CN115073043A - Slow-release polycarboxylate superplasticizer and preparation method thereof - Google Patents

Abstract

The invention provides a slow-release polycarboxylate superplasticizer and a preparation method thereof.A water reducer inner core is wrapped in a protective shell composed of nano silicon dioxide and other components, so that water reducer molecules can be slowly released, and the release rate does not have sudden swelling; the release speed can not be obviously changed at high temperature, so that the slump loss resistant agent still has good long-time slump retaining capability in a high-temperature environment, and the fluidity change of the mixed concrete is more stable and controllable. In addition, the protective shell is generated while the polycarboxylate superplasticizer is synthesized, the steps are simple, and the whole preparation process is safe, reliable and environment-friendly. The slow-release type polycarboxylate water reducer has strong adaptability to concrete, low sensitivity to mud contained in raw materials and slow release rate, and greatly solves the problems that the slump retaining time is shortened and the workability of mixed concrete is poor due to the fact that carboxyl is released too fast in the concrete alkaline environment.

Description

Slow-release polycarboxylate superplasticizer and preparation method thereof

Technical Field

The invention belongs to the technical field of concrete admixtures, and particularly relates to a slow-release type polycarboxylate superplasticizer and a preparation method thereof.

Background

The water reducing agent is an important component in concrete and plays an important role in improving the performance of the concrete. The polycarboxylate water reducer serving as a concrete additive has the advantages of high water reducing rate, high plasticity retention, strong adaptability to cement, high strength of formed concrete, small later-stage drying, energy conservation and environmental protection, and is incomparable with other various water reducers. However, the concrete is in a strong alkaline environment, so that the water reducer is easy to hydrolyze in the concrete, has the characteristics of concentrated release and difficult maintenance, and therefore, the polycarboxylate water reducer still has defects in certain special application scenes.

Chinese patent (CN201810885426.8, published: 2019, 1 month and 25 days) discloses a crosslinking type polycarboxylic acid slow-release water reducing agent and a preparation method thereof, wherein a crosslinking structure can still be effectively opened under an alkaline environment under extremely high crosslinking degree, but the hydrolysis speed and the release speed of the polycarboxylic acid water reducing agent under a high-temperature environment are obviously accelerated, so that adsorption groups of the polycarboxylic acid water reducing agent are completely released within 1 hour after concrete is discharged, the slump retaining capability is poor for a long time, and the adsorption groups are intensively released within a short time, so that concrete bleeding in the process is easy to occur, construction accidents such as pump blockage and the like are caused, and the construction safety of the concrete is influenced.

Chinese patent (CN201110199695.7, published: 10/16/2013) discloses a preparation method of a slow-release water reducer microcapsule, which is characterized in that a polycarboxylate water reducer is coated in a protective shell layer to form a slow-release microcapsule water reducer. Due to the protection effect of the shell layer of the capsule, the water reducing agent molecules can be stably stored in the microcapsule. When the microcapsule is mixed with cement, the cement concrete is in strong basicity, the microcapsule swells, a shell layer is changed from compact to loose, and the coated and encapsulated water reducing agent molecules are slowly released and continuously supplemented and adsorbed to the surfaces of cement particles, so that the later-stage dispersing performance is improved, and the cement concrete slump loss in the actual engineering use is prevented. However, this method also has some drawbacks: a large amount of organic solvent is used in the process of preparing the capsule type superplasticizer, and the recovery treatment of the solvent increases additional production cost and environmental cost.

Chinese patent (CN202010339165.7, published: 3/18/2022) discloses a preparation method of microcapsule type polycarboxylate superplasticizer with high-temperature long-term slump retaining performance, the microcapsule type polycarboxylate superplasticizer is synthesized from components such as polyether macromonomer, unsaturated carboxylic acid monomer, initiator azobisisobutyronitrile, chain transfer agent, macromolecular dispersant, sulfonic acid monomer and crosslinking monomer, and because of containing sulfonic acid monomer, the microcapsule type polycarboxylate superplasticizer has obvious response to external stimulus, and can generate corresponding appearance and shape changes to the change of solvent polarity, the change of counter ion type and concentration thereof.

Disclosure of Invention

In order to solve the problems in the prior art, the technical scheme provided by the invention is as follows:

a slow-release polycarboxylate superplasticizer comprises a protective shell consisting of methacrylic acid dodecafluoroheptane, cyanopropyl dimethyl fluorosilane, acrylamide and nano-silica, wherein an inner core of the polycarboxylate superplasticizer is wrapped in the protective shell, the core-shell ratio of the inner core of the polycarboxylate superplasticizer to the protective shell is 2: 1-3: 1, and the wrapping ratio of the shell is 45% -55%.

