Accelerating admixture for mine filling and sealing material and preparation method thereof

Abstract

The application discloses a mine filling and plugging material quick-setting additive and a preparation method thereof. The water-retaining agent in the quick-setting additive is a composite water-retaining system formed by hydroxypropyl methyl cellulose and modified starch. The hydroxypropyl methyl cellulose physically wraps free water in the slurry; the modified starch adsorbs water molecules through hydrogen bonding, and the double mechanism significantly reduces the bleeding rate; the coagulation accelerator adopts a spray drying wrapping technology, and a core-shell structure composite particle is constructed, in which aluminum lithium sulfate is used as a 'quick-release core', and active calcium silicate gel slurry obtained by the reaction of nano calcium silicate and sodium silicate is used as a'slow-release wrapping layer', so that the coagulation accelerator can promote coagulation, prevent sodium silicate from being consumed too early, and realize sustained coagulation. The early strength agent adopts a gel-gelling method, so that the early strength agent can provide persistent early strength excitation and solve the problem of weak late strength growth. The interface reinforcing agent can make the interface transition zone structure more strong and tough, and improve the integrity and damage resistance after the slurry coagulation and hardening.

Description

Technical Field

[0001] This invention relates to the field of mining engineering materials technology, and in particular to a quick-setting admixture for mine filling and sealing materials and its preparation method. Background Technology

[0002] In mine backfilling and sealing engineering, mine backfilling and sealing materials are backfill slurries made by mixing backfill material and water based on the water-to-solid ratio. The concentration of the backfill slurry is a key factor affecting its performance. Traditional backfill slurries typically require a high concentration (70%-85%), where the concentration is the mass concentration of the backfill material in the slurry, to ensure sufficient strength and resistance to bleeding. However, in actual engineering, due to limitations such as long transportation distances, the amount of backfill material used is relatively low, thus requiring the use of low-concentration (30%-60%) backfill slurries for mine backfilling and sealing.

[0003] However, low-concentration filling grout has the following problems: high moisture content, which easily leads to bleeding and segregation, resulting in poor stability; prolonged setting time; slow strength development and low early strength, affecting project progress, etc. Summary of the Invention

[0004] This application provides an accelerator for mine filling and sealing materials and its preparation method. This accelerator is designed for low-concentration filling slurries of 30%-60%. The water-retaining agent in the accelerator is a composite water-retaining system formed by hydroxypropyl methylcellulose and modified starch. Hydroxypropyl methylcellulose physically encapsulates free water in the slurry; modified starch adsorbs water molecules through hydrogen bonding, significantly reducing bleeding rate through this dual mechanism. The coagulant uses spray drying encapsulation technology to construct a core-shell structure composite particle with lithium aluminum sulfate as the "rapid-release core" and an active calcium silicate gel slurry obtained by reacting nano-calcium silicate with sodium silicate as the "slow-release encapsulation layer." This structure promotes coagulation, prevents premature consumption of sodium silicate, and achieves continuous coagulation. The early-strength agent uses a gel-gel method, providing sustained early-strength activation and addressing the problem of weak strength growth in later stages. The interface reinforcement agent strengthens the structure of the interface transition zone, improving the overall integrity and resistance to damage after the slurry has coagulated and hardened.

[0005] In a first aspect, the present invention provides a quick-setting admixture for mine filling and sealing materials, comprising the following components by mass parts: 30-50 parts of a coagulant accelerator, 20-35 parts of an early-strength agent, 15-25 parts of a water-retaining agent, and 5-15 parts of an interface reinforcing agent; wherein, the water-retaining agent comprises the following components by mass parts: 8-12 parts of hydroxypropyl methylcellulose and 7-13 parts of modified starch; the interface reinforcing agent comprises the following components by mass parts: 2-5 parts of plasma-treated polypropylene fiber and 3-10 parts of a silane coupling agent; the coagulant accelerator comprises the following components by mass parts: 40 parts of lithium aluminum sulfate powder and 60 parts of activated calcium silicate gel slurry; the activated calcium silicate gel slurry comprises the following components: nano-calcium silicate and sodium silicate; the lithium aluminum sulfate powder comprises aluminum sulfate and lithium sulfate in a molar ratio of 4:1; the early-strength agent comprises the following components: metakaolin, lithium carbonate, and tetraethyl orthosilicate.

[0006] Secondly, this application provides a method for preparing a quick-setting admixture for mine filling and plugging materials, the method comprising: The coagulant, early strength agent, water-retaining agent and interface enhancer are mixed in a segmented manner, wherein the segmented mixing includes mixing at a stirring speed of 300-400 rpm for 5 min, and then continuing to mix at a stirring speed of 800-1000 rpm for 5-10 min.

[0007] In some embodiments, the method further includes: A sodium silicate solution with a solid content of 30% was prepared using sodium silicate with a modulus of 3.2 and deionized water. Nano-sized calcium silicate was added to a sodium silicate solution and stirred at 60°C for 10 minutes to form an active calcium silicate gel slurry; wherein the mass ratio of the nano-sized calcium silicate to the sodium silicate solution was 1:8. Aluminum sulfate and lithium sulfate were melt-reacted at 85°C in a molar ratio of 4:1 to prepare an aluminum-lithium sulfate composite salt. The aluminum-lithium sulfate composite salt was then water-cooled and pulverized to ensure that the particle size distribution of the resulting aluminum-lithium sulfate powder had a D90 < 10 μm. The aluminum-lithium sulfate powder was continuously added to the activated calcium silicate gel slurry in the feed tank of a high-speed centrifugal spray dryer, forming a uniform first suspension under strong shear. The mass ratio of the aluminum-lithium sulfate powder added to the activated calcium silicate gel slurry to the activated calcium silicate gel slurry was 40:60. The first suspension is atomized and dried in a spray drying tower to form a coagulant; the inlet temperature of the spray drying tower is 220°C and the outlet temperature is 95°C.

