating solution Add 20 g / L potassium humate, 0.5 g / L naphthaleneacetic acid pre-dissolved in a small amount of ethanol, 5 g / L complex amino acids (glycine + glutamic acid + arginine, total amino acids ≥50%), and 10 g / L sodium carboxymethyl cellulose to deionized water in sequence. After stirring evenly, adjust the pH of the system to 7.0 for later use.

[0029] (2) Preparation of aqueous phase and oil phase Based on 100 parts by weight of acrylic acid monomer, the acrylic acid was neutralized to 70% neutralization degree with 40% sodium hydroxide solution under ice-water bath conditions. After cooling to room temperature, 15 parts by weight of 200 mesh sodium bentonite and 10 parts by weight of 300 mesh coconut shell biochar were added, followed by 300 parts by weight of deionized water. The mixture was stirred at 1000 rpm for 30 min to form a uniform dispersion. Then, 0.08% by weight of N,N'-methylenebisacrylamide crosslinking agent was added and stirred to dissolve, thus obtaining an aqueous phase. Cyclohexane was added to the reactor, and the volume ratio of cyclohexane to the aforementioned aqueous phase was controlled at 2:1. Span-60, accounting for 3% of the mass of cyclohexane, was added, and the mixture was heated to 50 °C and stirred until the emulsifier was completely dissolved to obtain the oil phase.

[0030] (3) Preparation of porous water-retaining framework materials by reverse suspension polymerization After continuously introducing nitrogen gas at a rate of 0.5 L / min into the reactor to deoxygenate the oil phase for 30 min, the aqueous phase was slowly added dropwise to the oil phase. After the addition was completed, the temperature was raised to 65 °C, and a composite initiator of ammonium persulfate and sodium bisulfite (molar ratio 1:1) with a total addition amount of 0.5% of the acrylic acid monomer mass was added. The mixture was stirred at 300 rpm and reacted at a constant temperature for 3 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid particles were collected. The solid particles were washed three times with anhydrous ethanol and then with deionized water until the filtrate was neutral. The solid particles were dried in an oven at 60 °C for 12 h until constant weight was achieved. The particles with a particle size of 1-3 mm were screened and used as porous water-retaining skeleton material. Tests showed that the porous water-retaining skeleton material has a water absorption rate of ≥450 g / g for deionized water, a water absorption rate of ≥60 g / g for 0.9% sodium chloride saline, and an open porosity of ≥40%.

[0031] (4) Preparation of immobilized bacterial agent microspheres Two powders, sodium alginate and xanthan gum, were weighed at a mass ratio of 4:1. Deionized water was added to prepare a carrier solution with a total mass-volume concentration of 2.5%. The solution was magnetically stirred in a 60°C water bath until completely dissolved, then cooled to 30°C. A composite bacterial suspension, consisting of arbuscular mycorrhizal (AM) fungal spore suspension, Bacillus subtilis bacterial suspension, and yeast bacterial suspension, was mixed at a volume ratio of 1:2:1. This composite bacterial suspension was then mixed with the carrier solution at a volume ratio of 1:4. The mixture was gently stirred for 10 min to obtain a gel-bacteria mixture. Using a peristaltic pump, the mixture was dripped at a flow rate of 2 mL / min through a needle with an inner diameter of 0.8 mm and a height of 8 cm above the liquid surface. The mixture was then allowed to stand for 30 min while being gently stirred throughout to prevent microsphere adhesion. After curing, the microspheres were washed three times with 0.9% sterile physiological saline, and particles with a mass concentration of 0.5–1.2 mm were collected by sieving. mm immobilized bacterial agent microspheres; Tests showed that the breakage rate of the immobilized microspheres was ≤8% under stirring at 500 rpm for 30 min.

