Non-sintered corundum reinforced geopolymer flat sheet membrane and preparation method thereof

Abstract

The application discloses a non-sintering corundum reinforced geopolymer flat membrane and a preparation method thereof, and comprises 100 parts of aluminosilicate, 80-130 parts of alkaline activator solution, 50-150 parts of corundum powder, 0.3-2.0 parts of plasticizer, 0.5-5.0 parts of organic fiber and 0-40 parts of soluble pore-forming agent. The above components are prepared into the non-sintering corundum reinforced geopolymer flat membrane through the steps of raw material pretreatment and dry mixing, slurry preparation, vacuum degassing, extrusion molding, programmed curing and drying and post-processing. The application realizes the non-sintering preparation of the flat membrane, reduces the production energy consumption and emission, effectively overcomes the defects of large brittleness and easy cracking of the pure geopolymer material in drying, and reduces the warping and cracking of the flat membrane in the drying process through process adjustment, and improves the yield.

Description

Technical Field

[0001] This invention belongs to the field of polymer flat sheet membrane technology, and relates to a non-sintered corundum reinforced geopolymer flat sheet membrane and its preparation method. Background Technology

[0002] Inorganic separation membranes, especially ceramic membranes, possess irreplaceable advantages in separation processes under harsh environments due to their excellent chemical stability, thermal stability, and mechanical strength. However, traditional ceramic membranes generally rely on high-temperature sintering exceeding 1000℃ to achieve densification and high strength, resulting in enormous energy consumption, high carbon emissions, and the products being prone to deformation or cracking due to sintering shrinkage. To reduce energy consumption, researchers have explored low-temperature sintering or binder routes, but these often come at the cost of sacrificing the membrane's chemical resistance or mechanical strength.

[0003] Geopolymers are three-dimensional network inorganic polymers formed from aluminosilicates through a dissolution-condensation reaction at room temperature (or low temperature) in an alkaline environment. Their preparation process has extremely low energy consumption, and the products possess good chemical stability and early strength, providing a new approach for developing non-sintered inorganic membranes. Currently, the technology for extruding geopolymers into building panels is mainly for structural load-bearing and lacks the porous structure required for separation membranes. Other methods, such as foamed geopolymer membranes, while producing porous bodies, often result in blocky or amorphous structures with low strength, failing to meet the stringent requirements of flat-sheet separation membranes for thin layers, large-area flatness, and a specific strength-porosity matching relationship. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a non-sintered corundum-reinforced geopolymer flat sheet film and its preparation method, which effectively solves the problems in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A non-sintered corundum-reinforced geopolymer flat sheet membrane, comprising:

[0007] 100 parts aluminosilicate, 80-130 parts alkaline activator solution, 50-150 parts corundum powder, 0.3-2.0 parts plasticizer, 0.5-5.0 parts organic fiber, and 0-40 parts soluble pore-forming agent.

[0008] Optionally, the corundum powder comprises at least two types of corundum particles.

[0009] Optionally, the aluminosilicate includes one or more of metakaolin, fly ash, and slag.

[0010] Optionally, the alkaline activator solution is a mixture of sodium silicate solution and sodium hydroxide solution.

[0011] Optionally, the organic fiber is a polypropylene fiber or a polyvinyl alcohol fiber with a length of 1-6 mm.

[0012] Optionally, the soluble pore-forming agent includes one or more of starch, sodium chloride, sodium sulfate, or sodium bicarbonate.

[0013] A preparation method, wherein the method is a preparation method of any of the above-mentioned non-sintered corundum reinforced geopolymer flat sheet films, comprising:

[0014] S1. Raw material pretreatment and dry mixing: Dry mix aluminosilicate with corundum powder of different particle sizes, organic fiber and soluble pore-forming agent in a high-speed mixer for 10-20 minutes, and pour the mixed dry material into a kneader.

[0015] S2. Slurry preparation: Premix the alkaline activator solution with the plasticizer, and slowly add it to the kneader while stirring. Continue stirring for 5-15 minutes to form a uniform paste-like slurry that can be extruded.

[0016] S3. Vacuum degassing: Place the slurry obtained in step S2 in a vacuum mixer and degas it for 2-5 minutes under a vacuum of -0.095MPa to -0.1MPa.

[0017] S4. Extrusion molding: The degassed slurry is fed into a twin-screw extruder and extruded through a flat die to obtain a wet flat film preform. The extrusion temperature is controlled at 25-40℃.

