High-carboxyl-content starch water reducing agent based on two-step oxidation method and preparation method of high-carboxyl-content starch water reducing agent

Abstract

The invention provides a preparation method of a starch water reducer with high carboxyl content based on a two-step oxidation method, which comprises the following steps: S1, selecting natural starch with amylose content of 20-30%, degreasing, desugaring and drying for later use; s2, the pretreated starch and 30% H2O2 are mixed according to the mass ratio of 1: 1, a CuSO4 catalyst accounting for 0.03%-0.07% of the mass of the starch is added, the mixture is stirred and reacts for 20 min under the H2O2 environment at the temperature of 70 DEG C, and surface oxidation activation is completed; s3, transferring a product in the step S2 into an acid solution, supplementing H2O2 until the total dosage is at least three times of the mass of the starch, and reacting for 2-2.5 hours in an environment of 55 DEG C to realize deep oxidation; s4, adding ethanol with the volume three times that of the product in the step S3 into the product for precipitation, and drying to obtain the starch water reducing agent; the preparation method of the high-carboxyl-content starch water reducing agent based on the two-step oxidation method is simple in process, low in cost and suitable for industrial production, and the working performance of concrete is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of water reducers, and particularly relates to a high-carboxyl starch water reducer based on a two-step oxidation method and a preparation method thereof. Background Art

[0002] Water reducer is a kind of concrete admixture, which is mainly used to reduce the amount of water required for concrete mixing while maintaining its workability (fluidity, slump, etc.) unchanged, or to improve the strength and durability of concrete by improving fluidity. It is one of the core materials of modern high-performance concrete technology and is widely used in construction engineering, bridges, tunnels, water conservancy projects and other fields.

[0003] In the existing technology, it is difficult to fully oxidize the molecular weight of starch using a single oxidation method, the oxidation efficiency is low, and the carboxyl content is usually less than 2%, resulting in insufficient water reduction rate (generally less than 20%); and the process is complicated, requiring multiple esterification, etherification or grafting modifications, the process is cumbersome and the cost is high; in addition, the ratio of linear and branched starch is usually not accurately controlled, and the product performance fluctuates greatly; in addition, the reaction activity of oxidants such as sodium hypochlorite is low, and it is difficult to break through the bottleneck of carboxyl content. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a high carboxyl content starch water reducer based on a two-step oxidation method, which has high carboxyl content, improves water reduction rate, reduces process complexity, and has stable product performance, and a preparation method thereof.

[0005] The technical solution of the present invention is: a preparation method of a high carboxyl content starch water reducer based on a two-step oxidation method, comprising the following steps: Step S1: selecting natural starch with an amylose content of 20% to 30%, and pre-treating it by defatting, desugaring, and drying for later use; Step S2: the pretreated starch was mixed with 30% H2O2 at a mass ratio of 1:1, and a CuSO4 catalyst of 0.03% to 0.07% by mass of the starch was added, and the mixture was stirred and reacted at 70°C for 20 minutes to complete surface oxidation activation; Step S3: transferring the product in step S2 to an acidic solution, adding H2O2 to a total amount of at least three times the mass of the starch, and reacting at 55°C for 2 to 2.5 hours to achieve deep oxidation; Step S4: adding three times the volume of ethanol to the product in step S3 for precipitation, and obtaining a starch water-reducing agent after drying.

[0006] Furthermore, in step S1, the natural starch having an amylose content of 20% to 30% is potato starch, corn starch or cassava starch.

[0007] Furthermore, in step S1, the defatting is to wash the starch with petroleum ether to remove fat on the starch surface until the fat content is ≤0.5%.

[0008] Furthermore, in step S1, desugaring is performed by washing with 85% ethanol to remove soluble sugars until the sugar content is ≤1%.

[0009] Furthermore, in step S1, drying is performed at a temperature of 105° C. until the moisture content is ≤8%.

[0010] Furthermore, the amount of CuSO4 catalyst added in step S2 is 0.05% of the mass of the added starch.

[0011] Furthermore, in step S2, sulfuric acid is added before the reaction to adjust the pH value to 3.8-4.2.

[0012] Furthermore, in step S3, the acidic aqueous solution is a sulfuric acid solution with a pH value of 3.8 to 4.2.

