Salt-tolerant water-absorbent resin and preparation method thereof

Abstract

The invention relates to the technical field of water-absorbent resin, in particular to salt-resistant water-absorbent resin and a preparation method thereof. The preparation method comprises the following steps: weighing acrylic acid, acrylamide, sulfobetaine methacrylate, hexadecyl dimethyl allyl ammonium chloride, sodium alginate, a cross-linking agent, an initiator, an antioxidant, an emulsifier, polyethylene glycol diacrylate and nano montmorillonite; carrying out ultrasonic emulsification on hexadecyl dimethyl allyl ammonium chloride and an emulsifier in ethanol; mixing neutralized acrylic acid, acrylamide and sulphobetaine methacrylate, and introducing nitrogen to remove oxygen; adding sodium alginate for dissolving, and injecting the microemulsion and the organic montmorillonite; adding a cross-linking agent and polyethylene glycol diacrylate, and adding an initiator and an antioxidant; and cross-linking, drying and sieving to obtain a finished product. According to the invention, by reducing the proportion of the ion-sensitive components and forming a salt-resistant interpenetrating network through the organic montmorillonite, the salt resistance of the water-absorbent resin is ensured.

Description

Technical Field

[0001] This invention relates to the field of absorbent resin technology, and more specifically, to a salt-resistant absorbent resin and its preparation method. Background Technology

[0002] Superabsorbent polymers (SAPs) are synthetic resins with a three-dimensional network structure containing strong hydrophilic groups. They can absorb hundreds to thousands of times their own weight in water and retain it without loss. Their core characteristics include high absorbency, high water retention, effective and lasting absorption, and safety.

[0003] CN111793169B discloses a highly salt-resistant superabsorbent resin and its preparation process. The highly salt-resistant superabsorbent resin comprises the following raw materials by weight: 5-10 parts sodium alginate, 80-100 parts acrylic acid, 50-60 parts acrylamide, 20-30 parts chitosan, 10-20 parts diatomaceous earth, 10-20 parts humic acid, 0.05-2.5 parts initiator, 0.3-5 parts crosslinking agent, and 0.05-3 parts antioxidant. The preparation process of this invention utilizes sodium alginate to improve the resin's biodegradability, thus protecting the environment. The porous structure of diatomaceous earth provides support for the other raw materials and increases the resin's water absorption rate. The reaction between diatomaceous earth and sodium alginate enhances the flocculation performance of the diatomaceous earth.

[0004] The problem lies in the fact that, in the aforementioned absorbent resins and their preparation processes, acrylic acid is a strong anionic monomer, and its water absorption mainly relies on the osmotic pressure generated by the carboxylate ion. Cations in salt solutions, such as Na+... + Ca 2+ It shields electrical charges, significantly reducing osmotic pressure; moreover, sodium alginate and humic acid contain a large number of carboxyl / phenolic hydroxyl groups, further increasing anion density and exacerbating salt sensitivity; in addition, the proportion of total ionic components (acrylic acid + sodium alginate + humic acid + protonated chitosan) in the above raw material formulation is too high, far exceeding the proportion of non-ionic components (acrylamide 50-60 parts), resulting in extreme sensitivity of the system to salt ions. That is, the proportion of ionicly sensitive components in the water-absorbing resin in the above patent is too high, and it relies excessively on ionic components. In high ionic strength environments such as physiological saline and farmland soil, the water absorption rate will decrease significantly, and its salt resistance performance is not ideal. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that the proportion of ion-sensitive components in existing water-absorbing resins is too high, resulting in poor salt resistance and decreased water absorption rate in high ionic strength environments.

[0006] The purpose of this invention is to provide a salt-resistant superabsorbent resin and its preparation method. By reducing the proportion of ion-sensitive components and using organo-modified montmorillonite to guide the polymerization of monomers between layers, a salt-resistant interpenetrating network is formed, thereby ensuring the salt resistance of the superabsorbent resin and avoiding the problem of a significant decrease in water absorption rate in high ionic strength environments.

