WO2024164754A1 - Method for preparing nano-modified styrene-acrylic/siloxane graft copolymerized composite emulsion - Google Patents

Abstract

A method for preparing a nano-modified styrene-acrylic/siloxane graft copolymerized composite emulsion. The prepared composite emulsion has a styrene-acrylic molecule with a glass transition temperature that gradiently changes and a siloxane molecular chain, both of which are bonded together by means of a strong covalent bond, such that the cross-linking degree and compatibility of the styrene-acrylic component and the siloxane component can be effectively improved at a nanoscale level. The emulsion enables a treated cement-based material to simultaneously form a surface protective layer and an internal crystalline waterproof layer, such that the composite protective emulsion is endowed with good rheological properties, waterproof performance, ion permeation resistance, carbonization resistance, acid and alkali corrosion resistance, and aging resistance.

Description

A method for preparing nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion

This application claims the priority of the Chinese invention patent application filed with the State Intellectual Property Office of China on February 10, 2023, with application number 2023101087001 and application name “A method for preparing a nano-modified styrene-acrylic-silicone grafted copolymer composite emulsion”, the entire contents of which are incorporated by reference into this application.

Technical Field

The present application relates to the technical field of protective coatings, and in particular to a method for preparing a nano-modified styrene acrylic-siloxane graft copolymer composite emulsion.

Background Art

The mechanical properties and durability of cement-based cementitious materials in coastal environments determine the safety and long-term reliability of hydraulic concrete structures. Since the coastal environment is characterized by high erosion, multiple erosion factors, and high uncertainty in deterioration risks, it is extremely necessary to take necessary durability protection measures for concrete materials in coastal environments. Using multifunctional, fast-acting, and easy-to-apply polymer protective coatings to protect the surface of cement-based cementitious materials can significantly improve the durability of concrete structures. In recent years, it has been widely used in the durability protection of concrete materials in complex environments.

Styrene-acrylic (styrene-acrylate) coatings are a type of surface film-forming polymer coating prepared by addition polymerization of styrene and acrylate monomers. Siloxane coatings are a type of permeable crystalline protective coating with a spatial network molecular structure based on Si-O-Si bonds as the main chain. Both have been proven to effectively improve the resistance of cementitious materials and steel bars to external corrosive media. The advantages of styrene-acrylic coatings are good chemical corrosion resistance, low cost and high weather resistance, but their environmental stability, water resistance and unstable bonding with cementitious materials. Siloxane coatings have the advantages of high hydrophobicity, high leveling and high permeability, but their poor anti-corrosion performance makes them unable to adapt well to the durability protection requirements of concrete materials in harsh environments. Therefore, some scholars and engineering technicians have come up with the idea of using nanoscale intermolecular copolymerization to prepare styrene-acrylic-siloxane composite coatings, so as to achieve the complementary advantages of the two polymer coatings, and then achieve the dual protective effects of long-term stable surface isolation and internal crystalline hydrophobicity for cement-based materials. However, many technicians have also noticed the significant differences in molecular structure and synthesis methods between styrene acrylic components and siloxane components. Therefore, new molecular copolymerization pathways and chain segment regulation methods have been continuously proposed in recent years.

Styrene acrylic-siloxane composite coatings prepared in the prior art all use silane monomers or silane coupling agents containing unsaturated bonds, and are cross-linked composite polymers prepared based on seed emulsion polymerization and controlled free radical polymerization. The cross-linking effect between the styrene acrylic component and the siloxane component is poor, the physical and chemical stability is low, and the degree of phase separation is low during the film formation and curing process of the coating, which seriously reduces the synergistic protective effect of styrene acrylic and siloxane on the cement matrix.

Summary of the invention

In view of this, the purpose of the present application is to provide a method for preparing a nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion. The nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion obtained by the preparation method provided in the present application has a good protective effect.

In order to achieve the above application objectives, this application provides the following technical solutions:

The present application provides a method for preparing a nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion, comprising the following steps:

(1) mixing tetraethyl orthosilicate, water and anhydrous ethanol, and performing a hydrolysis reaction in an alkaline environment to obtain a _SiO2 sol;

(2) mixing the _SiO2 sol, the buffer and dopamine hydrochloride, and carrying out a hydroxylation polymerization reaction under alkaline conditions to obtain a hydroxylation polymerization reaction system;

(3) mixing the hydroxylation polymerization reaction system and the amide compound to carry out a hydroxylation grafting reaction to obtain modified _SiO2 particles;

(4) mixing styrene and acrylate monomers with the modified _SiO2 particles to obtain a styrene-acrylate monomer mixed solution I;

(5) mixing styrene and acrylate monomers with the modified _SiO2 particles to obtain a styrene-acrylate monomer mixed solution II;

(6) mixing the acrylate functional monomer and vinyl silane to obtain a composite crosslinking agent;

(7) mixing polydimethylsiloxane, vinyl silane monomer, hydrophilic chain extender and the modified _SiO2 particles to obtain a silane monomer mixed solution III;

(8) mixing the hydrophobic silane, the chain extender and the modified _SiO2 particles to obtain a silane monomer mixed solution IV;

(9) mixing the styrene-acrylic monomer mixed solution I, an emulsifier, an initiator and water to perform a first addition polymerization reaction to obtain a pre-emulsion;

(10) mixing the pre-emulsion, the styrene-acrylic monomer mixed solution II, an emulsifier, an initiator and water to carry out a second addition polymerization reaction to obtain a second addition polymerization reaction system;

(11) mixing the second addition polymerization reaction system and the composite cross-linking agent to perform a third addition polymerization reaction to obtain a third addition polymerization reaction system;

(12) mixing the third addition polymerization reaction system, the silane monomer mixed solution III, an emulsifier and water to carry out a first polycondensation reaction to obtain a first polycondensation reaction system;

(13) mixing the first polycondensation reaction system, the silane monomer mixed solution IV, an emulsifier and water to carry out a second polycondensation reaction to obtain the nano-modified styrene acrylic-siloxane graft copolymer composite emulsion;

There is no chronological order for (3), (4), (5), (6), (7) and (8);

In terms of glass transition temperature, the styrene-acrylic monomer mixed solution I> the styrene-acrylic monomer mixed solution II> the silane monomer mixed solution III> the silane monomer mixed solution IV.

Preferably, in steps (4) and (5):

The acrylate monomers independently include one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, acrylic acid and methacrylic acid;

The mass percentage of the styrene in the styrene-acrylic monomer mixed solution I and the styrene-acrylic monomer mixed solution II is independently 5% to 20%;

The mass percentage of the modified _SiO2 particles in the styrene-acrylic monomer mixed solution I and the styrene-acrylic monomer mixed solution II is independently 0.05% to 0.3%.

Preferably, in step (6):

The acrylate functional monomer includes hydroxyethyl acrylate and/or hydroxypropyl acrylate;

The vinyl silane includes vinyl triethoxysilane, dimethoxymethyl vinyl silane, One or more of vinyl triisopropoxy silane and methyl vinyl diethoxy silane;

The mass percentage of the acrylic acid ester functional monomer in the composite cross-linking agent is 30% to 80%.

Preferably, in step (7):

The type of the vinyl silane is consistent with the type of the vinyl silane described in step (6);

The hydrophilic chain extender includes one or more of dimethylol propionic acid, dimethylol butyric acid, polyethylene imine and diethyl toluene diamine;

The mass of the hydrophilic chain extender is 5% to 25% of the mass of the polydimethylsiloxane;

The mass of the vinyl silane is 10% to 30% of the mass of the polydimethylsiloxane;

The mass percentage of the modified _SiO2 particles in the silane monomer mixed solution III is 0.05% to 0.3%.

Preferably, in step (8):

The hydrophobic silane includes one or more of n-octyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane and hexadecyltrimethoxysilane;

The chain extender includes one or more of 1,4-butanediol, 1,6-hexanediol, glycerol, diethylene glycol, triethylene glycol, neopentyl glycol, trimethylolpropane and ethylenediamine;

The mass of the chain extender is 5% to 25% of the mass of the hydrophobic silane;

The mass percentage of the modified _SiO2 particles in the silane monomer mixed solution IV is 0.05% to 0.3%.

Preferably, in step (9):

The emulsifier includes one or more of OP-10, sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate;

The mass of the emulsifier is 2% to 10% of the mass of the styrene-acrylic monomer mixed solution I;

The mass of the water is 50% to 100% of the mass of the styrene-acrylic monomer mixed solution I;

The initiator includes one or more of sodium persulfate, ammonium persulfate, potassium persulfate, azobisisobutyronitrile and dimethyl azobisisobutyrate;

The mass of the initiator is 0.2% to 0.7% of the mass of the styrene-acrylic monomer mixed solution I;

The pH value of the first addition polymerization reaction is 7.5 to 8.3;

The temperature of the first addition polymerization reaction is 70-85°C and the time is 2h;

The first addition polymerization reaction is carried out under stirring conditions, and the stirring speed is 200-500 r/min.