[0008] In some embodiments, the method further includes: Prepare a 0.5 mol / L Ca(NO3)2 solution with calcium nitrate tetrahydrate and let it stand for 24 hours; Prepare a 0.5 mol / L sodium silicate solution using sodium silicate with a modulus of 3.2 and let it stand for 24 hours to age. Take a statically aged Ca(NO3)2 solution and a statically aged sodium silicate solution; wherein the molar ratio of Ca(NO3)2 in the statically aged Ca(NO3)2 solution to sodium silicate in the statically aged sodium silicate solution is 1:1; heat the statically aged Ca(NO3)2 solution to 58-62℃ in a water bath; under stirring at a stirring speed of 600 rpm, uniformly add the statically aged sodium silicate solution within 45 minutes, and maintain the pH value at a constant 10.5-11.0 using 25% ammonia water; while adding the statically aged sodium silicate solution, add an ethanol solution containing polycarboxylate dispersant; the volume ratio of the added ethanol solution containing polycarboxylate dispersant to the added statically aged sodium silicate solution is 1-5:100. After the addition was complete, the mixture was stirred and aged at 60°C for 2 hours to obtain a white suspension. The white suspension was centrifuged to obtain a solid substance; the solid substance was washed three times alternately with anhydrous ethanol and deionized water to obtain the washed solid substance. The washed solid material was dried in a vacuum drying oven at 70°C for 12 hours to obtain dried soft aggregates. The dried soft agglomerates were deagglomerated in an air jet mill with a classifying wheel speed of 5000 rpm to obtain nano-calcium silicate.

[0009] In some embodiments, the method further includes: Thermal activation of metakaolin at 650℃ yields thermally activated metakaolin. Thermally activated metakaolin was added to anhydrous ethanol to form a second suspension, wherein the ratio of thermally activated metakaolin to anhydrous ethanol was 20 g / 100 mL. Under continuous stirring and nitrogen protection, lithium carbonate and tetraethyl orthosilicate were dissolved together in anhydrous ethanol at a mass ratio of 1:2, and dilute hydrochloric acid was added dropwise to obtain a mixed solution. The mixed solution was slowly added dropwise to the second suspension, and the mixture was reacted in a water bath at 50°C for 6 hours. After the reaction was completed, the mixture was aged at 80℃ for 12 hours, dried at 110℃ for 8-12 hours, and finally calcined at 350℃ for 2 hours to obtain the early strength agent.

[0010] In some embodiments, the method further includes: Hydroxypropyl methylcellulose was mixed with modified starch for 15 minutes to obtain a water-retaining agent.

[0011] In some embodiments, the method further includes: Deionized water was added to cassava starch and stirred at a stirring speed of 300-400 rpm to obtain a uniformly dispersed starch slurry. The pH was adjusted to 9.5-10.5 using a 3% sodium hydroxide aqueous solution and then swollen and activated at 48-52℃ for 30 min to obtain the activated starch slurry. Sodium tripolyphosphate (STMP) and sodium chloride are added to the activated starch slurry under continuous stirring; the pH is maintained at 10.5-11.5, the reaction temperature is raised to 45-50℃, and the reaction is continued for 2-4 hours; wherein the mass of the sodium tripolyphosphate accounts for 0.3%-0.8% of the mass of the cassava starch; Maintain pH at 10.5-11.5, raise the reaction temperature to 45-50℃, and continue the reaction for 2-4 hours; After the reaction is complete, propylene oxide and sodium sulfate are added simultaneously; the temperature is raised to 70-75℃, the pressure is 0.2-0.3MPa, and the reaction is carried out for 6-10 hours to obtain modified starch.

[0012] In some embodiments, the mass ratio of the cassava starch to the deionized water is 100:150-180.

[0013] In some embodiments, the method further includes: The interface reinforcing agent is obtained by mixing plasma-treated polypropylene fibers with a silane coupling agent for 10-15 minutes.

[0014] In some embodiments, the method further includes: After the equipment chamber of the plasma device is pre-evacuated to a background vacuum, a mixture of oxygen and argon or oxygen as the working gas is introduced to maintain a stable gas flow rate, so that the dynamic working pressure in the chamber is maintained at 20-50 Pa. Turn on the RF power supply and set the power to 100-300 W; Polypropylene fibers that have been cleaned and dried with anhydrous ethanol are laid on the rolling device of a plasma equipment, and the temperature is controlled below 60℃ for 3-8 minutes to obtain plasma-treated polypropylene fibers.

[0015] This invention provides a rapid-setting admixture for mine filling and sealing materials and its preparation method. This rapid-setting admixture addresses the problems of slow setting, low early strength, and severe bleeding in slurries with a low concentration of 30%-60%. The admixture innovatively employs spray-drying encapsulation technology to construct a core-shell structured composite particle with lithium aluminum sulfate as the "rapid-release core" and an active calcium silicate gel slurry obtained from the reaction of nano-calcium silicate and sodium silicate as the "slow-release encapsulation layer." This accelerates setting time and prevents premature consumption of sodium silicate, achieving continuous setting. The early-strength agent uses a gel-gel method, providing sustained early-strength activation and solving the problem of weak later-stage strength growth. The water-retaining agent in the rapid-setting admixture is a composite water-retaining system formed by hydroxypropyl methylcellulose and modified starch. Hydroxypropyl methylcellulose forms a three-dimensional network structure in the slurry, physically encapsulating free water; modified starch adsorbs water molecules through hydrogen bonding, and the dual mechanism significantly reduces the bleeding rate; the interface reinforcing agent can make the structure of the interface transition zone stronger and tougher, improving the integrity and resistance to damage after the slurry coagulates and hardens. Detailed Implementation

[0016] To better understand the above technical solutions, the technical solutions of this application will be described in detail below through specific implementation methods.

[0017] To address the aforementioned technical problems, this application provides a rapid-setting admixture for mine filling and sealing materials and its preparation method. This rapid-setting admixture targets low-concentration slurries of 30%-60%, solving problems such as slow setting, low early strength, and severe bleeding. The water-retaining agent in the rapid-setting admixture is a composite water-retaining system formed by hydroxypropyl methylcellulose and modified starch. Hydroxypropyl methylcellulose physically encapsulates free water in the slurry; modified starch adsorbs water molecules through hydrogen bonding, and this dual mechanism significantly reduces the bleeding rate. The coagulant uses spray drying encapsulation technology to construct a core-shell structured composite particle with lithium aluminum sulfate as the "rapid-release core" and an active calcium silicate gel slurry obtained by reacting nano-calcium silicate with sodium silicate as the "slow-release encapsulation layer." This structure promotes coagulation, prevents premature consumption of sodium silicate, and achieves continuous setting. The early-strength agent uses a gel-gel method, enabling it to provide sustained early-strength activation and solving the problem of weak later-stage strength growth. Interface enhancers can make the structure of the interface transition zone stronger and tougher, and improve the integrity and resistance to damage after the slurry sets and hardens.

