High water-absorbing resin for concrete mixture and method for producing the same

Abstract

The application discloses a high water-absorbing resin for concrete mixture and a preparation method thereof. The product is a three-dimensional network formed by linear cyclic polycarboxylic acid crosslinking, and the linear cyclic polycarboxylic acid is composed of high-density carboxyl, cyclic lactone and polyethylene glycol vinyl ether random copolymerization. The preparation method comprises the following steps: dissolving acrylic acid or methacrylic acid, maleic acid, fumaric acid, 2-vinyl ether ethoxy acrylate compound and polyethylene glycol vinyl ether in an organic solvent to prepare a low-concentration monomer solution; adding an initiator to obtain linear cyclic polycarboxylic acid; adding polyether amine to obtain a micro-crosslinked cyclic polycarboxylic acid solution, and then drying to obtain a high water-absorbing resin powder for concrete mixture. The product has excellent water-absorbing capacity in a high-alkaline and high-salt ion concentration of a cement-based material, and can prevent the problem of failure of the high water-absorbing resin due to rapid water release during the concrete mixing and construction process. Meanwhile, the product can slowly release free water according to the humidity change of a hardened concrete matrix, so that a long-term internal curing effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a superabsorbent resin for concrete mixtures and its preparation method. Background Technology

[0002] To meet the demands of modern engineering, lightweight and high-strength concrete is a key direction in current concrete technology development. In practical engineering applications, reducing the water-cement ratio of concrete mixtures is often used to improve concrete strength. However, this reduction in water content can lead to insufficient curing, resulting in numerous curing defects and irreversible volume shrinkage, ultimately causing cracking and decreased durability. In recent years, the use of pre-absorbent polymers (SAPs) as internal curing agents has become a research hotspot in high-strength concrete.

[0003] In the prior art, Chinese patent CN111116088A discloses a special binder for self-curing permeable concrete and its application. This patented technology applies starch-based superabsorbent resin, cellulose-based superabsorbent resin, and synthetic polymer superabsorbent resin to the special binder for permeable concrete, achieving the dual functions of absorbing excess water and internal curing. Chinese patent CN108516866A discloses a method for preparing a modified superabsorbent resin internal curing agent. The specific implementation method is as follows: polyunsaturated aliphatic primary amine monomers, unsaturated ester monomers, and unsaturated polyoxyethylene ether macromonomers undergo free radical polymerization under the action of an initiator and a reducing agent. After the reaction is completed, modified sodium silicate and a dispersant are added to obtain the modified superabsorbent resin internal curing agent. Chinese patent CN102558574B discloses a method for surface modification of carboxyl-containing superabsorbent resin. The method uses monofunctional compounds as modifiers to perform surface modification treatment on carboxyl-containing superabsorbent resin. In particular, monofunctional compounds with long hydrophobic chains are used as modifiers to transform some hydrophilic structures on the surface of superabsorbent resin into hydrophobic structures, thereby reducing water diffusion channels and effectively reducing the liquid absorption rate of superabsorbent resin.

[0004] Although current technologies disclose the application effects of superabsorbent polymers (SAPs) in concrete technology, and can synthesize SAPs with high water absorption ratios and low liquid absorption rates, in actual use, due to the high salt and alkalinity conditions of concrete, the SAPs, after becoming saturated with water, will rapidly release water during the mixing process. This significantly reduces the internal curing effect and makes the plasticizing capacity of the concrete mixture uncontrollable, easily leading to problems such as sudden loss of plasticity and mid-process bleeding. Summary of the Invention

[0005] 1. The technical problem to be solved:

[0006] To address the aforementioned technical problems, this invention provides a superabsorbent polymer (SAP) for concrete mixes and its preparation method. This SAP possesses a three-dimensional network composed of linear cyclic polycarboxylic acid crosslinks, wherein the linear cyclic polycarboxylic acid is randomly copolymerized from high-density carboxyl groups, cyclic lactones, and polyethylene glycol ethylene ether. The high-density carboxyl groups and the three-dimensional network crosslinks endow the SAP with excellent water saturation capacity. Furthermore, the introduction of polycyclic lactones significantly increases the rigidity of the gel after water saturation, effectively resisting physical shear loss during mechanical mixing. On the other hand, in the high alkalinity and high salt ion concentration of cement-based materials, the ring-opening of the cyclic lactone releases carboxyl groups, resulting in a slower water release rate for the SAP. The polyethylene glycol structure in the molecular chain and the ethylene glycol released by the ring-opening of the cyclic lactone give the SAP better wetting properties at the interface with the concrete matrix, enabling rapid response to changes in humidity gradients.

