Polycarboxylic acid viscosity-reducing and flow-increasing super plasticizer as well as preparation method and application thereof

Abstract

The invention discloses a polycarboxylic acid viscosity-reducing flow-increasing type super plasticizer and a preparation method and application thereof, and belongs to the technical field of cement-based composite material admixtures, the super plasticizer comprises the following structural units: a main chain is a polycarboxylic acid skeleton; at least a portion of the side chain is attached to the main chain by a dynamic covalent bond selected from the group consisting of an imine bond (-CH = N-) or a borate bond (-B (OR) 2); the reversible chemical bond is selected from one or two of an imine bond and a borate bond; the side chain comprises a carboxylic acid group, a sulfonic acid group, or a polyethylene glycol chain. The functional side chains are connected through dynamic covalent bonds, so that high initial fluidity is maintained, small-molecule dispersed fragments are released in the middle and later periods of hydration, and the workability of the concrete is continuously maintained.

Description

Technical Field

[0001] This invention belongs to the technical field of cement-based composite material admixtures, specifically relating to a polycarboxylate-based superplasticizer with side chains linked by dynamic covalent bonds (imine bonds or borate ester bonds). This superplasticizer can respond to changes in the microenvironment during cement hydration, achieving synergistic regulation of initial high dispersion and subsequent slow-release plasticity retention, and is particularly suitable for high-temperature, long-distance transportation, or systems containing mud-containing aggregates. Specifically, it relates to a polycarboxylate viscosity-reducing and flow-enhancing superplasticizer, its preparation method, and its applications. Background Technology

[0002] Traditional polycarboxylate superplasticizers (PCEs) exhibit excellent initial dispersion properties in cement pastes, but their plasticity retention gradually declines as the hydration process progresses. This invention aims to address this issue by introducing dynamic covalent bonds (such as imine or borate ester bonds) that enable PCEs to automatically adjust their structure and function at different hydration stages.

[0003] Traditional polycarboxylate superplasticizers (PCEs) have their main chain and side chains linked by irreversible covalent bonds (such as ester and ether bonds). While exhibiting excellent initial dispersibility, in the later stages of hydration, the surface of cement particles becomes covered by hydration products (CSH, AFt), reducing PCE adsorption sites. This makes it difficult for high-molecular-weight PCEs to effectively adsorb onto the surface of the nascent phase, leading to rapid loss of flowability. To address this issue, existing technologies have attempted: introducing phosphate ester / sulfonic acid groups to enhance adsorption capacity, but this fails to solve the problem of insufficient adsorption sites in the later stages; microencapsulation for sustained release, which is complex and costly; and low-molecular-weight PCE, which offers good plasticity retention but poor initial dispersion. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, one of the objectives of this invention is to provide a polycarboxylic acid viscosity-reducing and flow-enhancing superplasticizer that, through dynamic covalent bonding of functional side chains, releases small molecule dispersed fragments in the middle and late stages of hydration while maintaining high initial fluidity, thereby continuously maintaining the workability of concrete.

[0005] The second objective of this invention is to provide a method for preparing a polycarboxylic acid viscosity-reducing and flow-promoting superplasticizer, which is simple to prepare and convenient for on-site application.

[0006] The third objective of this invention is to provide the application of polycarboxylate superplasticizers in cement-based materials to improve the initial fluidity and later plastic retention properties of cement paste.

[0007] One of the objectives of this invention is achieved through the following technical solution:

[0008] A polycarboxylic acid viscosity-reducing and flow-enhancing superplasticizer, the superplasticizer comprising the following structural units:

[0009] The main chain is a polycarboxylic acid backbone;

[0010] At least a portion of the side chains are connected to the main chain via dynamic covalent bonds, wherein the dynamic covalent bonds are selected from one or both of imine bonds and borate ester bonds;

[0011] The side chain contains a carboxylic acid group, a sulfonic acid group, or a polyethylene glycol chain.

[0012] Furthermore, the imine bond is formed by the condensation of an aldehyde group on the main chain and an amino group on the side chain; the borate ester bond is formed by the condensation of a borate group on the main chain and a diol group on the side chain; the carboxylic acid group or sulfonic acid group in the side chain can be adsorbed onto the surface of cement particles to provide a dispersing effect.

[0013] Furthermore, the superplasticizer remains stable in a highly alkaline environment (pH > 12). In the early hydration stage (0-2 hours), due to local microenvironment pH fluctuations or water activity changes, some side chains dissociate from the main chain, releasing small molecular fragments that continue to adsorb onto the surface of the newly formed hydration product CSH, maintaining fluidity.

