Chlorine-free environment-friendly oxidized cut starch water reducing agent as well as preparation method and application method thereof

Abstract

The invention provides a chlorine-free environment-friendly oxidized cut starch water reducing agent as well as a preparation method and an application method thereof. A preparation method of a chlorine-free environment-friendly oxidized cut starch water reducing agent comprises the following steps: S1, oxidation pretreatment: carrying out two-step oxidation reaction on natural starch and 30% hydrogen peroxide under the action of a catalyst to prepare oxidized starch; step S2, acid cutting: gelatinizing the oxidized starch, adjusting the pH value to 1-3, cutting for 1.2-2 hours in an environment of 70-110 DEG C, and controlling the molecular weight to be 1500-2000; and S3, carrying out neutralization separation, adjusting the pH value to 6.5-7.5, adding ethanol, precipitating, taking the precipitate, washing, and drying to obtain the chlorine-free environment-friendly oxidized cut starch water reducing agent. The invention provides a preparation method of a starch-based water reducing agent without chloride ion residues, and solves the problem of corrosion of reinforcing steel bars in a traditional acid cutting method. Natural starch is used as a main raw material, the raw material is easy to obtain and low in cost; the process is simplified, no complex graft copolymerization equipment is needed, and the existing starch processing plant equipment can be directly transformed and utilized.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete water reducers, and particularly relates to a chlorine-free and environment-friendly oxidized cutting starch water reducer and a preparation method and an application method thereof. Background Art

[0002] Water reducers are a type of concrete admixture, primarily used to reduce the amount of water required to mix concrete while maintaining its workability (flowability, slump, etc.), or to enhance the strength and durability of concrete by improving its flowability. They are a core material in modern high-performance concrete technology and are widely used in construction, bridges, tunnels, water conservancy projects, and other fields.

[0003] There are three key problems in the application of traditional naphthalene-based and aliphatic petroleum-based water reducers: first, their raw materials rely on fossil resources; second, the production process produces nitrogen / sulfur-containing toxic wastewater, causing serious environmental pollution; third, some hydrochloric acid cutting products have residual chloride ions (Cl - Content 0.1%-0.5%), far exceeding the reinforced concrete admixture Cl specified in GB / T 50119-2013 - If the content is ≤0.06%, there is a risk of steel bar corrosion.

[0004] Although natural starch has the hydrophobic-hydrophilic dual structure (hydrophobic helical core and hydrophilic hydroxyl side chains) required for water reducers, it faces three technical bottlenecks: its ultra-high molecular weight (5000 degrees of polymerization of amylose and over one million degrees of amylopectin) leads to excessive solution viscosity and low dispersion efficiency; the Cl generated by traditional hydrochloric acid hydrolysis method is - The residue (0.1% to 0.5%) is difficult to meet the needs of high-end concrete; at the same time, the hydrolysis process parameters (pH, temperature, time) have not been systematically optimized, resulting in a wide molecular weight distribution range of the product (500-10000), causing quality problems such as large fluctuations in water-reducing performance and insufficient stability. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a chlorine-free and environmentally friendly oxidized cutting starch water reducer with no chloride ion residue, improved water reduction efficiency, and enhanced cement particle adsorption capacity.

[0006] The technical solution of the present invention is: a method for preparing a chlorine-free and environmentally friendly oxidative cutting starch water reducer, comprising the following steps:

[0007] Step S1, oxidation pretreatment, wherein natural starch is subjected to a two-step oxidation reaction with 30% hydrogen peroxide in the presence of a catalyst to produce oxidized starch;

[0008] Step S2, acid cutting, after gelatinizing the oxidized starch, adjusting the pH to 1-3, cutting at 70°C-110°C for 1.2-2 hours, and controlling the molecular weight to 1500-2000;

[0009] Step S3: neutralization and separation, adjusting the pH to 6.5-7.5, adding ethanol for precipitation, washing and drying the precipitate to obtain a chlorine-free and environmentally friendly oxidized cutting starch water reducer.

[0010] Furthermore, in step S1, the mass ratio of natural starch to 30% hydrogen peroxide is 1:2.5-3.

[0011] Furthermore, in step S1, the temperature of the first oxidation reaction is 70° C., and the reaction time is 20 min; the temperature of the second oxidation reaction is 55° C., and the reaction time is 2 h.