[0032] (5) Preparation of water-retaining skeleton particles coated with root-promoting coating The aforementioned porous water-retaining skeleton material and coating solution were mixed at a solid-liquid ratio of 1 g: 5 mL, and the mixture was shaken and soaked at 50 rpm for 30 min at room temperature. After filtration, the wet particles were spread evenly on a stainless steel mesh tray and dried in a 40 ℃ hot air drying oven for 2-3 h until the surface was no longer sticky, thus obtaining water-retaining skeleton particles coated with a root-promoting coating.

[0033] (6) Final assembly of water-retaining skeleton particles coated with root-promoting coating and immobilized microspheres The coated water-retaining skeleton particles and immobilized bacterial agent microspheres were added to a three-dimensional mixer at a volume ratio of 40:1 and mixed at 20 rpm for 10 min to ensure that the microspheres were uniformly embedded in the open pores of the skeleton particles. After mixing, the material was laid in a thin layer under sterile conditions and allowed to stand for 12 h at a controlled temperature of 28 ℃~30 ℃ and a relative humidity of 50 %~60%. Finally, the finished water-retaining composite material was obtained by vacuum sealing in an aluminum-plastic bag to prevent light.

[0034] Testing revealed that the average viable count of Bacillus subtilis in the finished water-retaining composite material was ≥3.5 × 10⁻⁶. 7 CFU / g, yeast ≥1.8×10 6 CFU / g, AM fungal effective spores ≥5 / g; after 20 water absorption-dehydration cycles, the water retention rate of the material still remains above 72% of the initial water absorption ratio; the release rate of the fungal agent in the soil simulation solution is about 45% in the first 7 days and about 90% cumulatively in 30 days.

[0035] Example 2 (1) Preparation of root-promoting coating solution Add 20 g / L potassium humate, 1.0 g / L naphthaleneacetic acid pre-dissolved in a small amount of ethanol, 5 g / L complex amino acids (glycine + glutamic acid + arginine, total amino acids ≥50%), and 10 g / L sodium carboxymethyl cellulose to deionized water in sequence. After stirring evenly, adjust the pH of the system to 7.0 for later use (compared to Example 1, the concentration of naphthaleneacetic acid is increased to 1.0 g / L in this step).

[0036] (2) Preparation of aqueous phase and oil phase Based on 100 parts by weight of acrylic acid monomer, the acrylic acid was neutralized to 70% neutralization degree with 40% sodium hydroxide solution under ice-water bath conditions. After cooling to room temperature, 15 parts by weight of 200-mesh sodium bentonite and 15 parts by weight of 300-mesh coconut shell biochar were added, followed by 300 parts by weight of deionized water. The mixture was stirred at 1000 rpm for 30 min to form a uniform dispersion. Then, 0.08% by weight of N,N'-methylenebisacrylamide crosslinking agent was added and stirred to dissolve, thus obtaining an aqueous phase (compared to Example 1, the amount of biochar in the porous water-retaining framework material was increased to 15 parts). Cyclohexane was added to the reactor, and the volume ratio of cyclohexane to the aforementioned aqueous phase was controlled at 2:1. Span-60, accounting for 3% of the mass of cyclohexane, was added, and the mixture was heated to 50 °C and stirred until the emulsifier was completely dissolved to obtain the oil phase.

[0037] (3) Preparation of porous water-retaining framework materials by reverse suspension polymerization After continuously introducing nitrogen gas at a rate of 0.5 L / min into the reactor to deoxygenate the oil phase for 30 min, the aqueous phase was slowly added dropwise to the oil phase. After the addition was completed, the temperature was raised to 65 °C, and a composite initiator of ammonium persulfate and sodium bisulfite (molar ratio 1:1) with a total addition amount of 0.5% of the acrylic acid monomer mass was added. The mixture was stirred at 300 rpm and reacted at a constant temperature for 3 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid particles were collected. The solid particles were washed three times with anhydrous ethanol and then washed with deionized water until the filtrate was neutral. The solid particles were dried in an oven at 60 °C for 12 h until constant weight was achieved. The particles with a particle size of 1-3 mm were screened and used as porous water-retaining skeleton material. Tests showed that the porous water-retaining skeleton material has a water absorption rate of ≥480 g / g for deionized water, a water absorption rate of ≥60 g / g for 0.9% sodium chloride salt water, and an open porosity of ≥40%.

