Modified chitosan, preparation method thereof, setting retarding type water reducing agent and application thereof

Abstract

The application belongs to the technical field of building materials, and discloses a modified chitosan, a preparation method thereof, a retarding water reducing agent and application. The modified chitosan is a compound with an amino acid chelating structure linked to a chitosan molecular chain. The amino acid chelating structure can synergistically play a role with the steric hindrance effect of the spatial structure of chitosan itself. The addition of the modified chitosan can make the metal ion concentration in the early concrete paste in a dynamic balance state, thereby reducing the early hydration rate. In addition, the modified chitosan molecular chain also retains a certain amount of hydroxyl groups, which can chelate metal ions while adsorbing a large amount of water, thereby promoting the progress of the later hydration reaction of concrete. The water reducing agent obtained by compounding the modified chitosan with polycarboxylic acid and other components has excellent water reducing performance, retarding performance and slump retention performance, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of building materials, and particularly relates to a modified chitosan and its preparation method, a retarding water-reducing agent, and its application. Background Technology

[0002] Polycarboxylate superplasticizers, commonly used chemical admixtures in concrete, are widely applied due to their advantages such as low dosage, high water reduction, customizable molecular structure, and environmental friendliness. However, the interaction between polycarboxylate superplasticizers and concrete can affect the flowability of cement paste and cause abnormal setting. Currently, the addition of retarder substances such as chitosan and polyether to polycarboxylate superplasticizers aims to improve the deterioration of concrete paste flowability caused by their addition.

[0003] However, in practical applications, the addition of chitosan, polyether, and other substances can mitigate the impact of polycarboxylate superplasticizers on concrete paste to some extent. However, these substances often also create compatibility issues with cement, manufactured sand, and mineral admixtures (fly ash, mineral powder, etc.) in concrete, thus adversely affecting concrete performance (such as hydration setting, curing performance, strength, and hardness), or even the water-reducing effect of polycarboxylate superplasticizers, significantly limiting their application. Therefore, it is necessary to develop more adaptable retarding substances to meet practical needs. Summary of the Invention

[0004] The primary objective of this invention is to address the adverse effects of adding retarders to the water-reducing effect of polycarboxylate and the performance of concrete in the prior art, thereby obtaining a modified chitosan that possesses excellent water-reducing, retarding, and slump-retaining properties.

[0005] The second objective of this invention is to provide a method for preparing modified chitosan.

[0006] A third objective of this invention is to provide modified chitosan prepared by the above method.

[0007] The fourth objective of this invention is to provide a retarding water-reducing agent.

[0008] The fifth objective of this invention is to provide the application of modified chitosan and / or retarding water-reducing agents in the construction field.

[0009] Specifically, the modified chitosan is a compound with an amino acid-like chelate structure bonded to the chitosan molecular chain, and the modified chitosan structure includes at least one of the structural unit 1 shown in formula (1), structural unit 2 shown in formula (2), and structural unit 3 shown in formula (3).

[0010]

[0011] In formulas (1) to (3), R1, R2, R3, R4, R5, and R6 are independently carbonyl, C1-C4 alkylene, C1-C4 haloalkylene, C1-C4 carboxylic acid group, C1-C4 halocarboxylic acid group, C1-C4 acylene, or C1-C4 haloacylene. In some specific embodiments, in formulas (1) to (3), R1, R2, R3, R4, R5, and R6 are independently -CH2CO-, -CH2CH2CO-, -CH2CH2CH2CO-, -CH2CH2-, -CH[CH2(Cl)COOH]-, or -CH[CH2(Br)COOH]-.

[0012] In some specific embodiments, the chitosan is oligochitosan and / or polymeric chitosan.

[0013] In some specific embodiments, the modified chitosan has a weight-average molecular weight of 300 to 50,000 and a molecular weight distribution of 1.2 to 1.35.

[0014] The method for preparing modified chitosan provided by the present invention includes: taking chitosan and a halocarboxylic acid and carrying out a halocarboxylic acid reaction under the action of a catalyst to obtain the modified chitosan.

[0015] In some specific embodiments, the weight-average molecular weight of the chitosan is 300 to 50,000.

[0016] In some specific embodiments, the halocarboxylic acid is selected from one or more of 3-chloropyruvic acid, 3-bromopyruvic acid, 2-dichlorosuccinic acid, 2,3-dichlorosuccinic acid, 3-chloropropionic acid, and 3-bromopropionic acid.