[0007] 2. Technical Solution:

[0008] A superabsorbent resin for concrete mixtures, characterized in that it has a three-dimensional network composed of linear cyclic polycarboxylic acid crosslinking; the linear cyclic polycarboxylic acid is composed of high-density carboxyl groups, cyclic lactones, and polyethylene glycol ethylene ether in random copolymerization; its molecular structure is shown in Formula I:

[0009] (I)

[0010] In the above formula, R1 and R2 are both H atoms or methyl groups; x is an integer from 0 to 5, y is an integer from 1 to 20; n is an integer from 5 to 24; a is an integer from 1 to 5, b is an integer from 105 to 330, c is an integer from 150 to 300, d is an integer from 150 to 300, e is an integer from 1 to 5, and f is an integer from 50 to 300.

[0011] A method for preparing a superabsorbent polymer for concrete mixtures includes the following steps:

[0012] Step 1: Dissolve acrylic acid or methacrylic acid, maleic acid, fumaric acid, compound of formula II, and polyethylene glycol ethylene ether in an organic solvent to prepare a low-concentration monomer solution. Then add an initiator and react at 70~120℃ for 24h to obtain linear cyclic polycarboxylic acid.

[0013] (II);

[0014] In the above formula, R1 is a H atom or a methyl group;

[0015] Step 2: Add polyetheramine to the linear cyclic polycarboxylic acid and continue the reaction for 1 hour to obtain a micro-crosslinked cyclic polycarboxylic acid solution;

[0016] Step 3: The micro-crosslinked cyclic polycarboxylic acid solution is dried using a spray drying process to obtain superabsorbent resin powder for concrete mixtures.

[0017] Furthermore, the specific molecular structure of the polyethylene glycol ethylene ether is shown in Formula III.

[0018] (III);

[0019] In the above formula, n is an integer from 5 to 24.

[0020] Furthermore, the organic solvent is one or more of benzene, toluene, cyclohexane, xylene, chlorobenzene, dimethylformamide, and dimethyl sulfoxide.

[0021] Furthermore, in step one, a low-concentration monomer solution is prepared by fully dissolving the monomer, at which point the mass concentration of the low-concentration monomer solution is 5-20%.

[0022] Furthermore, the initiator is one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert-butyl peroxide.

[0023] Furthermore, the specific molecular structure of the polyetheramine in step two is shown in Formula IV:

[0024] (IV)

[0025] In the above formula, x is an integer from 0 to 5, and y is an integer from 1 to 20.

[0026] 3. Beneficial effects:

[0027] (1) The superabsorbent resin for concrete mixtures of the present invention uses maleic acid and fumaric acid as the main water-absorbing groups, which can obtain a higher carboxyl group density than ordinary polyacrylic acid, thereby having a higher water absorption ratio.

[0028] (2) The superabsorbent resin for concrete mixtures of the present invention uses polyamine and cyclic lactone, which can undergo a rapid cross-linking reaction to form a three-dimensional network structure, thereby further improving the water absorption saturation capacity of the superabsorbent resin for concrete mixtures of the present invention.

[0029] (3) In this preparation method, the diene monomer composed of ethylene ether / ethylene ester and the symmetrical monomer can be rapidly obtained by free radical polymerization at low reaction concentration. The introduction of polycyclic lactone greatly increases the rigidity of the gel after the superabsorbent resin for concrete mixture is saturated with water, effectively resisting physical shear water loss during mechanical stirring.

[0030] (4) When using the superabsorbent resin for concrete mixtures of this application, as the pH in the concrete mixture solution gradually increases, the ring-opening of the cyclic lactone will release carboxyl groups to resist the water release caused by the increase in pH and salt ion concentration, so that the superabsorbent resin for concrete mixtures can have a slower water release rate. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments.

[0032] Example 1

[0033] 10,000 parts of toluene were added to a reaction vessel equipped with a stirrer. Then, 353 parts of 2-vinyl ether ethoxymethacrylate, 318 parts of maleic acid, 250 parts of fumaric acid, 189 parts of polyethylene glycol ethylene ether with a molecular weight of 484, and 59 parts of methacrylic acid were added to the reaction vessel. After complete dissolution, 8.6 parts of azobisisobutyronitrile were added. The temperature was then raised to 85°C, and the reaction was carried out for 24 hours. Then, 1.9 parts of polyetheramine were added to the product, and the reaction was continued for another hour. Finally, the reaction product was spray-dried to prepare the target superabsorbent resin P-1 for concrete mixtures, with the following structural formula:

