Polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention discloses a polycarboxylate superplasticizer and a preparation method thereof. The polycarboxylate superplasticizer disclosed by the invention is synthesized by reacting ethylene glycol monovinyl polyglycol ether, modified acrylic microspheres, hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres; the modified acrylic acid microsphere is prepared by taking a porous inner core sphere as a carrier, taking acrylic acid as a main adsorption substance in the carrier and taking PNIPAM as a carrier outer layer, the modified reducing agent microsphere is prepared by taking a porous inner core sphere as a carrier, taking a reducing agent as a main adsorption substance in the carrier and taking PNIPAM as a carrier outer layer. According to the preparation method, the modified acrylic acid microspheres and the modified reducing agent microspheres are prepared, the polycarboxylate superplasticizer is added at the same time in the compounding process, the sustained release effect of the microspheres in the modification process and control of PNIPAM on a sustained release channel are utilized, and stable and continuous release of acrylic acid and a reducing agent is achieved; the water reducing agent with stable and excellent performance is prepared from acrylic acid and EPEG under proper synthesis conditions.

Description

Technical Field

[0001] The invention relates to a concrete admixture, in particular to a polycarboxylate water reducer and a preparation method thereof. Background Art

[0002] The synthetic macromonomers of traditional polycarboxylic acid water reducers are mainly three-carbon macromonomer APEG and four-carbon and five-carbon macromonomers HPEG, TPEG, etc. When using these macromonomers for polycarboxylic acid synthesis, it is often necessary to increase the synthesis temperature under the premise of using an initiator to ensure the smooth progress of the polymerization reaction, and factors such as the half-life and decomposition temperature of the initiator must also be considered. Not only is the production process complicated, but it also has a great impact on product performance. At the same time, higher synthesis temperatures mean increased energy consumption and increased costs, which not only leads to a decline in product competitiveness, but also is not conducive to energy conservation and emission reduction and the realization of dual carbon goals. In this context, the new generation of macromonomer EPEG can synthesize polycarboxylic acid water reducers at low temperature and in a short time due to its high activity, low temperature, low energy consumption, and short reaction time required in the polymerization process. Moreover, its copolymerization process with acrylic acid is closer to ideal copolymerization, and the synthesis process is easier to control, becoming the focus of research. However, due to its high activity, EPEG's accelerated synthesis rate when the temperature rises often leads to a smaller molecular weight of the generated water reducer, an increase in the disorder of the molecular structure, and a weakening of its dispersibility. Therefore, temperature control during the room temperature synthesis of EPEG is crucial. At present, the main equipment measures used are constant temperature water bath conditions to lower the reaction temperature. The specific synthesis method mainly uses a peristaltic pump to extend the addition time and drop rate of the synthetic material and reduce the reaction rate to control the reaction temperature. However, constant temperature water bath conditions and peristaltic pump drop time control measures mean an increase in the cost of reaction equipment. Real-time temperature monitoring of the reaction process is also required, which increases labor costs. Summary of the invention

[0003] In view of the problems existing in the above-mentioned background technology, the present invention proposes a synthesis technology that does not require synthesis droplet speed control, and provides a low-cost synthesis method that realizes automatic temperature control for the room-temperature synthesis of polycarboxylic acid water-reducing agent.

[0004] The invention provides a polycarboxylate water reducer, which is synthesized by reacting ethylene glycol monovinyl polyethylene glycol ether (EPEG-3000), modified acrylic acid microspheres (AA), hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres;

[0005] The modified acrylic microspheres are made of porous inner core balls as carriers, acrylic acid as the main adsorbent in the carrier, and PNIPAM (polyisopropylacrylamide) as the outer wrapping layer of the carrier; wherein the porous inner core balls are polymer porous microspheres;

[0006] The modified reducing agent microspheres are made of porous inner core balls as carriers, reducing agents as main adsorbed substances in the carriers, and PNIPAM (polyisopropylacrylamide) as outer wrapping layers of the carriers; wherein the porous inner core balls are polymer porous microspheres.

[0007] Furthermore, the reducing agent of the present invention is a mixture of ferrous sulfate (FeSO4) and α-ascorbic acid (VC).

[0008] The purpose of the modified reducing agent microspheres of the present invention is to slowly release the reducing agent component to avoid excessive and rapid reaction between the oxidant and the reducing agent, resulting in implosion and affecting the stability of the entire reaction system.

