Double-layer composite microcapsules suitable for asphalt surface layers with self-repairing, high energy storage and ice and snow resistance, as well as preparation method and application thereof

Abstract

Double-layer composite microcapsules suitable for asphalt surface layers that are both self-repairing, have high energy storage, and are resistant to ice and snow, as well as their preparation method and application, relate to a microcapsule preparation method and its application. The invention aims to address the technical problems of existing self-repairing microcapsules for asphalt pavements, such as poor core material release and self-healing effects, unstable shell wall materials, low thermal conductivity, easy leakage, and single functionality. The double-layer composite microcapsules of the present invention are composed, from the inside to the outside, of an inner phase-change microcapsule core, an inner phase-change microcapsule shell, an outer self-repairing microcapsule core, and an outer self-repairing microcapsule shell; the inner phase-change microcapsule core is prepared using n-octanoic acid and tetradecane; the inner phase-change microcapsule shell is prepared using carbon nanotubes and a double polymer; the outer self-repairing microcapsule core is prepared using bio-oil and carbon nanotubes; and the outer self-repairing microcapsule shell is prepared using carbon nanotubes and a double polymer. Compared to ordinary asphalt pavement, the healing index of the asphalt pavement surface layer prepared using the double-layer composite microcapsules is increased by 8.1% to 26.3%. It can be used in the highway field.

Description

Technical Field

[0001] The present invention relates to the technical field of microcapsule preparation, and belongs to the field of self-repairing high-energy storage anti-icing / deicing asphalt preparation. Background Art

[0002] During the winter service of asphalt pavements, they are inevitably affected by the low temperature environment, resulting in defects such as low-temperature cracking. Asphalt, as a viscoelastic material, has a certain self-healing ability. However, the self-healing process of asphalt is complex and slow, and asphalt pavements do not have sufficient self-healing time during normal service. Therefore, improving the self-healing ability of asphalt and shortening its self-healing time play an important role in improving the durability of asphalt pavements. Among them, self-healing microcapsule technology is known as one of the effective methods to improve the self-healing ability of asphalt materials due to its durability and long-term effects. At the same time, phase change material is a latent heat storage material with great potential in road engineering applications. It can effectively improve road defects such as rutting, deformation, and frost cracking of asphalt pavements under high and low temperature conditions.

[0003] Current self-healing microcapsules used in asphalt pavement applications suffer from issues such as poor core material release and self-healing properties, unstable shell materials, and poor self-healing performance. Furthermore, traditional solid-liquid phase change materials suffer from shortcomings such as low thermal conductivity, high leakage, and limited functionality, significantly limiting their practical application in energy conversion and storage. Summary of the Invention

[0004] The present invention aims to solve the technical problems of poor core material release effect, unstable shell wall material, poor self-repair effect, and low thermal conductivity, easy leakage, and single application function of traditional solid-liquid phase change materials in the application process of asphalt pavement in existing self-repairing microcapsules used in asphalt pavement. The present invention provides double-layer composite microcapsules suitable for asphalt surface layers that have both self-repairing, high energy storage, and resistance to ice and snow, as well as their preparation method and application.

[0005] The double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer of the present invention is composed of an inner phase change microcapsule core, an inner phase change microcapsule shell, an outer self-repairing microcapsule core and an outer self-repairing microcapsule shell from the inside to the outside.

[0006] The core of the internal phase-change microcapsules is a mixture of octanoic acid, tetradecane, sodium polyacrylate emulsifier, and deionized water. At low temperatures, octanoic acid and tetradecane transform from liquid to solid. This process releases heat, slowing the cooling rate of the asphalt pavement, regulating the low-temperature environment of the road project, and thus improving the low-temperature crack resistance of the asphalt binder.

[0007] The inner phase-change microcapsule shell is made from a mixture of carbon nanotubes, a dual polymer, and deionized water; the dual polymer is made from polyvinyl alcohol and methylated hexamethylolmelamine resin. The carbon nanotubes and the dual polymer are entangled and deposited within the inner shell wall. The dual polymer improves the strength and chemical stability of the phase-change microcapsules as an inner shell material. The carbon nanotubes, acting as a photothermal material, convert light energy into heat, enhancing the energy storage efficiency of the phase-change material. Furthermore, the carbon nanotubes generate heat under the influence of an external electric or magnetic field, further enhancing the energy storage of the phase-change material.

[0008] The core of the external self-healing microcapsule is made of a mixture of bio-oil, carbon nanotubes, styrene maleic anhydride emulsifier, polyether F127 surfactant and deionized water; among them, the carbon nanotubes increase the filling effect of bio-oil on cracks and pores in asphalt pavement, improve the permeability and repairability of bio-oil, and thus improve the self-healing performance of asphalt materials.