[0012] Furthermore, in step S2, the mass volume ratio of oxidized starch to water during the gelatinization of oxidized starch is 1:3, the gelatinization temperature is 90° C., and the gelatinization time is 1 h.

[0013] Furthermore, in step S2, concentrated sulfuric acid or phosphoric acid is used as the cutting reagent. During the cutting process, the pH is adjusted to 2, and the cutting is carried out at 100° C. for 1.6 hours.

[0014] Furthermore, in step S3, sodium hydroxide with a concentration of 5% to 10% is used to adjust the pH, and the volume ratio of starch to the added ethanol during the precipitation process is 1:8 to 10.

[0015] Furthermore, in step S3, after the pH adjustment is completed, ethanol is added and stirred for 30 minutes until the flocculent precipitate is completely precipitated, and the mixture is filtered using a Buchner funnel, and the filter cake is washed with deionized water; the washed wet filter cake is dried in an oven at 60° C. for 12 hours, crushed and sieved to obtain a slightly yellow powdery chlorine-free and environmentally friendly oxidized cutting starch water reducer.

[0016] Furthermore, the catalyst in step S1 is copper sulfate, and the amount of copper sulfate added is 0.05% of the mass of natural starch; and the natural starch in step S1 is potato starch.

[0017] A chlorine-free and environment-friendly oxidized-cut starch water reducer is prepared by the preparation method of the chlorine-free and environment-friendly oxidized-cut starch water reducer as described in any one of the above items.

[0018] The application method of the chlorine-free and environment-friendly oxidized cutting starch water reducer is as follows: the chlorine-free and environment-friendly oxidized cutting starch water reducer is added into concrete at a dosage of 0.8% to 1.5%.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention provides a method for preparing a starch-based water-reducing agent without residual chloride ions, which solves the problem of steel bar corrosion in the traditional acid cutting method;

[0021] (2) A two-step method of "oxidation activation-cutting viscosity reduction" was proposed. The starch hydroxyl groups were converted into carboxyl groups through oxidation reaction to enhance the electrostatic adsorption capacity. Then, the α-1,4 / α-1,6 glycosidic bonds were broken by acid cutting to reduce the molecular weight and optimize the steric hindrance. The synergistic effect of the two makes the water reducer molecules have strong adsorption, low viscosity and chlorine-free environmental protection.

[0022] (3) Natural starch is used as the main raw material, which is easy to obtain and has low cost; the process is simplified and does not require complex graft copolymerization equipment, and the existing starch processing plant equipment can be directly modified and utilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a flow chart of the method for preparing the chlorine-free and environment-friendly oxidative cutting starch water reducer. DETAILED DESCRIPTION

[0024] 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, 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 convey 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 components and steps, the composition of materials, numerical expressions, and numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary and not as limiting.

[0025] The terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are simply used to distinguish different parts. Terms such as "include" or "comprising" mean that the elements preceding the term include the elements listed after the term, and do not exclude the possibility of also including other elements. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0026] like Figure 1 As shown, the preparation method of the chlorine-free environmentally friendly oxidized cutting starch water reducer comprises the following steps:

[0027] Step S1, oxidation pretreatment, wherein natural starch is subjected to a two-step oxidation reaction with 30% hydrogen peroxide in the presence of a catalyst to produce oxidized starch;

[0028] Step S2, acid cutting, after gelatinizing the oxidized starch, adjusting the pH to 1-3, cutting at 70°C-110°C for 1.2-2 hours, and controlling the molecular weight to 1500-2000;

[0029] Step S3: neutralization and separation, adjusting the pH to 6.5-7.5, adding ethanol for precipitation, washing and drying the precipitate to obtain a chlorine-free and environmentally friendly oxidized cutting starch water reducer.

[0030] In the above embodiment, a method for preparing a starch-based water-reducing agent without residual chloride ions is provided to solve the problem of steel bar corrosion in the traditional acid cutting method.

[0031] In the above embodiment, a two-step method of "oxidation activation-cutting and viscosity reduction" is proposed. The starch hydroxyl groups are converted into carboxyl groups through oxidation reaction to enhance the electrostatic adsorption capacity, and then the α-1,4 / α-1,6 glycosidic bonds are broken by acid cutting to reduce the molecular weight and optimize the steric hindrance. The synergistic effect of the two makes the water reducer molecules have strong adsorption, low viscosity and chlorine-free environmental protection.

