Polycarboxylic acid cement grinding aid and preparation method thereof

Abstract

The invention discloses a polycarboxylic acid cement grinding aid and a preparation method thereof, and the preparation method comprises the following steps: carrying out free radical polymerization on an unsaturated polyether monomer, an unsaturated acid monomer A and an unsaturated acid monomer B under the action of an initiator, a reducing agent and a chain transfer agent to obtain a carboxylic acid polymer; and carrying out dicarboxylic acid self-condensation cyclization reaction on the carboxylic acid polymer under the catalysis of nano Ca (OH) 2, nano ZnO and tetrabutylammonium bromide to obtain the polycarboxylic acid cement grinding aid with an annular structure main chain. The high-adsorption and high-dispersity polycarboxylic acid cement grinding aid with high temperature resistance and mechanical grinding resistance is synthesized by combining cement mineral components with industrial grinding characteristics and utilizing designability of molecular structures of organic matters, so that the grinding fineness of the cement is greatly reduced, the grinding efficiency of the cement is improved, and the cement grinding efficiency is improved. The cement grinding aid has excellent performances of assisting grinding, improving the working performance of cement and improving the strength.

Description

Technical Field

[0001] The invention belongs to the technical field of materials, and particularly relates to a polycarboxylic acid cement grinding aid and a preparation method thereof. Background Art

[0002] Cement grinding is one of the most energy-intensive steps in cement production. Reducing this electricity consumption plays a crucial role in the industry's green and low-carbon transformation, reducing production costs, and achieving sustainable development. Adding a small amount of cement grinding aid during the cement grinding process can effectively prevent fine particle agglomeration and improve grinding efficiency.

[0003] Currently, common cement grinding aids are compounds of small-molecule organic compounds such as polyolamines and polyols, which can increase the hourly output of cement mills by approximately 10-15%. Due to the low molecular weight of these small-molecule substances, their adsorption strength on the surface of cement particles is weak, making them easily stripped by mechanical forces during high-intensity grinding, unable to continuously reduce particle surface energy or prevent agglomeration. Cement is a micron-sized powder with a large specific surface area, making it difficult for small molecules to form a uniform and complete adsorption coating, resulting in localized particle adhesion or agglomeration. Small-molecule organic compounds easily volatilize under high-temperature grinding conditions and lose their grinding aid effect. The structure of small-molecule organic grinding aids determines the upper limit of their grinding aid ability.

[0004] With the iterative upgrade of grinding aid technology, high-molecular cement grinding aids represented by polycarboxylic acid compounds have become a research hotspot due to their unique molecular design advantages. From the perspective of molecular mechanism of action, the carboxylic acid group (-COOH) in the polycarboxylic acid molecule can selectively anchor to the surface of calcium-rich mineral phases (such as C3S, C2S) in silicate cement through chemical coordination, reducing the surface energy of particles and inhibiting agglomeration; at the same time, its long-chain topological structure can provide a steric hindrance effect, further enhancing the dispersion stability of particles. Laboratory studies have confirmed that compared with traditional small-molecule grinding aids, polycarboxylic acid grinding aids have significant advantages in powder fineness control (such as a 15%~20% reduction in D50) and particle grading optimization. However, its application effect in industrial grinding scenarios is far lower than theoretical expectations, and the core failure mechanism can be attributed to the following multi-scale coupling factors: 1. Interface adsorption mismatch The local distribution density of carboxylic acid groups is insufficient (such as the random distribution of functional groups in random copolymers), making it difficult to establish high-density anchoring points on the mineral surface, resulting in insufficient mechanical stability of the adsorption layer and susceptibility to shear force peeling.

[0005] 2. Thermal-mechanical coupling degradation effect The high temperature (>100°C) and high shear (shear rate >10³ s⁻¹) environment of industrial grinding systems pose a dual threat to the integrity of polycarboxylic acid molecular chains: thermal degradation, where carboxylic acid groups are prone to decarboxylation reactions at high temperatures (such as generating CO2 and unsaturated chain segments), and free radical mechanisms may induce crosslinking or chain scission within or between molecular chains, resulting in the loss of grinding-aid active functional groups; mechanical shear degradation, where the high shear force generated by the impact and friction of grinding media (such as steel balls) can cut the polymer backbone, destroy its steric structure, and reduce the uniformity of molecular weight distribution.

[0006] Therefore, the existing polycarboxylic acid cement grinding aid technology has limited grinding aid effect in the actual industrial grinding process of cement.

[0007] CN117164771A discloses a heat-resistant polycarboxylate superplasticizer, its preparation method, and application. The steps include dispersing an unsaturated polyoxyethylene ether monomer in water and heating the mixture to 25-30°C; adding an oxidizing agent and stirring for 5-15 minutes; and adding solution A and solution B dropwise to the reaction system over a period of 1-1.5 hours. The unsaturated functional monomer and the heat-resistant functional monomer are dispersed in water to form solution A; a chain transfer agent and a reducing agent are dispersed in water to form a mixed solution B; an organic neutralizer is added to adjust the pH to 6-7; and heat-resistant auxiliary materials are added to produce the heat-resistant polycarboxylate superplasticizer. The heat-resistant polycarboxylate superplasticizer produced by this invention still has a long C—C chain backbone and side chains consisting of long-chain polyethers with a molecular weight of 2000-5000 g / mol. Under high-temperature cement grinding conditions, the organic molecules are susceptible to degradation or crosslinking, which can render them ineffective. This results in reduced dispersibility of the cement powder and limited grinding aid effectiveness in industrial cement grinding.

