A cross-linked sodium carboxymethyl cellulose and a method for producing the same

Abstract

The application relates to the technical field of cellulose derivative preparation, and discloses crosslinked sodium carboxymethyl cellulose and a preparation method thereof. The crosslinked sodium carboxymethyl cellulose is prepared from sodium carboxymethyl cellulose as raw material by adopting a disulfide crosslinking agent-epoxy chloropropane composite crosslinking system, and through raw material pretreatment, phosphoric acid catalytic activation, microwave-ultrasonic synergistic crosslinking, pH adjustment and anhydrous ethanol post-treatment. The composite crosslinking system forms a double crosslinking network, the microwave-ultrasonic synergistic strengthening reaction is uniform, and an additional impurity removal step is not needed. The application simplifies the process, reduces the cost, and the product has high light transmittance, large viscosity, excellent swelling degree and good substitution uniformity, and can be used for high polymer materials.

Description

Technical Field

[0001] This invention relates to the field of cellulose derivative preparation technology, specifically to a cross-linked sodium carboxymethyl cellulose and its preparation method. Background Technology

[0002] Crosslinked sodium carboxymethyl cellulose (CCNa) is a crosslinked polymer of sodium carboxymethyl cellulose. It is an odorless, white or off-white powder that is insoluble in water but can rapidly expand to 4-8 times its original volume upon contact with water. Due to its excellent disintegration properties, it is widely used in polymer materials.

[0003] Currently, the preparation of crosslinked sodium carboxymethyl cellulose (CMC) mainly uses cellulose derived from wood pulp or cotton fiber as raw material. After alkalization and carboxymethylation reactions, CMC is obtained and then prepared through a crosslinking reaction. In traditional preparation methods, the selection and use of the crosslinking agent are key factors affecting product performance. Commonly used crosslinking agents include borates, aluminum salts, and polyaldehyde compounds. However, these crosslinking agents have significant drawbacks: borates are only effective for cellulose ethers containing dihydroxyl groups and have poor crosslinking effects on sodium carboxymethyl cellulose (which lacks a cis-diol structure); aluminum salts require the addition of chelating agents to remove aluminum ions after crosslinking to achieve complete dissolution, increasing process steps and costs; polyaldehyde crosslinking agents are mainly suitable for nonionic cellulose ethers and are not ideal for treating anionic sodium carboxymethyl cellulose.

[0004] Furthermore, existing preparation processes suffer from problems such as poor product substitution uniformity, low light transmittance, and insufficient viscosity and swelling, leading to unstable disintegration efficiency and limited applicability in practical applications. Therefore, developing a simple, cost-effective method for preparing high-performance cross-linked sodium carboxymethyl cellulose has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a cross-linked sodium carboxymethyl cellulose and its preparation method, which solves the problems of performance defects and complex processes of existing products, and prepares cross-linked sodium carboxymethyl cellulose with high light transmittance, high viscosity, excellent swelling degree and good substitution uniformity, while simplifying process steps and reducing production costs.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a cross-linked sodium carboxymethyl cellulose, which is made by cross-linking sodium carboxymethyl cellulose as raw material using a disulfide-based cross-linking agent-epoxychloropropane composite cross-linking system;

[0007] In the composite crosslinking system, the mass ratio of disulfide-based crosslinking agent to epichlorohydrin is (1.2~2.0):1;

[0008] The preparation method of the disulfide-based crosslinking agent is as follows: dimethyl sulfoxide and 3-mercapto-1,2-propanediol are mixed and fully dissolved in a reaction flask, heated to 85-90°C in an oil bath, and stirred for 10-12 hours. After the reaction system is cooled to room temperature, it is precipitated 2-3 times with 45-50 times the volume of dichloromethane. The resulting solid is dried under vacuum at 45-50°C to obtain the disulfide-based crosslinking agent.

[0009] The composite crosslinking system is prepared by modifying a disulfide-based crosslinking agent-epoxychloropropane composite crosslinking system. Its molecular chains simultaneously contain a rigid ether bond (-COC-) network constructed by epichlorohydrin and a flexible hydrogen bond network constructed by disulfide-based crosslinking agent. In the composite crosslinking system, the mass ratio of disulfide-based crosslinking agent to epichlorohydrin is (1.2~2.0):1. This specific ratio ensures the synergistic effect of rigid nodes and flexible chain segments, so that the product can be greatly extended (high swelling) without breaking (high viscosity) when absorbing water and swelling.

