Preparation method and application of bentonite mineral interpenetrating network gel

Abstract

This invention discloses a preparation method and application of bentonite-based mineral interpenetrating network gel, belonging to the field of collapsible loess improvement technology. The invention prepares a bentonite-based mineral interpenetrating network gel (BT-PAA / PEG / PVA), using bentonite as the crosslinking node, and constructing a triple interpenetrating structure in conjunction with the PAA ionic network, PEG flexible segments, and PVA rigid hydroxyl network. This structure possesses high water absorption, compression resistance, salt tolerance, and long-term stability. When applied to the improvement of collapsible loess, it enables the gel particles to bond with soil particles, forming an "anchoring effect," reducing soil permeability and preventing soil collapse.

Description

Technical Field

[0001] This invention relates to the field of collapsible loess improvement technology, and in particular to a preparation method and application of bentonite mineral interpenetrating network gel. Background Technology

[0002] The collapsibility of loess refers to the weakening of interparticle bonding in loess layers under humid conditions due to water infiltration and adsorption, resulting in significant volume deformation and a decrease in strength. This phenomenon is particularly prominent in the Loess Plateau and its surrounding areas, severely impacting the stability and safety of infrastructure such as buildings, roads, and bridges. Deformation of collapsible soil not only leads to uneven foundation settlement, causing cracks and deformation in buildings, but can also trigger serious engineering accidents. The collapsibility of loess is a complex and challenging engineering problem, and eliminating loess collapsibility is crucial for ensuring the long-term stability and safety of infrastructure.

[0003] In recent years, soil improvement using gel materials has become a research hotspot. Due to their excellent mechanical properties and water absorption, gels have become a key direction for soil improvement. Through scientific improvement methods, the stability of loess can be significantly enhanced, providing reliable foundation support for infrastructure. Currently, methods for improving collapsible loess include dynamic compaction and replacement, the use of resin-based materials or chemical curing agents, and microbial-induced calcium carbonate precipitation reinforcement. However, all of these methods have some problems. For example, dynamic compaction and replacement has limited effectiveness and depth in reinforcing water-sensitive soils (collapsible loess), and cannot completely eliminate soil collapsibility. Resin-based materials (SAP, BT-SAP, etc.) have poor long-term stability and excessive liquid absorption ratio, failing to thoroughly improve the contact state of soil particles and offering limited improvement in soil properties (strength, impermeability, water retention). Chemical curing agents (cement, calcium lignosulfonate, etc.) have a significant impact on plant growth and groundwater, easily leading to soil salinization and cracking during subsequent soil wetting. Microbial-induced calcium carbonate precipitation reinforcement of collapsible loess has high environmental requirements, low reinforcement efficiency, and a long reinforcement cycle.

[0004] To address the aforementioned issues, a collapsible loess amendment based on bentonite mineral interpenetrating network gel is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying bentonite mineral interpenetrating network gels, in order to solve the problems in the background art.

[0006] To achieve the above objectives, the present invention provides a method for preparing a bentonite mineral interpenetrating network gel, comprising the following steps:

[0007] S1. Place powdered sodium bentonite in deionized water and stir magnetically until no visible agglomerates are visible to obtain bentonite dispersion solution A.

[0008] S2. Dissolve acrylic acid monomer in deionized water, and slowly add sodium hydroxide solution dropwise under water bath conditions to neutralize it, adjusting the neutralization degree of the solution to 50-90%. Then add bentonite dispersion solution A and stir magnetically to obtain mixed solution B.

[0009] S3. Under gradient heating conditions, polyethylene glycol and polyvinyl alcohol are added to mixed solution B in stages, and after magnetic stirring until homogeneous, mixed solution C is obtained.

[0010] S4. Dissolve N,N-methylenebisacrylamide in deionized water to obtain a crosslinking agent solution; dissolve potassium persulfate in deionized water to obtain an initiator solution;

[0011] S5. Add the crosslinking agent solution to the mixed solution C, stir magnetically until well mixed, then slowly add the initiator solution, stir magnetically again to obtain the bentonite mineral interpenetrating network gel mixture, then stop stirring and precipitate the bentonite mineral interpenetrating network gel.

