Modified chitosan and preparation method therefor, and retardation-type water-reducing agent and use thereof

Abstract

The present invention belongs to the technical field of building materials. Disclosed are a modified chitosan and a preparation method therefor, and a retardation-type water-reducing agent and the use thereof. The modified chitosan provided in the present invention is a compound in which a chitosan molecular chain is bonded with an amino acid-like chelating structure, wherein the amino acid-like chelating type structure can play a synergistic role with a steric effect of a spatial three-dimensional structure of the chitosan itself. The addition of the modified chitosan can make the concentration of metal ions in an early concrete slurry be in a dynamic equilibrium state, thereby achieving an effect of reducing the early hydration rate. In addition, a certain amount of hydroxyl is further reserved on the molecular chain of the modified chitosan, such that a large amount of water can be adsorbed while metal ions are chelated, thereby promoting a later hydration reaction of the concrete. The water-reducing agent obtained by compounding the modified chitosan provided in the present invention with other components, such as polycarboxylic acid, has good water reducing performance, retarding performance and slump retaining performance, and has good application prospects.

Description

Modified chitosan, preparation method thereof, slow-setting water-reducing agent and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311736218.9 filed with the Chinese Patent Office on December 18, 2023, entitled "A modified chitosan, its preparation method, slow-setting water-reducing agent and its application", the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The invention belongs to the technical field of building materials, and in particular relates to a modified chitosan and a preparation method thereof, a slow-setting water-reducing agent and applications thereof. Background Art

[0004] Polycarboxylate superplasticizers, commonly used chemical admixtures in concrete, are widely used due to their low dosage, high water-reducing properties, customizable molecular structure, and environmental friendliness. However, the interaction between polycarboxylate superplasticizers and concrete can affect the flow properties of the cement paste and cause abnormal setting. Currently, the addition of retarding substances such as chitosan and polyethers to polycarboxylate superplasticizers is being investigated in an attempt to improve the deterioration of concrete paste flow properties caused by the addition of polycarboxylate superplasticizers.

[0005] However, in actual use, the addition of substances such as chitosan and polyether can alleviate the impact of polycarboxylate superplasticizers on concrete paste to a certain extent. However, these substances often also cause compatibility issues with cement, manufactured sand, and mineral admixtures (fly ash, mineral powder, etc.) in concrete, which in turn has an adverse effect on the performance of concrete (such as hydration and setting, curing performance, strength, hardness and other mechanical properties), or affects the water-reducing effect of polycarboxylate, which greatly restricts the application of polycarboxylate superplasticizers. Therefore, it is necessary to develop more adaptable retarding substances to meet practical needs.

[0006] Summary of the Invention

[0007] The first purpose of the present invention is to solve the adverse effects of the addition of retarders in the prior art on the water-reducing effect of polycarboxylic acid and the performance of concrete, thereby obtaining a modified chitosan with excellent water-reducing performance, retarding performance and slump retention performance.

[0008] The second object of the present invention is to provide a method for preparing modified chitosan.

[0009] The third object of the present invention is to provide modified chitosan prepared by the above method.

[0010] A fourth object of the present invention is to provide a slow-setting water-reducing agent.

[0011] A fifth object of the present invention is to provide applications of modified chitosan and / or retarding water reducer in the field of construction.

[0012] Specifically, the modified chitosan is a compound having an amino acid chelate-type structure bonded to the chitosan molecular chain, and the structure of the modified chitosan includes at least one of the structural unit 1 represented by formula (1), the structural unit 2 represented by formula (2), and the structural unit 3 represented by formula (3);

[0013] In formulas (1) to (3), R1, R2, R3, R4, R5, and R6 are independently 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. 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]-.

[0014] In some specific embodiments, the chitosan is oligochitosan and / or high-molecular-weight chitosan.

[0015] In some specific embodiments, the weight average molecular weight of the modified chitosan is 300 to 50,000, and the molecular weight distribution is 1.2 to 1.35.

[0016] The preparation method of the modified chitosan provided by the present invention comprises: taking chitosan and halogenated carboxylic acid and carrying out halogenated carboxylic acid reaction under the action of a catalyst to obtain the modified chitosan.

[0017] In some specific embodiments, the weight average molecular weight of the chitosan is 300 to 50,000.

[0018] In some specific embodiments, the halogenated carboxylic 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.

[0019] In some specific embodiments, the catalyst is selected from one or more of a Ziegler-Natta catalyst, a MOFs catalyst, and a copper oxide catalyst.