[0013] Furthermore, in step S4, three times the volume of ethanol precipitation is added to the product in step S3, and the product is dried by air blowing at 50° C. until the moisture content is ≤5%, and then crushed and sieved through a 100-mesh sieve to obtain starch water-reducing agent powder.

[0014] The high carboxyl starch water reducer based on the two-step oxidation method is prepared by the preparation method of the high carboxyl starch water reducer based on the two-step oxidation method as described in any one of the above items.

[0015] Beneficial effects of the present invention: (1) The preparation method of the high carboxyl content starch water reducer based on the two-step oxidation method of the present invention is simple in process and low in cost, suitable for industrial production, and significantly improves the working performance of concrete; (2) This method achieves high-performance products with a carboxyl content of ≥7% and a water reduction rate of ≥25% through surface activation, deep oxidation, Cu2+ catalytic synergy, and optimization of key parameters such as pH, H2O2 dosage, and reaction temperature; (3) This method does not require subsequent modification steps such as esterification and etherification, which significantly reduces production costs; (4) This method uses H2O2 as the oxidant throughout the process, leaving no chloride ion residue, and complies with green building material standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a line graph showing the effect of H2O2 dosage on carboxyl content in the present invention.

[0017] Figure 2 It is a line graph showing the effect of pH value on oxidation efficiency in the present invention.

[0018] Figure 3 It is a line graph showing the relationship between the amount of CuSO4 catalyst and the carboxyl content in the present invention.

[0019] Figure 4 It is a line graph showing the effect of the second step oxidation temperature on the hydroxyl content in the present invention.

[0020] Figure 5 It is a kinetic line graph of oxidation time and carboxyl content in the present invention. DETAILED DESCRIPTION

[0021] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The description of the exemplary embodiments is merely illustrative and is in no way intended to limit the present invention and its application or use. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the present invention thorough and complete and to fully express the scope of the present invention to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the parts and steps, the composition of the materials, the numerical expressions and the numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary, rather than as limitations.

[0022] The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different parts. The words "include" or "comprise" and similar words mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of including other elements. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0023] This embodiment discloses a method for preparing a high carboxyl content starch water reducer based on a two-step oxidation method, comprising the following steps: Step S1: selecting natural starch with an amylose content of 20% to 30%, and pre-treating it by defatting, desugaring, and drying for later use; Step S2: the pretreated starch was mixed with 30% H2O2 at a mass ratio of 1:1, and a CuSO4 catalyst of 0.03% to 0.07% by mass of the starch was added, and the mixture was stirred and reacted at 70°C for 20 minutes to complete surface oxidation activation; Step S3: transferring the product in step S2 to an acidic solution, adding H2O2 to a total amount of at least three times the mass of the starch, and reacting at 55°C for 2 to 2.5 hours to achieve deep oxidation; Step S4: adding three times the volume of ethanol to the product in step S3 for precipitation, and obtaining a starch water-reducing agent after drying.

[0024] In the above embodiment, surface activation and deep oxidation are used as two-step oxidation steps to avoid excessive molecular chain breakage caused by single oxidation; Cu2+ and H2O2 form a Fenton reaction system, which significantly improves the efficiency of hydroxyl radical generation; Cu2+ catalytic synergy and key parameters such as pH, H2O2 dosage, and reaction temperature are optimized to achieve high-performance products with a carboxyl content ≥7% and a water reduction rate ≥25%; no subsequent modification steps such as esterification and etherification are required, which significantly reduces production costs; H2O2 is used as an oxidant throughout the process, and there is no chloride ion residue, which meets the green building material standards; the fluidity of cement paste is increased to 265~275mm, and the water reduction rate is 25%~28%, which is better than existing starch-based products.

[0025] For the experimental study on the amount of H2O2 in step S3, when the amount of H2O2 is lower than the maximum value, the carboxyl content increases significantly with the increase of hydrogen peroxide, such as Figure 1 As shown in the figure, when H2O2 exceeds 2 times the mass of starch, the carboxyl content does not increase significantly, so the oxidant is selected to be twice the mass of amylose (such as 100 g amylose, H2O2 = 200 ml).

