Cationic superabsorbent and highly salt-resistant hydrogel and method for preparing the same

Abstract

The application discloses a cationic strong water-absorbing and high salt-resistant hydrogel and a preparation method thereof. The method comprises the following steps: under stirring, a monomer DMDAAC solution is firstly added into a reactor, and then an initiator, a crosslinking agent, a metal ion complexing agent and deionized water are added at one time; a programmed temperature rising is performed to add the reaction liquid in sections to initiate a polymerization reaction; the polymerization reaction is kept warm to perform a polymerization reaction and polymerization reaction curing; a PDMDAAC hydrogel gel product is obtained; and after granulation, the product is dried to obtain a PDMDAAC hydrogel solid particle. The PDMDAAC hydrogel prepared by the application has strong water-absorbing property and high salt resistance; the water-absorbing ratio is above 3800.00 g / g in deionized water under normal temperature conditions, the water-absorbing ratio is above 100.00 g / g in physiological saline, and the monomer conversion rate is 91.32%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation of cationic hydrogel, and relates to a cationic hydrogel with strong water absorption and high salt tolerance and a preparation method thereof. BACKGROUND

[0002] The hydrogel is a material composed of hydrophilic polymer chains and formed by physical crosslinking or chemical crosslinking. Due to the presence of highly hydrophilic functional groups in the molecular structure, the hydrogel has the function of absorbing several hundred times or even several thousand times of water of its own weight, and has very good water retention capacity. Even under pressure, it is not easy to dehydrate. According to the charge property of the polymer network, the hydrogel is roughly divided into electrolyte type and non-electrolyte type. Among them, according to the distribution of positive and negative charges in the crosslinked network structure, the electrolyte type hydrogel can be divided into cationic, anionic and zwitterionic hydrogels. For the cationic hydrogel, since it contains cationic groups in the network, it is not easy to be affected by metal ions such as Na + , Ca 2+ and Mg 2+ , so it has good salt tolerance.

[0003] Dimethyl Diallyl Ammonium Chloride (DMDAAC) as a multifunctional cationic monomer, due to its high positive charge density, good water solubility, good temperature resistance, low price and certain bactericidal effect, its related polymers are widely used as sewage flocculants, petroleum additives, modified adsorbents, antibacterial and bacteriostatic agents and other products. In recent years, researchers have applied it in the synthesis of hydrogel and made a series of explorations on its function. However, most of the related reports are only related to the synthesis of straight-chain and branched-chain polymers in terms of graft modification and copolymerization, and there are very few systematic studies on polydimethyl diallyl ammonium chloride (PDMDAAC) hydrogel. So far, the related literature reports are as follows.

[0004] Document 1 (Ren Jing, Zhang Yang, Yi Min, et al. Radiation polymerization and properties of dimethyl diallyl ammonium chloride [J]. Acta Chimica Sinica, 2002 (08): 1507-1512 + 1354.) uses radiation polymerization to prepare polydimethyl diallyl ammonium chloride (PDMDAAC) hydrogel with a water absorption ratio of about 38 g / g in distilled water and a monomer conversion rate of about 60%. The specific steps are: 1% (molar percentage of monomer) crosslinking agent N,N-methylene bisacrylamide (MBA) is added to a 50% DADMAC solution. After the crosslinking agent is fully dissolved, high-purity nitrogen is passed for 15 minutes to remove oxygen, and the opening is sealed. Then, gamma rays are used to initiate polymerization. After the radiation dose reaches 21 kGy, the gel is removed, cut into small columns of approximately the same height, and placed in a vacuum oven for drying at 50°C until the weight is constant. The water gel solid particles are obtained. The water absorption ratio of the hydrogel product synthesized in this document is low, and the monomer conversion rate is low.