[0017] In some specific embodiments, the catalyst is selected from one or more of Ziegler-Natta catalysts, MOF catalysts, and copper oxide catalysts.

[0018] In some specific embodiments, the molar ratio of chitosan to halocarboxylic acid is (0.01-2):1.

[0019] In some specific embodiments, the amount of catalyst added is 0.01 to 0.5 wt%, based on the total molar amount of chitosan and halocarboxylic acid.

[0020] In some specific embodiments, the temperature of the halocarboxylate reaction is 85–95°C, and the time is 4–10 h.

[0021] This invention provides modified chitosan prepared by the above method.

[0022] The retarding water-reducing agent provided by this invention includes the above-mentioned modified chitosan.

[0023] In some specific embodiments, the retarding water-reducing agent also includes polycarboxylic acid, air-entraining agent, and water-retaining agent.

[0024] In some specific embodiments, the modified chitosan content in the retarding water-reducing agent is 15-50 parts by weight, the polycarboxylic acid content is 50-80 parts by weight, the air-entraining agent content is 0.1-0.5 parts by weight, and the water-retaining agent content is 0.1-0.5 parts by weight.

[0025] This invention also provides the application of the above chitosan and / or retarding water-reducing agents in the construction field.

[0026] This invention introduces an amino acid-like chelating structure into the basic molecular chain structure of chitosan, thereby obtaining a modified chitosan. Using this modified chitosan as a retarder, the resulting water-reducing agent, when compounded with other components such as polycarboxylic acid, exhibits excellent water-reducing, retarding, and slump-retaining properties, showing promising application prospects. It is speculated that the modified chitosan provided by this invention possesses these excellent properties because the amino acid-like chelating structure introduced into the chitosan molecular chain structure works synergistically with the steric hindrance effect of the chitosan's own spatial structure. This endows the modified chitosan with a good ability to chelate metal ions such as calcium, aluminum, and magnesium dissolved in concrete paste, as well as a certain water-reducing and dispersing effect. This allows the concentration of metal ions in the early-stage concrete paste containing the modified chitosan to be in a dynamic equilibrium state, thereby reducing the early hydration rate. Furthermore, because the modified chitosan retains a certain amount of hydroxyl groups, it can adsorb a large amount of water while chelating metal ions, thus promoting the later-stage hydration reaction of concrete. Detailed Implementation

[0027] The modified chitosan provided by the present invention is a compound with an amino acid-like chelate structure bonded to the chitosan molecular chain. The modified chitosan structure includes at least one of the structural unit 1 shown in formula (1), structural unit 2 shown in formula (2), and structural unit 3 shown in formula (3).

[0028]

[0029] In formulas (1) to (3), R1, R2, R3, R4, R5, and R6 are independently carbonyl, C1-C4 alkylene, C1-C4 haloalkylene, C1-C4 carboxylic acid group, C1-C4 halocarboxylic acid group, C1-C4 acylene, or C1-C4 haloacylene. Examples of C1-C4 alkylene include, but are not limited to: -CH2-, -CH2CH2-, -CH(CH3)-, -CH2CH2CH2-, -C(CH3)2-, or -CH2CH2CH2CH2-. Examples of C1-C4 haloalkylene include, but are not limited to: -CH(Cl)-, -CH(Br)CH2-, -C[Br(CH3)]-, -CH(Br)CH2CH2-, -C[CH2(Cl)CH3]-, or -CH2CH2CH(Br)CH2-. Examples of C1-C4 carboxylic acid groups include, but are not limited to: -CH(COOH)-, -CH2CH(COOH)-, or -CH(CH3)CH(COOH)-. Examples of C2-C4 acyl groups include, but are not limited to: -CH2CO-, -CH2CH2CO-, -CH(CH3)CO-, -CH2CH2CH2CO-, or -C(CH3)2CO-. Examples of C2-C4 haloacyl groups include, but are not limited to: -CH(Br)CO-, -CH2CH(Cl)CO-, or -CH(CH3)CH(Br)CO-. In some preferred embodiments, R1, R2, R3, R4, R5, and R6 are independently -CH2CO-, -CH2CH2CO-, -CH2CH2CH2CO-, -CH2CH2-, -CH[CH2(Cl)COOH]-, or -CH[CH2(Br)COOH]-.

