Silicate composite material as well as preparation method and application thereof

Abstract

The invention provides a silicate composite material as well as a preparation method and application thereof, and the method comprises the following steps: hydroxyapatite surface modification: mixing hydroxyapatite with acid, and washing to be neutral to obtain activated hydroxyapatite; the activated hydroxyapatite is modified through a silane coupling agent, and hydroxyapatite suspension liquid is obtained; water glass depolymerization: diluting the high-modulus water glass until the SiO2 concentration is 0.1-0.3 mol / L, and carrying out hydrolysis depolymerization to generate active silica sol; preparing a reaction precursor: adding the hydroxyapatite suspension into a second mixed solvent, then adding the active silicic acid sol to obtain a mixed solution, slowly dropwise adding lime milk into the mixed solution, and stirring after dropwise adding to obtain the reaction precursor; and preparing the silicate composite material: transferring the reaction precursor into a high-pressure kettle, and carrying out solvothermal reaction to obtain the silicate composite material. When the silicate composite material is used as a papermaking filler, the tensile strength, the whiteness and the moisture resistance of paper are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of papermaking filler, and particularly relates to a silicate composite material and a preparation method and application thereof. BACKGROUND

[0002] Calcium silicate is an inorganic compound, which is a material with high specific surface area and rich pore structure. The calcium silicate has the characteristics of small particle size, low density, high oil absorption value and large specific surface area. The physical and chemical properties of calcium silicate are very stable, and the calcium silicate is mainly used in thermal insulation refractory materials, building materials, metallurgical ceramics, papermaking fillers, adsorbent materials, rubber and plastics.

[0003] In recent years, the calcium silicate as a papermaking filler has been widely concerned and applied. The calcium silicate not only saves fiber raw materials, reduces production cost and transportation cost, but also provides higher opacity and brightness than traditional fillers (such as calcium carbonate and kaolin), and the porous structure makes the calcium silicate have high porosity and ink absorption capacity, which can quickly absorb printing ink, reduce drying time and improve printing suitability.

[0004] However, with the high-efficiency and high-quality development of the papermaking industry, the paper has more stringent requirements, such as higher tensile strength. Although the addition of single calcium silicate has an effect on the improvement of the tensile strength, the calcium silicate has a single function, and it is difficult to meet the higher tensile strength requirement of the papermaking industry. SUMMARY

[0005] The present application provides a silicate composite material and a preparation method and application thereof to solve the problems mentioned in the background.

[0006] In a first aspect, the present application provides a preparation method of a silicate composite material, which comprises the following steps: (1) Surface modification of hydroxyapatite: hydroxyapatite is stirred and mixed with acid for 20-40 min, and washed with water until neutral to obtain activated hydroxyapatite; The activated hydroxyapatite is dispersed into a first mixed solvent, and a silane coupling agent is added, and the pH value is adjusted to 4-5 with acid, and stirred at 20-30 DEG C for 30-60 min to obtain a hydroxyapatite suspension; (2) Depolymerization of water glass: the high modulus water glass is diluted to a SiO2 concentration of 0.1-0.3 mol / L with deionized water, and the high modulus water glass is hydrolyzed and depolymerized to generate an active silicic acid sol; (3) Preparation of reaction precursor: the hydroxyapatite suspension is added to a second mixed solvent, stirred for 5-10 min, and then the active silicic acid sol is added, stirred for 5-10 min, to obtain a mixed solution, and the lime milk is slowly added to the mixed solution, and stirred for 10-30 min after the addition is completed to obtain a reaction precursor; (4) Preparation of silicate composite material: The reaction precursor is transferred into a high-pressure reactor for solvothermal reaction to obtain the above silicate composite material.

[0007] Optionally, in the preparation of activated hydroxyapatite, the acid used is hydrochloric acid or nitric acid with a molar concentration of 0.2-0.4 mol / L, and the weight-volume ratio of hydroxyapatite to acid is 1-1.5 g / 30 mL.

[0008] Optionally, during the preparation of the hydroxyapatite suspension, The weight ratio of activated hydroxyapatite to silane coupling agent is 1:1-2, and the weight-volume ratio of the sum of the weights of activated hydroxyapatite and silane coupling agent to the first mixed solvent is 1-5 g / 100 mL. The acid used is hydrochloric acid or nitric acid with a molar concentration of 0.2-0.4 mol / L.

[0009] Optionally, during the preparation of the reaction precursor, the molar ratio of the amount of active silica sol to lime milk added is Ca / Si = 1.0-1.2; The weight ratio of the sum of the active silica sol and lime milk to the weight of the hydroxyapatite suspension is 1:1-3.

