Dispersion method and application of basalt chopped fiber for reinforcing calcium silicate board

Abstract

The invention belongs to the technical field of calcium silicate boards, and discloses a dispersion method and application of basalt chopped fibers for reinforcing a calcium silicate board. The dispersion method comprises the following steps: mixing basalt chopped fibers with an aqueous solution of hypohalite, stirring and dispersing, and washing with water to obtain unbundled basalt fibers; the preparation method comprises the following steps: dissolving phosphate in water, then adding microcrystalline cellulose, uniformly dispersing, finally adding unbundled basalt fibers, and dispersing by using a high-speed dispersion machine to obtain the basalt fiber dispersion liquid. According to the preparation method, a synergistic effect mechanism of electrostatic repulsion, steric hindrance and network isolation is adopted, so that the dispersion stability of basalt fibers in smaller single-strand and monofilament states can be remarkably improved, and the reinforcing effect of the basalt fibers on a calcium silicate board can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of calcium silicate board technology, and specifically relates to a method for dispersing basalt short-cut fibers for reinforcing calcium silicate boards and its application. Background Technology

[0002] Currently, widely used calcium silicate boards primarily use siliceous and calcareous materials as cementing agents, supplemented with plant fibers as reinforcing materials, and are manufactured through multiple processes in specific proportions. They represent a new generation of green and environmentally friendly building materials. Their strength performance depends not only on the properties of the cementing materials but also on the fiber materials used as reinforcement. However, because calcium silicate boards require prolonged steam curing in a high-temperature, high-alkaline environment, the plant fibers inevitably undergo peeling reactions or intermolecular breakage, leading to a decrease in the degree of polymerization of the plant fibers. Macroscopically, this manifests as irreversible damage to the strength and toughness of the board. Given this situation, there is an urgent need to develop a high-strength reinforcing fiber that does not degrade or break in a high-temperature, high-alkaline steam curing environment to replace or partially replace plant fibers.

[0003] Basalt fiber is a continuous fiber produced by rapidly drawing basalt rock at high speed through a spinneret after it has melted at 1450℃-1500℃. Basalt fiber exhibits excellent mechanical properties, with a tensile strength of 3000-4800 MPa; good temperature resistance, with an operating temperature range of -260℃ to 700℃ (softening point 960℃); and outstanding chemical stability, maintaining high stability in saturated Ca(OH)₂ solutions and alkaline media such as cement. Therefore, basalt fiber is an ideal and superior reinforcing material for calcium silicate boards in terms of technical characteristics, and is one of the important options for promoting the upgrading of the calcium silicate board industry towards higher performance and more environmentally friendly directions.

[0004] In the production of calcium silicate boards, whether using the slurry forming or sheet forming method, high fiber dispersion is required. However, basalt fibers are typically present in short, bundled form in practical applications. If directly added to the calcium silicate board slurry, they will form "cotton-like" agglomerates within the slurry, leading to a series of problems such as web blockage and uneven mechanical strength of the finished board. Furthermore, the bundling effect embeds a large number of fiber filaments, significantly reducing the number of fibers actually in contact with the reinforcing substrate, thus failing to realize the high specific strength characteristics of many fiber filaments. Therefore, before adding basalt fibers to the calcium silicate board slurry, the short basalt fibers should be unbundled and dispersed.

[0005] Regarding methods for dispersing basalt chopped fibers, some researchers have developed specialized methods based on their applications in specific fields. For example, Chinese patent application CN 109486120 A employs a series of physical methods to uniformly disperse basalt chopped fibers in a three-dimensional spatial form within vinyl ester resin, preparing a basalt chopped fiber-reinforced vinyl ester resin composite material. However, this method does not involve the process of dispersing basalt fibers in an aqueous system. Chinese patent application CN 106673474 A uses the synergistic effect of mechanical stirring and ultrasound to initially disperse basalt chopped fibers, followed by the addition of anionic surfactants and composite foaming agents, and is then applied to foamed concrete materials. However, this method generates a large amount of foam, which, if applied to the production process of calcium silicate boards, would make the molding process difficult, increase energy consumption, and even reduce product quality. Summary of the Invention

[0006] To address the problems of insufficient unbundling, clumping, and uneven dispersion of basalt chopped fibers in calcium silicate board slurry, the primary objective of this invention is to provide a method for dispersing basalt chopped fibers used in calcium silicate board reinforcement.