[0007] To achieve the above objectives, one objective of this invention is to provide a salt-resistant water-absorbing resin, comprising the following raw materials in the following mass percentages:

[0008] Acrylic acid 30-40%, acrylamide 20-30%, sulfobetaine methacrylate 5-10%, hexadecyl dimethyl allyl ammonium chloride 2-5%, sodium alginate 3-8%, crosslinking agent 0.1-0.5%, initiator 0.05-0.30%, antioxidant 0.1-0.5%, emulsifier 0.1-0.5%, polyethylene glycol diacrylate 0.5-2.0%, with the balance being nano-montmorillonite.

[0009] As a further improvement to this technical solution, the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate.

[0010] As a further improvement to this technical solution, the antioxidant is ascorbic acid.

[0011] In this invention, sulfobetaine methacrylate serves as a charge-adaptive salt-resistant core, forming a strongly hydrated layer through a zwitterionic internal salt structure to resist Na+. + / Ca 2+ Charge shielding effect maintains osmotic pressure balance under high ionic strength; hexadecyl dimethyl allyl ammonium chloride triggers dynamic association through hydrophobic long chains in high salt environment, forming a physical cross-linking network to compensate for electrostatic repulsion loss.

[0012] Acrylic acid and acrylamide form a copolymer backbone. Partially neutralized acrylic acid and nonionic acrylamide synergistically regulate ion density and avoid polyelectrolyte collapse. Nano-montmorillonite guides monomer intercalation polymerization through its layered structure. Gradient heating triggers the intercalation of clay sheet covalent crosslinking agent and polyethylene glycol diacrylate flexible chain to form a rigid-elastic composite network.

[0013] Sodium alginate is used to block multivalent ion penetration attacks; the initiator, antioxidant, and emulsifier are used to maintain network integrity.

[0014] A second objective of this invention is to provide a method for preparing the salt-resistant water-absorbing resin described above, comprising the following steps:

[0015] Step S1: Weigh the raw materials according to the mass ratio, and then neutralize the acrylic acid;

[0016] The nano-montmorillonite was modified to obtain organo-montmorillonite;

[0017] Step S2: Dissolve hexadecyl dimethyl allyl ammonium chloride and emulsifier in anhydrous ethanol, and then emulsify by ultrasonication to form a microemulsion;

[0018] Then, the above-neutralized acrylic acid, acrylamide, and sulfobetaine methacrylate were added to the reaction vessel, and nitrogen gas was introduced to remove oxygen.

[0019] Step S3: Add sodium alginate to the reaction vessel and stir at 40°C until it dissolves into a homogeneous viscous liquid. Then add microemulsion and organo-modified montmorillonite dropwise.

[0020] Continue adding crosslinking agent and polyethylene glycol diacrylate to the reactor, then add initiator and antioxidant dropwise for prepolymerization treatment;

[0021] Step S4: Heat the reactor to perform cross-linking and curing treatment to obtain a gel product, and wash it three times with 70% ethanol to remove unreacted monomers;

[0022] The gel product is crushed into 3-5mm particles, then dried and sieved to obtain the finished product, which is then sealed and stored.

[0023] As a further improvement to this technical solution, in step S1, the neutralization treatment involves neutralizing acrylic acid with 5% NaOH solution to a neutralization degree of 60-70%, and then cooling it in an ice-water bath for later use.

[0024] The modification process involved dispersing nano-montmorillonite in deionized water, adding 0.2% silane coupling agent KH-570, ultrasonically treating at 70℃ for 20-30 minutes, and centrifuging and drying to obtain organo-modified montmorillonite.

[0025] As a further improvement to this technical solution, in step S2, the nitrogen deoxygenation time is 10-20 minutes.

[0026] As a further improvement to this technical solution, in step S3, after adding the microemulsion, it is dispersed at high speed of 600-1000 rpm for 5-15 min, and then the organic montmorillonite is added and ultrasonically vibrated at 40℃ for 20-30 min.

[0027] As a further improvement to this technical solution, in step S3, the prepolymerization treatment is carried out at 35-45℃ for 1-3 hours.

[0028] As a further improvement to this technical solution, in step S4, the crosslinking and curing treatment involves heating the reactor to 40-50℃ for 2 hours and then heating it to 65-70℃ for 1 hour.