[0008] CN113336740B discloses a method for preparing a cyclic slightly cross-linked polycarboxylic acid intermediate. The method comprises the following steps: adding a polyol and an organic solvent to a reactor, stirring uniformly, adding an acid-binding agent, purging with nitrogen, adding an unsaturated acid chloride dropwise at 0-5°C for 1-8 hours, extracting with a saturated salt solution to obtain an extract, and then distilling the extract under reduced pressure to evaporate the organic solvent, thereby obtaining a cyclic slightly cross-linked polycarboxylic acid intermediate. This invention utilizes a polyol and an unsaturated acid chloride to directly and efficiently esterify to obtain a cyclic slightly cross-linked polycarboxylic acid intermediate. The obtained intermediate is then applied to carboxylic acid polymerization to obtain a polycarboxylic acid water-reducing agent with a cyclic structure and slightly cross-linked molecular chains. The cyclic slightly cross-linked polycarboxylic acid intermediate has reduced reactivity due to steric hindrance and differences in reactivity with other monomers. The reaction product is a polycarboxylic acid water-reducing agent with a diester ring structure. However, the diester structure is unstable during cement grinding and easily decomposes, destroying the ring structure. This has limited grinding-aiding effect in the actual industrial grinding process of cement. Summary of the Invention

[0009] In view of the characteristics of cement mineral components combined with industrial grinding, the present invention utilizes the designability of organic molecular structure to provide a high-adsorption and high-dispersion polycarboxylic acid cement grinding aid that is resistant to high temperature and mechanical grinding. It greatly reduces the fineness of cement grinding and improves cement grinding efficiency. It has excellent grinding aid properties, improves cement working performance and increases strength.

[0010] In order to achieve the above purpose, the technical solutions adopted are as follows: A polycarboxylic acid cement grinding aid having the following molecular structure:

[0011] wherein: R1 is hydrogen or carboxyl; R2 is hydrogen or carboxymethyl; R3 is hydrogen or methyl; R4 is hydrogen or methyl; R5 is hydrogen or methyl; R6 is hydrogen or methyl; R7 is methylene or ethyleneoxy; R8 is methylene or ethylene; R9 is methylene or ethylene; The degree of polymerization a is an integer of 9-16; the degree of polymerization p is an integer of 2-23, the degree of polymerization n is an integer of 7-48, the degree of polymerization m is an integer of 20-105, and p:n:m=1:(2-4):(4-16), n:m=1:(2-4).

[0012] According to the above scheme, the weight average molecular weight of the polycarboxylic acid cement grinding aid is 10,000-30,000 g / mol.

[0013] The present invention also provides a method for preparing the polycarboxylic acid cement grinding aid, comprising the following steps: (1) Unsaturated polyether monomer and initiator are added to a reactor, water is added to adjust the system concentration to 40-60 wt%, and the temperature is raised to 20-40°C with stirring until the solid bottom material in the reactor is completely dissolved; dropwise addition material A consisting of unsaturated acid monomer A and unsaturated acid monomer B and dropwise addition material B consisting of chain transfer agent and reducing agent aqueous solution are added dropwise for 2-4 hours, and then the temperature is raised to 40-60°C and kept warm for 1-2 hours to obtain a carboxylic acid polymer solution; (2) The carboxylic acid polymer solution obtained in step (1) is added with water to prepare a solution with a concentration of 0.5-1.0 wt%, and a nano-Ca(OH)2 / nano-ZnO / tetrabutylammonium bromide catalyst system is added thereto and uniformly dispersed. The pH of the system is adjusted to 9-12 with a dilute alkali solution, and the temperature is raised to 40-80°C for reaction for 12-24 hours. After the reaction is completed, the solid is centrifuged and separated, and a dilute acid solution is added to adjust the pH to 6-7. The solution is dialyzed and purified, and concentrated to a polycarboxylic acid cement grinding aid solution with a concentration of 30-60 wt%.

[0014] According to the above scheme, the molar ratio of the unsaturated acid monomer A, unsaturated polyether monomer, unsaturated acid monomer B, initiator, reducing agent and chain transfer agent in step (1) is 1:(2-4):(4-16):(0.05-0.12):(0.15-0.30):(0.005-0.02), wherein the molar ratio of the unsaturated polyether monomer to the unsaturated acid monomer B is 1:(2-4).

[0015] According to the above scheme, the unsaturated acid monomer A in step (1) is a straight-chain unsaturated dicarboxylic acid with a carbon chain length of 6-8; specifically, it is one of trans-3-hexenedioic acid, 3-heptene-1,7-dioic acid, and oct-4-enedioic acid, or any mixture thereof.

[0016] According to the above scheme, the unsaturated acid monomer B in step (1) is one or any combination of acrylic acid, methacrylic acid, maleic anhydride, and aconitic acid.

[0017] According to the above scheme, the unsaturated polyether monomer in step (1) is one of allyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, ethylene glycol monovinyl polyoxyethylene ether or any mixture thereof with a molecular weight of 400-800 g / mol.

[0018] According to the above scheme, the initiator in step (1) is one or any combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate.

[0019] According to the above scheme, the chain transfer agent in step (1) is one or any combination of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, and sodium methallyl sulfonate.

[0020] According to the above scheme, the reducing agent in step (1) is one or any combination of sodium bisulfite, bleaching powder, sodium ascorbate, and isoascorbic acid.

[0021] According to the above scheme, the molar ratio of the amount of nano-Ca(OH)2 used in step (2) to the unsaturated acid monomer A is (1-1.5):1; the molar ratio of the amount of nano-ZnO used to the unsaturated acid monomer A is (0.2-0.6):1; and the molar ratio of the amount of tetrabutylammonium bromide used to the unsaturated acid monomer A is (0.1-0.3):1.

[0022] According to the above scheme, the particle size of the nano-Ca(OH)2 in step (2) is less than or equal to 100 nm; the particle size of the nano-ZnO is less than or equal to 50 nm.

[0023] According to the above scheme, the dilute alkaline solution in step (2) is a 0.1-0.5 mol / L NaOH or KOH solution.