Preferably, in step (10):

The emulsifier includes one or more of OP-10, sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate;

The mass of the emulsifier is 2% to 10% of the mass of the styrene-acrylic monomer mixed solution II;

The mass of the water is 50% to 100% of the mass of the styrene-acrylic monomer mixed solution II;

The type and amount of the initiator are consistent with the type and amount of the initiator described in step (9);

The pH value of the second addition polymerization reaction is 7.5 to 8.3;

The temperature of the second addition polymerization reaction is 75-85°C and the time is 1-2h;

The second addition polymerization reaction is carried out under stirring conditions, and the stirring speed is 200-500 r/min.

Preferably, in step (11):

The mass of the composite cross-linking agent is 5-20% of the mass of the styrene-acrylic monomer mixed solution II;

The temperature of the third addition polymerization reaction is 75-85°C and the time is 20-40 minutes;

The third polyaddition reaction is carried out under stirring conditions, and the stirring speed is 200-400 r/min.

Preferably, in step (12):

The emulsifier includes one or more of OP-10, Peregal, Span 60, Span 80, Tween 60 and Tween 80;

The mass of the emulsifier is 2% to 10% of the mass of the silane monomer mixed solution III;

The mass of the water is 50% to 100% of the mass of the silane monomer mixed solution III;

The temperature of the first polycondensation reaction is 40 to 60° C. and the time is 0.5 to 2 hours;

The first polycondensation reaction is carried out under stirring conditions, and the stirring speed is 800-1200 r/min.

Preferably, in step (13):

The emulsifier includes one or more of OP-10, Peregal, Span 60, Span 80, Tween 60 and Tween 80;

The mass of the emulsifier is 2% to 10% of the mass of the silane monomer mixed solution IV;

The mass of the water is 50% to 100% of the mass of the silane monomer mixed solution IV;

The temperature of the second polycondensation reaction is 30 to 50° C. and the time is 1 to 3 hours;

The second polycondensation reaction is carried out under stirring conditions, and the stirring speed is 800-1200 r/min.

The present application provides a method for preparing a nano-modified styrene acrylic-siloxane graft copolymer composite emulsion.

Compared with the prior art, the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion obtained by the preparation method provided in this application has the following excellent technical effects:

(1) The nano-modified styrene-acrylic-siloxane graft copolymer composite latex coating obtained by the preparation method provided in the present application has excellent hydrophobic and waterproof properties:

The styrene-acrylic molecules and siloxane molecular chains with glass transition temperature gradient in the composite emulsion prepared by the present application are combined with powerful covalent bonds, so that the water molecule isolation effect and hydrophobic effect of the coating formed by the composite emulsion can be fully exerted. Due to the presence of a certain degree of microphase separation trend between several components on the nanoscopic scale, the styrene-acrylic linear molecular network and the siloxane branched molecular chain can exist simultaneously on the surface of the cementitious material matrix and in the internal capillary pores. After solidification and film formation, the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion can not only form a relatively dense waterproof polymer coating on the cement-based material surface, but also form a stable new hydration product structure inside the cementitious material through penetration crystallization, thereby effectively suppressing the diffusion and transmission of water molecules in the external environment inside the matrix. In addition, the internal styrene-acrylic linear structure weakens the cohesive force and disordered entanglement between the siloxane molecules through the swelling promotion effect, so that the hydrophobic hydrocarbon long chain in the siloxane molecule can be orderly and fully stretched and freely moved in the latex particle hydration layer. Importantly, the outer branched siloxane molecules also Due to the effect of directional chain extension, it has a larger free volume and lower surface energy, which enables the hydrophobicity of the polymer system to be fully exerted.

(2) The nano-modified styrene-acrylic-siloxane graft copolymer composite latex coating obtained by the preparation method provided in the present application can form a stable and good bonding and adhesion performance with the surface of the cement substrate:

The linear styrene-acrylic molecular chain as the backbone structure in the nano-modified styrene-acrylic-siloxane graft copolymer composite latex can fully improve the configuration and spatial state of the outer siloxane branched molecules, promote the further hydrolysis of the shell siloxane molecules, increase the number of silanol groups in the composite latex particle structure and improve its reactivity. The free-floating silanol groups can undergo a more complete secondary hydration reaction with the silanol groups in the cement hydration product, thereby enhancing the bonding effect with the cement matrix. In addition, due to the strong adsorption and penetration ability of siloxane molecules, the evaporation of the peripheral free water during the film formation process and the migration of the small molecular weight styrene-acrylic components into the capillaries and gel channels are promoted, thereby inducing the styrene-acrylic polymer network to be more stably adsorbed on the surface of the cement matrix.

(3) The nano-modified styrene-acrylic-siloxane graft copolymer composite latex coating obtained by the preparation method provided in the present application has excellent resistance to chloride and sulfate corrosion:

After the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion forms a film on the surface of cement-based materials, it can not only form a relatively dense protective film to isolate corrosive ions on the surface of the cement matrix, but also penetrate into the gel pores of the cement-based materials to form a stable hydrophobic layer. The styrene-acrylic main chain improves the hydrophobicity and surface adhesion of the siloxane molecules, while the siloxane side chains enhance the cross-linking and cohesive force, weakening the diffusion and transmission of water molecules and corrosive ions such as chloride ions and sulfate ions on the surface of concrete and inside the capillary pores. The strong covalent bond between the styrene-acrylic component and the siloxane component enhances the bonding between the composite coating and the substrate, thereby inhibiting the adsorption and diffusion movement of corrosive ions along the interface.

(4) The nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion obtained by the preparation method provided in the present application has excellent resistance to steel bar corrosion:

The surface isolation film and internal hydrophobic permeation layer formed by the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion can inhibit the diffusion of water-soluble _CO2 in the concrete pores, maintain the alkaline environment inside the concrete, protect the passivation film on the surface of the steel bar, and effectively inhibit the diffusion and transmission of chloride ions and sulfate ions inside the concrete. At the same time, the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion coating has excellent electrochemical properties, and its high resistivity can effectively inhibit the diffusion and migration of corrosive ions. In addition, the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion can form a stable secondary hydration product crystal layer of a certain depth in the cementitious material matrix, fully protecting the internal steel bars from the intrusion of complex and harsh external environmental factors.

(5) The nano-modified styrene-acrylic-siloxane graft copolymer composite latex coating obtained by the preparation method provided in the present application has excellent acid and alkali corrosion resistance:

Nano-modified styrene acrylic-siloxane graft copolymer composite emulsion has excellent leveling and adhesion properties, can adapt to various complex rough interfaces and produce strong bonding properties, and can form a stable and long-lasting high-efficiency protective layer on the surface of various cement-based materials. There is a strong cross-linking and hydrophobic association between the styrene acrylic main chain and the siloxane side chain, which can effectively resist the continuous erosion and damage of H ⁺ and OH ^- to the cross-linking structure of the composite coating. Importantly, the nano-modified styrene acrylic-siloxane graft copolymer composite emulsion coating has relatively high non-polar characteristics and internal hydrogen bonding, and its high polymer crystallinity It can significantly resist the development of polar ionization.

(6) The nano-modified styrene-acrylic-siloxane graft copolymer composite latex coating obtained by the preparation method provided in the present application has excellent anti-aging properties;

The styrene-acrylic-siloxane graft copolymer structure in the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion not only ensures the good anti-aging performance of the gradient styrene-acrylic main chain, but also promotes the strong grafting, cross-linking and bonding between the styrene-acrylic molecules and the siloxane molecules, thereby improving the synergistic working performance and environmental adaptability of the two. At the same time, the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion coating has a high cross-linking density and crystallinity, which is conducive to the realization of the heat-resistant and radiation-resistant anti-aging performance of the composite coating. In addition, the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion coating has a gradient dendritic structure with dynamic and thermodynamic characteristics, which not only improves the bond energy of the main chemical bonds in the system, but also facilitates the recovery of the molecular network from the electronic excited state to the ground state under the action of ultraviolet radiation and thermal radiation, and reduces the destructive effect of free radicals on the polymer system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a photo of the surface morphology and optical microscope morphology of the composite emulsion obtained in each experimental group;

FIG2 is a transmission electron microscope scanning photo of the composite emulsion obtained in each experimental group;

FIG3 is a graph showing the water contact angle and self-cleaning performance of cement paste specimens of each experimental group;

FIG4 is a static capillary water absorption curve of concrete specimens of each experimental group;

FIG5 is a graph showing the carbonization depth of cement mortar specimens of each experimental group;

FIG6 is a morphological diagram of the composite coatings of each experimental group after UV aging and thermal aging;

FIG7 is an apparent morphology of the cracked mortar specimens after treatment in each experimental group;

FIG8 is a static water absorption test diagram of the cracked mortar specimens after treatment in each experimental group;

FIG9 is a scanning electron microscope photograph of the composite coating surface of each experimental group.