[0007] Another objective of this invention is to provide a basalt fiber dispersion for reinforcing calcium silicate boards prepared by the above method.

[0008] Another object of the present invention is to provide the application of the above-mentioned basalt fiber dispersion for reinforcing calcium silicate boards in the preparation of calcium silicate boards. Adding calcium powder and silica powder to the basalt fiber dispersion of the present invention for mixing and then preparing the board can significantly improve the reinforcing effect of basalt fibers on calcium silicate boards.

[0009] The objective of this invention is achieved through the following solution:

[0010] A method for dispersing basalt short-cut fibers for calcium silicate board reinforcement, comprising the following steps:

[0011] (1) Unbundling: Basalt short-cut fibers are mixed with an aqueous solution of hypohalite, stirred and dispersed, and then washed with water to obtain unbundled basalt fibers;

[0012] (2) Dispersion: First, dissolve the phosphate in water, then add microcrystalline cellulose (MCC) and disperse it evenly, and finally add the unbundled basalt fiber obtained in step (1) and disperse it with a high-speed disperser to obtain a basalt fiber dispersion.

[0013] The basalt short-cut fiber length mentioned in step (1) is 6-12 mm.

[0014] The hypohalate mentioned in step (1) includes at least one of hypochlorite, hypobromite, and hypoiodide; preferably hypochlorite, including but not limited to at least one of calcium hypochlorite, lithium hypochlorite, sodium hypochlorite, and potassium hypochlorite; more preferably sodium hypochlorite.

[0015] The effective halogen content in the aqueous solution of hypohalate mentioned in step (1) is 1%-15%, preferably 5%-10%. The effective halogen content refers to the effective chlorine content, effective bromine content, or effective iodine content. Taking the effective chlorine content of x% as an example, it means that the oxidizing power of 100 grams of hypochlorite aqueous solution is equivalent to the oxidizing power of x grams of chlorine gas.

[0016] The basalt short-cut fibers mentioned in step (1) are mixed with the aqueous solution of hypohalite at a mass ratio of 1:(4~8).

[0017] The stirring and dispersing mentioned in step (1) refers to stirring and dispersing at 50-200 rpm for 30-60 min.

[0018] The water washing mentioned in step (1) refers to washing with water until the washing solution is close to neutral, specifically with a pH of 6.5-7.5.

[0019] The phosphate mentioned in step (2) includes at least one of sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, and sodium polyphosphate, preferably sodium hexametaphosphate.

[0020] The dispersion using a high-speed disperser mentioned in step (2) refers to high-speed dispersion at 1000 rpm-2000 rpm for 20-60 minutes.

[0021] The amounts of phosphate, water, microcrystalline cellulose and unbundled basalt fiber used in step (2) are as follows: the concentration of phosphate in the obtained basalt fiber dispersion is 0.01wt%-0.05wt%, the concentration of microcrystalline cellulose is 0.5wt%-1.5wt%, the concentration of basalt fiber is 2wt%-4wt%, and the remainder is water.

[0022] Preferably, in the basalt fiber dispersion obtained in step (2), the mass ratio of phosphate to microcrystalline cellulose is 0.02:1.

[0023] A basalt fiber dispersion for reinforcing calcium silicate boards prepared by the above method.

[0024] The above-mentioned basalt fiber dispersion for reinforcing calcium silicate boards is used in the preparation of calcium silicate boards.

[0025] A calcium silicate board is prepared by the following method: calcium powder and silica powder are added to the above-mentioned basalt fiber dispersion for reinforcing calcium silicate board, and water is added to dilute it to a solid content of 9 wt%-20 wt%. After stirring and mixing, the board is formed to obtain the calcium silicate board.

[0026] The siliceous powder is at least one of quartz powder, diatomaceous earth, etc.; the calcareous powder is at least one of slaked lime, carbide sludge, cement, etc.