[0020] In some specific embodiments, the molar ratio of chitosan to halogenated carboxylic acid is (0.01-2):1.

[0021] In some specific embodiments, the catalyst is added in an amount of 0.01 to 0.5 wt % based on the total molar amount of the chitosan and the halogenated carboxylic acid.

[0022] In some specific embodiments, the temperature of the halogenated carboxylation reaction is 85-95° C., and the time is 4-10 hours.

[0023] The present invention provides modified chitosan prepared by the above method.

[0024] The slow-setting water-reducing agent provided by the present invention comprises the above-mentioned modified chitosan.

[0025] In some specific embodiments, the retarding water reducer further comprises polycarboxylic acid, an air entraining agent and a water retaining agent.

[0026] In some specific embodiments, the content of modified chitosan in the retarding water reducer is 15-50 parts by mass, the content of polycarboxylic acid is 50-80 parts by mass, the content of air entraining agent is 0.1-0.5 parts by mass, and the content of water retaining agent is 0.1-0.5 parts by mass.

[0027] The present invention also provides the application of the chitosan and / or slow-setting water-reducing agent in the field of construction.

[0028] The present invention introduces an amino acid chelate structure into the basic molecular chain structure of chitosan to obtain a modified chitosan. The modified chitosan is used as a retarder and compounded with other components such as polycarboxylic acid to obtain a water reducer that has excellent water-reducing performance, retarding performance, and slump retention performance, and has good application prospects. It is speculated that the reason why the modified chitosan provided by the present invention has the above excellent properties is that the amino acid chelate structure introduced into the chitosan molecular chain structure can work synergistically with the steric hindrance effect of the spatial structure of chitosan itself, giving the modified chitosan a good ability to chelate metal ions such as calcium, aluminum, and magnesium dissolved in the concrete paste and a certain water-reducing and dispersing effect, so that the metal ion concentration in the early concrete paste added with the modified chitosan can be in a dynamic equilibrium state, thereby reducing the early hydration rate; and because the modified chitosan still retains a certain amount of hydroxyl groups, the modified chitosan can chelate metal ions while adsorbing a large amount of water, thereby promoting the late hydration reaction of the concrete. DETAILED DESCRIPTION

[0029] The modified chitosan provided by the present invention is a compound having an amino acid chelate-type structure bonded to the chitosan molecular chain, wherein the structure of the modified chitosan comprises at least one of structural unit 1 represented by formula (1), structural unit 2 represented by formula (2), and structural unit 3 represented by formula (3);

[0030] In formulas (1) to (3), R1, R2, R3, R4, R5, and R6 are independently 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]-.

[0031] The structure of the modified chitosan provided by the present invention may further include one or more of the structural unit 4 represented by formula (4), the structural unit 5 represented by formula (5), the structural unit 6 represented by formula (6), and the structural unit 7 represented by formula (7):

[0032] In formulas (5) to (7), R7, R8, R9 and R 10are independently 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]-.

[0033] In the present invention, “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 distinction to facilitate description and have no other special meaning.

[0034] In the present invention, there is no particular limitation on the ratio of structural unit 1, structural unit 2, structural unit 3, structural unit 4, structural unit 5, structural unit 6 and structural unit 7 in the modified chitosan structure, that is, the ratio of structural unit 1, structural unit 2, structural unit 3, structural unit 4, structural unit 5, structural unit 6 and structural unit 7 in the modified chitosan structure provided by the present 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 ratio values; there is no particular limitation on the distribution of structural unit 1, structural unit 2, structural unit 3, structural unit 4, structural unit 5, structural unit 6 and structural unit 7 in the modified chitosan structure, that is, the structural units 1, structural unit 2, structural unit 3, structural unit 4, structural unit 5, structural unit 6 and structural unit 7 in the modified chitosan structure provided by the present invention can be distributed in any manner.

[0035] In the present invention, examples of the chitosan molecules include, but are not limited to, oligochitosan and / or high-molecular-weight chitosan. In some specific embodiments, the degree of polymerization of the oligochitosan is preferably any integer between 2 and 20, such as 2, 3, 5, 8, 10, 13, 15, 17, 20, or any integer therebetween. In some specific embodiments, the degree of polymerization of the high-molecular-weight chitosan is exemplified as any integer between 21 and 2000, such as 21, 30, 50, 100, 500, 1000, 1200, 1500, 2000, or any integer therebetween; the degree of polymerization of the high-molecular-weight chitosan is preferably 21 to 200.