[0010] Optionally, during the preparation of the reaction precursor, lime slurry is added dropwise to the second mixed solvent at a rate of 0.8-1.2 mL / min; The weight-to-volume ratio of the sum of the hydroxyapatite suspension, the active silica sol, and the lime slurry to the second mixed solvent is 10-20 g / 100 mL.

[0011] Optionally, the first mixed solvent is prepared by mixing ethanol and deionized water in a volume ratio of 1:1, and the second mixed solvent is prepared by mixing ethylene glycol and deionized water in a volume ratio of 1:2.

[0012] Optionally, during the preparation of the reaction precursor, after the lime slurry is added dropwise, the mixture is stirred at a temperature of 60-80℃ for 2-5 hours to obtain the reaction precursor.

[0013] Optionally, the conditions for the solvothermal reaction are: temperature 160-200℃, reaction time 1-4h, and heating rate 5-8℃ / min during the reaction.

[0014] Secondly, this application provides a silicate composite material, which is prepared by the above-described method for preparing silicate composite materials.

[0015] Thirdly, this application provides an application of the above-mentioned silicate composite material in the papermaking field.

[0016] The silicate composite material, its preparation method, and its application provided in this application realize the preparation of silicate composite materials and have the following advantages compared with the prior art: (1) This application improves the surface activity and dispersibility of hydroxyapatite by modifying its surface, thereby increasing the activity of hydroxyl groups (-OH) on the surface of hydroxyapatite, enhancing the interfacial bonding strength with CaSiO3, and preventing the physical detachment of the CaSiO3 shell. This results in a more uniform coating of calcium silicate on the surface of hydroxyapatite, thus improving the uniformity of the calcium silicate composite material. Depolymerization of high-modulus water glass facilitates efficient reaction, allowing Ca adsorption on the surface of hydroxyapatite to proceed more effectively. 2+ With SiO3 2- CaSiO3 was directionally deposited on the surface of hydroxyapatite. Finally, using water glass as the silicon source and lime milk as the calcium source, calcium silicate was used to coat the nano-hydroxyapatite through a solvothermal reaction, resulting in the formation of silicate (SiO3) groups. 2- ) and calcium ions (Ca 2+ A CaSiO3 shell is directionally formed on the surface of hydroxyapatite to create a calcium silicate composite material. After coating with a water glass-lime slurry system, the composite material is better dispersed among pulp fibers, forming hydrogen bonds or chemical bonds with the fibers. This significantly improves the tensile strength, bursting strength, and folding endurance of the paper, while reducing fiber usage. As a filler, it can partially replace plant fibers, lowering production costs. Furthermore, the coating further optimizes the paper's refractive index, improving its whiteness and light scattering ability. The surface charge of the coated calcium silicate composite material is more compatible with the fibers, making it easier to adsorb onto them, thus improving retention rates, increasing raw material utilization, reducing waste, and lowering enterprise costs.

[0017] (2) The silicate composite material (calcium silicate composite material) provided in this application, as a papermaking filler, can significantly improve the moisture resistance of paper. This is beneficial for the storage of paper in humid environments, reduces the stringent environmental requirements for paper storage, and enables the paper to be used in a wider range of environments, improving the utilization rate of paper and enhancing the economic benefits of manufacturing enterprises. This performance is attributed to the coating of nano-hydroxyapatite with calcium silicate through a solvothermal reaction, which allows the silicate ions (SiO3) to be coated onto the nano-hydroxyapatite. 2- ) and calcium ions (Ca 2+ A CaSiO3 shell is directionally generated on the surface of hydroxyapatite. This core-shell structure prevents the hydrophilic groups on the surface of hydroxyapatite from being exposed and interacting with the fibers and external water molecules. When the hydrophilic groups on the surface of the calcium silicate composite material are mixed with the fibers, hydrogen bonds or chemical bonds are formed, which greatly reduces the binding between the paper structure and water molecules in the environment, giving the paper better moisture-proof performance.

