Composite latex for cement-based material modification and preparation method thereof

Abstract

The invention relates to the field of polymer modified cement-based materials, in particular to composite latex for modifying a cement-based material and a preparation method of the composite latex. Starting from the composition structure design of the composite latex, the energy dissipation capacity is improved by introducing the inorganic nanoparticles into the polymer microspheres, the damping performance after film forming is better, the damping temperature range is wider, and the toughening and impact-resistant modification effects on a cement-based material are better. Wherein the inner layer is mainly composed of soft monomers, vibration energy dissipation of inorganic nanoparticles is facilitated, meanwhile, a large number of branched chain structures are introduced into an inner layer polymer, intermolecular slippage can be increased, the latex film loss factor can be increased, and the toughening modification effect on the cement-based material is further improved; the middle layer is mainly composed of hard monomers, certain strength is kept, and a space is provided for vibration energy dissipation of internal particles; the outer layer is mainly composed of soft units, so that the composite latex has a good film forming effect and a good bonding effect in a cement-based material. The composite latex prepared by the invention is simple in preparation process, has small influence on the working performance of a cement-based material mixture, and can obviously improve the fracture energy of a cement-based material hardened body under the condition of low mixing amount.

Description

Technical Field

[0001] The present invention relates to the field of polymer-modified cement-based materials, and in particular to a composite latex for modifying cement-based materials and a preparation method thereof. Background Art

[0002] Cement-based materials used in railway engineering are subjected to the coupling effects of complex factors such as impact loads, temperature fatigue loads, and erosion by environmental media for a long time, and their durability faces severe tests. One of the important reasons is that the native micro-defects commonly found in cement-based materials are easily expanded to form macro-cracks under the action of periodic impact loads, providing a fast channel for corrosive media to enter the interior of the concrete structure, ultimately damaging the durability of the concrete structure. Therefore, it is particularly important to toughen and modify cement-based materials, improve their impact resistance, and reduce the initiation and expansion of micro-cracks. Adding polymer emulsions is one of the most common ways to modify cement-based materials. Invention patent application CN106145817A proposes a modified epoxy emulsion mortar specially designed for ultra-high-strength waterproof reinforcement on the back water surface. It has good workability and is easy to operate. It adheres tightly to materials such as concrete, cement mortar, stone and ceramic tiles, metal, and wood, and has the advantages of high mechanical strength, water resistance, acid and alkali resistance, corrosion resistance, and strong durability. Invention patent application CN108753159A discloses an organosilicon emulsion concrete waterproofing agent and its preparation method. The product is prepared from silane oligomers, emulsifiers, amino silicone oil, polyethylene glycol, glacial acetic acid, a fungicide, and deionized water. The resulting organosilicon emulsion has a high content of active ingredients, low VOC emissions, and low cost. Invention patent application CN107473645 B discloses a high-damping concrete based on internal structural design and its preparation method. The concrete is modified with a polymer emulsion. The resulting high-damping concrete has good energy absorption and dissipation properties, and mechanical properties such as flexural and compressive strength can be controlled within reasonable ranges. The use of pure polymer emulsions to modify cement-based materials still has some problems. The main drawback is that the toughening and impact resistance are not significantly improved when added in small amounts, and the strength of the cement-based material decreases significantly when added in large amounts. If a new latex can be developed that can achieve effective concrete toughening effects at lower dosages, it will have great practical application value. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems and provide a composite latex for modifying cement-based materials and a method for preparing the material.

[0004] A composite latex for modifying cement-based materials and a preparation method thereof, wherein the composite latex has a multilayer structure in which inorganic nanoparticles are coated with copolymer layers, wherein the copolymer molecules are copolymerized from three types of monomers: hard monomers, soft monomers, and functional monomers, wherein the functional monomers are unsaturated acid ester compounds, and wherein the chemical formula thereof is CH2=CR1-COO-CH(-CX H 2X+1 )-(OCH2CH2) Y -A, In the formula, R1 is any one of hydrogen and methyl; 2≤X≤5, 2≤Y≤4, X and Y are positive integers; A is any one of an epoxy group, a carboxyl group, a hydroxyl group, a vinyl group or a phosphate group.

