Composite gel matrix of high-porosity material and preparation method thereof

Abstract

The present invention discloses a method for preparing a composite gel matrix of a high-porosity material, wherein the composite gel matrix is composed of water, a water-soluble alkali-resistant high molecular polymer, sodium alginate, dicalcium silicate, tricalcium silicate, microsilica, a soluble silicate, a soluble organic acid calcium salt, and polyvinyl alcohol fiber in a specific proportion. By constructing an "egg-box" structure composite hydrogel of "high molecular polymer-sodium alginate-organic acid calcium salt", combining it with a sol mixing process, and drying and forming it at room temperature or under heating conditions, a porous material with a porosity greater than 70% and an extremely low density is obtained. When preparing high-porosity materials using this gel matrix, no freeze-drying technology is required, the process is simple, the cost is low, and it is suitable for use in the fields of ultra-light materials, thermal insulation, catalyst carriers, and bio-scaffolds.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of micro-nano materials, and particularly relates to a composite gel matrix of a high-porosity material and a preparation method thereof. Background Art

[0002] Ultra-high-porosity materials have a porosity greater than 70%, combining extremely high porosity with exceptionally low density. Due to their unique structure and properties, ultra-high-porosity materials have broad applications and play a vital role in a wide range of fields, including thermal insulation and heat preservation, adsorption and separation, energy storage and conversion, biomedicine, environmental protection, acoustics and vibration control, electronics and optoelectronics, aerospace, and defense. With the continuous advancement of technology and the deepening of its application, ultra-high-porosity materials will play a vital role in even more areas, driving the development and progress of related industries.

[0003] The preparation of ultra-high porosity materials usually involves complex processes, such as the sol-gel method, supercritical drying, and template methods, which have extremely high requirements for equipment, environment, and technology. For example, processes such as supercritical drying require high temperature and high pressure conditions, high energy consumption, and increased production costs; industrial production requires special equipment, and the initial investment cost is high; laboratory-scale production processes are difficult to directly scale up to industrial production. Ultra-high porosity silicates are usually prepared through foaming agents or freeze-drying processes, which have problems such as complex processes, high energy consumption, and high costs. In the existing technology, although the hydrogel template method can improve the porosity, it relies on freeze-drying technology to remove moisture, which limits its industrial application. In addition, existing materials still have shortcomings in mechanical strength, alkali resistance, and environmental friendliness. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite gel matrix of high-porosity material. The material prepared from the gel matrix has high porosity and low density, does not require freeze-drying, and can effectively solve the problem of complex preparation process of traditional high-porosity materials.

[0005] To achieve the above object, the present invention provides a method for preparing a composite gel matrix of a high-porosity material, comprising the following steps:

[0006] S1. After dissolving a water-soluble alkali-resistant polymer and sodium alginate in water, the solution is dropped into a soluble organic acid calcium salt aqueous solution for cross-linking to obtain a composite hydrogel;

[0007] S2. Grinding the composite hydrogel obtained in S1 into a granular sol;

[0008] S3 S2 obtained sol was divided into two parts, one part and dicalcium silicate, tricalcium silicate mixed, the sol secondary cross-linking to form a high fluidity gel to prepare component A; while the other part and the soluble silicate, microsilica powder, polymer fiber mixed to prepare component B;

[0009] S4. Components A and B in S3 are mixed to form a composite gel, which is cast or sprayed into a desired shape, and allowed to stand and solidify to obtain a composite gel matrix of the high-porosity material.

[0010] Furthermore, in the preparation method of the composite gel matrix of the high-porosity material, the mass ratio of water, water-soluble alkali-resistant polymer, sodium alginate, dicalcium silicate, tricalcium silicate, microsilica powder, soluble silicate, soluble organic acid calcium salt, and polyvinyl alcohol fiber is 0.6~0.85: 0.025~0.035: 0.005~0.015: 0.06~0.1: 0.03~0.05: 0.01~0.05: 0.03~0.05: 0.02~0.04: 0.01~0.03.

