Preparation method and application of water-absorbent resin with controllable water retention capacity

Abstract

The invention relates to the technical field of high polymer materials, and particularly discloses a preparation method and application of water-absorbent resin with controllable water retention capacity, the preparation method of the water-absorbent resin combines a reversed-phase suspension polymerization method and a solution polymerization method to obtain particles with small particle size difference, and through specific selection of reaction monomers and introduction of temperature-sensitive monomers, the water-absorbent resin with controllable water retention capacity is prepared. When the self-heating body is heated, the water-absorbent resin tends to interact with water molecules to form hydrogen bonds and show hydrophilicity at a lower temperature, and when the self-heating body is heated, polymer chains of the water-absorbent resin tend to be gathered and curled and show hydrophobicity, namely, an electrolyte solution is released, so that the water-retaining capacity is controllable.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a preparation method and application of a water-absorbing resin with controllable water-retention capacity. Background Art

[0002] Water-absorbing resin is a macromolecular substance with a three-dimensional cross-linked network internal structure formed by the polymerization of monomer molecules. It carries a large number of hydrophilic groups and can absorb water tens to thousands of times more than its own mass, and has excellent water retention. According to the different synthetic raw materials, water-absorbing resins are mainly divided into starch-based, cellulose-based, synthetic polymer-based and other naturally derived polymers; they are widely used in agriculture, industry, medical treatment, daily life and environmental protection. For example, patent CN113667061B provides a water-absorbing resin with excellent water retention and a preparation method thereof, wherein the polymerized monomers are selected from acrylic acid and / or acrylamide. On this basis, the hydration product obtained by the gel activity of volcanic ash active materials fills the gaps left after the water-absorbing resin loses water, which can effectively reduce the reduction of concrete strength. For example, patent CN113943393B uses rice particles as a cross-linking agent, introduces cationic monomers as counterions, and adjusts the neutralization degree of anionic monomers and the ion type of water-absorbing resin by a neutralizer, thereby obtaining a potassium ion-based polymer water-absorbing resin with good water absorption and salt resistance, aiming to solve the problem that sodium ion-based water-absorbing resins are easy to cause soil compaction when used as agricultural water-retaining agents.

[0003] The above-mentioned water-absorbing resins have all been improved to better adapt to their application range. However, once the water-absorbing resin obtained by the prior art absorbs water and swells into a hydrogel, it is difficult to separate the water even under pressure. In the field of self-heating elements, based on the principle of the primary battery reaction, the heat generation requires electrolytes. The water-absorbing resin is mainly used to absorb and release electrolytes to ensure the normal progress of the primary battery reaction. However, when the water retention of the water-absorbing resin is too high, the electrolyte release is limited, resulting in the temperature rise rate of the self-heating element being affected.

[0004] Therefore, the present invention provides a water-absorbing resin having good salt tolerance and controlled water retention capacity. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention obtains a water-absorbing resin with small particle size difference by optimizing the reaction process, and through the specific selection of reaction monomers and the introduction of temperature-sensitive monomers, the water-absorbing resin tends to interact with water molecules to form hydrogen bonds at a relatively low temperature, showing hydrophilicity, and when the self-heating body heats up, the polymer chains of the water-absorbing resin tend to aggregate and curl up, showing hydrophobicity, that is, releasing electrolyte solution, thereby achieving controllable water retention capacity.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention provides a method for preparing a water-absorbing resin with controllable water-retention capacity, which specifically comprises the following steps:

[0008] S1, stirring and dissolving the dispersant, the temperature-sensitive monomer and the alkane to obtain a reaction base liquid;

[0009] S2, stirring acrylic acid and 20-40 wt% sodium hydroxide solution at -5-5°C until the solution is clear to obtain an acrylic acid neutralization solution;

[0010] S3, at room temperature, dissolving acrylamide, N,N-methylenebisacrylamide and potassium persulfate in water to obtain acrylamide solution, N,N-methylenebisacrylamide solution and potassium persulfate solution, respectively, and mixing the three solutions with the acrylic acid neutralization solution obtained in S2 to obtain an aqueous phase;

[0011] S4. Add the aqueous phase obtained in S3 to the reaction base liquid in S1, stir at 30-60°C for 1-3h, then heat to 60-90°C at a rate of 3-8°C / h, continue stirring for 1-4h, wash, vacuum dry to constant weight, crush and sieve to obtain a water-absorbing resin.