[0029] As a further improvement to this technical solution, in step S4, the drying and sieving process is to vacuum dry to constant weight at 50-60℃, and finally pass through an 80-120 mesh sieve to obtain the finished product.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] In this salt-resistant water-absorbing resin and its preparation method, a charge-adaptive salt-resistant core is first constructed using sulfobetaine methacrylate. Its zwitterionic internal salt structure resists Na+ through a strong hydration layer. + / Ca 2+ The charge shielding effect maintains the osmotic pressure balance under high ionic strength; the hydrophobic long chain of hexadecyl dimethyl allyl ammonium chloride triggers dynamic association in a high-salt environment, forming a physical cross-linking network to compensate for the loss of electrostatic repulsion; the nonionic skeleton of acrylamide and the partially neutralized carboxyl groups of acrylic acid synergistically construct the swelling backbone, and avoid the collapse of polyelectrolytes by regulating the ion density.

[0032] Furthermore, the polymerization is directionally guided by the layered structure of organic montmorillonite, which promotes monomer intercalation in the prepolymerization stage. Gradient heating triggers covalent cross-linking between clay layers and interpenetration of flexible chains, forming a "rigid-elastic" composite network. The functional integrity is maintained by low temperature initiation and microemulsion process, which improves the water absorption rate in high ionic strength environments such as physiological saline, thus obtaining a water-absorbing resin with good salt resistance. Attached Figure Description

[0033] Figure 1 This is a flowchart of the present invention;

[0034] Figure 2 A schematic diagram showing the brine water absorption rate of water-absorbing resins with different mass percentages of sulfobetaine methacrylate.

[0035] Figure 3 This diagram illustrates the brine absorption rate of the superabsorbent resin when the mass percentage of hexadecyl dimethyl allyl ammonium chloride is different. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0037] One objective of this invention is to provide a salt-resistant water-absorbing resin, comprising the following raw materials in the indicated mass percentages:

[0038] The composition includes 30-40% acrylic acid, 20-30% acrylamide, 5-10% sulfobetaine methacrylate, 2-5% hexadecyl dimethyl allyl ammonium chloride, 3-8% sodium alginate, 0.1-0.5% crosslinking agent, 0.05-0.30% initiator, 0.1-0.5% antioxidant, 0.1-0.5% emulsifier, 0.5-2.0% polyethylene glycol diacrylate, and the balance being nano-montmorillonite. The layered structure enhances mechanical properties, and the surface hydroxyl groups participate in crosslinking, thereby improving salt resistance through cation exchange capacity.

[0039] Furthermore, the crosslinking agent is N,N'-methylenebisacrylamide, and the crosslinking network density is controlled by a low dosage setting. The initiator is ammonium persulfate, and low-temperature initiation is used to avoid degradation.

[0040] Furthermore, the antioxidant is ascorbic acid, which is used to protect the network structure.

[0041] Please see Figure 1 As shown, a second objective of this invention is to provide a method for preparing the aforementioned salt-resistant water-absorbing resin, comprising the following steps:

[0042] Step S1: Weigh the raw materials according to the mass ratio, and then neutralize the acrylic acid.

[0043] The neutralization process involves neutralizing acrylic acid with 5% NaOH solution to a neutralization degree of 60-70% (pH≈6.0), followed by cooling in an ice-water bath for later use (to reduce the ionization of carboxyl groups and decrease subsequent salt sensitivity).

[0044] Nano-montmorillonite was modified to obtain organo-montmorillonite. The modification process involved dispersing nano-montmorillonite in deionized water (solid-liquid ratio 1:20), adding 0.2% silane coupling agent KH-570, ultrasonically treating at 70℃ for 20-30 min, and centrifuging and drying to obtain organo-montmorillonite, which is used to enhance the compatibility between clay and polymer and improve the efficiency of interlayer crosslinking.

[0045] Step S2: Dissolve hexadecyl dimethyl allyl ammonium chloride and emulsifier in anhydrous ethanol, and then emulsify by ultrasonication to form a microemulsion.