[0009] Furthermore, the preparation method of the modified acrylic microspheres of the present invention comprises: firstly, adding polymer porous microspheres to acrylic acid, sealing and pressurizing to 0.3-0.5 MPa, so that the acrylic acid is completely adsorbed; then, adding PNIPAM aqueous solution, stirring the solution evenly, rapidly heating it to 40-60° C., and at this temperature, continuously stirring for 60s-90s, then filtering out the water, to obtain the modified acrylic microspheres;

[0010] The mass concentration of the PNIPAM aqueous solution is above 5%;

[0011] The mass fractions of the above raw material components are as follows:

[0012] 20-30 parts of acrylic acid,

[0013] 3-5 parts of polymer porous microspheres,

[0014] PNIPAM 1 to 3 parts.

[0015] The modified acrylic microspheres of the present invention are prepared at a temperature of 40-60° C. This temperature range can ensure that PNIPAM quickly changes from hydrophilic to hydrophobic, shrinks from a dissolved state to a gel state, wraps and binds the microspheres, and constrains the acrylic acid inside to prevent the acrylic acid from dissolving in water.

[0016] Furthermore, in the preparation of the modified acrylic microspheres of the present invention, the porosity of the polymer porous microspheres should be controlled at 70% to 90%, and the size distribution of the microspheres is 0.1 mm to 0.4 mm, accounting for 15% to 20%, 0.4 to 0.8 mm, accounting for 20% to 45%, and 0.8 mm to 1.2 mm, accounting for 35% to 70%; if the porosity of the microspheres is too low, the dosage will be too high, affecting the synthesis reaction; if the dosage is too low, the porosity will be too high, resulting in too much single adsorption of acrylic acid, too fast dissolution, and difficult to control; the reason why different sizes account for different proportions is that the smaller the size, the smaller the adsorption amount, the faster the dissolution, and the larger the size, the slower the dissolution. In order to ensure the stability of the dissolution rate during the entire reaction process, different microsphere sizes are used for control.

[0017] Furthermore, the preparation method of the modified reducing agent microspheres of the present invention comprises: adding ferrous sulfate (FeSO4) and α-ascorbic acid (VC) to water to completely dissolve them, then adding polymer porous microspheres, sealing and pressurizing to 0.3-0.5MPa, so that the ferrous sulfate (FeSO4) and α-ascorbic acid (VC) are completely adsorbed; after complete adsorption, drying the polymer porous microspheres adsorbing the reducing agent below 60°C, then adding them to the PNIPAM solution, stirring evenly, raising the temperature to 40-60°C, continuously stirring for 60s-90s and filtering to obtain the modified reducing agent microspheres;

[0018] The amount of water added is based on the minimum amount required for complete dissolution. Excessive water addition may result in incomplete adsorption of microspheres.

[0019] The mass concentration of the PNIPAM aqueous solution is above 5%;

[0020] The mass fractions of the above raw material components are as follows:

[0021]

[0022] Furthermore, the mass fractions of the above-mentioned raw materials of the present invention are as follows:

[0023]

[0024] The modified reducing agent microspheres contain 0.4 to 0.8 parts of effective ferrous sulfate (FeSO4) and 0.4 to 0.8 parts of effective α-ascorbic acid (VC);

[0025] The effective content of acrylic acid in the modified acrylic microspheres (AA) is 20 to 30 parts;

[0026] The mass concentration of the hydrogen peroxide is 27.5%.

[0027] Furthermore, the polymer porous microspheres in the preparation of the modified reducing agent microspheres of the present invention should be controlled at 70% to 90%, and the microsphere size distribution is that the microspheres with a size of 0.1 mm to 0.4 mm account for 30% to 40%, and the microspheres with a size of 0.4 mm to 0.8 mm account for 60% to 70%; at this ratio, after the microspheres are adsorbed, they are further wrapped with PNIPAM, which can effectively achieve their slow release.

[0028] The proportion of PNIPAM added in the preparation of the modified reducing agent microspheres of the present invention is relatively high compared to the proportion of modified acrylic acid in the preparation of modified acrylic acid microspheres, mainly because after the addition amount is increased, the thickness of the covering film increases after being dissolved in water, which can effectively control the overflow and migration speed of the reducing agent.

[0029] Furthermore, the present invention also provides a preparation method of the above-mentioned polycarboxylic acid water reducer, which is as follows: ethylene glycol monovinyl polyethylene glycol ether (EPEG-3000), modified acrylic microspheres (AA), hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres are reacted and synthesized at a temperature not higher than 40°C, and when the reaction is complete, water at 40 to 60°C is added, and the mixed solution is heated to 40 to 60°C to reduce the concentration of the synthesized polycarboxylic acid; while reducing the concentration of the solution, the microspheres and the PNIPAM attached to the surface thereof are filtered out while standing to obtain the final polycarboxylic acid water reducer of the present invention.