The preparation method of the slow-release polycarboxylate superplasticizer comprises the following steps:

step 1: 100 parts of nano-silica is put into 800-1200 parts of deionized water to obtain nano-silica aqueous dispersion; fully mixing 10-15 parts of methacrylic acid dodecafluoroheptane, 15-25 parts of cyanopropyl dimethyl fluorosilane and 1-3 parts of acrylamide, adding the mixture into the nano silicon dioxide water dispersion, and stirring and reacting at the temperature of 30-40 ℃ for 60-120min to form a stable white solution;

step 2; uniformly mixing 50-80 parts of unsaturated polyether macromonomer, 150-210 parts of unsaturated carboxylic acid/anhydride small monomer and 0.3-1 part of initiator to obtain an oil phase;

and step 3: fully mixing the white solution obtained in the step 1 with the oil phase obtained in the step 2 to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting at the temperature of 30-35 ℃ for 4-6h to obtain a slow-release polycarboxylic acid water reducer product;

the above parts are all parts by mass.

The unsaturated polyether macromonomer comprises one or more of vinyl polyoxyethylene ether, allyl polyoxyethylene ether, hydroxybutyl vinyl polyoxyethylene ether, isobutenol polyoxyethylene ether and prenol polyoxyethylene ether with the molecular weight of 800-3000.

The unsaturated carboxylic acid/anhydride comprises one or more of methacrylic acid, acrylic acid, maleic anhydride, itaconic acid, itaconic anhydride.

The initiator is one of ammonium persulfate and potassium persulfate.

Compared with the prior art, the invention has the following advantages: 1. according to the polycarboxylate water reducer provided by the invention, the inner core of the water reducer is wrapped in the protective shell consisting of dodecafluoroheptane methacrylate, cyanopropyl dimethyl fluorosilane, acrylamide and nano-silica, so that molecules of the water reducer can be slowly released, and the release rate is free from sudden swelling; 2. the release speed can not be obviously changed at high temperature, so that the slump loss resistant agent still has good long-time slump retaining capability in a high-temperature environment, and the fluidity change in the whole process is more stable and controllable; 3. the method takes the nano silicon dioxide as a main raw material, generates the protective shell while synthesizing the polycarboxylate superplasticizer, has simple steps, is safe and reliable in the whole preparation process, does not use an organic solvent, is non-toxic and pollution-free, and is environment-friendly; 4. the slow-release polycarboxylate superplasticizer provided by the invention has strong adaptability to concrete, low sensitivity to mud content of raw materials and mild slow-release rate, and greatly solves the problems of shortened slump retaining time and poor workability of mixed concrete caused by over-quick release of carboxyl in a concrete alkaline environment.

Detailed Description

Embodiments of the present invention will be described below.

Example 1:

putting 100 parts of nano silicon dioxide in 1200 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; fully mixing 13 parts of methacrylic acid dodecafluoroheptane, 22 parts of cyanopropyl dimethyl fluorosilane and 2.5 parts of acrylamide, adding into the nano silicon dioxide aqueous dispersion, and stirring and reacting at 38 ℃ for 110min to form a stable white solution; uniformly mixing 50 parts of hydroxybutyl vinyl polyoxyethylene ether, 210 parts of itaconic acid and 0.8 part of potassium persulfate to obtain an oil phase; and fully mixing the nano silicon dioxide water dispersion and the oil phase to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting for 6 hours at the temperature of 35 ℃ to obtain the slow-release polycarboxylic acid water reducer product S1.

Example 2:

adding 100 parts of nano silicon dioxide into 800 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; fully mixing 10 parts of methacrylic acid dodecafluoroheptane, 16 parts of cyanopropyl dimethyl fluorosilane and 1.2 parts of acrylamide, adding into the nano silicon dioxide aqueous dispersion, and stirring and reacting at 32 ℃ for 90min to form a stable white solution; uniformly mixing 60 parts of allyl polyoxyethylene ether, 150 parts of methacrylic acid and 0.3 part of ammonium persulfate to obtain an oil phase; and fully mixing the nano silicon dioxide water dispersion and the oil phase to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting for 5 hours at the temperature of 35 ℃ to obtain the slow-release polycarboxylic acid water reducer product S2.