[0046] Then, the acrylic acid, which has been neutralized as described above, along with acrylamide and sulfobetaine methacrylate, are added to the reactor, and nitrogen gas is purged to remove oxygen for 10-20 minutes.

[0047] Step S3: Slowly add sodium alginate to the reactor and stir at 40°C until it dissolves into a homogeneous viscous liquid. Then add microemulsion and organo-modified montmorillonite dropwise. Specifically, after adding the microemulsion, disperse it at high speed of 600-1000 rpm for 5-15 minutes, and then add the organo-modified montmorillonite and sonicate it at 40°C for 20-30 minutes to promote monomer insertion into the clay layers.

[0048] Continue adding crosslinking agent and polyethylene glycol diacrylate to the reactor, then add initiator and antioxidant dropwise for prepolymerization treatment.

[0049] The prepolymerization treatment involves reacting at 35-45℃ for 1-3 hours.

[0050] Step S4: Heat the reactor to perform cross-linking and curing treatment to obtain a gel product, and wash it three times with 70% ethanol to remove unreacted monomers.

[0051] The cross-linking curing process involves heating the reactor to 40-50℃ for 2 hours, and then heating it to 65-70℃ for 1 hour to complete the interlayer polymerization of clay.

[0052] The gel product is crushed into 3-5mm particles, then dried and sieved to obtain the finished product, which is then sealed and stored.

[0053] The drying and sieving process involves vacuum drying at 50-60℃ until constant weight, followed by passing through an 80-120 mesh sieve to obtain the finished product.

[0054] The following specific embodiments will further illustrate the salt-resistant water-absorbing resin and its preparation method provided by the present invention.

[0055] Example 1

[0056] Step S1: Weigh out 30% acrylic acid, 30% acrylamide, 5% sulfobetaine methacrylate, 5% hexadecyl dimethyl allyl ammonium chloride, 3% sodium alginate, 0.5% crosslinking agent, 0.05% initiator, 0.5% antioxidant, 0.1% emulsifier, and 2.0% polyethylene glycol diacrylate according to the mass ratio, with the balance being nano-montmorillonite. Then, neutralize the acrylic acid.

[0057] The neutralization process involved neutralizing the acrylic acid with a 5% NaOH solution to a neutralization degree of 60% (pH≈6.0), followed by cooling in an ice-water bath for later use.

[0058] The nano-montmorillonite was modified to obtain organo-montmorillonite. The modification process involved dispersing the nano-montmorillonite in deionized water (solid-liquid ratio 1:20), adding 0.2% silane coupling agent KH-570, ultrasonically treating at 70℃ for 30 min, and centrifuging and drying to obtain organo-montmorillonite.

[0059] Step S2: Dissolve hexadecyl dimethyl allyl ammonium chloride and emulsifier in anhydrous ethanol, and then emulsify by ultrasonication to form a microemulsion.

[0060] Then, the acrylic acid, which has been neutralized as described above, along with acrylamide and sulfobetaine methacrylate, are added to the reactor, and nitrogen gas is purged for 10 minutes to remove oxygen.

[0061] Step S3: Add sodium alginate to the reaction vessel and stir at 40°C until it dissolves into a homogeneous viscous liquid. Then add microemulsion and organo-modified montmorillonite dropwise. Specifically, after adding the microemulsion, disperse it at 1000 rpm for 5 minutes, then add the organo-modified montmorillonite and sonicate at 40°C for 30 minutes.

[0062] Continue adding crosslinking agent and polyethylene glycol diacrylate to the reactor, then add initiator and antioxidant dropwise for prepolymerization treatment.

[0063] The prepolymerization treatment involved reacting at 35°C for 3 hours.

[0064] Step S4: Heat the reactor to perform cross-linking and curing treatment to obtain a gel product, and wash it three times with 70% ethanol to remove unreacted monomers.

[0065] The cross-linking curing process involves heating the reactor to 40°C for 2 hours, followed by heating to 70°C for 1 hour of curing.

[0066] The gel product was crushed into 3mm particles, then dried and sieved to obtain the finished product, which was then sealed and stored.

[0067] The drying and sieving process involves vacuum drying at 60°C to constant weight, followed by passing through an 80-mesh sieve to obtain the finished product.