[0010] Further, the mass ratio of dimethyl sulfoxide to 3-mercapto-1,2-propanediol is (10.4-10.8):(5.2-5.64).

[0011] Furthermore, it includes the following steps:

[0012] Step (1), raw material pretreatment: by weight, take 100 parts of sodium carboxymethyl cellulose and add them to 300-400 parts of ethanol-water mixed solvent, stir and disperse for 15-25 minutes to obtain sodium carboxymethyl cellulose dispersion;

[0013] Step (2), catalytic activation: Add 2-5 parts of phosphoric acid catalyst to the dispersion obtained in step (1), stir and activate at room temperature to obtain an activated solution; the H⁺ provided by phosphoric acid converts the carboxylate group on its molecular chain into a carboxyl group. This "protonated" state not only weakens the electrostatic repulsion between molecular chains and reduces steric hindrance, but more importantly, it activates the lone pair electrons of the carboxyl oxygen atom, making it easier for it to form a stable hydrogen bond anchor with the disulfide group / hydroxyl group in the disulfide crosslinking agent;

[0014] Step (3), Microwave-ultrasound synergistic crosslinking: Slowly add 8-15 parts of the composite crosslinking system to the activation solution obtained in step (2), stir evenly, and place it in a microwave-ultrasound synergistic reaction device. Control the microwave power to be 200-300W and the ultrasonic power to be 80-120W, and react at 50-60℃ for 6-8 hours to obtain the crosslinking reaction solution; Microwave thermal effect: Directly acts on polar molecules (water and crosslinking agent) to achieve "internal heating", so that the internal temperature of the particles quickly reaches the reaction threshold, eliminates heat conduction hysteresis, and ensures that the crosslinking degree inside and outside the particles is consistent; Ultrasonic cavitation effect: Generates microjets and shear force, continuously peeling off the dense layer of crosslinked particles on the surface of the particles, which not only prevents particle agglomeration, but also promotes the mass transfer and diffusion of the crosslinking agent into the deep layers of the particles; Under this environment, epichlorohydrin undergoes rapid etherification reaction to "lock" the skeleton, and the disulfide crosslinking agent is inserted into it to form an "elastic ligament", completing the construction of the dual network.

[0015] Step (4), preparation of crude product solution: Add alkaline adjustment solution slowly to the crosslinking reaction solution obtained in step (3) to adjust the pH of the system to neutral, stir the reaction for 10~15 min to obtain crude product solution; terminate the acid catalytic reaction, and at the same time convert the unreacted carboxyl groups back into sodium salt form (-COONa) to restore the high hydrophilicity and water absorption capacity of the product.

[0016] Step (5), post-processing: The crude liquid obtained in step (4) is filtered, the filter cake is collected, and washed with anhydrous ethanol to remove residual solvent and impurities, so as to obtain the cross-linked carboxymethyl cellulose sodium product.

[0017] Further, in step (1), the volume ratio of ethanol to water in the ethanol-water mixed solvent is (1.5~2.5):1.

[0018] Furthermore, in step (2), the stirring activation time is 30~40 min.

[0019] Furthermore, in step (3), the composite crosslinking system is added by dripping at a rate of 0.5~1.0 mL / min, and the stirring speed is maintained at 300~500 r / min during the dripping process.

[0020] Furthermore, in step (4), the alkaline conditioning solution is a sodium hydroxide solution with a mass fraction of 5-10%.

[0021] Furthermore, in step (5), the anhydrous ethanol washing is performed 3 to 4 times.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] 1. In this invention, the disulfide-based crosslinking agent contains disulfide bonds / hydroxyl groups that can form a hydrogen bond network with the carboxyl groups on the sodium carboxymethyl cellulose molecular chain. Epichlorohydrin achieves inter-chain crosslinking through an etherification reaction. The two work together to construct a dual crosslinking network. The disulfide bonds in the main chain of the disulfide-based crosslinking agent provide excellent flexibility, while the hydroxyl groups on the side chain can form a hydrogen bond network with the sodium carboxymethyl cellulose molecular chain. Together with the rigid ether bond network of epichlorohydrin, this perfectly matches the structural characteristics of anionic sodium carboxymethyl cellulose, solving the problems of low crosslinking efficiency and loose network caused by the incompatibility between traditional single crosslinking agents and raw material structures.