[0018] In this embodiment of the application, a rapid-setting admixture for mine filling and sealing materials comprises the following components by mass parts: 30-50 parts of a coagulant accelerator, 20-35 parts of an early-strength agent, 15-25 parts of a water-retaining agent, and 5-15 parts of an interface reinforcing agent. The water-retaining agent comprises the following components by mass parts: 8-12 parts of hydroxypropyl methylcellulose and 7-13 parts of modified starch; the interface reinforcing agent comprises the following components by mass parts: 2-5 parts of plasma-treated polypropylene fiber and 3-10 parts of a silane coupling agent; the coagulant accelerator comprises the following components by mass parts: 40 parts of lithium aluminum sulfate powder and 60 parts of activated calcium silicate gel slurry; the activated calcium silicate gel slurry comprises the following components: nano-calcium silicate and sodium silicate; the lithium aluminum sulfate powder comprises aluminum sulfate and lithium sulfate in a molar ratio of 4:1; the early-strength agent comprises the following components: metakaolin, lithium carbonate, and tetraethyl orthosilicate.

[0019] In this embodiment, the accelerator is prepared using spray drying encapsulation technology to construct a core-shell composite particle, i.e., the accelerator, with lithium aluminum sulfate as the "rapid-release core" and an active calcium silicate gel slurry obtained from the reaction of nano-calcium silicate and sodium silicate as the "slow-release encapsulation layer." Thus, at the moment of spray drying and spherical formation, sodium silicate does not exist in a free crystalline form, but rather forms a dense, continuous amorphous calcium silicate-sodium silicate composite gel encapsulation layer with nano-calcium silicate during water evaporation. This dried encapsulation layer is dense and has low solubility. When the accelerator is initially added to water, water molecules cannot instantly disperse and dissolve it as they would dissolve pure sodium silicate powder. The encapsulation layer acts more like a "microcapsule shell" that needs to be slowly wetted and penetrated, similar to a physical barrier. In the initial alkaline environment of the cement in the filling slurry, the encapsulation layer is relatively stable and dissolves slowly. Therefore, the sodium silicate in the encapsulation layer will not completely and rapidly dissolve and release a large amount of Na during the initial stirring stage, as it would when added alone. + and SiO3² - It's not an ionic process, but a slow one. The alkalinity increases due to the combined effects of cement hydration and the rapid reaction of lithium aluminum sulfate. Specifically, when silicate cement comes into contact with water, the alkali metal salts (such as K₂O and Na₂O) dissolve rapidly, causing the slurry liquid phase to become highly alkaline within minutes. Additionally, lithium aluminum sulfate in the coating layer dissolves initially in small amounts through the micropores of the coating layer or through slight swelling upon contact with water, releasing Al³⁺. + and SO4² -Ions react violently with tricalcium aluminate (C3A) and gypsum (CaSO4) in cement, rapidly generating a large number of needle-like ettringite crystals. This reaction consumes a large amount of water and significantly accelerates the hydration process of cement minerals (especially C3S). As hydration accelerates, more Ca(OH)2 (calcium hydroxide) is generated and dissolves, causing the alkalinity to continuously increase. Under increasingly alkaline conditions, the structural stability of the coating layer begins to decrease, and it gradually dissolves. At this point, the nano-calcium silicate particles encapsulated in the gel network are released. These nano-calcium silicate particles provide nucleation sites, accelerating the precipitation of hydration products and promoting setting. + (Sodium ions): Provide and maintain the highly alkaline environment of the slurry. As the coating gradually dissolves in the later stages, the sodium silicate (Na2O·nSiO2) in its composition releases two key substances: active silicate ions (SiO3²⁻). - (etc.), this is the core of "alkali activation". These soluble silicate ions can react with the large amount of Ca(OH)2 (calcium hydroxide) produced during cement hydration to undergo a pozzolanic reaction, rapidly generating additional, gelling hydrated calcium silicate gel. In this way, through the synergistic effect of nano-calcium silicate and sodium silicate in the active calcium silicate gel slurry with lithium aluminum sulfate, the timing of the setting reaction is optimized and synergistically enhanced, continuously promoting setting.

[0020] In this embodiment, the early-strength agent is prepared using a sol-gel method. A silica sol formed by the hydrolysis and condensation of tetraethyl orthosilicate carries lithium ions and is deposited in situ into the nanopores and surface defects between the metakaolinite layers. This directly embeds the lithium carbonate precursor (lithium source) into the mesoporous structure of the metakaolinite, achieving molecular-scale composite formation and stable, slow-release of lithium ions. In the cement hydration environment, the external lithium carbonate can still take effect rapidly, while the lithium ions embedded within the structure are slowly released as the metakaolinite layers gradually dissociate, providing sustained early-strength activation and effectively avoiding the problem of weak later-stage strength growth that may be caused by excessively high early-stage ion concentrations.

[0021] The water-retaining agent in this embodiment is a composite water-retaining system formed by hydroxypropyl methylcellulose and modified starch. Hydroxypropyl methylcellulose forms a three-dimensional network structure in the slurry, physically encapsulating free water and reducing the water loss rate. Furthermore, starch molecules themselves are rich in hydroxyl groups (-OH), naturally forming hydrogen bonds with water molecules. However, the strong hydrogen bond network of natural starch makes it difficult to disperse and absorb water. By modifying starch with propylene oxide to increase the hydrogen bond strength, this reaction introduces hydroxypropyl groups (-CH2CHOHCH3) onto the starch molecular chain. The newly introduced hydroxypropyl group itself carries a new hydroxyl group, directly increasing the number of active sites on the starch molecule that can form hydrogen bonds with water molecules. Simultaneously, the large hydroxypropyl branching inserts into the originally tightly packed starch molecular chains, physically disrupting the tight hydrogen bond network inside the starch granules, making the starch molecular chains "loose." This is like untangling a ball of yarn, allowing the internal hydroxyl groups to be more easily exposed and contact water. The introduced hydroxypropyl groups greatly enhance the hydrophilicity of starch and its ability to bind water molecules. In this way, the water exudation rate is reduced through the combined action of hydroxypropyl methylcellulose and modified starch.

[0022] The interface reinforcing agent in this embodiment comprises plasma-treated polypropylene fibers and a silane coupling agent. The surface of the plasma-treated polypropylene fibers is rich in oxygen-containing functional groups, forming chemical bonds with the slurry rather than simple physical embedding; the silane coupling agent builds "molecular bridges" between the inorganic and organic phases, improving the structure of the interfacial transition zone. Specifically, plasma treatment grafts carboxyl and hydroxyl groups onto the surface of the polypropylene fibers, forming an active surface. During cement hydration, a large number of calcium ions are rapidly generated, and these Ca²⁺ ions... + Derived from the dissolution of minerals such as tricalcium silicate, it is widely present in hydrated calcium silicate gels and pore fluids. In an alkaline slurry environment, the carboxyl groups on the fiber surface dissociate into negatively charged carboxylate ions. These negatively charged functional groups exhibit strong electrostatic attraction with the positively charged calcium ions, forming ionic bonds. Simultaneously, the oxygen atoms in the carboxyl and hydroxyl groups possess lone pairs of electrons, which can act as electron donors to form coordinate bonds with calcium ions. The resulting structure: Ultimately, a layer of fiber-COO2 is formed between the fiber surface and the cement matrix. - ...Ca² + ... - OOC—Cement Gel or Fiber—O - ...Ca² + ... - A strong ionic-coordination cross-linked network composed of "O-Si" bonds. This structure tightly "rivets" the organic fibers to the inorganic cement matrix.