[0030] The modified chitosan structure provided by the present invention may further include one or more of the following: structural unit four shown in formula (4), structural unit five shown in formula (5), structural unit six shown in formula (6), and structural unit seven shown in formula (7):

[0031]

[0032]

[0033] In equations (5) to (7), R7, R8, R9 and R 10Independently, it is a carbonyl group, a C1-C4 alkylene group, a C1-C4 haloalkylene group, a C1-C4 carboxylic acid group, a C1-C4 halocarboxylic acid group, a C1-C4 acyl group, or a C1-C4 haloacyl group. Examples of C1-C4 alkylene groups include, but are not limited to: -CH2-, -CH2CH2-, -CH(CH3)-, -CH2CH2CH2-, -C(CH3)2-, or -CH2CH2CH2CH2-. Examples of C1-C4 haloalkylene groups include, but are not limited to: -CH(Cl)-, -CH(Br)CH2-, -C[Br(CH3)]-, -CH(Br)CH2CH2-, -C[CH2(Cl)CH3]-, or -CH2CH2CH(Br)CH2-. Examples of C1-C4 carboxylic acid groups include, but are not limited to: -CH(COOH)-, -CH2CH(COOH)-, or -CH(CH3)CH(COOH)-. Examples of C2-C4 acyl groups include, but are not limited to: -CH2CO-, -CH2CH2CO-, -CH(CH3)CO-, -CH2CH2CH2CO-, or -C(CH3)2CO-. Examples of C2-C4 haloacyl groups include, but are not limited to: -CH(Br)CO-, -CH2CH(Cl)CO-, or -CH(CH3)CH(Br)CO-. In some preferred embodiments, R1, R2, R3, R4, R5, and R6 are independently -CH2CO-, -CH2CH2CO-, -CH2CH2CH2CO-, -CH2CH2-, -CH[CH2(Cl)COOH]-, or -CH[CH2(Br)COOH]-.

[0034] In this invention, the terms "one", "two", "three", "four", "five", "six" and "seven" in structural unit one, structural unit two, structural unit three, structural unit four, structural unit five, structural unit six and structural unit seven are merely for differentiation and ease of description, and have no other special meaning.

[0035] In this invention, the proportions of structural units one, two, three, four, five, six, and seven in the modified chitosan structure are not particularly limited. That is, the proportions of structural units one, two, three, four, five, six, and seven in the modified chitosan structure provided in this invention can be 1:2:1:1:3:6:2, 2:5:9:3:1:1:1, 9:1:8:2:1:7, 100:5:135:1:4:3:6, or other arbitrary proportions. Similarly, the distribution of structural units one, two, three, four, five, six, and seven in the modified chitosan structure is not particularly limited. That is, structural units one, two, three, four, five, six, and seven in the modified chitosan structure provided in this invention can be distributed in any manner.

[0036] In this invention, examples of chitosan molecules include, but are not limited to, oligochitosan and / or polymeric chitosan. In some specific embodiments, the degree of polymerization of the oligochitosan is preferably any integer from 2 to 20, such as 2, 3, 5, 8, 10, 13, 15, 17, 20, or any integer between them. In some specific embodiments, the degree of polymerization of the polymeric chitosan is preferably any integer from 21 to 2000, such as 21, 30, 50, 100, 500, 1000, 1200, 1500, 2000, or any integer between them; the degree of polymerization of the polymeric chitosan is preferably 21 to 200.

[0037] In this invention, the weight-average molecular weight of the modified chitosan is preferably 300–50,000, such as 300, 500, 1000, 2000, 4000, 4210, 4300, 4520, 5000, 6000, 7500, 7801, 8000, 9000, 10000, 20000, 30000, 40000, 50000, or any value between them. The molecular weight distribution of the modified chitosan is preferably 1.2–1.35, such as 1.2, 1.21, 1.24, 1.27, 1.3, 1.33, 1.35, or any value between them.

[0038] The method for preparing modified chitosan provided by the present invention includes: subjecting chitosan and a halocarboxylic acid to a halogenation carboxylation reaction under the action of a catalyst to obtain the modified chitosan.

[0039] In the preparation of the modified chitosan described above, the weight-average molecular weight of the chitosan is preferably 300 to 50,000, such as 300, 500, 1000, 2000, 1000, 2000, 3000, 7500, 10000, 10200, 14600, 20000, 30000, 40000, 50000 or any value between them.