[0030] The polymer porous microspheres and PNIPAM in the present invention can be reused without affecting their effects. The reuse method is: adding the mixture of microspheres and PNIPAM into water below 20°C to completely dissolve PNIPAM, and then separating the microspheres and the PNIPAM aqueous solution by filtering to achieve reuse.

[0031] The synthesis temperature of the polycarboxylate water-reducing agent of the present invention shall not be higher than 40° C. If the temperature is higher than 40° C., the dispersibility of the synthesized water-reducing agent will decrease rapidly.

[0032] In the preparation of the modified acrylic microspheres of the present invention, porous microspheres and PNIPAM are added to acrylic acid, acrylic acid is adsorbed in the porous microspheres, and then PNIPAM is used to form an outer coating layer of the microspheres. In the preparation of the modified reducing agent microspheres, ferrous sulfate and VC are adsorbed in the porous microspheres, and then PNIPAM is used to form an outer coating layer of the microspheres. Furthermore, in the synthesis process of the polycarboxylate water-reducing agent, when the synthesis temperature is low and not higher than the LCST of PNIPAM, the acrylic acid inside the porous microspheres is slowly released through the connected pores of the coating layer to participate in the reaction, and the reducing agent inside the porous microspheres is also slowly released to participate in the reaction, and the release rates of the two are controlled by the content of PNIPAM (the thickness of the PNIPAM coating layer and the size of the connected pores) and the size distribution of the polymer porous microspheres. When the temperature is higher than LCST, PNIPAM shrinks and the connected pores are closed, which means it has a hydrophobic function. At this time, PNIPAM completely attaches and shrinks on the surface of the microspheres and in the pores, preventing the internal acrylic acid from continuing to release. When the ambient temperature is lower than LCST, PNIPAM re-forms a sol state, develops connected pores, promotes the release of acrylic acid, and participates in the polycarboxylic acid synthesis reaction. Temperature control is not required during the entire polycarboxylic acid synthesis reaction, realizing a synthesis technology with automatic control of the synthesis temperature. This technology can ensure that the entire reaction temperature is controlled below 36°C, without affecting the performance of the EPEG macromonomer in synthesizing polycarboxylic acid water reducer.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention realizes the simultaneous addition of polycarboxylic acid water reducer during compounding by preparing modified acrylic acid microspheres and modified reducing agent microspheres. The sustained release effect of the microspheres during the modification process and the control of the sustained release channel by PNIPAM are utilized to realize the stable and sustained release of acrylic acid and reducing agent, and to realize the preparation of a water reducer with stable and excellent performance under suitable synthesis conditions of acrylic acid and EPEG.

[0035] (2) The LCST of PNIPAM used in the present invention is between 32 and 36°C, and the optimal synthesis temperature for synthesizing EPEG using the components of the present invention is below 40°C. If the temperature exceeds 40°C, the molecular weight of the polymer will be small, the polymer structure will be unstable, and its dispersibility will deteriorate. Therefore, the LCST of PNIPAM can achieve structural transformation just below 40°C (between 32 and 36°C). When it is below LCST, the components in the PNIPAM gel can be released outward at a constant rate by free diffusion, and the gel is in an open state; when it is above LCST, the PNIPAM gel shrinks, and a dense layer is formed on the surface to prevent the release of the components inside the gel, thereby preventing the overflow and release of acrylic acid and the reducing agent when the temperature of the reactant solution is higher than the optimal temperature of the synthesis reaction, and controlling the reaction process to always be at an appropriate temperature.

[0036] Through the above technical measures, the slow dripping process in the polycarboxylic acid synthesis process is avoided, and the temperature control in the reaction process is achieved, and the stable synthesis and production of polycarboxylic acid water reducer with excellent performance is achieved. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form.

[0038] The parts of raw materials in each embodiment and comparative example are parts by mass.

[0039] Example 1

[0040] The synthetic raw materials of the polycarboxylate water-reducing agent of the present invention include:

[0041]

[0042] Modified reducing agent microspheres: effective content: 0.4 parts of ferrous sulfate (FeSO4), 0.8 parts of α-ascorbic acid (VC);

[0043] The preparation steps are as follows:

[0044] (1) Preparation of modified acrylic microspheres: First, weigh 20 parts of acrylic acid, then add 3 parts of polymer porous microspheres, and under a pressure of 0.3 MPa, completely adsorb the acrylic acid; the porosity of the polymer porous microspheres should be controlled at 70%, and the size distribution of the microspheres is 20% of 0.1 mm to 0.4 mm, 20% of 0.4 mm to 0.8 mm, and 60% of 0.8 mm to 1.2 mm; add PNIPAM aqueous solution to the above microspheres, with a PNIPAM content of 1 part; then stir the above solution evenly, quickly heat it to 40°C, and at this temperature, continue stirring for 90 seconds and then filter out the water to form modified acrylic microspheres;

