CN106496447B

CN106496447B - Star-shaped amphoteric polycarboxylate superplasticizer with efficient anti-mud effect and preparation method thereof

Info

Publication number: CN106496447B
Application number: CN201611020326.6A
Authority: CN
Inventors: 唐新德; 胡秀颖; 徐大举; 徐静; 庞来学; 周德杰; 王可良
Original assignee: Shandong Jiaotong University
Current assignee: Shandong Jiaotong University
Priority date: 2016-11-21
Filing date: 2016-11-21
Publication date: 2021-06-25
Anticipated expiration: 2036-11-21
Also published as: CN106496447A

Abstract

The invention discloses a star-shaped amphoteric polycarboxylate superplasticizer with high-efficiency anti-mud effect and a preparation method thereof, which comprises the steps of carrying out esterification reaction on beta-cyclodextrin and a disulfide compound containing acyl halide groups to obtain a reversible addition-fragmentation chain transfer agent (RAFT reagent) with a star-shaped structure, initiating RAFT polymerization of polyethylene glycol (meth) acrylate, (meth) acrylic acid and (meth) acryloyloxyethyl trimethyl ammonium chloride under the action of the chain transfer agent and an initiator to obtain a star-shaped amphoteric copolymer, and further processing to obtain the star-shaped amphoteric polycarboxylate superplasticizer with the high-efficiency anti-mud effect and the solid content of which is 20%. The polycarboxylate superplasticizer prepared by the invention has high water reducing rate, has high-efficiency anti-mud effect and can meet higher construction requirements.

Description

Star-shaped amphoteric polycarboxylate superplasticizer with efficient anti-mud effect and preparation method thereof

Technical Field

The invention relates to a polycarboxylate superplasticizer and a preparation method thereof, in particular to a star-shaped amphoteric polycarboxylate superplasticizer with a high-efficiency anti-mud effect and a preparation method thereof, and belongs to the technical field of concrete admixtures in building materials.

Background

The polycarboxylate superplasticizer serving as a third-generation high-performance concrete superplasticizer has the outstanding advantages of low mixing amount, high water reducing rate, good slump retaining performance, strong molecular structure adjustability, large high-performance potential and the like, and is successfully applied to a series of major projects such as high-speed railways, bridges, tunnels and the like at present.

The polycarboxylic acid high-efficiency water reducing agent also meets a plurality of technical problems in practical application, such as adaptability to cement/admixture, sensitivity to the using amount and water consumption of the water reducing agent, influence on the mud content of aggregate, temperature and the like. A large number of researches and engineering practices show that when the mud content of the aggregate is high, negative influence can be generated on the performance of concrete, mainly shown in that the water reducing dispersion performance of the water reducing agent is reduced, and the workability of concrete mixtures is influenced. In order to avoid the negative effect on concrete caused by high mud content of aggregate, the current commonly used solving measure is to wash the aggregate with high mud content or add a water reducing agent in an excessive amount. But aggregate grading can be damaged during flushing, and procedures can be increased during flushing, so that the construction period is influenced; super-doped water reducers typically cause initial bleeding and segregation of the concrete, and super-doped water reducers add cost. The mud in the sand and stone material is mainly montmorillonite soil and kaolin, has higher specific surface area and a layered structure, and is preferential to cement to adsorb a water reducing agent and free water, so that the problems of large slump loss, poor rheological property, reduced durability and strength and the like of concrete are caused.

At present, the preparation of the polycarboxylate water reducer is mainly based on the traditional free radical polymerization technology, but due to the nature of free radical polymerization (slow initiation, fast growth, easy chain transfer and chain termination and the like), uncontrollable polymerization reaction is determined, the polymerization product is often caused to be in wide distribution, the molecular weight and the structure are uncontrollable, and even branching and crosslinking occur, so that the performance of the polymer is influenced, and therefore the polycarboxylate water reducer with the multiple functions and high reaction activity of a regular structure is more and more paid attention to the research and development of the water reducer and the application field.