DETAILED DESCRIPTION

The present application provides a method for preparing a nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion, comprising the following steps:

(1) mixing tetraethyl orthosilicate, water and anhydrous ethanol, and performing a hydrolysis reaction in an alkaline environment to obtain a _SiO2 sol;

(2) mixing the _SiO2 sol, the buffer and dopamine hydrochloride, and performing a hydroxylation polymerization reaction under alkaline conditions to obtain a hydroxylation polymerization reaction system;

(3) mixing the hydroxylation polymerization reaction system and the amide compound to carry out a hydroxylation grafting reaction to obtain modified _SiO2 particles;

(4) mixing styrene and acrylate monomers with the modified _SiO2 particles to obtain a styrene-acrylate monomer mixed solution I;

(5) mixing styrene and acrylate monomers with the modified _SiO2 particles to obtain a styrene-acrylate monomer mixed solution II;

(6) mixing the acrylate functional monomer and vinyl silane to obtain a composite crosslinking agent;

(7) mixing polydimethylsiloxane, vinyl silane monomer, hydrophilic chain extender and the modified _SiO2 particles to obtain a silane monomer mixed solution III;

(8) mixing the hydrophobic silane, the chain extender and the modified _SiO2 particles to obtain a silane monomer mixed solution IV;

(9) mixing the styrene-acrylic monomer mixed solution I, an emulsifier, an initiator and water to perform a first addition polymerization reaction to obtain a pre-emulsion;

(10) mixing the pre-emulsion, the styrene-acrylic monomer mixed solution II, an emulsifier, an initiator and water to carry out a second addition polymerization reaction to obtain a second addition polymerization reaction system;

(11) mixing the second addition polymerization reaction system and the composite cross-linking agent to perform a third addition polymerization reaction to obtain a third addition polymerization reaction system;

(12) mixing the third addition polymerization reaction system, the silane monomer mixed solution III, an emulsifier and water to carry out a first polycondensation reaction to obtain a first polycondensation reaction system;

(13) mixing the first polycondensation reaction system, the silane monomer mixed solution IV, an emulsifier and water to carry out a second polycondensation reaction to obtain the nano-modified styrene acrylic-siloxane graft copolymer composite emulsion;

There is no chronological order for (3), (4), (5), (6), (7) and (8);

In terms of glass transition temperature, the styrene-acrylic monomer mixed solution I> the styrene-acrylic monomer mixed solution II> the silane monomer mixed solution III> the silane monomer mixed solution IV.

In this application, unless otherwise specified, the raw materials used in this application are preferably commercially available products.

In the present application, tetraethyl orthosilicate, water and anhydrous ethanol are mixed, and a hydrolysis reaction is carried out in an alkaline environment to obtain _SiO2 sol. In the present application, the water preferably includes deionized water. In the present application, the mass of the tetraethyl orthosilicate is preferably 1% to 6% of the mass of the anhydrous ethanol, more preferably 2% to 5%, and more preferably 3% to 4%. In the present application, the mass of the water is preferably 50% to 300% of the mass of the tetraethyl orthosilicate. In the present application, the pH value of the alkaline environment is preferably 7.5 to 8.5; the alkaline environment is preferably adjusted by an alkaline reagent; the alkaline reagent preferably includes one or more of ammonia water, sodium bicarbonate, sodium carbonate, sodium hydrogen phosphate, barbital buffer and acetate buffer. In the present application, the temperature of the hydrolysis reaction is preferably 20°C to 40°C, more preferably 30°C; the time is preferably 0.5 to 2h; the hydrolysis reaction is preferably carried out under stirring, and the stirring speed is preferably 100 to 300r/min.

After obtaining _SiO2 sol, the present application mixes the _SiO2 sol, a buffer and dopamine hydrochloride, and performs a hydroxylation polymerization reaction under alkaline conditions to obtain a hydroxylation polymerization reaction system. In the present application, the buffer preferably includes one or more of a barbiturate buffer, trishydroxymethylaminomethane and an acetate buffer. In the present application, the mass of the buffer is preferably 0.5% to 3% of the mass of the _SiO2 sol. In the present application, the mass of the dopamine hydrochloride is preferably 0.1% to 1% of the mass of the _SiO2 sol. In the present application, the alkaline pH value is preferably 7.5 to 8.3. In the present application, the mixing of the _SiO2 sol, a buffer and dopamine hydrochloride, and performing a hydroxylation polymerization reaction under alkaline conditions preferably includes: ultrasonically dispersing the _SiO2 sol, and then sequentially adding a buffer and dopamine hydrochloride to perform a hydroxylation polymerization reaction. In the present application, the ultrasonic dispersion time is preferably 20 to 60 minutes. In the present application, the temperature of the hydroxylation polymerization reaction is preferably room temperature, the time is preferably 0.5 to 2 hours, and the hydroxylation polymerization reaction is preferably carried out under ultrasonic conditions. After the hydroxylation polymerization reaction, the present application directly proceeds to the next step without any reaction.

After obtaining the hydroxylation polymerization reaction system, the present application mixes the hydroxylation polymerization reaction system with an amide compound to carry out a hydroxylation grafting reaction to obtain modified _SiO2 particles. In the present application, the amide compound preferably includes one or more of acetamide, acrylamide, crotonamide, N,N-dimethylformamide and N,N-dimethylacetamide. In the present application, the mass of the amide compound is The amount is preferably 1% to 10% of the mass of the tetraethyl orthosilicate. In the present application, the temperature of the hydroxylation grafting reaction is preferably room temperature, and the time is preferably 30min to 60min; the hydroxylation grafting reaction is preferably carried out under ultrasonic conditions. After the hydroxylation grafting reaction, the present application preferably also includes centrifugation, washing, drying and grinding in sequence. In the present application, the speed of the centrifugation is preferably 8000 to 20000r/min, and more preferably 10000r/min; the time is preferably 10 to 60min. In the present application, the washing reagent is preferably an ethanol aqueous solution; the mass concentration of the ethanol aqueous solution is preferably 60 to 100%; the number of washings is preferably 3 to 6 times. In the present application, the drying temperature is preferably 40 to 70°C, and more preferably 50 to 60°C; the time is preferably 6h. In the present application, the fineness of the modified _SiO2 particles obtained by grinding is preferably 200 to 800 meshes.

The modified _SiO2 particles prepared in this application have stronger surface activity and dispersibility.

In the present application, styrene and acrylate monomers are mixed with the modified _SiO2 particles to obtain a styrene-acrylic monomer mixed solution I. In the present application, the acrylate monomer preferably includes one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, acrylic acid and methacrylic acid. In the present application, the mass percentage of styrene in the styrene-acrylic monomer mixed solution I is preferably 5% to 20%. In the present application, the mass percentage of the modified _SiO2 particles in the styrene-acrylic monomer mixed solution I is preferably 0.05% to 0.3%, and more preferably 0.1 to 0.2%. In the present application, the mixing of styrene, acrylate monomers and the modified _SiO2 particles is preferably carried out under stirring. In the present application, the glass transition temperature of the styrene-acrylic monomer mixed solution I is preferably 270K to 300K.

In the present application, styrene and acrylate monomers are mixed with the modified _SiO2 particles to obtain a styrene-acrylic monomer mixed solution II. In the present application, the acrylate monomer preferably includes one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, acrylic acid and methacrylic acid. In the present application, the mass percentage of styrene in the styrene-acrylic monomer mixed solution II is preferably 5% to 20%. In the present application, the mass percentage of the modified _SiO2 particles in the styrene-acrylic monomer mixed solution II is preferably 0.05% to 0.3%, and more preferably 0.1 to 0.2%. In the present application, the mixing of styrene, acrylate monomers and the modified _SiO2 particles is preferably carried out under stirring. In the present application, the glass transition temperature of the styrene-acrylic monomer mixed solution II is preferably 250K to 270K.

In terms of glass transition temperature, the styrene-acrylic monomer mixed solution I> the styrene-acrylic monomer mixed solution II.

In the present application, acrylate functional monomers are mixed with vinyl silanes to obtain a composite crosslinking agent. In the present application, the acrylate functional monomers preferably include hydroxyethyl acrylate and/or hydroxypropyl acrylate. In the present application, the vinyl silane preferably includes one or more of vinyl triethoxysilane, dimethoxymethyl vinyl silane, vinyl triisopropoxy silane and methyl vinyl diethoxy silane. In the present application, the mass percentage of the acrylate functional monomer in the composite crosslinking agent is preferably 30% to 80%, more preferably 40% to 70%, and more preferably 50% to 60%. In the present application, the mixing of the acrylate functional monomers with the vinyl silane is preferably carried out under stirring.