[0011] Furthermore, in step S1, the water-soluble alkali-resistant polymer is one or more of polyvinyl alcohol, polyacrylamide, and polyethylene glycol, and the added amount of the water-soluble alkali-resistant polymer is 2 to 3 times the mass of sodium alginate.

[0012] Furthermore, the soluble organic acid calcium salt is one or more of calcium acetate, calcium citrate, calcium formate, calcium gluconate, and calcium lactate, and the concentration of the organic acid calcium salt aqueous solution is 5% to 20% w / w.

[0013] Furthermore, the particle size of the sol in S2 is not greater than 100 nm.

[0014] Furthermore, the soluble silicate is one or more of sodium silicate, potassium silicate, lithium silicate or ammonium silicate.

[0015] Furthermore, the high molecular polymer fiber does not react with soluble silicate, including polyvinyl alcohol fiber.

[0016] Furthermore, the amount of the high molecular weight polymer fiber added in S3 is 30-60% of the mass of the silicate, and the amount of tricalcium silicate added is 50% of the mass of the dicalcium silicate.

[0017] A composite gel matrix of a high-porosity material is prepared by the method for preparing a composite gel matrix of a high-porosity material. The gel contains sol microparticles, polymer fibers and hydrated calcium silicate crystals. The hydrated calcium silicate crystals form a three-dimensional network-like spatial skeleton between the sol microparticles and the polymer fibers. The sol microparticles are an interpenetrating network structure formed by calcium alginate and a water-soluble alkali-resistant polymer. The water content of the composite gel matrix is not less than 60%, and the compressive strength ranges from 0.1 to 10 MPa.

[0018] The composite gel is suitable for the fields of building thermal insulation materials, industrial equipment thermal insulation coatings, solid water storage and heat storage, or agricultural water retention materials.

[0019] Beneficial effects:

[0020] The composite gel matrix prepared by the present invention has a porosity greater than 70% after air-drying or oven-drying at normal pressure and a density as low as 0.1-0.5 g / cm³. The preparation process does not require freeze-drying, which reduces energy consumption by more than 50%. The process is simple, no toxic or harmful chemicals are used in the preparation, and the composite gel matrix has excellent biocompatibility. It can be effectively applied in the fields of ultra-light structures, thermal insulation, catalyst carriers, and biological scaffolds. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the SEM micrograph of the composite gel;

[0022] Figure 2 This is a picture of sol microparticles observed under an optical microscope. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to examples, but the scope of protection is not limited thereto.

[0024] The present invention forms an "egg-box" structure composite hydrogel by combining a water-soluble alkali-resistant high molecular polymer with sodium alginate, and combines the calcium silicate hydration reaction and fiber reinforcement to construct a composite gel matrix of an ultra-high porosity material.

[0025] A method for preparing a composite gel matrix of a high-porosity material comprises the following steps:

[0026] S1. After dissolving a water-soluble alkali-resistant polymer and sodium alginate in water, the solution is dropped into a soluble organic acid calcium salt aqueous solution for cross-linking to obtain a hydrogel with "egg-box" characteristics;

[0027] The water-soluble alkali-resistant high molecular polymer is polyvinyl alcohol (PVA), polyacrylamide (PAM) or polyethylene glycol (PEG), the easily soluble organic acid calcium salt is one or more of calcium acetate, calcium citrate, calcium formate, calcium gluconate, and calcium lactate, and the concentration of the organic acid calcium salt aqueous solution is 5% to 20% w / w.

[0028] S2. Grind the hydrogel obtained in S1 into small-particle gel with a particle size of less than 100 nm.

[0029] S3 S2 obtained small particle size gel was divided into two parts, one part was mixed with dicalcium silicate, tricalcium silicate, the sol was secondary cross-linked to form a high fluidity gel to prepare component A; while the other part was mixed with a soluble silicate, microsilica, polyvinyl alcohol fiber to prepare component B;

[0030] The readily soluble silicate is one or more of sodium silicate, potassium silicate, lithium silicate or ammonium silicate;

[0031] S4. Mix components A and B in S3 to form a composite gel, cast or spray the gel into the desired shape, and let it stand and solidify to meet the design requirements to obtain the composite gel matrix of the high-porosity material. Figure 2 shown.