[0009] The shell of the external self-repairing microcapsule is made of a mixture of carbon nanotubes, a double polymer and deionized water; the double polymer is prepared from polyvinyl alcohol and methylated hexahydroxymethyl melamine resin; the carbon nanotubes and the double polymer are entangled and deposited in the shell wall. The double polymer as a shell material can improve the responsiveness of the self-repairing microcapsule to the external environment; polyvinyl alcohol is a vulnerable part of the shell material of the external self-repairing microcapsule, which is more susceptible to damage and can accelerate the release of the core material; methylated hexahydroxymethyl melamine resin has the advantages of high stability and harmlessness due to its high cross-linking density and low formaldehyde content; carbon nanotubes give the external self-repairing microcapsule a dual mechanism of thermal induction and self-healing, enhancing the damage resistance of the shell material and the release effect of the core material. At the same time, the thermal induction of carbon nanotubes can also improve the self-healing ability of the asphalt material.

[0010] The preparation method of the above-mentioned double-layer composite microcapsules with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layers is carried out according to the following steps:

[0011] 1. Preparation of internal phase change microcapsule core solution: Sodium polyacrylate emulsifier, n-octanoic acid, tetradecane and deionized water are weighed respectively in a mass ratio of 1:(95-100):(95-100):(190-210); n-octanoic acid and tetradecane are first mixed, then added to deionized water and mixed evenly, and heated until the raw materials are completely dissolved to obtain a mixed solution; then the pH value of the mixed solution is adjusted to 3.5-4.5 with 1-1.5 mol / L citric acid; finally, sodium polyacrylate emulsifier is added to the mixed solution, and stirred at a temperature of 65-75°C for 20-40 minutes for emulsification to obtain a uniform and stable internal phase change microcapsule core solution;

[0012] 2. Preparation of internal phase change microcapsule shell solution: polyvinyl alcohol, methyl ether hexahydroxymethyl melamine resin, carbon nanotubes and deionized water are weighed respectively according to the mass ratio of 1: (65-70): (1.2-1.5): (140-155); polyvinyl alcohol is added to deionized water and mixed evenly, and then methyl ether hexahydroxymethyl melamine resin is added and mixed evenly to obtain a mixed solution; the pH value of the mixed solution is adjusted to 7.5-8.5 with sodium hydroxide solution, and then stirred at a temperature of 65-75°C and a stirring speed of 500-700 r / min for 20-40 minutes; finally, carbon nanotubes are added to the mixed solution, and ultrasonically treated to entangle the carbon nanotubes with the double polymer and mix evenly to obtain an internal phase change microcapsule shell solution;

[0013] 3. Preparation of internal high energy storage phase change microcapsules: The internal phase change microcapsule shell solution is added dropwise to the internal phase change microcapsule core solution, and the pH value of the solution is adjusted to 3.5-4.5 with citric acid; after the internal phase change microcapsule shell solution is added dropwise, the mixture is stirred at a temperature of 65-75°C and a stirring speed of 1000-1500 r / min for 60-90 minutes to allow the inner wall material to undergo a cross-linking and curing reaction on the surface of the core material, and the stirring is stopped after the solution temperature is naturally cooled to room temperature; the reaction solution is then filtered, washed with anhydrous ethanol, and vacuum dried to obtain internal high energy storage phase change microcapsules;

[0014] 4. Preparation of external self-repairing microcapsule core solution: According to the mass ratio of 1: (1.5-2): (2-3): (85-95): (185-200), weigh 15-20 g / L of polyether F127 surfactant, carbon nanotubes, styrene maleic anhydride emulsifier, bio-oil and deionized water respectively; first swell the styrene maleic anhydride emulsifier in deionized water for 20-24 hours, heat the expanded styrene maleic anhydride solution to 45-55 ° C, and then add sodium hydroxide solution to adjust the pH of the solution to 9.5-10.5; then add bio-oil, carbon nanotubes and polyether F127 surfactant to the styrene maleic anhydride solution, and stir with a high-speed shearing machine at a stirring speed of 500-700 r / min for 25-35 minutes to obtain a stable and uniform external self-repairing microcapsule core solution;

[0015] 5. Preparation of external self-repairing microcapsule shell solution: polyvinyl alcohol, methyl ether hexahydroxymethyl melamine resin, carbon nanotubes and deionized water were weighed respectively according to the mass ratio of 1: (65-70): (1.2-1.5): (140-155); polyvinyl alcohol and deionized water were stirred evenly, and added to the methyl ether hexahydroxymethyl melamine resin, stirred evenly to obtain a mixed solution; the pH value of the mixed solution was adjusted to 7.5-8.5 with sodium hydroxide solution; then stirred at a temperature of 65-75°C and a stirring speed of 500-700 r / min for 20-40 minutes; finally, carbon nanotubes were added, and after ultrasonic treatment, they were entangled with the double polymer and mixed evenly to obtain an external microcapsule shell solution;

[0016] 6. Preparation of double-layer composite microcapsules: Add the inner high energy storage phase change microcapsules to the outer self-repairing microcapsule core solution at a temperature of 20-30°C, and then add them dropwise to the outer self-repairing microcapsule shell solution. The outer self-repairing microcapsule core material containing the inner high energy storage phase change microcapsules attracts the outer wall material to the surrounding area through electrostatic adsorption; after the outer self-repairing microcapsule shell solution is added, the temperature is increased at a rate of 1-5°C / min. When the solution temperature rises to 65°C, citric acid is added to adjust the solution pH value to 4-5, and the temperature is continued to be increased at a rate of 1-5°C / min until the solution temperature reaches 80°C and stirred at this temperature at a stirring speed of 1000-1500r / min for 60-90min. The outer wall material undergoes cross-linking and curing reaction on the surface of the core material through mechanical stirring. The solution temperature is naturally cooled to room temperature and stirring is stopped; finally, the reaction liquid is filtered, washed with anhydrous ethanol, and vacuum dried to obtain double-layer composite microcapsules with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layers.