[0045] (2) Preparation of modified reducing agent microspheres: Add a small amount of water to completely dissolve ferrous sulfate and α-ascorbic acid (VC), then add 0.5 parts of polymer porous microspheres (microspheres with a size of 0.1 mm to 0.4 mm account for 30%, and microspheres with a size of 0.4 mm to 0.8 mm account for 70%). After completely adsorbing them under a pressure of 0.3 MPa, dry the microspheres below 60°C, then add the microspheres to a PNIPAM solution with a PNIPAM content of 0.3 parts, stir evenly, raise the temperature to 60°C, continue stirring for 90 seconds, and filter to obtain modified reducing agent microspheres;

[0046] (3) Synthesis of polycarboxylic acid water reducer: Ethylene glycol monovinyl polyethylene glycol ether (EPEG-3000), modified acrylic microspheres (AA), hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres are reacted and synthesized at room temperature of 20°C. After the reaction is complete, water at 40°C is added in an amount such that the solid content of the product is controlled at 40% (after deducting the mass of the microspheres and PNIPAM), and the mixed solution is heated to 40°C to reduce the concentration of the synthesized polycarboxylic acid. While reducing the concentration of the solution, the microspheres and PNIPAM attached to the surface are filtered out while standing to obtain the final polycarboxylic acid water reducer.

[0047] The microspheres and PNIPAM can be reused without affecting their effects; the reuse method is to add the mixture of microspheres and PNIPAM into water below 20°C, so that PNIPAM is completely dissolved, and then use a filtration method to separate the microspheres and the PNIPAM aqueous solution for reuse.

[0048] Example 2

[0049] The synthetic raw materials of the polycarboxylate water-reducing agent of the present invention include:

[0050]

[0051] Modified reducing agent microspheres: effective content: 0.8 parts of ferrous sulfate (FeSO4), 0.4 parts of α-ascorbic acid (VC);

[0052] The preparation steps are as follows:

[0053] (1) Preparation of modified acrylic microspheres: First, 30 parts of acrylic acid are weighed, and then 5 parts of polymer porous microspheres are added, and the polymer porous microspheres are completely adsorbed on the acrylic acid under a pressure of 0.4 MPa; the porosity of the polymer porous microspheres should be controlled at 90%, and the size distribution of the microspheres is 0.1 mm to 0.4 mm, accounting for 15%, 0.4 to 0.8 mm, accounting for 45%, and 0.8 mm to 1.2 mm, accounting for 40%; PNIPAM aqueous solution is added to the above microspheres, and the PNIPAM content is 3 parts; then the above solution is stirred evenly, and then the temperature is quickly raised to 60°C. At this temperature, the stirring is continued for 60 seconds and the water is filtered out to form modified acrylic microspheres;

[0054] (2) Preparation of modified reducing agent microspheres: Add a small amount of water to completely dissolve ferrous sulfate and α-ascorbic acid (VC), then add 0.1 parts of polymer porous microspheres (microspheres with a size of 0.1 mm to 0.4 mm account for 40%, and microspheres with a size of 0.4 mm to 0.8 mm account for 60%). After completely adsorbing them under a pressure of 0.4 MPa, dry the microspheres at below 60°C, then add the microspheres to a PNIPAM solution with a PNIPAM content of 0.1 parts, stir evenly, raise the temperature to 40°C, continue stirring for 60 seconds, and filter to obtain modified reducing agent microspheres;

[0055] (3) Synthesis of polycarboxylic acid water reducer: Ethylene glycol monovinyl polyethylene glycol ether (EPEG-3000), modified acrylic microspheres (AA), hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres are reacted and synthesized at room temperature of 20°C. After the reaction is complete, 50°C water is added in an amount such that the solid content of the product is controlled at 40% (after deducting the mass of the microspheres and PNIPAM), and the mixed solution is heated to 50°C to reduce the concentration of the synthesized polycarboxylic acid. While reducing the concentration of the solution, the microspheres and PNIPAM attached to the surface are filtered out while standing to obtain the final polycarboxylic acid water reducer.

[0056] The microspheres and PNIPAM can be reused without affecting their effects. The reuse method is to add the mixture of microspheres and PNIPAM into water below 20°C, dissolve PNIPAM completely, and then separate the microspheres and PNIPAM aqueous solution by filtering to achieve reuse.