[0032] The composite gel matrix has a moisture content of not less than 60%, a porosity of greater than 70% after air drying or drying at normal pressure, and a density of 0.1 g / cm³ to 0.5 g / cm³.

[0033] Example 1

[0034] Prepare the materials according to the following mass percentages: water 72%, polyvinyl alcohol 3%, sodium alginate 1%, dicalcium silicate 8%, tricalcium silicate 4%, microsilica fume 3%, potassium silicate 4%, calcium citrate 3%, and polyvinyl alcohol fiber 2%.

[0035] A method for preparing a composite gel matrix of a high-porosity material comprises the following steps:

[0036] (1) Water, polyvinyl alcohol, and sodium alginate were mixed and dissolved, and 5% calcium citrate solution was added dropwise to obtain a hydrogel with "egg-box" characteristics;

[0037] (2) After draining off the excess calcium citrate solution, the resulting hydrogel was crushed into a sol with a particle size of 80 nm using a colloid crusher;

[0038] (3) The microparticle sol obtained in step (2) is divided into two parts: component A: 50% sol mixed with dicalcium silicate and tricalcium silicate; component B: 50% sol mixed with potassium silicate, microsilica powder, and polyvinyl alcohol fiber;

[0039] (4) Components A and B were mixed and cast into a cubic shape in a mold. The mold was removed after standing for 2 days. After the gel matrix obtained in this example was naturally air-dried for 20 days, the material had a porosity of 78%, a density of 0.15 g / cm³, and a compressive strength of 0.8 MPa.

[0040] The Na in the G unit of sodium alginate +It can undergo ion exchange with soluble calcium ions in aqueous solution, so that multiple G units and calcium ions are cross-linked to form an "egg-box" model, which can form a cross-linked sodium alginate calcium layer on the outer layer of sodium alginate and a non-cross-linked sodium alginate area on the inside. However, the research results published in "Time dependent gelling properties of cuboidalginate gels made by external gelation method: Effects of alginate-CaCl2solution ratios and pH" show that sodium alginate temporarily forms a gel after mixing with soluble calcium ions, and the gel shrinks as the gelation time increases. In addition, in alkaline media, the carboxyl groups of alginate gel dissociate, and the negatively charged carboxylate ions repel each other, absorbing water to fill the space in the alginate calcium network. Under strong alkaline conditions, sodium ions or potassium ions will replace the calcium ions in the gel, weakening the gel strength. In step (1), polyvinyl alcohol (PVA) resistant to strong alkali is added. PVA can be incorporated into the alginate gel as a matrix. Firstly, PVA and sodium alginate have good mutual solubility. The introduction of sodium alginate into PVA helps to form a tight three-dimensional network interpenetrating structure, thereby improving the mechanical properties and shrinkage resistance of the gel. Secondly, PVA has good hydrophilicity and water retention, and can absorb and retain water, thereby reducing the shrinkage of the gel during the drying process. Thirdly, the hydroxyl groups (-OH) on the PVA molecular chain and the carboxyl groups on the sodium alginate molecular chain can form hydrogen bonds. This hydrogen bonding can stabilize the carboxyl groups and reduce their dissociation. Fourthly, the hydrophilicity of PVA can regulate the moisture environment inside the gel, maintain a relatively stable pH value, thereby reducing the dissociation of the carboxyl groups. The formed sodium alginate-PVA composite glue can maintain good stability and be relatively hard after being mixed with component A and the sodium alginate-PVA composite glue is mixed with calcium silicate. After the sodium alginate-PVA composite adhesive is mixed with the dicalcium silicate, tricalcium silicate and sodium (potassium) silicate system, Figure 1 As shown, a three-dimensional network-like space skeleton (calcium silicate hydrate crystals) can be generated between the gaps of the sol microparticles, thereby increasing the strength of the space skeleton and preventing the gel from shrinking when drying without the need for freezing.