[0014] The second objective of this invention is achieved by the following technical solution:

[0015] A method for preparing a polycarboxylic acid viscosity-reducing and flow-promoting superplasticizer includes the following steps:

[0016] S1. Synthesize polycarboxylic acid backbone containing aldehyde or borate groups;

[0017] S2. By means of mechanochemical internal mixing polymerization, side links containing amine or diol groups are branched onto the polycarboxylic acid backbone containing aldehyde or borate groups.

[0018] S3. Purify and dry the resulting polymer, which is the polycarboxylic acid viscosity-reducing and flow-increasing superplasticizer.

[0019] The third objective of this invention is achieved by the following technical solution:

[0020] An application of the polycarboxylate superplasticizer described above, wherein the superplasticizer is used in cement-based materials to improve the initial fluidity and later plasticity retention properties of cement paste.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention provides a polycarboxylic acid viscosity-reducing and flow-enhancing superplasticizer that releases active fragments only when needed, i.e., at the end of the hydration induction period, avoiding ineffective release in the early stages of hydration induction; it has dual plasticity protection, with the polymer backbone and small molecule fragments working together to maintain fluidity, and the imine bonds selectively hydrolyzing to release negatively charged carboxylic acid fragments. These small molecule fragments continuously adsorb onto the surface of newly formed CSH, inhibiting flocculation and maintaining fluidity (plasticity protection).

[0023] Temperature-sensitive regulation: At low temperatures (<32℃), PNIPAM stretches, increasing yield stress and preventing segregation; at high temperatures, it shrinks, reducing viscosity.

[0024] Simple process: Mechanochemical method requires no solvent, green and efficient. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments. It should be noted that, without conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0026] Although the macroscopic pH of the cement paste pore fluid is approximately 12.5-13.5 (maintained by the CH and AFm phases), the chemical environment on the surface of different mineral phases varies greatly at the microscale during the initial hydration stage (0-2 hours). C3A is produced by the hydrolysis of Al3+ when there is no gypsum or when gypsum is depleted, and the local pH can drop to 4-6 (Lothenbach et al., Cem. Concr. Res. 2008); even with gypsum, there are still transient acidic micro-regions on its surface within the first 30 minutes.

[0027] Some carboxylic acid side chains are attached to the main chain via imine bonds (instead of direct covalent bonds), initial state (0-30 min):

[0028] The system pH rapidly rises to 13, dynamic bonds stabilize, and PCE provides strong steric hindrance in its intact polymer form. The overall pH is still being established, with lower pH in local micro-regions, especially near C3A. However, the imine bond kinetics are slow, and not many bonds have broken yet. PCE maintains its intact polymer configuration, further enhancing steric hindrance and high dispersibility. 30-120 min (end of hydration induction period): Local Ca2+ concentration increases, and the pH in local micro-regions temporarily drops to 10-11 due to gypsum depletion, secondary dissolution of C3A, etc., or a decrease in free water. Imine bonds selectively hydrolyze, releasing negatively charged carboxylic acid fragments. These small molecule fragments continuously adsorb onto the surface of newly formed CSH, inhibiting flocculation and maintaining fluidity (plasticity retention). While imine bonds are feasible, boronic ester bonds (RB(OR'-)2) may be more robust in cement environments, stable at pH > 10, and suitable for cement applications. Water activity response: In the later stages of hydration, water is bound by the CSH gel, reducing free water and accelerating the reverse reaction of boronic esters. Unlike imine bonds, which are susceptible to metal ion-catalyzed hydrolysis, boronic esters are not affected by Ca2+. 2+ interference.

[0029] Example 1

[0030] This embodiment provides a polycarboxylic acid viscosity-reducing and flow-promoting superplasticizer, which comprises the following structural units:

[0031] The main chain is a polycarboxylic acid backbone;

[0032] At least a portion of the side chains are connected to the main chain via dynamic covalent bonds, wherein the dynamic covalent bonds are selected from imine bonds (–CH=N–) or borate ester bonds (–B(OR)2), and the reversible chemical bonds are selected from two of the imine bonds and borate ester bonds;

[0033] The side chain contains a carboxylic acid group, a sulfonic acid group, or a polyethylene glycol chain.

[0034] The specific preparation method of polycarboxylate viscosity-reducing and flow-promoting superplasticizer is as follows:

[0035] Step 1: Synthesize polycarboxylic acid backbone containing aldehyde or borate groups

[0036] Raw material preparation:

[0037] Methacrylic acid (MAA), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and ammonium persulfate (APS) were used as initiators.

[0038] Functional monomers containing aldehyde or borate groups (such as 4-vinylbenzaldehyde, 4-vinylphenylboronic acid).

[0039] Polymerization reaction:

[0040] Under nitrogen protection, methacrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, the functional monomer 4-vinylbenzaldehyde, and ammonium persulfate were dissolved in deionized water and stirred until homogeneous.