[0012] When the water-absorbing resin of the present invention is used in a self-heating body, it needs to be mixed with active metal powder, conductive agent, adhesive and other materials and then pressed to obtain a membrane, and then an electrolyte solution is placed on the membrane and packaged. When used, the outer packaging is destroyed to cause an oxidation reaction between oxygen and active metal powder, thereby generating heat. When the temperature reaches above body temperature, the water-absorbing resin will slowly release steam.

[0013] The water-absorbing resin obtained by the present invention has small differences in particle sizes, and the mixing uniformity will not be low due to different mixing speeds of particles with different particle sizes during the mixing stage, so that the water-absorbing resin is evenly distributed in the self-heating membrane, and then the electrolyte absorbed subsequently is also evenly distributed; the polymerization monomers thereof include a temperature-sensitive monomer, acrylamide and acrylic acid, the cross-linking agent is N,N-methylenebisacrylamide, the initiator is potassium persulfate, and the molecular chain contains hydrophilic hydroxyl groups, anionic groups and amide groups through polymerization, and has good water absorption.

[0014] The preparation steps combine the reverse suspension polymerization method and the solution polymerization method. In the present invention, the solution polymerization method is specifically embodied in that the monomer, the initiator and the cross-linking agent are all dissolved in a suitable solvent. The advantages of this method are that the polymerization system has low viscosity, easy heat transfer and can avoid local overheating; the reverse suspension polymerization method is specifically manifested in that the water phase is dispersed and suspended in the reaction bottom liquid under the action of a dispersant and stirring to carry out polymerization. On the one hand, it alleviates the problems of low conversion rate, slow polymerization rate and easy formation of blocky polymers causing difficulty in discharging in the solution polymerization method; on the other hand, suspended particles with a narrow particle size distribution are obtained.

[0015] In some embodiments, in step S1 , the dispersant comprises Span 60 and / or Span 85 .

[0016] Preferably, the dispersant comprises Span 60 and Span 85.

[0017] Span 60 can work better in water-in-oil formulations due to its higher HLB value, while Span 85 performs well in reaction base liquids due to its low HLB value and good solubility. This combination can provide better dispersion performance in applications that require emulsification capabilities of both the oil phase (reaction base liquid) and the water phase.

[0018] In some embodiments, in step S1, the preparation steps of the temperature-sensitive monomer are as follows:

[0019] Dissolve maleic anhydride in acetone, add isopropylamine and stir for 1 to 4 hours. After the reaction is completed, rotary evaporate and recrystallize to obtain a thermosensitive monomer.

[0020] In some embodiments, the molar ratio of maleic anhydride to isopropylamine is 1:(1.0-1.5).

[0021] The hydrophilic groups such as amide groups on the polymer chain of the water-absorbing resin provided by the present invention tend to interact with water molecules to form hydrogen bonds at relatively low temperatures, showing hydrophilicity; when the temperature of the self-heating body reaches above body temperature, the hydrogen bonding effect weakens, and the hydrophobic isopropyl group begins to dominate, causing the polymer chain to tend to aggregate and curl up, showing hydrophobicity, that is, releasing the electrolyte solution, and prolonging the self-heating time.

[0022] In some embodiments, in step S2, the mass ratio of the acrylic acid to the sodium hydroxide solution is 1:(0.2-2.8).

[0023] In the present invention, acrylic acid is neutralized by sodium hydroxide solution, so that a large number of sodium carboxylate groups are contained in the molecular network of the water-absorbing resin, which provides hydrophilic anionic groups on the one hand; on the other hand, after contacting with the electrolyte, the water molecules in the liquid first gradually penetrate from the surface to the internal cross-linked network through capillary action, and the sodium carboxylate ionizes a large number of Na + , and then the resin reaches its maximum water absorption rate through osmotic pressure; finally, when the water-absorbing resin releases water as the temperature rises, the water also flows out to form the electrolyte solution required for the self-heating body.

[0024] In some embodiments, in step S1, the molar ratio of the temperature-sensitive monomer to the acrylic acid in step S2 is 1:(1-3).

[0025] In some embodiments, in step S3, the molar ratio of acrylamide to acrylic acid in step S2 is (0.5-2.5):1.

[0026] The present invention controls the usage ratio of the reaction monomers and regulates the content of the related groups so as to exert the function of the water-absorbing resin.

[0027] In some embodiments, in step S3, the concentrations of the acrylamide solution, the N,N-methylenebisacrylamide solution and the potassium persulfate solution are 5-30 wt%, 5-20 wt% and 0.1-2.0 wt%, respectively.

[0028] Preferably, the concentrations of the acrylamide solution, N,N-methylenebisacrylamide solution and potassium persulfate solution are 20wt%, 10wt% and 1wt% respectively.