[0017] Furthermore, the ultrasonic treatment in step 2 is performed using a cell disruptor with an ultrasonic power of 85 to 95 W, an amplitude of 50% to 60%, and a duration of 60 to 90 min.

[0018] Furthermore, in step three, the mass ratio of the internal phase change microcapsule shell solution to the internal phase change microcapsule core solution is 1:(1.4-1.6).

[0019] Furthermore, the concentration of the citric acid solution in step 3 and step 6 is 1-1.5 mol / L.

[0020] Furthermore, the vacuum drying in step 3 is carried out in a vacuum drying oven at a temperature of 20 to 30° C. for 20 to 24 hours.

[0021] Furthermore, the concentration of the sodium hydroxide solution in step 2, step 4 and step 5 is 1-2 mol / L.

[0022] Furthermore, the ultrasonic treatment in step five is performed using a cell disruptor, and the ultrasonic power is 85-95 W, the amplitude is 50%-60%, and the time is 60-90 min.

[0023] Furthermore, the mass ratio of the external self-repairing microcapsule shell solution to the external self-repairing microcapsule core solution in step six is ​​1:(1.4-1.6).

[0024] Furthermore, the vacuum drying in step six is ​​carried out in a vacuum drying oven at a temperature of 20 to 30° C. for 20 to 24 hours.

[0025] The aforementioned self-repairing, high-energy-storage, and ice-snow resistant double-layer composite microcapsules, suitable for asphalt surface layers, are used to prepare asphalt pavement surface layers. The specific method is to add the self-repairing, high-energy-storage, and ice-snow resistant double-layer composite microcapsules, suitable for asphalt surface layers, to molten asphalt, stirring for 30 to 45 minutes at a mechanical stirring speed of 200 to 300 rpm. Finally, the mixture is maintained at the asphalt's molten temperature for 10 to 15 minutes to produce the road surface asphalt prepared with the double-layer composite microcapsules. The added mass of the double-layer composite microcapsules is 3% to 5% of the asphalt mass.

[0026] The double-layer composite microcapsules of the present invention, which are suitable for asphalt surface layers and have both self-repairing, high energy storage and ice and snow resistance, are composed of inner high energy storage phase change microcapsules and outer self-repairing microcapsules, specifically including an inner microcapsule core structure composed of energy storage phase change material, an inner microcapsule shell structure composed of a polymer doped with a carbon-based photothermal material, an outer microcapsule core structure composed of a bio-oil-based repair agent, and an outer microcapsule shell structure composed of a polymer doped with nanoparticles.

[0027] The present invention adopts an in-situ polymerization method to prepare double-layer composite microcapsules, specifically: first preparing an inner high-energy storage phase-change microcapsule; then preparing an outer microcapsule core structure and an outer microcapsule shell structure; finally, the inner high-energy storage phase-change microcapsule and the outer microcapsule core structure are mixed, and the outer microcapsule shell structure is slowly added to form a double-layer composite microcapsule.

[0028] Compared with the existing technology, the present invention breaks through the defects of the single function of traditional microcapsule composite materials and realizes the multifunctionality of self-repair, high energy storage, and long-term resistance to ice and snow. The double-layer composite microcapsules with self-repair, high energy storage and long-term resistance to ice and snow prepared by the present invention and suitable for asphalt surface layers can not only achieve a high survival rate of microcapsules and a high healing and repair rate of asphalt pavement cracks, but also have the advantages of high encapsulation rate of phase change materials, high thermal conductivity, good sealing performance, good thermal stability, and good mechanical properties. The heat and high energy storage generated will increase the temperature of the asphalt material, melt the ice and snow on the asphalt pavement and inhibit the formation of ice layers, ultimately achieving a mechanism of self-repair, high energy storage and long-term resistance to ice and snow. Compared with ordinary 70# matrix asphalt, the asphalt prepared using the double-layer composite microcapsules of the present invention has a healing index increased by 8.1% to 26.3%, a needle penetration at 25°C increased by 6.5% to 17.5%, a softening point reduced by 1.9% to 8.4%, and an ductility increased by 12.2% to 23.6%.

[0029] To improve the performance of self-healing microcapsules and enhance their application in asphalt, this invention selects appropriate materials for the microcapsule shell and core to form self-healing microcapsules with different structures and functions. Furthermore, to better utilize solar energy, a photothermal conversion and storage technology based on photothermal composite phase change materials is used to effectively convert solar energy into thermal energy and store it. Furthermore, to ensure a balance between the thermal management requirements, mechanical strength, and environmental load of asphalt pavements, microcapsule phase change materials are introduced. These microcapsule phase change materials can actively regulate the temperature of the asphalt pavement, thereby mitigating temperature-related damage.

