Gypsum-organic composite super absorbent resin as well as preparation method and application thereof
Through nano-gypsum particle modification and polymer chain mesh wrapping technology of gypsum-organic composite superabsorbent resin, the problem of unfavorable pores after traditional SAP water release is solved, and the self-filling and strength improvement of cement-based materials is achieved, which simplifies the process flow and reduces costs.
Patent Information
- Application Number
- CN202510722503.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-30
- Publication Date
- 2025-08-29
AI Technical Summary
The pores formed by traditional superabsorbent resins (SAPs) after water release are not good for the strength of cement-based materials, and the prior art has failed to effectively solve the problem of pore residue after water release. The uniform distribution of external blends has a spatial and temporal mismatch between SAP gradient water release and local micropores, which increases the complexity of material cost and mix ratio.
Using gypsum-organic composite superabsorbent resin, nanogypsum particles with a Zeta potential less than -30 mV were prepared by using nanogypsum particles surface modification and polymer chain mesh encapsulation, combined with ion crosslinking, nanogypsum particles with a Zeta potential less than -30 mV were controlled to generate ettringite (AFt/AFm) during water release in cement-based materials, achieving in-situ filling and repair of pores.
Effectively reduce the shrinkage of cement-based materials, improve strength, and reduce strength reduction. Compared with commercially available SAP, it significantly improves material performance, simplifies process flow, and reduces costs.
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Figure CN120554592A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of building materials, in particular to a hydration-activated in-situ self-filling internal curing agent for cement-based materials and its preparation, in particular to a gypsum-organic composite super absorbent resin, a preparation method and application. Background Art
[0002] During the cement hydration process, water loss inevitably leads to problems such as inadequate hydration, shrinkage, and cracking in cement-based materials. Internal curing technology can effectively address this issue. Super absorbent polymer (SAP) is a widely used, low-cost, and highly effective internal curing agent. SAP pre-stores water within the internal curing agent and slowly releases it within cement-based materials (such as paste, mortar, and concrete) to regulate the hydration process, significantly reducing initial defects and improving material performance.
[0003] However, traditional SAP forms cavities after water release. These pores negatively impact the strength of cementitious materials, significantly limiting their application. Existing technologies primarily focus on improving SAP's slow water release and environmental friendliness, but fail to address the issue of residual pores after water release. Alternatively, they rely on additional admixtures (such as expansive agents and nanomaterials) to compensate for these pore defects. However, the uniform distribution of these admixtures is mismatched with SAP's gradient water release and the presence of localized micropores in both time and space, increasing material costs and mix complexity.
[0004] Engineering applications attach great importance to material strength and process simplicity. Therefore, in future applications, SAP, which has both internal maintenance and water-releasing pore self-repair functions, has broad application prospects and huge value space. Summary of the Invention
[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a gypsum-organic composite super absorbent polymer, which can integrate internal curing and defect self-repair functions to comprehensively improve the performance of cement-based materials.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: a gypsum-organic composite super absorbent resin (SAP), comprising the following raw materials: surface-modified nano-gypsum particles; acrylic acid (AA) and acrylamide (AM) monomers, wherein the acrylic acid is neutralized to a degree of neutralization of 65%-80%, and the mass ratio of acrylamide to acrylic acid is 0.5-0.7; a cross-linking agent, N,N'-methylenebisacrylamide (MBA), added in an amount of 0.02%-0.12% of the total mass of the acrylic acid AA and the acrylamide AM; and an initiator, potassium persulfate (KPS), added in an amount of 0.05%-0.9% of the total mass of the acrylic acid AA and the acrylamide AM; the nano-gypsum particles added in an amount of 5%-20% of the total mass of the acrylic acid AA and the acrylamide AM, and the particle size of the nano-gypsum particles is less than 100 nm and the zeta potential is less than -30 mV.
[0007] Furthermore, the surface-modified nano-gypsum particles are prepared by the following method: in the first stage, waste hardened gypsum, desulfurized gypsum, or phosphogypsum is ground in a ball mill for 2-4 hours; in the second stage, a mixed solution of a silane coupling agent and water in a mass ratio of 1:20 is added to a ball mill, and intermittent grinding is carried out for 4-8 hours at a temperature of ≤60°C, wherein the mass ratio of the silane coupling agent to the gypsum is 0.5%-2%.
