A bio-based modified hydrogel material and a preparation method and application thereof

Abstract

The application belongs to the technical field of hydrogel and provides a bio-based modified hydrogel material and a preparation method and application thereof, and comprises chitosan, acrylamide, ammonium persulfate and N,N-methylene bisacrylamide; wherein the degree of deacetylation of the chitosan is greater than or equal to 90%, the mass ratio of acrylamide to chitosan is 2.8-3.2:1, the dosage of ammonium persulfate is 0.5% of the mass of acrylamide, and the dosage of N,N-methylene bisacrylamide is 0.5% of the mass of acrylamide. The application can not only significantly improve the compression resistance and shear resistance of expansive soil, but also effectively enhance the rain erosion resistance and dry-wet cycle resistance of the expansive soil, thereby realizing comprehensive reinforcement of the slope soil body; the expansive soil slope modified by the material can still maintain good structural stability under long-term rainfall and complex service conditions, thereby providing a green, durable and practical new solution for the prevention and control of expansive soil disasters in road, railway and urban infrastructure engineering.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogel, and particularly relates to a bio-based modified hydrogel material and a preparation method and application thereof. BACKGROUND

[0002] Swelling soil is a special kind of cohesive soil, which exhibits significant water-swelling and dry-shrinkage cracking characteristics due to the presence of a large amount of hydrophilic minerals such as montmorillonite. This volume change often leads to uneven settlement of the foundation, cracking of the roadbed, slope instability, and even landslides and other engineering hazards. Therefore, how to improve the stability and durability of swelling soil engineering has always been a key issue in the field of civil and geotechnical engineering.

[0003] Existing swelling soil improvement measures mainly include physical methods, chemical solidification methods, and biological reinforcement methods. Physical methods such as drainage, replacement, and reinforcement can only improve soil structure or slow down water infiltration in the short term, but cannot improve the cementation between soil particles at the micro level, thus limiting their adaptability to long-term rain erosion and repeated wet-dry cycles. Chemical solidification methods such as lime, cement, and fly ash solidification can significantly improve soil strength, but the high energy consumption and large carbon emissions during preparation and use not only do not meet the requirements of green and low-carbon development, but also can lead to brittle fracture and peeling due to excessive rigidity under long-term service conditions, resulting in rapid decay of the improvement effect. Although the application of synthetic polymer materials can compensate for the above shortcomings to some extent, they are mostly dependent on petroleum-based raw materials, which may cause environmental pollution and other hidden dangers.

[0004] In recent years, emerging methods such as microbial-induced carbonate precipitation (MICP) have also been tried for swelling soil modification, but such methods are sensitive to environmental conditions and are greatly affected by temperature, humidity, and curing conditions, making it difficult to ensure stability and controllability in engineering practice. Therefore, from the perspectives of durability, environmental friendliness, and engineering adaptability, the existing technologies have obvious shortcomings.

[0005] It is an urgent need to develop a green, environmentally friendly, and renewable new type of improvement material, especially for rain erosion control of swelling soil slopes. Traditional improvement agents generally cannot form a flexible and continuous three-dimensional network structure, which cannot effectively fill soil pores, enhance particle bonding, and maintain structural integrity under long-term rainfall erosion. Therefore, there is an urgent need for a new material made of renewable biomass that has excellent mechanical enhancement effect and long-term rain erosion resistance to break through the limitations of existing technologies. SUMMARY

[0006] The purpose of the embodiments of the present application is to provide a bio-based modified hydrogel material to solve the problems raised in the background.

[0007] The embodiment of the present application is implemented in a way that a bio-based modified hydrogel material comprises chitosan, acrylamide, ammonium persulfate, N,N-methylene bisacrylamide;

[0008] The deacetylation degree of the chitosan is greater than or equal to 90%, the mass ratio of acrylamide to chitosan is 2.8-3.2:1, the dosage of ammonium persulfate is 0.5% of the mass of acrylamide, and the dosage of N,N-methylene bisacrylamide is 0.2% of the mass of acrylamide.

[0009] Another object of the embodiment of the present application is to provide a preparation method of the bio-based modified hydrogel material, comprising the following steps: dissolving chitosan in an acetic acid aqueous solution and stirring; adding acrylamide monomers to the solution and continuing to stir; adding an ammonium persulfate solution to initiate a reaction; dropping an N,N-methylene bisacrylamide solution and performing constant-temperature reaction; and washing and drying the obtained product to obtain the bio-based modified hydrogel material.