[0012] S6. Chop the bentonite mineral interpenetrating network gel into small pieces, soak them in a mixture of water and ethanol to wash away unreacted acrylic monomers, obtain gel fragments, dry them, pulverize and sieve them to obtain powdered bentonite mineral interpenetrating network gel.

[0013] Preferably, in S1, the concentration of bentonite dispersion solution A is 30-60 wt%.

[0014] Preferably, in step S2, the neutralization degree of the solution is adjusted to 60-80%.

[0015] Preferably, in step S2, the amount of deionized water is 1 to 3 times that of the acrylic monomer, the water bath temperature is below 30°C, and the amount of bentonite in the mixed solution B is 10 to 50% of the mass of the acrylic monomer.

[0016] Preferably, the specific steps of S3 are as follows: First, the mixed solution B is slowly heated to 40-60°C, polyethylene glycol is added and magnetically stirred. After stirring evenly, the temperature is raised to 70-80°C, polyvinyl alcohol is added, and after magnetic stirring, mixed solution C is obtained.

[0017] The amount of both polyethylene glycol and polyvinyl alcohol used is 5-25 wt% of acrylic acid monomer, and the molecular weight of polyethylene glycol is 4000-10000.

[0018] Preferably, in S1-S3, the magnetic stirring time is 10-20 min and the stirring speed is 500-800 r / min.

[0019] Preferably, in step S4, the amount of N,N-methylenebisacrylamide is 0.1 to 0.5 wt% of the acrylic acid monomer, and the amount of potassium persulfate is 0.5 to 2.5 wt% of the acrylic acid monomer.

[0020] Preferably, in step S5, the magnetic stirring time after adding the crosslinking agent solution and the initiator solution is both 5 to 10 minutes, and the magnetic stirring speed is 500 to 1000 r / min.

[0021] Preferably, in step S6, the volume ratio of water to ethanol is 1:9, and the soaking time is 10-30 min; the drying process adopts a gradient temperature increase, specifically: drying at 50℃ for 2 h, drying at 60℃ for 4 h, and drying at 80℃ for 12 h.

[0022] The crushing process involves coarse crushing with a jaw crusher to a particle size ≤5mm, followed by fine crushing with a ball mill to a D50 ≤50μm.

[0023] The sieving process involves screening through a 100-mesh sieve.

[0024] The present invention also provides a bentonite mineral interpenetrating network gel, which is prepared by the above preparation method.

[0025] Preferably, the prepared bentonite mineral interpenetrating network gel is used as a modifier in the improvement of collapsible loess. Specifically, the powdered bentonite mineral interpenetrating network gel is incorporated into the loess at a dosage of 0.25 to 1 wt% of the loess.

[0026] Therefore, the preparation method and application of the bentonite mineral interpenetrating network gel of the present invention have the following beneficial effects:

[0027] (1) This invention breaks through the limitations of the traditional bentonite-PAA single network structure. It uses bentonite as the crosslinking node and constructs a triple interpenetrating structure in conjunction with the PAA ionic network, PEG flexible segments and PVA rigid hydroxyl network. By controlling the neutralization degree of acrylic monomer and premixing the bentonite dispersion, a multi-level interpenetrating structure is formed with PAA-bentonite as the main ionic crosslinking network and PEG-PVA as the secondary physical entanglement network. The flexible segments of PEG and the rigid hydroxyl groups of PVA work together to form multiple action sites of hydrogen bonds and van der Waals forces in the bentonite interlayer and polymer interface, forming a physical / chemical crosslinking interpenetrating network, which makes the gel have high water absorption, compression resistance, salt resistance and long-term stability.

[0028] (2) This invention relates to a gradient heating and stepwise crosslinking process. First, PEG is introduced at 40–60°C, utilizing its temperature-sensitive properties to promote molecular chain extension and pre-crosslinking with PAA. Then, PVA is added at 70–80°C, strengthening the interfacial bonding through the intercalation of hydroxyl groups with bentonite sheets. Finally, under the synergistic effect of initiators and crosslinking agents, free radical polymerization and chemical crosslinking reactions are triggered in stages to form a hierarchical three-dimensional network. Through temperature-time coupling control, dynamic matching of bentonite dispersion, polymer intercalation, and crosslinking reactions is achieved, significantly increasing the gel crosslinking density and avoiding phase separation and localized stress concentration.