[0018] (3) The paper prepared by using the silicate composite material provided in this application as a papermaking filler can be applied to a wider range of environments and is suitable for large-scale production. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0020] In a first aspect, this application provides a method for preparing a silicate composite material, comprising the following steps: (1) Surface modification of hydroxyapatite: Hydroxyapatite is stirred and mixed with acid for 20-40 min, and washed with water until neutral to obtain activated hydroxyapatite; Activated hydroxyapatite is dispersed in the first mixed solvent, then a silane coupling agent is added, the pH is adjusted to 4-5 with acid, and the mixture is stirred at 20-30℃ for 30-60 min to obtain a hydroxyapatite suspension. (2) Depolymerization of water glass: Dilute high modulus water glass with deionized water to a SiO2 concentration of 0.1-0.3 mol / L, and depolymerize the high modulus water glass to generate active silica sol; (3) Preparation of reaction precursor: Add hydroxyapatite suspension to the second mixed solvent and stir for 5-10 min. Then add active silica sol and stir for 5-10 min to obtain a mixed solution. Slowly add lime milk to the mixed solution and stir for 10-30 min after the addition is complete to obtain the reaction precursor. (4) Preparation of silicate composite material: The reaction precursor is transferred into a high pressure vessel for solvothermal reaction to obtain calcium silicate composite material, namely the silicate composite material mentioned above.

[0021] Specifically, the silicate composite material provided in this application uses high-modulus water glass as the silicon source and lime milk as the calcium source. The coating of nano-hydroxyapatite with calcium silicate is achieved through a solvothermal reaction, resulting in the formation of silicate ions (SiO3). 2- ) and calcium ions (Ca 2 + A CaSiO3 shell is directionally generated on the surface of hydroxyapatite.

[0022] First, the surface of hydroxyapatite is modified to enhance its surface activity and dispersibility, achieving a particle size of 50-200 nm and a specific surface area ≥30 m² / g. This ensures sufficient hydroxyl density on the hydroxyapatite surface. Hydroxyapatite is then mixed with acid, which further increases the surface roughness and hydroxyl density, thereby enhancing the activity of the hydroxyl groups (-OH) on the hydroxyapatite surface. This strengthens the interfacial bonding with CaSiO3 and prevents the physical detachment of the CaSiO3 shell. Then, a silane coupling agent is added to form a uniform hydroxyapatite suspension, facilitating its uniform dispersion. During subsequent coating, this results in more uniform coating of calcium silicate on the hydroxyapatite surface, thus improving the uniformity of the calcium silicate composite material. The silane coupling agent is selected from γ-aminopropyltriethoxysilane (KH550).

[0023] High-modulus water glass was diluted with deionized water to a SiO2 concentration of 0.1-0.3 mol / L, and then hydrolyzed and depolymerized to further dissociate into SiO3. 2- An active silica sol is generated, and the modulus of the high-modulus water glass solution is 2.5-3.5. Depolymerization of the high-modulus water glass facilitates efficient reaction, allowing Ca to be adsorbed on the surface of hydroxyapatite. 2+ With SiO3 2- CaSiO3 is directionally deposited on the surface of hydroxyapatite to match the reaction rate of the two with the adsorption rate of the hydroxyapatite surface, thus avoiding the formation of free CaSiO3 particles and strengthening the interfacial bonding between CaSiO3 and hydroxyapatite.

[0024] Furthermore, during the depolymerization of high-modulus water glass, maintaining a temperature of 60-80℃ accelerates the depolymerization rate and shortens the reaction time; simultaneously, it promotes Ca... 2+ Diffusion causes Ca on the n-HA surface to diffuse. 2+ Uniform concentration and improved shell thickness consistency; however, excessively high temperatures can cause lime slurry to dehydrate and form CaO. 2+ The concentration drops sharply, and n-HA may dissolve on the surface.

[0025] Nano-hydroxyapatite (n-HA) possesses high strength and rigidity. After being coated with a water glass-lime slurry system, it disperses better among pulp fibers, forming hydrogen or chemical bonds with them. This significantly improves the tensile strength, bursting strength, and folding endurance of paper, while reducing fiber usage. As a filler, it can partially replace plant fibers, lowering production costs. Furthermore, the coating optimizes the paper's refractive index, improving whiteness and light scattering. Hydroxyapatite decomposes endothermally at high temperatures, releasing phosphates that promote charring layer formation, imparting flame-retardant properties to the paper, making it suitable for specialty packaging or fire-retardant paper. The water glass-lime slurry coating prevents nHA agglomeration, improves the uniform dispersion of fillers in the pulp, reduces sedimentation problems, and the surface charge of the coated calcium silicate composite material is more compatible with the fibers, making it easier to adsorb onto the fibers, improving retention rate, increasing raw material utilization, reducing waste, and lowering enterprise costs. Meanwhile, the calcium silicate composite material provided in this application has a high specific surface area and porosity, which can further enhance the bonding strength between the calcium silicate composite material and the fiber, which is beneficial to improving the tensile strength of the paper and making the paper have a suitable bulk.