In the present application, polydimethylsiloxane, vinyl silane monomer, hydrophilic chain extender and the modified _SiO2 particles are mixed to obtain a silane monomer mixed solution III. In the present application, the type of the vinyl silane is consistent with the type of the vinyl silane in the composite crosslinking agent. In the present application, the hydrophilic chain extender preferably includes dimethylol propionic acid, dimethylol butyric acid, polyethylene imine and diethyl toluene diamine. One or more of amines. In the present application, the mass of the hydrophilic chain extender is preferably 5% to 25% of the mass of the polydimethylsiloxane, and more preferably 10% to 20%. In the present application, the mass of the vinyl silane is preferably 10% to 30% of the mass of the polydimethylsiloxane, and more preferably 20%. In the present application, the mass percentage of the modified _SiO2 particles in the silane monomer mixed solution III is preferably 0.05% to 0.3%, and more preferably 0.1% to 0.2%. In the present application, the mixing of polydimethylsiloxane, vinyl silane monomer, hydrophilic chain extender and modified _SiO2 particles is preferably carried out under stirring. In the present application, the glass transition temperature of the silane monomer mixed solution III is preferably 200K to 250K.

In terms of glass transition temperature, the styrene acrylic monomer mixed solution II> the silane monomer mixed solution III.

The present application mixes hydrophobic silanes, chain extenders and the modified SiO ₂ particles to obtain a silane monomer mixture IV. In the present application, the hydrophobic silane preferably includes one or more of n-octyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane and hexadecyltrimethoxysilane. In the present application, the chain extender preferably includes one or more of 1,4-butanediol, 1,6-hexanediol, glycerol, diethylene glycol, triethylene glycol, neopentyl glycol, trimethylolpropane and ethylenediamine, and is further preferably 1,4-butanediol. In the present application, the mass of the chain extender is preferably 5% to 25% of the mass of the hydrophobic silane. In the present application, the mass percentage of the modified SiO ₂ particles in the silane monomer mixture IV is preferably 0.05% to 0.3%, and is further preferably 0.1% to 0.2%. In the present application, the mixing of the hydrophobic silane, the chain extender and the modified SiO ₂ particles is preferably carried out under stirring. In the present application, the glass transition temperature of the silane monomer mixture IV is preferably ≤200K.

In terms of glass transition temperature, the silane monomer mixed solution III is greater than the silane monomer mixed solution IV.

In the present application, the styrene-acrylic monomer mixture I, an emulsifier, an initiator and water are mixed to carry out a first polyaddition reaction to obtain a pre-emulsion. In the present application, the emulsifier preferably includes one or more of OP-10, sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate, and more preferably OP-10 and sodium dodecylbenzene sulfonate. In the present application, the mass of the emulsifier is preferably 2% to 10% of the mass of the styrene-acrylic monomer mixture I, and more preferably 4% to 8%, and more preferably 5% to 6%. In the present application, the initiator preferably includes one or more of sodium persulfate, ammonium persulfate, potassium persulfate, azobisisobutyronitrile and dimethyl azobisisobutyrate, and more preferably ammonium persulfate. In the present application, the mass of the initiator is preferably 0.2% to 0.7% of the mass of the styrene-acrylic monomer mixture I, and more preferably 0.4% to 0.6%. In the present application, the water preferably includes deionized water. In the present application, the mass of the water is preferably 50% to 100% of the mass of the styrene-acrylic monomer mixture I. In the present application, the pH value of the first addition polymerization reaction is preferably 7.5 to 8.3. In the present application, the temperature of the first addition polymerization reaction is preferably 70° C. to 85° C., and the time is preferably 2 hours. In the present application, the first addition polymerization reaction is preferably carried out under stirring, and the stirring speed is preferably 200 to 500 r/min, and more preferably 300 to 400 r/min.

In the present application, the step of mixing the styrene-acrylic monomer mixture I, an emulsifier, an initiator and water to conduct a first addition polymerization reaction preferably comprises: mixing the styrene-acrylic monomer mixture I and the emulsifier, adding the mixture dropwise to water, adjusting the pH value, adding the initiator under stirring, and conducting a first addition polymerization reaction. In the present application, the dropping speed of the mixture obtained by mixing the styrene-acrylic monomer mixture I and the emulsifier is not In the present application, the time of the first addition polymerization reaction is preferably counted from the time when the initiator is added.

After obtaining the pre-emulsion, the present application mixes the pre-emulsion, the styrene-acrylic monomer mixture II, the emulsifier, the initiator and water, and performs a second addition polymerization reaction to obtain a second addition polymerization reaction system. In the present application, the emulsifier preferably includes one or more of OP-10, sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate. In the present application, the mass of the emulsifier is preferably 2% to 10% of the mass of the styrene-acrylic monomer mixture II, more preferably 4% to 8%, and more preferably 5% to 6%. In the present application, the type and amount of the initiator are preferably consistent with the type and amount of the initiator described in the first addition polymerization reaction. In the present application, the water preferably includes deionized water. In the present application, the mass of the water is preferably 50% to 100% of the mass of the styrene-acrylic monomer mixture II. In the present application, the pH value of the second addition polymerization reaction is preferably 7.5 to 8.3, the temperature is preferably 75° C. to 85° C., and the time is preferably 1 to 2 hours. In the present application, the second addition polymerization reaction is preferably carried out under stirring, and the stirring speed is preferably 200-500r/min, and more preferably 300-400r/min. In the present application, the mixing of the pre-emulsion, the styrene-acrylic monomer mixture II, the emulsifier, the initiator and water to carry out the second addition polymerization reaction preferably includes: adding water, the styrene-acrylic monomer mixture II and the emulsifier to the pre-emulsion in sequence, adjusting the pH value, adding the initiator under stirring, and carrying out the second addition polymerization reaction. In the present application, the time of the second addition polymerization reaction is preferably counted from the time when the initiator is added.

After obtaining the second addition polymerization reaction system, the present application mixes the second addition polymerization reaction system and the composite cross-linking agent, performs a third addition polymerization reaction, and obtains a third addition polymerization reaction system. In the present application, the mass of the composite cross-linking agent is preferably 5% to 20% of the mass of the styrene-acrylic monomer mixed solution II, and more preferably 10% to 12%. In the present application, the temperature of the third addition polymerization reaction is preferably 75 to 85°C, and the time is preferably 20 to 40 minutes. In the present application, the third addition polymerization reaction is preferably carried out under stirring, and the stirring speed is preferably 200 to 400 r/min.

After obtaining the third polyaddition reaction system, the present application mixes the third polyaddition reaction system, the silane monomer mixture III, the emulsifier and water, and performs a first polycondensation reaction to obtain a first polycondensation reaction system. In the present application, the emulsifier preferably includes one or more of OP-10, peregrin, Span 60, Span 80, Tween 60 and Tween 80. In the present application, the mass of the emulsifier is preferably 2% to 10% of the mass of the silane monomer mixture III. In the present application, the water preferably includes deionized water. In the present application, the mass of the water is preferably 50% to 100% of the mass of the silane monomer mixture III. In the present application, the temperature of the first polycondensation reaction is preferably 40°C to 60°C, and the time is preferably 0.5 to 2h. In the present application, the first polycondensation reaction is preferably carried out under stirring, and the stirring speed is preferably 500 to 1200r/min.

After obtaining the first polycondensation reaction system, the present application mixes the first polycondensation reaction system, the silane monomer mixture IV, the emulsifier and water to carry out a second polycondensation reaction to obtain the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion. In the present application, the emulsifier preferably includes one or more of OP-10, Perpenta, Span 60, Span 80, Tween 60 and Tween 80. In the present application, the mass of the emulsifier is preferably 2% to 10% of the mass of the silane monomer mixture IV. In the present application, the water preferably includes deionized water. In the present application, the mass of the water is preferably 50% to 100% of the mass of the silane monomer mixture IV. In the present application, the temperature of the second polycondensation reaction is preferably 30°C to 50°C, and more preferably 40°C; the time is preferably 1 to 3h. In the present application, The second polycondensation reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 800 to 1200 r/min, and more preferably 1000 r/min.

The preparation method of the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion provided by the present application is described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

Example 1

(1) To a mixture of 3 g of ethyl orthosilicate, 3 g of deionized water and 50 g of anhydrous ethanol, 3 mL of aqueous ammonia was added dropwise to adjust the pH value to 7-8.5. The mixture was stirred at 300 r/min at 30°C for 30 min to obtain 55 g of SiO ₂ sol.