[0029] (3) This invention uses bentonite mineral interpenetrating network gel as a modifier in the improvement of collapsible loess. The gel absorbs water and expands to fill soil pores, reducing permeability; when dehydrated, the network shrinks to provide support and prevent soil collapse. The gel particles combine with soil particles to form an "anchoring effect," improving shear strength and compressive modulus. Using natural bentonite as the framework reduces the amount of synthetic polymers used, lowering costs; the preparation process uses no toxic solvents, and the product is biodegradable, making it environmentally friendly.

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 This is a SEM image of Embodiment 1 of the present invention;

[0032] Figure 2 This is a SEM image of a comparative example of the present invention;

[0033] Figure 3 These are FTIR analysis graphs of Examples 1-5 and the comparative examples of the present invention;

[0034] Figure 4 The XRD patterns are those of Embodiment 1 and the comparative example of the present invention;

[0035] Figure 5 The graph shows the liquid absorption ratio of the products in Examples 1-5 of this invention. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0038] Example 1

[0039] The preparation of bentonite mineral interpenetrating network gel includes the following steps:

[0040] S1. Add powdered sodium bentonite to deionized water and stir magnetically at 600 r / min for 15 min until no visible agglomerates are found to obtain a 50 wt% bentonite dispersion solution A.

[0041] S2. Dissolve the acrylic monomer in deionized water, add NaOH solution dropwise under a 25°C water bath to neutralize, adjust the neutralization degree of the solution to 70%, then add bentonite dispersion solution A, and magnetically stir at a rate of 600 r / min for 15 min to obtain mixed solution B. In mixed solution B, the mass of acrylic monomer is 20 g, and the amount of bentonite is 20% of the mass of acrylic monomer.

[0042] S3. First, slowly heat the mixed solution B to 50°C, add PEG-4000, and magnetically stir at a rate of 600 r / min for 15 min. The amount of PEG is 30 wt% of the acrylic monomer. Then, heat to 75°C, add PVA, and magnetically stir at a rate of 600 r / min for 15 min. The amount of PVA is 15 wt% of the acrylic monomer, to obtain mixed solution C.

[0043] S4. Dissolve N,N-methylenebisacrylamide in deionized water to obtain a crosslinking agent solution; dissolve potassium persulfate (1 wt% acrylic acid monomer) in deionized water to obtain an initiator solution;

[0044] S5. Add the crosslinking agent solution dropwise to the mixed solution C, and stir magnetically at a rate of 600 r / min for 8 min. The amount of N,N-methylenebisacrylamide is 0.1 wt% of the acrylic monomer. Then slowly add the initiator solution dropwise, and stir magnetically at a rate of 800 r / min for 8 min. The amount of potassium persulfate is 1.5 wt% of the acrylic monomer. After stopping stirring, bentonite mineral interpenetrating network gel precipitates.

[0045] S6. The bentonite mineral interpenetrating network gel was chopped into small pieces and soaked in a mixture of water and ethanol at a volume ratio of 1:9 for 20 minutes to wash away unreacted acrylic monomers, resulting in gel fragments. These fragments were then dried sequentially at 50°C for 2 hours, 60°C for 4 hours, and 80°C for 12 hours until constant weight was achieved. After drying, the fragments were pulverized. First, a jaw crusher was used for coarse crushing to a particle size ≤5mm, and then a ball mill was used for fine crushing to D50 ≤50μm. After passing through a 100-mesh sieve, powdered bentonite mineral interpenetrating network gel was obtained.

[0046] Example 2

[0047] This embodiment follows the same steps as in Example 1, except that the amount of N,N-methylenebisacrylamide is changed to 0.1 wt% of the acrylic monomer.

[0048] Example 3

[0049] This embodiment follows the same steps as in Example 1, except that the amount of N,N-methylenebisacrylamide is changed to 0.2 wt% of the acrylic monomer.

[0050] Example 4

[0051] This embodiment follows the same steps as in Example 1, except that the amount of N,N-methylenebisacrylamide is changed to 0.4 wt% of the acrylic monomer.

[0052] Example 5

[0053] This embodiment follows the same steps as in Example 1, except that the amount of N,N-methylenebisacrylamide is changed to 0.5 wt% of the acrylic monomer.

[0054] Comparative Example 1

[0055] Pure bentonite was used as a comparative example.