[0029] In some embodiments, in step S4, the particle size of the water absorbing resin is 100-300 meshes.

[0030] The second aspect of the present invention provides the use of the water-absorbing resin with controllable water-retention capacity obtained by the above preparation method in a self-heating body, and the steps are as follows:

[0031] Active metal powder, conductive agent, binder, absorbent resin and filler are mixed and pressed to obtain a membrane. Electrolyte solution is placed on the membrane, first put into an inner bag made of non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrapped with an oxygen-isolating plastic outer bag to obtain a self-heating body.

[0032] In some embodiments, the electrolyte solution is a 2-50 wt % sodium chloride solution.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The invention provides a water-absorbing resin with small particle size difference and suitable for a self-heating body. By specifically selecting a reaction monomer and introducing a temperature-sensitive monomer, the water-absorbing resin tends to interact with water molecules to form hydrogen bonds at a relatively low temperature, showing hydrophilicity. When the temperature of the self-heating body rises, the hydrogen bonding effect weakens, and the hydrophobic isopropyl group begins to dominate, so that the polymer chains of the water-absorbing resin tend to aggregate and curl, showing hydrophobicity, that is, releasing water, thereby achieving controllable water retention capacity. In addition, the water-absorbing resin combines a reverse suspension polymerization method and a solution polymerization method during preparation, so that heat transfer is easy, reaction is uniform, conversion rate is high, polymerization rate is fast, and material discharging is simple. DETAILED DESCRIPTION

[0035] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0036] It is worth noting that the raw materials used in the following preparation examples and embodiments, unless otherwise specified, can be obtained from any commercially available manufacturer.

[0037] Preparation Example

[0038] The preparation steps of the thermosensitive monomer are as follows:

[0039] Dissolve 1 mol of maleic anhydride in 1 L of acetone, add 1.2 mol of isopropylamine and stir for 3 hours. After the reaction is completed, rotary evaporation and recrystallization with acetone are performed to obtain a thermosensitive monomer.

[0040] Example 1

[0041] A method for preparing a water-absorbing resin with controllable water-retention capacity, specifically comprising the following steps:

[0042] S1, 0.3 mol of Span 60, 0.2 mol of Span 85, 2 mol of the temperature-sensitive monomer and 5 L of cyclopentane were stirred and dissolved to obtain a reaction base solution;

[0043] S2. At 0° C., 5 mol of acrylic acid and 30 wt % of sodium hydroxide solution are stirred until the solution becomes clear, to obtain an acrylic acid neutralization solution, wherein the mass ratio of acrylic acid to sodium hydroxide solution is 1:1.8;

[0044] S3, at room temperature, dissolving 5 mol acrylamide, 0.012 mol N,N-methylenebisacrylamide and 0.012 mol potassium persulfate in water to obtain 20 wt% acrylamide solution, 10 wt% N,N-methylenebisacrylamide solution and 1 wt% potassium persulfate solution, respectively, and mixing the three solutions with the acrylic acid neutralization solution obtained in S2 to obtain an aqueous phase;

[0045] S4. Add the aqueous phase obtained in S3 to the reaction base liquid in S1, stir at 50°C for 2h, then heat to 70°C at a rate of 5°C / h, continue stirring for 3h, wash with anhydrous ethanol, dry under vacuum at 60°C to constant weight, crush, and pass through a 100-mesh sieve to obtain a water-absorbing resin.

[0046] Example 2

[0047] A method for preparing a water-absorbing resin with controllable water-retention capacity, specifically comprising the following steps:

[0048] S1, 0.3 mol of Span 60, 0.2 mol of Span 85, 2 mol of the temperature-sensitive monomer and 5 L of cyclopentane were stirred and dissolved to obtain a reaction base solution;

[0049] S2. Stir 2 mol of acrylic acid and 20 wt % of sodium hydroxide solution at 5° C. until the solution is clear, to obtain an acrylic acid neutralization solution, wherein the mass ratio of acrylic acid to sodium hydroxide solution is 1:1.8;

[0050] S3, at room temperature, dissolving 1 mol of acrylamide, 0.005 mol of N,N-methylenebisacrylamide and 0.005 mol of potassium persulfate in water to obtain 5 wt% acrylamide solution, 5 wt% N,N-methylenebisacrylamide solution and 0.1 wt% potassium persulfate solution, respectively, and mixing the three solutions with the acrylic acid neutralization solution obtained in S2 to obtain an aqueous phase;

[0051] S4. Add the aqueous phase obtained in S3 to the reaction base liquid in S1, stir at 60°C for 1 hour, then heat to 90°C at a rate of 5°C / h, continue stirring for 1 hour, wash with anhydrous ethanol, vacuum dry at 60°C to constant weight, crush, and pass through a 100-mesh sieve to obtain a water-absorbing resin.