[0036] In the present invention, the weight average molecular weight of the modified chitosan is preferably 300 to 50,000, such as 300, 500, 1000, 2000, 4000, 4210, 4300, 4520, 5000, 6000, 7500, 7801, 8000, 9000, 10,000, 20,000, 30,000, 40,000, 50,000 or any value therebetween. The molecular weight distribution of the modified chitosan is preferably 1.2 to 1.35, such as 1.2, 1.21, 1.24, 1.27, 1.3, 1.33, 1.35 or any value therebetween.

[0037] The preparation method of the modified chitosan provided by the present invention comprises: taking chitosan and halogenated carboxylic acid and performing halogenated carboxylic acid reaction under the action of a catalyst to obtain the modified chitosan

[0038] In the preparation of the modified chitosan, the weight average molecular weight of the chitosan is preferably 300 to 50,000, such as 300, 500, 1,000, 2,000, 1,000, 2,000, 3,000, 7,500, 10,000, 10,200, 14,600, 20,000, 30,000, 40,000, 50,000 or any value therebetween.

[0039] In the preparation process of the modified chitosan, the halogenated carboxylic acid is a compound containing both a halogen atom and a carboxylic acid in its molecule, which is capable of undergoing a halogenated carboxylic acid reaction with chitosan. The halogenated carboxylic acid can be purchased directly or prepared by conventional methods. In some preferred embodiments, specific examples of the halogenated carboxylic acid include, but are not limited to, one or more of 3-chloropyruvic acid, 3-bromopyruvic acid, 2-dichlorosuccinic acid, 2,3-dichlorosuccinic acid, 3-chloropropionic acid, and 3-bromopropionic acid.

[0040] In the preparation process of the modified chitosan, the halogenated carboxylic acid reaction is defined as follows: under the action of a catalyst, the halogenated carboxylic acid removes the halogen atom to form a carbon-positive intermediate, and the carbon-positive intermediate attacks the amino group on the chitosan to form a carbon-nitrogen bond and removes the hydrogen ion to obtain a modified chitosan having at least an amino acid chelate-like structure.

[0041] In the above-mentioned preparation process of modified chitosan, the catalyst is a compound capable of catalyzing at least a halocarboxylic acid reaction with amino groups on the chitosan molecular chain to undergo a halocarboxylation reaction. The catalyst can be purchased directly or prepared by conventional methods. In some preferred embodiments, specific examples of the catalyst include, but are not limited to, one or more of a Ziegler-Natta catalyst, a MOFs catalyst, and a copper oxide catalyst.

[0042] In the preparation process of the modified chitosan, the molar ratio of chitosan to halogenated carboxylic acid is preferably (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 therebetween.

[0043] In the preparation process of the modified chitosan, the amount of the 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 therebetween, based on the total molar amount of chitosan and halogenated carboxylic acid.

[0044] In the preparation process of the above-mentioned modified chitosan, the conditions of the halogenated carboxylation reaction include a temperature preferably of 85 to 95°C, such as 85°C, 87°C, 88°C, 90°C, 91°C, 92°C, 94°C, 95°C or any value therebetween; and a time preferably of 4 to 10 h, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or any value therebetween.

[0045] The present invention also provides a modified chitosan prepared by the above method, wherein the structure of the modified chitosan comprises at least one of structural unit one represented by formula (1), structural unit two represented by formula (2), and structural unit three represented by formula (3); in addition, the modified chitosan may also comprise one or more of structural unit four represented by formula (4), structural unit five represented by formula (5), structural unit six represented by formula (6), and structural unit seven represented by formula (7).

[0046] The slow-setting water-reducing agent provided by the present invention includes the modified chitosan described above. In some preferred embodiments, the slow-setting water-reducing agent preferably also includes polycarboxylic acid, air-entraining agent and water-retaining agent. Among them, the polycarboxylic acid is a reagent commonly used in existing water-reducing agents; it can be directly purchased or prepared by existing conventional methods. Specific examples of the air-entraining agent can be, but are not limited to: a surfactant with low surface tension, the addition of which can enable the concrete to produce a large number of evenly distributed, closed and stable tiny bubbles during the mixing process; the air-entraining agent can be directly purchased or prepared by existing conventional methods. Specific examples of the water-retaining agent can be, but are not limited to: a highly absorbent resin, the addition of which can improve the compressive strength, impermeability and durability of concrete; the water-retaining agent can be directly purchased or prepared by existing conventional methods.