[0018] S5. Programmed curing and drying: The wet flat sheet membrane preform obtained in step S4 is placed in a curing box for curing to obtain a non-sintered corundum-reinforced geopolymer flat sheet membrane.

[0019] S6. Post-treatment: Immerse the non-sintered corundum-reinforced geopolymer flat sheet membrane obtained in step S5 into deionized water, change the water every 2 hours until the conductivity of the leachate remains unchanged, and then dry it at 80°C.

[0020] Optionally, step S5 includes:

[0021] S5.1 Closed and constant humidity curing stage: Curing for 12-36 hours under conditions of temperature 25±2℃ and relative humidity ≥95%;

[0022] S5.2 Segmented Controlled Drying Stage: The humidity is gradually reduced from 95% to 50% at a rate of 1-2% per hour, while the temperature is gradually increased from 25℃ to 60℃. This stage lasts for 24-48 hours.

[0023] S5.3 Constant temperature and low humidity stabilization stage: Drying at 60℃ and humidity <30% until the film preform reaches constant weight to obtain a non-sintered corundum reinforced geopolymer flat sheet film.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. By utilizing the low-temperature chemical polymerization characteristics of geopolymers, "non-sintering preparation" of flat sheet membranes was achieved, and the highest temperature throughout the preparation process did not exceed 80°C, which reduced energy consumption and carbon emissions in the flat sheet membrane production process and reduced the problem of high-temperature cracking during high-temperature production.

[0026] 2. Using graded corundum powder as a rigid reinforcing skeleton, it is combined with a geopolymer gel matrix at room temperature to construct a "rigid skeleton-gel binder phase" composite structure, which effectively overcomes the shortcomings of pure geopolymer materials such as high brittleness and easy cracking when drying. This structure, combined with soluble pore-forming agents, achieves high mechanical strength and controllable porous characteristics of non-sintered corundum-reinforced geopolymer flat sheet film.

[0027] 3. By using the process of "extrusion molding + programmed temperature and humidity control curing", the uniformity and flatness of the preform are ensured. At the same time, the phased curing strategy of "first high humidity curing to promote polymerization, then slow dehumidification to control drying" is used to match the chemical shrinkage and physical shrinkage of the prepared material, thereby reducing the warping and cracking of the flat film during the drying process and improving the yield.

[0028] 4. By adjusting the gradation of corundum powder and the content of soluble pore-forming agent, the bending strength and average pore size of the membrane product can be synergistically controlled within the same non-sintering process system, so that the flat sheet membrane has both mechanical properties close to those of sintered ceramics and adjustable separation precision. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention discloses a non-sintered corundum-reinforced geopolymer flat sheet membrane, comprising 100 parts of aluminosilicate, 80-130 parts of alkaline activator solution, 50-150 parts of corundum powder, 0.3-2.0 parts of plasticizer, 0.5-5.0 parts of organic fiber, and 0-40 parts of soluble pore-forming agent, wherein the parts are by mass ratio.

[0031] In some feasible methods, aluminosilicates include one or more of metakaolin, fly ash, and slag. The alkaline activator solution is a mixture of sodium silicate and sodium hydroxide solutions, with the sodium silicate solution having a modulus of 1.2-2.0. The organic fibers are 1-6 mm long polypropylene or polyvinyl alcohol fibers, used to suppress plastic cracking of the extruded preform during the initial drying stage. Soluble pore-forming agents include one or more of starch, sodium chloride, sodium sulfate, or sodium bicarbonate, used to form through-pores or semi-through-pores within the membrane.

[0032] To improve the structural strength of non-sintered corundum-reinforced geopolymer flat sheet membranes, the corundum powder comprises at least two types of corundum particles, and the particle gradation is set to facilitate close packing and construct a high-strength flat sheet membrane support framework. For example, the corundum particle gradation can be set as 10% d10, 40% d50, and 50% d90, wherein the d10 particle size is 1-10 μm, the d50 particle size is 10-50 μm, and the d90 particle size is 50-150 μm.

[0033] In some feasible ways, the corundum particles are α-Al2O3.

[0034] To facilitate the preparation of the non-sintered corundum-reinforced geopolymer flat sheet film of this application, this application also discloses a preparation method, including:

[0035] S1. Raw material pretreatment and dry mixing: Dry mix aluminosilicate with corundum powder of different particle sizes, organic fiber and soluble pore-forming agent in a high-speed mixer for 10-20 minutes, and pour the mixed dry material into a kneader.

[0036] S2. Slurry preparation: Premix the alkaline activator solution with the plasticizer, and slowly add it to the kneader while stirring. Continue stirring for 5-15 minutes to form a uniform paste-like slurry that can be extruded.