[0068] Example 2

[0069] Step S1: Weigh out the following components according to the mass ratio: 35% acrylic acid, 25% acrylamide, 8% sulfobetaine methacrylate, 3% hexadecyl dimethyl allyl ammonium chloride, 6% sodium alginate, 0.3% crosslinking agent, 0.15% initiator, 0.2% antioxidant, 0.3% emulsifier, 1.0% polyethylene glycol diacrylate, with the remainder being nano-montmorillonite. Then, neutralize the acrylic acid.

[0070] The neutralization process involved neutralizing the acrylic acid with a 5% NaOH solution to a neutralization degree of 65% (pH≈6.0), followed by cooling in an ice-water bath for later use.

[0071] The nano-montmorillonite was modified to obtain organo-montmorillonite. The modification process involved dispersing the nano-montmorillonite in deionized water (solid-liquid ratio 1:20), adding 0.2% silane coupling agent KH-570, ultrasonically treating at 70℃ for 25 min, and centrifuging and drying to obtain organo-montmorillonite.

[0072] Step S2: Dissolve hexadecyl dimethyl allyl ammonium chloride and emulsifier in anhydrous ethanol, and then emulsify by ultrasonication to form a microemulsion.

[0073] Then, the acrylic acid, which has been neutralized as described above, along with acrylamide and sulfobetaine methacrylate, are added to the reactor, and nitrogen gas is purged for 14 minutes to remove oxygen.

[0074] Step S3: Add sodium alginate to the reactor and stir at 40°C until it dissolves into a homogeneous viscous liquid. Then add microemulsion and organo-modified montmorillonite dropwise. Specifically, after adding the microemulsion, disperse it at 800 rpm for 10 min, then add the organo-modified montmorillonite and sonicate at 40°C for 25 min.

[0075] Continue adding crosslinking agent and polyethylene glycol diacrylate to the reactor, then add initiator and antioxidant dropwise for prepolymerization treatment.

[0076] The prepolymerization treatment involved reacting at 40°C for 2 hours.

[0077] Step S4: Heat the reactor to perform cross-linking and curing treatment to obtain a gel product, and wash it three times with 70% ethanol to remove unreacted monomers.

[0078] The cross-linking curing process involves heating the reactor to 45°C for 2 hours, followed by heating to 65°C for 1 hour of curing.

[0079] The gel product was crushed into 4mm particles, then dried and sieved to obtain the finished product, which was then sealed and stored.

[0080] The drying and sieving process involves vacuum drying at 55°C until constant weight, followed by passing through a 100-mesh sieve to obtain the finished product.

[0081] Example 3

[0082] Step S1: Weigh out 40% acrylic acid, 20% acrylamide, 10% sulfobetaine methacrylate, 2% hexadecyl dimethyl allyl ammonium chloride, 8% sodium alginate, 0.1% crosslinking agent, 0.30% initiator, 0.1% antioxidant, 0.5% emulsifier, and 0.5% polyethylene glycol diacrylate according to the mass ratio, with the balance being nano-montmorillonite. Then, neutralize the acrylic acid.

[0083] The neutralization process involved neutralizing the acrylic acid with a 5% NaOH solution to a neutralization degree of 70% (pH≈6.0), followed by cooling in an ice-water bath for later use.

[0084] The nano-montmorillonite was modified to obtain organo-montmorillonite. The modification process involved dispersing the nano-montmorillonite in deionized water (solid-liquid ratio 1:20), adding 0.2% silane coupling agent KH-570, ultrasonically treating at 70℃ for 20 min, and centrifuging and drying to obtain organo-montmorillonite.

[0085] Step S2: Dissolve hexadecyl dimethyl allyl ammonium chloride and emulsifier in anhydrous ethanol, and then emulsify by ultrasonication to form a microemulsion.

[0086] Then, the acrylic acid, which has been neutralized as described above, along with acrylamide and sulfobetaine methacrylate, are added to the reactor, and nitrogen gas is purged for 20 minutes to remove oxygen.