[0024] 2. The microwave field in this invention can quickly penetrate the reaction system to achieve uniform heating and reduce the local concentration gradient; the ultrasonic cavitation effect can break up raw material agglomerates and accelerate molecular diffusion. The synergistic effect of the two allows the crosslinking agent to fully contact the sodium carboxymethyl cellulose molecular chain, avoiding local over-crosslinking or under-crosslinking, improving the uniformity of substitution from the root, and reducing the generation of impurities.

[0025] 3. The double cross-linking bonds formed by the composite cross-linking system have higher bond energy and more uniform cross-linking points. Compared with traditional single cross-linking bonds, they can resist water molecule erosion and external forces more effectively, so that the product can maintain structural integrity during the swelling process, thereby improving the stability of viscosity and swelling performance.

[0026] 4. The phosphoric acid catalyst in this invention specifically activates the reactive sites on the sodium carboxymethyl cellulose molecular chain, reducing the activation energy of the crosslinking reaction. Combined with the synergistic effect of microwave-ultrasound, it shortens the reaction cycle. No additional chelation purification steps are required, and the ethanol-water mixed solvent can be recovered and reused through distillation, reducing process steps, raw material consumption, and environmental impact. The disulfide-based crosslinking agent is purified by dichloromethane precipitation, resulting in extremely low residual impurities. Subsequent multiple washings with anhydrous ethanol thoroughly remove unreacted raw materials, catalysts, and byproducts, preventing impurities from affecting the product's transmittance. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0028] Example 1

[0029] Preparation of disulfide-based crosslinking agent

[0030] Dimethyl sulfoxide and 3-mercapto-1,2-propanediol were mixed in a mass ratio of 10.4:5.2 and dissolved completely in a reaction flask. The mixture was heated to 85°C in an oil bath and stirred for 10 hours. After the reaction system cooled to room temperature, it was precipitated twice with 45 times its volume of dichloromethane. The resulting solid was dried under vacuum at 45°C to obtain the disulfide crosslinking agent.

[0031] Preparation of cross-linked carboxymethyl cellulose sodium

[0032] Step (1) Raw material pretreatment: Take 100 parts by weight of sodium carboxymethyl cellulose and add it to 300 parts of ethanol-water mixed solvent (ethanol to water volume ratio 1.5:1). Stir and disperse for 15 min to obtain sodium carboxymethyl cellulose dispersion.

[0033] Step (2) Catalytic activation: Add 2 parts of phosphoric acid catalyst to the dispersion and stir at room temperature for 30 min to obtain the activated solution;

[0034] Step (3) Microwave-ultrasound synergistic crosslinking: Add 8 parts of the composite crosslinking system (disulfide crosslinking agent to epichlorohydrin mass ratio 1.2:1) to the activation solution at a rate of 0.5 mL / min. During the addition, maintain the stirring speed at 300 r / min. After stirring evenly, place it in a microwave-ultrasound synergistic reaction device, control the microwave power at 200 W and the ultrasonic power at 80 W, and react at 50 °C for 6 h to obtain the crosslinking reaction solution.

[0035] Step (4) Preparation of crude product solution: Slowly add 5% sodium hydroxide solution to the cross-linking reaction solution, adjust the pH of the system to neutral, stir the reaction for 10 min, and obtain crude product solution;

[0036] Step (5) Post-processing: The crude product liquid is filtered, the filter cake is collected, and washed three times with anhydrous ethanol to remove residual solvent and impurities, so as to obtain the cross-linked carboxymethyl cellulose sodium product.

[0037] Example 2

[0038] Preparation of disulfide-based crosslinking agent

[0039] Dimethyl sulfoxide and 3-mercapto-1,2-propanediol were mixed in a mass ratio of 10.6:5.4 and dissolved completely in a reaction flask. The mixture was heated in an oil bath to 87°C and stirred for 11 hours. After the reaction system cooled to room temperature, it was precipitated twice with 48 times its volume of dichloromethane. The resulting solid was dried under vacuum at 47°C to obtain the disulfide-based crosslinking agent.

