Retarder for delaying cement setting time and preparation method thereof

Abstract

The invention discloses a retarder for delaying cement setting time and a preparation method thereof, and belongs to the field of cement admixtures. The retarder is anionic polymer modified chitosan, and the preparation method comprises the following steps: (1) fully dissolving chitosan in a weak acid solution to obtain a chitosan solution; (2) fully dissolving an anionic polymer in a solvent to obtain an anionic polymer solution; and (3) adding the anionic polymer solution into the chitosan solution, fully stirring, carrying out electrostatic adsorption reaction, and centrifuging, washing, drying and crushing after the electrostatic adsorption reaction is finished to obtain the anionic polymer modified chitosan. Chitosan is modified through electrostatic adsorption of an anionic polymer to form a compound, the compound is added into cement, and the coagulation time of the cement is prolonged by utilizing the complexing action of functional groups of the compound on calcium ions and the surface adsorption action on cement particles, so that the construction operability is favorably improved; and the preparation process is simple, and the cost is low.

Description

Technical Field

[0001] The present invention belongs to the field of cement admixtures, and particularly relates to a retarder for delaying the setting time of cement and a preparation method thereof. Background Art

[0002] For cement, especially the properties of freshly mixed cement, have a very significant impact on pumping and pouring in actual construction, directly affecting the hardened cement structure performance, quality, and durability. Therefore, controlling the setting time of cement is a key technology effectively applied in various engineering construction fields. In Portland-sulfoaluminate cement, due to the addition of calcium sulfoaluminate mineral phase, the setting time of cement is too short, which is not conducive to construction. Therefore, it is necessary to adjust its setting time.

[0003] A Chinese patent with the publication number CN108821632A discloses a cement retarder. In its background art, it is mentioned that the existing cement retarders mainly include tannin derivatives, lignite preparations, saccharide compounds, boric acid and its salts, organic phosphides, lignosulfonates and their modified products, etc. Although they all have certain effects, the retardation time is limited, and they have a great impact on the strength of cement.

[0004] Chitosan, as a natural polysaccharide derivative, is green, non-toxic, and environmentally friendly, and is an environmentally friendly and biodegradable biomass resource. The amino and hydroxyl groups in the chitosan molecule have specific chemical reactions, which provide a basis for the application of chitosan in cement and concrete. However, the existence of intermolecular and intramolecular hydrogen bonds in the chitosan molecule makes the chitosan molecule insoluble in water, affecting its high efficiency in the use of cement-based materials. Therefore, it is necessary to modify chitosan to improve its application performance in cement. Summary of the Invention

[0005] Object of the Invention: The first object of the present invention is to provide a retarder for delaying the setting time of cement that can reduce the impact on the early strength of cement. The second object of the present invention is to provide a preparation method of the above-mentioned retarder for delaying the setting time of cement.

[0006] Technical Solution: The retarder for delaying the setting time of cement described in the present invention is an anion polymer-modified chitosan.

[0007] Further, the mass ratio of the anion polymer to chitosan is 1-2:1.

[0008] Further, the anion polymer is polystyrene sulfonic acid, sodium polystyrene sulfonate, or sodium polyacrylate, preferably polystyrene sulfonic acid.

[0009] Further, the deacetylation degree of the chitosan is 85-95%.

[0010] Further, the cement is a Portland-sulfoaluminate cement.

[0011] The method for preparing the retarder for retarding the setting time of cement includes the following steps:

[0012] (1) Dissolve chitosan fully in a weak acid solution to obtain a chitosan solution;

[0013] (2) Dissolve an anionic polymer fully in a solvent to obtain an anionic polymer solution;

[0014] (3) Add the anionic polymer solution to the chitosan solution, stir well, carry out an electrostatic adsorption reaction, and after completion, centrifuge, wash, dry, and pulverize to obtain an anionic polymer-modified chitosan.

[0015] Further, in step (1), the weak acid solution is an acetic acid solution with a mass fraction of 1-2 wt%, and the time for full dissolution is 2-4 h; the mass ratio of chitosan to the weak acid in the acetic acid solution is 1:1-2.

[0016] Further, in step (2), the solvent is water, and the time for full dissolution is 4-6 h.

[0017] Further, in step (3), the conditions for the electrostatic adsorption reaction are: reacting at 40-60 °C for 4-8 h; the conditions for centrifugation are: a centrifugation rate of 3500-5000 rpm and a centrifugation time of 10-15 min; the conditions for drying are: drying at 60-70 °C for 6-8 h.