[0087] Step S3: Add sodium alginate to the reactor and stir at 40°C until it dissolves into a homogeneous viscous liquid. Then add microemulsion and organo-modified montmorillonite dropwise. Specifically, after adding the microemulsion, disperse it at 600 rpm for 15 min, then add the organo-modified montmorillonite and sonicate at 40°C for 20 min.

[0088] Continue adding crosslinking agent and polyethylene glycol diacrylate to the reactor, then add initiator and antioxidant dropwise for prepolymerization treatment.

[0089] The prepolymerization treatment involved reacting at 45°C for 1 hour.

[0090] Step S4: Heat the reactor to perform cross-linking and curing treatment to obtain a gel product, and wash it three times with 70% ethanol to remove unreacted monomers.

[0091] The cross-linking curing process involves heating the reactor to 50°C for 2 hours, followed by heating to 65°C for 1 hour of curing.

[0092] The gel product was crushed into 5mm particles, then dried and sieved to obtain the finished product, which was then sealed and stored.

[0093] The drying and sieving process involves vacuum drying at 50°C to constant weight, followed by passing through a 120-mesh sieve to obtain the finished product.

[0094] According to the raw material ratios and preparation methods provided in Examples 1-3, water-absorbing resins were prepared. Then, in order to determine the saturated water absorption capacity of the resin in deionized water, as well as its water absorption capacity and salt resistance in salt solutions, the prepared water-absorbing resins were subjected to water absorption performance tests and salt resistance tests.

[0095] The water absorption performance test steps are as follows:

[0096] Accurately weigh 0.10±0.01g of the dried resin sample (denoted as W0) and place it in a 100-mesh nylon mesh bag; immerse the mesh bag in 500mL of deionized water and let it stand at room temperature (25±1℃) for 30min; remove the mesh bag and hang it to stand for 15min until no liquid drips; weigh the gel mass after water absorption (denoted as W1), and calculate the pure water absorption rate (Q0) = (W1-W0) / W0. Record the measured pure water absorption rate results in Table 1.

[0097] The salt resistance test procedure is as follows:

[0098] Dissolve 9g of sodium chloride in 1L of deionized water; follow the same steps as the water absorption test method described above. Then immerse the sample in 500mL of salt solution for 30min; weigh it after 15min (recorded as Ws). The water absorption rate of the salt water (Qs) = (Ws-W0) / W0. Similarly, record the measured water absorption rate of the salt water in Table 1.

[0099] Table 1. Pure water absorption rate and salt water absorption rate of the water-absorbing resins prepared in Examples 1-3

[0100] Example 1 Example 2 Example 3 Pure water absorption rate (g / g) 436 448 442 Salt water absorption rate (g / g) 70 74 71

[0101] As shown in Table 1, the water absorption rates of the absorbent resins prepared in Examples 1-3 are all higher than 436 g / g in pure water and higher than 70 g / g in salt water. This indicates that the salt-resistant absorbent resin and its preparation method provided by the present invention can prepare absorbent resins with good salt resistance.

[0102] In this invention, a charge-adaptive salt-resistant core is first constructed using sulfobetaine methacrylate, whose zwitterionic internal salt structure resists Na+ through a strong hydration layer. + / Ca 2+ The charge shielding effect maintains the osmotic pressure balance under high ionic strength; the hydrophobic long chain of hexadecyl dimethyl allyl ammonium chloride triggers dynamic association in a high-salt environment, forming a physical cross-linking network to compensate for electrostatic repulsion loss; the acrylamide nonionic skeleton and the partially neutralized carboxyl groups of acrylic acid synergistically construct the swelling backbone, and avoid the collapse of polyelectrolytes by regulating the ion density (total anion ratio ≤45%).

[0103] Furthermore, the polymerization is directionally guided by the layered structure of organic montmorillonite, which promotes monomer intercalation in the prepolymerization stage. Gradient heating triggers covalent cross-linking between clay layers and interpenetration of flexible chains, forming a "rigid-elastic" composite network. The functional integrity is maintained by low temperature initiation and microemulsion process, which improves the water absorption rate in high ionic strength environments such as physiological saline, thus obtaining a water-absorbing resin with good salt resistance.