[0027] The preferred mixing time is 400 rpm for 5-10 minutes. After thorough mixing, flocculant can be added to the mixture.

[0028] The oven-dry slurry mass of the basalt fiber dispersion for calcium silicate board reinforcement accounts for 5.5%-8% of the sum of the oven-dry slurry mass of the basalt fiber dispersion for calcium silicate board reinforcement, the mass of calcareous powder, and the mass of siliceous powder.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] This invention employs a synergistic mechanism of "electrostatic repulsion," "steric hindrance," and "network isolation" to significantly improve the dispersion stability of smaller single-strand and monofilament basalt fibers. Specifically, it utilizes a two-component system of phosphate and microcrystalline cellulose, particularly a system of sodium hexametaphosphate and microcrystalline cellulose. Sodium hexametaphosphate, a glassy polyphosphate, is a long-chain inorganic salt composed of helical polymers of many basic structural units. In an aqueous system, it hydrolyzes to form negatively charged long chains. These negatively charged chains adsorb onto the surface of the basalt fibers, giving them a strong negative charge and resolving the repulsion problem between fibers over medium and long distances, preventing them from approaching each other. Microcrystalline cellulose disperses in water, forming a three-dimensional, loose network structure. When basalt fibers are added to this system, the numerous cellulose microfibers released by the microcrystalline cellulose interweave between the basalt fibers, forming a physical barrier that prevents direct contact and entanglement of the basalt fibers, thus providing steric stabilization. The advantages of this combination are:

[0031] (1) More stable effect: The single electrostatic stabilization mechanism is more sensitive to pH value and ionic strength, while the combination of the steric hindrance mechanism means that even if the electrostatic repulsion is slightly weakened due to environmental changes, the physical barrier can still play a role, making the dispersion system more stable.

[0032] (2) Effectively prevent “bridging” agglomeration: For basalt fibers with a large aspect ratio, simple electrostatic repulsion is sometimes insufficient to prevent their ends from hooking and entangled with each other. The network formed by microcrystalline cellulose can effectively “isolate” the basalt fibers in the grid and prevent this mechanical agglomeration.

[0033] (3) Applicable to high concentration systems: At high concentrations, fibers are very close to each other, and a single stabilization mechanism may be overwhelmed. The dual protection of "static electricity + space" can better maintain the stability of the system. Attached Figure Description

[0034] Figure 1 The images show the raw material basalt short-cut fibers (a), unbundled basalt fibers (b), the obtained basalt fiber dispersion (c), and the prepared calcium silicate plate sample (d) in Example 1. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0036] The dimensions of the basalt chopped fibers used in the embodiment are: length × width × thickness = 9 mm × 1 mm × 0.1 mm, as shown below. Figure 1 As shown in (a) above. The CAS number of microcrystalline cellulose is 9004-34-6, and the particle size is 20-80 μm.

[0037] Unless otherwise specified, "%" in the embodiments refers to mass percentage.

[0038] Example 1

[0039] (1) Unbundling: Basalt short-cut fibers and sodium hypochlorite solution with an effective chlorine content of 10% were mixed at a mass ratio of 1:5, stirred and dispersed at 100 rpm for 30 min, and then washed with water (pH=7) to obtain unbundled basalt fibers. (See attached diagram) Figure 1 As shown in (b).

[0040] (2) Dispersion: Sodium hexametaphosphate was first dissolved in water, then microcrystalline cellulose was added and allowed to disperse fully. Finally, the unbundled basalt fibers obtained in step (1) were added, and the mixture was dispersed at 1500 rpm for 30 min using a high-speed disperser to obtain a basalt fiber dispersion with a sodium hexametaphosphate concentration of 0.02%, a microcrystalline cellulose concentration of 1%, and a basalt fiber concentration of 3%. A photograph of the basalt fiber dispersion is attached. Figure 1 As shown in (c), visual observation revealed no obvious agglomeration or clumping of the fibers; they were uniformly dispersed, indicating good dispersibility.

[0041] Example 2:

[0042] (1) Unbundling: Same as in Example 1.