[0024] According to the above scheme, the dilute acid solution in step (2) is a 0.1-0.5 mol / L acetic acid or citric acid solution.

[0025] According to the above protocol, the dialysis process in step (2) includes dialysis using a 10 kDa dialysis bag under magnetic stirring for 24-48 hours.

[0026] Unsaturated dicarboxylic acid monomers, unsaturated acid monomers, and unsaturated polyethers are first subjected to solution free radical polymerization in the presence of a chain transfer agent, an initiator, and a reducing agent to produce a carboxylic acid polymer. The carboxylic acid polymer aqueous solution is then subjected to a dicarboxylic acid self-condensation ring reaction using a nano-Ca(OH)2 / nano-ZnO / tetrabutylammonium bromide catalytic system to produce a polycarboxylic acid cement grinding aid with a cyclic backbone. This synthetic route is reliable, efficient, and provides a high yield of the target product.

[0027] A linear unsaturated dicarboxylic acid with a carbon chain length of 6-8 is used. If the carbon chain is too short, it cannot form a ring due to tension constraints; if the carbon chain is too long, the linear chain folds, resulting in a sharp decrease in the probability of ring formation.

[0028] Using Ca(OH)2 / nano ZnO / tetrabutylammonium bromide composite catalytic system: dicarboxylic acid reacts with Ca(OH)2 to form carboxylic acid calcium salt, which reduces the ionization degree of carboxylic acid (-COO - → -COOCa + ), promoting condensation activity. Calcium salts bring carboxylic acid groups closer through chelation, promoting low-temperature dehydration and ring formation. The surface of ZnO is rich in Lewis acid sites (Zn 2+ Empty orbital), which can adsorb carboxylate (-COO - ) and polarizes its electron cloud, promoting dehydration condensation. ZnO forms an acid-base pair with Ca(OH)2, which simultaneously activates carboxylic acid and stabilizes the transition state in the local microenvironment, reducing the reaction activation energy and significantly improving the low-temperature cyclization efficiency. Tetrabutylammonium bromide can pull hydrophilic calcium ions near the polymer chain, - It is transported to the carboxylic acid site to accelerate the formation of calcium salts; as a surfactant, it can reduce the tendency of nanoparticles to agglomerate; it acts as a molecular lubricant to soften the movement of polymer chain segments; the hydrophobic chain guides the polymer folding and promotes the cyclization conformation, thereby achieving efficient low-temperature cyclization reactions.

[0029] The carboxyl content of the polymer is regulated by controlling the ratio of unsaturated acid to unsaturated polyether and the molecular weight of the polyether. Compared with conventional polycarboxylic acid concrete water reducers, the polycarboxylic acid cement grinding aid prepared by the present invention has a higher carboxyl content. This is to match the large amount of Ca-O bond breaking during cement grinding. Increasing the carboxyl content will increase the molecule's adsorption capacity for calcium ions and provide more potential binding sites. The present invention controls a certain upper limit of carboxyl content, the purpose of which is to increase the adsorption of Ca 2+Increase, the positive charge on the molecular surface or local area increases, which has a great impact on the subsequent positively charged Ca 2+ At high density, the coordination ranges of adjacent carboxyl groups may overlap, making a single Ca 2+ It is difficult to effectively bind to multiple carboxyl groups at the optimal positions at the same time. Therefore, the present invention effectively adsorbs Ca by controlling the appropriate carboxyl content. 2+ , shielding static electricity during the grinding process and improving the grinding effect.

[0030] The introduction of a cyclic structure into the backbone effectively enhances the segmental and molecular chain rigidity of the polycarboxylic acid polymer, strengthens intermolecular forces, and improves bond energy and chemical stability. This prevents chemical reactions such as chain scission (thermal degradation, mechanochemical degradation), oxidation, or crosslinking under the high temperatures and mechanical grinding conditions of cement, effectively preserving the original molecular structure and achieving stable and efficient grinding aid performance. The cyclic structure inherently possesses a fixed geometry and significant steric hindrance. The hindered rotation around single bonds directly increases the rigidity of local segments of the molecular chain, thereby enhancing the rigidity of the entire molecular chain. Stronger intermolecular forces require higher energy to break interchain interactions, disentangle or vaporize the molecular chains. Consequently, the thermal decomposition temperature is increased. Strong intermolecular forces bind the molecular chains more tightly together, significantly enhancing the cohesive strength and tear resistance of the polycarboxylic acid grinding aid. The rigid cyclic structure effectively blocks the propagation path of microcracks in cement raw material particles within the material. When a crack tip encounters the rigid cyclic unit, it requires more energy to deform or break, or is forced to change its propagation direction, consuming more energy. This crack blunting or crack deflection effect makes it more effective in promoting the expansion of particle cracks during cement grinding and effectively improving the grinding aid effect.

[0031] Compared with conventional polycarboxylic acid concrete water reducers as cement grinding aids, the use of low molecular weight unsaturated polyethers can increase the proportion of carboxyl groups in the entire polymer, effectively improving adsorption capacity; avoid excessively long polyether side chains that lead to chain breakage and decomposition under high temperature and mechanical grinding; control the strength of the side chain steric hindrance, while achieving dispersion of cement particles, avoiding excessive steric hindrance of individual polymer molecules that affects the adsorption of other molecules.

[0032] Compared with conventional polycarboxylic acid concrete water reducers used as cement grinding aids, the polycarboxylic acid cement grinding aid obtained in the present invention has heat resistance and mechanical grinding resistance, and can maintain its original molecular structure and remain in the cement after cement grinding. It acts as a water reducer after water is added to the cement, thereby greatly improving the construction performance of the cement.

[0033] Compared with the prior art, the present invention has the following beneficial effects: 1. The preparation method of the polycarboxylic acid cement grinding aid provided by the present invention is simple, efficient and reliable, the raw materials are non-toxic and pollution-free, and industrialization can be realized.