Example 3:

100 parts of nano silicon dioxide is put into 1000 parts of deionized water to obtain nano silicon dioxide water dispersion; fully mixing 15 parts of methacrylic acid dodecafluoroheptane, 15 parts of cyanopropyl dimethyl fluorosilane and 3 parts of acrylamide, adding the mixture into the nano silicon dioxide aqueous dispersion, and stirring and reacting at the temperature of 30 ℃ for 60min to form a stable white solution; uniformly mixing 80 parts of vinyl polyoxyethylene ether, 160 parts of acrylic acid and 1 part of ammonium persulfate to obtain an oil phase; fully mixing the nano silicon dioxide water dispersion and the oil phase to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting for 4 hours at the temperature of 30 ℃ to obtain a slow-release polycarboxylic acid water reducer product S3;

example 4:

100 parts of nano-silica is put into 800-1200 parts of deionized water to obtain nano-silica aqueous dispersion; fully mixing 15 parts of methacrylic acid dodecafluoroheptane, 25 parts of cyanopropyl dimethyl fluorosilane and 1 part of acrylamide, adding the mixture into the nano silicon dioxide aqueous dispersion, and stirring and reacting at 40 ℃ for 120min to form a stable white solution; uniformly mixing 70 parts of prenyl polyoxyethylene ether, 180 parts of maleic anhydride and 0.6 part of ammonium persulfate to obtain an oil phase; fully mixing the nano silicon dioxide water dispersion and the oil phase to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting for 4 hours at the temperature of 30 ℃ to obtain a slow-release polycarboxylic acid water reducer product S4;

example 5:

step 1: 100 parts of nano silicon dioxide is put into 1100 parts of deionized water to obtain nano silicon dioxide water dispersion; fully mixing 10 parts of methacrylic acid dodecafluoroheptane, 20 parts of cyanopropyl dimethyl fluorosilane and 1.8 parts of acrylamide, adding into the nano silicon dioxide aqueous dispersion, and stirring and reacting at 40 ℃ for 100min to form a stable white solution; uniformly mixing 50 parts of isobutylene alcohol polyoxyethylene ether, 200 parts of maleic acid and 0.5 part of potassium persulfate to obtain an oil phase; fully mixing the nano silicon dioxide water dispersion and the oil phase to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting for 5 hours at the temperature of 35 ℃ to obtain a slow-release polycarboxylic acid water reducer product S5;

example 6:

putting 100 parts of nano silicon dioxide in 1200 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; fully mixing 12 parts of methacrylic acid dodecafluoroheptane, 18 parts of cyanopropyl dimethyl fluorosilane and 2 parts of acrylamide, adding the mixture into the nano silicon dioxide aqueous dispersion, and stirring and reacting at 40 ℃ for 60min to form a stable white solution; uniformly mixing 80 parts of prenyl polyoxyethylene ether, 210 parts of itaconic anhydride and 1 part of potassium persulfate to obtain an oil phase; fully mixing the nano silicon dioxide water dispersion and the oil phase to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting for 6 hours at the temperature of 30 ℃ to obtain a slow-release polycarboxylic acid water reducer product S6;

comparative example:

uniformly mixing 60 parts of allyl polyoxyethylene ether, 150 parts of methacrylic acid and 0.3 part of ammonium persulfate to obtain an oil phase; and (3) placing the oil phase in an ultraviolet reactor, and stirring and reacting for 5 hours at the temperature of 35 ℃ to obtain a slow-release polycarboxylate superplasticizer product D1.

The slow-release polycarboxylic acid water reducer and the intermediate product in the preparation process are analyzed and characterized as follows:

1. optical microscopy characterization

The products of examples S1-S6 and comparative example D1 were characterized by an optical microscope, and the stability of the emulsion was judged by taking a suitable amount of the product with a pipette, spreading the product evenly on a slide, placing the slide on a stage, and observing the slide with a magnification of 500X, comparing the size and distribution of the droplets.

2. Scanning electron microscopy characterization

The prepared products S1-S6 of the examples and the products D1 of the comparative examples are centrifugally purified, diluted to a proper concentration (the solution is nearly transparent) by deionized water, and a drop of the solution is dripped on a clean silicon wafer and dried at room temperature. And adhering the silicon wafer on an electric microscope table by using a conductive adhesive and observing.