Due to the strong designability of the molecular structure of the polycarboxylate superplasticizer, the high performance of the polycarboxylate superplasticizer is realized by controlling the polymerization degree of a main chain, the length of a side chain and the types of functional groups through the optimized combination of different functional structural units, and the high-performance water reducer is prepared so as to solve the problem of field construction. The common polycarboxylate superplasticizer is a comb-shaped polymer consisting of a main chain of poly (methyl) acrylate with negative charges and polyethylene glycol side chains, wherein in cement paste, the main chain with negative charges can be adsorbed on the surface of cement hydration particles with positive charges, and the side chains are in a stretching state. The soil in the sand and stone material is mainly montmorillonite soil and kaolin, has higher specific surface area and a layered structure, and is preferential to cement to adsorb a water reducing agent and free water, so that the problems of large slump loss, poor rheological property, reduced durability and strength and the like of concrete are caused. The surface of the soil particles is negatively charged, so that the components containing cations are doped in the polycarboxylate superplasticizer, and the soil particles can be coated by electrostatic adsorption, so that a good anti-soil effect is achieved. Therefore, the amphoteric polycarboxylate superplasticizer containing anions and cations in molecules can simultaneously generate adsorption effect on cement hydrated particles and soil particles, and realize dual functions of water reduction and mud resistance.

The molecular configuration of the polycarboxylate superplasticizer itself is also receiving wide attention to the effect of the anti-mud effect. The molecules of the star polymer contain a large number of short branched chains, the winding among the molecules is less, the acting force among the molecules is small, and the intrinsic viscosity of the star polymer is far smaller than that of linear molecules; the star polymer has a three-dimensional spherical structure, and molecules are not intertwined, so that the space volume is larger than that of a linear polymer with the same molecular weight, and the steric hindrance effect is stronger, so that the polycarboxylic acid water reducing agent with the star structure has higher adaptability and a dispersing effect. On the other hand, molecules or groups with larger steric hindrance are introduced into the polycarboxylate superplasticizer, so that an effective 'blocking' effect can be generated between soil layers, and the quantity of the polycarboxylate superplasticizer entering the soil layers can be effectively reduced, so that the problem of adaptability of the polycarboxylate superplasticizer to soil is well solved. The beta-cyclodextrin (beta-CD) molecular structure is slightly conical, a large number of hydroxyl groups exist outside a conical cavity to show hydrophilicity, and the conical cavity is hydrophobic and has obvious steric hindrance effect. The cyclodextrin is used as a functional group to be introduced into the polycarboxylic acid water reducing agent to produce a good effect. However, the research finds that the polycarboxylate superplasticizers described in most of the prior patents achieve the anti-mud effect mainly by adjusting the content of the components per se or compounding the polycarboxylate superplasticizers with the anti-mud agent, and few polycarboxylic superplasticizers change the structure of a polymer through molecular structure design or adopt a new polymerization method to realize the excellent application performance.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a star-shaped amphoteric polycarboxylic acid water reducer with high-efficiency anti-mud effect and a preparation method thereof.

This patent star amphiprotic polycarboxylic acids water reducing agent with high-efficient anti mud effect, its characterized in that: the water reducing agent is a compound with a structural general formula shown in a formula (I):

wherein:

R₁，R₂or R₃H or CH₃；

m, n represent the degree of polymerization: m is 10-100, n is 9-65; x, y, z represent the mole percent of monomer: 15-40% of x, 50-75% of y and 1-10% of z.

The preparation method of the polycarboxylic acid water reducer with the high-efficiency anti-mud effect comprises the steps of carrying out esterification reaction on beta-cyclodextrin and a disulfide compound containing acyl halide groups to obtain a star-shaped reversible addition-fragmentation chain transfer agent (RAFT reagent); under the action of a chain transfer agent and an initiator, RAFT polymerization of polyethylene glycol (meth) acrylate, (meth) acrylic acid and (meth) acryloyloxyethyl trimethyl ammonium chloride is initiated to obtain a star amphoteric copolymer, and the star amphoteric polycarboxylate water reducer with the solid content of 20% is obtained after further treatment. The method comprises the following specific steps:

(1) preparation of star chain transfer agent: mixing and stirring O-ethyl potassium xanthate and halogenated acyl halide in an ice water bath for reaction for 60-120 min, and then stirring and reacting at room temperature for 12-24 h to obtain a disulfide compound containing acyl halide groups, wherein the molar ratio of the O-ethyl potassium xanthate to the halogenated acyl halide is 1 (1-1.5), and the halogenated acyl halide is 2-bromopropionyl bromide, 2-bromopropionyl chloride, 2-chloropropionyl bromide or 2-chloropropionyl chloride; mixing beta-cyclodextrin and a disulfide compound containing acyl halide groups in an ice water bath, stirring and reacting for 60-120 min, then stirring and reacting for 12-24 h at room temperature, and precipitating reaction liquid in petroleum ether after the reaction is finished to obtain a star-shaped chain transfer agent, wherein the molar ratio of the beta-cyclodextrin to the disulfide compound containing acyl halide groups is 1 (7-15);

(2) the preparation of the star-shaped amphoteric polycarboxylate superplasticizer with the high-efficiency anti-mud effect comprises the following steps: mixing the star-shaped chain transfer agent obtained in the step (1), an initiator, polyethylene glycol (meth) acrylate, (meth) acrylic acid and (meth) acryloyloxyethyl trimethyl ammonium chloride, dissolving the mixture in N, N-Dimethylformamide (DMF), reacting for 5-10 h at 60-90 ℃ in a nitrogen atmosphere after deoxygenation, dialyzing to remove residual monomers and other impurities to obtain a star-shaped amphoteric copolymer, and adding 20% sodium hydroxide solution to adjust to obtain a star-shaped amphoteric polycarboxylic acid water reducing agent with a high-efficiency anti-mud effect and a solid content of 20%;

wherein; the molar ratio of the star chain transfer agent to the initiator to the polyethylene glycol (meth) acrylate to the (meth) acrylic acid to the (meth) acryloyloxyethyltrimethyl ammonium chloride is (1-1.5) to (1-7) to (7-150) to (21-300) to (1-40); the initiator is Azobisisobutyronitrile (AIBN), dibenzoyl peroxide (BPO) or potassium persulfate.

The preparation method of the polycarboxylic acid water reducer with the efficient mud resistance function comprises the following steps: the preferred molar ratio of the star chain transfer agent, the initiator, the polyethylene glycol (meth) acrylate, the (meth) acrylic acid and the (meth) acryloyloxyethyl trimethyl ammonium chloride in the step (2) is 1:7:35 (105-125): 10-20).

The preparation method of the polycarboxylic acid water reducer with the efficient mud resistance function comprises the following steps: the initiator in the step (2) is preferably Azobisisobutyronitrile (AIBN) or Benzoyl Peroxide (BPO).

The preparation method of the polycarboxylic acid water reducer with the efficient mud resistance function comprises the following steps: the molecular weight of the (methyl) acrylic acid polyethylene glycol ester is 500-3000 g/mol.

The invention takes a cyclodextrin esterification product as an initiator, utilizes an active polymerization technology to prepare a star-shaped amphoteric polycarboxylate superplasticizer with high-efficiency mud-resistant function, provides a new method for preparing the polycarboxylate superplasticizer, and endows the polycarboxylate superplasticizer with new functions.

The invention has the beneficial effects that:

1. the obtained star amphoteric polycarboxylate superplasticizer is regular in structure, controllable in molecular weight and narrow in molecular weight distribution by adopting the RAFT polymerization technology;

2. the star-shaped amphoteric polycarboxylate superplasticizer can effectively increase the adsorption capacity of water reducer molecules on cement hydrated particles, has strong affinity and dispersing capacity, and improves the fluidity of concrete;

3. the star-shaped amphoteric water reducing agent takes beta-cyclodextrin as a core and polycarboxylic acid linear molecules as arms, the viscosity of the star-shaped amphoteric water reducing agent is far lower than that of linear molecules with the same molecular weight, the intermolecular force is small, and the star-shaped amphoteric water reducing agent has higher adaptability and dispersibility;

4. cations in the star-shaped amphoteric polycarboxylic acid water reducing agent can form a coating effect on soil particles through electrostatic adsorption, and a good anti-soil effect is achieved;

5. the amphoteric polycarboxylate superplasticizer containing anions and cations in molecules can simultaneously generate adsorption effect on cement hydrated particles and soil particles, thereby realizing the dual functions of water reduction and mud resistance;

6. compared with the polyol micromolecules, the beta-cyclodextrin has larger steric hindrance, so that the water reducer molecules taking the beta-cyclodextrin as the core are difficult to enter the interlayer of soil, the adsorption effect of the soil on the polycarboxylic acid water reducer is effectively inhibited, and the adaptability of the water reducer to the soil is further improved.

