Dispersing agent and preparation method thereof

Abstract

The invention relates to a dispersing agent which comprises the following components in parts by weight: 5-15 parts of polymerizable silicon dioxide; 70 to 80 parts of a polyether macromonomer; 10 to 15 parts of an unsaturated acid monomer; 0.1 to 1 part of an initiator; 0.1-1 part of a chain transfer agent; and water. The silane coupling agent is adopted as a bridging molecule, covalent bond connection between hydrophilic fumed silica and a PCE molecular chain is achieved, the chemical bonding mode thoroughly avoids the defect that silica is prone to desorption in physical blending, the technical obstacle that direct copolymerization cannot be achieved due to mismatching of reactivity rates is also overcome, and the preparation method has the advantages of being simple and convenient to operate and high in practicability. The obtained composite dispersant is stable in structure and lasting in performance.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures, specifically to a dispersant and its preparation method. Background Technology

[0002] Polycarboxylate ether (PCE) high-performance water-reducing agents are currently the mainstream products in the field of concrete admixtures. They achieve efficient dispersion of cement particles through electrostatic repulsion and steric hindrance by adsorbing onto the surface of cement particles, significantly improving the fluidity and workability of concrete. However, when stabilizing suspensions of high-solids-content nanomaterials (such as nano-calcium carbonate), PCE alone is insufficient to overcome the strong agglomeration and rapid sedimentation problems caused by the large specific surface area and high surface energy of nanoparticles. Therefore, in industrial applications, thixotropic agents (such as fumed silica) are often introduced to form a three-dimensional network structure in the system, increasing the viscosity and shear dilution behavior of the slurry, thereby delaying particle sedimentation.

[0003] The commonly used method for improvement is to physically blend PCE with fumed silica. While this method can improve the initial stability of the system to some extent, it has significant drawbacks: Firstly, silica only acts on PCE molecules through physical adsorption, and desorption easily occurs under shear forces or during long-term static storage, leading to a gradual decrease in dispersion stability. Secondly, fumed silica itself is composed of nanoparticles, which are highly susceptible to self-aggregation due to van der Waals forces, affecting its uniform dispersion in the system and its final performance.

[0004] If one attempts to directly add fumed silica during the PCE synthesis stage—that is, the free radical copolymerization process—a fundamental technical obstacle arises: fumed silica is an inorganic nanoparticle lacks active functional groups such as carbon-carbon double bonds on its surface that can participate in free radical polymerization. Its polymerization reactivity differs greatly from that of PCE monomers (such as acrylic acid and polyether macromonomers), making it essentially unable to participate in the copolymerization reaction. Therefore, silica can only exist in physical form in the polymerization system, failing to achieve chemical bonding and potentially interfering with the normal progress of the polymerization process, even causing polymerization instability.

[0005] Therefore, no composite dispersant with a simple and feasible process has yet been developed that enables a strong chemical bond between fumed silica and PCE molecules. Developing such a product to simultaneously leverage the dispersing ability of PCE and the network stabilizing effect of silica, thereby fundamentally solving the problems of agglomeration and sedimentation in high-solids-content nano-slurries, has become a key technological challenge urgently needing breakthroughs in this field. Summary of the Invention

[0006] Therefore, it is necessary to provide a dispersant and its preparation method.

[0007] To achieve the above objectives, the present invention provides a technical solution:

[0008] A dispersant, in parts by weight, comprising:

[0009]

[0010] Preferably, the raw materials for preparing the polymerizable silica include silica and a silane coupling agent containing polymerizable double bonds.

[0011] Preferably, the silane coupling agent containing polymerizable double bonds includes at least one of vinyltrimethoxysilane and methacryloxypropyltrimethoxysilane.

[0012] Preferably, the amount of the silane coupling agent containing polymerizable double bonds is 5%-15% of the mass of silica.

[0013] Preferably, the polyether macromonomer includes at least one of polyethylene glycol monomethyl ether methacrylate and allyl polyethylene glycol.

[0014] Preferably, the initiator includes ammonium persulfate and hydrogen peroxide.

[0015] Preferably, the chain transfer agent includes at least one of mercaptoethanol and mercaptopropionic acid.

[0016] This invention also provides a method for preparing a dispersant, comprising the steps of:

[0017] The dispersant is obtained by reacting the polymerizable silica, polyether macromonomer, unsaturated acid monomer, initiator, chain transfer agent and water.

[0018] Preferably, the preparation steps of the polymerizable silica include:

[0019] The polymerizable silica is obtained by reacting silica with a silane coupling agent containing polymerizable double bonds.