[0018] Further, in step (3), the particle size range of the pulverized anionic polymer-modified chitosan is below 50 μm.

[0019] Principle of the invention: In the present invention, an anionic polymer is used to modify chitosan through electrostatic adsorption, hydrogen bond interaction, etc. The anions in the anionic polymer and the amino groups (-NH 2 ) and hydroxyl groups (-OH) in chitosan can be combined together through electrostatic adsorption, hydrogen bond interaction, etc. And the charged organic molecule shows an affinity for the surface of unhydrated cement particles or hydrated products, and through electrostatic action, hydrogen bond interaction, complexation / chelation, etc., shows a significant adsorption behavior, so the setting time of cement can be prolonged.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following remarkable effects: (1) A new retarder is obtained by modifying chitosan with an anionic polymer. Traditional chitosan has certain limitations as a cement additive (such as poor water solubility, poor dispersibility, etc.). Through modification, its solubility and dispersibility in water can be significantly improved; (2) Compared with other chitosan modification methods, the preparation method of the present invention for modifying chitosan with an anionic polymer has a simple process, a low temperature required for the process, the reagents used are green and non-toxic, and the experimental equipment requirements are low. Moreover, compared with traditional retarders, chitosan itself is a natural polymer material, reflecting the environmental protection characteristics of cement; (3) The retarder prepared by the present invention can extend the setting time of cement by complexing calcium ions in cement hydration and through adsorption with particles, delaying the hydration of cement, controlling its hydration temperature rise, and having less impact on the strength of cement compared with common retarders. Description of the Drawings

[0021] Figure 1 It is the ionization diagram of chitosan dissolved in acetic acid solution in Example 1;

[0022] Figure 2 It is the ionization diagram of polystyrene sulfonic acid dissolved in water in Example 1;

[0023] Figure 3 It is the electrostatic adsorption diagram of chitosan and polystyrene sulfonic acid in Example 1;

[0024] Figure 4 It is the scanning electron microscope diagram of chitosan in Example 1;

[0025] Figure 5 It is the scanning electron microscope diagram of polystyrene sulfonic acid-modified chitosan in Example 1;

[0026] Figure 6 It is the scanning electron microscope diagram of polystyrene sulfonic acid-modified chitosan in Example 2. Detailed Description of the Invention

[0027] The present invention will be further described in detail below in conjunction with examples and drawings.

[0028] Example 1: The retarder for delaying the setting time of cement provided in this example is polystyrene sulfonic acid-modified chitosan, and the preparation method is as follows:

[0029] (1) Dissolve 1 g of chitosan in 100 ml of acetic acid solution with a mass fraction of 1%, and continuously stir until completely dissolved to obtain an acetic acid solution of chitosan. The ionization diagram of chitosan dissolved in acetic acid solution is as Figure 1 shown;

[0030] (2) Dissolve 1 g of anionic polymer (polystyrene sulfonic acid) in 100 ml of deionized water, and continuously stir until completely dissolved to obtain a polystyrene sulfonic acid solution. The ionization of polystyrene sulfonic acid dissolved in water is as shown in Figure 2 shown;

[0031] (3) While stirring, add the polystyrene sulfonic acid solution to the acetic acid solution of chitosan for an electrostatic adsorption reaction. Continuously stir at 40 °C for 4 h, and mix well after complete dissolution to obtain a mixed solution. The electrostatic adsorption diagram of chitosan and polystyrene sulfonic acid is as shown in Figure 3 shown;

[0032] (4) Centrifuge the above mixed solution at a speed of 3500 rpm for 10 min, remove the supernatant, and then add deionized water and centrifuge 2 - 3 times;

[0033] (5) Put the product obtained above into a drying oven at 60 °C and dry for 6 h, then grind it to obtain a solid powder, and obtain polystyrene sulfonic acid - modified chitosan.

[0034] Example 2: The retarder for delaying the setting time of cement provided in this example is polystyrene sulfonic acid - modified chitosan, and the preparation method is as follows:

[0035] (1) Dissolve 1 g of chitosan in 100 ml of acetic acid solution with a mass fraction of 1%, and continuously stir until completely dissolved to obtain an acetic acid solution of chitosan;

[0036] (2) Dissolve 2 g of anionic polymer (polystyrene sulfonic acid) in 100 ml of deionized water, and continuously stir until completely dissolved to obtain a polystyrene sulfonic acid solution;

[0037] (3) While stirring, add the polystyrene sulfonic acid solution to the acetic acid solution of chitosan, continuously stir for 4 h, and mix well after complete dissolution to obtain a mixed solution;

[0038] (4) Centrifuge the above mixed solution at a speed of 3500 rpm for 10 min, remove the supernatant, and then add deionized water and centrifuge 2 - 3 times;

[0039] (5) Put the product obtained above into a drying oven at 60 °C and dry for 6 h, then grind it to obtain a solid powder, and obtain polystyrene sulfonic acid - modified chitosan.