[0052] Example 3

[0053] A method for preparing a water-absorbing resin with controllable water-retention capacity specifically comprises the following steps:

[0054] S1, 0.3 mol of Span 60, 0.2 mol of Span 85, 2 mol of the temperature-sensitive monomer and 5 L of cyclopentane were stirred and dissolved to obtain a reaction base solution;

[0055] S2. At -5°C, 6 mol of acrylic acid and 40 wt% of sodium hydroxide solution are stirred until the solution is clear to obtain an acrylic acid neutralization solution, wherein the mass ratio of acrylic acid to sodium hydroxide solution is 1:1.8;

[0056] S3, at room temperature, dissolving 15 mol acrylamide, 0.03 mol N,N-methylenebisacrylamide and 0.03 mol potassium persulfate in water to obtain 30 wt% acrylamide solution, 20 wt% N,N-methylenebisacrylamide solution and 2.0 wt% potassium persulfate solution, respectively, and mixing the three solutions with the acrylic acid neutralization solution obtained in S2 to obtain an aqueous phase;

[0057] S4. Add the aqueous phase obtained in S3 to the reaction base liquid in S1, stir at 30°C for 3 hours, then heat to 60°C at a rate of 5°C / h, continue stirring for 4 hours, wash with anhydrous ethanol, vacuum dry at 60°C to constant weight, crush, and pass through a 100-mesh sieve to obtain a water-absorbing resin.

[0058] Example 4

[0059] This embodiment provides a method for preparing a water-absorbing resin with controllable water-retention capacity. The specific implementation method is the same as that of Example 1, except that in step S1, the amount of the temperature-sensitive monomer used is 5.1 mol.

[0060] Example 5

[0061] This embodiment provides a method for preparing a water-absorbing resin with controllable water-retention capacity. The specific implementation method is the same as that of Example 1, except that in step S1, the amount of the temperature-sensitive monomer used is 1.6 mol.

[0062] Example 6

[0063] This embodiment provides a method for preparing a water-absorbing resin with controllable water-retention capacity. The specific implementation method is the same as that of Example 1, except that in step S3, the amount of acrylamide used is 1.4 mol.

[0064] Example 7

[0065] This embodiment provides a method for preparing a water-absorbing resin with controllable water-retention capacity. The specific implementation method is the same as that of Example 1, except that in step S3, the amount of acrylamide used is 13 mol.

[0066] Example 8

[0067] This embodiment provides a method for preparing a water-absorbing resin with controllable water-retention capacity. The specific implementation method is the same as that of Embodiment 1, except that:

[0068] S1. Stir and dissolve 0.5 mol of Span 60, 2 mol of the thermosensitive monomer and 5 L of cyclopentane to obtain a reaction base solution.

[0069] Example 9

[0070] This embodiment provides a method for preparing a water-absorbing resin with controllable water-retention capacity. The specific implementation method is the same as that of Embodiment 1, except that:

[0071] S1. Stir and dissolve 0.5 mol of Span 85, 2 mol of the thermosensitive monomer and 5 L of cyclopentane to obtain a reaction base solution.

[0072] Comparative Example 1

[0073] This comparative example provides a method for preparing a water-absorbing resin with controllable water-retention capacity. The specific implementation method is the same as that of Example 1, except that:

[0074] S1. Stir and dissolve 0.3 mol of Span 60 and 0.2 mol of Span 85 with 5 L of cyclopentane to obtain a reaction base solution.

[0075] Performance Testing:

[0076] 1. Water absorption test:

[0077] 0.50 g of the water-absorbent resin provided in Examples 1 to 7 and Comparative Example 1 was taken and put into a 200-mesh nylon mesh bag, and the total mass m1 of the nylon mesh bag and the water-absorbent resin before liquid absorption was weighed. The mesh bag was soaked in tap water and a 30 wt% sodium chloride solution, respectively. After soaking for 2 hours, the nylon mesh bag was taken out and hung for 15 minutes until the mesh bag stopped dripping water, and then the mass of the nylon mesh bag after liquid absorption and the total mass m2 of the water-absorbent resin were weighed; liquid absorption rate = [(m2-m1) / 0.5]×100%.