[0026] During the preparation of the reaction precursor, lime slurry is slowly added dropwise to the mixture of hydroxyapatite suspension and active silica sol, thus avoiding localized Ca2+ contamination. 2+ Too high a concentration causes Ca 2+ With SiO3 2- The reaction proceeds stepwise on the n-HA surface to ensure uniform deposition of the shell layer. During the solvothermal reaction, silicate ions (SiO3)... 2- ) and calcium ions (Ca 2+ ) is directionally polymerized on the n-HA surface and coated on the hydroxyapatite surface to form a calcium silicate composite material.

[0027] Further, after the solvothermal reaction is completed, the reaction system is cooled to room temperature, and solid-liquid separation is performed by centrifugation (8000-10000 r / min, 15-20 min) or vacuum filtration. The solid phase (product) is collected and washed repeatedly with deionized water 3-5 times. It is then vacuum dried at 60-80℃ for 12-16 h to remove surface adsorbed water. The dried product is then placed in a muffle furnace and heated to 500-650℃ at a heating rate of 2-5℃ / min, held at that temperature for 2-3 h, and naturally cooled to room temperature. This process improves the crystallinity of the CaSiO3 shell, enhances its mechanical strength and corrosion resistance, and yields a calcium silicate composite material.

[0028] This application achieves the preparation of silicate composite materials through the above-described scheme. By modifying the surface of hydroxyapatite, the surface activity and dispersibility of hydroxyapatite are enhanced, the activity of hydroxyl groups (-OH) on the hydroxyapatite surface is increased, and the interfacial bonding strength with CaSiO3 is improved, preventing the physical detachment of the CaSiO3 shell. This results in a more uniform coating of calcium silicate on the surface of hydroxyapatite, thereby improving the uniformity of the calcium silicate composite material. Depolymerization of high-modulus water glass facilitates efficient reaction, allowing Ca adsorption on the hydroxyapatite surface to proceed more effectively. 2+ With SiO3 2- CaSiO3 was directionally deposited on the surface of hydroxyapatite. Finally, using water glass as the silicon source and lime milk as the calcium source, calcium silicate was used to coat the nano-hydroxyapatite through a solvothermal reaction, resulting in the formation of silicate (SiO3) groups. 2- ) and calcium ions (Ca 2+ A CaSiO3 shell is directionally formed on the surface of hydroxyapatite, resulting in a calcium silicate composite material. After coating with a water glass-lime slurry system, the composite material is better dispersed among pulp fibers, forming hydrogen bonds or chemical bonds with the fibers. This significantly improves the tensile strength, bursting strength, and folding endurance of the paper, while reducing fiber usage. As a filler, it can partially replace plant fibers, lowering production costs. Furthermore, the coating further optimizes the paper's refractive index, improving its whiteness and light scattering ability. The surface charge of the coated calcium silicate composite material is more compatible with the fibers, making it easier to adsorb onto them, thus improving retention rates, increasing raw material utilization, reducing waste, and lowering enterprise costs.

[0029] Optionally, in the preparation of activated hydroxyapatite, the acid used is hydrochloric acid or nitric acid with a molar concentration of 0.2-0.4 mol / L, and the weight-volume ratio of hydroxyapatite to acid is 1-1.5 g / 30 mL.

[0030] Optionally, during the preparation of the hydroxyapatite suspension, the weight ratio of activated hydroxyapatite to silane coupling agent is 1:1-2, and the weight-volume ratio of the sum of the weights of activated hydroxyapatite and silane coupling agent to the first mixed solvent is 1-5 g / 100 mL. The acid used is hydrochloric acid or nitric acid with a molar concentration of 0.2-0.4 mol / L.

[0031] Optionally, during the preparation of the reaction precursor, the molar ratio of active silica sol to lime slurry is Ca / Si = 1.0-1.2; to avoid excessive Si generating free silica or excessive Ca generating Ca(OH)2. The weight ratio of the sum of the active silica sol and lime milk to the weight of the hydroxyapatite suspension is 1:1-3.

[0032] Optionally, during the preparation of the reaction precursor, lime slurry is added dropwise to the second mixed solvent at a rate of 0.8-1.2 mL / min; the dropping rate of the lime slurry is controlled to avoid localized Ca2+ accumulation. 2+ Too high a concentration causes Ca 2+ With SiO3 2- The reaction proceeds gradually on the n-HA surface to ensure uniform shell deposition. Simultaneously, the active silica sol must not be dripped into the lime slurry to avoid localized Ca2+ deposition. 2+ Excessive amounts will instantly generate a large number of free CaSiO3 particles, leading to coating failure.