(2) 55 g of SiO ₂ sol was ultrasonically pre-dispersed for 1 hour, and 500 mg of tris(hydroxymethyl)aminomethane and 200 mg of dopamine hydrochloride were added in sequence, and ultrasonically dispersed for 2 hours at 30°C. Then 100 mg of acrylamide was added, and ultrasonically dispersed for 1 hour at 30°C. After that, the precipitate was separated and collected by centrifugation at a speed of 10,000 r/min for 60 minutes, and washed three times with 50% ethanol aqueous solution. It was dried at 50°C for 6 hours and ground to obtain modified SiO ₂ particles with a fineness of 200 to 800 mesh.

(3) 20 g of methyl methacrylate, 15 g of butyl acrylate, 5 g of acrylic acid, 10 g of styrene and ₂₅ mg of modified SiO2 particles were mixed together and stirred evenly to prepare a styrene-acrylic monomer mixed solution I, wherein the glass transition temperature was 290±2K.

(4) 10 g of methyl methacrylate, 25 g of butyl acrylate, 5 g of acrylic acid, 10 g of styrene and ₂₅ mg of modified SiO2 particles were mixed together and stirred evenly to prepare a styrene-acrylic monomer mixed solution II, wherein the glass transition temperature was 260±2K.

(5) 10 g of polydimethylsiloxane, 2 g of vinyltriethoxysilane, 2 g of dihydroxymethylbutyric acid and 10 mg of modified SiO2 _particles were mixed together and stirred evenly to prepare a silane monomer mixed solution III, wherein the glass transition temperature was 240±2K.

(6) 40 g of n-octyltriethoxysilane, 10 g of 1,4-butanediol and 25 mg _of modified SiO2 particles were mixed together and stirred evenly to prepare a silane monomer mixed solution IV, wherein the glass transition temperature was ≤200K.

(7) 3 g of hydroxyethyl acrylate and 3 g of vinyltriethoxysilane were mixed together and stirred evenly to obtain a composite crosslinking agent.

(8) 50 g of styrene acrylic monomer mixed solution I, 1.2 g OP-10 and 1.8 g sodium dodecyl sulfate were mixed and added dropwise to 50 g of deionized water. The pH value was adjusted to 7.5 with sodium bicarbonate. The mixture was stirred at 300 r/min at 78 °C and 200 mg of ammonium persulfate was slowly added. After the addition of ammonium persulfate, stirring was continued for 2 h to obtain a pre-emulsion.

(9) Slowly add 50 g of deionized water, 50 g of styrene acrylic monomer mixture II, 1.2 g of OP-10, and 1.8 g of sodium dodecyl sulfate to the pre-emulsion, adjust the pH value to 7-8.5, stir at 300 r/min at 83 °C, and add 200 mg of ammonium persulfate. After the addition of ammonium persulfate, continue stirring for 2 h.

(10) Slowly add 6 g of composite cross-linking agent and continue stirring at 300 r/min for 20 min.

(11) The temperature was lowered to 60°C, and the mixture was stirred at a speed of 500 r/min. 16 g of deionized water, 20 g of silane monomer mixture III, 300 mg of OP-10 emulsifier, and 300 mg of OP-25 were slowly added. After all the materials were added, stirring was continued for 1 h.

(12) The temperature was lowered to 40°C, stirred at 1000 r/min, and 40 g of deionized water was slowly added. water, 50g silane monomer mixed solution IV and 750mg Tween 80, 750mg Span 80. After the materials are added, continue stirring for 3h to obtain a nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion.

Example 2

(1) To a mixture of 3 g of ethyl orthosilicate, 3 g of deionized water and 50 g of anhydrous ethanol, 3 mL of aqueous ammonia was added dropwise to adjust the pH value to 7-8.5. The mixture was stirred at 300 r/min at 30°C for 30 min to obtain 55 g of SiO ₂ sol.

(2) 55 g of SiO ₂ sol was ultrasonically pre-dispersed for 1 hour, and 400 mg of barbiturate buffer and 200 mg of dopamine hydrochloride were added in sequence, and ultrasonically dispersed for 2 hours at 30°C. Then 120 mg of acrylamide was added, and ultrasonically dispersed for 1 hour at 30°C. After that, the precipitate was separated and collected at a speed of 10000 r/min for 60 minutes, and washed three times with 50% ethanol aqueous solution. It was dried at 50°C for 6 hours and ground to obtain modified SiO ₂ particles with a fineness of 200 to 800 mesh.

(3) 20 g of methyl acrylate, 15 g of butyl acrylate, 5 g of acrylic acid, 10 g of styrene and ₇₅ mg of modified SiO2 particles were mixed together and stirred evenly to prepare a styrene-acrylic monomer mixed solution I, wherein the glass transition temperature was 290±2K.

(4) 10 g of methyl acrylate, 25 g of butyl acrylate, 5 g of acrylic acid, 10 g of styrene and ₇₅ mg of modified SiO2 particles were mixed together and stirred evenly to prepare a styrene-acrylic monomer mixed solution II, wherein the glass transition temperature was 260±2K.

(5) 10 g of polydimethylsiloxane, 2 g of vinyltriethoxysilane, 2 g of dihydroxymethylbutyric acid and 30 mg of modified SiO2 _particles were mixed together and stirred evenly to prepare a silane monomer mixed solution III, wherein the glass transition temperature was 240±2K.

(6) 40 g of n-octyltriethoxysilane, 10 g of 1,4-butanediol and 75 mg of modified SiO ₂ particles were mixed together and stirred evenly to prepare a silane monomer mixed solution IV, wherein the glass transition temperature was ≤200K.

(7) 3 g of hydroxyethyl acrylate and 3 g of vinyltriethoxysilane were mixed together and stirred evenly to obtain a composite crosslinking agent.

(8) 50 g of styrene acrylic monomer mixed solution I, 1.2 g of OP-10 and 1.8 g of sodium dodecyl sulfate were mixed and added dropwise to 50 g of deionized water. The pH value was adjusted to 7.5 with sodium bicarbonate. The mixture was stirred at 300 r/min at 78 °C and 200 mg of ammonium persulfate was slowly added. After the addition of ammonium persulfate, stirring was continued for 2 h to obtain a pre-emulsion.

(9) Slowly add 50 g of deionized water, 50 g of styrene acrylic monomer mixture II, 1.2 g of OP-10, and 1.8 g of sodium dodecyl sulfate to the pre-emulsion, adjust the pH value to 7-8.5, stir at 300 r/min at 83 °C, and add 200 mg of ammonium persulfate. After the addition of ammonium persulfate, continue stirring for 2 h.

(10) Slowly add 6 g of composite cross-linking agent and continue stirring at 300 r/min for 20 min.

(11) The temperature was lowered to 60°C, and the mixture was stirred at a speed of 500 r/min. 16 g of deionized water, 20 g of silane monomer mixture III, 300 mg of OP-10 emulsifier, and 300 mg of OP-25 were slowly added. After all the materials were added, stirring was continued for 1 h.

(12) The temperature was lowered to 40°C, the mixture was stirred at a speed of 1000 r/min, and 40 g of deionized water, 50 g of silane monomer mixed solution IV, 750 mg of Tween 60, and 750 mg of Span 80 were slowly added. After the addition of the materials was completed, stirring was continued for 3 h to obtain a nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion.

Example 3

(1) To a mixture of 3 g of ethyl orthosilicate, 3 g of deionized water and 50 g of anhydrous ethanol, 3 mL of aqueous ammonia was added dropwise to adjust the pH value to 7-8.5. The mixture was stirred at 300 r/min at 30°C for 30 min to obtain 55 g of SiO ₂ sol.

(2) 55 g of SiO ₂ sol was ultrasonically pre-dispersed for 1 hour, and 500 mg of barbiturate buffer and 200 mg of dopamine hydrochloride were added in sequence, and ultrasonically dispersed for 2 hours at 30°C. Then 100 mg of acrylamide was added, and ultrasonically dispersed for 1 hour at 30°C. After that, the precipitate was separated and collected by centrifugation at a speed of 10000 r/min for 60 minutes, and washed three times with 50% ethanol aqueous solution. It was dried at 50°C for 6 hours and ground to obtain modified SiO ₂ particles with a fineness of 200 to 800 mesh.

(3) 20 g of methyl acrylate, 15 g of butyl acrylate, 5 g of acrylic acid, 10 g of styrene and ₅₀ mg of modified SiO2 particles were mixed together and stirred evenly to prepare a styrene-acrylic monomer mixed solution I, wherein the glass transition temperature was 290±2K.

(4) 10 g of methyl acrylate, 25 g of butyl acrylate, 5 g of acrylic acid, 10 g of styrene and ₅₀ mg of modified SiO2 particles were mixed together and stirred evenly to prepare a styrene-acrylic monomer mixed solution II, wherein the glass transition temperature was 260±2K.