[0040] In the preparation of the modified chitosan described above, the halocarboxylic acid is a class of compounds that simultaneously contain halogen atoms and carboxylic acids in their molecules. It can undergo a halocarboxylation reaction with chitosan. This halocarboxylic acid can be purchased directly or prepared using conventional methods. In some preferred embodiments, specific examples of the halocarboxylic acid include, but are not limited to, one or more of the following: 3-chloropyruvic acid, 3-bromopyruvic acid, 2-dichlorosuccinic acid, 2,3-dichlorosuccinic acid, 3-chloropropionic acid, and 3-bromopropionic acid.

[0041] In the preparation process of the above-mentioned modified chitosan, the halogenated carboxylic acidification reaction is defined as follows: under the action of a catalyst, the halogenated carboxylic acid removes halogen atoms to form a carbocation intermediate, which attacks the amino group on the chitosan to form a carbon-nitrogen bond and removes hydrogen ions to obtain modified chitosan with at least an amino acid-like chelate structure.

[0042] In the preparation of the modified chitosan described above, the catalyst is a compound capable of catalyzing the halogenation and carboxylation reaction between halocarboxylic acids and amino groups on the chitosan molecular chain. This catalyst can be purchased directly or prepared using conventional methods. In some preferred embodiments, specific examples of the catalyst include, but are not limited to, one or more of Ziegler-Natta catalysts, MOF catalysts, and copper oxide catalysts.

[0043] In the preparation process of the modified chitosan described above, the preferred molar ratio of chitosan to halocarboxylic acid is (0.01-2):1, such as 0.01:1, 0.05:1, 0.1:1, 0.18:1, 0.21:1, 0.5:1, 0.9:1, 1.02:1, 1.5:1, 2:1 or any value between them.

[0044] In the preparation process of the modified chitosan described above, based on the total molar amount of chitosan and halocarboxylic acids, the amount of catalyst added is preferably 0.01 to 0.5 wt%, such as 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.35 wt%, 0.4 wt%, 0.5 wt%, or any value between them.

[0045] In the preparation process of the modified chitosan described above, the conditions for the halogenated carboxylate reaction include a temperature preferably of 85–95°C, such as 85°C, 87°C, 88°C, 90°C, 91°C, 92°C, 94°C, 95°C or any value between them; and a time preferably of 4–10 h, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or any value between them.

[0046] The present invention also provides a modified chitosan prepared by the above method, wherein the modified chitosan has at least one of the structural unit 1 shown in formula (1), structural unit 2 shown in formula (2), and structural unit 3 shown in formula (3); in addition, it may also have one or more of the structural unit 4 shown in formula (4), structural unit 5 shown in formula (5), structural unit 6 shown in formula (6), and structural unit 7 shown in formula (7).

[0047] The retarding water-reducing agent provided by this invention includes the modified chitosan described above. In some preferred embodiments, the retarding water-reducing agent preferably further includes polycarboxylic acid, an air-entraining agent, and a water-retaining agent. The polycarboxylic acid is a commonly used reagent in existing water-reducing agents; it can be purchased directly or prepared using conventional methods. Specific examples of the air-entraining agent include, but are not limited to, low-surface-tension surfactants, whose addition enables the concrete to generate a large number of uniformly distributed, closed, and stable microbubbles during mixing; this air-entraining agent can be purchased directly or prepared using conventional methods. Specific examples of the water-retaining agent include, but are not limited to, superabsorbent resins, whose addition can improve the compressive strength, impermeability, and durability of concrete; this water-retaining agent can be purchased directly or prepared using conventional methods.

[0048] In this invention, the retarding water-reducing agent contains modified chitosan, and preferably also contains polycarboxylic acid, an air-entraining agent, and a water-retaining agent. The modified chitosan content is preferably 15-50 parts by weight, such as 15, 20, 25, 30, 35, 40, 45, 50 parts by weight, or any value between them. The polycarboxylic acid content is preferably 50-80 parts by weight, such as 50, 55, 60, 65, 70, 75, 80 parts by weight, or any value between them. The air-entraining agent content is preferably 0.1-0.5 parts by weight, such as 0.1, 0.2, 0.3, 0.4, 0.5 parts by weight, or any value between them. The water-retaining agent content is preferably 0.1-0.5 parts by weight, such as 0.1, 0.2, 0.3, 0.4, 0.5 parts by weight, or any value between them.