[0008] Furthermore, the neutralization treatment is as follows: sodium hydroxide is slowly added dropwise to the acrylic acid solution under ice bath conditions to adjust the pH to a neutralization degree of 65%-80%.
[0009] A preparation method for a gypsum-organic composite super absorbent resin comprises the following steps: mixing a neutralized acrylic acid solution (AA), acrylamide (AM) and surface-modified nano-gypsum particles at 25°C, and ultrasonically dispersing the mixture to form a homogeneous mixed liquid; adding the mixed liquid, N,N'-methylenebisacrylamide (MBA) and potassium persulfate (KPS) into a reaction vessel, introducing N2 protective gas, heating the reaction vessel to 70°C at a rate of 5°C / h and continuously stirring the reaction vessel until the reaction is complete; after the reaction is completed, stirring the reaction vessel for 6-12 hours using the residual heat, chopping the product, washing with ethanol, vacuum drying the product at 70-100°C, and grinding the product into 30-200 mesh particles.
[0010] Furthermore, during the reaction process, the nano-gypsum particles are combined with acrylic acid and acrylamide polymer chains through surface adsorption, polymer chain network wrapping, coupling agent bridging and ionic cross-linking.
[0011] A gypsum-organic composite superabsorbent resin is used in cement-based materials. The superabsorbent resin (SAP) is added in an amount of 0-0.5% of the mass of the cementitious material. The superabsorbent resin (SAP) releases CaSO4 during water release, reacting with cement hydration products to form ettringite (AFt / AFm), thereby achieving in-situ pore filling and repair.
[0012] When gypsum-organic composite SAP is applied to cement-based materials, the SAP addition amount is 0-0.5% of the cementitious material mass; during the water release process, the SAP releases CaSO4 to participate in hydration, generating an expansion reaction, and reacts with the cement hydration products to form ettringite (AFt / AFm), achieving in-situ pore filling and repair. The specific reaction is as follows:
[0013] The water-releasing pores of the super absorbent resin SAP are self-filled in the cement-based material through the expansion of ettringite.
[0014] The Zeta potential is less than -30 mV, which is used to ensure the dispersion of gypsum particles. During preparation, modified SAP with uniform dispersion of the modifier can be obtained.
[0015] The liquid absorption capacity of the synthesized SAP in cement-based materials can be controlled by adjusting the mass ratio of AM / AA. Generally speaking, the larger the AM / AA ratio, the greater the liquid absorption capacity of the prepared SAP in cement-based materials.
[0016] By adjusting the mass ratio of nanogypsum particles to monomers (AA + AM), the self-filling capacity of SAP within the cementitious material during water release can be controlled. The greater the amount of nanogypsum particles added, the greater the self-filling capacity of SAP within the cementitious material. The specific capacity depends on the SAP's inherent liquid absorption capacity, the modifier (gypsum), and relevant cementitious material parameters, such as the SAP's equilibrium liquid absorption rate, gypsum particle size, gypsum content, and water-cement ratio.
[0017] The MBA synthesis ratio is 0.02%-0.12% of the monomer mass, which can take into account both water absorption rate and strength.
[0018] The KPS synthesis ratio is 0.05%-0.9% of the total mass of (AA+AM). The actual amount needs to be fine-tuned according to the monomer type, reaction temperature and target performance.
[0019] When the gypsum-organic composite super absorbent resin prepared by the present invention is applied to cement-based materials, the gypsum component of the composite SAP releases CaSO4 during the water release process to participate in hydration, thereby generating an expansion reaction and forming expansion products, thereby achieving self-filling of the SAP water release pores, effectively reducing shrinkage and inhibiting strength reduction. Compared with currently commercially available SAP, the strength is significantly improved and the shrinkage ratio is significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 The invention relates to a synthesis process of gypsum-organic composite super absorbent resin.
[0021] Figure 2 Schematic diagram of the preparation process of nano-gypsum particles.