[0005] Document 2 (Li Xiaoxiao, Chen Lin, Zheng Kang, et al. Preparation method of high relative molecular mass micro-crosslinked polydimethyl diallyl ammonium chloride [P]. Anhui Province: CN108239223A, 2018-07-08.) uses a two-step temperature rising aqueous solution polymerization method to synthesize high relative molecular mass micro-crosslinked polydimethyl diallyl ammonium chloride with a characteristic viscosity of 1.50 dL / g to 4.00 dL / g. The specific steps are: First, under constant temperature stirring, industrial cationic monomer dimethyl diallyl ammonium chloride is added with crosslinking agent tetraallyl ammonium chloride (TAAC), metal ion chelating agent sodium diethylenetriamine pentaacetate, and appropriate deionized water, and stirred uniformly to prepare the reaction solution. Then, after nitrogen is passed to remove oxygen, a composite initiator is added, and the stirring is continued. The uniformly stirred reaction solution is heated to 35°C to 50°C, and the stirring and nitrogen are stopped after the reaction system becomes sticky. The reaction is kept at temperature for 1h to 6h, and then the temperature is further increased to 55°C to 70°C for 2h to 24h of maturation reaction to obtain micro-crosslinked PDMDAAC soluble colloid product.

[0006] From the above, the following defects still exist in the research reports on PDMDAAC homopolymer hydrogel:

[0007] (1) So far, there have been very few reports on PDMDAAC homopolymer hydrogel both at home and abroad, and the water absorption ratio of the reported hydrogel in distilled water is only about 38 g / g, and the monomer conversion rate is only about 60%. Therefore, the water absorption ratio and monomer conversion rate of PDMDAAC homopolymer hydrogel need to be further improved.

[0008] (2) In the synthesis of hydrogel or micro-crosslinking product, one-step or two-step heating methods are usually used in the literature. The one-step heating method is not conducive to the continuous initiation of the initiator, and one-time initiation can easily cause "explosion", and further, due to the decrease of monomer and initiator concentration in the system in the subsequent reaction stage, it is difficult for the residual monomer to react completely, which is not conducive to improving the overall monomer conversion rate. If a hydrogel is formed, the network structure is simple due to the rapid formation and lack of sufficient winding, which is not conducive to locking the absorbed water. However, the two-step heating method has improved, but it still has problems such as incomplete polymerization of residual monomers, limited improvement of monomer conversion rate, and limited improvement of hydrogel water absorption performance. In addition, the micro-crosslinking product is not a water-absorbing resin. SUMMARY

[0009] The purpose of the present application is to prepare a cationic strong water-absorbing hydrogel with high salt resistance and a preparation method thereof.

[0010] The technical solution for achieving the purpose of the present application is:

[0011] The preparation method of the cationic strong water-absorbing hydrogel with high salt resistance comprises the following steps:

[0012] Industrial monomer dimethyl diallyl ammonium chloride (DMDAAC) is used as raw material, and under stirring conditions, monomer DMDAAC solution is first added to the reactor, and then initiator, crosslinking agent triallylamine (TAA), metal ion complexing agent and deionized water are added at one time, so that the mass fraction of the monomer is 64.0% to 68.0%, the initiator accounts for 0.25% to 0.45% of the mass fraction of the monomer, the reaction liquid is heated by programmed temperature rise, and the initiation polymerization reaction is carried out by sectional heating, and the polymerization reaction and the polymerization reaction curing are carried out by temperature respectively at 43.0℃ to 47.0℃, 50.0℃ to 54.0℃ and 70.0℃ to 80.0℃, to obtain PDMDAAC hydrogel colloidal product. After granulation, the product is dried to obtain PDMDAAC hydrogel solid particles.

[0013] Preferably, the solid content of the industrial monomer dimethyl diallyl ammonium chloride is 80.0% to 82.0%.

[0014] Preferably, the initiator is ammonium persulfate (APS), sodium persulfate (NaPS) or potassium persulfate (KPS).

[0015] Preferably, the mass fraction of the industrial monomer dimethyl diallyl ammonium chloride is 66.0% to 68.0%.

[0016] Preferably, the initiator accounts for 0.35% to 0.45% of the mass fraction of the monomer.

[0017] Preferably, the cross-linking agent triallylamine accounts for 0.05% to 0.15% of the monomer mass fraction, and more preferably 0.10% to 0.15%.

[0018] Preferably, the complexing agent accounts for 0.005% to 0.010% of the monomer mass fraction.

[0019] Preferably, the metal ion complexing agent is ethylenediaminetetraacetic acid tetrasodium (Na4EDTA) or ethylenediaminetetraacetic acid disodium (Na2EDTA).

[0020] Preferably, the holding, polymerization, and curing times are all (3.0 ± 0.1) h.