[0038] (4) Preparation of immobilized bacterial agent microspheres Two powders, sodium alginate and xanthan gum, were weighed at a mass ratio of 4:1. Deionized water was added to prepare a carrier solution with a total mass-volume concentration of 2.5%. The solution was magnetically stirred in a 60°C water bath until completely dissolved, then cooled to 30°C. A composite bacterial suspension, consisting of arbuscular mycorrhizal (AM) fungal spore suspension, Bacillus subtilis bacterial suspension, and yeast bacterial suspension, was mixed at a volume ratio of 1:2:1. This composite bacterial suspension was then mixed with the carrier solution at a volume ratio of 1:4. The mixture was gently stirred for 10 min to obtain a gel-bacteria mixture. Using a peristaltic pump, the mixture was dripped at a flow rate of 2 mL / min through a needle with an inner diameter of 0.8 mm and a height of 8 cm above the liquid surface into a sterile calcium chloride curing solution containing 0.5% Tween-80 and a mass concentration of 3%. The mixture was allowed to stand for 30 min while being gently stirred throughout to prevent microsphere adhesion. After curing, the microspheres were washed three times with 0.9% sterile physiological saline, and particles with a mass size of 0.5–1.2 mm were collected by sieving. mm immobilized bacterial agent microspheres; Testing revealed that the immobilized bacterial microspheres contained 5 × 10⁶ Bacillus subtilis. 8 CFU / mL, yeast 2.5×10 7 CFU / mL, AM spores ≥30 / mL.

[0039] (5) Preparation of water-retaining skeleton particles coated with root-promoting coating The aforementioned porous water-retaining skeleton material and coating solution were mixed at a solid-liquid ratio of 1 g: 5 mL, and the mixture was shaken and soaked at 50 rpm for 30 min at room temperature. After filtration, the wet particles were spread evenly on a stainless steel mesh tray and dried in a 40 ℃ hot air drying oven for 3 h until the surface was no longer sticky, thus obtaining water-retaining skeleton particles coated with a root-promoting coating. Tests showed that the weight gain of the particulate coating was 9% to 13%.

[0040] (6) Final assembly of water-retaining skeleton particles coated with root-promoting coating and immobilized microspheres The water-retaining skeleton particles coated with the coating and the immobilized bacterial agent microspheres were put into a three-dimensional mixer at a volume ratio of 40:1 and mixed at 20 rpm for 10 min to make the microspheres evenly embedded in the open pores of the skeleton particles. After mixing, the material was laid in a thin layer under sterile conditions and allowed to stand for 12 h with the ambient temperature controlled at 28 ℃~30 ℃ and relative humidity at 50 %~60%. Finally, the finished water-retaining composite material was obtained by vacuum sealing in an aluminum-plastic bag to prevent light. Testing revealed that the average viable count of Bacillus subtilis in the finished water-retaining composite material was ≥3.5 × 10⁻⁶. 7 CFU / g, yeast ≥1.8×10 6 CFU / g, effective AM fungal spores ≥5 / g; after 20 water absorption-dehydration cycles, the water retention rate of the material still remains above 75% of the initial water absorption ratio.

[0041] Example 3 The difference from Example 1 is that in step (4) of this example, when preparing immobilized bacterial microspheres, the mass ratio of sodium alginate to xanthan gum is 3:1, and the other preparation steps and control parameters are the same; Testing showed that the breakage rate of the immobilized microspheres was ≤5% under stirring at 500 rpm for 30 min; the immobilized microspheres contained 5 × 10⁶ Bacillus subtilis. 8 CFU / mL, yeast 2.5×10 7 CFU / mL, AM spores ≥30 / mL; In the finished water-retaining composite material, the average viable count of Bacillus subtilis is ≥3.5×10⁻⁶. 7 CFU / g, yeast ≥1.8×10 6 CFU / g, AM fungal effective spores ≥5 / g, after 20 water absorption-dehydration cycles, the water retention rate still maintains more than 72% of the initial water absorption ratio; the release rate of the fungal agent in the soil simulation solution is about 35% in the first 7 days and about 80% cumulatively in 30 days.