[0041] The potassium silicate and microsilica in component B of step (3) do not react with the polyvinyl alcohol fiber. The polyvinyl alcohol fiber and 50% of the sol act as diluents for the potassium silicate, uniformly dispersing the potassium silicate and microsilica, reducing their local concentrations, and avoiding excessively high local concentrations after the potassium silicate and microsilica are directly added to component A, which would cause the rapid formation of hydrated calcium silicate crystals between the sol microparticles. This prevents local agglomeration, hinders stirring, and hinders the dispersion of potassium silicate, and also prevents uneven pore structure of the gel. The polyvinyl alcohol fiber in component B, when added to component A, can also enhance the strength and crack resistance of the gel.

[0042] In addition, component A is more viscous than component B. It is difficult to stir the polyvinyl alcohol fiber in component A, and the dispersion is uneven. B is thinner and has better fluidity. It is easier to disperse the fiber evenly if it is placed in component B first.

[0043] Example 2

[0044] Formula ratio (mass percentage):

[0045] Water 65%, polyacrylamide 3.5%, sodium alginate 1.5%, dicalcium silicate 10%, tricalcium silicate 5%, microsilica 3%, sodium silicate 5%, calcium acetate 4%, polyvinyl alcohol fiber 3%.

[0046] The preparation method is the same as that of Example 1, the main difference being that polyacrylamide is used instead of polyvinyl alcohol. Polyacrylamide and polyvinyl alcohol have the same function. The preparation method comprises:

[0047] Water, polyvinyl alcohol and sodium alginate were mixed and dissolved, and 5% calcium acetate solution was added to solidify to prepare a composite hydrogel;

[0048] The hydrogel was crushed into a sol with a particle size of 50 nm;

[0049] Prepare component A: Mix 50% sol with dicalcium silicate and tricalcium silicate;

[0050] Prepare component B: mix 50% sol with sodium silicate, microsilica powder, and polyvinyl alcohol fiber;

[0051] Components A and B are mixed and sprayed on the metal surface with a coating thickness of 5mm.

[0052] After the gel matrix obtained in this example was naturally air-dried, the material had a porosity of 70%, a density of 0.21 g / cm³, a compressive strength of 0.91 MPa, and a thermal conductivity of 0.03 W / (m·K).

[0053] In this embodiment, polyacrylamide and sodium alginate can form a double network hydrogel, which combines the advantages of the two polymers. The carboxyl groups in sodium alginate and the Ca² + When a cross-linking reaction occurs to form a calcium alginate cross-linked network, polyacrylamide provides additional mechanical properties through its own polymer network, so that the composite gel has higher mechanical strength and stability.

[0054] Comparative Example 1

[0055] The difference from Example 1 is that the readily soluble silicate (potassium silicate) is replaced by calcium chloride, and polyvinyl alcohol fiber is not added.

[0056] Prepare the materials according to the following mass percentages: water 72%, polyvinyl alcohol 3%, sodium alginate 0.8%, dicalcium silicate 12%, tricalcium silicate 3.2%, microsilica fume 3%, calcium chloride 4%, calcium acetate 2%, and polyvinyl alcohol fiber 0%.

[0057] A method for preparing a high-porosity composite gel comprises the following steps:

[0058] (1) Water, polyvinyl alcohol, and sodium alginate were mixed and dissolved, and 5% calcium acetate solution was added dropwise to obtain a hydrogel with "egg-box" characteristics;

[0059] (2) After draining off the excess calcium acetate solution, the resulting hydrogel was crushed into a sol with a particle size of 80 nm using a colloid mill;

[0060] (3) The microparticle sol obtained from S2 was divided into two parts: component A: 50% sol mixed with dicalcium silicate and tricalcium silicate; component B: 50% sol mixed with calcium chloride and microsilica powder;

[0061] (4) Components A and B were mixed and cast into a cubic shape in a mold. The mold was removed after standing for 2 days. The gel material obtained in this example had a porosity of 61.3%, a density of 0.32 g / cm³, and a compressive strength of 0.12 MPa after natural air drying for 20 days.