[0026] For the experimental investigation of the oxidation temperature in step S3, Figure 4 As shown in the figure, after the surface is fully oxidized in the first step, the optimal oxidation temperature in the second step is 55°C. When the temperature is lower than 55°C, the oxidizing activity of hydrogen peroxide is not fully exerted. As the temperature increases, the carboxyl content of oxidized amylose increases continuously. However, when the temperature exceeds 55°C, not only the oxidizing activity of hydrogen peroxide increases, but its own decomposition and evaporation degree will also be further enhanced, and finally the carboxyl content of oxidized starch decreases, and the fluidity of cement paste also decreases.

[0027] For the exploration of the optimal oxidation time in step S3, Figure 5 As shown, when the oxidation time is less than 2 hours, the degree of oxidation increases significantly with the increase of oxidation time. When it exceeds 2 hours, the increase is not obvious, and the carboxyl content remains basically unchanged, that is, the starch has been fully oxidized in 2 hours, and the oxidation time is selected to be 2 hours.

[0028] In some embodiments, in step S1, the natural starch having an amylose content of 20% to 30% is potato starch, corn starch or tapioca starch.

[0029] In some embodiments, in step S1, the degreasing is performed by washing the starch with petroleum ether to remove fat on the starch surface until the fat content is ≤0.5%.

[0030] In some embodiments, in step S1, desugaring is performed by washing with 85% ethanol to remove soluble sugars until the sugar content is ≤1%.

[0031] In some embodiments, in step S1, drying is performed at a temperature of 105° C. until the moisture content is ≤8%.

[0032] In some embodiments, the amount of CuSO4 catalyst added in step S2 is 0.05% of the mass of the added starch; for experimental exploration of the amount of catalyst CuSO4 in step S2, the optimal amount is 0.05%, such as Figure 3 As shown in the figure, when the dosage of the catalyst is less than 0.05%, the carboxyl content will continue to increase significantly with the increase of the catalyst dosage. When it exceeds 0.05%, the carboxyl content remains basically unchanged. When the catalyst dosage is too much, the starch will form a complex with Cu2+, the oxidized starch will turn yellow, and the degree of oxidation will decrease, which is not conducive to the application of water reduction.

[0033] In some embodiments, in step S2, sulfuric acid is added before the reaction to adjust the pH value to 3.8-4.2; in step S3, the acidic aqueous solution is a sulfuric acid solution with a pH value of 3.8-4.2; for the experimental exploration of the pH value of the reaction environment in steps S2 and S3, the pH value of the oxidation system has a great influence on the oxidation capacity of hydrogen peroxide. It has been experimentally verified that Figure 2 As shown, at pH = 4, hydrogen peroxide has the best oxidation ability, the highest carboxyl content and the greatest fluidity of cement paste. When the pH is lower or higher than 4, the carboxyl content of oxidized starch decreases, so the pH of the oxidation system is selected as 4.

[0034] In some embodiments, in step S4, three times the volume of ethanol precipitate is added to the product in step S3, and the product is dried by air blowing at 50° C. until the moisture content is ≤5%, and then crushed and sieved through a 100-mesh sieve to obtain starch water-reducing agent powder.

[0035] The technical solution of the present invention is further illustrated and described below through two more specific embodiments.

[0036] Example 1: Preparation of potato starch water reducing agent Step S1: 100 g potato starch (linear / branched ratio 1.5:1, moisture 7.2%) was taken, defatted and desugared with petroleum ether and 85% ethanol, and dried for later use; Step S2: the pretreated starch was stirred with 100 ml of 30% H2O2 and 0.05 g of CuSO4 catalyst at 70° C. for 20 minutes; Step S3: transferring the product in step S2 into 600 ml of an acidic solution, adding 200 ml of H2O2, and reacting at 55°C for 2 hours to achieve deep oxidation; Step S4: adding 800 ml of ethanol to the product in step S3 for precipitation, filtering and drying to obtain a starch water-reducing agent.

[0037] Performance test: carboxyl content: 7.18% (determined by titration); cement paste fluidity: 275mm (GB / T 8077-2012 standard); water reduction rate: 27.3% (compared with benchmark concrete).