[0030] The road surface asphalt prepared by the double-layer composite microcapsules with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer of the present invention has an action process divided into two stages, such as Figure 2 shown.

[0031] Phase 1: Under the concentrated stress caused by the expansion of cracks in the asphalt pavement, its shell structure is destroyed, and the repair agent contained in the outer core is released and fills the crack defects. At the same time, the conductive nanomaterials contained in the shell structure will generate heat energy under the action of the external electric field or magnetic field, increase the fluidity of the core material, soften the asphalt around the self-healing microcapsules, improve the mixing degree of the core material and the asphalt material, promote the self-repair ability of the asphalt cracks in the pavement, and achieve the purpose of extending the service life of the asphalt pavement and ensuring its normal service function.

[0032] The second stage: The repair agent that fills the cracks contains undamaged high-energy storage phase change microcapsules. After the composite microcapsule shell and outer core structure realize thermal induction and self-repair functions, the high-energy storage phase change microcapsules at the cracks continue to play a high energy storage role. The photothermal material contained in the wall of the high-energy storage phase change microcapsule not only stores light and heat in the phase change material, but also generates heat energy under the action of an external electric field or magnetic field and then stores it in the phase change material, jointly achieving comprehensive performance such as high heat storage capacity, excellent light-heat conversion performance and good thermal conductivity, realizing the temperature regulation function of asphalt pavement in low temperature environment, thereby solving the problem of cracking of asphalt binder of pavement under low temperature conditions in winter and effectively inhibiting the formation of ice on the surface layer of asphalt pavement. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic structural diagram of the double-layer composite microcapsule of the present invention that is suitable for asphalt surface layers and has both self-repairing, high energy storage and ice and snow resistance; 1 is the internal phase change microcapsule core, 2 is the internal phase change microcapsule shell; 3 is the external self-repairing microcapsule core, and 4 is the external self-repairing microcapsule shell.

[0034] Figure 2 This is a schematic diagram of the two stages of the action of highway surface layer asphalt prepared with double-layer composite microcapsules that are suitable for asphalt surface layers and have both self-repairing, high energy storage and ice and snow resistance. DETAILED DESCRIPTION

[0035] The beneficial effects of the present invention are demonstrated with the following examples.

[0036] Example 1: The preparation method of the double-layer composite microcapsules with self-repairing, high energy storage and ice and snow resistance applicable to asphalt surface layers of this embodiment is carried out according to the following steps:

[0037] 1. Preparation of internal phase change microcapsule core solution:

[0038] Sodium polyacrylate emulsifier, n-octanoic acid, tetradecane and deionized water were weighed according to the mass ratio of 1:95:95:190;

[0039] Adding n-octanoic acid and tetradecane to deionized water, mixing uniformly, and heating until the raw materials are completely dissolved to obtain a mixed solution; then adjusting the pH value of the mixed solution to 4 with 1 mol / L citric acid; then adding sodium polyacrylate emulsifier to the mixed solution, stirring for 30 minutes at a temperature of 70°C for emulsification, and obtaining a uniform and stable internal phase change microcapsule core solution;

[0040] 2. Preparation of internal phase change microcapsule shell solution:

[0041] Polyvinyl alcohol, methylated hexamethylol melamine resin, carbon nanotubes and deionized water were weighed according to the mass ratio of 1:65:1.2:140 among polyvinyl alcohol, methylated hexamethylol melamine resin, carbon nanotubes and deionized water;

[0042] Polyvinyl alcohol was added to deionized water and mixed uniformly, and then methylated hexahydroxymethyl melamine resin was added and mixed uniformly to obtain a mixed solution; the pH value of the mixed solution was adjusted to 8 with a 1.5 mol / L sodium hydroxide solution, and then stirred at a temperature of 70° C. and a stirring speed of 600 r / min for 30 minutes; finally, carbon nanotubes were added to the mixed solution and ultrasonically treated for 70 minutes using a cell crusher at an ultrasonic power of 90 W and an amplitude of 50% to cause the carbon nanotubes to entangle with the dual polymers and be deposited in the inner shell wall, thereby obtaining an inner phase change microcapsule shell solution;

[0043] 3. Preparation of internal high energy storage phase change microcapsules:

[0044] The internal phase change microcapsule shell solution was added dropwise to the internal phase change microcapsule core solution at a mass ratio of 1:1.5, and citric acid with a concentration of 1 mol / L was added to adjust the pH value of the solution to 4; after the internal phase change microcapsule shell solution was added dropwise, the mixture was stirred at a temperature of 70°C and a stirring speed of 1000 r / min for 70 minutes to allow the inner wall material to undergo a cross-linking and curing reaction on the surface of the core material, and the stirring was stopped after the solution temperature naturally cooled to room temperature; the reaction solution was then filtered, washed with anhydrous ethanol, and dried in a vacuum drying oven at a temperature of 25°C for 24 hours to obtain internal high energy storage phase change microcapsules;

[0045] 4. Preparation of external self-repairing microcapsule core solution:

[0046] According to the mass ratio of polyether F127 surfactant, carbon nanotubes, styrene maleic anhydride emulsifier, bio-oil and deionized water of 1:1.5:2:85:185, 15g / L of polyether F127 surfactant, carbon nanotubes, styrene maleic anhydride emulsifier, bio-oil and deionized water were taken respectively;

[0047] Styrene maleic anhydride emulsifier was first swelled in deionized water for 24 hours. The expanded styrene maleic anhydride solution was heated to 50°C, and then 1.5 mol / L sodium hydroxide solution was added to adjust the pH of the solution to 10. The solution was then stirred at a high-speed shearing machine at a stirring speed of 600 r / min for 30 minutes to obtain a stable and uniform external self-healing microcapsule core solution.

[0048] 5. Preparation of external self-repairing microcapsule shell solution:

[0049] Polyvinyl alcohol, methylated hexahydroxymethyl melamine resin, carbon nanotubes and deionized water were weighed according to the mass ratio of polyvinyl alcohol, methylated hexahydroxymethyl melamine resin, carbon nanotubes and deionized water of 1:65:1.2:140;

[0050] The polyvinyl alcohol and deionized water were mixed evenly, and then added to the methylated hexahydroxymethyl melamine resin and stirred evenly to obtain a mixed solution; the pH value of the mixed solution was adjusted to 8 with a 1.5 mol / L sodium hydroxide solution; the mixed solution was stirred at a temperature of 70°C and a stirring speed of 600 r / min for 30 minutes; carbon nanotubes were then added and ultrasonically treated for 70 minutes using a cell crusher at an ultrasonic power of 90 W and an amplitude of 50% to entangle the carbon nanotubes with the double polymer and deposit them in the shell wall, thereby obtaining an external self-repairing microcapsule shell solution;

[0051] 6. Preparation of double-layer composite microcapsules

[0052] According to the mass ratio of the external self-repairing microcapsule shell solution to the external self-repairing microcapsule core solution of 1:1.5, the internal high energy storage phase change microcapsules were first added to the external self-repairing microcapsule core solution at a temperature of 25°C, and then added dropwise to the external self-repairing microcapsule shell solution. The external self-repairing microcapsule core material containing the internal high energy storage phase change microcapsules attracted the outer wall material to the surrounding area through electrostatic adsorption. After the external self-repairing microcapsule shell solution was added, the temperature was increased at a rate of 2°C / min. When the solution temperature rose to 65°C, 1 mol / L citric acid solution was added. The pH value of the solution was adjusted to 4, and the temperature was continued to rise at a rate of 2°C / min until the solution temperature reached 80°C and stirred at a stirring speed of 1000r / min for 60min. The outer wall material was cross-linked and cured on the surface of the core material through mechanical stirring. The solution temperature was naturally cooled to room temperature and stirring was stopped. Finally, the reaction liquid was filtered, washed with anhydrous ethanol, and vacuum dried at a temperature of 25°C for 24 hours to obtain a double-layer composite microcapsule suitable for asphalt surface layer with self-repairing, high energy storage and ice and snow resistance.

[0053] Comparative Example 1: This comparative example is to prepare a single self-repairing microcapsule, and the specific steps are as follows:

[0054] 1. Preparation of self-repairing microcapsule core solution:

[0055] According to the mass ratio of polyether F127 surfactant, carbon nanotubes, styrene maleic anhydride emulsifier, bio-oil and deionized water of 1:1.5:2:85:185, 15g / L of polyether F127 surfactant, carbon nanotubes, styrene maleic anhydride emulsifier, bio-oil and deionized water were taken respectively;

[0056] Styrene maleic anhydride emulsifier was first swelled in deionized water for 24 hours. The expanded styrene maleic anhydride solution was heated to 50°C and then adjusted to a pH of 10 by adding 1.5 mol / L sodium hydroxide solution. Bio-oil, carbon nanotubes, and polyether F127 surfactant were then added to the styrene maleic anhydride solution. The solution was then stirred at 600 r / min using a high-speed shearing machine for 30 minutes to obtain a stable and uniform self-healing microcapsule core solution.

[0057] 2. Preparation of self-repairing microcapsule shell solution:

[0058] Polyvinyl alcohol, methylated hexahydroxymethyl melamine resin, carbon nanotubes and deionized water were weighed according to the mass ratio of polyvinyl alcohol, methylated hexahydroxymethyl melamine resin, carbon nanotubes and deionized water of 1:65:1.2:140;

[0059] The polyvinyl alcohol and deionized water were mixed uniformly, and then added to the methylated hexahydroxymethyl melamine resin and stirred uniformly to obtain a mixed solution; the pH value of the mixed solution was adjusted to 8 with a 1.5 mol / L sodium hydroxide solution; the mixed solution was stirred at a temperature of 70°C and a stirring speed of 600 r / min for 30 minutes; carbon nanotubes were then added and ultrasonically treated for 70 minutes using a cell crusher at an ultrasonic power of 90 W and an amplitude of 50% to cause the carbon nanotubes to entangle with the dual polymers and deposit in the shell wall, thereby obtaining a self-repairing microcapsule shell solution;