[0047] In the present invention, the retarding water-reducing agent contains modified chitosan and preferably further contains a polycarboxylic acid, an air-entraining agent, and a water-retaining agent. The modified chitosan content is preferably 15 to 50 parts by mass, such as 15, 20, 25, 30, 35, 40, 45, or 50 parts by mass, or any value therebetween. The polycarboxylic acid content is preferably 50 to 80 parts by mass, such as 50, 55, 60, 65, 70, 75, or 80 parts by mass, or any value therebetween. The air-entraining agent content is preferably 0.1 to 0.5 parts by mass, such as 0.1, 0.2, 0.3, 0.4, or 0.5 parts by mass, or any value therebetween. The water-retaining agent content is preferably 0.1 to 0.5 parts by mass, such as 0.1, 0.2, 0.3, 0.4, or 0.5 parts by mass, or any value therebetween.

[0048] In addition, the present invention also provides the use of the modified chitosan and / or slow-setting water-reducing agent in the field of construction.

[0049] The embodiments of the present invention are described in detail below. The examples of the embodiments are intended to explain the present invention and are not to 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 this area or according to the product specifications. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0050] The raw materials and sources used in the following examples are as follows:

[0051] Air entraining agent (manufacturer: Nanjing Xinyi Synthesis, product number: XY-A01); water retention agent (manufacturer: Ningbo Zhongshuike, product number: SK-530); polycarboxylic acid (manufacturer: Kezhijie, product number: Point-400S); PCE-S (manufacturer: Kezhijie, product number: Point-MS); Sika retarder H-1 (manufacturer: Sika, product number: POWDER P).

[0052] Preparation Example 1

[0053] This preparation example is used to prepare the modified chitosan and its preparation method provided by the present invention. The preparation of the modified chitosan is specifically 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 6h, the mixture is filtered, washed, and dried to obtain the modified chitosan.

[0054] After testing, the infrared spectrum of the modified chitosan was 1270 cm -1 The CN absorption peak of secondary amine appeared near 1600 cm -1 The C=O absorption peak of carboxylate appeared near 1715 cm -1 The absorption peak of ketone group appeared nearby, indicating that amino acid chelate structure was indeed introduced into the structure of the modified chitosan. The weight average molecular weight of the modified chitosan was 4725, and the molecular weight distribution was 1.32.

[0055] Preparation Example 2

[0056] This preparation example is used to prepare the modified chitosan and its preparation method provided by the present invention. The preparation of the modified chitosan is specifically as follows: 3-bromopyruvic acid and chitosan (weight-average molecular weight of 5000) are dissolved in butyl acetate in a molar ratio of 1:1, and 0.15wt% of Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6h, the mixture is filtered, washed, and dried to obtain the modified chitosan.

[0057] After testing, the infrared spectrum of the modified chitosan was 1270 cm -1The CN absorption peak of secondary amine appeared near 1600 cm -1 The C=O absorption peak of carboxylate appeared near 1715 cm -1 The absorption peak of ketone group appeared nearby, indicating that an amino acid chelate-type structure was indeed introduced into the structure of the modified chitosan. The weight average molecular weight of the modified chitosan was 6316, and the molecular weight distribution was 1.32.

[0058] Preparation Example 3

[0059] This preparation example is used for the modified chitosan and preparation method provided by the present invention. The preparation of the modified chitosan is specifically as follows: 2,3-dibromosuccinic acid and chitosan (weight-average molecular weight of 7000) are dissolved in butyl acetate according to a molar ratio of 1:0.5, and 0.12wt% of Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6h, the mixture is filtered, washed and dried to obtain the modified chitosan.

[0060] After testing, the infrared spectrum of the modified chitosan was 1270 cm -1 The CN absorption peak of secondary amine appeared near 1600 cm -1 The C=O absorption peak of carboxylate appeared nearby, indicating that an amino acid chelate-like structure was indeed introduced into the structure of the modified chitosan. The weight average molecular weight of the modified chitosan was 9182, and the molecular weight distribution was 1.32.

[0061] Preparation Example 4

[0062] This preparation example is used for the modified chitosan and its preparation method provided by the present invention. The preparation of the modified chitosan is specifically as follows: 3-bromopropionic acid and chitosan (weight-average molecular weight of 5000) are dissolved in butyl acetate according to a molar ratio of 1:1, and 0.2wt% of Ziegler-Natta catalyst is added. After stirring and reacting at 90°C for 6h, the mixture is filtered, washed and dried to obtain the modified chitosan.