The star-shaped amphoteric polycarboxylate superplasticizer provided by the invention has the advantages of controllable molecular structure, high water reducing rate, good fluidity and dispersibility, strong adaptability to soil and the like, can meet higher construction requirements, and has good application prospects.

Detailed Description

The present invention will be further understood from the following specific examples, which should not be construed as limiting the scope of the invention.

Example 1:

(1) preparation of star chain transfer agent

Potassium O-ethylxanthate (16.03g, 0.1mol) was dissolved in 80mL of anhydrous Tetrahydrofuran (THF), added to a 150mL three-necked flask, and triethylamine (10.1, 0.1mol) was added as a proton absorbent. Stirred in an ice-water bath for 0.5h under nitrogen atmosphere. 2-Bromopropionyl bromide (26.1g, 0.1mol) was dissolved in 20mL of anhydrous THF, and added dropwise into a three-necked flask from a constant pressure dropping funnel. After the addition, the reaction was carried out at room temperature for 24 hours under a nitrogen atmosphere. And (3) filtering the reaction solution after the reaction is finished, and removing the solvent from the filtrate by rotary evaporation to obtain the dithioester compound containing the acyl bromide groups.

Beta-cyclodextrin (11.35g, 0.01mo) was dissolved in 60mL dry N, N-Dimethylformamide (DMF) and added to a 100mL three-necked flask, followed by triethylamine (7.07g, 0.07mol) as a proton absorber. Stirred in an ice-water bath for 0.5h under nitrogen atmosphere. The dithioester compound containing an acyl bromide group (17.9g, 0.07mol) was dissolved in 10mL of anhydrous DMF, and then added to a constant pressure dropping funnel and dropped dropwise into a three-necked flask. After the addition, the reaction was carried out at room temperature for 24 hours under a nitrogen atmosphere. And (3) filtering the reaction solution after the reaction is finished, placing the filtrate in a separating funnel, washing by using a saturated sodium bicarbonate solution to remove residual triethylamine salt, washing by using deionized water to be neutral, drying, performing rotary evaporation to remove most of the solvent, then dropwise adding into cold ether for precipitation, filtering, washing, dissolving, re-precipitating, filtering, washing again, repeating for three times, and performing vacuum drying at 50 ℃ for overnight to obtain the star chain transfer agent containing the terminal bromine (marked as ST 1).

(2) Preparation of star-shaped amphoteric polycarboxylic acid water reducing agent

Dissolving the star chain transfer agent (2.56g, 0.01mol) obtained in the step (1), an initiator AIBN (11.5g, 0.07mol), polyethylene glycol methacrylate (molecular weight is 1500g/mol, 525g, 0.35mol), methacrylic acid (1.05mol) and methacryloyloxyethyl trimethyl ammonium chloride (0.2mol) in dimethyl sulfoxide (DMSO) so that the molar ratio of the chain transfer agent, the initiator, the polyethylene glycol methacrylate, the methacrylic acid and the methacryloyloxyethyl trimethyl ammonium chloride is 1:7:35: 105: 20. after deoxygenation, the reaction was carried out at 70 ℃ for 10h under a nitrogen atmosphere. Dialyzing to remove residual monomers and other impurities to obtain a star-shaped amphoteric copolymer, and adding 20% sodium hydroxide solution to adjust to obtain a star-shaped amphoteric polycarboxylate superplasticizer (marked as SZP1) with the solid content of 20%, namely the polycarboxylate superplasticizer with the high-efficiency anti-mud effect.

(3) Neat paste fluidity test

Referring to GB8077-2000 'test method for homogeneity of concrete admixture', when the solid content of the water reducing agent is 0.2% of the mass of cement and the water-cement ratio is 0.29, the net slurry fluidity is 302mm (see Table 1).