[0041] The mixture was placed in a constant temperature water bath at 60°C and reacted for 4 hours to obtain a polycarboxylic acid backbone containing aldehyde or boric acid groups.

[0042] Step 2: Grafting side chains via mechanochemical internal mixing polymerization

[0043] Raw material preparation:

[0044] Monomers containing amine or glycol groups (such as diethanolamine and ethylene glycolamine).

[0045] A polycarboxylic acid backbone containing aldehyde or borate groups (obtained in step 1);

[0046] Mechatronics internal polymerization:

[0047] A polycarboxylic acid backbone containing aldehyde or borate groups is mixed with monomers containing amine or diol groups in a certain proportion, and an appropriate amount of solvent (such as deionized water or ethanol) is added.

[0048] The monomers containing amino groups were ground in a ball mill at room temperature to 60°C for 2-8 hours to induce a condensation reaction between the amine-containing monomers and the aldehyde-containing polycarboxylic acid backbone, generating side chains containing reversible imine bonds. Simultaneously, the monomers containing diol groups were condensed with the borate-containing polycarboxylic acid backbone, generating side chains containing borate ester bonds, thus yielding a polymer solution. FTIR: 1620 cm⁻¹ -1 (BOC stretching) confirms the formation of borate ester bonds.

[0049] Step 3: Purify and dry

[0050] purification:

[0051] The resulting polymer solution was filtered to remove unreacted monomers and byproducts;

[0052] Wash the polymer precipitate with plenty of deionized water until the filtrate is neutral.

[0053] Drying: The purified polymer precipitate was placed in a vacuum oven and dried at 60°C for 24 hours to obtain the final product.

[0054] Comparative Example 1: Traditional HPEG-PCE (ester bond linkage), i.e., PCE prepared by copolymerization of methoxy polyethylene glycol monomethacrylate (HPEG) and acrylic acid (AA).

[0055] Comparative Example 2: PCE without dynamic bonds (ether linkage, TPEG type). The main chain of TPEG type PCE is usually an acrylic or methacrylic acid polymer, and the side chains are connected to the main chain through ether bonds (–O–). The side chains themselves are polyoxyethylene (such as TPEG, methoxy polyethylene glycol methacrylate). This ether linkage is an irreversible covalent bond, hence the term "without dynamic bonds," in contrast to reversible dynamic bonds such as imine bonds or borate ester bonds.

[0056] Experiment Example 1: Slump Test

[0057] Cement: P·O 42.5, 320 kg / m³ 3 ;

[0058] Water-to-binder ratio: 0.38;

[0059] Sand ratio: 40%;

[0060] The dosage of the polycarboxylate viscosity-reducing and flow-promoting superplasticizer provided in Example 1 is 0.25% of the mass of the cementitious material;

[0061] The slump was determined according to GB / T50080-2016, and the compressive strength was determined according to GB / T50081-2019.

[0062] Mixing: First, dry mix for 30 seconds, then add water and polycarboxylate superplasticizer (viscosity reducer and flow promoter), and wet mix for 60 seconds;

[0063] Slump test: Use a standard slump cone (100mm inner diameter, 300mm height); fill in three layers, tamp each layer 25 times; after lifting the cone, measure the slump height (mm); record the initial slump (T=0min).

[0064] Slump Loss at 2h

[0065] Test standard: Section 4.1 of GB / T50080-2016

[0066] Test procedure: Pour the concrete mixture into a sealed container, cover it with a film to prevent moisture evaporation; let it stand at room temperature of 20℃±2℃ for 2 hours; measure the slump again;

[0067] Calculate the slump loss: Slump loss = Initial slump - 2h slump

[0068] 1-day compressive strength

[0069] Test standard: GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete"

[0070] Test steps:

[0071] Molding: Pour the concrete mixture into a 100×100×100mm mold and compact it;

[0072] Standard curing: 20℃±2℃, RH≥95%, curing for 7 days;

[0073] After demolding, the specimens were cured in water for another 7 days.

[0074] The compressive strength was measured using a press, and the average value of three specimens was taken. The test results are shown in Table 1.

[0075] Table 1 Performance Tests

[0076] sample Initial slump (mm) 1h slump retention rate 2h slump retention rate 7-day concrete strength (MPa) Example 1 220 95% 94% 42.0 Comparative Example 1 220 82% 65% 33.5 Comparative Example 2 218 85% 70% 34.0

[0077] As can be seen from Table 1, the polycarboxylate viscosity-reducing and flow-enhancing superplasticizer provided in Example 1, when used in cement mortar mixtures, increases the slump retention rate by 20 percentage points after 2 hours, far exceeding the industry "significant" threshold (≥15%); and increases the strength by 10%, due to the small molecule fragments promoting hydration nucleation.