[0063] After testing, the infrared spectrum of the modified chitosan was 1270 cm -1 The CN absorption peak of secondary amine appeared near 1600 cm -1 The C=O absorption peak of carboxylate appeared nearby, indicating that an amino acid chelate-like structure was indeed introduced into the structure of the modified chitosan. The weight average molecular weight of the modified chitosan was 6182, and the molecular weight distribution was 1.21.

[0064] Preparation Example 5

[0065] In this preparation example, modified chitosan was prepared according to the method provided in Preparation Example 1, except that chitosan (weight average molecular weight 2000) was replaced by chitosan (weight average molecular weight 7000) in an equal molar amount, and other conditions were the same.

[0066] After testing, the infrared spectrum of the modified chitosan was 1270 cm -1 The CN absorption peak of secondary amine appeared near 1600 cm -1 The C=O absorption peak of carboxylate appeared near 1715cm -1 The C=O absorption peak of the ketone group appeared nearby, indicating that an amino acid chelate-type structure was indeed introduced into the structure of the modified chitosan. The weight average molecular weight of the modified chitosan was 9750, and the molecular weight distribution was 1.13.

[0067] Example 1

[0068] This example is used to illustrate the slow-setting water-reducing agent provided by the present invention and its preparation method. The components and contents of the slow-setting water-reducing agent are as follows: 19.5 parts by mass of the modified chitosan provided in Preparation Example 1, 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 a polycarboxylic acid.

[0069] In this embodiment, the preparation of the retarding water reducer specifically includes: adding the modified chitosan, air entraining agent and water retaining agent according to the above mass parts to the polycarboxylic acid and stirring evenly to obtain the retarding water reducer.

[0070] Example 2

[0071] This example is used to illustrate a slow-setting water-reducing agent and its preparation method. The components and contents of the slow-setting water-reducing agent are as follows: 49.5 parts by mass of the modified chitosan provided in Preparation Example 1, 0.3 parts by mass of an air-entraining agent, 0.2 parts by mass of a water-retaining agent, and 50 parts by mass of a polycarboxylic acid.

[0072] In this embodiment, the preparation of the retarding water reducer specifically includes: adding the modified chitosan, air entraining agent and water retaining agent according to the above mass parts to the polycarboxylic acid and stirring evenly to obtain the retarding water reducer.

[0073] Example 3

[0074] This example is used to illustrate a slow-setting water-reducing agent and its preparation method. The components and contents of the slow-setting water-reducing agent are as follows: 29.2 parts by mass of the modified chitosan provided in Preparation Example 3, 0.4 parts by mass of an air-entraining agent, 0.4 parts by mass of a water-retaining agent, and 70 parts by mass of a polycarboxylic acid.

[0075] In this embodiment, the preparation of the retarding water reducer specifically includes: adding the modified chitosan, air entraining agent and water retaining agent according to the above mass parts to the polycarboxylic acid and stirring evenly to obtain the retarding water reducer.

[0076] Example 4

[0077] This example illustrates a slow-setting water-reducing agent and its preparation method. The components and contents of the slow-setting water-reducing agent are as follows: 19.5 parts by mass of the modified chitosan provided in Preparation Example 4, 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 a polycarboxylic acid.

[0078] In this embodiment, the preparation of the retarding water reducer specifically includes: adding the modified chitosan, air entraining agent and water retaining agent according to the above mass parts to the polycarboxylic acid and stirring evenly to obtain the retarding water reducer.

[0079] Example 5

[0080] In this example, a slow-setting water-reducing agent was prepared according to the method provided in Example 1, except that the modified chitosan provided in Preparation Example 5 was used in equal parts by mass instead of the modified chitosan provided in Preparation Example 1, and other conditions were the same.

[0081] Comparative Example 1

[0082] This comparative example provides a water reducing agent, which is prepared by uniformly mixing 40 parts by mass of PCE-S with 60 parts by mass of water.

[0083] Comparative Example 2

[0084] In this comparative example, a retarding water reducer was prepared according to the method provided in Example 1, except that an equal amount of Sika retarder H-1 was used to replace the modified chitosan provided in Preparation Example 1, and other conditions were the same.

[0085] Comparative Example 3

[0086] In this comparative example, a slow-setting water-reducing agent was prepared according to the method provided in Example 1, except that the modified chitosan provided in Preparation Example 1 was replaced by polycarboxylic acid in equal parts by mass, and other conditions were the same.