[0032] In the above embodiment, the water reducer prepared by the preparation method of the chlorine-free environmentally friendly oxidative cutting starch water reducer has a carboxyl content of 7.07%, which is 3 times higher than that of natural starch, enhances the electrostatic repulsion of cement particles, and has strong adsorption; the molecular weight is reduced to 1500-2500 (the molecular weight of traditional starch-based water reducers is greater than 5000), the solution viscosity is reduced by 60%, the dispersion efficiency is significantly improved, and it has low viscosity characteristics; sulfuric acid / phosphoric acid is used instead of hydrochloric acid throughout the process, Cl - The residue is less than 0.01%, meeting the drinking water grade standard (GB 5749-2022), and is chlorine-free and environmentally friendly. In addition, natural starch is used as the main raw material, which is easily available and low in cost. The process is simplified and does not require complex graft copolymerization equipment. Existing starch processing plant equipment can be directly modified and utilized.

[0033] In the above embodiment, the purpose of step S1, oxidation pretreatment, is to increase the content of active groups; the purpose of step S2, acid cleavage, is to precisely control the molecular weight; and the purpose of step S3, neutralization separation, is to remove impurities and control morphology.

[0034] In some embodiments, in step S1, the mass ratio of natural starch to 30% hydrogen peroxide is 1:2.5-3; by adjusting the amount of hydrogen peroxide, the mass ratio of natural starch to hydrogen peroxide is 1:2.7, so that the carboxyl content reaches 7.07% (determined by potentiometric titration); preferably, in step S1, the mass ratio of natural starch to 30% hydrogen peroxide is 1:2.7.

[0035] In some embodiments, in step S1, the temperature of the first oxidation reaction is 70°C, and the reaction time is 20 minutes, which promotes the oxidation of hydroxyl groups to aldehyde groups; specifically, preheating at 40°C for 15 minutes, and stirring at 70°C for 20 minutes; the temperature of the second oxidation reaction is 55°C, and the reaction time is 2 hours, which deeply oxidizes aldehyde groups to carboxyl groups; specifically, the product after the first oxidation is first transferred to a buffer solution with a pH of 4 (adjusted with dilute sulfuric acid), hydrogen peroxide is added, and the reaction is carried out at a constant temperature of 55°C for 2 hours.

[0036] In some embodiments, in step S2, the mass volume ratio of oxidized starch to water in the gelatinization process of the oxidized starch is 1:3, the gelatinization temperature is 90°C, and the gelatinization time is 1 hour; specifically, deionized water is used, and the oxidized starch and deionized water are mixed at a mass volume ratio of 1:3 (g / ml), heated in an oil bath at 90°C for 1 hour, and mechanically stirred at a speed of 200 rpm to form a uniform and transparent gelatinized liquid (viscosity ≤500 mPa·s).

[0037] In some embodiments, in step S2, the cutting agent is concentrated sulfuric acid (98%, AR grade) or phosphoric acid (85%, AR grade); preferably, the cost of concentrated sulfuric acid is only 1 / 15 of that of phosphoric acid; during the cutting process, the pH is preferably 2, at which the glycosidic bond cleavage rate is fastest; the cutting temperature is preferably 100°C, which is higher than the starch gelatinization temperature to promote molecular chain stretching and improve cutting efficiency; the cutting time is preferably 1.6h, at which time the molecular weight drops to 1531 and the cement paste fluidity reaches a peak of 217mm. The cutting process follows the glycosidic bond acid-catalyzed cleavage mechanism, and the reaction rate equation is:

[0038]

[0039] Where DP is the degree of polymerization, k is the rate constant, n=1.2(H + The concentration influence index on the reaction rate, E a =45 kJ / mol (activation energy, obtained by fitting the Arrhenius equation).

[0040] In some embodiments, in step S3, a concentration of 5% to 10% sodium hydroxide is used to adjust the pH; specifically, after the cutting is completed, a 5% NaOH solution is immediately added (dropping rate 1 ml / min) to adjust the system pH to 6.5-7.5 (phenolphthalein indicator appears colorless) to avoid excessive neutralization leading to starch degradation; during the precipitation process, the volume ratio of starch to the added ethanol is 1:8 to 10.

