CN115073043B

CN115073043B - Sustained-release polycarboxylate superplasticizer and preparation method thereof

Info

Publication number: CN115073043B
Application number: CN202210888492.7A
Authority: CN
Inventors: 仇影; 倪锐; 马彬彬
Original assignee: Jiangsu Aachen Material Technology Co ltd
Current assignee: Jiangsu Aachen Material Technology Co ltd
Priority date: 2022-07-26
Filing date: 2022-07-26
Publication date: 2023-07-07
Anticipated expiration: 2042-07-26
Also published as: CN115073043A

Abstract

The invention provides a slow-release polycarboxylate water reducer and a preparation method thereof, wherein the inner core of the water reducer is wrapped in a protective shell composed of nano silicon dioxide and the like, so that molecules of the water reducer can be slowly released, and sudden swelling does not exist at the release rate; the release speed does not change obviously at high temperature, so the concrete has better long-time slump retaining capacity in a high-temperature environment, and the fluidity change of the mixed concrete is smoother and controllable. In addition, the protective shell is generated during the synthesis of the polycarboxylate superplasticizer, the steps are simple, and the whole preparation process is safe, reliable and environment-friendly. The slow-release polycarboxylate water reducer has strong adaptability to concrete, low sensitivity to mud contained in raw materials and slow-release speed, and greatly solves the problems of short slump retention time and poor workability of mixing concrete caused by too fast release of carboxyl in the alkaline environment of the concrete.

Description

Sustained-release polycarboxylate superplasticizer and preparation method thereof

Technical Field

The invention belongs to the technical field of concrete additives, and particularly relates to a slow-release polycarboxylate water reducer 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 is used as a concrete additive, has high water reducing rate, high plasticity, strong adaptability to cement, high strength of formed concrete, small post-drying shrinkage, energy conservation and environmental protection, and is incomparable with other various water reducers. However, because the concrete is in a strong alkaline environment, the hydrolysis of the water reducer in the concrete is easier, and the characteristics of concentrated release and difficult maintenance after the concentrated release exist, the polycarboxylate water reducer still has the defects in some special application scenes.

Chinese patent (CN 201810885426.8, publication day: 2019, 1 month and 25 days) discloses a cross-linked polycarboxylic acid slow-release water reducer and a preparation method thereof, wherein under extremely high cross-linking degree, a cross-linked structure can be effectively opened under an alkaline environment, but the hydrolysis speed and release speed of the polycarboxylic acid water reducer under a high-temperature environment are obviously accelerated, so that an adsorption group of the polycarboxylic acid water reducer is completely released within 1 hour after a concrete is discharged, the long-term slump retaining capacity is poor, and because the adsorption group is intensively released within a short time, concrete segregation and bleeding are easy to occur in the process, construction accidents such as pump blocking are caused, and the construction safety of the concrete is influenced.

Chinese patent (CN 201110199695.7, bulletin day: 2013, 10 month and 16 day) discloses a preparation method of a slow-release water reducer microcapsule, wherein a polycarboxylate water reducer is coated in a protective shell layer to form the slow-release microcapsule water reducer. Due to the protection effect of the shell layer of the capsule, the water reducer molecules can be stably stored in the microcapsule. When the microcapsule is mixed with cement, the cement concrete is strongly alkaline, the microcapsule swells, the shell layer is changed from compact to loose, and the wrapped water reducing agent molecules are slowly released and continuously and complementarily adsorbed on the surfaces of cement particles, so that the later dispersion performance is improved, and the slump loss of the cement concrete in practical 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 superplasticizer, and the recovery treatment of the solvent increases additional production cost and environmental cost.

Chinese patent (CN 202010339165.7, bulletin day: 2022, 3, 18) discloses a preparation method of a microcapsule type polycarboxylate water reducer with high-temperature long-term slump retaining performance, which comprises the steps of synthesizing a microcapsule type polycarboxylate water reducer by adopting components such as a polyether macromonomer, an unsaturated carboxylic acid monomer, an initiator azodiisobutyronitrile, a chain transfer agent, a macromolecular dispersing agent, a sulfonic acid monomer, a crosslinking monomer and the like, wherein the microcapsule type polycarboxylate water reducer has obvious response to external stimulus and can generate corresponding shape and change to the polarity change of a solvent, the counter ion type and the concentration change of the counter ion.