[0057] Example 3

[0058] The synthetic raw materials of the polycarboxylate water-reducing agent of the present invention include:

[0059]

[0060] Modified reducing agent microspheres: effective content: 0.6 parts of ferrous sulfate (FeSO4), 0.6 parts of α-ascorbic acid (VC);

[0061] The preparation steps are as follows:

[0062] (1) Preparation of modified acrylic microspheres: First, weigh 28 parts of acrylic acid, then add 4 parts of polymer porous microspheres, and under a pressure of 0.5 MPa, completely adsorb the acrylic acid; the porosity of the polymer porous microspheres should be controlled at 80%, and the size distribution of the microspheres is 0.1 mm to 0.4 mm, accounting for 18%, 0.4 to 0.8 mm, accounting for 32%, and 0.8 mm to 1.2 mm, accounting for 50%; add PNIPAM aqueous solution to the above microspheres, with a PNIPAM content of 2 parts; then stir the above solution evenly, quickly heat it to 50°C, continue stirring at this temperature for 80 seconds, and then filter out the water to form modified acrylic microspheres;

[0063] (2) Preparation of modified reducing agent microspheres: Add a small amount of water to completely dissolve ferrous sulfate and α-ascorbic acid (VC), then add 0.3 parts of polymer porous microspheres (microspheres with a size of 0.1 mm to 0.4 mm account for 35%, and microspheres with a size of 0.4 mm to 0.8 mm account for 65%). After completely adsorbing them under a pressure of 0.5 MPa, dry the microspheres at below 60°C, then add the microspheres to a PNIPAM solution with a PNIPAM content of 0.2 parts, stir evenly, raise the temperature to 50°C, continue stirring for 80 seconds, and filter to obtain modified reducing agent microspheres;

[0064] (3) Synthesis of polycarboxylic acid water reducer: Ethylene glycol monovinyl polyethylene glycol ether (EPEG-3000), modified acrylic microspheres (AA), hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres are reacted and synthesized at room temperature of 20°C. After the reaction is complete, 50°C water is added in an amount such that the solid content of the product is controlled at 40% (after deducting the mass of the microspheres and PNIPAM), and the mixed solution is heated to 50°C to reduce the concentration of the synthesized polycarboxylic acid. While reducing the concentration of the solution, the microspheres and PNIPAM attached to the surface are filtered out while standing to obtain the final polycarboxylic acid water reducer.

[0065] The microspheres and PNIPAM can be reused without affecting their effects. The reuse method is to add the mixture of microspheres and PNIPAM into water below 20°C, dissolve PNIPAM completely, and then separate the microspheres and PNIPAM aqueous solution by filtering to achieve reuse.

[0066] Comparative Example 1

[0067] Compared with Example 3, the acrylic acid and the reducing agent are not modified, and Step 1 and Step 2 are omitted, that is, only unmodified acrylic acid and the reducing agent are used in Step 3.

[0068] Comparative Example 2

[0069] Compared with Example 3, no modification of acrylic acid and reducing agent is performed, step 1 and step 2 are omitted, and in step 3, the constant temperature water bath is 20°C.

[0070] Comparative Example 3

[0071] Compared with Example 3, the modification of acrylic acid and reducing agent is not performed, and Step 1 and Step 2 are omitted. In Step 3, the dropping time of acrylic acid is controlled at 10 min, the dropping time of reducing agent is controlled at 20 min, and the initial temperature is 20°C.

[0072] Comparative Example 4

[0073] Compared with Example 3, the modification of acrylic acid and reducing agent is not performed, and Step 1 and Step 2 are omitted. In Step 3, the dropping time of acrylic acid is controlled at 10 min, the dropping time of reducing agent is controlled at 20 min, and the constant temperature water bath is 20°C.

[0074] Comparative Example 5

[0075] Compared with Example 3, the modification of acrylic acid and reducing agent is not performed, and Step 1 and Step 2 are omitted. In Step 3, the dropping time of acrylic acid is controlled at 40 min, the dropping time of reducing agent is controlled at 50 min, and the constant temperature water bath is 20° C. (this condition is the optimal condition when the components of the present invention are synthesized by room temperature).

[0076] Comparative Example 6

[0077] Compared to Example 3, no modification of acrylic acid was performed.

[0078] Comparative Example 7

[0079] Compared with Example 3, 1 part of polymer porous microspheres was added during the preparation of modified acrylic microspheres.

[0080] Comparative Example 8

[0081] Compared with Example 3, 8 parts of polymer porous microspheres were added during the preparation of modified acrylic microspheres.

[0082] Comparative Example 9

[0083] Compared with Example 3, in the preparation of modified acrylic microspheres, the polymer porous microspheres were selected to have a single size of 1 mm.