[0034] 2. The preparation method of the polycarboxylic acid cement grinding aid provided by the present invention can obtain a polymer with high carboxyl content, which can efficiently absorb the Ca generated during cement grinding. 2+ , has excellent adsorption capacity; 3. The preparation method of the polycarboxylic acid cement grinding aid provided by the present invention can obtain a carboxylic acid polymer with a ring structure in the main chain, which can effectively avoid thermal degradation and mechanochemical degradation during the cement grinding process, overcome the defect of conventional polycarboxylic acid cement grinding aids that are not resistant to grinding, and achieve excellent grinding aid effect; 4. The preparation method of the polycarboxylic acid cement grinding aid provided by the present invention can obtain a carboxylic acid polymer with a ring structure in the main chain, which effectively promotes the expansion of particle cracks during cement grinding, thereby improving the grinding aid effect.

[0035] 5. The preparation method of the polycarboxylic acid cement grinding aid provided by the present invention can obtain a carboxylic acid polymer with a relatively low molecular weight polyether side chain, further improving the adsorption capacity and grinding resistance; 6. The heat-resistant and mechanical grinding-resistant polycarboxylic acid cement grinding aid obtained by the preparation method of the polycarboxylic acid cement grinding aid provided by the present invention can maintain its original molecular structure and remain in the cement after cement grinding. After the cement is added with water, it acts as a water reducer, greatly improving the construction performance of the cement. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 : Example 1, Comparative Example 2: Appearance of samples before and after drying and miscibility. DETAILED DESCRIPTION

[0037] The following examples further illustrate the technical solutions of the present invention, but are not intended to limit the scope of protection of the present invention. The following specific examples are only some preferred embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, modifications, substitutions, and improvements made by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0038] A specific embodiment provides a method for preparing a polycarboxylic acid cement grinding aid, comprising the following steps: (1) Unsaturated polyether monomer and initiator are added to a reactor, water is added to adjust the system concentration to 40-60 wt%, and the temperature is raised to 20-40 ° C while stirring. After the solid base material in the reactor is completely dissolved, the dropwise addition material A consisting of unsaturated acid monomer A and unsaturated acid monomer B and the dropwise addition material B consisting of chain transfer agent and reducing agent aqueous solution are simultaneously added dropwise for 2-4 hours, and then the mixture is kept at 40-60 ° C for 1-2 hours to obtain a carboxylic acid polymer solution; (2) The carboxylic acid polymer solution obtained in step (1) is added with water to prepare a solution with a concentration of 0.5-1.0 wt %, and nano-Ca(OH)2 is added thereto. Ultrasonic dispersion is performed for 20-40 min, and then nano-ZnO and tetrabutylammonium bromide are added. The pH of the system is adjusted to 9-12 with a dilute alkaline solution while stirring at 400-600 r / min. The temperature is raised to 40-80° C. and the reaction is carried out for 12-24 h. After the reaction is completed, the temperature is lowered to room temperature, and the solid is separated by centrifugation. A dilute acid solution is added to adjust the pH to 6-7, and the solution is purified by dialysis and concentrated to a concentration of 30-60 wt % to obtain a polycarboxylic acid cement grinding aid solution.

[0039] Specifically, the molar ratio of the unsaturated acid monomer A, the unsaturated polyether monomer, the unsaturated acid monomer B, the initiator, the reducing agent, and the chain transfer agent is 1:(2-4):(4-16):(0.05-0.12):(0.15-0.30):(0.005-0.02), wherein the molar ratio of the unsaturated polyether monomer to the unsaturated acid monomer B is 1:(2-4).

[0040] Specifically, the molar ratio of the unsaturated acid monomer A to nano-Ca(OH)2 is 1:(1-1.5), the molar ratio of the unsaturated acid monomer A to nano-ZnO is 1:(0.2-0.6), and the molar ratio of the unsaturated acid monomer A to tetrabutylammonium bromide is 1:(0.1-0.3).

[0041] Specifically, the unsaturated acid monomer A is a linear unsaturated dicarboxylic acid with a carbon chain length of 6-8; specifically, one of trans-3-hexenedioic acid, 3-heptene-1,7-dioic acid, and oct-4-enedioic acid, or any combination thereof. The unsaturated acid monomer B is one of acrylic acid, methacrylic acid, maleic acid, and aconitic acid, or any combination thereof. The unsaturated polyether monomer is one of allyl polyoxyethylene ether, methallyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, and ethylene glycol monovinyl polyoxyethylene ether, or any combination thereof, having a molecular weight of 400-800 g / mol.

[0042] Specifically, the initiator is one or any combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate. The chain transfer agent is one or any combination of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, and sodium methallyl sulfonate. The reducing agent is one or any combination of sodium bisulfite, bleaching agent, sodium ascorbate, and isoascorbic acid.

[0043] Specifically, the nano-Ca(OH)2 has a particle size of 100 nm or less and is manufactured by Hubei Guoding Huaming Nano New Materials Co., Ltd. The nano-ZnO has a particle size of 50 nm or less and is manufactured by Zhejiang Manli Nano Technology Co., Ltd. Tetrabutylammonium bromide was commercially available from Hubei Wonder Chemical Co., Ltd. All other raw materials, unless otherwise specified, were commercially available.