[0042] Comparative Example 1 The difference from Example 1 is that step (4) of Comparative Example 1 is the preparation of free bacterial suspension (without gel microsphere preparation process). The operation process includes: mixing arbuscular mycorrhizal (AM) fungal spore suspension, Bacillus subtilis bacterial suspension and yeast bacterial suspension in a volume ratio of 1:2:1 to obtain a composite bacterial suspension, diluting the composite bacterial suspension 5 times with sterile water for later use, without preparing sodium alginate-xanthan gum immobilized microspheres; Step (5) of Comparative Example 1 involves coating and loading free bacterial suspension. The process includes: soaking the water-retaining skeleton particles coated with root-promoting coating and the diluted free composite bacterial suspension at a solid-liquid ratio of 1 g: 5 mL for 30 min, filtering, and then drying with hot air at 40 ℃ until the surface is dry; no embedded assembly step is performed.

[0043] The remaining steps and control parameters are the same as in Example 1.

[0044] In Comparative Example 1, a large number of microorganisms died during the drying process of the water-retaining composite material. The survival rate of Bacillus subtilis was only about 12%, the survival rate of yeast was about 8%, and the activity of AM fungal spores was lost by about 70%. Further testing revealed that the Bacillus subtilis content in the finished product was only 4.2 × 10⁻⁶. 6 CFU / g, yeast count only 1.4×10 5 CFU / g, AM fungal effective spores <2 / g; after 30 days of storage at room temperature and protected from light, the overall viable count decreased to less than 30% of the initial total.

[0045] Comparative Example 2 The difference from Example 1 is that Comparative Example 2 does not perform step (1) of preparing the root-promoting coating solution, nor does it perform step (5) of preparing the water-retaining skeleton particles coated with the root-promoting coating; The final assembly process of the water-retaining skeleton particles and the immobilized microbeads is a simple manual mixing. The bare porous water-retaining skeleton particles and the immobilized microbeads are poured into a container at a volume ratio of 40:1 and manually stirred for 5 minutes. The aseptic curing step is omitted. After stirring, the mixture is directly vacuum-sealed in an aluminum-plastic bag.

[0046] Tests showed that the microsphere shedding rate after transportation vibration was about 35%; the amount of rhizosphere fungicide detected in the potted plant test was only 60% of that in Example 1, and the rooting speed of the seedlings was significantly lower than that of the sample in Example 1.

[0047] Comparative Example 3 The difference from Example 1 is that Comparative Example 3 does not perform step (1) of preparing the root-promoting coating solution and step (5) of preparing the water-retaining skeleton particles coated with the root-promoting coating; Commercially available sodium polyacrylate with a particle size of 1-3 mm was selected as the base material. The deionized water absorption ratio of this water-retaining agent is about 400 g / g. A compound bacterial suspension was prepared by mixing arbuscular mycorrhizal (AM) fungal spore suspension, Bacillus subtilis bacterial suspension, and yeast bacterial suspension at a volume ratio of 1:2:1. The commercially available sodium polyacrylate water-retaining agent and the compound bacterial suspension were mixed evenly at a mass ratio of 10:1. The resulting water-retaining composite material must be applied immediately and cannot be stored for a long time. The comparative material has no root-promoting functional components, and the bacterial agent only adheres to the surface of the water-retaining agent. When watering, the bacteria are easily lost with the water, and there is no three-layer synergistic structure of water-retaining carrier, microorganisms, and root-promoting agents.