[0023] The quick-setting admixture in this application embodiment is specifically designed for slurries with low concentrations of 30%-60%. Through the synergistic effect of various functional components such as "accelerating coagulation, early strength, water retention, and interface enhancement", it improves the setting speed, enhances early strength, and solves the problem of severe bleeding.

[0024] This application provides a method for preparing a quick-setting admixture for mine filling and sealing materials, comprising: The coagulant, early strength agent, water-retaining agent and interface enhancer are mixed in a segmented manner, wherein the segmented mixing includes mixing at a stirring speed of 300-400 rpm for 5 min, and then continuing to mix at a stirring speed of 800-1000 rpm for 5-10 min.

[0025] In this embodiment, the segmented mixing first uses low-speed mixing for 5 minutes, and then high-speed mixing for 5-10 minutes, which can ensure that each component is evenly dispersed.

[0026] In the embodiments of this application, the quick-setting admixture includes the following components by mass parts: 30-50 parts of accelerator, 20-35 parts of early strength agent, 15-25 parts of water-retaining agent, and 5-15 parts of interface enhancer.

[0027] In some embodiments, the method further includes: Prepare a 0.5 mol / L Ca(NO3)2 solution with calcium nitrate tetrahydrate and let it stand for 24 hours; Prepare a 0.5 mol / L sodium silicate solution using sodium silicate with a modulus of 3.2 and let it stand for 24 hours to age. Take a statically aged Ca(NO3)2 solution and a statically aged sodium silicate solution; wherein the molar ratio of Ca(NO3)2 in the statically aged Ca(NO3)2 solution to sodium silicate in the statically aged sodium silicate solution is 1:1; heat the statically aged Ca(NO3)2 solution to 58-62℃ in a water bath; under stirring at a stirring speed of 600 rpm, uniformly add the statically aged sodium silicate solution within 45 minutes, and maintain the pH value at a constant 10.5-11.0 using 25% ammonia water; while adding the statically aged sodium silicate solution, add an ethanol solution containing polycarboxylate dispersant; the volume ratio of the added ethanol solution containing polycarboxylate dispersant to the added statically aged sodium silicate solution is 1-5:100.

[0028] In one example, a Ca(NO3)2 solution that has been allowed to stand and age is placed in a four-necked flask, heated to 58-62°C in a water bath, and a sodium silicate solution that has been allowed to stand and age is added dropwise at a uniform rate under vigorous mechanical stirring at 600 rpm, with the dropping rate controlled to be completed within 45 minutes. Simultaneously with the addition of the sodium silicate solution, a 25% ammonia solution is used to maintain a constant pH of 10.5-11.0, and an ethanol solution containing a polycarboxylate dispersant is added dropwise through a constant-pressure dropping funnel. The preparation step of the ethanol solution containing the polycarboxylate dispersant includes adding the polycarboxylate dispersant to the ethanol solution and stirring to obtain the ethanol solution containing the polycarboxylate dispersant, wherein the mass ratio of the polycarboxylate dispersant to the ethanol solution is 2-5:100.

[0029] In one example, the polycarboxylate dispersant could be Tuyile® DS-191 organic powder dispersant produced by Tianjin Hepfele New Material Co., Ltd.

[0030] After the addition was complete, the mixture was stirred and aged at 60°C for 2 hours to obtain a white suspension. The white suspension was centrifuged to obtain a solid substance; the solid substance was washed three times alternately with anhydrous ethanol and deionized water to obtain the washed solid substance. In this embodiment, washing can completely remove sodium ions, nitrate ions, and residual polycarboxylate dispersant.

[0031] The washed solid material was dried in a vacuum drying oven at 70°C for 12 hours to obtain dried soft aggregates. The dried soft agglomerates were deagglomerated in an air jet mill with a classifying wheel speed of 5000 rpm to obtain nano-calcium silicate.

[0032] In some embodiments, the method further includes: A sodium silicate solution with a solid content of 30% was prepared using sodium silicate with a modulus of 3.2 and deionized water. Nano-sized calcium silicate was added to a sodium silicate solution and stirred at 60°C for 10 minutes to form an active calcium silicate gel slurry; wherein the mass ratio of the nano-sized calcium silicate to the sodium silicate solution was 1:8. Aluminum sulfate and lithium sulfate are melted and reacted at 85°C in a molar ratio of 4:1 to prepare an aluminum-lithium sulfate composite salt. The aluminum-lithium sulfate composite salt is then water-cooled and pulverized to obtain aluminum-lithium sulfate powder, wherein the particle size distribution of the aluminum-lithium sulfate powder is D90 < 10 μm. The aluminum-lithium sulfate powder is continuously added to the active calcium silicate gel slurry in the feed tank of a high-speed centrifugal spray dryer, forming a uniform first suspension under strong shear. The mass ratio of aluminum-lithium sulfate powder to active calcium silicate gel slurry added to the active calcium silicate gel slurry is 40:60.

[0033] In one example, the high-speed centrifugal spray dryer could be the LPG100 spray dryer from Hangzhou Qianjiang Drying Equipment Co., Ltd.

[0034] In this embodiment, the high-speed centrifugal spray dryer includes a feed tank and a spray drying tower, and the feed tank can agitate the liquid. For example, the agitation rate corresponding to strong shear is 5000 rpm.

[0035] The first suspension is atomized and dried in a spray drying tower to form a coagulant; the inlet temperature of the spray drying tower is 220°C and the outlet temperature is 95°C.

[0036] In this embodiment, after the first suspension is obtained, it is immediately atomized and dried in a spray drying tower to form a coagulant.

[0037] In this way, during the instant the micron-sized droplets obtained by atomizing the first suspension are rapidly dried, the calcium silicate-sodium silicate gel (i.e., active calcium silicate gel slurry) encapsulates and solidifies on the surface of lithium aluminum sulfate powder particles, forming solid spherical composite particles with a particle size of 30-60μm, which is the coagulant.