[0044] Example 1 (1) 0.2 mol of allyl polyoxyethylene ether with a molecular weight of 400 g / mol and 0.005 mol of ammonium persulfate were added to a reactor, and water was added to adjust the system concentration to 40 wt%. The temperature was raised to 20°C while stirring. After the solid base material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.1 mol of trans-3-hexenedioic acid and 0.4 mol of acrylic acid and a dropwise addition material B consisting of 0.015 mol of mercaptopropionic acid and 0.0005 mol of an aqueous solution of isoascorbic acid were simultaneously added dropwise. The addition time was 2 h, and then the mixture was kept at 40°C for 1 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.5 wt %, 0.1 mol of Ca(OH)2 with a particle size of 60 nm was added thereto, and ultrasonic dispersion was carried out for 20 min. Then, 0.02 mol of ZnO with a particle size of 20 nm and 0.01 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 9 with 0.5 mol / L KOH solution while stirring at 400 r / min. The temperature was raised to 40°C and the reaction was carried out for 12 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.1 mol / L acetic acid solution was added to adjust the pH to 6, and the solution was dialyzed with a 10 kDa dialysis bag under magnetic stirring for 24 h. The solution was concentrated to a concentration of 30 wt % to obtain a polycarboxylic acid cement grinding aid.

[0045] Example 2 (1) 0.4 mol of allyl polyoxyethylene ether with a molecular weight of 800 g / mol and 0.012 mol of ammonium persulfate were added to a reactor, and water was added to adjust the system concentration to 60 wt%. The temperature was raised to 40°C while stirring. After the solid bottom material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.1 mol of trans-3-hexenedioic acid and 1.6 mol of methacrylic acid and a dropwise addition material B consisting of 0.03 mol of mercaptopropionic acid and 0.002 mol of an aqueous solution of isoascorbic acid were simultaneously added dropwise. The addition time was 4 h, and then the mixture was kept at 60°C for 2 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 1.0 wt%, 0.15 mol of Ca(OH)2 with a particle size of 80 nm was added thereto, and ultrasonic dispersion was carried out for 40 min. Then, 0.06 mol of ZnO with a particle size of 30 nm and 0.03 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 12 with 0.2 mol / L NaOH solution while stirring at 600 r / min. The temperature was raised to 80°C and the reaction was carried out for 24 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.5 mol / L citric acid solution was added to adjust the pH to 7, and the solution was dialyzed using a 10 kDa dialysis bag under magnetic stirring for 48 h. The solution was concentrated to a concentration of 60 wt% to obtain a polycarboxylic acid cement grinding aid.

[0046] Example 3 (1) 0.3 mol of methyl allyl polyoxyethylene ether with a molecular weight of 600 g / mol and 0.01 mol of hydrogen peroxide were added to a reactor, and water was added to adjust the system concentration to 47 wt%. The temperature was raised to 28°C while stirring. After the solid base material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.1 mol of 3-heptene-1,7-dioic acid and 0.9 mol of maleic acid and a dropwise addition material B consisting of 0.018 mol of mercaptoethanol and 0.0008 mol of sodium bisulfite aqueous solution were simultaneously added dropwise for 3 h. The mixture was then kept at 53°C for 1.5 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.7 wt %, 0.13 mol of Ca(OH)2 with a particle size of 100 nm was added thereto, and ultrasonic dispersion was carried out for 26 min. Then, 0.05 mol of ZnO with a particle size of 50 nm and 0.02 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 11 with 0.5 mol / L KOH solution while stirring at 586 r / min. The temperature was raised to 73°C and the reaction was carried out for 19 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.3 mol / L acetic acid solution was added to adjust the pH to 6.5, and the solution was dialyzed with a 10 kDa dialysis bag under magnetic stirring for 36 h. The solution was concentrated to a concentration of 54 wt % to obtain a polycarboxylic acid cement grinding aid.

[0047] Example 4 (1) 0.3 mol of isopentyl polyoxyethylene ether with a molecular weight of 400 g / mol and 0.008 mol of sodium persulfate were added to a reactor, and water was added to adjust the system concentration to 42 wt%. The temperature was raised to 36°C while stirring. After the solid base material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.1 mol of oct-4-enedioic acid and 0.72 mol of aconitic acid and a dropwise addition material B consisting of 0.027 mol of thioglycolic acid and 0.0017 mol of a solution of bleaching powder were simultaneously added dropwise. The addition time was 2.3 h, and then the mixture was kept warm at 47°C for 1.3 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.8 wt %, 0.12 mol of Ca(OH)2 with a particle size of 60 nm was added thereto, and ultrasonic dispersion was carried out for 33 min. Then, 0.02 mol of ZnO with a particle size of 30 nm and 0.015 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 10 with 0.3 mol / L NaOH solution while stirring at 423 r / min. The temperature was raised to 43°C and the reaction was carried out for 13 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.4 mol / L acetic acid solution was added to adjust the pH to 6.8, and the solution was dialyzed with a 10 kDa dialysis bag under magnetic stirring for 26 h. The solution was concentrated to a concentration of 38 wt % to obtain a polycarboxylic acid cement grinding aid.

[0048] Example 5 (1) 0.1 mol of ethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 400 g / mol and 0.007 mol of potassium persulfate were added to a reactor, and water was added to adjust the system concentration to 58 wt%. The temperature was raised to 24°C while stirring. After the solid base material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.05 mol of 3-heptene-1,7-dioic acid, 0.05 mol of trans-3-hexenedioic acid, and 1.52 mol of maleic acid and a dropwise addition material B consisting of 0.02 mol of mercaptopropionic acid and 0.001 mol of sodium ascorbate aqueous solution were simultaneously added dropwise for 3.2 h, and then the mixture was kept warm at 50°C for 1.8 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.5 wt %, 0.1 mol of Ca(OH)2 with a particle size of 80 nm was added thereto, and ultrasonic dispersion was carried out for 22 min. Then, 0.06 mol of ZnO with a particle size of 20 nm and 0.03 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 12 with 0.4 mol / L KOH solution while stirring at 558 r / min. The temperature was raised to 76°C and the reaction was carried out for 23 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.5 mol / L citric acid solution was added to adjust the pH to 6.9, and the solution was dialyzed with a 10 kDa dialysis bag under magnetic stirring for 35 h. The solution was concentrated to a concentration of 55 wt % to obtain a polycarboxylic acid cement grinding aid.