[0033] The weight-to-volume ratio of the sum of the hydroxyapatite suspension, the active silica sol, and the lime slurry to the second mixed solvent is 10-20 g / 100 mL.

[0034] Optionally, the first mixed solvent is prepared by mixing ethanol and deionized water in a volume ratio of 1:1, and the second mixed solvent is prepared by mixing ethylene glycol and deionized water in a volume ratio of 1:2.

[0035] Optionally, during the preparation of the reaction precursor, after the lime slurry is added dropwise, the mixture is stirred at a temperature of 60-80℃ for 2-5 hours to obtain the reaction precursor.

[0036] Increased temperature can promote Ca 2+ Diffusion causes Ca on the n-HA surface to diffuse. 2+ The concentration is uniform, the shell thickness is consistent, and the uniformity of calcium silicate composite materials is improved.

[0037] Optionally, the conditions for the solvothermal reaction are: temperature 160-200℃, reaction time 1-4h, and heating rate 5-8℃ / min during the reaction.

[0038] Secondly, this application provides a silicate composite material, which is prepared by the above-described method for preparing silicate composite materials.

[0039] Thirdly, this application provides an application of the above-mentioned silicate composite material in the papermaking field.

[0040] The silicate composite material (calcium silicate composite material) provided in this application is used as a papermaking filler in the papermaking field. After coating hydroxyapatite with a water glass-lime slurry system, it can be better dispersed between pulp fibers and form hydrogen bonds or chemical bonds with the fibers, significantly improving the tensile strength of the paper. At the same time, the activation of hydroxyapatite by acid and the modification of hydroxyapatite by adding silane coupling agents improve the activity of hydroxyapatite surface hydroxyl groups (-OH), enhance the interfacial bonding strength with CaSiO3, and facilitate the uniform dispersion of hydroxyapatite. In the subsequent coating process, the calcium silicate is more uniformly coated on the surface of hydroxyapatite, thereby improving the uniformity of the calcium silicate composite material. This allows the calcium silicate composite material to be evenly distributed in the fiber pulp, which is beneficial to improving the retention rate of the papermaking filler. In addition, the calcium silicate composite material provided in this application has a high specific surface area and porosity, which can further enhance the bonding strength between the calcium silicate composite material and the fibers, which is beneficial to improving the tensile strength of the paper and giving the paper a suitable bulk.

[0041] The technical solution of this application will be illustrated in detail below with specific embodiments.

[0042] Example 1 A method for preparing a silicate composite material includes the following steps: (1) Surface modification of hydroxyapatite: Hydroxyapatite was mixed with hydrochloric acid with a molar concentration of 0.2 mol / L for 20 min and washed with water until the pH value was 6.5 to obtain activated hydroxyapatite; The weight-to-volume ratio of hydroxyapatite to acid is 1 g / 30 mL; Activated hydroxyapatite was dispersed in the first mixed solvent, and then silane coupling agent (KH550) was added. The pH value was adjusted to 4 with hydrochloric acid with a molar concentration of 0.2 mol / L. The mixture was stirred at 20°C for 60 min to obtain a hydroxyapatite suspension. The weight ratio of activated hydroxyapatite to silane coupling agent is 1:2, and the weight-volume ratio of the sum of the weights of activated hydroxyapatite and silane coupling agent to the first mixed solvent is 1 g / 100 mL. The first mixed solvent is prepared by mixing ethanol and deionized water in a volume ratio of 1:1.

[0043] (2) Depolymerization of water glass: High modulus water glass is diluted with deionized water to a SiO2 concentration of 0.1 mol / L, and the high modulus water glass is hydrolyzed and depolymerized to generate active silica sol.

[0044] (3) Preparation of reaction precursor: Add hydroxyapatite suspension to the second mixed solvent and stir for 5 min. Then add active silica sol and stir for 5 min to obtain a mixed solution. Add lime milk slowly to the mixed solution at a rate of 0.8 mL / min. After the addition is completed, stir for 10 min to obtain the reaction precursor. The molar ratio of active silica sol to lime milk is Ca / Si = 1.0; the weight ratio of the sum of the active silica sol and lime milk to the hydroxyapatite suspension is 1:1; the weight-volume ratio of the sum of the hydroxyapatite suspension, active silica sol, and lime milk to the second mixed solvent is 10 g / 100 mL; and the second mixed solvent is prepared by mixing ethylene glycol and deionized water in a volume ratio of 1:2.