[0022] Figure 3 Schematic diagram of the reaction process of gypsum particle surface modification by silane coupling agent.
[0023] Figure 4 Chemical reaction process for the synthesis of gypsum-organic composite superabsorbent polymer.
[0024] Figure 5 Appearance morphology of two types of 30-60 mesh SAP.
[0025] Figure 6 The absorption dynamics of SAP in cement paste filtrate.
[0026] Figure 7 Schematic diagram comparing the curing and water-release processes of traditional and composite superabsorbent polymers in cement-based materials. DETAILED DESCRIPTION
[0027] To illustrate the present invention more clearly, the present invention is further described in detail below with reference to the accompanying drawings. The embodiments are only used to explain the present invention and are not intended to limit the present invention in any way. Example
[0028] The present invention takes the synthesis of hybrid SAP from desulfurized gypsum as an example, and the whole synthesis process is as follows: Figure 1 The details are as follows: (1) Preparation of surface-modified nano-gypsum particles. Figure 2 As shown, in the first stage, the desulfurized gypsum is placed in a ball mill and ground for 4 hours. In the second stage, a silane coupling agent aqueous solution (silane coupling agent and water mass ratio is 1:20) is prepared, and then the solution is placed in a ball mill and intermittently ground for 4 to 8 hours. During the intermittent grinding process, the temperature must be controlled not to exceed 60°C, thereby obtaining surface-modified nano-gypsum particles. The modification mechanism is as follows: Figure 3 As shown. Silane coupling agent hydrolysis produces silanol groups, which react with hydroxyl groups on the nano-gypsum surface, removing molecular water and forming stable siloxane bonds (Si-O-Ca). The mass ratio of silane coupling agent to gypsum is 1%, which can be adjusted according to actual grinding conditions.
[0029] (2) In an ice bath, use sodium hydroxide to neutralize acrylic acid, as shown in Formula ③. Slowly add the sodium hydroxide solution to reduce the intensity of the reaction. After the reaction is complete, allow the solution to cool to room temperature to obtain a sodium acrylate solution with a neutralization degree of 70%.
[0030]
[0031] (3) Add the surface-modified gypsum particles and AM into a triangular flask containing sodium acrylate solution. The surface-modified gypsum particles are added in an amount of 20% of the total mass of AM and AA monomers. Ultrasonic stirring is used to uniformly disperse the materials. The mass ratio of AM to AA is 0.6.
[0032] (4) Then, the mixed solution, initiator, and cross-linking agent in the conical flask were added to the three-necked flask, stirred continuously, and the constant temperature water bath was heated to 50°C. The mixture was stirred at this temperature for 3 hours, and then slowly heated to 70°C (5°C / h). During the heating process, polymerization and cross-linking occurred between the reactant monomers, and the gypsum particles could form effective connections with the AA and AM polymer chains through surface adsorption, polymer chain network wrapping, coupling agent bridging, and ionic cross-linking during the polymerization process, such as Figure 4 After the monomers in the three-necked flask have completely reacted, stirring is continued for 6 hours using the residual heat to allow for full reaction.
[0033] (5) The product was taken out, chopped, washed with anhydrous ethanol and dehydrated twice to remove unreacted monomers. Finally, the purified product was dried in a vacuum drying oven at 80°C to constant weight, and then ground into SAP particles of 30-600 μm, marked as SAP1, and sieved using standard sieves to form the commonly used mesh sizes for cement-based materials (30-60 mesh, 60-100 mesh, 100-200 mesh), and stored in a sealed container at room temperature. The prepared 30-60 mesh SAP1 is as follows: Figure 5 shown.