(4) Test for anti-clay Properties

The water-cement ratio is fixed to be 0.5, and the fluidity of the obtained neat paste is 182mm when the water reducing agent and the clay are not mixed; the water cement ratio is 0.5, the solid content of the water reducing agent is 0.2 percent of the mass of the cement, and the measured neat paste fluidity is 303 mm; when the water-cement ratio is 0.5, the solid content of the water reducing agent is 0.2 percent of the mass of the cement, and the solid content of the clay is 1 percent of the mass of the cement, the measured net slurry fluidity is 275mm, and the net slurry loss rate is (303-processed sand 275)/(302-processed sand 182) is 23.3 percent (see table 1).

Example 2:

this example prepares a star ampholytic polycarboxylate water reducer (labeled SZP2) in the same manner as in example 1, except that the amount of methacryloyloxyethyl trimethyl ammonium chloride is 0.1mol, and the molar ratio of chain transfer agent, initiator, polyethylene glycol methacrylate, methacrylic acid and methacryloyloxyethyl trimethyl ammonium chloride is 1:7:35: 105: 10.

this example was tested for neat paste fluidity and soil resistance in the same manner as in example 1, and the test results are shown in Table 1.

Example 3

This example prepares a star amphoteric polycarboxylate superplasticizer (labeled SZP3) in the same manner as in example 1, except that the polyethylene glycol methacrylate has a molecular weight of 1000g/mol in step (2).

Example 4:

this example prepares a star amphoteric polycarboxylate superplasticizer (labeled SZP4) in the same manner as in example 1, except that the polyethylene glycol methacrylate has a molecular weight of 500g/mol in step (2).

Example 5:

this example prepares a star-shaped amphoteric polycarboxylic acid water reducing agent (designated as SZP5) in the same manner as in example 1 except that the amount of the acid bromide group-containing disulfide compound in step (1) is 25.6g (0.10mol), and the star-shaped chain transfer agent thus obtained is designated as ST 2.

Example 6:

this example prepares a star amphoteric polycarboxylate superplasticizer (labeled SZP6) in the same manner as in example 5, except that the polyethylene glycol methacrylate has a molecular weight of 1000g/mol in step (2).

Example 7:

this example prepares a star amphoteric polycarboxylate superplasticizer (labeled SZP7) in the same manner as in example 5, except that the polyethylene glycol methacrylate has a molecular weight of 500g/mol in step (2).

Example 8:

this example prepares a star ampholytic polycarboxylate superplasticizer (labeled SZP8) in the same manner as in example 5 except that in step (2) the amount of polyethylene glycol methacrylate is 0.35mol, the amount of methacrylic acid is 1.225mol, and the molar ratio of chain transfer agent, initiator, polyethylene glycol methacrylate, methacrylic acid and methacryloyloxyethyl trimethyl ammonium chloride is 1:7:35: 122.5: 20.

Example 9:

this example prepares a star amphoteric polycarboxylate water reducing agent (labelled SZP9) in the same manner as in example 5 except that in step (2) it is reacted at 80 ℃ for 8 hours under a nitrogen atmosphere.

Example 10:

this example prepares a star polycarboxylic acid water reducing agent (designated as SZP10) in the same manner as in example 5 except that it is reacted at 90 ℃ for 5 hours under a nitrogen atmosphere in step (2).

TABLE 1 Net slurry fluidity and mud resistance test results for Star-shaped amphoteric polycarboxylate Water reducers

Claims

1. The star-shaped amphoteric polycarboxylate superplasticizer with the efficient mud-resisting effect is characterized in that: the water reducing agent is a compound with a structural general formula shown in a formula (I):

wherein:

R₁，R₂or R₃H or CH₃；

2. The preparation method of the star-shaped amphoteric polycarboxylic acid water reducer with high-efficiency anti-mud effect of claim 1 comprises the following steps:

wherein; the molar ratio of the star chain transfer agent to the initiator to the (methyl) acrylic acid polyethylene glycol ester to the (methyl) acrylic acid to the (methyl) acryloyloxyethyl trimethyl ammonium chloride is 1:7:35 (105-125) to (10-20); the initiator is Azobisisobutyronitrile (AIBN) or Benzoyl Peroxide (BPO).