[0038] In some embodiments, the method further includes: Metakaolin was heated to 550-600℃ at a heating rate of 10℃ / min to obtain thermally activated metakaolin. Thermally activated metakaolin was dispersed in anhydrous ethanol to form a second suspension, wherein the ratio of thermally activated metakaolin to anhydrous ethanol was 20 g / 100 mL. In this embodiment, the specific surface area of ​​the thermally activated metakaolin is ≥1200 m² / kg.

[0039] Under continuous stirring and nitrogen protection, lithium carbonate and tetraethyl orthosilicate (TEOS) were dissolved together in anhydrous ethanol at a mass ratio of 1:2, and 2% dilute hydrochloric acid was added dropwise to obtain a mixed solution. In one example, the mass ratio of anhydrous ethanol, lithium carbonate, tetraethyl orthosilicate, and 2% dilute hydrochloric acid is 10:1:2:1.

[0040] It should be noted that the anhydrous ethanol used to dissolve lithium carbonate and tetraethyl orthosilicate and the anhydrous ethanol used to add thermally activated metakaolin are not the same amount of anhydrous ethanol. In this embodiment, dilute hydrochloric acid is used as a catalyst.

[0041] The mixed solution was slowly added dropwise to the second suspension, and the mixture was reacted in a 50°C water bath for 6 hours. During this process, the silica sol formed by the hydrolysis and condensation of TEOS, carrying lithium ions, was deposited in situ and filled into the nanopores and surface defects between the metakaolinite layers.

[0042] In one example, the volume ratio of the mixed solution to the second suspension is 1:1.

[0043] After the reaction was completed, the mixture was aged at 80℃ for 12 hours; dried at 110℃ for 8-12 hours; and finally calcined at 350℃ for 2 hours to obtain the early strength agent.

[0044] In this embodiment, calcination at 350°C for 2 hours stabilizes the structure, yielding an early-strength agent. The early-strength agent is a composite powder in which a lithium-silicon network is tightly bonded to metakaolin at the microscopic level.

[0045] In some embodiments, the method further includes: Hydroxypropyl methylcellulose was mixed with modified starch for 15 minutes to obtain a water-retaining agent.

[0046] In some embodiments, the water-retaining agent comprises the following components by weight: 8-12 parts of hydroxypropyl methylcellulose and 7-13 parts of modified starch.

[0047] In some embodiments, the method further includes preparing modified starch. Specifically, the method further includes: Deionized water was added to cassava starch and stirred at a stirring speed of 300-400 rpm to obtain a uniformly dispersed starch slurry. The pH was adjusted to 9.5-10.5 using a 3% sodium hydroxide aqueous solution and then swollen and activated at 48-52℃ for 30 min to obtain the activated starch slurry. In some embodiments, the mass ratio of cassava starch to deionized water is 100:150-180.

[0048] In this embodiment, cassava starch was chosen because of its low gelatinization temperature, high viscosity, and readily available raw materials.

[0049] In one example, cassava starch is placed in a reaction vessel, deionized water is added, and the mixture is dispersed evenly at a stirring rate of 300-400 rpm to obtain a starch slurry. This application does not limit the mixing time for obtaining the starch slurry, as long as it ensures that a uniformly dispersed starch slurry can be obtained.

[0050] In the embodiments of this application, swelling activation allows the starch granules to fully expand, so that subsequent chemical reagents can penetrate and react.

[0051] Sodium tripolyphosphate (STMP) and sodium chloride are added to the activated starch slurry under continuous stirring; the pH is maintained at 10.5-11.5, the reaction temperature is raised to 45-50℃, and the reaction is continued for 2-4 hours; wherein the mass of the sodium tripolyphosphate accounts for 0.3%-0.8% of the mass of the cassava starch. This process is a cross-linking process, which can enhance the network structure.

[0052] In this embodiment of the application, a 3% sodium hydroxide aqueous solution can be used to maintain the pH at 10.5-11.5.

[0053] In this embodiment, the mass ratio of sodium chloride to cassava starch is 0.5-1:100. Sodium chloride acts as an osmosis inhibitor.

[0054] In the embodiments of this application, sodium trimetaphosphate is a crosslinking agent.

[0055] In the crosslinking process described in this application, sodium trimetaphosphate phosphate bonds are introduced between the starch molecular chains of the activated starch paste to form a moderately crosslinked three-dimensional network structure, thereby significantly improving the mechanical shear stability and high-temperature resistance of the starch particles. This is the key to its ability to maintain its structure without disintegration in the alkaline environment of cement hydration and during stirring.

[0056] After the reaction is complete, propylene oxide and sodium sulfate are added simultaneously; the temperature is raised to 70-75℃, the pressure is 0.2-0.3 MPa, and the reaction is carried out for 6-10 hours to obtain modified starch. This process introduces hydrophilic groups into the etherification reaction.

[0057] In this process, propylene oxide accounts for 8%-15% of the mass of cassava starch, and is used as an etherifying agent. Sodium sulfate accounts for 2%-5% of the mass of cassava starch, and is used as a swelling inhibitor to prevent excessive swelling of the granules.

[0058] Specifically, after the cross-linking reaction is completed, the system is kept in the same reactor without separation. Propylene oxide and sodium sulfate are added to the system simultaneously. The reaction temperature is raised to 70-75℃, the pressure is controlled at 0.2-0.3 MPa, and the reaction is continued for 6-10 hours. Under these conditions, propylene oxide undergoes an etherification reaction with the hydroxyl groups of starch molecules, introducing hydroxypropyl hydrophilic groups. This step is a key innovation; the introduced hydroxypropyl groups greatly enhance the hydrophilicity of starch and its ability to bind water molecules.

[0059] In some embodiments, the method further includes: The interface reinforcing agent is obtained by mixing plasma-treated polypropylene fibers with a silane coupling agent for 10-15 minutes.

[0060] In some embodiments, the interface reinforcing agent comprises the following components by weight: 2-5 parts of plasma-treated polypropylene fiber and 3-10 parts of silane coupling agent.

[0061] In some embodiments, the method further includes: preparing plasma-treated polypropylene fibers; specifically, it includes: After the plasma equipment chamber is pre-evacuated to a background vacuum (usually ≤10 Pa), a mixture of oxygen and argon or oxygen alone is introduced as the working gas to maintain a stable gas flow rate (e.g., 30-50 sccm) so that the dynamic working pressure in the chamber is maintained at 20-50 Pa. In one example, the plasma device is manufactured by Ninebot Inc., and its model number is NE-PE210F. The plasma device includes a chamber, an RF power supply, and a rolling device, among other components.