[0078] 2. Water release capacity test

[0079] Take 0.50g of resin and obtain the water-absorbed resin in the same performance test 1. Place the water-absorbed resin on a 50-mesh filter and suspend it in air at 40°C and room temperature. Since the volume of the water-absorbent resin will decrease after releasing water, record the time when the resin starts to fall. 30 minutes is the time recording node. If it exceeds 12 hours, it is recorded as NO.

[0080] The results are shown in Table 1.

[0081] Table 1 Performance test results

[0082]

[0083] It can be seen from the data in Table 1 that the water-absorbent resins of Examples 1 to 3 have good liquid absorption rates for both water and salt solutions, and exhibit different water-releasing effects at room temperature and 40° C., indicating that the water-absorbent resins of the present invention have good salt resistance and controlled water retention capacity.

[0084] Compared with Example 1, Examples 4 to 7 change the dosage ratio of the polymerized monomers in the water-absorbing resin, wherein Examples 4 to 5 change the dosage of the thermosensitive monomer, thereby affecting the content of the hydrophobic group, and further affecting the water absorption and release functions of the water-absorbing resin; Examples 6 to 7 change the dosage of acrylamide, which also affects the water absorption and release functions of the water-absorbing resin.

[0085] Combining the examples and examples 8 to 9, it can be seen that the use of a single dispersant will reduce the salt resistance of the water-absorbing resin to a certain extent. The possible reason is that the composite dispersant will promote the formation of suspended particles with a narrow particle size distribution, facilitate the uniform formation of a semi-interpenetrating network structure with PVA, and enhance the absorption of the electrolyte solution.

[0086] Compared with Example 1, Comparative Example 1 does not introduce a temperature-sensitive monomer. As can be seen from the water release time at room temperature and 40° C., this makes it impossible to control the release of the absorbed water.

[0087] The embodiments and comparative examples described above do not impose any form of limitation on the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a water-absorbing resin with controllable water-retention capacity, characterized in that: The specific steps include: S1, stirring and dissolving the dispersant, the temperature-sensitive monomer and the alkane to obtain a reaction base liquid; S2, stirring acrylic acid and 20-40 wt% sodium hydroxide solution at -5-5°C until the solution is clear to obtain an acrylic acid neutralization solution; S3, at room temperature, dissolving acrylamide, N,N-methylenebisacrylamide and potassium persulfate in water to obtain acrylamide solution, N,N-methylenebisacrylamide solution and potassium persulfate solution, respectively, and mixing the three solutions with the acrylic acid neutralization solution obtained in S2 to obtain an aqueous phase; S4. Add the aqueous phase obtained in S3 to the reaction base liquid in S1, stir at 30-60°C for 1-3h, then heat to 60-90°C at a rate of 3-8°C / h, continue stirring for 1-4h, wash, vacuum dry to constant weight, crush and sieve to obtain a water-absorbing resin.

2. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 1, characterized in that: In step S1 , the dispersant includes Span 60 and / or Span 85 .

3. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 1, characterized in that: In step S1, the preparation steps of the temperature-sensitive monomer are as follows: Dissolve maleic anhydride in acetone, add isopropylamine and stir for 1 to 4 hours. After the reaction is completed, rotary evaporate and recrystallize to obtain a thermosensitive monomer.

4. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 3, characterized in that: The molar ratio of maleic anhydride to isopropylamine is 1:(1.0-1.5).

5. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 1, characterized in that: In step S2, the mass ratio of the acrylic acid to the sodium hydroxide solution is 1:(0.2-2.8).

6. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 1, characterized in that: In step S1, the molar ratio of the temperature-sensitive monomer to the acrylic acid in step S2 is 1:(1-3).

7. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 1, characterized in that: In step S3, the molar ratio of acrylamide to acrylic acid in step S2 is (0.5-2.5):

1.

8. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 1, characterized in that: In step S3, the concentrations of the acrylamide solution, the N,N-methylenebisacrylamide solution and the potassium persulfate solution are 5-30 wt%, 5-20 wt% and 0.1-2.0 wt% respectively.

9. The method for preparing a water-absorbing resin with controllable water-retention capacity according to claim 1, characterized in that: In step S4, the particle size of the water-absorbing resin is 100-300 meshes.

10. Use of a water-absorbing resin with controllable water-retention capacity obtained by the preparation method according to any one of claims 1 to 9 in a self-heating body, comprising the following steps: Active metal powder, conductive agent, binder, absorbent resin and filler are mixed and pressed to obtain a membrane. Electrolyte solution is placed on the membrane, first put into an inner bag made of non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrapped with an oxygen-isolating plastic outer bag to obtain a self-heating body.

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