[0005] The nanoparticles are composed of one or more of SiO2, Al2O3, CeO2, Fe3O4, and TiO2 nanoparticles, and the particle size of the nanoparticles is 10-50 nm.

[0006] The multilayer structure is a multilayer structure in which a copolymer layer in a single latex particle covers an average of 5 to 50 nanoparticles.

[0007] The copolymer layer comprises, by weight, 5 to 20 parts of a hard monomer, 15 to 25 parts of a soft monomer, 2 to 10 parts of a functional monomer, 1 to 5 parts of an emulsifier, and 0.1 to 0.5 parts of an initiator. The hard monomer is an aromatic vinyl compound, the soft monomer is one or more of butyl acrylate, pentyl acrylate, hexyl acrylate, lauryl acrylate, butyl methacrylate, pentyl methacrylate, and hexyl methacrylate, and the hard monomer is one or more of styrene, allylbenzene, methyl acrylate, acrylonitrile, methyl methacrylate, acrylamide, and p-vinylbenzene.

[0008] The copolymer layer has a multilayer structure of an inner layer, an outer layer and a middle layer, wherein the mass fraction of the soft monomer in the inner layer is 50% to 70%, the mass fraction of the functional monomer is 10% to 20%, the soft monomer content in the outer layer is 50% to 70%, and the mass fraction of the hard monomer in the middle layer is 60% to 75%.

[0009] The composite latex has a positive tensile bonding strength greater than 2.0 MPa after forming a film on the concrete surface.

[0010] The loss factor of the latex film obtained from the composite latex at room temperature is greater than or equal to 2.

[0011] The preparation method of the composite latex comprises the following steps: (1) Deionized water and emulsifier are placed in a beaker, and then dispersed for 2 minutes using a high-speed disperser at a speed of 10,000 r / min. Then, the outer layer monomers mixed in a certain proportion are added and dispersed for another 10 minutes at a speed of 10,000 r / min to obtain a pre-emulsified dispersion A of the outer layer monomers. The intermediate layer monomers are treated according to the above steps to obtain a pre-emulsified dispersion B.

[0012] (2) Weigh a small amount of water and emulsifier into a three-necked flask, then add the inner layer polymerization monomer C and nanoparticles mixed in a certain proportion, stir with a stirring paddle at a speed of 350r / min, heat to 80℃, and then add the initiator solution.

[0013] (3) After the emulsion turns light blue and thickens, the pre-emulsified dispersions A and B are sequentially added to the three-necked flask using a peristaltic pump over a period of 2.5 to 3.5 hours. The initiator solution is added at the same time. After the addition is completed, the mixture is reacted for another hour, cooled, and filtered to obtain a styrene-acrylic latex.

[0014] The composite latex has a synthesis conversion rate higher than 96%, a PDI lower than 0.1, and a zeta potential absolute value greater than 30 mV.

[0015] The positive effects of the composite latex for modifying cement-based materials and the preparation method thereof of the present invention are: Starting from the design of the composite latex composition structure, the energy dissipation capacity is increased by introducing inorganic nanoparticles into the polymer microspheres, the damping performance after film formation is better, the damping temperature range is wider, and the toughening and impact resistance modification effect on cement-based materials is better. Among them, the inner layer is mainly composed of soft monomers, which is convenient for the vibration energy consumption of inorganic nanoparticles. At the same time, a large number of branched structures are introduced into the inner polymer layer, which can increase the intermolecular slip, improve the latex film loss factor, and further enhance the toughening and modification effect on cement-based materials; the middle layer is mainly composed of hard monomers, which maintains a certain strength and provides space for the internal particles to consume energy by vibration; the outer layer is mainly composed of soft units, so that the composite latex has good film-forming and bonding effects in cement-based materials. The composite latex prepared by the present invention has a simple preparation process, little effect on the working performance of cement-based material mixtures, and can significantly improve the fracture energy of the hardened body of cement-based materials at a low dosage. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to the embodiments. Example 1