[0043] (2) Dispersion: Sodium hexametaphosphate was first dissolved in water, then microcrystalline cellulose was added and allowed to disperse fully. Finally, the unbundled basalt fibers obtained in step (1) were added, and the mixture was dispersed at 1500 rpm for 30 min using a high-speed disperser to obtain a basalt fiber dispersion. Visual observation showed no obvious agglomeration or clumping of the fibers, indicating a uniform dispersion, suggesting good dispersibility. The concentration of sodium hexametaphosphate in the basalt fiber dispersion was 0.01%, the concentration of microcrystalline cellulose was 1.5%, and the concentration of basalt fiber was 3%.

[0044] Example 3:

[0045] (1) Unbundling: Basalt short-cut fibers and sodium hypochlorite solution with an effective chlorine content of 7.5% are mixed at a mass ratio of 1:5, stirred and dispersed at 100 rpm for 45 min, and then washed with water (pH=7) to obtain unbundled basalt fibers.

[0046] (2) Dispersion: Same as in Example 1. Visual observation showed no obvious agglomeration or clumping of the fibers, indicating that they were uniformly dispersed, and it was preliminarily determined that their dispersibility was good.

[0047] Example 4:

[0048] (1) Unbundling: Same as in Example 3.

[0049] (2) Dispersion: Same as in Example 2. Visual observation showed no obvious agglomeration or clumping of the fibers, and they were uniformly dispersed, indicating that their dispersibility was good.

[0050] Example 5:

[0051] (1) Unbundling: Basalt short-cut fibers and sodium hypochlorite solution with an effective chlorine content of 5% are mixed at a mass ratio of 1:5, stirred and dispersed at 100 rpm for 60 min, and then washed with water (pH=7) to obtain unbundled basalt fibers.

[0052] (2) Dispersion: Same as in Example 1. Visual observation showed no obvious agglomeration or clumping of the fibers, indicating that they were uniformly dispersed, and it was preliminarily determined that their dispersibility was good.

[0053] Example 6:

[0054] (1) Unbundling: Same as in Example 5.

[0055] (2) Dispersion: Same as in Example 2. Visual observation showed no obvious agglomeration or clumping of the fibers, and they were uniformly dispersed, indicating that their dispersibility was good.

[0056] Comparative Example 1:

[0057] Basalt chopped fibers were added to water to prepare a 3% concentration, and then dispersed at 1500 rpm for 30 min using a high-speed disperser to obtain a basalt fiber dispersion. Visual observation revealed that the basalt chopped fibers were not fully unbundled and showed clumping, indicating that the fibers were not effectively dispersed.

[0058] Comparative Example 2:

[0059] (1) Unbundling: Basalt short-cut fibers and 10% sodium hydroxide solution are mixed at a mass ratio of 1:5, stirred and dispersed at 100 rpm for 30 min, and then washed with water (pH=7) to obtain unbundled basalt fibers.

[0060] (2) Dispersion: Same as in Example 1. Visual observation showed no obvious agglomeration or clumping of the fibers, indicating that they were uniformly dispersed, and it was preliminarily determined that their dispersibility was good.

[0061] Comparative Example 3:

[0062] (1) Unbundling: Basalt short-cut fibers and 7.5% hydrogen peroxide solution were mixed at a mass ratio of 1:5, stirred and dispersed at 100 rpm for 45 min, and then washed with water (pH=7) to obtain unbundled basalt fibers.

[0063] (2) Dispersion: Same as in Example 1. Visual observation revealed a small amount of clumps in the fibers, indicating that their dispersibility was generally poor.

[0064] Comparative Example 4:

[0065] (1) Unbundling: Same as in Example 1.

[0066] (2) Dispersion: Sodium hexametaphosphate was not added, but the concentration of microcrystalline cellulose in the basalt fiber dispersion was modified to 1.02%, and the other conditions were the same as in Example 1. Visual observation showed that the fibers had very few flocs and were scattered in a sporadic state, which initially determined that their dispersibility was good.

[0067] Comparative Example 5:

[0068] (1) Unbundling: Same as in Example 1.