3. Thermogravimetric analysis test

Testing the coating ratio of the slow-release polycarboxylate superplasticizer by using a thermogravimetric analyzer, centrifuging the prepared slow-release polycarboxylate superplasticizer, placing the centrifuged slow-release polycarboxylate superplasticizer in a freeze vacuum drying oven to be dried into powder, testing the nano-silica water dispersion and a comparative product D1 under the same conditions, and calculating the coating ratio according to the following formula:

wherein: er is the coating ratio of the slow-release polycarboxylate superplasticizer;

W _M800℃ the residual rate of the comparative product at 800 ℃;

W _C800℃ the residue rate of the example product at 800 ℃ is shown.

4. Optical contact Angle analysis

And (3) measuring the hydrophilicity and hydrophobicity and the rolling angle of the slow-release polycarboxylate water reducer coating by using a contact angle measuring instrument.

And (3) characterization results:

through microscopic observation, the products of the 6 examples have small particle size, uniform particle size distribution and good dispersibility. The product of the comparative example, however, had a non-uniform droplet size and poor dispersibility.

Further observing the products S1-S6 and the product D1 of the comparative example through a scanning electron microscope, the products S1-S6 of the examples are regular spheres with the diameter of about 30-50 μm, and the observation of single particles shows that the surfaces of the particles are rough, the surfaces of the particles are provided with a layer of compact nano particles, and the particle diameters of the particles are about 20 nm. The electron micrograph of comparative product D1 showed clustered particles, varying sizes, and poor dispersion.

The thermogravimetric analyzer measures the thermogravimetric curves of example products S1 to S6 and comparative example product D1, and the coating ratios of example product S1, example product S2, example product S3, example product S4, example product S5 and example product S6 were calculated as 47%, 51%, 45%, 48%, 55% and 53% respectively from the residual rates after the three samples were decomposed.

Analyzing and characterizing a concrete sample:

1. neat paste fluidity test

The slurry tests were carried out on example products S1-S6, a comparative example product D1 and a commercially available polycarboxylate superplasticizer D2 of a certain brand. Refer to GB/T8077 and 2012, the homogeneity test method of concrete admixture. The flow speed of the cement paste doped with the product of the comparative example D1 is rapidly increased within 0-60min, the flow speed reaches the maximum within 60min, and then the flow speed loss is rapid; the flow velocity of the cement paste blended with the products S1 to S6 of the examples and the commercial product D2 gradually increased within 0 to 60min, and reached a maximum at 120min, and then the flow velocity of the cement paste blended with the commercial product D2 rapidly lost, while the flow velocity of the cement paste blended with the products S1 to S6 lost less by 240 min. According to test results, the flow speed of the cement paste doped with the products S1-S6 in the embodiment is not rapidly increased in the early stage, concrete is not slowly released and isolated, the later loss is slow, and the cement can be kept continuously dispersed.

2. Mortar extension test

Clay is used for replacing part of manufactured sand by 1.5%, 3.0% and 4.5% respectively, and the sensitivity of water reducing agent products S1-S6 of comparative example products, D1 of comparative example products and D2 of a certain brand of commercially available high slump retaining type polycarboxylate water reducing agent products to the mud content of raw materials is improved when the mixing amount of the water reducing agent is the same (0.2%). The test is carried out according to a rapid test method for the compatibility of the concrete admixture in appendix A of GB/T50119 and 2013 concrete admixture application technical Specification.

Under the same clay content condition, the initial spreading degree of the blended example products S1-S6 mortar is greater than that of the blended commercial product D2 mortar in the time course of 120min, 180min and 240min, and the spreading degree of the blended commercial product D2 mortar is greater than that of the blended comparative example D1 mortar in the time course of. With the increase of the clay content, the spreading degree is in a trend of reducing, but the reduction of the colloidal sand doped in the products S1-S6 is obviously smaller, which shows that the dispersibility of the products S1-S6 of the examples is less influenced by the change of the clay content and is lower in the sensitivity to the mud content of raw materials.

3. Temperature sensitivity test

Under the conditions that the environmental temperature is respectively 5 ℃, 25 ℃ and 40 ℃, the net slurry dispersibility of a plurality of water reducing agent products respectively blended with the products S1-S6 of the examples, the product D1 of the comparative example and the high slump retaining type polycarboxylate water reducing agent D2 of a certain brand on the market is compared.

At 5 ℃, few cement particles participate in hydration, ester groups are slowly hydrolyzed, the net slurry fluidity of the blended example products S1-S6 and the commercial product D2 is slightly higher than that of the blended comparative example D1, and the net slurry fluidity of the blended water reducing agent products is continuously increased along with the time.