[0037] S3. Vacuum degassing: Place the slurry obtained in step S2 in a vacuum mixer and degas it for 2-5 minutes under a vacuum of -0.095MPa to -0.1MPa.

[0038] S4. Extrusion molding: The degassed slurry is fed into a twin-screw extruder and extruded through a flat die to obtain a wet flat film preform. The extrusion temperature is controlled at 25-40℃.

[0039] S5. Programmed curing and drying: The wet flat sheet membrane preform obtained in step S4 is placed in a curing box for curing to obtain a non-sintered corundum-reinforced geopolymer flat sheet membrane.

[0040] S6. Post-treatment: Immerse the non-sintered corundum-reinforced geopolymer flat sheet membrane obtained in step S5 into deionized water, change the water every 2 hours until the conductivity of the leachate remains unchanged, and then dry it at 80°C.

[0041] Specifically, step S5 includes:

[0042] S5.1 Closed and constant humidity curing stage: Curing for 12-36 hours under conditions of temperature 25±2℃ and relative humidity ≥95%;

[0043] S5.2 Segmented Controlled Drying Stage: The humidity is gradually reduced from 95% to 50% at a rate of 1-2% per hour, while the temperature is gradually increased from 25℃ to 60℃. This stage lasts for 24-48 hours.

[0044] S5.3 Constant temperature and low humidity stabilization stage: Drying at 60℃ and humidity <30% until the film preform reaches constant weight to obtain a non-sintered corundum reinforced geopolymer flat sheet film.

[0045] Specifically, corundum powder with different particle size distributions is used as a rigid framework and composited with a geopolymer gel matrix (a mixture of sodium silicate solution and sodium hydroxide solution) at room temperature. The corundum framework provides the main mechanical support, effectively overcoming the shortcomings of pure geopolymer materials, such as high brittleness and easy cracking when drying. The geopolymer matrix acts as a binder phase, encapsulating and solidifying the framework particles to form a stable whole. The synergy between the two enables the flexural strength of the non-sintered film to reach 15-40 MPa, achieving the level of low-temperature sintered ceramic films. At the same time, the high-temperature sintering step of traditional ceramic films is eliminated, and the highest temperature in the entire preparation process does not exceed 80℃, greatly reducing energy consumption in the production process.

[0046] The preparation process employs extrusion molding combined with temperature and humidity controlled curing. The extrusion process ensures the large-area flatness and uniform thickness of the flat sheet membrane. The phased curing strategy of high-humidity polymerization followed by slow dehumidification matches the chemical reaction shrinkage and physical drying shrinkage processes of the geopolymer, suppressing the warping and cracking problems of the flat sheet membrane during the drying process and significantly improving the yield. Simultaneously, by adjusting the gradation of the corundum skeleton and the type and amount of pore-forming agent, the pore structure of the flat sheet membrane can be finely controlled within a certain range, such as an average pore size of 0.1-10 μm, thus adapting to different separation precision requirements such as microfiltration and ultrafiltration. Furthermore, the flat sheet membrane itself exhibits excellent resistance to acids, alkalis, and organic solvents.

[0047] Experimental example:

[0048] To facilitate the verification of this application, two experimental examples and a comparative example were set up for experimentation. The experimental ratios are shown in Table S1:

[0049]

[0050] The preparation steps for Example 1 are as follows:

[0051] S1. Dry mix aluminosilicate, corundum powder and organic fiber for 15 minutes and then pour into a kneader.

[0052] S2. Mix the plasticizer and alkaline activator solution, and slowly add it to the kneader while stirring. Stir for 10 minutes to form a paste-like slurry.

[0053] S3. Degas the paste obtained in S2 under vacuum for 3 minutes, at a pressure of -0.098 MPa to -0.08 MPa;

[0054] S4. The degassed slurry is fed into a twin-screw extruder and extruded through a flat die to obtain a wet flat film preform. The extrusion temperature is controlled at 30℃.

[0055] S5. Place the wet-process flat sheet film preform in a curing chamber for curing: first, cure at 25℃ and 98% humidity for 24 hours, then gradually adjust the humidity to 50% by decreasing it by 1% per hour and gradually adjust the temperature to 60℃ by increasing it by 0.78℃ per hour over 48 hours, and finally adjust it to 60℃ and 25% humidity and dry it to constant weight.

[0056] Steps S1-S5 of Example 2 and the comparative example are the same as those of Example 1, except that step S6 is added in Example 2:

[0057] S6. Immerse the dried membrane in flowing deionized water for 24 hours to dissolve sodium chloride, and then dry it at 80°C.