(5) 10 g of polydimethylsiloxane, 2 g of vinyltriethoxysilane, 2 g of dihydroxymethylbutyric acid and 20 mg of modified SiO2 _particles were mixed together and stirred evenly to prepare a silane monomer mixed solution III, wherein the glass transition temperature was 240±2K.

(6) 40 g of n-octyltriethoxysilane, 10 g of 1,4-butanediol and 50 mg _of modified SiO2 particles were mixed together and stirred evenly to prepare a silane monomer mixed solution IV, wherein the glass transition temperature was ≤200K.

(7) 3 g of hydroxyethyl acrylate and 3 g of vinyltriethoxysilane were mixed together and stirred evenly to obtain a composite crosslinking agent.

(8) 50 g of styrene acrylic monomer mixed solution I, 1.2 g OP-10 and 1.8 g sodium dodecylbenzene sulfonate were mixed and added dropwise to 50 g of deionized water. The pH value was adjusted to 7.5 with sodium bicarbonate. The mixture was stirred at 300 r/min at 78 °C and 200 mg of ammonium persulfate was slowly added. After the addition of ammonium persulfate, stirring was continued for 2 h to obtain a pre-emulsion.

(9) Slowly add 50 g of deionized water, 50 g of styrene acrylic monomer mixture II, 1.2 g of OP-10, and 1.8 g of sodium dodecylbenzene sulfonate to the pre-emulsion, adjust the pH value to 7-8.5, stir at 300 r/min at 83 °C, and add 200 mg of ammonium persulfate. After the addition of ammonium persulfate, continue stirring for 2 h.

(10) Slowly add 6 g of composite cross-linking agent and continue stirring at a speed of 300 r/min for 20 min;

(11) The temperature was lowered to 60°C, and the mixture was stirred at a speed of 500 r/min. 16 g of deionized water, 20 g of silane monomer mixture III, 300 mg of OP-10 emulsifier, and 300 mg of OP-25 were slowly added. After all the materials were added, stirring was continued for 1 h.

(12) The temperature was lowered to 40°C, the mixture was stirred at a speed of 1000 r/min, and 40 g of deionized water, 50 g of silane monomer mixed solution IV, 750 mg of Tween 60, and 750 mg of Span 60 were slowly added. After the addition of the materials was completed, stirring was continued for 3 h to obtain a nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion.

Comparative Example 1

This comparative example adopts the same method as Example 1 to prepare pure styrene acrylic emulsion, omitting steps (1) to (2) on the preparation of modified _SiO2 , steps (5) to (7) on the preparation of silane monomer mixed solution and composite crosslinking agent, and steps (10) to (13) on the preparation of graft copolymer composite. Preparation of emulsion.

Comparative Example 2

This comparative example adopts a method similar to that of Example 1 to prepare a styrene-acrylic-siloxane random copolymer composite emulsion, except that: step (8) and step (13) are omitted, and the four monomer mixed solutions prepared in steps (3) to (6) and the emulsifiers and initiators related thereto in steps (7) to (10) are directly stirred at 70°C and a speed of 600 r/min for 5 hours, and then gradually cooled to 50°C.

Comparative Example 3

Steps (1) to (8) of this comparative example adopt the same preparation method as Example 3, except that steps (9) to (10) are changed to:

9) Add 50 g of deionized water, 50 g of mixed solution II, 1.2 g of OP-10, and 1.8 g of sodium dodecylbenzene sulfonate, adjust the pH value to 7.5 with sodium bicarbonate, and stir at 300 r/min for 2 h at 83°C to obtain pre-emulsion B.

10) Pre-emulsion B and the composite cross-linking agent were slowly added dropwise to the pre-emulsion, stirred at 83°C and 500 r/min for 2 h, and 400 mg of ammonium persulfate was added.

The subsequent steps are the same as steps (11) to (12) in Example 3, and finally a nano _-SiO2 styrene acrylic-siloxane block copolymer composite emulsion is obtained.

Performance Testing

The nano-modified styrene acrylic-siloxane graft copolymer composite emulsion prepared in the present application was coated on the surface of the cement-based material specimen twice at a dosage of 600 g/m ² , with an interval of 5 to 7 hours between the two times.

Figure 1 is a photo of the surface morphology and an optical microscope morphology of the composite emulsion obtained in each experimental group. As can be seen from Figure 1: the styrene-siloxane graft copolymer composite emulsion prepared in the present application has excellent homogeneity and stability, higher dispersion of emulsion particles, and more concentrated particle size distribution. The composite emulsion prepared in the example will not flocculate, stratify or segregate after being placed for a long time. Compared with Comparative Example 1 and Comparative Example 2, the structural integrity of the latex particles in the composite emulsion prepared in the example is higher, and the aggregation and demulsification of the latex particles are significantly alleviated.

FIG2 is a transmission electron microscope scanning photo of the composite emulsion obtained in each experimental group. As can be seen from FIG2, the latex particle size of the composite emulsion prepared in Examples 1 to 3 is more uniform, which is consistent with the results observed under an optical microscope. The dyeing characteristics inside the emulsion particles in the examples reflect that the nano-modified graft copolymerization synthesis method used in this application can make the styrene acrylic component and the siloxane component well cross-linked and form a stable microphase separation structure inside the micelle cluster.

1. Basic properties of emulsion

Table 1 Basic performance parameters of the composite emulsions obtained in each experimental group

As can be seen from Table 1, the solid content of the composite emulsions obtained in Examples 1 to 3 is higher than that in the comparative example. 1, and significantly higher than Comparative Example 2 and Comparative Example 3, all maintained above 46.5%. The gel fractions of the composite emulsions obtained in Examples 1 to 3 were all below 1.0, better than the gel fraction of 1.4% in Comparative Example 1, indicating that no flocculation or implosion occurred in the composite emulsion during the synthesis process. The monomer conversion rate and grafting rate of the composite emulsions obtained in Examples 1 to 3 were above 87.6% and 86.2%, respectively, indicating that the preparation method of the nano _-SiO2 modified styrene-acrylic-siloxane graft copolymer composite emulsion proposed in the present application not only promoted the free polymerization reaction of the styrene-acrylic component and the siloxane component, but also improved the cross-linking and synergistic effect of the two.

Table 2 Stability of the composite emulsions obtained in each experimental group

As can be seen from Table 2, the physical and chemical stability of the composite emulsions of Examples 1 to 3 are better than those of Comparative Examples 1 to 3, and they have dilution stability, Ca ²⁺ stability and high temperature stability, indicating that the components of the prepared composite emulsions have excellent synergistic performance. Although the centrifugal stability and low temperature stability of the composite emulsions obtained in Examples 1 to 3 are not very ideal, they are still significantly better than those of Comparative Examples 1 to 3.

The particle size characteristics of the composite emulsion obtained in each experimental group were tested using a nanoparticle size analyzer.

Table 3 Particle size and dispersibility of the composite emulsions obtained in each experimental group

It can be found from Table 3 that the average particle size of the composite emulsions obtained in Examples 1 to 3 is less than 110 nm, indicating that the synthesized composite emulsions meet the basic requirements of uniform surface film formation and capillary penetration. The PDI homogeneity index of the composite emulsions obtained in Examples 1 to 3 is less than 0.172, and Example 3 has the highest homogeneity of the emulsion micromorphology. The absolute value of the Zeta potential of the composite emulsions obtained in Examples 1 to 3 is significantly higher than that of Comparative Examples 1 to 3, reflecting the superior dispersibility and stability of the composite dendritic structure. When the content of modified _SiO2 particles is 0.2%, the dispersibility and stability of the composite emulsion are optimal.

2. Hydrophobic and waterproof properties of composite emulsion

The water contact angle of the cement paste surface treated with the composite emulsion obtained in each experimental group was measured using a static surface contact angle meter, and the self-cleaning property of the specimen surface was evaluated accordingly.

Figure 3 is a test diagram of the water contact angle and self-cleaning performance of the cement paste specimen surface of each experimental group.

Table 4 Static contact angle of cement specimen surface in each experimental group

As can be seen from Figure 3 and Table 4, compared with Comparative Examples 1 to 3, the static contact angle of the test piece surface in Examples 1 to 3 can be increased to more than 123°, showing excellent hydrophobic performance. In addition, the surface of the cement test piece treated with the composite emulsion in Examples 1 to 3 has excellent self-cleaning properties, allowing water droplets to slide freely from the inclined surface. This shows that the graft copolymer system with styrene-acrylic molecules as the main chain can fully improve the molecular configuration of siloxane, allowing the long alkyl branched chains in the outer layer to stretch freely, and giving full play to the hydrophobic properties of the composite polymer components.

Select a non-casting surface of the dry concrete specimen as the coating surface, and seal the four sides with epoxy resin. Place the specimen with the coating surface facing down in distilled water, with the bottom of the specimen about 5mm from the water surface, and measure the static capillary water absorption of the concrete specimen at different water absorption times.