[0069] (2) Dispersion: No microcrystalline cellulose was added, but the concentration of sodium hexametaphosphate in the basalt fiber dispersion was modified to 1.02%, and the other conditions were the same as in Example 1. Visual observation revealed a large number of flocs in the fibers, indicating that their dispersibility was poor.

[0070] Application Examples:

[0071] Preparation of calcium silicate board: First, according to the ratio of basalt fiber content (i.e., the oven-dry slurry mass of basalt fiber dispersion) to the total mass of raw materials (i.e., the oven-dry slurry mass of basalt fiber dispersion, the total mass of calcium powder and silica powder), calcium powder and silica powder are added to the basalt fiber dispersion, and water is added to dilute it to a solid content of 15wt%. After thorough mixing, the board is made.

[0072] In the application examples, it was ensured that the raw material composition of the calcium silicate board slurry (quartz powder, hydrated lime, P·Ⅱ 52.5R silicate cement, calcium-silicon molar ratio of 0.82), molding process (mixed slurry concentration controlled at 15 wt%, flocculant addition at 10 mg / L, stirring speed of mixed slurry after adding flocculant at 200 rpm for 2 min, filter mesh at 80 mesh), pressing process (12 MPa, holding pressure for 2 min), steam curing process (curing steam temperature 180℃, holding temperature for 10 h), and drying process (105℃ / 4 h) were kept consistent in each example during the preparation of calcium silicate board samples. Subsequently, six 120 mm × 20 mm strips were cut from different parts of the prepared calcium silicate board samples (as shown in the attached figure). Figure 1 (d) is shown.

[0073] Evaluation method for basalt fiber dispersibility: The dispersibility of basalt fibers is indirectly evaluated by testing the flexural strength of calcium silicate boards. Six 120 mm × 20 mm strips were cut from different parts of the prepared calcium silicate board samples (see attached). Figure 1 As shown in (d), the flexural strength of the specimens was determined using a tensile-compression testing machine via a three-point bending test method (test conditions: span 80 mm, loading speed 0.5 mm / min). The dispersibility of basalt fibers was evaluated by comparing the coefficient of variation (CV) of the measured flexural strength data. The coefficient of variation (CV) was calculated using the following formula:

[0074] ;

[0075] In the formula, CV is the coefficient of variation.

[0076] s — Standard deviation of the flexural strength of the spline (MPa);

[0077] — Average flexural strength of the spline (MPa).

[0078] The test method for the average flexural strength (MPa) of the specimens is as described in GB / T 7019-2014 "Test Methods for Fiber Cement Products" regarding the plate test method. If CV < 5%, the data dispersion is small, indicating good fiber dispersion; if 5% ≤ CV ≤ 10%, the data dispersion is moderate, indicating average fiber dispersion; if CV > 10%, the data dispersion is large, indicating poor fiber dispersion. The results are shown in Table 1.

[0079] Table 1. Evaluation results of basalt fiber dispersibility in Examples 1-6 and Comparative Examples 1-5

[0080]

[0081] As shown in Table 1, the calcium silicate board samples prepared in Examples 1-6 all had coefficients of variation (CV) of less than 5% for flexural strength, indicating low data dispersion and good fiber dispersibility. The calcium silicate board sample prepared in Comparative Example 1 had significantly lower flexural strength than Examples 1-6, with a coefficient of variation (CV) much greater than 10%, indicating high data dispersion and poor fiber dispersibility. This suggests that mechanical dispersion alone cannot effectively achieve uniform dispersion of basalt chopped fibers, resulting in insufficient fiber continuity in the matrix and significantly limiting its "skeleton"-like function. The calcium silicate board sample prepared in Comparative Example 2 had a coefficient of variation (CV) of less than 5% for flexural strength, indicating low data dispersion and good fiber dispersibility. However, its flexural strength was slightly lower than that of Examples 1-6, indicating that the basalt fiber surface was slightly damaged due to chemical etching after treatment with inorganic strong alkali solution, leading to a decrease in the sample's flexural strength. The calcium silicate board sample prepared in Comparative Example 3 had a coefficient of variation (CV) of 5% - Within the 10% range, the data dispersion was moderate, indicating average fiber dispersibility. The flexural strength of this sample was lower than that of Examples 1-6 and lower than that of Comparative Example 2. This suggests that the disintegration of the basalt chopped fibers after treatment with hydrogen peroxide solution was insufficient, making it difficult to obtain a uniformly dispersed basalt fiber aqueous solution. It also indicates that the quality of basalt fiber dispersibility has a greater impact on the flexural strength of the calcium silicate board than the slight damage to the basalt fiber surface. The coefficients of variation (CV) of the flexural strength data for the calcium silicate board samples prepared in Comparative Examples 4 and 5 were both greater than those in Example 1, and their flexural strengths were both lower than those in Example 1. This suggests that the simultaneous addition of sodium hexametaphosphate and microcrystalline cellulose can have a synergistic effect.