[0049] Furthermore, the present invention also provides the application of the modified chitosan and / or retarding water-reducing agent in the construction field.

[0050] The embodiments of the present invention are described in detail below. These embodiments are intended to explain the present invention and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0051] The raw materials and their sources used in the following examples are shown below:

[0052] Air-entraining agent (manufacturer: Nanjing Xinyi Synthetic, item number: XY-A01); water-retaining agent (manufacturer: Ningbo Zhongshuike, item number: SK-530); polycarboxylate (manufacturer: Kezhijie, item number: Point-400S); PCE-S (manufacturer: Kezhijie, item number: Point-MS); Sika retarder H-1 (manufacturer: Sika, item number: POWDER P).

[0053] Preparation Example 1

[0054] This preparation example uses the modified chitosan and its preparation method provided by the present invention. The preparation of the modified chitosan is as follows: 3-bromopyruvic acid and chitosan (weight average molecular weight of 2000) are dissolved in butyl acetate at a molar ratio of 1:0.1, and 0.05wt% of Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6 hours, the mixture is filtered, washed and dried to obtain the modified chitosan.

[0055] The infrared spectrum of the obtained modified chitosan was measured to be within 1270 cm⁻¹. -1 A CN absorption peak for secondary amines appeared nearby; at 1600 cm⁻¹ -1 A C=O absorption peak for carboxylate appeared nearby, at 1715 cm⁻¹. -1 The presence of ketone absorption peaks indicates that an amino acid-like chelate structure has indeed been introduced into the structure of the modified chitosan. Furthermore, the weight-average molecular weight of the modified chitosan obtained from this modified chitosan is 4725, and the molecular weight distribution is 1.32.

[0056] Preparation Example 2

[0057] This preparation example uses the modified chitosan and its preparation method provided by the present invention. The modified chitosan is prepared as follows: 3-bromopyruvic acid and chitosan (weight average molecular weight of 5000) are dissolved in butyl acetate at a molar ratio of 1:1, and 0.15wt% Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6 hours, the mixture is filtered, washed and dried to obtain the modified chitosan.

[0058] The infrared spectrum of the obtained modified chitosan was measured to be within 1270 cm⁻¹. -1A CN absorption peak for secondary amines appeared nearby; at 1600 cm⁻¹ -1 A C=O absorption peak for carboxylate appeared nearby, at 1715 cm⁻¹. -1 The presence of ketone absorption peaks indicates that an amino acid-like chelate structure has indeed been introduced into the structure of the modified chitosan. Furthermore, the weight-average molecular weight of the modified chitosan is 6316, and the molecular weight distribution is 1.32.

[0059] Preparation Example 3

[0060] This preparation example uses the modified chitosan and its preparation method provided by the present invention. The modified chitosan is prepared as follows: 2,3-dibromosuccinic acid and chitosan (weight average molecular weight of 7000) are dissolved in butyl acetate at a molar ratio of 1:0.5, and 0.12wt% of Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6 hours, the mixture is filtered, washed and dried to obtain the modified chitosan.

[0061] The infrared spectrum of the obtained modified chitosan was measured to be within 1270 cm⁻¹. -1 A CN absorption peak for secondary amines appeared nearby; at 1600 cm⁻¹ -1 The presence of a C=O absorption peak of carboxylate nearby indicates that an amino acid-like chelate structure has indeed been introduced into the structure of the modified chitosan. Furthermore, the weight-average molecular weight of the modified chitosan is 9182, and the molecular weight distribution is 1.32.

[0062] Preparation Example 4

[0063] This preparation example uses the modified chitosan and its preparation method provided by the present invention. The modified chitosan is prepared as follows: 3-bromopropionic acid and chitosan (weight average molecular weight of 5000) are dissolved in butyl acetate at a molar ratio of 1:1, and 0.2 wt% Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6 h, the mixture is filtered, washed and dried to obtain the modified chitosan.

[0064] The infrared spectrum of the obtained modified chitosan was measured to be within 1270 cm⁻¹. -1 A CN absorption peak for secondary amines appeared nearby; at 1600 cm⁻¹ -1 The presence of a C=O absorption peak of carboxylate nearby indicates that an amino acid-like chelate structure has indeed been introduced into the structure of the modified chitosan. Furthermore, the weight-average molecular weight of the modified chitosan is 6182, and the molecular weight distribution is 1.21.