[0045] (4) Preparation of calcium silicate composite material: The reaction precursor was transferred to a high-pressure reactor for solvothermal reaction to obtain calcium silicate composite material. The solvothermal reaction conditions were: temperature 160℃, reaction time 4h, and heating rate 5℃ / min during the reaction. Example 2

[0046] A method for preparing a silicate composite material includes the following steps: (1) Surface modification of hydroxyapatite: Hydroxyapatite was mixed with hydrochloric acid with a molar concentration of 0.3 mol / L for 30 min and washed with water until the pH value was 7 to obtain activated hydroxyapatite; The weight-to-volume ratio of hydroxyapatite to acid is 1.2 g / 30 mL; Activated hydroxyapatite was dispersed in the first mixed solvent, and then silane coupling agent (KH550) was added. The pH value was adjusted to 5 with hydrochloric acid with a molar concentration of 0.3 mol / L. The mixture was stirred at 25°C for 40 min to obtain a hydroxyapatite suspension. The weight ratio of activated hydroxyapatite to silane coupling agent is 1:2, and the weight-volume ratio of the sum of the weights of activated hydroxyapatite and silane coupling agent to the first mixed solvent is 3 g / 100 mL. The first mixed solvent is prepared by mixing ethanol and deionized water in a volume ratio of 1:1.

[0047] (2) Depolymerization of water glass: High modulus water glass is diluted with deionized water to a SiO2 concentration of 0.2 mol / L, and the high modulus water glass is hydrolyzed and depolymerized to generate active silica sol.

[0048] (3) Preparation of reaction precursor: Add hydroxyapatite suspension to the second mixed solvent and stir for 10 min. Then add active silica sol and stir for 10 min to obtain a mixed solution. Add lime milk slowly to the mixed solution at a rate of 1.0 mL / min. After the addition is completed, stir for 20 min to obtain the reaction precursor. The molar ratio of active silica sol to lime milk is Ca / Si = 1.1; the weight ratio of the sum of the active silica sol and lime milk to the hydroxyapatite suspension is 1:2; the weight-volume ratio of the sum of the hydroxyapatite suspension, active silica sol, and lime milk to the second mixed solvent is 15 g / 100 mL; and the second mixed solvent is prepared by mixing ethylene glycol and deionized water in a volume ratio of 1:2.

[0049] (4) Preparation of calcium silicate composite material: The reaction precursor was transferred to a high-pressure reactor for solvothermal reaction to obtain calcium silicate composite material. The solvothermal reaction conditions were: temperature 180℃, reaction time 2h, and heating rate 7℃ / min during the reaction. Example 3

[0050] A method for preparing a silicate composite material includes the following steps: (1) Surface modification of hydroxyapatite: Hydroxyapatite was mixed with hydrochloric acid with a molar concentration of 0.4 mol / L for 40 min and washed with water until the pH value was 7 to obtain activated hydroxyapatite. The weight-to-volume ratio of hydroxyapatite to acid is 1.5 g / 30 mL; Activated hydroxyapatite was dispersed in the first mixed solvent, and then silane coupling agent (KH550) was added. The pH value was adjusted to 5 with hydrochloric acid with a molar concentration of 0.4 mol / L. The mixture was stirred at 30°C for 60 min to obtain a hydroxyapatite suspension. The weight ratio of activated hydroxyapatite to silane coupling agent is 1:2, and the weight-volume ratio of the sum of the weights of activated hydroxyapatite and silane coupling agent to the first mixed solvent is 5 g / 100 mL. The first mixed solvent is prepared by mixing ethanol and deionized water in a volume ratio of 1:1.

[0051] (2) Depolymerization of water glass: High modulus water glass is diluted with deionized water to a SiO2 concentration of 0.3 mol / L, and the high modulus water glass is hydrolyzed and depolymerized to generate active silica sol.

[0052] (3) Preparation of reaction precursor: Add hydroxyapatite suspension to the second mixed solvent and stir for 10 min. Then add active silica sol and stir for 10 min to obtain a mixed solution. Add lime milk slowly to the mixed solution at a rate of 1.2 mL / min. After the addition is completed, stir for 30 min to obtain the reaction precursor. The molar ratio of active silica sol to lime milk is Ca / Si = 1.2; the weight ratio of the sum of the active silica sol and lime milk to the hydroxyapatite suspension is 1:3; the weight-volume ratio of the sum of the hydroxyapatite suspension, active silica sol, and lime milk to the second mixed solvent is 20 g / 100 mL; and the second mixed solvent is prepared by mixing ethylene glycol and deionized water in a volume ratio of 1:2.