[0048] Performance testing The tested plant was Acacia nilotica, one of the main afforestation tree species in Benin.

[0049] The tested soil was topsoil (0-30 cm) from northern Benin (Borgou Province), sandy loam with an organic matter content of 0.8% and a field water holding capacity of 22%.

[0050] Test method: The six groups of water-retaining composite materials obtained in Examples 1-3 and Comparative Examples 1-3, as well as one blank control (bare porous water-retaining skeleton material), were applied to potted seedlings (seedling height 15±2 cm, with intact root systems). Each group of water-retaining composite material / bare porous water-retaining skeleton material was applied to 20 pots (seedling height 15±2 cm, with intact root systems), with 10 g of material applied to each pot (mixed thoroughly with the 0-20 cm soil layer). After planting, the seedlings were thoroughly watered once (2 L per pot), and then subjected to simulated Benin dry season conditions without watering for 60 days. Soil moisture content was measured on days 0, 15, 30, 45, and 60; on day 60, seedling survival rate, plant height increase, aboveground dry weight, root dry weight, and rhizosphere inoculant survival count were recorded. The test results are shown in Table 1 (the following data are calculated averages): Table of changes in seedlings after 60 days of application of different water-retaining composite materials

[0051] Analyzing the test data shown in Table 1, in terms of survival rate and growth, the survival rate of seedlings in Examples 1-3 was ≥93%, significantly higher than that of Comparative Examples 1-3 (58%~71%) and the blank control (23%). Example 2 (high biochar + high rooting agent) showed the best results, with a survival rate of 96% and a plant height increase more than 7 times that of the blank control. This demonstrates that the water-retaining composite material of this invention, with its synergistic design of a water-retaining framework, immobilized bacterial agent, and root-promoting coating, has significant advantages. Further analysis of the survival effect of the inoculant showed that after 60 days of treatment, the number of viable bacteria in the rhizosphere of the example group remained at 10. 6 CFU / g soil level, while comparative groups 1-3 only had 10. 3 ~10 4CFU / g soil. This demonstrates the embedded structure of the immobilized microbeads and the water-retaining framework particles coated with a root-promoting coating, and that the immobilized microbeads effectively protect the microbeads, enabling them to survive and function for a long time during the dry season.

[0052] Further analysis of soil water retention capacity revealed that the average soil moisture content of the example group (16.5%–17.5%) was significantly higher than that of the comparative group (11.8%–13.6%) and the blank control (8.4%). This indicates that the long-term survival of the microbial agent, in turn, promotes the formation of soil micro-aggregates, enhances the soil's own water retention capacity, and forms a virtuous cycle.

[0053] Furthermore, Example 2 showed slightly better survival rate, growth, and water retention than Examples 1 and 3, indicating that appropriately increasing the amount of biochar (to improve the porosity and adsorption capacity of the framework) and increasing the concentration of the rooting agent had a positive impact on plant growth promotion. Example 3 had a greater advantage in the slow-release performance of the inoculant, making it suitable for areas with longer dry seasons.

[0054] Therefore, it can be seen that the composite materials prepared in Examples 1-3 of this invention, with the synergistic integrated structural design of porous water-retaining skeleton, immobilized bacterial agent microspheres and root-promoting coating, can achieve a seedling survival rate of 93%~96% under extreme drought conditions simulating the Benin dry season (60 days without watering), which is significantly better than the comparative example (58%~71%) and the blank control (23%). It effectively maintains the long-term survival of rhizosphere functional flora and improves the soil water retention capacity.