[0049] Example 6 (1) 0.1 mol of methyl allyl polyoxyethylene ether with a molecular weight of 400 g / mol and 0.005 mol of ammonium persulfate were added to a reactor, and water was added to adjust the system concentration to 53 wt%. The temperature was raised to 36°C while stirring. After the solid bottom material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.05 mol of 3-heptene-1,7-dioic acid, 0.05 mol of oct-4-enedioic acid, and 0.75 mol of methacrylic acid and a dropwise addition material B consisting of 0.021 mol of sodium methyl allyl sulfonate and 0.0013 mol of an aqueous solution of isoascorbic acid were simultaneously added dropwise for 2.1 h, and then the mixture was kept warm at 43°C for 1.1 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.6 wt %, 0.14 mol of Ca(OH)2 with a particle size of 100 nm was added thereto, and ultrasonic dispersion was carried out for 29 min. Then, 0.04 mol of ZnO with a particle size of 50 nm and 0.023 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 10 with 0.4 mol / L NaOH solution while stirring at 401 r / min. The temperature was raised to 43°C and the reaction was carried out for 20 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.2 mol / L acetic acid solution was added to adjust the pH to 6.2, and the solution was dialyzed with a 10 kDa dialysis bag under magnetic stirring for 25 h. The solution was concentrated to a concentration of 31 wt % to obtain a polycarboxylic acid cement grinding aid.

[0050] Example 7 (1) 0.24 mol of isopentyl polyoxyethylene ether with a molecular weight of 600 g / mol and 0.01 mol of sodium persulfate were added to a reactor, and water was added to adjust the system concentration to 59 wt%. The temperature was raised to 26°C while stirring. After the solid bottom material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.03 mol of trans-3-hexenedioic acid, 0.03 mol of 3-heptene-1,7-dioic acid, 0.04 mol of oct-4-enedioic acid, 0.276 mol of acrylic acid, and 0.228 mol of maleic acid and a dropwise addition material B consisting of 0.016 mol of mercaptopropionic acid and 0.002 mol of sodium ascorbate aqueous solution were simultaneously added dropwise for 2.3 h, and then the mixture was kept warm at 50°C for 1.9 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.8 wt %, 0.13 mol of Ca(OH)2 with a particle size of 80 nm was added thereto, and ultrasonic dispersion was carried out for 32 min. Then, 0.03 mol of ZnO with a particle size of 30 nm and 0.029 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 10 with 0.3 mol / L NaOH solution while stirring at 433 r / min. The temperature was raised to 41°C and the reaction was carried out for 23 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.3 mol / L citric acid solution was added to adjust the pH to 6.6, and the solution was dialyzed with a 10 kDa dialysis bag under magnetic stirring for 37 h. The solution was concentrated to a concentration of 57 wt % to obtain a polycarboxylic acid cement grinding aid.

[0051] Example 8 (1) 0.37 mol of ethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 800 g / mol and 0.009 mol of hydrogen peroxide were added to a reactor, and water was added to adjust the system concentration to 44 wt%. The temperature was raised to 30°C while stirring. After the solid base material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.050 mol of trans-3-hexenedioic acid, 0.025 mol of 3-heptene-1,7-dioic acid, 0.025 mol of oct-4-enedioic acid, 0.352 mol of acrylic acid, 0.278 mol of methacrylic acid, and 0.702 mol of maleic acid and a dropwise addition material B consisting of 0.029 mol of mercaptoethanol and 0.0016 mol of a bleaching powder aqueous solution were simultaneously added dropwise for 3.4 h, and then the mixture was kept warm at 49°C for 1.3 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.9 wt %, 0.14 mol of Ca(OH)2 with a particle size of 100 nm was added thereto, and ultrasonic dispersion was carried out for 21 min. Then, 0.04 mol of ZnO with a particle size of 30 nm and 0.03 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 9 with 0.1 mol / L NaOH solution while stirring at 401 r / min. The temperature was raised to 44°C and the reaction was carried out for 13 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.3 mol / L citric acid solution was added to adjust the pH to 6.6, and the solution was dialyzed with a 10 kDa dialysis bag under magnetic stirring for 37 h. The solution was concentrated to a concentration of 31 wt % to obtain a polycarboxylic acid cement grinding aid.

[0052] Example 9 (1) 0.1 mol of allyl polyoxyethylene ether with a molecular weight of 400 g / mol, 0.1 mol of methyl allyl polyoxyethylene ether with a molecular weight of 800 g / mol, 0.1 mol of isopentenyl polyoxyethylene ether with a molecular weight of 400 g / mol, 0.1 mol of ethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 400 g / mol, and 0.006 mol of potassium persulfate were added to a reactor, and water was added to adjust the system concentration to 46 wt%. The temperature was raised to 31 ° C while stirring. After the solid bottom material in the reactor was completely dissolved, the addition material A consisting of 0.1 mol of oct-4-enedioic acid and 1.4 mol of aconitic acid and the addition material B consisting of 0.03 mol of thioglycolic acid and 0.0011 mol of a solution of bleaching powder were added dropwise at the same time. The addition time was 2 h, and then the mixture was kept warm at 43 ° C for 1.1 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 1.0 wt%, 0.15 mol of Ca(OH)2 with a particle size of 80 nm was added thereto, and ultrasonic dispersion was performed for 20 min. Then, 0.05 mol of ZnO with a particle size of 20 nm and 0.01 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 12 with 0.5 mol / L KOH solution while stirring at 576 r / min. The temperature was raised to 48°C and the reaction was carried out for 15 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.5 mol / L acetic acid solution was added to adjust the pH to 6.7, and the solution was dialyzed using a 10 kDa dialysis bag under magnetic stirring for 44 h. The solution was concentrated to a concentration of 57 wt% to obtain a polycarboxylic acid cement grinding aid.