[0010] Another object of the embodiment of the present application is to provide an application of the bio-based modified hydrogel material in the prevention and treatment of rain erosion of an expansive soil slope.

[0011] The bio-based modified hydrogel material provided by the embodiment of the present application uses chitosan with a high deacetylation degree (derived from biomass (shrimp shells, crab shells), which is natural, renewable and degradable, and solves the environmental hidden danger of petroleum-based polymers), so that enough active amino groups and hydroxyl groups on the molecular chain are ensured for grafting modification; ammonium persulfate is used for initiation, and N,N-methylene bisacrylamide is used for crosslinking, so that a stable three-dimensional crosslinked network is formed between the chitosan main chain and the polyacrylamide side chain, and the structural stability and regulation and control capability of the hydrogel are greatly improved.

[0012] The bio-based modified hydrogel material forms a flexible and continuous three-dimensional network structure after water absorption and expansion, can effectively fill the pores and microfractures in the expansive soil, and can also chemically and physically interact with the surface of soil particles, so as to realize the reinforcement and stabilization of the expansive soil, and then can be applied in the prevention and treatment of rain erosion of an expansive soil slope.

[0013] The hydrogel fills the gaps between the expansive soil particles after water absorption and expansion, closes the capillary channels, reduces the rainfall infiltration and water migration, and inhibits the softening and volume expansion of the expansive soil when it meets water from the source;

[0014] The amide groups (-CONH2) on the chain segments of the hydrogel can form hydrogen bonds or complex bonds with the hydroxyl groups (-OH), siloxyl groups (Si-O) and aluminum-oxyl groups (Al-O) on the surface of the soil particles, so as to significantly enhance the cementation force between the soil particles and improve the compressive strength and shear strength of the soil body.

[0015] The three-dimensional flexible network constructed by the hydrogel has scalability, and can adjust its own morphology according to the volume change of the swelling soil in the dry-wet cycle process, so as to buffer the stress concentration in the soil body and avoid the structural damage caused by brittle fracture;

[0016] The hydrogel is derived from renewable biomass raw materials (chitosan), has good biodegradability and environmental compatibility while improving the mechanical properties, and can maintain stable modification effect for a long time under complex climate conditions;

[0017] Through the above synergistic effect, the modified hydrogel prepared in the embodiment of the application can not only significantly improve the compression and shear resistance of the swelling soil, but also effectively enhance the rain erosion resistance and dry-wet cycle resistance of the swelling soil, and realizes the comprehensive reinforcement of the slope soil body; the swelling soil slope modified by the material can still maintain good structural stability under long-term rainfall and complex service conditions, thereby providing a green, durable and practical new solution for the prevention and control of swelling soil disasters in road, railway and urban infrastructure engineering. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The SEM images of the sample prepared in the embodiment 1 of the application and CS (a is CS, and b is the modified hydrogel);

[0019] Figure 2 The FTIR comparison chart of the sample prepared in the embodiment 1 of the application and CS;

[0020] Figure 3 The particle size distribution structure schematic diagram of the bentonite provided in the embodiment 2 of the application;

[0021] Figure 4 The post-strength change chart of the modified hydrogel solidified soil provided in the embodiment 2 of the application;

[0022] Figure 5 The rain erosion change chart of the modified hydrogel solidified soil provided in the embodiment 2 of the application;

[0023] Figure 6 The SEM chart after compression failure provided in the embodiment 2 of the application (a is unmodified soil, and b is modified soil);

[0024] Figure 7 The crosslinking reaction mechanism schematic diagram of the modified hydrogel provided in the embodiment of the application;

[0025] Figure 8 The particle size change chart of the modified hydrogel solidified soil provided in the embodiment of the application. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0027] The specific implementation of the present application is described in detail below in combination with specific examples.