[0034]

[0035] Example 2

[0036] 10,000 parts of cyclohexane were added to a reaction vessel equipped with a stirrer. Then, 233 parts of 2-vinyl ether ethoxymethacrylate, 260 parts of maleic acid, 425 parts of fumaric acid, 13 parts of polyethylene glycol ethylene ether with a molecular weight of 968, and 64 parts of methacrylic acid were added to the reaction vessel. After complete dissolution, 10.4 parts of benzoyl peroxide were added. The temperature was then raised to 75°C, and the reaction was carried out for 24 hours. Then, 4.5 parts of polyetheramine were added to the product, and the reaction was continued for another hour. Finally, the reaction product was spray-dried to prepare the target superabsorbent resin P-2 for concrete mixtures, with the following structural formula:

[0037]

[0038] Example 3

[0039] 10,000 parts xylene were added to a reaction vessel equipped with a stirrer. Then, 262 parts 2-vinyl ether ethoxyacrylate, 288 parts maleic acid, 350 parts fumaric acid, 12 parts polyethylene glycol ethylene ether with a molecular weight of 264, and 85 parts acrylic acid were added to the reaction vessel. After complete dissolution, 7.4 parts benzoyl peroxide were added. The temperature was then raised to 95°C, and the reaction was carried out for 24 hours. Then, 2 parts polyetheramine were added to the product, and the reaction was continued for another hour. Finally, the reaction product was spray-dried to prepare the target superabsorbent resin P-3 for concrete mixtures, with the following structural formula:

[0040]

[0041] Example 4

[0042] 10,000 parts of dimethyl sulfoxide were added to a reaction vessel equipped with a stirrer. Then, 312 parts of 2-vinyl ether ethoxymethacrylate, 312 parts of maleic acid, 257 parts of fumaric acid, 49 parts of polyethylene glycol ethylene ether with a molecular weight of 880, and 57 parts of methacrylic acid were added to the reaction vessel. After complete dissolution, 8.2 parts of tert-butyl peroxide were added. The temperature was then raised to 100°C, and the reaction was carried out for 24 hours. Then, 13 parts of polyether amine were added to the product, and the reaction was continued for another hour. Finally, the reaction product was spray-dried to prepare the target superabsorbent resin P-4 for concrete mixtures, with the following structural formula:

[0043]

[0044] Example 5

[0045] 10,000 parts of dimethyl sulfoxide were added to a reaction vessel equipped with a stirrer. Then, 313 parts of 2-vinyl ether ethoxyacrylate, 217 parts of maleic acid, 307 parts of fumaric acid, 15 parts of polyethylene glycol ethylene ether with a molecular weight of 440, and 133 parts of methacrylic acid were added to the reaction vessel. After complete dissolution, 10.5 parts of tert-butyl peroxide were added. The temperature was then raised to 80°C, and the reaction was carried out for 24 hours. Then, 16 parts of polyether amine were added to the product, and the reaction was continued for another hour. Finally, the reaction product was spray-dried to prepare the target superabsorbent resin P-5 for concrete mixtures, the structural formula of which is as follows:

[0046]

[0047] Test example: water absorption ratio

[0048] Accurately weigh 0.5g of concrete mixture and place it in 1L of deionized water and 1L of simulated cement pore solution, respectively. Test the mass ratio of the mixture after water saturation to that before water treatment. The simulated cement pore solution was prepared with the following proportions: 1.720 g / L CaSO4·2H2O, 6.959 g / L Na2SO4, and 4.757 g / L K2SO4. 4、 7.120 g / L KOH. Control groups 1 and 2 both used commercially available superabsorbent polymers for concrete mixtures.

[0049] Table 1. Water Absorption Ratio of Superabsorbent Resin for Concrete Mixtures

[0050]

[0051] As shown in Table 1, the superabsorbent polymer (SAP) for concrete mixtures prepared in this invention exhibits a significantly higher water absorption ratio than commercially available SAPs for concrete mixtures, exceeding 500 times. In simulated cement pore solutions, the SAP for concrete mixtures showed varying degrees of reduction, but the embodiments disclosed in this invention maintained a water absorption ratio of over 500 times, while the two commercially available SAPs for concrete mixtures showed a reduction of more than 5 times.

[0052] Test example: Workability of concrete mixtures

[0053] The performance test of concrete mixture was carried out in accordance with GB / T 8076-2012 "Concrete Admixtures". The concrete mixture was pre-treated with deionized water saturation by superabsorbent resin. Then, 500g of water-saturated superabsorbent resin was weighed and added to the concrete mixture. The bleeding rate of the concrete mixture was tested at different mixing times.