[0040] Preparation of cross-linked carboxymethyl cellulose sodium

[0041] Step (1) Raw material pretreatment: By weight, take 100 parts of sodium carboxymethyl cellulose and add them to 350 parts of ethanol-water mixed solvent (ethanol to water volume ratio 2.0:1), stir and disperse for 20 min to obtain sodium carboxymethyl cellulose dispersion;

[0042] Step (2) Catalytic activation: Add 3 parts of phosphoric acid catalyst to the dispersion and stir at room temperature for 35 min to obtain the activated solution;

[0043] Step (3) Microwave-ultrasound synergistic crosslinking: 12 parts of the composite crosslinking system (disulfide crosslinking agent to epichlorohydrin mass ratio 1.6:1) were added dropwise to the activation solution at a rate of 0.7 mL / min. During the dropwise addition, the stirring speed was kept at 400 r / min. After stirring evenly, the mixture was placed in a microwave-ultrasound synergistic reaction device. The microwave power was controlled at 250 W and the ultrasonic power at 100 W. The reaction was carried out at 55 °C for 7 h to obtain the crosslinking reaction solution.

[0044] Step (4) Preparation of crude product solution: Slowly add 8% sodium hydroxide solution to the cross-linking reaction solution, adjust the pH of the system to neutral, stir the reaction for 12 min to obtain crude product solution;

[0045] Step (5) Post-processing: The crude product liquid is filtered, the filter cake is collected, and washed three times with anhydrous ethanol to remove residual solvent and impurities, so as to obtain the cross-linked carboxymethyl cellulose sodium product.

[0046] Example 3

[0047] Preparation of disulfide-based crosslinking agent

[0048] Dimethyl sulfoxide and 3-mercapto-1,2-propanediol were mixed in a mass ratio of 10.8:5.64 and dissolved completely in a reaction flask. The mixture was heated to 90°C in an oil bath and stirred for 12 hours. After the reaction system cooled to room temperature, it was precipitated three times with 50 times its volume of dichloromethane. The resulting solid was dried under vacuum at 50°C to obtain the disulfide crosslinking agent.

[0049] Preparation of cross-linked carboxymethyl cellulose sodium

[0050] Step (1) Raw material pretreatment: By weight, take 100 parts of sodium carboxymethyl cellulose and add them to 400 parts of ethanol-water mixed solvent (ethanol to water volume ratio 2.5:1), stir and disperse for 25 min to obtain sodium carboxymethyl cellulose dispersion;

[0051] Step (2) Catalytic activation: Add 5 parts of phosphoric acid catalyst to the dispersion and stir at room temperature for 40 min to obtain the activated solution;

[0052] Step (3) Microwave-ultrasound synergistic crosslinking: 15 parts of the composite crosslinking system (disulfide crosslinking agent to epichlorohydrin mass ratio 2.0:1) are added dropwise to the activation solution at a rate of 1.0 mL / min. During the dropwise addition, the stirring speed is maintained at 500 r / min. After stirring evenly, the mixture is placed in a microwave-ultrasound synergistic reaction device. The microwave power is controlled at 300 W and the ultrasonic power at 120 W. The reaction is carried out at 60 °C for 8 h to obtain the crosslinking reaction solution.

[0053] Step (4) Preparation of crude product solution: Slowly add 10% sodium hydroxide solution by mass to the cross-linking reaction solution, adjust the pH of the system to neutral, stir the reaction for 15 min, and obtain crude product solution;

[0054] Step (5) Post-processing: The crude product liquid is filtered, the filter cake is collected, and washed 4 times with anhydrous ethanol to remove residual solvent and impurities, and cross-linked carboxymethyl cellulose sodium product is obtained.

[0055] Comparative Example 1

[0056] The composite crosslinking system was replaced with 15 parts epichlorohydrin (without disulfide crosslinking agent), and the remaining steps and parameters were the same as in Example 3.

[0057] Comparative Example 2

[0058] In the composite crosslinking system, the mass ratio of disulfide crosslinking agent to epichlorohydrin is 1.0:1 (lower than 1.2~2.0:1), and the rest is the same as in Example 3.

[0059] Comparative Example 3

[0060] Preparation of disulfide-based crosslinking agent: Same as step 1 in Example 3;

[0061] Preparation of cross-linked carboxymethyl cellulose sodium

[0062] Steps (1)-(2): Same as steps (1)-(2) in Example 3;

[0063] Step (3) Crosslinking reaction: Add 15 parts of the composite crosslinking system (ratio 2.0:1) to the activation solution at a rate of 1.0 mL / min, stir at 500 r / min, place in a conventional water bath (without microwave-ultrasound), react at 60℃ for 8 h to obtain the crosslinking reaction solution;

[0064] Steps (4)-(5): Same as steps (4)-(5) in Example 3.