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 water reducer comprises a protective shell composed of dodecafluoroheptane methacrylate, cyanopropyl dimethyl fluorosilane, acrylamide and nano silicon dioxide, a water reducer inner core synthesized by an unsaturated polyether macromonomer, an unsaturated carboxylic acid/anhydride small monomer and an initiator, wherein the water reducer inner core is wrapped in the protective shell, the core-shell ratio of the polycarboxylate water reducer inner core 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 silicon dioxide is placed in 800-1200 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; mixing 10-15 parts of methacrylic acid dodecafluoroheptane, 15-25 parts of cyanopropyl dimethyl fluorosilane and 1-3 parts of acrylamide, adding into nano silicon dioxide aqueous dispersion, stirring and reacting for 60-120min at 30-40 ℃ to form stable white solution;

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

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 for 4-6 hours at the temperature of 30-35 ℃ to obtain a slow-release polycarboxylate water reducer product;

the parts are all parts by weight.

The unsaturated polyether macromonomer comprises one or more of vinyl polyoxyethylene ether, allyl polyoxyethylene ether, hydroxybutyl vinyl polyoxyethylene ether, isobutenyl alcohol polyoxyethylene ether and isopentenyl alcohol polyoxyethylene ether with 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. the polycarboxylate water reducer provided by the invention has the advantages that the water reducer inner core is wrapped in the protective shell consisting of the dodecafluoroheptane methacrylate, the cyanopropyl dimethyl fluorosilane, the acrylamide and the nano silicon dioxide, so that the water reducer molecules can be slowly released, and the release rate is free from sudden surge; 2. the release speed does not change obviously at high temperature, so the method still has better long-time slump retaining capacity in a high-temperature environment, and the fluidity change in the whole process is stable and controllable; 3. the method takes the nano silicon dioxide as the main raw material, generates the protective shell while synthesizing the polycarboxylate water reducer, has simple steps, is safe and reliable in the whole preparation process, does not use organic solvents, is nontoxic and pollution-free, and is environment-friendly; 4. the slow-release polycarboxylate water reducer provided by the invention has strong adaptability to concrete, low sensitivity to raw material mud, and slow-release rate is mild, so that the problems of shortened slump retention time and poor workability of mixed concrete caused by too fast release of carboxyl in an alkaline environment of the concrete are solved to a great extent.

Detailed Description

Next, embodiments of the present invention will be described.

Example 1:

100 parts of nano silicon dioxide is placed in 1200 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; 13 parts of methacrylic acid dodecafluoroheptane, 22 parts of cyanopropyl dimethyl fluorosilane and 2.5 parts of acrylamide are fully mixed and added into nano silicon dioxide aqueous dispersion, and stirring reaction is carried out for 110min at 38 ℃ to form 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 aqueous 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 polycarboxylate water reducer product S1.

Example 2:

100 parts of nano silicon dioxide is placed in 800 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; mixing 10 parts of dodecafluoroheptane methacrylate, 16 parts of cyanopropyl dimethyl fluorosilane and 1.2 parts of acrylamide, adding into nano silicon dioxide aqueous dispersion, and stirring at 32 ℃ for reaction 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 aqueous 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 polycarboxylate water reducer product S2.

Example 3:

100 parts of nano silicon dioxide is placed in 1000 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; mixing 15 parts of dodecafluoroheptane methacrylate, 15 parts of cyanopropyl dimethyl fluorosilane and 3 parts of acrylamide thoroughly, adding the mixture into a nano silicon dioxide aqueous dispersion, and stirring the mixture at 30 ℃ for reaction for 60 minutes 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 aqueous 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 polycarboxylate water reducer product S3;

example 4:

100 parts of nano silicon dioxide is placed in 800-1200 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; mixing 15 parts of dodecafluoroheptane methacrylate, 25 parts of cyanopropyl dimethyl fluorosilane and 1 part of acrylamide, adding into nano silicon dioxide aqueous dispersion, and stirring and reacting for 120min at 40 ℃ to form a stable white solution; uniformly mixing 70 parts of isopentenyl alcohol 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 aqueous 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 polycarboxylate water reducer product S4;

example 5:

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

example 6:

100 parts of nano silicon dioxide is placed in 1200 parts of deionized water to obtain nano silicon dioxide aqueous dispersion; in addition, 12 parts of dodecafluoroheptane methacrylate, 18 parts of cyanopropyl dimethyl fluorosilane and 2 parts of acrylamide are fully mixed and added into nano silicon dioxide aqueous dispersion, and the mixture is stirred and reacted for 60 minutes at 40 ℃ to form stable white solution; uniformly mixing 80 parts of isopentenol polyoxyethylene ether, 210 parts of itaconic anhydride and 1 part of potassium persulfate to obtain an oil phase; fully mixing the nano silicon dioxide aqueous 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 polycarboxylate 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 placing the oil phase in an ultraviolet reactor, and stirring and reacting for 5 hours at the temperature of 35 ℃ to obtain the slow-release polycarboxylate water reducer product D1.