[0053] Example 10 (1) 0.22 mol of isopentyl polyoxyethylene ether with a molecular weight of 800 g / mol and 0.007 mol of sodium persulfate were added to a reactor, and water was added to adjust the system concentration to 60 wt%. The temperature was raised to 40°C while stirring. After the solid bottom material in the reactor was completely dissolved, a dropwise addition material A consisting of 0.1 mol of 3-heptene-1,7-dioic acid and 0.704 mol of methacrylic acid and a dropwise addition material B consisting of 0.015 mol of sodium methyl allyl sulfonate and 0.0019 mol of sodium bisulfite aqueous solution were simultaneously added dropwise. The addition time was 1.3 h, and then the mixture was kept at 60°C for 2 h to obtain a carboxylic acid polymer. (2) The carboxylic acid polymer obtained in step (1) was added with water to prepare a solution with a concentration of 0.5 wt %, 0.1 mol of Ca(OH)2 with a particle size of 60 nm was added thereto, and ultrasonic dispersion was performed for 40 min. Then, 0.06 mol of ZnO with a particle size of 50 nm and 0.01 mol of tetrabutylammonium bromide were added. The pH of the system was adjusted to 11 with 0.3 mol / L KOH solution while stirring at 590 r / min. The temperature was raised to 68°C and the reaction was carried out for 20 h. After the reaction was completed, the temperature was lowered to room temperature, the solid was separated by centrifugation, 0.2 mol / L acetic acid solution was added to adjust the pH to 7, and the solution was dialyzed using a 10 kDa dialysis bag under magnetic stirring for 32 h. The solution was concentrated to a concentration of 52 wt % to obtain a polycarboxylic acid cement grinding aid.

[0054] Comparative Example 1 Example 1 was repeated, except that the allyl polyoxyethylene ether with a molecular weight of 400 g / mol was replaced by the allyl polyoxyethylene ether with a molecular weight of 2400 g / mol, and other conditions remained unchanged, to obtain a polymer.

[0055] Comparative Example 2 It is a commercially available polycarboxylate water reducer obtained by free radical polymerization of acrylic acid and allyl polyoxyethylene ether with a molecular weight of 2400 g / mol, wherein the molar ratio of acrylic acid to allyl polyoxyethylene ether is 4:1.

[0056] Comparative Example 3 It is a commercially available cement grinding aid, the main ingredients of which are polyol amines and polyols.

[0057] The performance of the polycarboxylic acid cement grinding aids prepared in Examples 1-10 above was tested and evaluated.

[0058] 1. Molecular weight test The molecular weights of the synthesized samples were determined using a Waters 1515 gel permeation chromatograph (Waters, USA). The mobile phase consisted of a 0.1 mol / L NaNO solution at a flow rate of 1.0 mL / min, and the stationary phase consisted of a gel-like porous filler. Molecular weight tests were performed on the polycarboxylate cement grinding aids prepared in Examples 1-10 above. The molecular weight test results are shown in Table 1.

[0059] Table 1

[0060] As can be seen from Table 1, the prepared polycarboxylic acid cement grinding aid is within the designed molecular weight range, indicating that the polymerization reaction is carried out efficiently according to the preparation method and the target product is effectively generated.

[0061] 2. Heat resistance test The sample was placed in a blast drying oven at 120°C (simulating the temperature inside the cement mill when grinding cement in a cement ball mill) and dried for 2 hours. The changes in the appearance of the sample before and after drying were observed. The dried sample was weighed at a mass ratio of 1:50 between the sample and distilled water, stirred thoroughly, and the water solubility test results of the sample were observed. The polycarboxylic acid cement grinding aids prepared in Examples 1 to 10 and Comparative Example 2 were subjected to heat resistance tests. The heat resistance test results are shown in Table 2. The appearance of the samples of Example 1 and Comparative Example 2 before and after drying and miscibility are shown in the attached table. Figure 1 shown.

[0062] Table 2

[0063] From the above heat resistance test results, it can be seen that under the simulated cement ball mill grinding temperature and blast conditions, the commercially available polycarboxylate water-reducing agent in Comparative Example 2 changed from a transparent liquid to a dark brown solid due to high temperature and oxidation, and was insoluble in water, producing a large amount of gel, indicating that the polycarboxylate water-reducing agent underwent thermal degradation, chain scission, oxidation, cross-linking and other chemical reactions; while the polycarboxylate cement grinding aid prepared according to the method of the present invention did not change in color and still had good water solubility, indicating that the polycarboxylate cement grinding aid prepared according to the method of the present invention has good heat resistance and oxidation resistance, and can maintain good structural stability under cement ball mill grinding temperature and blast conditions.

[0064] 3. Performance Testing Referring to the test method in GB / T 26748-2011 "Cement Grinding Aids," 5 kg of various cement raw materials were heated in an oven to 120°C according to the PO 42.5 cement mix ratio. The cement mix ratio was: 80% clinker, 4% slag, 11% fly ash, and 5% desulfurized gypsum. Before grinding, a grinding aid was added to the raw cement at a rate of 0.05%. The grinding time was set at 25 minutes to obtain a PO 42.5 cement sample. The fineness of the cement was tested using GB / T 1345-2005 "Determination of Cement Fineness - Sieve Analysis Method." The specific surface area of ​​the cement was tested using GB / T 8074-2008 "Determination of Specific Surface Area of ​​Cement - Blaine Method." The strength of the cement was tested using GB / T 17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)." The fluidity of cement paste was tested with reference to GB / T 8077-2023, "Test Method for Homogeneity of Concrete Admixtures." A comparative evaluation was conducted using the polycarboxylic acid cement grinding aids prepared in Examples 1 to 10, Comparative Examples 1 to 3, and a blank sample without cement grinding aid. The results are shown in Tables 3 and 4.