[0040] Characterization tests were carried out on the chitosan and polystyrene sulfonic acid - modified chitosan in Example 1 and Example 2, as shown in Figures 4 - 6As shown. It can be seen from the figure that the surface of unmodified chitosan is relatively uniform, showing a relatively clear arrangement, with a small pore structure and being relatively orderly as a whole. Granular, membranous or tiny aggregates appear on the surface of the modified substance, thus increasing the surface roughness. At a higher PSS ratio, the excess of PSS will lead to a more significant surface aggregation effect, forming a more irregular and rough surface structure, with a more uneven size and distribution of particles.

[0041] For performance testing, take 450 parts of portland cement and 50 parts of sulfoaluminate cement (portland cement - sulfoaluminate cement), 150 parts of water, and 3 parts of the retarder polystyrene sulfonic acid - modified chitosan prepared in Example 1 / Example 2. Determine the setting time of the cement from the above - mentioned raw materials according to GB / T 1346 - 2011 "Test Method for Setting Time of Cement Mortar". In addition, according to "Test Method for Strength of Cement Mortar (ISO Method)" GB / T 17671—2021, test the compressive strength of the specimens prepared by the above - mentioned method at the ages of 1d and 3d. In addition, use boric acid retarder to replace the retarder in this example as a comparison, and test the initial setting time of the portland cement - sulfoaluminate cement and the compressive strength at 1d and 3d. The results are shown in Table 1 below.

[0042] It can be seen from Table 1 that compared with the boric acid retarder, it can effectively improve the setting time of the portland cement - sulfoaluminate cement, but its early strength will decrease significantly. However, the anionic polymer - modified chitosan of the present invention can effectively extend the setting time of the cement while having a relatively small impact on the early strength of the cement.

[0043] Table 1 Performance test table of polystyrene sulfonic acid - modified chitosan, pure cement and boric acid retarder in the examples

[0044] Initial setting time (min) Final setting time (min) 1-day strength (Mpa) 3-day strength (Mpa) Pure cement 25 32 30.3 38.4 Example 1 62 78 28.5 34.2 Example 2 69 87 26.8 36.6 Boric acid retarder 58 69 18.5 26.3

Claims

1. A retarder for delaying the setting time of cement, characterized in that: The retarder is anionic polymer modified chitosan.

2. The retarder for delaying the setting time of cement according to claim 1, characterized in that: The mass ratio of the anionic polymer to chitosan is 1-2:

1.

3. The retarder for delaying cement setting time according to claim 1, characterized in that: The anionic polymer is polystyrene sulfonic acid, sodium polystyrene sulfonate or sodium polyacrylate.

4. The retarder for delaying cement setting time according to claim 1, characterized in that: The deacetylation degree of the chitosan is 85-95%.

5. The retarder for delaying the setting time of cement according to claim 1, characterized in that: The cement is silicate-sulphoaluminate cement.

6. A method for preparing a retarder for delaying cement setting time according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) fully dissolving chitosan in a weak acid solution to obtain a chitosan solution; (2) fully dissolving the anionic polymer in a solvent to obtain an anionic polymer solution; (3) adding the anionic polymer solution to the chitosan solution, stirring sufficiently, and then subjecting the solution to an electrostatic adsorption reaction. After the reaction is completed, the solution is centrifuged, washed, dried, and crushed to obtain anionic polymer-modified chitosan.

7. The preparation method according to claim 6, characterized in that: In step (1), the weak acid solution is an acetic acid solution with a mass fraction of 1-2wt%.

8. The preparation method according to claim 6, characterized in that: In step (1), the mass ratio of the chitosan to the weak acid in the weak acid solution is 1:1-2.

9. The preparation method according to claim 6, characterized in that: In step (3), the conditions for the electrostatic adsorption reaction are: reacting at 40-60° C. for 4-8 hours.

10. The preparation method according to claim 6, characterized in that: In step (3), the particle size of the anionic polymer modified chitosan obtained by pulverizing is less than 50 μm.

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