[0062] Turn on the radio frequency power supply and set the power to 100-300 W to generate uniform and stable plasma.

[0063] Polypropylene fibers, cleaned and dried with anhydrous ethanol, are laid on the rotating device of a plasma treatment apparatus. The temperature is controlled below 60°C, and the treatment lasts for 3-8 minutes to obtain plasma-treated polypropylene fibers. Maintaining the temperature below 60°C in this step prevents heat deformation of the polypropylene fibers.

[0064] In this embodiment, the polypropylene fiber needs to be laid in a single layer on the rolling device of the plasma equipment so that the polypropylene fiber can be fully exposed.

[0065] In this embodiment, the length of the plasma-treated polypropylene fiber is 1-3 mm, the diameter is 20-40 μm, and the aspect ratio is 50-100.

[0066] In one example, the volume ratio of oxygen to argon in the mixed gas is 1:4.

[0067] The technical solutions in the embodiments of this application will be described in detail below through Examples 1-5 and Comparative Examples 1-3.

[0068] Example 1 According to the mass fractions, 35 parts of accelerator, 25 parts of early strength agent, 20 parts of water retention agent and 12 parts of interface reinforcement agent are mixed at a stirring speed of 350 rpm for 5 min, and then mixed at a stirring speed of 900 rpm for 8 min.

[0069] The preparation steps of the coagulant include: preparing a sodium silicate solution with a solid content of 30% using sodium silicate with a modulus of 3.2 and deionized water; adding nano-calcium silicate to the sodium silicate solution and stirring at 60°C for 10 min to form an active calcium silicate gel slurry; wherein the mass ratio of the nano-calcium silicate to the sodium silicate solution is 1:8; melting aluminum sulfate and lithium sulfate at 85°C in a molar ratio of 4:1 to prepare an aluminum-lithium sulfate composite salt; and water-cooling and pulverizing the aluminum-lithium sulfate composite salt to obtain aluminum-lithium sulfate powder, wherein the particle size of the aluminum-lithium sulfate powder is... The density distribution has D90 < 10 μm; in the feed tank of a high-speed centrifugal spray dryer, the lithium aluminum sulfate powder is continuously added to the active calcium silicate gel slurry, forming a uniform first suspension under strong shear (corresponding to a stirring rate of 5000 rpm); wherein the mass ratio of the lithium aluminum sulfate powder added to the active calcium silicate gel slurry is 40:60; the first suspension is atomized and dried through a spray drying tower to form a coagulant; the inlet air temperature of the spray drying tower is 220℃ and the outlet air temperature is 95℃. The preparation steps of nano-calcium silicate include: preparing a 0.5 mol / L Ca(NO3)2 solution with calcium nitrate tetrahydrate and allowing it to stand for aging for 24 h; preparing a 0.5 mol / L solution with sodium silicate with a modulus of 3.2. A sodium silicate solution of mol / L was prepared and allowed to stand for 24 hours. The aged Ca(NO3)2 solution and the aged sodium silicate solution were then taken. The molar ratio of Ca(NO3)2 in the aged Ca(NO3)2 solution to sodium silicate in the aged sodium silicate solution was 1:1. The aged Ca(NO3)2 solution was heated to 60℃ in a water bath. The aged sodium silicate solution was added dropwise at a constant rate within 45 minutes under stirring at 600 rpm, while maintaining a constant pH of 11 using 25% ammonia. Simultaneously with the addition of the aged sodium silicate solution, an ethanol solution containing a polycarboxylate dispersant was added dropwise. The preparation of the ethanol solution containing the polycarboxylate dispersant included adding the polycarboxylate dispersant to the ethanol solution and stirring to obtain the ethanol solution containing the polycarboxylate dispersant, wherein the mass ratio of the polycarboxylate dispersant to the ethanol solution was 3:100. The volume ratio of the added ethanol solution containing polycarboxylate dispersant to the added sodium silicate solution after standing and aging is 1-5:100. After the addition is complete, the mixture is stirred and aged at 60°C for 2 hours to obtain a white suspension. The white suspension is centrifuged to obtain a solid substance. The solid substance is washed three times alternately with anhydrous ethanol and deionized water to obtain a washed solid substance. The washed solid substance is dried in a vacuum drying oven at 70°C for 12 hours to obtain a dried soft agglomerate. The dried soft agglomerate is depolymerized in an air jet mill with a classifying wheel speed of 5000 rpm to obtain nano-calcium silicate.

[0070] The preparation method of the early strength agent includes: thermally activating metakaolin at 650℃ to obtain thermally activated metakaolin; dispersing the thermally activated metakaolin (specific surface area ≥1200 m² / kg) in anhydrous ethanol to form a second suspension, wherein the ratio of thermally activated metakaolin to anhydrous ethanol is 20 g / 100 mL; under continuous stirring and nitrogen protection, dissolving lithium carbonate and tetraethyl orthosilicate (TEOS) in anhydrous ethanol at a mass ratio of 1:2, and adding 2% dilute hydrochloric acid dropwise to obtain a mixed solution, wherein the mass ratio of anhydrous ethanol, lithium carbonate, tetraethyl orthosilicate, and 2% dilute hydrochloric acid is 10:1:2:1; slowly adding the mixed solution dropwise to the second suspension, reacting in a 50℃ water bath for 6 h, wherein the volume ratio of the mixed solution to the second suspension is 1:1. After the reaction was completed, the mixture was aged at 80℃ for 12 hours, dried at 110℃ for 10 hours, and finally calcined at 350℃ for 2 hours to obtain the early strength agent.

[0071] The preparation steps of the water-retaining agent include: mixing 10 parts of hydroxypropyl methylcellulose and 8 parts of modified starch for 15 minutes according to the mass fraction to obtain the water-retaining agent. The preparation steps of the modified starch include: adding deionized water to cassava starch (the mass ratio of cassava starch to deionized water is 100:160), stirring at a stirring speed of 300-400 rpm to obtain a uniformly dispersed starch slurry; adjusting the pH to 10 with a 3% sodium hydroxide aqueous solution, and activating it at 48-52℃ for 30 min to obtain an activated starch slurry; adding sodium tripolyphosphate (0.5% of the mass of cassava starch) and sodium chloride (0.5:100 of the mass of sodium chloride to cassava starch) to the activated starch slurry under continuous stirring; maintaining the pH at 11, raising the reaction temperature to 50℃, and continuing the reaction for 3 h; after the reaction is completed, simultaneously adding propylene oxide (10% of the mass of cassava starch) and sodium sulfate (3% of the mass of cassava starch); raising the temperature to 75℃, the pressure to 0.2 MPa, and reacting for 8 h to obtain the modified starch. This process introduces hydrophilic groups into the etherification reaction.