[0038] Example 2: Preparation of corn starch water reducing agent Step S1: 100 g corn starch (linear / branched ratio 2:1, moisture 6.8%) was taken, defatted and desugared with petroleum ether and 85% ethanol, and dried for later use; Step S2: the pretreated starch was stirred with 100 ml of 30% H2O2 and 0.05 g of CuSO4 catalyst at 70° C. for 20 minutes; Step S3: transferring the product in step S2 into 600 ml of an acidic solution, adding 200 ml of H2O2, and reacting at 55° C. for 2.5 hours to achieve deep oxidation; Step S4: adding 800 ml of ethanol to the product in step S3 for precipitation, filtering and drying to obtain a starch water-reducing agent.

[0039] Performance test: carboxyl content: 6.94% (determined by titration); cement paste fluidity: 275mm (GB / T 8077-2012 standard); water reduction rate: 26.5% (compared with benchmark concrete).

[0040] In some embodiments, a high carboxyl starch water reducer based on a two-step oxidation method is disclosed, which is prepared using the preparation method of the high carboxyl starch water reducer based on a two-step oxidation method in any of the above embodiments.

[0041] So far, various embodiments of the present invention have been described in detail. In order to avoid obscuring the concept of the present invention, some details known in the art are not described. Based on the above description, those skilled in the art can fully understand how to implement the technical solution disclosed here.

[0042] The above-mentioned embodiments only express some implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for preparing a high carboxyl starch water reducer based on a two-step oxidation method, characterized in that: The following steps are involved: Step S1: selecting natural starch with an amylose content of 20% to 30%, and pre-treating it by defatting, desugaring, and drying for later use; Step S2: the pretreated starch was mixed with 30% H2O2 at a mass ratio of 1:1, and a CuSO4 catalyst of 0.03% to 0.07% by mass of the starch was added, and the mixture was stirred and reacted at 70°C for 20 minutes to complete surface oxidation activation; Step S3: transferring the product in step S2 to an acidic solution, adding H2O2 to a total amount of at least three times the mass of the starch, and reacting at 55°C for 2 to 2.5 hours to achieve deep oxidation; Step S4: adding three times the volume of ethanol to the product in step S3 for precipitation, and obtaining a starch water-reducing agent after drying.

2. The method for preparing the high carboxyl starch water reducer based on the two-step oxidation method according to claim 1, characterized in that: In the step S1, the natural starch having an amylose content of 20% to 30% is potato starch, corn starch or tapioca starch.

3. The method for preparing the high carboxyl starch water reducer based on the two-step oxidation method according to claim 1, characterized in that: In step S1, the degreasing is to wash the starch with petroleum ether to remove the fat on the starch surface until the fat content is ≤0.5%.

4. The method for preparing the high carboxyl starch water reducer based on the two-step oxidation method according to claim 1, characterized in that: In step S1, desugaring is performed by washing with 85% ethanol to remove soluble sugars until the sugar content is ≤1%.

5. The method for preparing the high carboxyl starch water reducer based on the two-step oxidation method according to claim 1, characterized in that: In step S1, drying is performed at a temperature of 105° C. until the moisture content is ≤8%.

6. The method for preparing the high carboxyl starch water reducer based on the two-step oxidation method according to claim 1, characterized in that: The amount of CuSO4 catalyst added in step S2 is 0.05% of the mass of the added starch.

7. The method for preparing the high carboxyl starch water reducer based on the two-step oxidation method according to claim 1, characterized in that: In the step S2, sulfuric acid is added before the reaction to adjust the pH value to 3.8-4.

2.

8. The method for preparing the high carboxyl starch water-reducing agent based on the two-step oxidation method according to claim 1, characterized in that: In step S3, the acidic aqueous solution is a sulfuric acid solution with a pH value of 3.8 to 4.

2.

9. The method for preparing the high carboxyl starch water reducer based on the two-step oxidation method according to claim 1, characterized in that: In the step S4, three times the volume of ethanol precipitation is added to the product in the step S3, and the product is dried by forced air at 50° C. until the water content is ≤5%. The product is crushed and sieved through a 100-mesh sieve to obtain starch water-reducing agent powder.

10. A high carboxyl starch water reducer based on a two-step oxidation process, characterized in that: The high carboxyl starch water reducer is prepared by the preparation method of the high carboxyl starch water reducer based on the two-step oxidation method as described in any one of claims 1 to 9.

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