[0084] Comparative Example 10

[0085] Compared with Example 3, in the preparation of modified acrylic acid microspheres, the polymer porous microspheres are selected to have a single size of 0.1 mm.

[0086] Comparative Example 11

[0087] Compared with Example 3, PNIPAM was not added in the preparation of modified acrylic microspheres.

[0088] Comparative Example 12

[0089] Compared with Example 3, 5 parts of PNIPAM were added in the preparation of modified acrylic microspheres.

[0090] Comparative Example 13

[0091] Compared with Example 3, no modification of the reducing agent was performed.

[0092] Comparative Example 14

[0093] Compared with Example 3, 1 portion of polymer porous microspheres was added during the preparation of the modified reducing agent microspheres.

[0094] Comparative Example 15

[0095] Compared with Example 3, in the preparation of modified reducing agent microspheres, the polymer porous microspheres are selected to have a single size of 0.5 mm.

[0096] Comparative Example 16

[0097] Compared with Example 3, in the preparation of modified reducing agent microspheres, the polymer porous microspheres are selected to have a single size of 0.05 mm.

[0098] Comparative Example 17

[0099] Compared with Example 3, PNIPAM was not incorporated in the preparation of the modified reducing agent microspheres.

[0100] Comparative Example 18

[0101] Compared with Example 3, 0.5 parts of PNIPAM was added in the preparation of the modified reducing agent microspheres.

[0102] The detection indexes and detection methods of the above embodiments and comparative examples are tested according to the provisions of "Polycarboxylic Acid High Performance Water Reducing Agent" JG / T223-2017, and the main detection indexes are water reduction rate, 1h slump loss over time, and 28d compressive strength ratio. At the same time, the synthesis temperature is detected during the reaction process, and when it exceeds 40°C, an early warning record is made.

[0103] Table 1 Water reduction performance index test results

[0104]

[0105]

[0106] The following conclusions can be drawn from Table 1:

[0107] Comparing Comparative Example 1 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, the 28d compressive strength is reduced, and the detected temperature during the synthesis process rises to 47.2°C. This shows that if the synthesis is carried out directly without the sustained release of porous microspheres and PNIPAM, the dispersibility of cement particles will be seriously affected compared with Example 3, resulting in a significant reduction in the performance of the water reducer.

[0108] Comparing Comparative Example 2 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This shows that even if the temperature is controlled during the synthesis process, the excessive drop acceleration will cause the reaction to be too fast, the product synthesis is unstable, and the acrylic acid itself self-polymerizes, and the EPEG self-polymerizes, and the formed products are complex, which makes the water reduction performance of the polycarboxylate water-reducing agent decrease rapidly, and the dispersibility of cement particles decreases, resulting in a decrease in the performance of the water-reducing agent. Only from the data, it is slightly better than the comparative example without temperature control.

[0109] Comparing Comparative Example 3 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, the 28d compressive strength is reduced, and the temperature rises to 42.8° C. during the synthesis process. This shows that if the temperature is not controlled during the synthesis process, it is very easy to cause excessive temperature rise, resulting in accelerated reaction and implosion, affecting the normal synthesis of polycarboxylic acid, resulting in poor dispersibility of the product and decreased fluidity.

[0110] Comparing Comparative Example 4 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This shows that even if the temperature is controlled during the synthesis process, the excessive drop acceleration will cause the reaction to be too fast, the product synthesis is unstable, the dispersibility of cement particles is reduced, and the fluidity is reduced. It is just slightly better than the control group without temperature control.

[0111] By comparing Comparative Example 5 (optimal synthesis scheme of room temperature synthesis process) with Example 3, it can be seen that compared with Comparative Example 5, the water reducing rate, slump retention type and improvement effect on mechanical properties of the water reducer prepared by the synthesis process Example 3 of the present invention have no obvious differences, indicating that the synthesis process of the present invention can synthesize a water reducer with excellent performance.

[0112] Comparing Comparative Example 6 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This is because the acrylic acid content is too high, and a large amount of self-polymerization reaction occurs, resulting in less polycarboxylic acid synthesis products, smaller molecular weight, smaller main chain carboxyl density, weaker adsorption to cement, weaker dispersibility, rapid decrease in fluidity, and reduced water reduction rate, thereby affecting the comprehensive performance of the water reducer.

[0113] Comparing Comparative Example 7 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This is because the number of polymer porous microspheres is reduced, and the adsorption of acrylic acid is insufficient, resulting in excessive acrylic acid in the early solution, causing acrylic acid to produce a polymerization reaction, affecting the synthesis of polycarboxylic acid, resulting in a certain decrease in its dispersibility and performance.