The following analysis and characterization are carried out on the slow-release polycarboxylate water reducer and intermediate products in the preparation process of the slow-release polycarboxylate water reducer:

1. optical microscope characterization

And (3) characterizing each product of the examples S1-S6 and the comparative example D1 by adopting an optical microscope, sucking a proper amount of the product by using a suction pipe, uniformly coating the product on a glass slide, placing the glass slide on a stage for observation, wherein the magnification is 500X, and comparing the size and the distribution condition of liquid drops to judge the emulsion stability.

2. Scanning electron microscope characterization

And (3) centrifugally purifying the prepared example products S1-S6 and the comparative example products D1, diluting with deionized water to a proper concentration (the solution is nearly transparent), dripping a drop of the solution on a clean silicon wafer, and drying at room temperature. The silicon wafer is stuck on an electronic stage by using conductive adhesive and is observed.

3. Thermogravimetric analysis test

And testing the coating ratio of the slow-release type polycarboxylate water reducer by utilizing a thermogravimetric analyzer, centrifuging the prepared slow-release type polycarboxylate water reducer, placing the polycarboxylate water reducer in a freeze vacuum drying oven for drying to powder, testing the nano silicon dioxide aqueous dispersion and the comparative product D1 under the same condition, wherein the coating ratio is calculated according to the following formula:

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

W _M800℃ residual rate at 800 ℃ for comparative example product;

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

4. Optical contact angle analysis

The hydrophilicity and the rolling angle of the slow-release polycarboxylate water reducer coating are measured by using a contact angle measuring instrument.

Characterization results:

the 6 examples of products have small particle size, uniform particle size distribution and good dispersibility through microscopic observation. The product of the comparative example was not uniform in droplet size and not good in dispersibility.

Further, the example products S1-S6 and the comparative example product D1 are observed by a scanning electron microscope, and the example products S1-S6 are regular spheres with the diameter of about 30-50 mu m, and single particles are observed, so 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 sizes of the particles are about 20nm. The particles in the electron micrograph of comparative example D1 were clustered, of different sizes, and poorly dispersed.

The thermogravimetric curves of the example products S1 to S6 and the comparative example product D1 were measured by a thermogravimetric analyzer, and the coating ratios of the example products S1, S2, S3, S4, S5 and S6 were 47%, 51%, 45%, 48%, 55% and 53% respectively, based on the residual ratios after decomposition of the three samples.

Analysis and characterization of concrete samples:

1. clean pulp fluidity test

And (3) performing a paste cleaning test on the example products S1-S6, the comparative example product D1 and the commercial high slump retaining polycarboxylate superplasticizer D2 of a certain brand. Reference is made to GB/T8077-2012 "concrete admixture homogeneity test method". 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 at 60min, and then the flow speed loss is relatively high; the flowing speed of the cement paste of the mixed products S1-S6 and the cement paste of the commercial products D2 is gradually increased within 0-60min, the cement paste reaches the maximum within 120min, then the flowing speed of the cement paste of the mixed products D2 is rapidly lost, and the flowing speed loss of the cement paste of the mixed products S1-S6 is smaller within 240 min. According to the test results, the cement paste early-stage flowing speed of the cement paste of the doped embodiment products S1-S6 is not increased rapidly, the slow release segregation of concrete is not caused, the later-stage loss is slower, and the cement can be kept to be dispersed continuously.

2. Mortar spread test

Clay is used for replacing part of machine-made sand according to the proportion of 1.5%, 3.0% and 4.5%, and the sensitivity of a plurality of water reducer products of the example products S1-S6, the comparative example product D1 and the commercial high slump-retaining type polycarboxylate water reducer D2 on the raw material mud content is compared with the same water reducer mixing amount (0.2%). And the quick test method for the compatibility of the concrete admixture is tested by referring to GB/T50119-2013 annex A of the technical Specification for the application of concrete admixture.