[0017] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 5 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 10%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 2

[0018] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 10%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 3

[0019] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 5 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 4

[0020] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 5

[0021] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 40%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 6

[0022] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 65%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 7

[0023] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 20%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 8

[0024] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer soft monomer: hexyl acrylate, mass fraction 25%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts. Example 9

[0025] The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 45%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0026] Example 10: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 60%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0027] Example 11: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 75%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0028] Comparative Example 1: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; There are no nanoparticles encapsulated in the copolymer layer in a single latex particle; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0029] Comparative Example 2: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated one nanoparticle on average; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0030] Comparative Example 3: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 30%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0031] Comparative Example 4: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 80%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0032] Comparative Example 5: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 0%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0033] Comparative Example 6: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer soft monomer: hexyl acrylate, mass fraction 10%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0034] Comparative Example 7: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer soft monomer: hexyl acrylate, mass fraction 50%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0035] Comparative Example 8: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 60%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0036] Comparative Example 9: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 30%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0037] Comparative Example 10: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 90%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0038] Comparative Example 11: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=0, Y=3; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0039] Comparative Example 12: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=0; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0040] Comparative Example 13: The relevant preparation parameters of the composite latex are: In the general formula of functional monomer, X=3, Y=7; The nanoparticles are TiO2 with an average particle size of 15nm; The copolymer layer in a single latex particle coated an average of 20 nanoparticles; Inner layer soft monomer: butyl acrylate, mass fraction 50%; Inner layer functional monomer: mass fraction 15%; Outer layer soft monomer: hexyl acrylate, mass fraction 35%; Middle layer hard monomer: styrene, mass fraction 70%; The remaining mass fraction not specified in the specific monomer composition of each layer is composed of the relevant mixed monomers; Emulsifier: sodium lauryl sulfate, 1.5 parts; Initiator: ammonium persulfate, 0.3 parts.

[0041] Effect description: project Film-forming properties Bond strength (MPa) Loss factor (normal temperature) Fracture energy (N / m) Example 1 good 1.8 2.1 201 Example 2 good 1.8 2.2 205 Example 3 good 1.8 2.3 210 Example 4 good 1.7 2.6 246 Example 5 good 1.9 2.1 198 Example 6 good 2.1 2.2 220 Example 7 good 1.8 2.3 206 Example 8 good 1.5 2.1 191 Example 9 good 1.6 2.2 197 Example 10 good 1.8 2.1 208 Example 11 good 1.7 2.1 220 Comparative Example 1 good 1.8 1.7 156 Comparative Example 2 good 1.8 1.8 165 Comparative Example 3 good 1.9 1.6 173 Comparative Example 4 good 1.8 1.8 146 Comparative Example 5 good 1.9 1.5 141 Comparative Example 6 Poor 0.7 / 86 Comparative Example 7 Poor 0.8 / 105 Comparative Example 8 Poor 0.6 / 97 Comparative Example 9 good 1.7 1 99 Comparative Example 10 good 1.7 1.5 98 Comparative Example 11 good 1.7 1.5 147 Comparative Example 12 good 1.7 1.5 145 Comparative Example 13 good 1.7 1.5 156 Specific characterization methods: (1) The PDI (polydispersity index) and Zeta potential of the latex were measured using the dynamic light scattering method, using the Zeta potential and nano-laser particle size analyzer; (2) The tensile bonding strength between the latex membrane and the concrete interface is tested in accordance with the provisions of GB50728-2011 "Technical Specifications for Safety Assessment of Engineering Structure Reinforcement Materials"; (3) The loss factor of the latex film was tested using a DMA (dynamic mechanical analyzer). The specific method is as follows: the prepared latex film was tested using a dynamic mechanical analyzer in uniaxial tension mode at a test frequency of 1 Hz. During the test, the sample chamber was first cooled to -60°C, kept at this temperature for 3 minutes, and then heated to 60°C at a rate of 2°C / min. The data was processed to obtain the loss factor of the latex film in the range of -60 to 60°C.