[0114] Comparing Comparative Example 8 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This is because the number of polymer porous microspheres increases, and the single microspheres are less attached with acrylic acid, resulting in a release rate that is too fast or too slow, which cannot be effectively controlled. In this process, the release rate does not match the reduction system, the molecular weight of the polycarboxylate water reducer is highly different, and the dispersibility is unstable, resulting in a decrease in the performance of the synthetic water reducer.

[0115] Comparing Comparative Example 9 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This shows that the use of a single larger-sized microsphere will cause an unreasonable reaction. This is mainly because if large-particle microspheres are used, the early release is slow, and more acrylic acid is released in the later stage, resulting in inconsistent rates before and after the synthesis, resulting in unstable performance of the synthetic product and decreased performance.

[0116] Comparing Comparative Example 10 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This shows that the use of a single smaller-sized microsphere will cause an unreasonable reaction. This is mainly because if small-particle microspheres are used, the early release is too fast, and less acrylic acid is released in the later stage, resulting in inconsistent rates before and after the synthesis, resulting in unstable performance of the synthetic product, resulting in a decrease in the performance of the water reducer.

[0117] Based on the problems existing in Comparative Examples 9 and 10, the present invention adjusts the particle sizes of different microspheres to match the release rate with the reaction rate, thereby obtaining a better reaction synthesis product.

[0118] Comparing Comparative Example 11 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, the 28d compressive strength is reduced, and the synthesis temperature reaches 41.2° C. This shows that without adding PNIPAM, only using a single polymer porous microsphere, the reaction process cannot be well controlled, especially the temperature control. During the reaction process, the temperature rises rapidly to 41.2° C., affecting the dispersibility of the synthetic product, resulting in a decrease in the performance of the synthetic water reducer.

[0119] Comparing Comparative Example 12 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This shows that if too much PNIPAM is added, the adhesion layer will be too thick, the cost will be too high, which is unnecessary, and the impurities in the reaction system will be increased. Third, the gel layer formed is too thick, which makes the release rate of acrylic acid too slow, affecting the reaction.

[0120] Comparing Comparative Example 13 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This is because if the reducing agent is not modified to achieve slow release of the reducing agent, the reducing agent concentration in the reaction solution is too high, resulting in an imbalance in the redox system, a large amount of EPEG self-polymerization reaction, and the redox system is aging, and basically no good water reducer product is synthesized.

[0121] Comparing Comparative Example 14 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This is because too many microspheres are added, resulting in too little adsorption of a single microsphere, and the release rate of the reduction system is difficult to control, which in turn makes the synthesis process difficult to control and the product unstable.

[0122] Comparing Comparative Example 15 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This shows that the use of a single larger-sized microsphere will cause an unreasonable reaction. This is mainly because if large-particle microspheres are used, the early release is slow, and more reducing agents are released in the later stage, resulting in inconsistent rates before and after the synthesis, resulting in unstable performance of the synthetic product.

[0123] Comparing Comparative Example 16 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This shows that the use of a single smaller-sized microsphere will cause an unreasonable reaction. This is mainly because if small-particle microspheres are used, the early release is too fast, and less reducing agent is released in the later stage, resulting in inconsistent rates before and after the synthesis, resulting in unstable performance of the synthetic product.

[0124] Based on the problems existing in Comparative Examples 15 and 16, the present invention adjusts the particle sizes of different microspheres to match the release rate of the reducing agent with the reaction rate, thereby obtaining a better reaction synthesis product.

[0125] Comparing Comparative Example 17 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This is because the modified reducing agent is not mixed with PNIPAM, and the release rate of the reducing agent cannot be controlled at all, which seriously affects the dispersibility and water reduction of the reaction product.

[0126] Comparing Comparative Example 18 with Example 3, it can be seen that the water reduction rate is reduced, the 1h slump loss over time is increased, and the 28d compressive strength is reduced. This is because the excess PNIPAM not only increases the cost, but also increases the impurities in the reaction system, and causes the release rate to be too slow, which is not conducive to the reaction. However, the mass proportion of PNIPAM incorporated into the reducing agent is higher than that in acrylic acid, and the incorporation of polymer microspheres below 0.1mm is cancelled (the smaller the microspheres, the faster the release), mainly to be able to controllably reduce the release rate of the reducing agent so as not to affect the normal reaction.

[0127] By comparing the above comparative examples, the size, dosage and amount of PNIPAM in the microspheres are selected to reasonably regulate the release rate of acrylic acid and the release rate of the reducing agent so as to match the reaction components and form a stable synthesis process. By using PNIPAM to control the temperature of the reaction process, once the temperature rises due to excessively high ambient temperature or abnormal reaction, the reaction process can be controlled in time, the reaction temperature can be adjusted in time, and a stable synthesis reaction can be achieved.