[0034] When the prepared gypsum modified super absorbent resin is used in cement-based materials, the cement slurry filtrate is prepared using the ratio of cement slurry (water mass / cement mass = 4:1) to test the liquid absorption rate of SAP1. It is comparable to the commercially available SAP (SAP2, see Figure 5 ) for the imbibition dynamics. Figure 6 . The initial setting time of cement-based materials is greater than 45 minutes. It can be seen that SAP1 and SAP2 have similar liquid absorption capabilities at 40-60 minutes, and SAP1 has more stable liquid absorption. At the same time, mortar samples were prepared based on the liquid absorption capacity of SAP. The water-cement ratio and mortar-sand ratio (both by mass) were 0.35 and 1:2, respectively. The SAP dosage was 0.12% (mass ratio with the cementitious material). The compressive strength and shrinkage were tested according to standard tests. The mortar without SAP was used as the benchmark mortar, and SAP2 was used as the control group. The 28d strength ratios of the SAP1 and SAP2 sample groups were 97.3% and 91.4%, respectively, and the 28d shrinkage ratios were 77.2% and 87.1%, respectively. It can be seen that when SAP1 is used, the effective component (CaSO4) of the cement-based material diffuses with water and reacts with the cement component to form an expansion product, thereby realizing the self-filling of the SAP water release pores, reducing shrinkage and inhibiting the reduction of strength. It is compared with the traditional SAP water release pore formation process. Figure 7 shown.
Claims
1. A gypsum-organic composite super absorbent resin, characterized in that: The invention comprises the following raw materials: surface-modified nano-gypsum particles; acrylic acid and acrylamide monomers, wherein the acrylic acid is neutralized to a degree of neutralization of 65%-80%, and the mass ratio of acrylamide to acrylic acid is 0.5-0.7; a cross-linking agent, N,N'-methylenebisacrylamide, whose addition amount is 0.02%-0.12% of the total mass of the acrylic acid and acrylamide; and an initiator, potassium persulfate, whose addition amount is 0.05%-0.9% of the total mass of the acrylic acid and acrylamide. The nano-gypsum particles are added in an amount of 5%-20% of the total mass of the acrylic acid and acrylamide, and the particle size of the nano-gypsum particles is less than 100 nm and the zeta potential is less than -30 mV.
2. The gypsum-organic composite super absorbent resin according to claim 1, characterized in that: The surface-modified nano-gypsum particles are prepared by the following method: in the first stage, waste hardened gypsum, desulfurized gypsum, or phosphogypsum is ground in a ball mill for 2-4 hours; in the second stage, a mixed solution of a silane coupling agent and water in a mass ratio of 1:20 is added to a ball mill and intermittently ground for 4-8 hours at a temperature of ≤60°C, wherein the mass ratio of the silane coupling agent to the gypsum is 0.5%-2%.
3. The gypsum-organic composite super absorbent resin according to claim 1, characterized in that: The neutralization treatment is as follows: sodium hydroxide is slowly added dropwise to the acrylic acid solution under ice bath conditions to adjust the pH to a neutralization degree of 65%-80%.
4. A method for preparing the gypsum-organic composite super absorbent resin according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: mixing a neutralized acrylic acid solution, acrylamide and surface-modified nano-gypsum particles at 25°C, and ultrasonically dispersing the mixture to form a homogeneous mixed liquid; adding the mixed liquid, N,N'-methylenebisacrylamide and potassium persulfate into a reaction container, introducing N2 protective gas, heating the reaction container to 70°C at a rate of 5°C / h and continuously stirring the reaction container until the reaction is complete; after the reaction is completed, stirring the reaction container for 6-12 hours using the residual heat, and chopping the product, washing it with ethanol, vacuum drying it at 70-100°C, and then grinding it into 30-200 mesh particles.
5. The method for preparing a gypsum-organic composite super absorbent resin according to claim 4, wherein: During the reaction process, nano-gypsum particles combine with acrylic acid and acrylamide polymer chains through surface adsorption, polymer chain network wrapping, coupling agent bridging and ionic cross-linking.
6. Use of the gypsum-organic composite super absorbent resin according to any one of claims 1 to 3 in cement-based materials, characterized in that: The addition amount of the super absorbent resin is 0-0.5% of the mass of the cementitious material; the super absorbent resin releases CaSO4 during the water release process, reacts with cement hydration products to form ettringite, and realizes in-situ filling and repair of pores.
7. The use of a gypsum-organic composite super absorbent resin in cement-based materials according to claim 6, characterized in that: The water-releasing pores of the superabsorbent resin are self-filled in the cement-based material through the expansion of ettringite.