Figure 4 is the static capillary water absorption curve of concrete specimens in each experimental group.

Table 5 Static capillary water absorption of concrete in each experimental group for 24 hours g/(m ² ·h ^0.5 )

As can be seen from Figure 4 and Table 5, compared with the styrene acrylic emulsion of Comparative Example 1 and the random copolymer emulsion of Comparative Example 2, the static capillary water absorption of the concrete specimens treated with the nano-modified copolymer composite emulsions in Comparative Example 3 and Examples 1 to 3 has been greatly reduced. In particular, the waterproof performance of the dendritic graft copolymer composite emulsion prepared by the step-by-step graft polymerization method is better than that of the block copolymer emulsion prepared by the step-by-step graft polymerization method in Comparative Example 3. Compared with the pure styrene acrylic emulsion, the static capillary water absorption of Examples 1, 2 and 3 is reduced by 26.6%, 32.8%, 37.1% and 40.2%, respectively, among which the static capillary water absorption of Example 3 is reduced to the greatest extent.

3. Concrete resistance to chloride and sulfate corrosion

Using a method similar to the static capillary water absorption test, the concrete specimens were immersed in 10% NaCl and Na ₂ SO ₄ solutions, respectively, and the penetration of chloride ions and sulfate ions inside the specimens was tested after 50 days.

Table 6 Concrete chloride ion and sulfate ion erosion g/m ² in each experimental group

Table 7 Corrosion potential of the composite coatings in each experimental group under chloride and sulfate corrosion /-V

As shown in Table 6, the chloride ion erosion and sulfate ion erosion of the concrete specimens treated with the nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion were significantly reduced. Compared with the concrete specimens treated with the ordinary styrene-acrylic emulsion, the chloride ion erosion of Example 1, Example 2 and Example 3 were reduced by 38.0%, 40.8% and 43.1%, respectively, while the sulfate ion erosion was reduced by The corrosion rates of the composite emulsions prepared in Example 3 were 26.6%, 31.0% and 34.9%, respectively. The chloride ion and sulfate ion corrosion rates of the composite emulsion obtained in Example 3 were the highest, showing the best anti-ion corrosion performance. In addition, Table 7 also shows that the corrosion potential of the graft copolymer coatings in Examples 1 to 3 under chloride and sulfate corrosion is also significantly higher than that of Comparative Examples 1 to 3. In particular, the absolute values of the corrosion potential of the composite coatings in Example 3 under chloride and sulfate attack all reached more than 0.4V. Compared with ordinary styrene-acrylic coatings, the absolute values of the corrosion potential of the composite coatings prepared in Example 3 under chloride and sulfate corrosion were increased by 0.14V and 0.12V, respectively. This shows that the styrene-acrylic-siloxane graft copolymer structure regulated by nanomaterials can effectively inhibit the diffusion and transmission of corrosive ions in the pores of concrete.

4. Acid and alkali corrosion resistance

The latex films prepared in each experimental group were placed in a dilute hydrochloric acid solution with a pH of 3 and a sodium hydroxide solution with a pH of 12, respectively, and immersed for 72 hours, and their mass loss rate and resistivity modulus were measured.

Table 8 Mass loss rate of latex film in each experimental group under acid and alkali corrosion

As can be seen from Table 8, the mass loss rate of the latex film of Examples 1 to 3 under acid and alkali corrosion is less than that of Comparative Examples 1 to 3, indicating that the nano-modified graft copolymer composite coating has a more superior acid and alkali corrosion resistance, and the alkali corrosion resistance of the composite coating prepared in this application is more prominent. Among them, Example 3 has the best acid and alkali corrosion resistance, and its mass loss rate can be controlled at 22% and 12%.

Table 9 Resistance modulus of latex films of each experimental group under acid and alkali corrosion/×10 ⁵ Ω/cm ²

It can be found from Table 9 that the nano-modified graft copolymer coatings prepared in Examples 1 to 3 have higher resistance modulus under acid and alkali corrosion than the styrene acrylic coatings, blended emulsion coatings and copolymer emulsion coatings in Comparative Examples 1, 2 and 3. Example 3 has the highest resistance modulus, which reaches 4.83×10 ⁵ Ω/cm ² and 7.21×10 ⁵ Ω.cm ² respectively under acid and alkali environments, which are 19.3% and 15.7% higher than the styrene acrylic coating respectively. Therefore, the composite emulsion prepared in the present application can have a stable protective effect on the cement matrix under acid and alkali environments.

5. Anti-carbonization performance

The composite emulsion prepared in each experimental group was coated on each surface of the cement mortar cube specimen, and then the mortar specimen was placed in a dedicated carbonation test box, and the carbon dioxide concentration in the box was set to (20±2)%. The carbonation depth of the mortar specimen was tested after 28 days of carbonization.

Figure 5 is a graph showing the carbonization depth of cement mortar specimens in each experimental group.

Table 10 Carbonation depth of mortar specimens in each experimental group at carbonization age of 28 days (mm)

Figure 5 and Table 10 show that the cement mortar specimens treated with the composite emulsions prepared in Examples 1 to 3 have smaller carbonization depths, which are only 2.7 mm, 2.4 mm, and 2.2 mm, respectively. This indicates that the nano-modified graft copolymer coating can effectively inhibit the diffusion and transmission of small molecules of _CO2 gas, thereby Maintain an alkaline environment inside the cement matrix.

6. Anti-aging properties

The latex films prepared in each experimental group were placed under artificial ultraviolet light with a radiation intensity of 50w/ ^m2 and a wavelength of 254nm for 72 hours, and the surface gloss loss rate, powdering degree and cracking degree were measured.

Table 11 Surface gloss loss rate of latex films in each experimental group/%

FIG6 is a morphological diagram of the composite coatings of each experimental group after UV aging and thermal aging.

Table 12 Powdering and cracking grades of latex films in each experimental group

It can be seen from Table 11 that the styrene acrylic emulsion coating in Comparative Example 1 has poor anti-ultraviolet aging performance, and its surface gloss loss rate is relatively high, while the gloss loss rate of the copolymer emulsion in Comparative Examples 2 and 3 is slightly reduced. The gloss loss rate of the nano-modified styrene acrylic-siloxane graft copolymer composite emulsion coating prepared in Examples 1 to 3 is significantly reduced, among which the surface gloss loss rate of Example 2 is the lowest, which is 54.3%. In addition, Table 12 also shows that compared with Comparative Examples 1 to 3, the nano-modified graft copolymer coating prepared in Examples 1 to 3 has a higher powdering grade and cracking grade. In particular, the powdering grade and cracking grade of Examples 2 and 3 both reached Grade I, showing extremely superior anti-aging performance.

7. Protective performance of cracked cement matrix

A crack of about 1mm was pre-set on a non-casting surface of the dry cement mortar specimen, which was used as the coating surface, and the four sides were sealed with epoxy resin. The specimen was placed in distilled water with the coating surface facing down, and the bottom of the specimen was about 5mm from the water surface. The static capillary water absorption of the concrete specimen was measured at 10h and 100h.

Figure 7 shows the apparent morphology of the cracked mortar specimens after treatment in each experimental group.

Figure 8 is a static water absorption test diagram of the cracked mortar specimens after treatment in each experimental group.

Figure 7 shows that compared with Comparative Examples 1 to 3, the nano-modified graft copolymer emulsion prepared in Examples 1 to 3 can better solidify into a film at the cracks of the cement matrix to achieve external repair. Figure 8 shows that the water absorption of the corresponding specimens in Examples 1 to 3 is significantly lower than that in Comparative Examples 1 to 3, indicating that the composite emulsion can effectively inhibit the capillary transmission of water molecules along the defects of the substrate. Among them, Example 3 has the best protective effect, and its water absorption at 10h and 100h is only 23.7% and 30.4% of that of ordinary styrene acrylic coating.

8. Composite coating surface micromorphology

The surface microscopic morphology of the composite emulsion coatings prepared in each experimental group was observed using a scanning electron microscope.

FIG9 is a scanning electron microscope photograph of the composite coating surface of each experimental group.

FIG9 shows that, compared with Comparative Examples 1 to 3, the surface of the graft copolymer composite emulsion coating prepared in Examples 1 to 3 is smoother, and the number and size of defects such as cracks and holes on the surface are also reduced accordingly, indicating that the composite coating prepared in the present application can better resist external erosion. Damage of the medium to the cement matrix.