[0028] Example 1, a bio-based modified hydrogel material, the preparation method comprising the following steps:

[0029] (1) 1.0 g of chitosan (CS) with a degree of deacetylation ≥ 90% is weighed and added into 100 mL of 2% acetic acid solution, and stirred and dissolved under a 40°C water bath for 4 h. Nitrogen is passed for at least 30 min before the completion of the step to remove dissolved oxygen, and then the subsequent steps are performed;

[0030] (2) 3.0 g of acrylamide monomer (AM) is added, and stirring is continued for 30 min;

[0031] (3) Ammonium persulfate (APS, initiator) is added to the solution, and the amount of ammonium persulfate is 0.5% of the mass of acrylamide, and the reaction is initiated at 60°C for 5 min;

[0032] (4) Then, N,N-methylenebisacrylamide (MBA, crosslinking agent) is added dropwise. The N,N-methylenebisacrylamide is in the form of an aqueous solution, and the mass of N,N-methylenebisacrylamide is 0.2% of the mass of acrylamide. The N,N-methylenebisacrylamide is added to 10 mL of deionized water to prepare an aqueous solution, and the reaction is carried out at 60°C for 90 min;

[0033] (5) The product is washed with ethanol and dried in a freeze-drying oven to obtain chitosan grafted acrylamide modified hydrogel powder (g-Am@CS).

[0034] The sample prepared in Example 1 is characterized, and the SEM image is as shown in Figure 1 According to Figure 1 It can be seen that the g-Am@CS sample presents a significantly different microstructure, and the overall structure is changed from the original rigid agglomerate to a highly dispersed, continuous and porous flexible network. The surface roughness of the modified material increases obviously, and the pore development is sufficient. A large number of wrinkles, fibrous stretching structures and multi-scale connected pores can be observed, showing typical crosslinked hydrogel characteristics;

[0035] The FTIR image is as shown in Figure 2 According to Figure 2 It can be seen that the hydrogen bond, amide and aliphatic side chain structure on the hydrogel segment are clearly visible, which is indirect evidence for the construction of three-dimensional crosslinked network structure; the absorption peak is shifted to 3410 cm -1Meanwhile, the peak shape became wider and the absorption intensity increased, indicating that the hydrogen bonding in the system was significantly enhanced by the grafting modification. This change reflected the enhanced intermolecular interaction and the more compact polymer network structure, supporting the formation of a three-dimensional network; in the amide I band region, CS exhibited a weak absorption peak at 1645 cm -1 , which was attributed to the residual amide groups in the main chain, while in g-Am@CS, the peak was significantly enhanced and shifted to 1656 cm -1 , corresponding to the stretching vibration of the C=O group in the polyacrylamide segment; similarly, the amide II band of CS shifted from 1548 cm -1 to 1556 cm -1 , and the absorption intensity increased, which was attributed to the enhancement of the -NH bending vibration. The shift in absorption peak position and the increase in intensity together indicated that the polyacrylamide (AM) segment was successfully grafted to the chitosan main chain under free radical initiation, forming a large number of new amide bonds; in addition, g-Am@CS exhibited a more pronounced -CH2 asymmetric stretching vibration absorption peak at 2926 cm -1 , which was slightly enhanced compared to 2924 cm -1 of CS, further confirming the introduction of aliphatic side chain structures and indicating the successful grafting of AM monomers; in the 1070-1030 cm -1 region, the characteristic peak of the C-O-C bond stretching vibration was observed before and after grafting, although the peak shape changed slightly but remained stable, indicating that the chitosan main chain skeleton was preserved during the grafting process, only with slight conformational perturbation.

[0036] Example 2: Application of the bio-based modified hydrogel material prepared in Example 1 in the prevention and treatment of rain erosion of expansive soil slopes, including the following steps:

[0037] (1) The expansive soil was naturally air-dried and passed through a 2 mm sieve (taken from Jilin Province Yanbian (127.27°E, 41.59°N), with a yellow-brown color and a mineral composition mainly composed of clay minerals. According to the "Standard for Soil Test Methods" (GB / T 50123-2019), the disturbed soil was placed in an oven at 105°C for 10 hours and then rolled through a 2 mm sieve. The measured particle size distribution is shown in Figure 3 , which is relatively concentrated);

[0038] (2) The modified hydrogel powder prepared in Example 1 was mixed with the expansive soil at a ratio of 1-5% of the dry mass of the soil sample, and an appropriate amount of water was added and stirred uniformly to obtain a mixture;

[0039] (3) The mixture was placed in a cylindrical mold with a diameter of 39.1 mm and a height of 80 mm, and was compacted and formed. The mold was then placed in a standard curing room (20±2°C, relative humidity 95%) for 28 days of curing;

[0040] (4) After curing, the prepared test piece is used for mechanical property test.