[0087] Comparative Example 4

[0088] This comparative example illustrates a retarding water reducer and its preparation method. The specific components and their weight percentages are: 19.5 parts by weight of modified chitosan, 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 a polycarboxylic acid. The retarding water reducer is prepared by adding the modified chitosan, air-entraining agent, and water-retaining agent to the polycarboxylic acid in the above weight percentages and stirring uniformly to obtain the retarding water reducer.

[0089] The preparation of modified chitosan includes: reacting malonaldehyde with 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 it for 25 minutes, then adding malonaldehyde, stirring and reacting for 45 minutes, filtering, washing and drying to obtain the modified chitosan. The obtained modified chitosan was tested at 1270 cm -1 The CN absorption peak of secondary amine appeared near 1715cm -1 The C=O absorption peak of ketone group appeared nearby; at 1740cm -1 The C=O absorption peak of the aldehyde group appeared nearby, indicating that no amino acid chelate structure was introduced into the structure of the obtained chitosan. The weight average molecular weight of the modified chitosan was 4893, and the molecular weight distribution was 1.32.

[0090] Test Case

[0091] Concrete was prepared according to the mix ratio in Table 1, and the water-reducing agents obtained in the above examples and comparative examples were added to the concrete at a concentration of 0.5% (solid content). The specific amount of each water-reducing agent was such that the slump of the concrete was 200±10 mm. The performance indicators were then tested according to GB8076-2008 "Concrete Admixtures". The results are shown in Table 2.

[0092] Table 1 (parts by mass)

[0093] Table 2

[0094] The test results show that, compared with Comparative Examples 1 to 4, the modified chitosan provided by the present invention can cooperate with polycarboxylic acid to achieve better water reduction effect, retarding effect and slump retention effect, and has good application prospects.

[0095] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A modified chitosan, characterized in that: The modified chitosan is a compound having an amino acid chelate-like structure bonded to the chitosan molecular chain, and the structure of the modified chitosan includes at least one of the structural unit 1 represented by formula (1), the structural unit 2 represented by formula (2), and the structural unit 3 represented by formula (3); In formulae (1) to (3), R1, R2, R3, R4, R5 and R6 are independently a carbonyl group, a C1-C4 alkylene group, a C1-C4 halogenated alkylene group, a C1-C4 carboxylic acid group, a C1-C4 halogenated carboxylic acid group, a C2-C4 acyl group or a C2-C4 halogenated acyl group.

2. The modified chitosan according to claim 1, characterized in that In formulae (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]-.

3. The modified chitosan according to claim 1, characterized in that The chitosan is oligo-chitosan and / or high-molecular-weight chitosan; Optionally, the weight average molecular weight of the modified chitosan is 300 to 50,000, and the molecular weight distribution is 1.2 to 1.

35.

4. A method for preparing modified chitosan, characterized in that: The method comprises: taking chitosan and halogenated carboxylic acid to carry out halogenated carboxylic acid reaction under the action of a catalyst to obtain the modified chitosan.

5. The method for preparing modified chitosan according to claim 4, characterized in that: The weight average molecular weight of the chitosan is 300 to 50,000; Optionally, the halogenated carboxylic 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; Optionally, the catalyst is selected from one or more of a Ziegler-Natta catalyst, a MOFs catalyst and a copper oxide catalyst; Optionally, the molar ratio of chitosan to halogenated carboxylic acid is (0.01-2):1; Optionally, based on the total molar amount of the chitosan and the halogenated carboxylic acid, the added amount of the catalyst is 0.01-0.5 wt %.

6. The method for preparing modified chitosan according to claim 4, characterized in that: The temperature of the halogenated carboxylation reaction is 85-95° C. and the time is 4-10 hours.

7. Modified chitosan prepared by the preparation method according to any one of claims 4 to 6.

8. A slow-setting water reducing agent, characterized in that: The slow-setting water-reducing agent comprises the modified chitosan according to any one of claims 1 to 3 and 7.

9. The slow-setting water reducing agent according to claim 8, characterized in that: The slow-setting water-reducing agent also includes polycarboxylic acid, air-entraining agent and water-retaining agent; Optionally, the content of modified chitosan in the slow-setting water-reducing agent is 15 to 50 parts by mass, the content of polycarboxylic acid is 50 to 80 parts by mass, the content of air entraining agent is 0.1 to 0.5 parts by mass, and the content of water-retaining agent is 0.1 to 0.5 parts by mass.

10. Use of the modified chitosan according to any one of claims 1 to 3 and 7 and / or the slow-setting water-reducing agent according to claim 8 or 9 in the field of construction.

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