[0065] Preparation Example 5

[0066] This preparation example prepares modified chitosan according to the method provided in Preparation Example 1, except that an equimolar amount of chitosan (weight average molecular weight of 7000) is used instead of chitosan (weight average molecular weight of 2000), while other conditions remain the same.

[0067] The infrared spectrum of the obtained modified chitosan was measured to be within 1270 cm⁻¹. -1 A CN absorption peak for secondary amines appeared nearby; at 1600 cm⁻¹ -1 A C=O absorption peak for carboxylate appeared nearby; at 1715 cm⁻¹. -1 The presence of a C=O absorption peak for a ketone group nearby indicates that an amino acid-like chelate structure has indeed been introduced into the structure of the modified chitosan. Furthermore, the weight-average molecular weight of the modified chitosan is 9750, and its molecular weight distribution is 1.13.

[0068] Example 1

[0069] This embodiment illustrates the retarded water-reducing agent and its preparation method provided by the present invention. The components and their contents of the retarded water-reducing agent are specifically: 19.5 parts by weight of modified chitosan provided in Preparation Example 1, 0.4 parts by weight of an air-entraining agent, 0.1 parts by weight of a water-retaining agent, and 80 parts by weight of polycarboxylic acid.

[0070] In this embodiment, the preparation of the retarded water-reducing agent specifically includes: taking the modified chitosan, air-entraining agent and water-retaining agent according to the above mass proportions, adding them to the polycarboxylic acid and stirring evenly to obtain the retarded water-reducing agent.

[0071] Example 2

[0072] This embodiment illustrates a retarding water-reducing agent and its preparation method. The components and their contents of the retarding water-reducing agent are as follows: 49.5 parts by weight of the modified chitosan provided in Preparation Example 1, 0.3 parts by weight of an air-entraining agent, 0.2 parts by weight of a water-retaining agent, and 50 parts by weight of polycarboxylic acid.

[0073] In this embodiment, the preparation of the retarded water-reducing agent specifically includes: taking the modified chitosan, air-entraining agent and water-retaining agent according to the above mass proportions, adding them to the polycarboxylic acid and stirring evenly to obtain the retarded water-reducing agent.

[0074] Example 3

[0075] This embodiment illustrates a retarding water-reducing agent and its preparation method. The components and their contents of the retarding water-reducing agent are as follows: 29.2 parts by weight of modified chitosan provided in Preparation Example 3, 0.4 parts by weight of an air-entraining agent, 0.4 parts by weight of a water-retaining agent, and 70 parts by weight of polycarboxylic acid.

[0076] In this embodiment, the preparation of the retarded water-reducing agent specifically includes: taking the modified chitosan, air-entraining agent and water-retaining agent according to the above mass proportions, adding them to the polycarboxylic acid and stirring evenly to obtain the retarded water-reducing agent.

[0077] Example 4

[0078] This embodiment illustrates a retarding water-reducing agent and its preparation method. The components and their contents of the retarding water-reducing agent are as follows: 19.5 parts by weight of modified chitosan provided in Preparation Example 4, 0.4 parts by weight of an air-entraining agent, 0.1 parts by weight of a water-retaining agent, and 80 parts by weight of polycarboxylic acid.

[0079] In this embodiment, the preparation of the retarded water-reducing agent specifically includes: taking the modified chitosan, air-entraining agent and water-retaining agent according to the above mass proportions, adding them to the polycarboxylic acid and stirring evenly to obtain the retarded water-reducing agent.

[0080] Example 5

[0081] This embodiment prepares a retarding water-reducing agent according to the method provided in Example 1, except that the modified chitosan provided in Preparation Example 5 is used instead of the modified chitosan provided in Preparation Example 1 in equal parts by mass, while other conditions are the same.

[0082] Comparative Example 1

[0083] The comparative example provides a water-reducing agent prepared by uniformly mixing 40 parts by weight of PCE-S with 60 parts by weight of water.

[0084] Comparative Example 2

[0085] The comparative example prepared a retarding water-reducing agent according to the method provided in Example 1, except that an equal mass of Sica retarder H-1 was used instead of the modified chitosan provided in Example 1, while other conditions were the same.

[0086] Comparative Example 3

[0087] The comparative example prepared a retarding water-reducing agent according to the method provided in Example 1, except that an equal mass of polycarboxylic acid was used instead of the modified chitosan provided in Example 1, while other conditions remained the same.

