Mechano-chemical preparation method of starch sulfate superplasticizer

Abstract

The invention belongs to the technical field of preparation of water reducing agents and the technical field of starch modification, and relates to a mechanochemical preparation method of a starch sulfate high-efficiency water reducing agent. The sulfamic acid is used as a sulfonating reagent, the urea is used as a catalyst, the sulfamic acid and the urea are simply mixed with the starch and then added into an internal mixer, and starch sulfate is prepared through a mechanical force and chemical modification one-pot method. Compared with all processes at present, the method has the outstanding advantages that the process is simple, the prepared starch sulfate water reducing agent is good in dispersing performance, short in reaction time and environmentally friendly, and the large-scale production potential is achieved. The cement paste fluidity experiment proves that the water reducing agent produced by the process has a very obvious effect on improving the cement dispersibility, and can be efficiently applied to concrete.

Description

Technical Field

[0001] The invention belongs to the technical field of water reducing agent preparation and starch modification, and relates to a mechanochemical preparation method of a starch sulfate high-efficiency water reducing agent, which is a method for preparing a water reducing agent under dry conditions. Background Art

[0002] Concrete, abbreviated as "concrete", is a basic building material in the construction industry. With the proposal of the national dual-carbon strategic development goals, the construction industry has higher requirements for the performance and quality of concrete. Among them, adding a small amount of concrete admixtures can significantly improve its performance, so higher requirements are also put forward for concrete admixtures.

[0003] Water reducer is the most widely used admixture in the construction industry. It has a dispersing effect on cement particles after being added to the concrete mixture, which can improve its workability, reduce unit water consumption, improve the fluidity of the concrete mixture; or reduce unit cement consumption and save cement.

[0004] Currently, the water reducers on the market include naphthalene-based water reducers, polycarboxylic acid-based water reducers and lignin-based water reducers. Among them, the synthesis process of naphthalene-based water reducers requires the use of harmful substances such as formaldehyde; the raw materials of polycarboxylic acid-based water reducers come from petrochemical products; and the water-reducing performance of lignin-based water reducers is poor. In addition, the synthesis process of water reducers mainly includes wet and dry methods. The wet method faces problems such as wastewater treatment, expensive reagents, high equipment requirements, and environmental pollution; the dry method faces problems such as solid-phase reaction, uneven reaction, low reaction efficiency, and complex preparation process. Therefore, the development of new green and environmentally friendly high-efficiency water reducers is an inevitable trend in the development of the concrete industry.

[0005] Starch is the second largest polysaccharide-based biomaterial produced in the world. It has the advantages of wide sources, environmental friendliness, and low cost. It meets the basic requirements of the "dual carbon" strategic goal and the reform idea of ​​recycling and regeneration. At the same time, starch has a natural polymer structure, and the multi-branched long glucose chain can provide steric hindrance in the dispersion mechanism of the water reducer. In addition, there are many hydroxyl groups in starch molecules that are easy to undergo chemical reactions. Polar anionic groups can be introduced through a variety of chemical modification reactions. On the one hand, they can provide adsorption sites for cement particles and electrostatic repulsion in the dispersion mechanism of the water reducer. On the other hand, it can solve the problem of poor water solubility of starch and prepare starch derivatives that meet the basic structural properties of the water reducer. In addition, the preparation process of starch-based water reducers is simple and the reaction conditions are mild. It is an ideal water reducer raw material to replace traditional petroleum-based water reducers.

[0006] However, starch granules have a unique crystal structure, including crystalline and amorphous regions. For different types of starch, there are certain differences in the double helix structure in the crystalline region. Each glucose unit in the starch molecule contains three hydroxyl groups, which is very hydrophilic. However, due to the strong hydrogen bonding within the molecule, it is difficult to dissolve in water and most organic solvents, which makes it difficult to use widely. It needs to be modified to make it widely used. For example, acid hydrolysis requires wastewater treatment and other problems; bioenzyme modification is expensive. Summary of the invention

[0007] In order to solve the problems of high cost, cumbersome complexity, serious environmental pollution and the like in the existing process, the present invention provides a one-pot method for preparing starch sulfate with simple production process, environmental friendliness and high application efficiency. The present invention uses aminosulfonic acid as a sulfonating agent and urea as a catalyst, and then simply mixes with starch and adds it to an internal mixer, which is conducive to the one-pot preparation of starch sulfate by mechanical force and chemical modification. The water reducer prepared by this method can meet the standard of high-efficiency water reducer.