[0020] Preferably, in the step of preparing the polymerizable silica, the reaction time is 4h-6h and the reaction temperature is 60℃-80℃.

[0021] Specifically, the molecular structural formula is shown below:

[0022]

[0023] Where n = 30-60, m = 5-20, z = 5-30, y = 1-20.

[0024] The beneficial effects of this invention are:

[0025] The invention utilizes a silane coupling agent as a "bridging" molecule to achieve covalent bonding between hydrophilic fumed silica and PCE molecular chains. This chemical bonding method completely avoids the defect of easy desorption of silica in physical blending and overcomes the technical obstacle of direct copolymerization due to mismatched polymerization rates. The resulting composite dispersant has a stable structure and long-lasting performance.

[0026] In the dispersant of this invention, the PCE segments continue to provide an excellent steric hindrance and electrostatic repulsion dispersion mechanism, while the silica nanoparticles fixed to the PCE by chemical bonds can construct a robust three-dimensional network structure within the slurry, endowing the system with significant shear dilution characteristics and yield stress. The synergistic effect of these two components ensures both initial dispersion and slurry stability under long-term storage and dynamic shear conditions.

[0027] This invention is based on an aqueous free radical copolymerization process, which is a mature and simple process, and is easy to scale up for industrial production. All selected raw materials meet environmental protection requirements, the production process requires no special equipment, and it has good feasibility for technology transfer.

[0028] When the composite dispersant prepared in this invention is applied to slurry systems such as high-solids-content nano-calcium carbonate, a uniform and stable slurry with high solids content, good fluidity, no stratification or sedimentation during long-term storage can be prepared without the addition of other suspending agents, which significantly improves the processability and stability of nanomaterials in practical applications. Detailed Implementation

[0029] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0030] Unless otherwise specified, the experimental methods used in the examples are conventional methods, and the materials and reagents used are commercially available. The hydrophilic fumed silica was purchased from Shaoxing Lijie Chemical Co., Ltd. (1000 mesh).

[0031] A dispersant, in parts by weight, comprising:

[0032]

[0033] Preferably, the raw materials for preparing the polymerizable silica include silica and a silane coupling agent containing polymerizable double bonds. Specifically, the silane coupling agent is used as a "bridging" molecule to achieve covalent bonding between hydrophilic fumed silica and PCE molecular chains. This chemical bonding method completely avoids the defect of easy desorption of silica in physical blending and overcomes the technical obstacle of direct copolymerization due to mismatched polymerization rates. The resulting composite dispersant has a stable structure and long-lasting performance.

[0034] Preferably, the silane coupling agent containing polymerizable double bonds includes at least one of vinyltrimethoxysilane and methacryloxypropyltrimethoxysilane.

[0035] Preferably, the amount of the silane coupling agent containing polymerizable double bonds is 5%-15% of the mass of silica. This range ensures the formation of an effective monomolecular capping layer, avoiding both incomplete modification due to insufficient dosage and the formation of a soft layer due to excessive coupling agent self-polymerization.

[0036] Preferably, the polyether macromonomer includes at least one of polyethylene glycol monomethyl ether methacrylate and allyl polyethylene glycol. More specifically, the two can be used alone or in combination. MPEG-MA has high reactivity and a well-defined copolymer structure; APEG has lower cost and is a mainstream raw material for traditional PCE. Using them in combination can adjust the polymerization rate and product properties.

[0037] Preferably, the initiator includes ammonium persulfate and hydrogen peroxide. More specifically, the initiator can be added in a single dose or dropwise to control the reaction rate.

[0038] Preferably, the unsaturated acid monomer is typically acrylic acid or methacrylic acid. Its main function is to copolymerize with the polyether macromonomer to form the polymer backbone, while its carboxyl anion (-COO-) provides crucial electrostatic repulsion, producing a synergistic dispersion effect with the steric hindrance of the polyether side chains.

[0039] Preferably, the chain transfer agent includes at least one of mercaptoethanol and mercaptopropionic acid, which are both highly efficient chain transfer agents, and their terminal hydroxyl or carboxyl groups can also increase the hydrophilicity of the product.

[0040] Chain transfer agents are used to adjust the molecular weight of polymers to prevent the formation of polymers with excessively high molecular weights, which could lead to a sharp increase in viscosity or a decrease in performance.

[0041] This invention also provides a method for preparing a dispersant, comprising the steps of:

[0042] The dispersant is obtained by reacting the polymerizable silica, polyether macromonomer, unsaturated acid monomer, initiator, chain transfer agent and water.

[0043] Preferably, the preparation steps of the polymerizable silica include:

[0044] The polymerizable silica is obtained by reacting silica with a silane coupling agent containing polymerizable double bonds.