[0041] The unmodified expansive soil is used to prepare a test piece as a comparative example. The unconfined compressive strength (UCS) of the test piece prepared in Example 2 and the test piece of the comparative example is tested, and the results are shown in Figure 4 The UCS of the modified expansive soil reaches 1142 kPa, which is about 2.67 times higher than that of the unmodified soil.

[0042] An artificial rainfall simulation experiment is adopted (a set of indoor rainfall simulation platform is built to simulate the rainfall-erosion process under the condition of heavy rain, the sample is installed on the support platform in an inclined manner, the inclination is set to 30° to simulate the typical slope topography, the simulation rainfall is completed by setting the spraying system, the water supply rate is accurately controlled by the valve to keep the rainfall intensity at 5 mm / min (equivalent to 300 mm / h), which corresponds to the extreme event level in the field heavy rain grade, the nozzles are uniformly arranged above the sample to make the water droplets vertically impact the surface to form a continuous and balanced hydrodynamic erosion process to drive the particle migration, with the development of erosion, the particles slide down the slope and collect in the bottom collection container), during the rainfall, the mass loss rate is recorded at 15, 30, 45 and 60 minutes (the calculation formula of the mass loss rate is wherein, MLR is the mass loss rate, M 0 is the initial mass, g, M 1 is the remaining mass, g), which is used as an evaluation index to test the rain erosion resistance, and the results are shown in Figure 5 As shown in the table, the unmodified soil shows obvious surface erosion after 30 min of rainfall cycle, and the particle loss amount is large, while the modified soil sample remains stable as a whole after 60 min of cycle, and the cumulative loss amount is reduced by more than 20%;

[0043] The SEM images of the unmodified test piece and the test piece modified by adding 3% g-Am@CS after compression failure are shown in Figure 6 As can be seen from the table, the modified expansive soil shows a more compact and uniform microstructure, and there is almost no visible pore between the soil particles, and the bonding force between the particles is significantly enhanced. After the treatment of the hydrogel, a more smooth and uniform gel network structure is formed on the surface of the soil, which not only helps to improve the water retention capacity of the soil, but also significantly improves the mechanical strength of the soil. The introduction of the hydrogel can also enhance the flexibility of the soil, so that it can better distribute the stress when bearing external pressure, thereby further improving the stability and compression resistance of the soil.

[0044] The action mechanism of the g-Am@CS prepared in the embodiment of the application in the process of curing and swelling soil is derived from the controllable molecular structure design and micro-interface coupling effect, and the whole embodies the synergistic effect of "molecular crosslinking-interface construction, structure regulation":

[0045] The molecular crosslinking mechanism is as shown in the following formula: Figure 7 Under the condition of nitrogen protection and constant temperature of 60 DEG C, the APS is decomposed to generate high-activity sulfate radical (SO4-·) by heating, the radical preferentially attacks the C2 amino group (-NH2) and C3 hydroxyl group (-OH) on the CS molecular chain, forms the chitosan radical active center by hydrogen extraction or addition reaction, the above active site can further induce the graft polymerization of AM monomer, generates the graft copolymer structure (CS-g-PAM) with CS as the main chain and polyacrylamide (PAM) as the side chain; after the radical polymerization reaction is carried out for 5 minutes, the MBA is introduced, the double bond at both ends in the molecule can occur addition reaction with different PAM chains or CS-g-PAM chain segments under the action of the radical, forms the stable C-C main chain or amide crosslinking bridge, realizes the construction of three-dimensional network structure; at the same time, the residual radical can also further enhance the network topology density by coupling with the C2 / C3 sites of chitosan; finally, the hydrogel system is mainly crosslinked by covalent bond, supplemented by the hydrogen bond and electrostatic interaction between CS and PAM chain segments, cooperatively constructs the spatial network structure with stable structure and excellent mechanical properties; in addition, the MBA can also occur self-polymerization and insert into the main network of the gel in the high radical concentration environment, further improves the compactness and crosslinking integrity of the system, the grafting and crosslinking strategy significantly improves the gelation property and network stability of chitosan, and at the same time, endows it with excellent structure regulation ability and application adaptability; at the same time, the FTIR and XRD analysis confirms that the content of amide bond in g-Am@CS is obviously increased, the crystal structure is changed into amorphous state, verifies the transition of the molecular structure from "rigid semi-crystalline state" to "flexible network state", and provides the structural basis for the subsequent coating and bonding in the soil body;