[0104] Example 4

[0105] In this invention, the mass percentage of sulfobetaine methacrylate is 5-10%. If the proportion of sulfobetaine methacrylate is too low, it will lead to insufficient charge shielding resistance. Due to insufficient zwitterionic unit density, an effective strong hydration layer cannot be formed, resulting in Na... + / Ca 2+ The charge shielding effect is aggravated, and the water absorption rate of brine decreases. If the proportion of sulfobetaine methacrylate is too high, the excessive zwitterionic groups will cause hydrophilic-hydrophobic microphase separation, which will destroy the network uniformity and reduce the gel strength. In addition, the quaternary ammonium groups of sulfobetaine methacrylate will compete with the crosslinking agent for reaction, resulting in a decrease in crosslinking density.

[0106] To verify that the 5-10% mass percentage of sulfobetaine methacrylate in the superabsorbent resin is one of the important factors contributing to the good salt resistance of the superabsorbent resin provided by this invention, this embodiment, based on Example 1 above, only changes the mass percentage of sulfobetaine methacrylate in the superabsorbent resin. The mass percentage of sulfobetaine methacrylate is set to 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or 12%. Then, the superabsorbent resin is prepared, and the superabsorbent resin is tested according to the salt resistance test method provided in the above embodiments. The results are as follows: Figure 2 As shown.

[0107] according to Figure 2 It can be seen that when the mass percentage of sulfobetaine methacrylate in the water-absorbing resin is 2%, 3%, 4%, or 12%, i.e., not 5-10%, the brine water absorption rate of the prepared water-absorbing resin is significantly lower than that of the water-absorbing resin prepared when the mass percentage of sulfobetaine methacrylate is 5%, 6%, 7%, 8%, 9%, or 10%.

[0108] This demonstrates that the 5-10% mass percentage of sulfobetaine methacrylate in the water-absorbing resin is one of the important factors contributing to the good salt resistance of the water-absorbing resin provided by this invention.

[0109] Example 5

[0110] In this invention, the mass percentage of hexadecyl dimethyl allyl ammonium chloride is 2-5%. If the mass percentage of hexadecyl dimethyl allyl ammonium chloride is too low, the C16 long chain density of hexadecyl dimethyl allyl ammonium chloride is insufficient, and an effective physical cross-linking network cannot be formed under high salt conditions. The electrostatic repulsion loss cannot be compensated, leading to the collapse of the gel network and thus a lack of hydrophobic microregion support. If the mass percentage of hexadecyl dimethyl allyl ammonium chloride is too high, the excessive hydrophobic groups will cause molecular chain aggregation, blocking the diffusion channels of water molecules, reducing the water absorption rate, and the dense hydrophobic layer will inhibit the ionization and swelling of zwitterions, resulting in a decrease in salt resistance.

[0111] To demonstrate that the 2-5% mass percentage of hexadecyl dimethyl allyl chloride in the superabsorbent resin is one of the key factors contributing to the good salt resistance of the superabsorbent resin provided by this invention, this embodiment, based on Example 1 above, only changes the mass percentage of hexadecyl dimethyl allyl chloride in the superabsorbent resin, setting it to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The superabsorbent resin is then prepared, and tested according to the salt resistance test method provided in the above embodiments. The results are as follows: Figure 3 As shown.

[0112] according to Figure 3 It can be seen that when the mass percentage of hexadecyl dimethyl allyl chloride in the water-absorbing resin is 1%, 6%, 7%, 8%, 9%, or 10%, i.e., not 2-5%, the brine water absorption rate of the prepared water-absorbing resin is significantly lower than that of the water-absorbing resin prepared when the mass percentage of hexadecyl dimethyl allyl chloride is 2%, 3%, 4%, or 5%.

[0113] This demonstrates that the 2-5% mass ratio of hexadecyl dimethyl allyl ammonium chloride in the water-absorbing resin is one of the important factors contributing to the good salt resistance of the water-absorbing resin provided by this invention.