[0065] Table 3

[0066] As can be seen from the data in Table 3, the polycarboxylate cement grinding aid prepared by the present invention significantly increases the specific surface area of ​​cement prepared from cement raw materials, reduces the 80 μm sieve residue and the 45 μm sieve residue, and effectively overcomes the problem of failure of conventional polycarboxylate water reducers under high temperature grinding conditions. The grinding aid effect is significantly better than that of commercially available cement grinding aids based on polyol amines and polyols.

[0067] Table 4

[0068] As can be seen from the data in Table 4, the polycarboxylate cement grinding aid prepared by the present invention significantly improved the fluidity and 3d / 28d strength of the cement paste compared with the long side chain polycarboxylate cement grinding aid and the commercially available polycarboxylate water reducer compared with the blank group without grinding aid, indicating that the polycarboxylate cement grinding aid prepared by the present invention can still maintain a good effect of improving the working performance of cement and enhancing it after high-temperature grinding. Compared with the commercially available cement grinding aid, the polycarboxylate cement grinding aid prepared by the present invention significantly improved the fluidity of the cement paste and had a higher 3d / 28d strength, indicating that the polycarboxylate cement grinding aid prepared by the present invention can overcome the adverse effects on the working performance of cement and has a better enhancement effect than ordinary cement grinding aids.

Claims

1. A polycarboxylic acid cement grinding aid, characterized in that It has the following molecular structure: wherein: R1 is hydrogen or carboxyl; R2 is hydrogen or carboxymethyl; R3 is hydrogen or methyl; R4 is hydrogen or methyl; R5 is hydrogen or methyl; R6 is hydrogen or methyl; R7 is methylene or ethyleneoxy; R8 is methylene or ethylene; R9 is methylene or ethylene; The degree of polymerization a is an integer of 9-16; the degree of polymerization p is an integer of 2-23, the degree of polymerization n is an integer of 7-48, the degree of polymerization m is an integer of 20-105, and p:n:m=1:(2-4):(4-16), n:m=1:(2-4).

2. The method for preparing the polycarboxylic acid cement grinding aid according to claim 1, characterized in that The following steps are involved: (1) Unsaturated polyether monomer and initiator are added to a reactor, water is added to adjust the system concentration to 40-60 wt%, and the temperature is raised to 20-40°C with stirring until the solid bottom material in the reactor is completely dissolved; dropwise addition material A consisting of unsaturated acid monomer A and unsaturated acid monomer B and dropwise addition material B consisting of chain transfer agent and reducing agent aqueous solution are added dropwise for 2-4 hours, and then the temperature is raised to 40-60°C and kept warm for 1-2 hours to obtain a carboxylic acid polymer solution; (2) The carboxylic acid polymer solution obtained in step (1) is added with water to prepare a solution with a concentration of 0.5-1.0 wt%, and a nano-Ca(OH)2 / nano-ZnO / tetrabutylammonium bromide catalyst system is added thereto and uniformly dispersed. The pH of the system is adjusted to 9-12 with a dilute alkali solution, and the temperature is raised to 40-80°C for reaction for 12-24 hours. After the reaction is completed, the solid is centrifuged and separated, and a dilute acid solution is added to adjust the pH to 6-7. The solution is dialyzed and purified, and concentrated to a polycarboxylic acid cement grinding aid solution with a concentration of 30-60 wt%.

3. The preparation method of polycarboxylic acid cement grinding aid as claimed in claim 2, characterized in that The molar ratio of the unsaturated acid monomer A, unsaturated polyether monomer, unsaturated acid monomer B, initiator, reducing agent and chain transfer agent in step (1) is 1:(2-4):(4-16):(0.05-0.12):(0.15-0.30):(0.005-0.02), wherein the molar ratio of the unsaturated polyether monomer to the unsaturated acid monomer B is 1:(2-4).

4. The method for preparing a polycarboxylic acid cement grinding aid as claimed in claim 2, wherein In step (1), the unsaturated acid monomer A is a straight-chain unsaturated dicarboxylic acid with a carbon chain length of 6-8; the unsaturated acid monomer B is one or any combination of acrylic acid, methacrylic acid, maleic anhydride, and aconitic acid.

5. The method for preparing a polycarboxylic acid cement grinding aid as claimed in claim 2, wherein The unsaturated polyether monomer in step (1) is one of allyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, and ethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 400-800 g / mol, or any mixture thereof.

6. The method for preparing a polycarboxylic acid cement grinding aid as claimed in claim 2, wherein The initiator in step (1) is one or any combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the chain transfer agent is one or any combination of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, and sodium methyl allyl sulfonate; and the reducing agent is one or any combination of sodium bisulfite, bleaching agent, sodium ascorbate, and isoascorbic acid.

7. The method for preparing a polycarboxylic acid cement grinding aid as claimed in claim 2, wherein In step (2), the molar ratio of the amount of nano-Ca(OH)2 to the unsaturated acid monomer A is (1-1.5):1; the molar ratio of the amount of nano-ZnO to the unsaturated acid monomer A is (0.2-0.6):1; and the molar ratio of the amount of tetrabutylammonium bromide to the unsaturated acid monomer A is (0.1-0.3):

1.

8. The method for preparing a polycarboxylic acid cement grinding aid as claimed in claim 2, wherein In step (2), the particle size of the nano-Ca(OH)2 is less than or equal to 100 nm; the particle size of the nano-ZnO is less than or equal to 50 nm.

9. The method for preparing a polycarboxylic acid cement grinding aid as claimed in claim 2, wherein The dilute alkaline solution in step (2) is a 0.1-0.5 mol / L NaOH or KOH solution; the dilute acid solution is a 0.1-0.5 mol / L acetic acid or citric acid solution.

10. The method for preparing the polycarboxylic acid cement grinding aid according to claim 2, wherein The dialysis process in step (2) includes dialysis using a 10 kDa dialysis bag under magnetic stirring for 24-48 hours.

Images