[0056] Scanning electron microscopy (SEM) was performed on the bentonite mineral interpenetrating network gel obtained in Example 1 and the bentonite in Comparative Example 1. Figure 1 , Figure 2 As shown, in this embodiment 1, the polymer is intercalated between the bentonite layers, and the excess polymer forms a porous structure on the bentonite surface.

[0057] Infrared spectroscopy analysis was performed on the products from Examples 1-5 above, such as... Figure 3 As shown, Example 1 is denoted as MBA0.3, Example 2 as MBA0.1, Example 3 as MBA0.2, Example 4 as MBA0.4, Example 5 as MBA0.5, and the comparative example as BT. At 3200–4000 cm⁻¹ -1 The wavenumber range is dominated by absorption peaks from the stretching vibrations of hydroxyl (-OH). Pure bentonite (BT) exhibits a broad absorption band in this range originating from its surface and interlayer hydroxyl groups. Upon addition of methylenebisacrylamide (MBA), the absorption peak intensity of the MBA 0.1–MBA 0.5 curve significantly increases, becoming more pronounced with increasing MBA content, and the peak shape also becomes broader. This is because polymers such as polyvinyl alcohol (PVA) and polyethylene glycol (PEG) contain a large number of hydroxyl groups. After intercalation into the bentonite interlayer, the number of hydroxyl groups in the system increases, and they form hydrogen bonds with the bentonite, altering the hydroxyl vibrational environment and strongly suggesting successful polymer intercalation.

[0058] 1720cm -1 The stretching vibration peak of the free carboxyl group (-COOH) of nearby polyacrylic acid appeared in the sample curve with MBA added, but not in the BT curve, proving the introduction of polymers such as polyacrylic acid; 1120 cm⁻¹ -1The position and shape of the stretching vibration peaks of the ether bonds (COC) in nearby polyethylene glycol remained largely stable after the addition of MBA. (Combined peaks: 3200–4000 cm⁻¹) -1 Based on evidence from various aspects, including changes in the absorption range, the appearance of polyacrylic acid carboxyl peaks, and the stability of bentonite characteristic peaks, it can be concluded that with the addition of MBA, the polymer successfully intercalated into the bentonite interlayer, forming a bentonite-polymer intercalation system.

[0059] X-ray diffraction was performed on the bentonite mineral interpenetrating network gel obtained in Example 1 and the bentonite in Comparative Example 1. The results are as follows: Figure 4 As shown, the 001 peak of bentonite is 6.94°, and the 001 peak of MBA0.3 is 4.74°. According to the Bragg equation:

[0060] nλ = 2d / sinθ;

[0061] Where n is the diffraction order (usually taken as 1), λ is the X-ray wavelength (Cu Kα radiation: λ = 0.15406 nm); θ is the diffraction angle (in radians, 2θ needs to be converted to θ); and d is the interplanar spacing (nm).

[0062] The calculation results showed that the interlayer spacing of bentonite was 1.28 nm and that of MBA0.3 was 1.87 nm, indicating that the polymer intercalation led to an increase in the interlayer spacing of bentonite.

[0063] The liquid absorption rate of the bentonite mineral interpenetrating network gels obtained in Examples 1-5 was measured, and the results are as follows: Figure 5 As shown, the absorption rate reaches its maximum when the MBA content is 0.06 g (i.e., 0.3 wt% of acrylic acid). The absorption rate gradually decreases with increasing MBA content. The optimal absorption rate in this example is 312.76 g / g.

[0064] Application Examples

[0065] The powdered bentonite mineral interpenetrating network gel obtained in Example 5 was uniformly incorporated into the loess at 1 wt% of its dry weight. The loess had a moisture content of 19% and a dry density of 1.62 g / cm³. 3 Add an appropriate amount of water to the soil, dry mix for 3 minutes, then add water and wet mix for 5 minutes. Compact it into a cylinder with a diameter of 3.91 cm and a height of 8 cm (compaction degree ≥ 95%). Test the performance after curing for 3 days.