[0060] 3. Preparation of self-repairing microcapsules:

[0061] According to the mass ratio of self-repairing microcapsule shell solution to self-repairing microcapsule core solution of 1:1.5, the self-repairing microcapsule core solution was added dropwise to the self-repairing microcapsule shell solution. After the self-repairing microcapsule shell solution was added, the temperature was increased at a rate of 2°C / min. When the solution temperature rose to 65°C, 1 mol / L citric acid solution was added to adjust the pH value of the solution to 4. The temperature was continued to be increased at a rate of 2°C / min until the solution temperature reached 80°C and stirred at a stirring speed of 1000 r / min for 60 minutes. The outer wall material was cross-linked and cured on the surface of the core material through mechanical stirring. The solution temperature was naturally cooled to room temperature and stirring was stopped. Finally, the reaction solution was filtered, washed with anhydrous ethanol, and vacuum dried at 25°C for 24 hours to obtain a single self-repairing microcapsule.

[0062] The performance of the double-layer composite microcapsules prepared in Example 1 and the single self-repairing microcapsules prepared in Comparative Example 1 were evaluated.

[0063] First, the double-layer composite microcapsules prepared in Example 1 and the single self-healing microcapsules prepared in Comparative Example 1 were tested for their impermeability and thermal stability. The single self-healing microcapsules and the double-layer composite microcapsules were immersed in the same volume of ethanol solvent, respectively. After soaking for the same time, the mass loss rate of the core of the two microcapsules before and after soaking was tested to evaluate their impermeability.

[0064] The thermal stability of single self-healing microcapsules and double-layer composite microcapsules was analyzed by thermogravimetric analyzer at temperatures of 230-300°C, and their mass loss rate was used as an evaluation indicator.

[0065] The exothermic enthalpy of single phase change microcapsules and double-layer composite microcapsules was tested by differential scanning calorimetry.

[0066] The yield stress of single phase-change microcapsules and double-layer composite microcapsules was tested using a nanoindentation tester. The load-displacement curves were set to 50 nN for 10 seconds with a displacement resolution of 0.01 nm. The yield stress values ​​of the single phase-change microcapsules and double-layer composite microcapsules at a pH of 5.0 were calculated based on the load-displacement curves.

[0067] The test results are listed in Table 1

[0068] Table 1 Performance comparison of the single phase change microcapsules of Comparative Example 1 and the double-layer composite microcapsules of Example 1

[0069]

[0070] Compared to the single self-healing microcapsules of Comparative Example 1, the double-layer composite microcapsules of Example 1 exhibited stronger impermeability and thermal stability, indicating greater stability and facilitating the self-healing function of the microcapsules. Compared to the single phase-change microcapsules, the double-layer composite microcapsules exhibited a greater yield stress and exothermic enthalpy, indicating superior mechanical properties and a greater ability to regulate the low-temperature environment of asphalt pavement, thereby improving the asphalt's low-temperature crack resistance.

[0071] The double-layer composite microcapsules prepared in Example 1 are used to prepare asphalt for the surface layer of a highway. The specific method is: the mass percentage of the double-layer composite microcapsules with self-repairing, high energy storage and ice and snow resistance prepared in Example 1 suitable for the surface layer of asphalt is 3%, 4% and 5% of the mass of asphalt, and the double-layer composite microcapsules with self-repairing, high energy storage and ice and snow resistance suitable for the surface layer of asphalt are added to the asphalt in a molten state, and stirred for 30 minutes under the condition that the stirring speed of the mechanical device is 300r / min; finally, the mixture is kept at the melting temperature of the asphalt for 10 minutes to obtain the surface layer asphalt of a highway containing the double-layer composite microcapsules.

[0072] The self-healing properties of highway surface asphalt containing double-layer composite microcapsules were first tested. Multiple intermittent fatigue tests based on DSR were performed to analyze the self-healing properties of asphalt containing different double-layer composite microcapsules (0%, 3%, 4%, and 5%). The multiple intermittent fatigue tests were conducted at a temperature of 25°C, a loading strain of 3.0%, a loading frequency of 10 Hz, and a loading cycle of 10 cycles, with intermittent times of 0 s and 3 s, respectively. Loading was terminated when the modulus dropped to 50% of the initial modulus. The slope of the line connecting the initial modulus and the modulus after loading was terminated was calculated for the fatigue curves with intermittent times of 0 s and 3 s, respectively. The ratio of the two was used as an evaluation index. The results are shown in Table 2 below. As shown in Table 2, the self-healing index of the asphalt significantly increased with increasing double-layer composite microcapsule content. Compared to conventional 70# base asphalt, the healing index increased by 8.1% to 26.3%, indicating enhanced self-healing properties.