[0065] Comparative Example 4

[0066] The amount of phosphoric acid catalyst used is 1 part (less than 2 to 5 parts), and the rest is the same as in Example 3.

[0067] Comparative Example 5

[0068] In step (3), the dropping rate of the composite crosslinking system is 1.5 mL / min (higher than 0.5~1.0 mL / min), and the rest is the same as in Example 3.

[0069] Comparative Example 6

[0070] In step (3), the crosslinking reaction temperature is 75℃ (higher than 50~60℃), and the rest is the same as in Example 3.

[0071] Sedimentation volume (reflecting swelling performance): Accurately weigh 1.0 g of dried sample and place it in a 100 mL stoppered graduated cylinder. Add distilled water to the mark, shake vigorously for 2 min to fully disperse the sample, and let it stand for 1 h. Then, read the volume (mL) of the sediment. The larger the sedimentation volume, the higher the water absorption and swelling ratio of the sample.

[0072] Viscosity determination: A 1% (w / w) aqueous solution of the sample was prepared, and its viscosity (mPas) was measured using an NDJ-79 rotational viscometer under constant temperature conditions of 25°C. Viscosity reflects the strength of the cross-linked network and the retention of molecular weight.

[0073] Transmittance determination (reflecting uniformity and impurity content): Prepare a 0.5% (w / w) sample aqueous solution, allow it to stand to defoam, and use distilled water as a blank control. Measure the transmittance (%) at 550 nm using a UV-Vis spectrophotometer. Higher transmittance indicates more uniform substitution and fewer unreacted fibers and impurities.

[0074] Substitution degree (DS) uniformity deviation: The degree of substitution was measured at different sampling points (5 points) of the same sample using the ashing titration method, and the relative standard deviation (RSD) was calculated. The smaller the RSD value, the more uniform the reaction and the more stable the product quality.

[0075] Table 1: Performance Tests

[0076] Group Sedimentation volume (mL / g) Viscosity (1% aqueous solution, mPas) Light transmittance (%) Replacement uniformity deviation (RSD, %) Example 1 38.5 850 92.5 1.8 Example 2 45.2 980 94.8 1.5 Example 3 52.6 1150 96.5 1.1 Comparative Example 1 22.4 420 81.2 4.5 Comparative Example 2 35.8 760 88.5 2.8 Comparative Example 3 31.5 620 75.4 6.2 Comparative Example 4 28.6 510 83.6 3.5 Comparative Example 5 33.2 680 85.1 4.1 Comparative Example 6 25.4 380 78.9 2.5

[0077] As shown in Table 1, in Comparative Example 1, the single crosslinking agent resulted in a simple network structure. Without the disulfide crosslinking agent, the double crosslinking network described in this invention could not be constructed by relying solely on the etherification reaction of epichlorohydrin. The single crosslinking network structure was relatively loose and had low crosslinking efficiency, resulting in significantly insufficient swelling capacity (settling volume) and gel strength (viscosity) of the product in water.

[0078] Comparative Example 2: The composite crosslinking ratio was unbalanced, and the content of disulfide crosslinking agent was insufficient, resulting in insufficient hydrogen bond network. The synergistic enhancement effect of the double crosslinking network could not be fully utilized, and the stability of the network was not as good as in Example 3, thus affecting the swelling performance and viscosity.

[0079] Comparative Example 3: Lack of microwave-ultrasound synergy resulted in uneven reaction. The lack of uniform internal heating from microwaves and cavitation effect from ultrasound (breaking up agglomerates and accelerating diffusion) led to a large local concentration gradient in the reaction system and extremely uneven cross-linking reaction. Uneven reaction resulted in the appearance of unreacted raw materials or over-cross-linked agglomerates in some areas, which seriously affected the light transmittance and substitution uniformity of the product (increased RSD).

[0080] Comparative Example 4: Insufficient catalyst and low activation level. The role of phosphoric acid catalyst is to activate the active sites on the sodium carboxymethyl cellulose molecular chain and reduce the activation energy of the reaction. Insufficient catalyst leads to incomplete activation of raw materials, low degree of cross-linking reaction, and inability to form a dense and effective gel network. Therefore, macroscopically, this is manifested as a decrease in viscosity and swelling capacity.