[0053] (4) Preparation of calcium silicate composite material: The reaction precursor was transferred to a high-pressure reactor for solvothermal reaction to obtain calcium silicate composite material. The solvothermal reaction conditions were: temperature 200℃, reaction time 1h, and heating rate 8℃ / min during the reaction.

[0054] Comparative Example 1 A method for preparing a silicate composite material includes the following steps: The difference from Example 2 is that: (3) Preparation of reaction precursor: The molar ratio of active silica sol to lime milk is Ca / Si=0.9.

[0055] Comparative Example 2 A method for preparing a silicate composite material includes the following steps: The difference from Example 2 is that: (3) Preparation of reaction precursor: The molar ratio of active silica sol to lime milk is Ca / Si=1.3.

[0056] Comparative Example 3 A method for preparing a silicate composite material includes the following steps: The difference from Example 2 is that: (4) Preparation of calcium silicate composite material: The conditions for the solvothermal reaction are: temperature 158℃, reaction time 4h.

[0057] Comparative Example 4 A method for preparing a silicate composite material includes the following steps: The difference from Example 2 is that: (4) Preparation of calcium silicate composite material: The conditions for the solvothermal reaction are: temperature 182℃, reaction time 4h.

[0058] Experimental Example 1 Paper performance testing Using the silicate composite materials provided in Examples 1-3 and Comparative Examples 1-4 as samples, paper was made from each sample, and the performance of the resulting paper was tested according to the provisions of GB / T20810-2018. Each test group had 3 replicates, and the average value was taken. The results are shown in Table 1.

[0059] The papermaking process is as follows: 1) After pulping the chemical softwood pulp and the chemical hardwood pulp separately, dilute them with water to a pulp concentration of 10-12%. Then, mix the chemical softwood pulp and the chemical hardwood pulp at a mass ratio of 1:4 and refine them. After refining, dilute the refined pulp with water to obtain a diluted pulp with a freeness of 30°SR. 2) Add 30wt% paper filler to the diluted pulp and mix thoroughly to form paper pulp. Add the additives to the paper pulp and mix for 20-40 seconds. Then, form the paper on a wire and produce a paper with a basis weight of 70g / m³. 2 The paper was produced using the following methods. In the papermaking fillers described above, the mass ratio of the test sample to talc was 2:1. Additives included 3 wt% of sizing agent AKD stock solution and 0.003 wt% of retention aid cationic polyacrylamide.

[0060] Table 1

[0061] As shown in Table 1, the calcium silicate composite material provided in this application has an excellent effect on improving paper performance as a papermaking filler. After coating hydroxyapatite with a water glass-lime slurry system, it can be better dispersed among pulp fibers, forming hydrogen bonds or chemical bonds with the fibers, significantly improving the tensile strength of the paper. Simultaneously, the calcium silicate composite material provided in this application has a high specific surface area and porosity, which can further enhance the bonding strength between the calcium silicate composite material and the fibers, thus improving the tensile strength of the paper and giving it a suitable bulk. Furthermore, the surface charge of the coated calcium silicate composite material is more compatible with the fibers, making it easier to adsorb onto the fibers, which is beneficial for improving retention rate, increasing raw material utilization, reducing raw material waste, and lowering enterprise costs.

[0062] Experiment Example 2 Using the calcium silicate composite materials provided in Example 2 and Comparative Examples 1-4 as samples, paper was produced in the same manner as in Experiment 1, and the resulting paper was tested for moisture resistance. The results are shown in Table 2. Each test group had three replicates, and the average value was taken.

[0063] Test method: After placing the paper in a high temperature and high humidity environment (40℃, 90%RH) for 24 hours, remove it and test the tensile strength and mass gain rate of the paper. Mass gain rate = m(后) -m (前) / m (前) .