At 25 ℃, the flow speed of the cement paste doped with the product of the comparative example D1 is rapidly increased within 0-60min, the flow speed reaches the maximum within 120min, and then the flow speed loss is rapid; the flow rate of the cement paste blended with the products S1-S6 of the example and the commercial product D2 increased gradually within 0-60min, and reached the maximum at 180min, and then the flow rate of the cement paste blended with the commercial product D2 lost rapidly, while the flow rate of the cement paste blended with the products S1-S6 lost less by 240 min.

At 40 ℃, the fluidity of the cement paste blended with the comparative product D1 and a commercial brand of high slump retaining type polycarboxylate superplasticizer D2 begins to be rapidly reduced after 60min, while the fluidity of the cement paste blended with the example products S1-S6 is slightly reduced after 120min, and is obviously reduced after 180 min.

It is shown that the dispersion retention of the example products is significantly better at high temperatures, indicating that the example products are less sensitive to ambient temperature.

4. Testing of concrete application Properties

Concrete is prepared by eight water reducing agent products of S1-S6 of products of examples, D1 of comparative products and D2 of commercially available high slump loss resistant polycarboxylate water reducing agents of certain brands according to the mixing amount of 0.2%, and the mechanical property of a C30 concrete sample is tested by referring to GB/T50081-2019 Standard of mechanical property test methods of ordinary concrete. According to the test data, the 28-day strength of the samples of the products S1-S6 of the blended examples is obviously higher than that of the samples of the products D2 blended in the market and is obviously better than that of the samples of the products D1 blended in the comparative examples, and the test temperature is 28 ℃.

TABLE 1 Net grout fluidity and concrete 28d Strength Performance test data

Finally, it should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and not intended to limit the present invention, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications and equivalents can be made in the technical solutions described in the foregoing embodiments, or some technical features thereof can be replaced. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. The slow-release type polycarboxylate superplasticizer is characterized by comprising the following raw materials:

and (2) component A: dodecyl heptane methacrylate, cyanopropyl dimethyl fluorosilane, acrylamide and nano silicon dioxide;

and B component: an unsaturated polyether macromonomer;

and C, component C: unsaturated carboxylic acid/anhydride small monomers;

and (D) component: an initiator;

the water reducer comprises a protective shell synthesized by a component A, and a water reducer inner core synthesized by a component B, a component C and a component D, wherein the water reducer inner core is wrapped in the shell.

2. The slow-release type polycarboxylate water reducer according to claim 1, characterized in that the ratio of the inner core to the shell of the polycarboxylate water reducer is 2: 1-3: 1.

3. The slow-release type polycarboxylate water reducer according to claim 1, wherein the coating ratio of the shell is 45-55%.

4. The slow-release type polycarboxylate water reducer according to claim 1, wherein the unsaturated polyether macromonomer comprises one or more of polyoxyethylene vinyl ether, polyoxyethylene allyl ether, polyoxyethylene hydroxybutyl ether, polyoxyethylene isobutylene ether and polyoxyethylene prenol ether with the molecular weight of 800-3000.

5. The slow release type polycarboxylate water reducer according to claim 1, wherein the unsaturated carboxylic acid/anhydride comprises one or more of methacrylic acid, acrylic acid, maleic anhydride, itaconic acid and itaconic anhydride.

6. The slow-release polycarboxylate water reducer according to claim 1, wherein the initiator is one of ammonium persulfate and potassium persulfate.

7. The preparation method of the slow-release type polycarboxylate water reducer according to any one of claims 1 to 6, characterized by comprising the following steps:

step 1: 100 parts of nano-silica is put into 800-1200 parts of deionized water to obtain nano-silica aqueous dispersion; fully mixing 10-15 parts of methacrylic acid dodecafluoroheptane, 15-25 parts of cyanopropyl dimethyl fluorosilane and 1-3 parts of acrylamide, adding the mixture into the nano silicon dioxide water dispersion, and stirring and reacting at the temperature of 30-40 ℃ for 60-120min to form a stable white solution;

step 2; uniformly mixing 50-80 parts of unsaturated polyether macromonomer, 150-210 parts of unsaturated carboxylic acid/anhydride small monomer and 0.3-1 part of initiator to obtain an oil phase;

and step 3: fully mixing the white solution obtained in the step 1 with the oil phase obtained in the step 2 to form stable emulsion, placing the emulsion in an ultraviolet reactor, and stirring and reacting at the temperature of 30-35 ℃ for 4-6h to obtain a slow-release polycarboxylic acid water reducer product;

the above parts are all parts by mass.