[0054] Table 2. Effect of mixing time on the bleeding rate of concrete with high water-absorbing resin

[0055]

[0056] As can be seen from Table 2, the superabsorbent resin for concrete mixtures disclosed in the embodiments of the present invention still has a low water release rate during long-term mechanical mixing, which greatly reduces the bleeding rate of concrete mixtures containing superabsorbent resin.

[0057] To further test the effect of superabsorbent polymer on the plasticizing properties of concrete mixtures, concrete mixture performance tests were conducted in accordance with GB / T 8076-2012 "Concrete Admixtures". The initial slump and spread, as well as the loss of slump and spread over time, were tested. The test results are shown in Table 3.

[0058] Table 3. Effect of superabsorbent polymer on the plasticizing properties of concrete mixtures

[0059]

[0060] Note: The units in the table are length units in mm.

[0061] As can be seen from Table 3, the superabsorbent resin for concrete mixtures disclosed in the embodiments of the present invention has little effect on the plasticizing performance of concrete mixtures, but can significantly extend the plasticizing time of concrete mixtures.

[0062] Test Example: Performance of Hardened Concrete

[0063] The 28-day shrinkage rate of concrete mixed with superabsorbent resin according to GB 50204-2015 "Code for Acceptance of Quality of Concrete Structures" was tested. At the same time, the 28-day compressive strength of concrete mixed with superabsorbent resin according to GB 50081-2019 "Test Methods for Physical and Mechanical Properties of Concrete" was tested. Each group of tests was mixed with 500g of pre-saturated superabsorbent resin. The test results are shown in Table 4.

[0064] Table 4. Effects of superabsorbent polymers on the properties of hardened concrete

[0065]

[0066] As shown in Table 4, the superabsorbent resin for concrete mixtures prepared by the technology of the present invention has a better shrinkage reduction effect than commercially available products, and also exhibits better mechanical properties of concrete.

[0067] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A superabsorbent resin for concrete mixtures, characterized in that: It has a three-dimensional network composed of linear cyclic polycarboxylic acid crosslinks; Its molecular structure is shown in Formula I: （Ⅰ） In the above formula, R1 and R2 are both H atoms or methyl groups; x is an integer from 0 to 5, y is an integer from 1 to 20; n is an integer from 5 to 24; a is an integer from 1 to 5, b is an integer from 105 to 330, c is an integer from 150 to 300, d is an integer from 150 to 300, e is an integer from 1 to 5, and f is an integer from 50 to 300.

2. A method for preparing the superabsorbent resin for concrete mixtures as described in claim 1, characterized in that: Includes the following steps: Step 1: Dissolve acrylic acid or methacrylic acid, maleic acid, fumaric acid, compound of formula II, and polyethylene glycol ethylene ether in an organic solvent to prepare a low-concentration monomer solution. Then add an initiator and react at 70~120℃ for 24h to obtain linear cyclic polycarboxylic acid. （Ⅱ）； In the above formula, R1 is a H atom or a methyl group; Step 2: Add polyetheramine to the linear cyclic polycarboxylic acid and continue the reaction for 1 hour to obtain a micro-crosslinked cyclic polycarboxylic acid solution; Step 3: The micro-crosslinked cyclic polycarboxylic acid solution is dried using a spray drying process to obtain superabsorbent resin powder for concrete mixtures.

3. The method for preparing a superabsorbent resin for concrete mixtures according to claim 2, characterized in that: The specific molecular structure of the polyethylene glycol ethylene ether is shown in Formula III: （Ⅲ）； In the above formula, n is an integer from 5 to 24.

4. The method for preparing a superabsorbent resin for concrete mixtures according to claim 2, characterized in that: The organic solvent is one or more of benzene, toluene, cyclohexane, xylene, chlorobenzene, dimethylformamide, and dimethyl sulfoxide.

5. The method for preparing a superabsorbent resin for concrete mixtures according to claim 2, characterized in that: In step one, a low-concentration monomer solution is prepared by fully dissolving the monomer. At this time, the mass concentration of the low-concentration monomer solution is 5-20%.

6. The method for preparing a superabsorbent resin for concrete mixtures according to claim 2, characterized in that: The initiator is one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert-butyl peroxide.

7. The method for preparing a superabsorbent resin for concrete mixtures according to claim 2, characterized in that: The specific molecular structure of the polyetheramine in step two is shown in Formula IV: （Ⅳ） In the above formula, x is an integer from 0 to 5, and y is an integer from 1 to 20.

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