[0008] To achieve the above objectives, the specific technical implementation plan is as follows:

[0009] A mechanochemical preparation method of starch sulfate high-efficiency water reducing agent comprises the following steps:

[0010] Step (1), first drying the starch in an oven at 100°C-110°C to obtain dry starch.

[0011] Step (2), the dried starch obtained in step (1) is mixed with aminosulfonic acid and urea in a molar ratio of 1: (0.4-1): 1, wherein the molar amount of the starch is based on the starch polysaccharide unit. Then 0%-6% of water by weight of the starch is added and mixed again, and the mixture is added to an internal mixer for stirring reaction, reacted at 110° C. for 20 min-100 min, and the product is ground to obtain a crude starch sulfate product.

[0012] Step (3), washing the starch sulfate crude product obtained in step (2) with 80%-95% ethanol aqueous solution and anhydrous methanol solution for multiple times, and then drying to obtain a starch sulfate high-efficiency water reducing agent.

[0013] The starch is corn starch.

[0014] Beneficial effects of the present invention:

[0015] The cement paste fluidity experiment proves that the water reducer produced by the process of the present invention has a very obvious effect in improving the fluidity of cement, which can reach more than 200mm. Compared with the existing process, the present invention has the following advantages through the simultaneous action of mechanical force and chemistry:

[0016] (1) Simple process. The existing process requires starch to be modified first to degrade the molecular weight, which is mainly a "wet method" - acid hydrolysis, which leads to serious "three wastes" problems, especially serious wastewater problems, leading to environmental pollution and post-processing difficulties. This process uses the dual effects of mechanical force and chemistry, does not require starch pretreatment, basically has no "three wastes" problem, and does not require post-processing.

[0017] (2) The reaction is uniform and no additional solvent is required. The dry reaction reported previously was uneven. In this method, the internal mixer can provide a dynamic mixing process. In addition, aminosulfonic acid and urea can form a low eutectic solvent, which can form a dough after mixing with starch in the internal mixer. The shearing and extrusion effect of the internal mixer promotes a uniform reaction.

[0018] (3) The prepared starch sulfate has good water-reducing performance. Compared with the naphthalene-based water-reducing agent currently on the market, its water-reducing performance is much stronger than that of the naphthalene-based water-reducing agent.

[0019] (4) Short reaction time. The reaction time of general water reducers is relatively long, generally more than 3 hours. However, the water reducer produced by this process can have good water reducing performance after only 20 minutes of reaction, which can reduce the reaction cost.

[0020] (5) Environmentally friendly. This reaction is a dry production process without the generation of "three wastes". The sulfonation reagent used is aminosulfonic acid, which is mild and non-toxic. In previous reports, concentrated sulfuric acid and organic solvent blends, SO3 and pyridine or DMF mixtures, chlorosulfonic acid, sodium trisulfonate ammonium, etc. were usually selected as sulfonation agents, which have problems such as strong toxicity and serious degradation of starch molecular weight.

[0021] (6) It has the potential for large-scale production. The synthesis process is simple, using only an internal mixer, and is very easy to prepare on an industrial scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the infrared spectrum of the reaction raw materials and starch derivatives in Example 1;

[0023] Figure 2 is the XRD diffraction spectrum of starch and starch derivatives in Example 1;

[0024] Figure 3 is a comparison chart of the water reduction performance of the starch sulfate prepared in Example 1 and the commercially available naphthalene-based reducing agent; DETAILED DESCRIPTION

[0025] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0026] Example 1

[0027] After the dry starch, aminosulfonic acid and urea were mixed uniformly in a molar ratio of 1:1:1, water with a weight percentage of 0% of the starch was added to an internal mixer, and the mixture was stirred and reacted at 110° C. for 20 minutes. After the reaction was completed, the product was collected and ground into powder.