[0081] Comparative Example 5: Excessive dropping speed led to localized cross-linking. The excessively rapid dropping caused the cross-linking agent to reach an excessively high local concentration upon contact, resulting in an insufficient time for dispersion before the reaction occurred. This resulted in excessive cross-linking in some areas (generating insoluble microparticles) while other areas experienced insufficient cross-linking. This directly led to poor product uniformity.

[0082] Comparative Example 6: Excessive reaction temperature leads to molecular chain degradation. Cellulose derivatives are prone to glycosidic bond breakage (degradation) at high temperatures. A temperature of 70℃ may cause degradation of the sodium carboxymethyl cellulose backbone, resulting in a significant decrease in molecular weight and severely damaging the strength of the gel network, leading to a sharp drop in viscosity. Simultaneously, increased side reactions may also affect light transmittance.

[0083] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0085] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A cross-linked sodium carboxymethyl cellulose, characterized in that, It is made from sodium carboxymethyl cellulose as raw material and cross-linked using a disulfide-based cross-linking agent-epoxychloropropane composite cross-linking system; In the composite crosslinking system, the mass ratio of disulfide-based crosslinking agent to epichlorohydrin is (1.2~2.0):1; The preparation method of the disulfide-based crosslinking agent is as follows: Dimethyl sulfoxide and 3-mercapto-1,2-propanediol are mixed and fully dissolved in a reaction flask, heated to 85-90°C in an oil bath, and stirred for 10-12 hours. After the reaction system is cooled to room temperature, it is precipitated 2-3 times with 45-50 times the volume of dichloromethane. The resulting solid is dried under vacuum at 45-50°C to obtain the disulfide-based crosslinking agent.

2. The cross-linked carboxymethyl cellulose sodium according to claim 1, characterized in that, The mass ratio of dimethyl sulfoxide to 3-mercapto-1,2-propanediol is (10.4-10.8):(5.2-5.64).

3. A method for preparing cross-linked carboxymethyl cellulose sodium as described in any one of claims 1-2, characterized in that, Includes the following steps: Step (1), raw material pretreatment: by weight, take 100 parts of sodium carboxymethyl cellulose and add them to 300-400 parts of ethanol-water mixed solvent, stir and disperse for 15-25 minutes to obtain sodium carboxymethyl cellulose dispersion; Step (2), catalytic activation: Add 2-5 parts of phosphoric acid catalyst to the dispersion obtained in step (1), stir and activate at room temperature to obtain an activated solution; Step (3), microwave-ultrasound synergistic crosslinking: slowly add 8-15 parts of the composite crosslinking system to the activation solution obtained in step (2), stir evenly, place it in a microwave-ultrasound synergistic reaction device, control the microwave power to be 200-300W and the ultrasonic power to be 80-120W, react at 50-60℃ for 6-8h to obtain the crosslinking reaction solution; Step (4), preparation of crude product solution: Add alkaline adjustment solution slowly to the crosslinking reaction solution obtained in step (3) to adjust the pH of the system to neutral, stir the reaction for 10~15 min to obtain crude product solution; Step (5), post-processing: The crude liquid obtained in step (4) is filtered, the filter cake is collected, and washed with anhydrous ethanol to remove residual solvent and impurities, so as to obtain the cross-linked carboxymethyl cellulose sodium product.

4. The method for preparing cross-linked carboxymethyl cellulose sodium according to claim 3, characterized in that, In step (1), the volume ratio of ethanol to water in the ethanol-water mixed solvent is (1.5~2.5):

1.

5. The method for preparing cross-linked carboxymethyl cellulose sodium according to claim 3, characterized in that, In step (2), the stirring activation time is 30~40 min.

6. The method for preparing cross-linked carboxymethyl cellulose sodium according to claim 2, characterized in that, In step (3), the composite crosslinking system is added by dripping at a rate of 0.5 to 1.0 mL / min, and the stirring speed is maintained at 300 to 500 r / min during the dripping process.

7. The method for preparing cross-linked carboxymethyl cellulose sodium according to claim 3, characterized in that, In step (4), the alkaline conditioning solution is a sodium hydroxide solution with a mass fraction of 5-10%.

8. The method for preparing cross-linked carboxymethyl cellulose sodium according to claim 3, characterized in that, In step (5), the anhydrous ethanol washing is performed 3 to 4 times.