[0045] Preferably, in the step of preparing the polymerizable silica, the reaction time is 4h-6h and the reaction temperature is 60℃-80℃.

[0046] More specifically, if the reaction time is too short (<4 hours), the grafting is incomplete / uneven, and the silane coupling agent containing double bonds does not have enough time to fully and uniformly bond with the silanol groups on the silica surface through hydrolysis and condensation reactions. This reduces its ability to participate in polymerization as an "active filler," affecting its reinforcing effect and interfacial bonding in the polymer matrix. Furthermore, with only some areas modified and others remaining as exposed hydrophilic silanol groups, the silica particles are prone to poor dispersibility and aggregation in organic monomers or resins. This also necessitates additional washing and purification steps, increasing costs.

[0047] Excessive reaction time (>6 hours) may promote the reaction between silane molecules not grafted onto silica, forming oligomers. These oligomers are physically adsorbed on the particle surface, affecting the modification effect and purity. Under certain conditions (especially high temperature with long duration), polymerizable double bonds such as vinyl and acryloyloxy groups may undergo prepolymerization or hydrolysis (for certain silane structures), leading to reduced reactivity. Extending the reaction time means increased energy consumption, prolonged equipment occupancy, and decreased production efficiency; continuing to extend the time after achieving optimal results is a waste of resources.

[0048] At excessively low reaction temperatures (<60℃), the rates of hydrolysis and condensation reactions decrease significantly. Even with extended reaction times, achieving a sufficient grafting rate may be difficult, resulting in a low and uneven grafting rate, similar to the consequence of "too short a reaction time." Low temperatures can also increase system viscosity, affecting mass transfer and mixing uniformity. Furthermore, the water produced by silane hydrolysis may be difficult to remove effectively through azeotropic methods, hindering the condensation reaction.

[0049] At excessively high reaction temperatures (>80℃), the acrylate or methacrylate groups on the silane may homopolymerize during the modification process, forming a polymer chain "shell." This not only consumes active sites available for polymerization with the resin but may also hinder the effective bonding of silica to the matrix. At high temperatures, the hydrolysis and condensation rates between silane coupling agent molecules are much faster than their reaction with the silica surface, leading to a large amount of silane self-polymerizing into oligomers instead of being grafted onto the target particles. High temperatures cause severe solvent evaporation, requiring stricter reflux control, increasing system pressure and safety risks, and potentially altering reactant concentrations, affecting reproducibility. Unnecessarily high temperatures result in energy waste.

[0050] Therefore, selecting the preferred conditions of 60-80℃ and 4-6 hours represents the optimal balance between ensuring sufficient grafting rate and maximizing the activity of polymerizable double bonds. Within this range, the reaction proceeds efficiently while effectively suppressing major side reactions, ensuring that the resulting polymerizable silica possesses a high density of active surface sites and good stability.

[0051] Specifically, the molecular structural formula of the dispersant is shown below:

[0052]

[0053] Where n is a positive integer from 30 to 60, m is a positive integer from 5 to 20, z is a positive integer from 5 to 30, and y is a positive integer from 1 to 20. Core refers to the nano-silica crystal nucleus.

[0054] Example 1

[0055] S100. Preparation of polymerizable silica (V-SiO2):

[0056] In a four-necked flask equipped with a stirrer, a condenser and a thermometer, 10g of hydrophilic fumed silica and 200g of anhydrous ethanol were added and ultrasonically dispersed for 30 minutes to obtain the first mixture.

[0057] Add 1.0 g of vinyltrimethoxysilane (VTMS) to the first mixture, add a few drops of glacial acetic acid, and adjust the pH of the solution to 4.5 to obtain the second mixture;

[0058] The second mixture was stirred and refluxed at 70°C for 5 hours. After the reaction was completed, it was centrifuged, washed three times with ethanol, and dried under vacuum at 60°C to obtain powdered V-SiO2, which is polymerizable silicon dioxide.

[0059] S200. Preparation of PCE-g-SiO2 composite dispersant:

[0060] In a reactor equipped with a stirrer, a dripping device, and a nitrogen inlet pipe, add 80g of polyethylene glycol monomethyl ether methacrylate (MPEG-MAA, molecular weight 1000), 8g of V-SiO2 obtained in step S100, 2g of hydrogen peroxide, and 150g of deionized water. Stir and heat to 70°C. After the system temperature stabilizes at 70°C, start to slowly add solution A and solution B to the reactor simultaneously, controlling the dripping time to be 2.5 hours.