[0028] As explained in conjunction with the accompanying drawings, the water reducing performance of the water reducing agent prepared by the method can reach 228.5 mm, which is 255.9% higher than the fluidity of cement paste without water reducing agent. Figure 1 It is the infrared spectrum of starch and starch sulfate. According to the spectrum analysis, 1257cm -1 and 823cm -1 The characteristic peaks appearing at represent the stretching vibration absorption peaks of S=O and SO in the sulfate group, that is, the starch sulfate group was successfully introduced into the starch; Figure 2 Figure 2 is the XRD spectrum of starch and starch derivatives. It can be seen from the spectrum that compared with native starch, the crystallization area of ​​SAS has been opened. On the one hand, this is due to the mechanical activation of the internal mixer; on the other hand, sulfate groups are grafted through esterification reaction, resulting in chemical modification; and the expansion of starch granules under high temperature causes the destruction of part of the crystallization area. Figure 3 This is a comparison chart of the water-reducing performance of starch sulfate and commercially available naphthalene-based water-reducing agents. It can be seen that compared with naphthalene-based water-reducing agents, starch sulfate has better cement paste fluidity.

[0029] Example 2

[0030] After the dry starch, aminosulfonic acid and urea were mixed evenly in a molar ratio of 1:0.4:1, water with a starch weight of 0% was added to the mixer, stirred and reacted at 110°C for 60 minutes. After the reaction was completed, the starch was collected and crushed with a grinder to obtain a crude starch sulfate product. The cement paste fluidity was similar to that of naphthalene-based water reducer.

[0031] Example 3

[0032] After the dry starch, aminosulfonic acid and urea are mixed evenly in a molar ratio of 1:0.6:1, 0% water by weight of starch is added to the internal mixer, stirred and reacted at 110°C for 60 minutes. After the reaction is completed, the starch is collected and crushed with a grinder to obtain a crude starch sulfate product. The cement paste fluidity can reach more than 220 mm, which is better than naphthalene-based water reducers.

[0033] Example 4

[0034] After the dry starch, aminosulfonic acid and urea are mixed evenly in a molar ratio of 1:1:1, 6% of the starch mass of water is added to the internal mixer, stirred and reacted at 110°C for 60 minutes. After the reaction is completed, the starch sulfate crude product is collected and crushed with a grinder to obtain the cement paste fluidity of about 200mm, which is better than naphthalene water reducer.

[0035] Example 5

[0036] After the dry starch, aminosulfonic acid and urea are mixed evenly in a molar ratio of 1:1:1, 0% water of the starch mass is added to the internal mixer, stirred and reacted at 110°C for 100 minutes. After the reaction is completed, the starch sulfate crude product is collected and crushed with a grinder to obtain the cement paste fluidity of more than 200 mm, which is better than the naphthalene water reducer.

[0037] Example 6

[0038] After mixing natural starch, aminosulfonic acid and urea in a molar ratio of 1:1:1, add 4% water of the starch mass into an internal mixer, stir and react at 110°C for 60 minutes. After the reaction is completed, collect and crush with a grinder to obtain a crude starch sulfate product. The cement paste fluidity can reach more than 200mm, which is better than naphthalene water reducer.

[0039] In summary, the present invention discloses a method for preparing a high-efficiency water reducing agent by mechanochemical method, provides a method for preparing starch sulfate with simple production process, environmental friendliness and high application efficiency, and proves through the experiment of cement paste fluidity that the water reducing agent produced by this process has a very obvious effect in improving the dispersibility of cement, and can be efficiently applied in concrete. This process has outstanding advantages, simple process, good dispersibility of the prepared starch sulfate, environmental friendliness, conforms to the concepts of "green chemistry" and "sustainable development", and has the potential for large-scale production.

Claims

1. A mechanochemical preparation method of starch sulfate high-efficiency water reducing agent, characterized in that: The following steps are involved: Step (1), first drying the starch in an oven at 100°C-110°C to obtain dry starch; Step (2), mixing the dried starch obtained in step (1) with aminosulfonic acid and urea in a molar ratio of 1:(0.4-1):1, wherein the molar amount of the starch is based on the starch polysaccharide unit; then adding 0%-6% water by weight of the starch and mixing again, adding to an internal mixer, stirring and reacting, reacting at 110° C. for 20 min-100 min, grinding the product to obtain a crude starch sulfate product; Step (3), washing the starch sulfate crude product obtained in step (2) with 80%-95% ethanol aqueous solution and anhydrous methanol solution for multiple times, and then drying to obtain a starch sulfate high-efficiency water reducing agent.

2. The mechanochemical preparation method of a starch sulfate high-efficiency water reducer according to claim 1, characterized in that: The starch is corn starch.

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