[0042] (4) The fracture energy of the polymer latex-modified cementitious material was calculated based on the results of a three-point bending test. The cementitious material used was concrete with a mix ratio of ordinary Portland cement: composite latex: water: sand: crushed stone: water reducer: defoamer = 100:2.5:39:200:250:1:1. The concrete was formed in a mold measuring 400 mm × 100 mm × 100 mm and subjected to a three-point bending test after 28 days of natural curing.

[0043] It can be seen from the results of Example 1 and Example 2 that increasing the number of nanoparticles within a suitable range can increase the loss factor of the latex film and the fracture energy of the modified specimen. This is because the vibration friction energy dissipation effect between the nanoparticles is more significant.

[0044] It can be seen from the results of Examples 1 and 3 that increasing the mass fraction of the inner layer functional monomer within a suitable range can improve the loss factor of the latex film and the fracture energy of the modified specimen. This is because the appropriate increase in the amount of functional monomer improves the energy consumption efficiency of the nanoparticles during vibration.

[0045] It can be seen from the results of Examples 1 to 4 that compared with increasing the mass fraction of the inner layer functional monomer or the number of nanoparticles alone, increasing both the mass fraction of the inner layer functional monomer and the number of nanoparticles within a suitable range can more significantly improve the loss factor of the latex film and the fracture energy of the modified specimen, indicating that the two have a synergistic effect.

[0046] From the results of Example 4 and Comparative Example 1, it can be seen that there are no nanoparticles in Comparative Example 1, and there is no particle vibration energy consumption factor, so the loss factor of the latex film is also reduced.

[0047] From the results of Example 4 and Comparative Example 3, it can be seen that in Comparative Example 3, the content of the soft monomer in the inner layer is too low, the rigidity is too large, which is not conducive to energy dissipation and the loss factor is low.

[0048] From the results of Example 4 and Comparative Example 4, it can be seen that the content of the inner soft monomer in Comparative Example 4 is too high, which causes the damping temperature range of the latex film to move toward low temperature. At room temperature, its loss factor decreases and the damping performance is reduced.

[0049] From the results of Example 4 and Comparative Example 5, it can be seen that in Comparative Example 5, there is no functional monomer, the intramolecular slip of the latex film is reduced, the loss factor at room temperature is reduced, and the damping performance is reduced.

[0050] The results of Comparative Examples 6 to 8 show that when the content of the soft monomer in the outer layer is too high or too low, the film-forming property of the composite latex is poor and the bonding effect is poor.

[0051] The results of Comparative Examples 9 and 10 show that when the hard monomer content of the middle layer is too high or too low, the vibration space provided for the internal nanoparticles is easily compressed and deformed or the energy conduction efficiency is reduced, resulting in a decrease in the overall damping effect.

[0052] The results of Comparative Examples 11 to 13 show that when the molecular structure of the functional monomer is unreasonable, the energy dissipation capacity of the inter-segment slippage decreases, resulting in a decrease in the overall damping effect.

[0053] In summary, the composite latex for modifying cement-based materials described in the present invention can achieve a positive tensile bonding strength greater than 2 MPa on the concrete surface; the loss factor of the latex film obtained under normal temperature conditions is greater than or equal to 2; and at a low dosage, it can significantly improve the fracture energy of concrete, thereby improving its impact resistance and toughness.

Claims

1. A composite latex for modifying cement-based materials and a preparation method thereof, characterized in that The composite latex has a multilayer structure of a copolymer layer covering inorganic nanoparticles, wherein the copolymer is copolymerized by three types of polymerizable monomers: a hard monomer, a soft monomer and a functional monomer, wherein the functional monomer is an unsaturated acid ester compound, and its general chemical formula is CH2=CR1-COO-CH(-C X H 2X+1 )-(OCH2CH2) Y -A, In the formula, R1 is any one of hydrogen and methyl; 2≤X≤5, 2≤Y≤4, X and Y are positive integers; A is any one of an epoxy group, a carboxyl group, a hydroxyl group, a vinyl group or a phosphate group.