[0088] Comparative Example 4

[0089] This comparative example illustrates a retarded water-reducing agent and its preparation method. The specific components and their mass fractions are: 19.5 parts by mass of modified chitosan, 0.4 parts by mass of an air-entraining agent, 0.1 parts by mass of a water-retaining agent, and 80 parts by mass of polycarboxylic acid. The preparation of this retarded water-reducing agent specifically includes: adding the modified chitosan, air-entraining agent, and water-retaining agent to the polycarboxylic acid according to the above mass fractions and stirring until homogeneous to obtain the retarded water-reducing agent.

[0090] The preparation of modified chitosan includes: reacting propoxylic acid and chitosan (weight-average molecular weight 2000) at a molar ratio of 1:0.1; first, adding chitosan to a 75% acetic acid solution and ultrasonically dispersing for 25 min; then adding propoxylic acid and stirring for 45 min; filtering, washing, and drying to obtain modified chitosan. The obtained modified chitosan was tested and found to have a viscosity of 1270 cm⁻¹. -1 A CN absorption peak for secondary amines appeared nearby; at 1715 cm⁻¹ -1 A C=O absorption peak for the ketone group appeared nearby; at 1740 cm⁻¹ -1 The presence of C=O absorption peaks of aldehyde groups nearby indicates that no amino acid-like chelate structures have been introduced into the structure of the obtained chitosan. Furthermore, the weight-average molecular weight of the modified chitosan is 4893, and the molecular weight distribution is 1.32.

[0091] Test case

[0092] Concrete was prepared according to the proportions in Table 1, and the water-reducing agents obtained from the above examples and comparative examples were added to the concrete at 0.5% (consolidated admixture). The specific dosage of each water-reducing agent was to make the concrete slump 200±10mm. Then, the performance indicators were tested according to GB8076-2008 "Concrete Admixtures", and the results are shown in Table 2.

[0093] Table 1 (Parts by weight)

[0094] Cement (C) Sand (S) Stone (G) water Runfeng PO 42.5R Manufactured sand, MX = 2.7 5-25mm tap water 360 784 1060 175

[0095] Table 2

[0096]

[0097]

[0098] The test results show that, compared with comparative examples 1 to 4, the modified chitosan provided by this invention can work synergistically with polycarboxylic acid to achieve better water reduction, retardation and slump retention effects, and has good application prospects.

[0099] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A retarding water-reducing agent, characterized in that, The retarding water-reducing agent comprises 15-50 parts by weight of modified chitosan, 50-80 parts by weight of polycarboxylic acid, 0.1-0.5 parts by weight of air-entraining agent, and 0.1-0.5 parts by weight of water-retaining agent. The preparation of the modified chitosan includes: taking chitosan and a halocarboxylic acid under the action of a catalyst to carry out a halocarboxylation reaction to obtain the modified chitosan; The halocarboxylic acid is selected from one or more of 3-chloropyruvic acid, 3-bromopyruvic acid, 2-dichlorosuccinic acid, 2,3-dichlorosuccinic acid, 3-chloropropionic acid, and 3-bromopropionic acid.

2. The retarding water-reducing agent according to claim 1, characterized in that, The chitosan is oligochitosan and / or high-molecular-weight chitosan.

3. The retarding water-reducing agent according to claim 1, characterized in that, The modified chitosan has a weight-average molecular weight of 300-50000 and a molecular weight distribution of 1.2-1.

35.

4. The retarding water-reducing agent according to claim 1, characterized in that, The weight-average molecular weight of the chitosan is 300-50000.

5. The retarding water-reducing agent according to claim 1, characterized in that, The catalyst is selected from one or more of Ziegler-Natta catalysts, MOF catalysts, and copper oxide catalysts.

6. The retarding water-reducing agent according to claim 1, characterized in that, The molar ratio of chitosan to halocarboxylic acid is (0.01~2):

1.

7. The retarding water-reducing agent according to claim 1, characterized in that, Based on the total molar amount of chitosan and halocarboxylic acid, the amount of catalyst added is 0.01~0.5wt%.

8. The retarding water-reducing agent according to claim 2, characterized in that, The halogenated carboxylate reaction is carried out at a temperature of 85-95°C for 4-10 hours.

9. The application of the retarding water-reducing agent according to any one of claims 1 to 8 in the construction field.

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