[0061] After the addition is complete, continue to heat and mature at 70℃ for 1.5 hours. After the end, cool to below 40℃ and adjust the pH to 6.5 with 30wt% sodium hydroxide aqueous solution to obtain a slightly milky white viscous liquid with a solid content of about 40%, which is the PCE-g-SiO2 composite dispersant.

[0062] Solution A is a mixture of 5g ammonium persulfate and 0.5g mercaptopropionic acid dissolved in 50g water.

[0063] Solution B is a mixture of 12g acrylic acid and 2g V-SiO2.

[0064] Example 2

[0065] The other steps are the same as in Example 1, except that:

[0066] The synthesis ratio was changed to: MPEG-MAA 75g, V-SiO2 12g, acrylic acid 15g.

[0067] Example 3

[0068] The other steps are the same as in Example 1, except that:

[0069] The synthesis ratio was changed to: MPEG-MAA 70g, V-SiO2 15g, acrylic acid 10g.

[0070] Comparative Example 1

[0071] The other steps are the same as in Example 1, except that:

[0072] Using simple physical blending:

[0073] Take an equal amount of commercially available Point-40H water-reducing agent (i.e., pure polycarboxylate water-reducing agent without SiO2) and 8g of unmodified hydrophilic fumed silica, as in Example 1, and mix them by simple mechanical stirring before use. Here, equal amounts mean that the mass of commercially available Point-40H water-reducing agent + the mass of unmodified silica = the mass of the dispersant prepared in Example 1.

[0074] Comparative Example 2

[0075] The other steps are the same as in Example 1, except that:

[0076] In step S200, 8g of V-SiO2 obtained in step S100 is replaced with an equal amount of unmodified hydrophilic fumed silica.

[0077] The dispersants obtained in Examples 1-3 and the samples of Comparative Examples 1-2 were used to prepare nano-calcium carbonate slurry with a solid content of 70%, and their performance was tested according to standard GB / T21089.1-2007. The results are shown in Table 1.

[0078] Table 1 Performance Test Results

[0079]

[0080] As shown in Table 1, compared with Comparative Examples 1 and 2, when the initial viscosity was similar, the sedimentation rate of Examples 1-3 after standing for 7 days was significantly smaller than that of Comparative Examples 1-2, and the appearance of the slurry of Examples 1-3 after standing for 30 days showed no significant change.

[0081] This demonstrates that the dispersants prepared in Examples 1-3 have significantly better performance than the comparative schemes. It is evident that the PCE-g-SiO2 composite dispersant prepared in this invention, with its unique chemical bonding structure, can impart extremely excellent long-term stability and significant thixotropy to the nano-calcium carbonate slurry, with effects far superior to traditional physical blending processes. It also proves that unbridged silica cannot be effectively bonded in polymerization.

[0082] It should be noted that the specific parameters or reagents in the above embodiments are specific or preferred embodiments under the concept of the present invention, and not limitations thereof; those skilled in the art can make adaptive adjustments within the concept and protection scope of the present invention.

Claims

1. A dispersant, characterized in that, The dispersant comprises, by weight parts:

2. The dispersant according to claim 1, characterized in that, The raw materials for preparing the polymerizable silica include silica and silane coupling agents containing polymerizable double bonds.

3. The dispersant according to claim 2, characterized in that, The silane coupling agent containing polymerizable double bonds includes at least one of vinyltrimethoxysilane and methacryloxypropyltrimethoxysilane.

4. The dispersant according to claim 2, characterized in that, The amount of the silane coupling agent containing polymerizable double bonds is 5%-15% of the mass of silica.

5. The dispersant according to claim 1, characterized in that, The polyether macromonomer includes at least one of polyethylene glycol monomethyl ether methacrylate and allyl polyethylene glycol.

6. The dispersant according to claim 1, characterized in that, The initiator includes ammonium persulfate and hydrogen peroxide.

7. The dispersant according to claim 1, characterized in that, The chain transfer agent includes at least one of mercaptoethanol and mercaptopropionic acid.

8. A method for preparing a dispersant as described in any one of claims 1 to 7, characterized in that, Including the following steps: The dispersant is obtained by reacting the polymerizable silica, polyether macromonomer, unsaturated acid monomer, initiator, chain transfer agent and water.

9. The preparation method according to claim 8, characterized in that, The preparation steps of the polymerizable silica include: The polymerizable silica is obtained by reacting silica with a silane coupling agent containing polymerizable double bonds.

10. The preparation method according to claim 9, characterized in that, In the step of preparing the polymerizable silica, the reaction time is 4h-6h and the reaction temperature is 60℃-80℃.

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