[0021] The present application also provides a PDMDAAC hydrogel prepared by the above preparation method.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) The present application uses triallylamine (TAA) as a cross-linking agent. On the one hand, triallylamine has less steric hindrance, and due to the presence of terminal double bonds, it is easy to connect monomers to form branches in long chains and bridge with another long chain during the cross-linking process, so the cross-linking efficiency is high. On the other hand, since the three branches of triallylamine can all be connected to the terminal double bonds of the branches in the long chain of the monomer, the grid structure of the hydrogel is three-dimensional, which is conducive to improving the water absorption capacity of the hydrogel. At the same time, TAA has a large solubility in water, which is 2.5 g / mL (at 20°C), and it can be easily and uniformly dispersed in the monomer solution system, which is conducive to the uniformity of the cross-linking process and the control of the cross-linking degree.

[0024] (2) The present application uses a three-step temperature rising method. During the reaction at the first and second stages, since the polymerization activity of the cross-linking agent triallylamine (TAA) is high, it participates in the polymerization process of the monomer DMDAAC to form macromolecular chains in the early stage of low-temperature polymerization, and a stable cross-linking structure with a large framework is formed first. In the second and third stages, when the temperature is subsequently raised, the cross-linking agent TAA has basically completely reacted. At this time, since the content of the monomer and the cross-linking agent has been reduced, the polymerization product gradually forms a micro-cross-linking structure with a small molecular weight or a short chain length, i.e., a small framework structure within the large framework, thereby simultaneously enhancing the water absorption (large framework) and water locking (small framework) capacity of the hydrogel and the strength after water absorption (small framework interpenetrating support in the large framework). In particular, in the third stage, i.e., the late stage of the reaction, the temperature is raised to promote the continuous initiation of the initiator and further consume the residual monomer in the system, thereby improving the monomer conversion rate.

[0025] (3) The synthetic hydrogel product has excellent water absorption and salt resistance. Under normal temperature conditions, the water absorption ratio in deionized water is 3800.00 g / g or more, and the water absorption ratio in physiological saline is 100.00 g / g or more. Compared with the highest level of water absorption ratio of PDMDAAC hydrogel in the literature, the improvement effect is more than 100 times. DETAILED DESCRIPTION

[0026] The application is further described below in combination with examples.

[0027] Examples 1-15

[0028] In the first step, a DMDAAC monomer aqueous solution with a solid content of 81.0% is fed into a polymerization reactor with a thermometer, stirring and nitrogen feeding device;

[0029] In the second step, a crosslinking agent triallylamine with a monomer mass fraction of a set value, a metal ion complexing agent tetrasodium ethylenediaminetetraacetate with a monomer mass fraction of a set value, and an initiator ammonium persulfate with a monomer mass fraction of a set value are added to the above aqueous solution, and deionized water is added to adjust the monomer starting mass fraction of the reaction solution to a set value. The addition amount of each component in the examples is shown in Table 1.

[0030] In the third step, after stirring for 20 min under a nitrogen atmosphere, the reaction solution is first heated to a set value to initiate polymerization. The first stage temperature T1 of each example is shown in Table 1. The polymerization time is (3.0±0.5) h.

[0031] In the fourth step, the reaction system is heated to a set value again. The second stage temperature T2 of each example is shown in Table 1. The polymerization time is (3.0±0.5) h.

[0032] In the fifth step, the reaction system is finally heated to a set value. The third stage temperature T3 of each example is shown in Table 1. After the polymerization time of (3.0±0.5) h, the heating is stopped.

[0033] In the sixth step, the PDMDAAC hydrogel product is cooled and discharged. After crushing and granulating, the PDMDAAC hydrogel solid particles are obtained after drying. The water absorption ratio in deionized water and physiological saline under normal temperature conditions, and the monomer conversion rate measured by bromination method are shown in Table 1.

[0034] Example 16

[0035] PDMDAAC hydrogel particles are synthesized by the same method as in Example 1, except that the complexing agent is disodium ethylenediaminetetraacetate. The related process conditions and characterization results are shown in Table 1.

[0036] Example 17

[0037] PDMDAAC hydrogel particles were synthesized by the same method as in Example 1, except that the initiator was potassium persulfate, and the related process conditions and characterization results are shown in Table 1.

[0038] Example 18

[0039] PDMDAAC hydrogel particles were synthesized by the same method as in Example 1, except that the initiator was potassium persulfate, and the related process conditions and characterization results are shown in Table 1.