The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims (13)

A method for preparing a nano-modified styrene-acrylic-siloxane graft copolymer composite emulsion, characterized in that it comprises the following steps: (1) mixing tetraethyl orthosilicate, water and anhydrous ethanol, and performing a hydrolysis reaction in an alkaline environment to obtain a _SiO2 sol; (2) mixing the _SiO2 sol, the buffer and dopamine hydrochloride, and carrying out a hydroxylation polymerization reaction under alkaline conditions to obtain a hydroxylation polymerization reaction system; (3) mixing the hydroxylation polymerization reaction system and the amide compound to carry out a hydroxylation grafting reaction to obtain modified _SiO2 particles; (4) mixing styrene and acrylate monomers with the modified _SiO2 particles to obtain a styrene-acrylate monomer mixed solution I; (5) mixing styrene and acrylate monomers with the modified _SiO2 particles to obtain a styrene-acrylate monomer mixed solution II; (6) mixing the acrylate functional monomer and vinyl silane to obtain a composite crosslinking agent; (7) mixing polydimethylsiloxane, vinyl silane monomer, hydrophilic chain extender and the modified _SiO2 particles to obtain a silane monomer mixed solution III; (8) mixing the hydrophobic silane, the chain extender and the modified _SiO2 particles to obtain a silane monomer mixed solution IV; (9) mixing the styrene-acrylic monomer mixed solution I, an emulsifier, an initiator and water to perform a first addition polymerization reaction to obtain a pre-emulsion; (10) mixing the pre-emulsion, the styrene-acrylic monomer mixed solution II, an emulsifier, an initiator and water to carry out a second addition polymerization reaction to obtain a second addition polymerization reaction system; (11) mixing the second addition polymerization reaction system and the composite cross-linking agent to perform a third addition polymerization reaction to obtain a third addition polymerization reaction system; (12) mixing the third addition polymerization reaction system, the silane monomer mixed solution III, an emulsifier and water to carry out a first polycondensation reaction to obtain a first polycondensation reaction system; (13) mixing the first polycondensation reaction system, the silane monomer mixed solution IV, an emulsifier and water to carry out a second polycondensation reaction to obtain the nano-modified styrene acrylic-siloxane graft copolymer composite emulsion; There is no chronological order for (3), (4), (5), (6), (7) and (8); In terms of glass transition temperature, the styrene-acrylic monomer mixed solution I> the styrene-acrylic monomer mixed solution II> the silane monomer mixed solution III> the silane monomer mixed solution IV. The preparation method according to claim 1 is characterized in that, in step (1), the mass of the tetraethyl orthosilicate is 1% to 6% of the mass of the anhydrous ethanol, the mass of the water is 50% to 300% of the mass of the tetraethyl orthosilicate, the pH value of the alkaline environment is 7.5 to 8.5, and the alkaline environment is adjusted by an alkaline reagent; the alkaline reagent includes one or more of ammonia water, sodium bicarbonate, sodium carbonate, sodium hydrogen phosphate, barbital buffer and acetate buffer, the temperature of the hydrolysis reaction is 20°C to 40°C, the time is 0.5 to 2h, and the hydrolysis reaction is carried out under stirring, and the stirring speed is 100 to 300r/min. The preparation method according to claim 1, characterized in that in step (2): the buffer comprises one or more of a barbiturate buffer, tris(hydroxymethyl)aminomethane and an acetate buffer, the mass of the buffer is 0.5% to 3% of the mass of the _SiO2 sol, and the dopamine hydrochloride The mass of is 0.1% to 1% of the mass of the _SiO2 sol, the pH value of the alkalinity is 7.5 to 8.3, the temperature of the hydroxylamine polymerization reaction is room temperature, and the time is 0.5 to 2 hours. The preparation method according to claim 1 is characterized in that in step (3): the amide compound includes one or more of acetamide, acrylamide, crotonamide, N,N-dimethylformamide and N,N-dimethylacetamide, the mass of the amide compound is 1% to 10% of the mass of the tetraethyl orthosilicate, the temperature of the hydroxylation grafting reaction is room temperature, and the time is 30 min to 60 min. The preparation method according to claim 1, characterized in that in steps (4) and (5): The acrylate monomers independently include one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, acrylic acid and methacrylic acid; The mass percentage of the styrene in the styrene-acrylic monomer mixed solution I and the styrene-acrylic monomer mixed solution II is independently 5% to 20%; The mass percentage of the modified _SiO2 particles in the styrene-acrylic monomer mixed solution I and the styrene-acrylic monomer mixed solution II is independently 0.05% to 0.3%. The preparation method according to claim 1, characterized in that in step (6): The acrylate functional monomer includes hydroxyethyl acrylate and/or hydroxypropyl acrylate; The vinyl silane includes one or more of vinyl triethoxysilane, dimethoxymethyl vinyl silane, vinyl triisopropoxy silane and methyl vinyl diethoxy silane; The mass percentage of the acrylic acid ester functional monomer in the composite cross-linking agent is 30% to 80%. The preparation method according to claim 1, characterized in that in step (7): The vinyl silane includes one or more of vinyl triethoxysilane, dimethoxymethyl vinyl silane, vinyl triisopropoxy silane and methyl vinyl diethoxy silane; The hydrophilic chain extender includes one or more of dimethylol propionic acid, dimethylol butyric acid, polyethylene imine and diethyl toluene diamine; The mass of the hydrophilic chain extender is 5% to 25% of the mass of the polydimethylsiloxane; The mass of the vinyl silane is 10% to 30% of the mass of the polydimethylsiloxane; The mass percentage of the modified _SiO2 particles in the silane monomer mixed solution III is 0.05% to 0.3%. The preparation method according to claim 1, characterized in that in step (8): The hydrophobic silane includes one or more of n-octyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane and hexadecyltrimethoxysilane; The chain extender includes one or more of 1,4-butanediol, 1,6-hexanediol, glycerol, diethylene glycol, triethylene glycol, neopentyl glycol, trimethylolpropane and ethylenediamine; The mass of the chain extender is 5% to 25% of the mass of the hydrophobic silane; The mass percentage of the modified _SiO2 particles in the silane monomer mixed solution IV is 0.05% to 0.3%. The preparation method according to claim 1, characterized in that in step (9): The emulsifier includes one or more of OP-10, sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate; The mass of the emulsifier is 2% to 10% of the mass of the styrene-acrylic monomer mixed solution I; The mass of the water is 50% to 100% of the mass of the styrene-acrylic monomer mixed solution I; The initiator includes one or more of sodium persulfate, ammonium persulfate, potassium persulfate, azobisisobutyronitrile and dimethyl azobisisobutyrate; The mass of the initiator is 0.2% to 0.7% of the mass of the styrene-acrylic monomer mixed solution I; The pH value of the first addition polymerization reaction is 7.5 to 8.3; The temperature of the first addition polymerization reaction is 70-85°C and the time is 2h; The first addition polymerization reaction is carried out under stirring conditions, and the stirring speed is 200-500 r/min. The preparation method according to claim 1, characterized in that in step (10): The emulsifier includes one or more of OP-10, sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate; The mass of the emulsifier is 2% to 10% of the mass of the styrene-acrylic monomer mixed solution II; The mass of the water is 50% to 100% of the mass of the styrene-acrylic monomer mixed solution II; The initiator comprises one or more of sodium persulfate, ammonium persulfate, potassium persulfate, azobisisobutyronitrile and dimethyl azobisisobutyrate, and the mass of the initiator is 0.2% to 0.7% of the mass of the styrene-acrylic monomer mixed solution II; The pH value of the second addition polymerization reaction is 7.5 to 8.3; The temperature of the second addition polymerization reaction is 75-85°C and the time is 1-2h; The second addition polymerization reaction is carried out under stirring conditions, and the stirring speed is 200-500 r/min. The preparation method according to claim 1, characterized in that in step (11): The mass of the composite cross-linking agent is 5-20% of the mass of the styrene-acrylic monomer mixed solution II; The temperature of the third addition polymerization reaction is 75-85°C and the time is 20-40 minutes; The third polyaddition reaction is carried out under stirring conditions, and the stirring speed is 200-400 r/min. The preparation method according to claim 1, characterized in that in step (12): The emulsifier includes one or more of OP-10, peregrin, Span 60, Span 80, Tween 60 and Tween 80; The mass of the emulsifier is 2% to 10% of the mass of the silane monomer mixed solution III; The mass of the water is 50% to 100% of the mass of the silane monomer mixed solution III; The temperature of the first polycondensation reaction is 40 to 60° C. and the time is 0.5 to 2 hours; The first polycondensation reaction is carried out under stirring conditions, and the stirring speed is 800-1200 r/min. The preparation method according to claim 1, characterized in that in step (13): The emulsifiers include OP-10, pingpingjia, span 60, span 80, tween 60 and tween 80 One or more of; The mass of the emulsifier is 2% to 10% of the mass of the silane monomer mixed solution IV; The mass of the water is 50% to 100% of the mass of the silane monomer mixed solution IV; The temperature of the second polycondensation reaction is 30 to 50° C. and the time is 1 to 3 hours; The second polycondensation reaction is carried out under stirring conditions, and the stirring speed is 800-1200 r/min.