[0041] In some embodiments, in step S3, the volume ratio of natural starch to ethanol is 1:8. After the addition of ethanol, the mixture is stirred for 30 minutes until the flocculent precipitate is completely precipitated, and filtered using a Buchner funnel (vacuum degree ≥ 0.08 MPa). The filter cake is washed three times with deionized water (50 ml each time to remove residual acid ions); the drying process is to dry the wet filter cake in a 60°C oven for 12 hours (temperature fluctuation ± 2°C), crush it through an 80-mesh sieve (particle size ≤ 180 μm), and obtain a slightly yellow powder product with a moisture content ≤ 5% (determined by GB / T 6284-2006).

[0042] In some embodiments, the catalyst in step S1 is copper sulfate, and the amount of copper sulfate added is 0.05% of the mass of the native starch.

[0043] In some embodiments, the natural starch in step S1 is potato starch; specifically, the potato starch is food grade and has an amylose content of ≥25%.

[0044] In some embodiments, a chlorine-free, environmentally friendly, oxidized-cut starch water reducer is disclosed, which is prepared using the preparation method of the chlorine-free, environmentally friendly, oxidized-cut starch water reducer in any of the above embodiments.

[0045] The core performance indicators of the chlorine-free, environmentally friendly, oxidatively cut starch water-reducing agent in the above embodiment are shown in Table 1 below.

[0046] Table 1 Core performance indicators of chlorine-free environmentally friendly oxidized cutting starch water reducer products

[0047]

[0048] In some embodiments, a method for applying a chlorine-free and environmentally friendly oxidized cutting starch water reducer is disclosed. The chlorine-free and environmentally friendly oxidized cutting starch water reducer in the above embodiments is added to concrete at a dosage of 0.8% to 1.5%.

[0049] The technical solution and technical effects of the present invention are further illustrated and described below through two specific embodiments and comparative examples.

[0050] Example 1: Preparation of Optimal Conditions for Sulfuric Acid Cutting

[0051] Step S1, weighing 100g of potato starch, adding 135ml of 30% hydrogen peroxide and 0.05g of copper sulfate, preheating at 40°C for 15min, then heating to 70°C, stirring and reacting for 20min;

[0052] Transfer to 200 ml of dilute sulfuric acid solution with a pH of 4, add the remaining 135 ml of hydrogen peroxide, and react at 55°C for 2 h to obtain oxidized starch (carboxyl content 7.07%);

[0053] Step S2: 100 g of oxidized starch was added with 300 ml of water, and gelatinized at 90° C. for 1 h, and 98% concentrated sulfuric acid was added to adjust the pH to 2;

[0054] The reaction was stirred in an oil bath at 100 °C for 1.6 h (stirring speed 250 rpm). The acidity was calibrated with a pH meter every 30 min during the reaction.

[0055] Step S3: The cutting liquid is cooled to room temperature, 5% NaOH is added dropwise to pH 7, 800 ml of ethanol is added for precipitation, and the mixture is filtered and washed with deionized water three times;

[0056] The filter cake was dried at 60°C for 12 h, crushed and passed through an 80-mesh sieve to obtain product A (molecular weight 1531, Cl - Not detected).

[0057] Performance test indicators of product A:

[0058] Cement paste fluidity: 217mm (dosage 1%, water 105g, GB / T 8077);

[0059] Water reduction rate: 20% (the slump of the benchmark concrete is 180mm, and the water consumption is reduced by 20% when the dosage is 1%);

[0060] Rebar corrosion: Passed ASTM G109 standard test, corrosion current density <0.1μA / cm 2 (No risk of rust).

[0061] Example 2: Phosphoric Acid Cleavage Comparative Example

[0062] The difference from Example 1 is that in step S2, "add 98% concentrated sulfuric acid to adjust pH = 2" is replaced by "add 85% phosphoric acid to adjust pH = 2", and the steps are the same as in Example 1 to obtain product B (molecular weight 1669, Cl - Not detected).

[0063] Performance comparison between product B and product A:

[0064] Cement paste fluidity: 215.4mm (slightly lower than sulfuric acid cutting, because the steric hindrance of phosphoric acid affects the cutting efficiency);

[0065] Cost: 12 yuan / kg (the cost of cutting product A with sulfuric acid is 8 yuan / kg, and the high price of phosphoric acid causes the cost to increase by 50%).