Under the condition of the same clay content, the initial and 120min, 180min and 240min time expansion degree of the rubber sand of the blended example products S1-S6 are larger than that of the rubber sand of the blended commercial product D2, and the time expansion degree of the rubber sand of the blended commercial product D2 is larger than that of the rubber sand of the blended comparative example D1. As the clay content increases, the expansion degree tends to decrease, but the reduction of the adhesive sand doped with the products S1-S6 of the embodiment is obviously smaller, which shows that the dispersibility of the products S1-S6 of the embodiment is less influenced by the change of the clay content and has lower sensitivity to the mud content of raw materials.

3. Temperature sensitivity test

Under the conditions that the ambient temperature is 5 ℃ and 25 ℃ and 40 ℃, the clear slurry dispersibility of several water reducer products of the example products S1-S6, the comparative example product D1 and the commercial high slump retaining polycarboxylate water reducer D2 of a certain brand are compared.

At 5 ℃, few cement particles participating in hydration and slowly hydrolyzing ester groups, the paste fluidity of the products S1-S6 of the mixing examples and the commercial product D2 is slightly higher than that of the product D1 of the mixing comparative example, and the paste fluidity of the products mixed with a plurality of water reducers 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 at 120min, and then the flow speed loss is relatively high; the flowing speed of the cement paste of the mixed products S1-S6 and the cement paste of the commercial products D2 is gradually increased within 0-60min, the cement paste reaches the maximum within 180min, then the flowing speed of the cement paste of the mixed products D2 is rapidly lost, and the flowing speed loss of the cement paste of the mixed products S1-S6 is smaller within 240 min.

At 40 ℃, the fluidity of cement paste mixed with the comparative example product D1 and the commercial high slump retaining polycarboxylate water reducer D2 of a certain brand begins to decrease rapidly after 60min, while the fluidity of cement paste mixed with the examples products S1-S6 decreases slightly after 120min, and obviously decreases after 180 min.

It shows that the dispersion retention of the example product is significantly better at high temperature, indicating that the example product has lower sensitivity to ambient temperature.

4. Concrete application performance test

Eight water reducer products, namely S1-S6, a comparative example product D1 and a commercial polycarboxylic acid water reducer D2 with high slump loss resistance of a certain brand, are mixed according to the mixing amount of 0.2 percent to prepare concrete, and the mechanical properties of a C30 concrete sample are tested by referring to GB/T50081-2019 common concrete mechanical property test method standard. According to the test data, the 28-day strength of the samples S1-S6 of the blending example product is obviously higher than that of the sample of the blending commercial product D2, the test temperature is 28 ℃ at room temperature, and the test data are obviously better than that of the sample of the blending comparative example product D1.

TABLE 1 paste fluidity and concrete 28d Strength Performance test data

Finally, it should be noted that the foregoing description is only a preferred embodiment of the present invention, and the present invention is not limited to the above-mentioned embodiment, but may be modified or some of the technical features thereof may be replaced by other technical solutions described in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The slow-release polycarboxylate water reducer is characterized by comprising the following raw materials in parts by weight:

and (3) a component A: dodecafluoroheptane methacrylate, cyanopropyl dimethyl fluorosilane, acrylamide, nano silica;

and the component B comprises the following components: unsaturated polyether macromonomers;

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

and D, a component: an initiator;

the water reducer comprises a protective shell formed by the component A, a water reducer inner core formed by the component B, the component C and the component D, and the water reducer inner core is wrapped in the protective shell; wherein the core-shell ratio of the polycarboxylate water reducer inner core to the protective shell is 2:1-3:1; wherein the coating ratio of the protective shell is 45% -55%; the preparation method of the slow-release polycarboxylate superplasticizer comprises the following steps of:

the parts are all parts by weight.

2. The slow release type polycarboxylate water reducer as claimed in claim 1, wherein the unsaturated polyether macromonomer comprises one or more of vinyl polyoxyethylene ether, allyl polyoxyethylene ether, hydroxybutyl vinyl polyoxyethylene ether, isobutylenol polyoxyethylene ether and isopentylenol polyoxyethylene ether with molecular weight of 800-3000.

3. A slow release polycarboxylate water reducer as claimed in claim 1, wherein the unsaturated carboxylic acid/anhydride comprises one or more of methacrylic acid, acrylic acid, maleic anhydride, itaconic acid, itaconic anhydride.

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