2. The composite latex for modifying cement-based materials and the preparation method thereof according to claim 1, characterized in that The inorganic nanoparticles are composed of one or more of SiO2, Al2O3, CeO2, Fe3O4, and TiO2 nanoparticles, and the particle size of the nanoparticles is 10-50nm.

3. The composite latex for modifying cement-based materials and the preparation method thereof according to claim 1, characterized in that The multilayer structure is a multilayer structure in which a copolymer layer in a single latex particle covers an average of 5 to 50 nanoparticles.

4. A composite latex for modifying cement-based materials and a preparation method thereof according to claim 1, characterized in that The copolymer layer comprises 5 to 20 parts of hard monomer, 15 to 25 parts of soft monomer, 2 to 10 parts of functional monomer, 1 to 5 parts of emulsifier, and 0.1 to 0.5 parts of initiator in the synthetic raw materials by mass. The hard monomer is an aromatic vinyl compound, the soft monomer is one or more of butyl acrylate, pentyl acrylate, hexyl acrylate, lauryl acrylate, butyl methacrylate, pentyl methacrylate, and hexyl methacrylate, and the hard monomer is one or more of styrene, allyl benzene, methyl acrylate, acrylonitrile, methyl methacrylate, acrylamide, and p-vinylbenzene.

5. A composite latex for modifying cement-based materials and a preparation method thereof according to claims 1 to 4, characterized in that The copolymer layer has a multilayer structure of an inner layer, an outer layer and a middle layer, wherein the mass fraction of the soft monomer in the inner layer is 40% to 65%, the mass fraction of the functional monomer is 10% to 20%, the content of the soft monomer in the outer layer is 25% to 45%, and the mass fraction of the hard monomer in the middle layer is 60% to 75%.

6. The composite latex for modifying cement-based materials and the preparation method thereof according to claim 1, characterized in that The composite latex has a positive tensile bonding strength greater than 2.0 MPa after forming a film on the concrete surface.

7. The composite latex for modifying cement-based materials and the preparation method thereof according to claim 1, characterized in that The loss factor of the latex film obtained from the composite latex at room temperature is greater than or equal to 2.

8. The composite latex for modifying cement-based materials and the preparation method thereof according to claim 1, characterized in that The following steps are involved: (1) Deionized water and emulsifier are placed in a beaker, and then dispersed for 2 minutes using a high-speed disperser at a speed of 10,000 r / min, and then the outer layer polymerization monomers mixed in a certain proportion are added, and the dispersion is continued for 10 minutes at a speed of 10,000 r / min to obtain a pre-emulsified dispersion liquid A of the outer layer polymerization monomers; the middle layer polymerization monomers are treated according to the above steps to obtain a pre-emulsified dispersion liquid B; (2) Weigh a small amount of water and emulsifier into a three-necked flask, then add the inner layer polymerization monomer C and nanoparticles mixed in a certain proportion, stir with a stirring paddle at a speed of 350 r / min, heat to 80°C, and then add the initiator solution; (3) After the latex turns light blue and thickens, the pre-emulsified dispersions A and B are sequentially added to the three-necked flask using a peristaltic pump over a period of 2.5 to 3.5 hours. The initiator solution is added at the same time. After the addition is completed, the mixture is reacted for another hour, cooled, and filtered to obtain a styrene-acrylic latex.

9. The composite latex for modifying cement-based materials and the preparation method thereof according to claim 1, characterized in that The composite latex has a synthesis conversion rate higher than 96%, a PDI lower than 0.1, and a zeta potential absolute value greater than 30 mV.

10. Use of the composite latex for modifying cement-based materials according to any one of claims 1 to 8 in cement-based materials.