[0066] Comparative example: Traditional hydrochloric acid cutting method (containing chloride ions)

[0067] The difference from Example 1 is that in step S2, "add 98% concentrated sulfuric acid to adjust pH = 2" is replaced by "add 37% hydrochloric acid to adjust pH = 2", which is the same as the steps in Example 1 to obtain product C (molecular weight 1800, Cl - content 0.25%).

[0068] Performance drawbacks:

[0069] Cement paste fluidity: 205mm (10% lower than the present invention);

[0070] Rebar corrosion: corrosion current density 1.2μA / cm 2 (far exceeding the GB 50119 safety threshold of 0.2μA / cm 2 ).

[0071] Thus far, various embodiments of the present invention have been described in detail. To avoid obscuring the concept of the present invention, some details well known in the art have not been described. Based on the above description, those skilled in the art can fully understand how to implement the technical solutions disclosed herein.

[0072] The above-described embodiments represent only some embodiments of the present invention. Although the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A method for preparing a chlorine-free, environmentally friendly, oxidatively cut starch water reducer, characterized in that: The following steps are involved: Step S1, oxidation pretreatment, wherein natural starch is subjected to a two-step oxidation reaction with 30% hydrogen peroxide in the presence of a catalyst to produce oxidized starch; Step S2, acid cutting, after gelatinizing the oxidized starch, adjusting the pH to 1-3, cutting at 70°C-110°C for 1.2-2 hours, and controlling the molecular weight to 1500-2000; Step S3: neutralization and separation, adjusting the pH to 6.5-7.5, adding ethanol for precipitation, washing and drying the precipitate to obtain a chlorine-free and environmentally friendly oxidized cutting starch water reducer.

2. The method for preparing the chlorine-free, environment-friendly, oxidatively cut starch water-reducing agent according to claim 1, wherein: In step S1, the mass ratio of natural starch to 30% hydrogen peroxide is 1:2.5-3.

3. The method for preparing the chlorine-free, environment-friendly, oxidatively cut starch water-reducing agent according to claim 1, characterized in that: In step S1, the temperature of the first oxidation reaction is 70° C. and the reaction time is 20 min; the temperature of the second oxidation reaction is 55° C. and the reaction time is 2 h.

4. The method for preparing the chlorine-free, environment-friendly oxidatively cut starch water reducer according to claim 1, characterized in that: In step S2, the mass volume ratio of oxidized starch to water during the gelatinization of oxidized starch is 1:3, the gelatinization temperature is 90° C., and the gelatinization time is 1 hour.

5. The method for preparing the chlorine-free, environment-friendly, oxidatively cut starch water-reducing agent according to claim 1, characterized in that: In step S2, concentrated sulfuric acid or phosphoric acid is used as the cutting reagent. During the cutting process, the pH is adjusted to 2, and the cutting is carried out at 100° C. for 1.6 hours.

6. The method for preparing the chlorine-free, environment-friendly oxidatively cut starch water-reducing agent according to claim 1, characterized in that: In step S3, the pH is adjusted using sodium hydroxide having a concentration of 5% to 10%, and the volume ratio of starch to the added ethanol during the precipitation process is 1:8 to 10.

7. The method for preparing the chlorine-free, environment-friendly, oxidatively cut starch water-reducing agent according to claim 1, characterized in that: In step S3, after the pH adjustment is completed, ethanol is added and stirred for 30 minutes until the flocculent precipitate is completely precipitated. The mixture is filtered using a Buchner funnel and the filter cake is washed with deionized water. The washed wet filter cake is dried in an oven at 60° C. for 12 hours, crushed and sieved to obtain a slightly yellow powdery chlorine-free and environmentally friendly oxidized cutting starch water reducer.

8. The method for preparing the chlorine-free, environment-friendly oxidatively cut starch water-reducing agent according to claim 1, characterized in that: The catalyst in step S1 is copper sulfate, and the amount of copper sulfate added is 0.05% of the mass of natural starch; the natural starch in step S1 is potato starch.

9. A chlorine-free, environmentally friendly oxidized cutting starch water reducer, characterized by: The water-reducing agent is prepared by the method for preparing the chlorine-free and environment-friendly oxidized cutting starch water-reducing agent according to any one of claims 1 to 8.

10. A method for applying a chlorine-free, environment-friendly, oxidatively cut starch water reducer, characterized in that: The chlorine-free and environment-friendly oxidized cutting starch water reducer as claimed in claim 9 is added to concrete in an amount of 0.8% to 1.5%.

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