[0082] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for dispersing basalt short-cut fibers for reinforcing calcium silicate boards, characterized in that... Includes the following steps: (1) Unbundling: Basalt short-cut fibers are mixed with an aqueous solution of hypohalite, stirred and dispersed, and then washed with water to obtain unbundled basalt fibers; (2) Dispersion: First, dissolve the phosphate in water, then add microcrystalline cellulose and disperse it evenly, and finally add the unbundled basalt fiber obtained in step (1) and disperse it with a high-speed disperser to obtain a basalt fiber dispersion.

2. The method for dispersing basalt short-cut fibers for calcium silicate board reinforcement according to claim 1, characterized in that: The basalt short-cut fiber length mentioned in step (1) is 6-12 mm; The hypohalite mentioned in step (1) includes at least one of hypochlorite, hypobromite, and hypoiodite; preferably hypochlorite, including but not limited to at least one of calcium hypochlorite, lithium hypochlorite, sodium hypochlorite, and potassium hypochlorite; more preferably sodium hypochlorite. The phosphate mentioned in step (2) includes at least one of sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, and sodium polyphosphate, preferably sodium hexametaphosphate.

3. The method for dispersing basalt short-cut fibers for calcium silicate board reinforcement according to claim 1, characterized in that: The effective halogen content in the aqueous solution of the hypohalite mentioned in step (1) is 1%-15%, preferably 5%-10%; The basalt short-cut fibers mentioned in step (1) are mixed with the aqueous solution of hypohalite at a mass ratio of 1:(4~8).

4. The method for dispersing basalt short-cut fibers for calcium silicate board reinforcement according to claim 1, characterized in that: The stirring and dispersing mentioned in step (1) refers to stirring and dispersing at 50-200 rpm for 30-60 minutes; The water washing mentioned in step (1) refers to washing with water until the washing solution is neutral.

5. The method for dispersing basalt short-cut fibers for calcium silicate board reinforcement according to claim 1, characterized in that: The amounts of phosphate, water, microcrystalline cellulose and unbundled basalt fiber used in step (2) are as follows: the concentration of phosphate in the obtained basalt fiber dispersion is 0.01wt%-0.05wt%, the concentration of microcrystalline cellulose is 0.5wt%-1.5wt%, the concentration of basalt fiber is 2wt%-4wt%, and the remainder is water.

6. The method for dispersing basalt short-cut fibers for calcium silicate board reinforcement according to claim 5, characterized in that: In the basalt fiber dispersion obtained in step (2), the mass ratio of phosphate to microcrystalline cellulose is 0.02:

1.

7. The method for dispersing basalt short-cut fibers for calcium silicate board reinforcement according to claim 1, characterized in that: The dispersion using a high-speed disperser mentioned in step (2) refers to high-speed dispersion at 1000 rpm-2000 rpm for 20-60 minutes.

8. A basalt fiber dispersion for reinforcing calcium silicate boards prepared by the method according to any one of claims 1-7.

9. The application of the basalt fiber dispersion for reinforcing calcium silicate boards according to claim 8 in the preparation of calcium silicate boards.

10. A calcium silicate board, characterized in that... The calcium silicate board is prepared by adding calcareous powder and silicate powder to the basalt fiber dispersion for reinforcing calcium silicate board as described in claim 8, and diluting it with water to a solid content of 9 wt%-20 wt%. After stirring and mixing, the board is formed to obtain the calcium silicate board.

Images