[0066] Using pure loess as a control, water sensitivity tests were conducted on collapsible loess. The results showed that the pure loess group collapsed within 5 seconds, and the collapsed soil consisted of scattered particles, with relatively turbid water, indicating that a large number of soil particles were scattered in the water. In contrast, the experimental group incorporating powdered bentonite mineral interpenetrating network gel in the application examples did not collapse until 30 seconds later. After the collapse, the water was relatively clear, and the collapsed blocks were larger, indicating that the material provided effective support for the soil structure and had an effective binding effect on the soil, significantly reducing the water sensitivity of the loess.

[0067] Therefore, this invention provides a method for preparing and applying bentonite mineral interpenetrating network gel. Using bentonite exfoliated nanosheets as crosslinking nodes, a triple interpenetrating structure is constructed in conjunction with PAA ion network, PEG flexible segments, and PVA rigid hydroxyl network. This structure combines high water absorption, compression resistance, salt resistance, and long-term stability. When applied to the improvement of collapsible loess, the gel particles combine with soil particles to form an "anchoring effect," reducing soil permeability and preventing soil collapse.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a bentonite mineral interpenetrating network gel, characterized in that, Includes the following steps: S1. Place powdered sodium bentonite in deionized water and stir magnetically until no visible agglomerates are visible to obtain bentonite dispersion solution A. The concentration of bentonite dispersion solution A is 30~60 wt%; S2. Dissolve acrylic acid monomer in deionized water, and slowly add sodium hydroxide solution dropwise under water bath conditions to neutralize it, adjusting the neutralization degree of the solution to 50~90%. Then add bentonite dispersion solution A and stir magnetically to obtain mixed solution B. S3. Under gradient heating conditions, polyethylene glycol and polyvinyl alcohol are added to mixed solution B in stages, and after magnetic stirring, mixed solution C is obtained. The specific steps are as follows: First, mixed solution B is slowly heated to 40~60℃, polyethylene glycol is added and magnetic stirring is performed. After stirring evenly, the temperature is raised to 70~80℃, polyvinyl alcohol is added, and mixed solution C is obtained after magnetic stirring. The amount of both polyethylene glycol and polyvinyl alcohol used is 5-25 wt% of acrylic acid monomer, and the molecular weight of polyethylene glycol is 4000-10000. S4. Dissolve N,N-methylenebisacrylamide in deionized water to obtain a crosslinking agent solution; dissolve potassium persulfate in deionized water to obtain an initiator solution; S5. Add the crosslinking agent solution to the mixed solution C, stir magnetically until well mixed, then slowly add the initiator solution, stir magnetically again, and after stopping the stirring, bentonite mineral interpenetrating network gel precipitates. S6. The bentonite mineral interpenetrating network gel was chopped into small pieces, soaked in a mixture of water and ethanol to wash away unreacted acrylic monomers, dried, pulverized, and sieved to obtain powdered bentonite mineral interpenetrating network gel; the volume ratio of water to ethanol was 1:9, and the soaking time was 10~30 min; the drying process adopted a gradient temperature increase, specifically: drying at 50℃ for 2 h, drying at 60℃ for 4 h, and drying at 80℃ for 12 h. The prepared bentonite mineral interpenetrating network gel was applied to the improvement of collapsible loess. Specifically, the powdered bentonite mineral interpenetrating network gel was incorporated into the loess at a dosage of 0.25~1wt% of the loess.

2. The method for preparing a bentonite mineral interpenetrating network gel according to claim 1, characterized in that: In S2, the amount of deionized water is 1 to 3 times that of the acrylic monomer, the water bath temperature is below 30°C, and in mixed solution B, the amount of bentonite is 10 to 50% of the mass of the acrylic monomer.

3. The method for preparing a bentonite mineral interpenetrating network gel according to claim 1, characterized in that: In S1-S3, the magnetic stirring time is 10-20 min and the stirring speed is 500-800 r / min.

4. The method for preparing a bentonite mineral interpenetrating network gel according to claim 1, characterized in that: In S4, the amount of N,N-methylenebisacrylamide used is 0.1 to 0.5 wt% of the acrylic acid monomer, and the amount of potassium persulfate used is 0.5 to 2.5 wt% of the acrylic acid monomer.

5. The method for preparing a bentonite mineral interpenetrating network gel according to claim 1, characterized in that: In step S5, the magnetic stirring time after adding the crosslinking agent solution and the initiator solution is 5-10 min, and the magnetic stirring speed is 500-1000 r / min.

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