[0062] Comparative Example 2

[0063] The difference from Example 1 is that the readily soluble silicate (potassium silicate) is replaced with magnesium phosphate, and all other aspects are the same. The gel material obtained in this Example, after natural air drying for 20 days, has a porosity of 60.2%, a density of 0.44 g / cm³, and a compressive strength of 0.06 MPa.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that the water-soluble alkali-resistant high molecular weight polymer is not added, and the rest is the same. In this example, components A and B are mixed and cast into a cubic block in a mold. After standing for 2 days, the mold is removed and the test block immediately shatters and has almost no compressive strength.

[0066] The above embodiment provides a detailed description of the present invention, but it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-porosity composite gel, characterized in that: The following steps are involved: S1. After dissolving a water-soluble alkali-resistant polymer and sodium alginate in water, the solution is dropped into a soluble organic acid calcium salt aqueous solution for cross-linking to obtain a composite hydrogel; S2. Grinding the composite hydrogel obtained in S1 into a granular sol; S3 S2 obtained sol was divided into two parts, one part and dicalcium silicate, tricalcium silicate mixed, the sol secondary cross-linking to form a high fluidity gel to prepare component A; while the other part and the soluble silicate, microsilica powder, polymer fiber mixed to prepare component B; S4. Components A and B in S3 are mixed to form a composite gel, the composite gel is cast or sprayed to form the desired shape, and the high porosity composite gel is obtained after standing and solidifying; The water-soluble alkali-resistant high molecular polymer is one or more of polyvinyl alcohol, polyacrylamide, and polyethylene glycol; The high molecular polymer fibers do not react with readily soluble silicates and include polyvinyl alcohol fibers; The particle size of the sol in S2 is not greater than 100 nm; The mass ratio of water, water-soluble alkali-resistant high molecular polymer, sodium alginate, dicalcium silicate, tricalcium silicate, microsilica fume, soluble silicate, soluble organic acid calcium salt and polyvinyl alcohol fiber is 0.6~0.85: 0.025~0.035: 0.005~0.015: 0.06~0.1: 0.03~0.05: 0.01~0.05: 0.03~0.05: 0.02~0.04: 0.01~0.

03.

2. The method for preparing a high-porosity composite gel according to claim 1, wherein: In step S1, the amount of the water-soluble alkali-resistant high molecular weight polymer added is 2 to 3 times the mass of the sodium alginate.

3. The method for preparing a high-porosity composite gel according to claim 1, wherein: The soluble organic acid calcium salt is one or more of calcium acetate, calcium citrate, calcium formate, calcium gluconate, and calcium lactate, and the concentration of the organic acid calcium salt aqueous solution is 5% to 20% w / w.

4. The method for preparing a high-porosity composite gel according to claim 1, wherein: The soluble silicate is one or more of sodium silicate, potassium silicate, lithium silicate or ammonium silicate.

5. The method for preparing a high-porosity composite gel according to claim 1, characterized in that: The amount of high molecular weight polymer fiber added in S3 is 30-60% of the mass of silicate, and the amount of tricalcium silicate added is 50% of the mass of dicalcium silicate.

6. A high-porosity composite gel, characterized in that: The composite gel is prepared by the method described in any one of claims 1 to 5, and the composite gel contains sol microparticles, polymer fibers and hydrated calcium silicate crystals. The hydrated calcium silicate crystals form a three-dimensional network-like spatial skeleton between the sol microparticles and the polymer fibers. The sol microparticles are an interpenetrating network structure formed by calcium alginate and a water-soluble alkali-resistant polymer. The water content of the composite gel is not less than 60%, the porosity after normal pressure air drying or baking is greater than 70%, the density is 0.1 g / cm³~0.5 g / cm³, and the compressive strength ranges from 0.1 to 10 MPa.

7. The use of the high-porosity composite gel according to claim 6, characterized in that: The composite gel is suitable for the fields of building thermal insulation materials, industrial equipment thermal insulation coatings, solid water storage and heat storage, or agricultural water retention materials.

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