[0072] The preparation steps of the interface reinforcing agent include mixing 4 parts by mass of plasma-treated polypropylene fiber with 8 parts by mass of silane coupling agent for 10 minutes to obtain the interface reinforcing agent. The preparation steps of the plasma-treated polypropylene fiber include: pre-evacuating the equipment chamber of the plasma device to a base vacuum (typically ≤10 Pa), then introducing a mixture of oxygen and argon (oxygen to argon volume ratio of 1:4) as the working gas, maintaining a stable gas flow rate (30-50 sccm) to keep the dynamic working pressure in the chamber at 20-50 Pa; turning on the radio frequency power supply and setting the power to 200 W; placing the polypropylene fiber, cleaned and dried with anhydrous ethanol, onto the rolling device of the plasma device, controlling the temperature below 60°C, and treating for 5 minutes to obtain the plasma-treated polypropylene fiber.

[0073] Example 2 Unlike Example 1, the mass fractions of the coagulant, early strength agent, water-retaining agent and interface enhancer are 40 parts, 28 parts, 18 parts and 14 parts, respectively.

[0074] Example 3 Unlike Example 1, the mass fractions of the coagulant, early strength agent, water-retaining agent and interface enhancer are 45 parts, 30 parts, 15 parts and 10 parts, respectively.

[0075] Example 4 Unlike Example 1, the mass fractions of the coagulant, early strength agent, water-retaining agent and interface enhancer are 30 parts, 20 parts, 25 parts and 15 parts, respectively.

[0076] Example 5 Unlike Example 1, the mass fractions of the coagulant, early strength agent, water-retaining agent and interface enhancer are 50 parts, 35 parts, 15 parts and 10 parts, respectively.

[0077] Comparative Example 1 Unlike Example 1, the mass fractions of the coagulant, early strength agent, water-retaining agent and interface enhancer are 60 parts, 15 parts, 10 parts and 5 parts, respectively.

[0078] Comparative Example 2 Unlike Example 1, the mass fractions of the coagulant, early strength agent, water-retaining agent and interface enhancer are 30 parts, 40 parts, 20 parts and 10 parts, respectively.

[0079] Comparative Example 3 Unlike Example 1, the mass fractions of the coagulant, early strength agent, water-retaining agent and interface enhancer are 35 parts, 25 parts, 0 parts and 30 parts, respectively.

[0080] Table 1 shows the component ratios of the quick-setting admixtures in Examples 1-5 and Comparative Examples 1-3.

[0081] Table 1

[0082] The performance test will be conducted below: The quick-setting admixtures obtained in Examples 1-5 and Comparative Examples 1-3 were added to low-concentration filling slurries, wherein the filling material accounted for 45% of the mass concentration of the filling slurry. The filling material, by mass fraction, included 1 part cement and 5 parts coal-based solid waste. The coal-based solid waste, by mass fraction, included 40 parts fly ash, 40 parts coal gangue, and 20 parts desulfurized gypsum; the mass ratio of the quick-setting admixture to cement was 2:100. The performance indicators of the filling slurry with the added quick-setting admixture were tested, and the results are shown in Table 2 below. Table 2

[0083] The test results in Table 2 show that: Examples 1-5 all exhibited excellent overall performance, with moderate setting time (initial setting 10-22 min, final setting 25-40 min), good early and late strength development (3-day strength 2.5-3.8 MPa, 28-day strength 8.0-10.5 MPa), and significantly reduced bleeding rate (1.5%-2.8%).

[0084] Example 3 exhibited the best overall performance, with an initial setting time of 12 min, a final setting time of 28 min, a 3-day strength of 3.5 MPa, a 28-day strength of 9.8 MPa, and a bleeding rate of only 1.8%. This is attributed to its balanced formulation design: 45 parts of accelerator, 30 parts of early strength agent, 15 parts of water-retaining agent, and 10 parts of interface enhancer.

[0085] Comparative Example 1 (excessive accelerator): The setting time was the shortest, but the early and late strengths were both low, and the bleeding rate was as high as 7.5%. This indicates that although excessive accelerator accelerates setting, it is not conducive to long-term strength development and stability.

[0086] Comparative Example 2 (excessive early strength agent): The setting time is too long, which cannot meet the requirements of rapid construction. Although the later strength is acceptable, the early strength development is slow.

[0087] Comparative Example 3 (without water-retaining agent): The bleeding rate was as high as 12.5%, and the strength development was poor, proving that the water-retaining agent is crucial to the stability of low-concentration slurry.

[0088] This application successfully solves the technical challenges of low-concentration mine filling and sealing materials through a carefully designed component ratio and synergistic mechanism, providing a highly efficient and reliable special admixture solution for mining engineering.

[0089] In summary, this invention provides a rapid-setting admixture for mine filling and sealing materials and its preparation method. This rapid-setting admixture addresses the problems of slow setting, low early strength, and severe bleeding in slurries with a low concentration of 30%-60%. The water-retaining agent in the rapid-setting admixture is a composite water-retaining system formed by hydroxypropyl methylcellulose and modified starch. Hydroxypropyl methylcellulose physically encapsulates free water in the slurry; modified starch adsorbs water molecules through hydrogen bonding, and this dual mechanism significantly reduces the bleeding rate. The coagulant uses spray drying encapsulation technology to construct a core-shell structure composite particle with lithium aluminum sulfate as the "rapid-release core" and an active calcium silicate gel slurry obtained by reacting nano-calcium silicate with sodium silicate as the "slow-release encapsulation layer." This structure promotes coagulation, prevents premature consumption of sodium silicate, and achieves continuous setting. The early-strength agent uses a gel-gel method, enabling it to provide sustained early-strength activation and solving the problem of weak strength growth in later stages. Interface enhancers can make the structure of the interface transition zone stronger and tougher, and improve the integrity and resistance to damage after the slurry sets and hardens.

[0090] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A quick-setting admixture for mine filling and sealing materials, characterized in that, The product comprises, by weight parts, the following components: 30-50 parts of coagulant accelerator, 20-35 parts of early-strength agent, 15-25 parts of water-retaining agent, and 5-15 parts of interface reinforcing agent; wherein, the water-retaining agent comprises, by weight parts, the following components: 8-12 parts of hydroxypropyl methylcellulose and 7-13 parts of modified starch; the interface reinforcing agent comprises, by weight parts, the following components: 2-5 parts of plasma-treated polypropylene fiber and 3-10 parts of silane coupling agent; the coagulant accelerator comprises, by weight parts, the following components: 40 parts of lithium aluminum sulfate powder and 60 parts of activated calcium silicate gel slurry; the activated calcium silicate gel slurry comprises, by weight parts, nano-calcium silicate and sodium silicate; the lithium aluminum sulfate powder comprises aluminum sulfate and lithium sulfate in a molar ratio of 4:1; the early-strength agent comprises, by weight parts, metakaolin, lithium carbonate, and tetraethyl orthosilicate.