[0046] The composite curing mechanism: after the g-Am@CS hydrogel enters the expansive soil, it forms a dense and flexible three-dimensional network by swelling and absorbing water, first fills the particle pores and coats the soil particle surface on the physical level, and builds a continuous gel bridge system, effectively inhibiting the structural dispersion of the soil body caused by wet swelling. The SEM image shows that a dense and uniform organic film is generated on the surface of the soil particles in the hydrogel treatment group, the contact between particles is more closely, and a "gap-filling-coating-anchoring" physical connection structure is formed; on the chemical level, the amide group (–CONH2) in the hydrogel can form hydrogen bonds and electrostatic complexes with the mineral surface hydroxyl group (Si–OH, Al–OH), and the chain end anchoring effect of the free radical residual end strengthens the organic-inorganic interface bonding; the O–H and N–H stretching peaks in the FTIR spectrum are all enhanced, and the montmorillonite diffraction peak in the XRD is weakened and slightly shifted, indicating that the g-Am@CS disturbs the layered structure of the expansive soil, partially limits the interlayer hydration behavior, and achieves the swelling inhibition effect; the structure reconstruction effect is reflected in the optimization of the particle size distribution, and the D90 of the hydrogel treated sample is reduced to 78.54 μm (as shown in Figure 8 ), the number of agglomerated particles increases, and the intergranular structure tends to be more uniform; at the same time, the flexibility of its network structure can absorb volume strain under wet-dry alternation, inhibit the initiation and expansion of microcracks, and improve the durability and stability of the soil body.

[0047] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. Application of a bio-based modified hydrogel material in the prevention and control of rain erosion of expansive soil slope, characterized in that, The bio-based modified hydrogel material comprises chitosan, acrylamide, ammonium persulfate and N,N-methylene bisacrylamide. The deacetylation degree of the chitosan is greater than or equal to 90%, the mass ratio of acrylamide to chitosan is 2.8-3.2:1, the amount of ammonium persulfate is 0.5% of the mass of acrylamide, and the amount of N,N-methylene bisacrylamide is 0.2% of the mass of acrylamide.

2. The use of the bio-based modified hydrogel material according to claim 1 in the prevention and control of rain erosion of expansive soil slope, characterized in that, The preparation method of the bio-based modified hydrogel material comprises the following steps: dissolving chitosan in an acetic acid aqueous solution and stirring; adding acrylamide monomers to the solution and continuing to stir; adding ammonium persulfate to initiate a reaction; adding N,N-methylene bisacrylamide dropwise and performing constant-temperature reaction; and washing and drying the obtained product to obtain the bio-based modified hydrogel material.

3. The use of the bio-based modified hydrogel material according to claim 2 in the prevention and control of rain erosion of expansive soil slope, characterized in that, In the step of dissolving chitosan in an acetic acid aqueous solution, the concentration of the acetic acid aqueous solution is 2%.

4. The use of the bio-based modified hydrogel material according to claim 2 in the prevention and control of rain erosion of expansive soil slope, characterized in that, In the step of adding ammonium persulfate to initiate a reaction, the temperature is 60 DEG C and the time is 5 min.

5. The use of the bio-based modified hydrogel material according to claim 2 in the prevention and control of rain erosion of expansive soil slope, characterized in that, In the step of adding N,N-methylene bisacrylamide dropwise and performing constant-temperature reaction, the temperature of the constant-temperature reaction is 60 DEG C.

6. The use of the bio-based modified hydrogel material according to claim 2 in the prevention and control of rain erosion of expansive soil slope, characterized in that, In the step of washing and drying the obtained product, ethanol is used for washing and a freeze-drying method is used.

7. The use of the bio-based modified hydrogel material according to claim 1 in the prevention and control of rain erosion of expansive soil slope, characterized in that, The method comprises the following steps: The bio-based modified hydrogel material is mixed into expanded soil at a mixing amount of 1-5% of the dry mass of the soil, water is added and stirred to be uniform, and then the mixture is compacted and formed and cured.

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