[0040] Comparative Example 1

[0041] PDMDAAC hydrogel particles were synthesized by the same method as in Example 1, except that the monomer mass fraction was 60.0%, and the related process conditions and characterization results are shown in Table 1. The results show that when the monomer mass fraction is too low, the reaction activity of the reaction system is low, the monomer forms short polymer chains, and the structure of the product after crosslinking is loose and the strength is low, and the hydrogel cannot be formed effectively.

[0042] Comparative Example 2

[0043] PDMDAAC hydrogel particles were synthesized by the same method as in Example 1, except that the monomer mass fraction was 72.0%, and the related process conditions and characterization results are shown in Table 1. The results show that when the monomer mass fraction is too high, the reaction is too violent at the beginning, the system temperature rises rapidly, the monomer cannot be effectively polymerized, and a large amount of low molecular weight polymer chains are formed, and the structure of the product after crosslinking is loose and the strength is low, and the hydrogel cannot be formed effectively.

[0044] Comparative Example 3

[0045] PDMDAAC hydrogel particles were synthesized by the same method as in Example 1, except that the initiator accounted for 0.10% of the monomer mass fraction, and the related process conditions and characterization results are shown in Table 1. The results show that when the amount of initiator is too low, the initiation reaction activity of the crosslinking agent in the system is low, the monomer cannot form long polymer chains, and the structure of the product after crosslinking is loose and the strength is low, and the hydrogel cannot be formed effectively.

[0046] Comparative Example 4

[0047] The same method as in Example 1 was used to synthesize PDMDAAC hydrogel particles, except that the mass fraction of initiator to monomer was 0.60%, and the relevant process conditions and characterization results are shown in Table 1. The results show that when the amount of initiator is too high, the initiation reaction activity of the crosslinking agent in the system is too high, making the reaction too intense at the beginning, the temperature of the system rises rapidly, the monomer cannot effectively polymerize, a large amount of low molecular weight polymer chains are formed, and the structure of the product after crosslinking is loose and the strength is low, and the hydrogel cannot be effectively formed.

[0048] Table 1: Process conditions of each sample and corresponding characterization results

[0049]

Claims

1. A method for preparing a cationic, highly absorbent, and salt-resistant hydrogel, characterized in that, Includes the following steps: Using industrial monomer dimethyl diallyl ammonium chloride as raw material, under stirring conditions, a solution of dimethyl diallyl ammonium chloride monomer was first added to a reactor, followed by the addition of an initiator, a crosslinking agent, triallylamine, a metal ion complexing agent, and deionized water, to achieve a monomer mass fraction of 64.0%–68.0% and an initiator mass fraction of 0.25%–0.45%. The reaction solution was heated in stages using a programmed temperature rise to initiate the polymerization reaction. The polymerization reaction and maturation were carried out at temperatures of 43.0℃–47.0℃, 50.0℃–54.0℃, and 70.0℃–80.0℃, respectively, to obtain a PDMDAAC hydrogel product. After granulation, the product was dried to obtain PDMDAAC hydrogel solid particles.

2. The preparation method according to claim 1, characterized in that, The solid content of the industrial monomer dimethyl diallyl ammonium chloride is 80.0% to 82.0%.

3. The preparation method according to claim 1, characterized in that, The initiator is ammonium persulfate, sodium persulfate, or potassium persulfate.

4. The preparation method according to claim 1, characterized in that, The industrial monomer dimethyl diallyl ammonium chloride has a mass fraction of 66.0% to 68.0%.

5. The preparation method according to claim 1, characterized in that, The initiator accounts for 0.35% to 0.45% of the monomer mass fraction.

6. The preparation method according to claim 1, characterized in that, The crosslinking agent, triallylamine, accounts for 0.05% to 0.15% of the monomer mass fraction.

7. The preparation method according to claim 1, characterized in that, The crosslinking agent, triallylamine, accounts for 0.1% to 0.15% of the monomer mass fraction.

8. The preparation method according to claim 1, characterized in that, The metal ion complexing agent is tetrasodium ethylenediaminetetraacetate or disodium ethylenediaminetetraacetate, and the complexing agent accounts for 0.005% to 0.010% of the monomer mass fraction.

9. The preparation method according to claim 1, characterized in that, The heat preservation, polymerization, and curing times are all (3.0±0.1)h.

10. PDMDAAC hydrogel prepared by any one of the preparation methods according to claims 1 to 9.

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