2. The method for preparing the quick-setting admixture of the mine filling and sealing material according to claim 1, characterized in that, include: The coagulant, early strength agent, water-retaining agent and interface enhancer are mixed in a segmented manner, wherein the segmented mixing includes mixing at a stirring speed of 300-400 rpm for 5 min, and then continuing to mix at a stirring speed of 800-1000 rpm for 5-10 min.

3. The method according to claim 2, characterized in that, Also includes: A sodium silicate solution with a solid content of 30% was prepared using sodium silicate with a modulus of 3.2 and deionized water. Nano-sized calcium silicate was added to a sodium silicate solution and stirred at 60°C for 10 minutes to form an active calcium silicate gel slurry; wherein the mass ratio of the nano-sized calcium silicate to the sodium silicate solution was 1:

8. Aluminum sulfate and lithium sulfate were melt-reacted at 85°C in a molar ratio of 4:1 to prepare an aluminum-lithium sulfate composite salt. The aluminum-lithium sulfate composite salt was then water-cooled and pulverized to ensure that the particle size distribution of the resulting aluminum-lithium sulfate powder had a D90 < 10 μm. The aluminum-lithium sulfate powder was continuously added to the activated calcium silicate gel slurry in the feed tank of a high-speed centrifugal spray dryer, forming a uniform first suspension under strong shear. The mass ratio of the aluminum-lithium sulfate powder added to the activated calcium silicate gel slurry to the activated calcium silicate gel slurry was 40:

60. The first suspension is atomized and dried in a spray drying tower to form a coagulant; the inlet temperature of the spray drying tower is 220°C and the outlet temperature is 95°C.

4. The method according to claim 3, characterized in that, Also includes: Prepare a 0.5 mol / L Ca(NO3)2 solution with calcium nitrate tetrahydrate and let it stand for 24 hours; Prepare a 0.5 mol / L sodium silicate solution using sodium silicate with a modulus of 3.2 and let it stand for 24 hours to age. Take a statically aged Ca(NO3)2 solution and a statically aged sodium silicate solution; wherein the molar ratio of Ca(NO3)2 in the statically aged Ca(NO3)2 solution to sodium silicate in the statically aged sodium silicate solution is 1:1; heat the statically aged Ca(NO3)2 solution to 58-62℃ in a water bath; under stirring at a stirring speed of 600 rpm, uniformly add the statically aged sodium silicate solution within 45 minutes, and maintain the pH value at a constant 10.5-11.0 using 25% ammonia water; while adding the statically aged sodium silicate solution, add an ethanol solution containing polycarboxylate dispersant; the volume ratio of the added ethanol solution containing polycarboxylate dispersant to the added statically aged sodium silicate solution is 1-5:

100. After the addition was complete, the mixture was stirred and aged at 60°C for 2 hours to obtain a white suspension. The white suspension was centrifuged to obtain a solid substance; the solid substance was washed three times alternately with anhydrous ethanol and deionized water to obtain the washed solid substance. The washed solid material was dried in a vacuum drying oven at 70°C for 12 hours to obtain dried soft aggregates. The dried soft agglomerates were deagglomerated in an air jet mill with a classifying wheel speed of 5000 rpm to obtain nano-calcium silicate.

5. The method according to claim 2, characterized in that, Also includes: Thermal activation of metakaolin at 650℃ yields thermally activated metakaolin. Thermally activated metakaolin was added to anhydrous ethanol to form a second suspension, wherein the ratio of thermally activated metakaolin to anhydrous ethanol was 20 g / 100 mL. Under continuous stirring and nitrogen protection, lithium carbonate and tetraethyl orthosilicate were dissolved together in anhydrous ethanol at a mass ratio of 1:2, and dilute hydrochloric acid was added dropwise to obtain a mixed solution. The mixed solution was slowly added dropwise to the second suspension, and the mixture was reacted in a water bath at 50°C for 6 hours. After the reaction was completed, the mixture was aged at 80℃ for 12 hours, dried at 110℃ for 8-12 hours, and finally calcined at 350℃ for 2 hours to obtain the early strength agent.

6. The method according to claim 2, characterized in that, Also includes: Hydroxypropyl methylcellulose was mixed with modified starch for 15 minutes to obtain a water-retaining agent.

7. The method according to claim 6, characterized in that, Also includes: Deionized water was added to cassava starch and stirred at a stirring speed of 300-400 rpm to obtain a uniformly dispersed starch slurry. After adjusting the pH to 9.5-10.5 with a 3% sodium hydroxide aqueous solution, the starch paste was swollen and activated at 48-52℃ for 30 minutes to obtain the activated starch paste. Sodium tripolyphosphate (STMP) and sodium chloride are added to the activated starch slurry under continuous stirring; the pH is maintained at 10.5-11.5, the reaction temperature is raised to 45-50℃, and the reaction is continued for 2-4 hours; wherein the mass of the sodium tripolyphosphate accounts for 0.3%-0.8% of the mass of the cassava starch; Maintain pH at 10.5-11.5, raise the reaction temperature to 45-50℃, and continue the reaction for 2-4 hours; After the reaction is complete, propylene oxide and sodium sulfate are added simultaneously; the temperature is raised to 70-75℃, the pressure is 0.2-0.3MPa, and the reaction is carried out for 6-10 hours to obtain modified starch.

8. The method according to claim 7, characterized in that, The mass ratio of the cassava starch to the deionized water is 100:150-180.

9. The method according to claim 2, characterized in that, Also includes: The interface reinforcing agent is obtained by mixing plasma-treated polypropylene fibers with a silane coupling agent for 10-15 minutes.

10. The method according to claim 9, characterized in that, Also includes: After the equipment chamber of the plasma device is pre-evacuated to a background vacuum, a mixture of oxygen and argon or oxygen as the working gas is introduced to maintain a stable gas flow rate, so that the dynamic working pressure in the chamber is maintained at 20-50 Pa. Turn on the RF power supply and set the power to 100-300W; Polypropylene fibers that have been cleaned and dried with anhydrous ethanol are laid on the rolling device of a plasma equipment, and the temperature is controlled below 60℃ for 3-8 minutes to obtain plasma-treated polypropylene fibers.

Images