[0064] Table 2

[0065] Moisture resistance tests on paper using calcium silicate composite material as filler revealed that in Examples 1-3, when the paper was placed in a high-temperature and high-humidity environment for an extended period, the tensile strength of the paper only decreased slightly and still maintained good tensile strength. Simultaneously, the volumetric growth rate of the paper was much smaller compared to Comparative Examples 1-4. This indicates that the calcium silicate composite material provided in this application, as a papermaking filler, can significantly improve the moisture resistance of paper. This facilitates the storage of paper in humid environments, reduces the stringent environmental requirements for paper storage, and allows the paper to be used in a wider range of environments, improving paper utilization and increasing the economic benefits for manufacturing enterprises. This performance is attributed to the coating of nano-hydroxyapatite with calcium silicate through a solvothermal reaction, which allows the silicate ions (SiO3) to form a coating. 2- ) and calcium ions (Ca 2+ A CaSiO3 shell is directionally generated on the surface of hydroxyapatite. This core-shell structure prevents the hydrophilic groups on the surface of hydroxyapatite from being exposed and interacting with the fibers and external water molecules. When the hydrophilic groups on the surface of the calcium silicate composite material are mixed with the fibers, they form hydrogen bonds or chemical bonds, which greatly reduces the binding between the paper structure and water molecules in the environment, giving the paper better moisture-proof performance.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a silicate composite material, characterized in that, Includes the following steps: (1) Surface modification of hydroxyapatite: Hydroxyapatite is stirred and mixed with acid for 20-40 min, and washed with water until neutral to obtain activated hydroxyapatite; The activated hydroxyapatite is dispersed in a first mixed solvent, then a silane coupling agent is added, the pH is adjusted to 4-5 with acid, and the mixture is stirred at 20-30°C for 30-60 minutes to obtain a hydroxyapatite suspension. (2) Depolymerization of water glass: Dilute high modulus water glass with deionized water to a SiO2 concentration of 0.1-0.3 mol / L, and hydrolyze and depolymerize the high modulus water glass to generate active silica sol; (3) Preparation of reaction precursor: The hydroxyapatite suspension is added to the second mixed solvent and stirred for 5-10 min. Then the active silica sol is added and stirred for 5-10 min to obtain a mixed solution. Lime milk is slowly added dropwise to the mixed solution. After the addition is completed, the mixture is stirred for 10-30 min to obtain the reaction precursor. (4) Preparation of silicate composite material: The reaction precursor is transferred into a high-pressure reactor for solvothermal reaction to obtain the silicate composite material.

2. The method for preparing the silicate composite material according to claim 1, characterized in that, In the preparation of activated hydroxyapatite, the acid used is hydrochloric acid or nitric acid with a molar concentration of 0.2-0.4 mol / L, and the weight-to-volume ratio of hydroxyapatite to acid is 1-1.5 g / 30 mL.

3. The method for preparing the silicate composite material according to claim 1, characterized in that, In the preparation of the hydroxyapatite suspension, the weight ratio of the activated hydroxyapatite to the silane coupling agent is 1:1-2, and the weight-volume ratio of the sum of the weights of the activated hydroxyapatite and the silane coupling agent to the weight of the first mixed solvent is 1-5 g / 100 mL. The acid used is hydrochloric acid or nitric acid with a molar concentration of 0.2-0.4 mol / L.

4. The method for preparing the silicate composite material according to claim 1, characterized in that, In the preparation of the reaction precursor, the molar ratio of the active silica sol to the lime slurry is Ca / Si = 1.0-1.

2. The weight ratio of the sum of the active silica sol and the lime milk to the weight of the hydroxyapatite suspension is 1:1-3.

5. The method for preparing the silicate composite material according to claim 1, characterized in that, During the preparation of the reaction precursor, the lime slurry is added dropwise to the second mixed solvent at a rate of 0.8-1.2 mL / min; The weight-to-volume ratio of the sum of the weights of the hydroxyapatite suspension, the active silica sol, and the lime slurry to the weight of the second mixed solvent is 10-20 g / 100 mL.

6. The method for preparing the silicate composite material according to claim 1, characterized in that, The first mixed solvent is prepared by mixing ethanol and deionized water in a volume ratio of 1:1, and the second mixed solvent is prepared by mixing ethylene glycol and deionized water in a volume ratio of 1:

2.

7. The method for preparing the silicate composite material according to claim 1, characterized in that, In the preparation of the reaction precursor, after the lime slurry is added dropwise, the mixture is stirred at a temperature of 60-80℃ for 2-5 hours to obtain the reaction precursor.

8. The method for preparing the silicate composite material according to claim 1, characterized in that, The conditions for the solvothermal reaction are: temperature 160-200℃, reaction time 1-4h, and heating rate 5-8℃ / min during the reaction.

9. A silicate composite material, characterized in that, The silicate composite material was prepared by the method described in any one of claims 1-8.

10. The application of a silicate composite material as described in claim 9 above in the papermaking field.

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