[0078] Experiment Example 2

[0079] Instrument: Waters 1515 GPC system;

[0080] Chromatographic column: PL aquagel-OH 30 + OH 60 (tandem);

[0081] Mobile phase: 0.1 M NaNO3 aqueous solution;

[0082] Flow rate: 1.0 mL / min;

[0083] Detector: Differential refractive index detector (RID);

[0084] Sample: The cement paste after hydration for 2 hours was centrifuged (10,000 rpm, 10 min), and the supernatant was filtered (0.22 μm), diluted, and injected. Gel permeation chromatography (GPC) was used to determine GPC: After hydration for 2 hours, the molecular weight of PCE-boronate decreased by 18%, proving the dissociation of the side chains;

[0085] Experimental Example 3

[0086] The cement mortar in Experiment Example 1 was hydrated to the target time of 2 hours: it was left to stand in a constant temperature chamber at 20°C;

[0087] Centrifugation: Take 10 g of the slurry and place it in a centrifuge tube;

[0088] Centrifuge at 10,000 rpm for 15 minutes or at 15,000 × g to ensure complete solid-liquid separation;

[0089] Take the supernatant and filter it through a 0.22 μm aqueous filter membrane to remove nanoscale colloids.

[0090] Determination of residual PCE concentration:

[0091] Total organic carbon (TOC): The organic carbon content in the supernatant was determined using a TOC analyzer (such as the Shimadzu TOC-L).

[0092] The carbon content of PCE is converted into PCE concentration.

[0093] Calculate the adsorption capacity:

[0094] Adsorption capacity (mg / g cement) = ((C0-C) e )×V) / m

[0095] Wherein, C0: initial PCE concentration (mg / mL)

[0096] C e PCE concentration in the supernatant (mg / mL)

[0097] V: Total solution volume (mL)

[0098] m: Cement mass (g)

[0099] Experimental results: Compared with Comparative Example 1, the adsorption amount of PCE polycarboxylate viscosity-reducing and flow-enhancing superplasticizer in Example 1 on CSH was 35% higher than that of the comparative example; compared with Comparative Example 2, the adsorption amount of PCE polycarboxylate viscosity-reducing and flow-enhancing superplasticizer in Example 1 on CSH was 30% higher than that of the comparative example.

[0100] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A polycarboxylic acid viscosity-reducing and flow-promoting superplasticizer, characterized in that, include The superplasticizer comprises the following structural units: The main chain is a polycarboxylic acid backbone; At least a portion of the side chains are connected to the main chain via dynamic covalent bonds, wherein the dynamic covalent bonds are selected from one or both of imine bonds and borate ester bonds; The side chain contains a carboxylic acid group, a sulfonic acid group, or a polyethylene glycol chain.

2. The polycarboxylate viscosity-reducing and flow-promoting superplasticizer according to claim 1, characterized in that, The imine bond is formed by the condensation of an aldehyde group on the main chain and an amino group on the side chain; the borate ester bond is formed by the condensation of a borate group on the main chain and a diol group on the side chain; the carboxylic acid group or sulfonic acid group in the side chain can be adsorbed onto the surface of cement particles to provide a dispersing effect.

3. The polycarboxylate viscosity-reducing and flow-promoting superplasticizer according to claim 1, characterized in that, The superplasticizer remains stable in a highly alkaline environment with pH > 12. In the early hydration stage, i.e., within 0-2 hours, due to local microenvironment pH fluctuations or water activity changes, some side chains dissociate from the main chain, releasing small molecular fragments that continue to adsorb onto the surface of the newly formed hydration product CSH, maintaining fluidity.

4. A method for preparing a polycarboxylate viscosity-reducing and flow-promoting superplasticizer according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Synthesize polycarboxylic acid backbone containing aldehyde or borate groups; S2. By means of mechanochemical internal mixing polymerization, side links containing amine or diol groups are branched onto the polycarboxylic acid backbone containing aldehyde or borate groups. S3. Purify and dry the resulting polymer, which is the polycarboxylic acid viscosity-reducing and flow-increasing superplasticizer.

5. The method for preparing a polycarboxylic acid viscosity-reducing and flow-promoting superplasticizer according to claim 4, characterized in that, The mechanochemical internal mixing polymerization method uses a ball mill for the reaction, with a reaction time of 2-8 hours and a reaction temperature of room temperature to 60°C.

6. The application of the polycarboxylate viscosity-reducing and flow-enhancing superplasticizer according to claim 1, characterized in that, The polycarboxylate viscosity-reducing and flow-enhancing superplasticizer is used in cement-based materials to improve the initial fluidity and subsequent plasticity retention of cement paste.