[0073] Table 2 Healing index of asphalt prepared using the double-layer composite microcapsules of Example 1

[0074] Asphalt Type Healing Index Ordinary 70# matrix asphalt 143.5 Microcapsule dosage 3% 155.1 Microcapsule dosage 4% 168.6 Microcapsule dosage 5% 181.2

[0075] The low-temperature crack resistance of highway surface asphalt containing double-layer composite microcapsules was then tested. Penetration, softening point, and ductility tests analyzed the low-temperature crack resistance of asphalt containing different double-layer composite microcapsules (0%, 3%, 4%, and 5%). The results are shown in Table 3 below. As shown in Table 3, as the double-layer composite microcapsule dosage increases, the asphalt penetration increases, the softening point decreases, and the ductility increases. Compared to ordinary 70# base asphalt, the 25°C penetration increases by 6.5% to 17.5%, the softening point decreases by 1.9% to 8.4%, and the ductility increases by 12.2% to 23.6%. This indicates that the double-layer composite microcapsules enhance the asphalt's low-temperature crack resistance.

[0076] Table 3 Low temperature crack resistance of asphalt prepared using the double-layer composite microcapsules of Example 1

[0077]

[0078] The double-layer composite microcapsules with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layers of the present invention use double polymers to prepare the shell wall, which can significantly improve the single response to the external environment of the single polymer shell material, and significantly improve the response ability of the microcapsules to the external environment and the release efficiency of the microcapsule core material; the methylated hexahydroxymethyl melamine resin has good environmental protection and safety due to its high cross-linking density and low formaldehyde content, and can also increase its reactivity and hydrophilicity, improve its wrapping of the core material, and enhance the stability of the core material; in addition, the methylated hexahydroxymethyl melamine resin has a good physical barrier effect, which can regulate the core material Release ability, thereby significantly improving the stability and functionality of the microcapsules; at the same time, the use of polyvinyl alcohol can be used as a vulnerable part of the external self-repairing microcapsule shell material, which is more susceptible to damage and can significantly improve the release ability of the core material; in addition, the use of carbon nanotubes can improve the thermal stability of the microcapsules and give the microcapsules conductive properties. Carbon nanotubes as photothermal materials can convert light energy into heat energy to improve the energy storage effect of the phase change material. Carbon nanotubes generate heat energy under the action of an external electric field or magnetic field to further improve the energy storage of the phase change material, and carbon nanotubes can increase the core material's filling effect on cracks and pores, improve the core material's permeability and repairability, and improve the material's self-healing properties. The double-layer composite microcapsules of the present invention, which are suitable for asphalt surface layers and have both self-repairing, high energy storage and ice and snow resistance, can achieve a high survival rate of microcapsules and a high healing and repair rate of asphalt pavement cracks under the synergistic effect of each layer of materials, and can also alleviate the problems of low thermal conductivity and easy leakage of phase change materials. The heat and high energy storage generated will increase the temperature of the asphalt material, melt the ice and snow on the asphalt pavement and inhibit the formation of ice layers, ultimately realizing the self-repair-high energy storage-long-term ice and snow resistance mechanism.

Claims

1. A method for preparing a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer, characterized in that: The method proceeds as follows:

1. Preparation of internal phase change microcapsule core solution: Sodium polyacrylate emulsifier, n-octanoic acid, tetradecane and deionized water were weighed respectively in a mass ratio of 1:(95~100):(95~100):(190~210); n-octanoic acid and tetradecane were first mixed, then added to deionized water and mixed evenly, and heated until the raw materials were completely dissolved to obtain a mixed solution; the pH value of the mixed solution was then adjusted to 3.5~4.5 with 1~1.5 mol / L citric acid; finally, sodium polyacrylate emulsifier was added to the mixed solution, and stirred at a temperature of 65~75°C for 20~40 minutes for emulsification to obtain a uniform and stable internal phase change microcapsule core solution; 2. Preparation of internal phase change microcapsule shell solution: polyvinyl alcohol, methyl ether hexahydroxymethyl melamine resin, carbon nanotubes and deionized water were weighed respectively according to the mass ratio of 1: (65~70): (1.2~1.5): (140~155); polyvinyl alcohol was added to deionized water and mixed evenly, and then methyl ether hexahydroxymethyl melamine resin was added and mixed evenly to obtain a mixed solution; the pH value of the mixed solution was adjusted to 7.5~8.5 with sodium hydroxide solution, and then stirred at a temperature of 65~75℃ and a stirring speed of 500~700r / min for 20~40min; finally, carbon nanotubes were added to the mixed solution, and ultrasonically treated to entangle the carbon nanotubes with the double polymer and mix evenly to obtain an internal phase change microcapsule shell solution; 3. Preparation of internal high energy storage phase change microcapsules: The internal phase change microcapsule shell solution is added dropwise to the internal phase change microcapsule core solution, and the pH value of the solution is adjusted to 3.5-4.5 with citric acid; after the internal phase change microcapsule shell solution is added dropwise, the mixture is stirred at a temperature of 65-75°C and a stirring speed of 1000-1500 r / min for 60-90 minutes to allow the inner wall material to undergo a cross-linking and curing reaction on the surface of the core material, and the stirring is stopped after the solution temperature is naturally cooled to room temperature; the reaction solution is then filtered, washed with anhydrous ethanol, and vacuum dried to obtain internal high energy storage phase change microcapsules; Preparation of external self-healing microcapsule core solution: polyether F127 surfactant, carbon nanotubes, styrene maleic anhydride emulsifier, bio-oil and deionized water with a concentration of 15-20 g / L were taken respectively according to the mass ratio of 1: (1.5-2): (2-3): (85-95): (185-200); the styrene maleic anhydride emulsifier was first swelled in deionized water for 20-24 h, the expanded styrene maleic anhydride solution was heated to 45-55 ° C, and then sodium hydroxide solution was added to adjust the pH of the solution to 9.5-10.5; then the bio-oil, carbon nanotubes and polyether F127 surfactant were added to the styrene maleic anhydride solution, and stirred for 25-35 min at a stirring speed of 500-700 r / min using a high-speed shearing machine to obtain a stable and uniform external self-healing microcapsule core solution; 5. Preparation of external self-repairing microcapsule shell solution: polyvinyl alcohol, methyl ether hexahydroxymethyl melamine resin, carbon nanotubes and deionized water are respectively taken in a mass ratio of 1: (65-70): (1.2-1.5): (140-155); polyvinyl alcohol and deionized water are stirred evenly, and then added to the methyl ether hexahydroxymethyl melamine resin and stirred evenly to obtain a mixed solution; the pH value of the mixed solution is adjusted to 7.5-8.5 with sodium hydroxide solution; the mixture is stirred at a temperature of 65-75°C and a stirring speed of 500-700 r / min for 20-40 minutes; finally, carbon nanotubes are added and ultrasonically treated to entangle and mix evenly with the double polymer to obtain an external microcapsule shell solution; 6. Preparation of double-layer composite microcapsules: Add the inner high energy storage phase change microcapsules to the outer self-repairing microcapsule core solution at a temperature of 20-30°C, and then add them dropwise to the outer self-repairing microcapsule shell solution. The outer self-repairing microcapsule core material containing the inner high energy storage phase change microcapsules attracts the outer wall material to the surrounding area through electrostatic adsorption; After the external self-repairing microcapsule shell solution is added, the temperature is increased at a rate of 1~5 ℃ / min. When the solution temperature reaches 65 ℃, citric acid solution is added to adjust the solution pH value to 4~5. The temperature is continued to be increased at a rate of 1~5 ℃ / min until the solution temperature reaches 80 ℃ and stirred at this temperature at a stirring speed of 1000~1500 r / min for 60~90 minutes. The outer wall material undergoes a cross-linking and curing reaction on the surface of the core material through mechanical stirring. The solution temperature is naturally cooled to room temperature and stirring is stopped. Finally, the reaction liquid is filtered, washed with anhydrous ethanol, and vacuum dried to obtain a double-layer composite microcapsule suitable for asphalt surface layer with self-repairing, high energy storage and ice and snow resistance. The double-layer composite microcapsule is composed of an internal phase change microcapsule core, an internal phase change microcapsule shell, an external self-repairing microcapsule core and an external self-repairing microcapsule shell from the inside to the outside.

2. The method for preparing a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer according to claim 1, characterized in that: The ultrasonic treatment described in step 2 is performed using a cell disruptor with an ultrasonic power of 85-95 W, an amplitude of 50%-60%, and a duration of 60-90 min.

3. The method for preparing a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer according to claim 1 or 2, characterized in that: In step three, the mass ratio of the internal phase change microcapsule shell solution to the internal phase change microcapsule core solution is 1:(1.4~1.6).

4. The method for preparing a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer according to claim 1 or 2, characterized in that: The concentration of the citric acid solution in step 3 and step 6 is 1-1.5 mol / L.

5. The method for preparing a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer according to claim 1 or 2, characterized in that: The concentration of the sodium hydroxide solution in step 2, step 4 and step 5 is 1-2 mol / L.

6. The method for preparing a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer according to claim 1 or 2, characterized in that: The ultrasonic treatment in step 5 is performed using a cell disruptor, with an ultrasonic power of 85-95 W, an amplitude of 50%-60%, and a duration of 60-90 min.

7. The method for preparing a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer according to claim 1 or 2, characterized in that: The mass ratio of the external self-repairing microcapsule shell solution to the external self-repairing microcapsule core solution described in step six is ​​1:(1.4~1.6).

8. Application of a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance prepared in claim 1 for asphalt surface layer, characterized in that The application is to apply double-layer composite microcapsules to the surface layer of asphalt pavement.

9. The use of a double-layer composite microcapsule with self-repairing, high energy storage and ice and snow resistance suitable for asphalt surface layer according to claim 8, characterized in that: The method for preparing highway surface asphalt using double-layer composite microcapsules is carried out as follows: double-layer composite microcapsules suitable for asphalt surface layers with self-repairing, high energy storage and ice and snow resistance are added to molten asphalt, and stirred for 30 to 45 minutes under the condition of a mechanical stirring speed of 200 to 300 r / min; finally, the mixture is kept at the melting temperature of the asphalt for 10 to 15 minutes to obtain highway surface asphalt prepared with double-layer composite microcapsules; wherein the added mass of the double-layer composite microcapsules is 3% to 5% of the mass of the asphalt.

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