Claims

1. A polycarboxylate water reducer, characterized in that: The polycarboxylate water reducer is synthesized by reaction of ethylene glycol monovinyl polyglycol ether, modified acrylic acid microspheres, hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres; The modified acrylic microspheres are made of porous inner core balls as carriers, acrylic acid as the main adsorbent in the carrier, and PNIPAM as the outer wrapping layer of the carrier; wherein the porous inner core balls are polymer porous microspheres; The modified reducing agent microspheres are made of porous inner core balls as carriers, reducing agents as main adsorbed substances in the carriers, and PNIPAM as outer wrapping layers of the carriers; wherein the porous inner core balls are polymer porous microspheres.

2. A polycarboxylate water reducer according to claim 1, characterized in that: The reducing agent is a mixture of ferrous sulfate and α-ascorbic acid.

3. A polycarboxylate water-reducing agent according to claim 2, characterized in that: The preparation method of the modified acrylic microspheres comprises: firstly, adding polymer porous microspheres to acrylic acid, sealing and pressurizing to 0.3-0.5 MPa, so that the acrylic acid is completely adsorbed; then, adding PNIPAM aqueous solution, stirring the solution evenly, rapidly heating it to 40-60° C., and at this temperature, continuously stirring for 60 seconds to 90 seconds, then filtering out the water, and obtaining the modified acrylic microspheres; The mass concentration of the PNIPAM aqueous solution is above 5%; The mass fractions of the above raw material components are as follows: 20-30 parts of acrylic acid, 3-5 parts of polymer porous microspheres, PNIPAM 1 to 3 parts.

4. A polycarboxylate water reducer according to claim 3, characterized in that: In the preparation of the modified acrylic microspheres, the porosity of the polymer porous microspheres is controlled at 70% to 90%, and the size distribution of the microspheres is 0.1 mm to 0.4 mm, accounting for 15% to 20%, 0.4 mm to 0.8 mm, accounting for 20% to 45%, and 0.8 mm to 1.2 mm, accounting for 35% to 70%.

5. A polycarboxylate water reducer according to claim 2, characterized in that: The preparation method of the modified reducing agent microspheres comprises: adding ferrous sulfate and α-ascorbic acid into water to completely dissolve them, then adding polymer porous microspheres, sealing and pressurizing to 0.3-0.5 MPa, so that the polymer porous microspheres adsorbing the ferrous sulfate and α-ascorbic acid can be completely adsorbed; after complete adsorption, drying the polymer porous microspheres adsorbing the reducing agent at below 60° C., then adding the polymer porous microspheres to the PNIPAM solution, stirring evenly, raising the temperature to 40-60° C., continuously stirring for 60s-90s, and filtering to obtain the modified reducing agent microspheres; The mass concentration of the PNIPAM aqueous solution is above 5%; The mass fractions of the above raw material components are as follows:

6. A polycarboxylate water reducer according to claim 5, characterized in that: The polymer porous microspheres in the preparation of the modified reducing agent microspheres are controlled at 70% to 90%, and the microsphere size distribution is that the microspheres with a size of 0.1 mm to 0.4 mm account for 30% to 40%, and the microspheres with a size of 0.4 mm to 0.8 mm account for 60% to 70%.

7. A polycarboxylate water-reducing agent according to any one of claims 1 to 6, characterized in that: The mass fractions of the above raw materials are as follows: The modified reducing agent microspheres contain 0.4 to 0.8 parts of ferrous sulfate and 0.4 to 0.8 parts of α-ascorbic acid; The effective content of acrylic acid in the modified acrylic microspheres is 20 to 30 parts; The mass concentration of the hydrogen peroxide is 27.5%.

8. The method for preparing a polycarboxylate water-reducing agent according to any one of claims 1 to 7, characterized in that: The preparation method comprises: reacting ethylene glycol monovinyl polyethylene glycol ether, modified acrylic microspheres, hydrogen peroxide, sodium hypophosphite and modified reducing agent microspheres at a temperature not higher than 40°C, adding water at 40 to 60°C after the reaction is complete, heating the mixed solution to 40 to 60°C, standing the solution to filter out the microspheres and PNIPAM attached to the surface thereof, and obtaining the polycarboxylic acid water reducer.

9. The preparation of a polycarboxylate water-reducing agent according to claim 8, characterized in that: The method for reusing the polymer porous microspheres and PNIPAM is as follows: adding a mixture of the microspheres and PNIPAM into water below 20° C. to completely dissolve the PNIPAM, and then separating the microspheres and the PNIPAM aqueous solution by filtering to achieve reuse.

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