[0058] The flat sheet membrane obtained in Example 1 had a thickness of 5.5 mm and a smooth, crack-free surface. Testing showed that its average pore size was 0.8 μm and its pure water flux was 800 L / (m²). 2 The average flexural strength was 28 MPa (·h·bar). The average pore size of the flat sheet membrane obtained in Example 2 increased to 5.2 μm, and the pure water flux reached 2500 L / (m²). 2 The slurry has an average flexural strength of 18 MPa (·h·bar), making it suitable for high-flow-rate microfiltration processes. However, in the comparative extrusion molding process, the slurry exhibits poor fluidity, a rough surface, and noticeable network cracks appear in the later stages of drying, resulting in a yield rate of less than 50% and an average flexural strength of only 9 MPa.

[0059] To facilitate the investigation of the impact of the curing method, a comparative example 2 was set up, using the formulation and process of example 1, but with the curing step S5 adjusted to direct placement in a 60°C oven for rapid drying. Severe curling and cracking occurred in the early stages of drying, making it impossible to obtain a complete flat film.

[0060] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A non-sintered corundum-reinforced geopolymer flat sheet membrane, characterized in that, include: 100 parts aluminosilicate, 80-130 parts alkaline activator solution, 50-150 parts corundum powder, 0.3-2.0 parts plasticizer, 0.5-5.0 parts organic fiber, and 0-40 parts soluble pore-forming agent.

2. The non-sintered corundum-reinforced geopolymer flat sheet membrane according to claim 1, characterized in that: The corundum powder comprises at least two types of corundum particles.

3. The non-sintered corundum-reinforced geopolymer flat sheet membrane according to claim 1, characterized in that: The aluminosilicate includes one or more of metakaolin, fly ash, and slag.

4. The non-sintered corundum-reinforced geopolymer flat sheet membrane according to claim 1, characterized in that: The alkaline activator solution is a mixture of sodium silicate solution and sodium hydroxide solution.

5. The non-sintered corundum-reinforced geopolymer flat sheet membrane according to claim 1, characterized in that: The organic fiber is a polypropylene fiber or a polyvinyl alcohol fiber with a length of 1-6 mm.

6. The non-sintered corundum-reinforced geopolymer flat sheet membrane according to claim 1, characterized in that: The soluble pore-forming agent includes one or more of starch, sodium chloride, sodium sulfate, or sodium bicarbonate.

7. A preparation method, wherein the method is the preparation method of the non-sintered corundum-reinforced geopolymer flat sheet film according to any one of claims 1-6, characterized in that, include: S1. Raw material pretreatment and dry mixing: Dry mix aluminosilicate with corundum powder of different particle sizes, organic fiber and soluble pore-forming agent in a high-speed mixer for 10-20 minutes, and pour the mixed dry material into a kneader. S2. Slurry preparation: Premix the alkaline activator solution with the plasticizer, and slowly add it to the kneader while stirring. Continue stirring for 5-15 minutes to form a uniform paste-like slurry that can be extruded. S3. Vacuum degassing: Place the slurry obtained in step S2 in a vacuum mixer and degas it for 2-5 minutes under a vacuum of -0.095MPa to -0.1MPa. S4. Extrusion molding: The degassed slurry is fed into a twin-screw extruder and extruded through a flat die to obtain a wet flat film preform. The extrusion temperature is controlled at 25-40℃. S5. Programmed curing and drying: The wet flat sheet membrane preform obtained in step S4 is placed in a curing box for curing to obtain a non-sintered corundum-reinforced geopolymer flat sheet membrane. S6. Post-treatment: Immerse the non-sintered corundum-reinforced geopolymer flat sheet membrane obtained in step S5 into deionized water, change the water every 2 hours until the conductivity of the leachate remains unchanged, and then dry it at 80°C.

8. The preparation method according to claim 7, characterized in that, Step S5 includes: S5.1 Closed and constant humidity curing stage: Curing for 12-36 hours under conditions of temperature 25±2℃ and relative humidity ≥95%; S5.2 Segmented Controlled Drying Stage: The humidity is gradually reduced from 95% to 50% at a rate of 1-2% per hour, while the temperature is gradually increased from 25℃ to 60℃. This stage lasts for 24-48 hours. S5.3 Constant temperature and low humidity stabilization stage: Drying at 60℃ and humidity <30% until the film preform reaches constant weight to obtain a non-sintered corundum reinforced geopolymer flat sheet film.

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