[0055] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0056] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0057] The present invention provides a detailed description of a water-retaining composite material and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only intended to help understand the method and core ideas of the present invention. At the same time, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a water-retaining composite material, characterized in that, The preparation method includes: Potassium humate, naphthaleneacetic acid, compound amino acids, sodium carboxymethyl cellulose and deionized water are mixed to form a coating solution; The neutralized acrylic monomer, bentonite, and biochar were mixed with deionized water to form a dispersion, and then the crosslinking agent N,N'-methylenebisacrylamide was added to prepare an aqueous phase. Cyclohexane and surfactant Span-60 were added to the reactor and heated to mix, forming an oil phase. The aqueous phase was slowly added dropwise to the oil phase, and an initiator was added. The reaction was carried out at a constant temperature of 55 ℃-80 ℃ for 2 h-5 h. The reactants were then filtered, washed, dried, and pulverized to obtain a porous water-retaining skeleton material with a particle size of 1~3 mm. Sodium alginate, xanthan gum, and deionized water are mixed to form a carrier solution, and a composite bacterial agent is added to the carrier solution to prepare a gel-bacterial mixture. The gel-bacterial mixture is then solidified using a drop bead curing process to form immobilized bacterial agent microspheres with a particle size of 0.5~1.2 mm. The porous water-retaining skeleton material is immersed in the coating solution for 30 min-120 min, and after filtration and drying, water-retaining skeleton particles coated with a root-promoting coating are obtained. The water-retaining skeleton particles coated with the root-promoting coating and the immobilized microbeads are placed in a three-dimensional mixer for three-dimensional mixing, so that the immobilized microbeads enter the open pores of the water-retaining skeleton particles coated with the root-promoting coating to obtain the water-retaining composite material.

2. The method for preparing the water-retaining composite material according to claim 1, characterized in that, By weight, the aqueous phase contains 100 parts of neutralized acrylic acid monomer, 12-18 parts of bentonite, 8-15 parts of biochar, and 250-350 parts of deionized water. The amount of the crosslinking agent N,N'-methylenebisacrylamide added is 0.06% to 0.1% of the mass of the neutralized acrylic monomer.

3. The method for preparing the water-retaining composite material according to claim 1, characterized in that, The initiator is composed of ammonium persulfate and sodium bisulfite in a molar ratio of 1:1; The amount of initiator added is 0.4% to 0.6% of the total mass of the neutralized acrylic monomers.

4. The method for preparing the water-retaining composite material according to claim 1, characterized in that, The volume ratio of cyclohexane in the oil phase to that in the aqueous phase is 1.8:1 to 2.2:1; The mass ratio of the surfactant Span-60 in the oil phase is 2% to 4%.

5. The method for preparing the water-retaining composite material according to claim 1, characterized in that, In the carrier solution, the total mass-volume concentration of sodium alginate and xanthan gum is 2.0%~3.0%; The mass ratio of sodium alginate to xanthan gum is 3:1 to 4:

1.

6. The method for preparing the water-retaining composite material according to claim 1, characterized in that, The compound microbial agent is obtained by mixing arbuscular mycorrhizal fungal spore suspension, Bacillus subtilis bacterial solution, and yeast bacterial solution in a volume ratio of 1:1.5:1 to 1:2.5:

1. In the gel-bacterial mixture, the volume ratio of the composite bacterial agent to the carrier solution is 1:3 to 1:

5.

7. The method for preparing the water-retaining composite material according to claim 1, characterized in that, The content of each component in the coating solution is as follows: potassium humate 15~25 g / L, naphthaleneacetic acid 0.4~1.0 g / L, complex amino acids 4~6 g / L, and sodium carboxymethyl cellulose 8~12 g / L.

8. The method for preparing the water-retaining composite material according to claim 1, characterized in that, The volume ratio of the water-retaining skeleton particles coated with the coating to the immobilized bacterial agent microspheres is 35:1 to 45:

1.

9. The method for preparing the water-retaining composite material according to claim 1, characterized in that, The preparation method further includes: After the three-dimensional mixing is completed, the resulting material is laid in a thin layer and matured in a sterile environment at a temperature of 28 ℃~30 ℃ and a relative humidity of 50 %~60% for 10~14 h.

10. A water-retaining composite material obtained by any of the preparation methods described in claims 1-9.

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