[0114] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a salt-resistant water-absorbing resin, characterized in that, Includes the following steps: Step S1: Weigh out the following components according to the mass ratio: 30-40% acrylic acid, 20-30% acrylamide, 5-10% sulfobetaine methacrylate, 2-5% hexadecyl dimethyl allyl ammonium chloride, 3-8% sodium alginate, 0.1-0.5% crosslinking agent, 0.05-0.30% initiator, 0.1-0.5% antioxidant, 0.1-0.5% emulsifier, 0.5-2.0% polyethylene glycol diacrylate, with the balance being nano-montmorillonite. Then, neutralize the acrylic acid. The nano-montmorillonite was modified to obtain organo-montmorillonite; Step S2: Dissolve hexadecyl dimethyl allyl ammonium chloride and emulsifier in anhydrous ethanol, and then emulsify by ultrasonication to form a microemulsion; Then, the above-neutralized acrylic acid, acrylamide, and sulfobetaine methacrylate were added to the reaction vessel, and nitrogen gas was introduced to remove oxygen. Step S3: Add sodium alginate to the reaction vessel and stir at 40°C until it dissolves into a homogeneous viscous liquid. Then add microemulsion and organo-modified montmorillonite dropwise. Continue adding crosslinking agent and polyethylene glycol diacrylate to the reactor, then add initiator and antioxidant dropwise for prepolymerization treatment; Step S4: Heat the reactor to perform cross-linking and curing treatment to obtain a gel product, and wash it three times with 70% ethanol to remove unreacted monomers; The gel product is crushed into 3-5mm particles, then dried and sieved to obtain the finished product, which is then sealed and stored.

2. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S1, the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate.

3. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S1, the antioxidant is ascorbic acid.

4. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S1, the neutralization process involves neutralizing acrylic acid with 5% NaOH solution to a neutralization degree of 60-70%, followed by cooling in an ice-water bath for later use. The modification process involved dispersing nano-montmorillonite in deionized water, adding 0.2% silane coupling agent KH-570, ultrasonically treating at 70℃ for 20-30 minutes, and centrifuging and drying to obtain organo-modified montmorillonite.

5. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S2, the nitrogen deoxygenation time is 10-20 minutes.

6. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S3, after adding the microemulsion, it is dispersed at high speed of 600-1000 rpm for 5-15 min, and then the organic montmorillonite is added and ultrasonically vibrated at 40℃ for 20-30 min.

7. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S3, the prepolymerization treatment is carried out at 35-45℃ for 1-3 hours.

8. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S4, the crosslinking and curing treatment involves heating the reactor to 40-50°C for 2 hours, and then heating it to 65-70°C for 1 hour of curing.

9. The method for preparing the salt-resistant water-absorbing resin according to claim 1, characterized in that: In step S4, the drying and sieving process involves vacuum drying at 50-60℃ to constant weight, followed by passing through an 80-120 mesh sieve to obtain the finished product.

10. The salt-resistant water-absorbing resin prepared by the preparation method according to any one of claims 1-9, characterized in that, Including the following raw materials: Acrylic acid, acrylamide, sulfobetaine methacrylate, hexadecyl dimethyl allyl ammonium chloride, sodium alginate, crosslinking agent, initiator, antioxidant, emulsifier, polyethylene glycol diacrylate, nano-montmorillonite, wherein: The sulfobetaine methacrylate, acting as a charge-adaptive salt-resistant core, forms a strong hydration layer through a zwitterionic internal salt structure, resisting Na+. + / Ca 2+ The charge shielding effect maintains the osmotic pressure balance under high ionic strength; the hexadecyl dimethyl allyl ammonium chloride triggers dynamic association through hydrophobic long chains in a high-salt environment, forming a physical cross-linking network to compensate for electrostatic repulsion loss. The acrylic acid and acrylamide form a copolymer backbone, and the partially neutralized acrylic acid and nonionic acrylamide synergistically regulate the ion density to avoid polyelectrolyte collapse; the nano-montmorillonite guides monomer intercalation polymerization through its layered structure, and gradient heating triggers the intercalation of clay sheet covalent crosslinking agent and polyethylene glycol diacrylate flexible chain to form a rigid-elastic composite network. The sodium alginate is used to block multivalent ion penetration attacks; the initiator, antioxidant, and emulsifier are used to maintain network integrity.

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