Polymethyl methacrylate nano-microsphere compounded Pickering emulsified asphalt and preparation method thereof

Abstract

The invention belongs to the technical field of emulsified asphalt, and particularly discloses polymethyl methacrylate nano-microsphere compounded Pickering emulsified asphalt and a preparation method thereof. Comprising the following steps: S1, carrying out amidation coupling reaction on carboxylated PMMA (Polymethyl Methacrylate) nano-microspheres and amino-terminated polyethylene glycol to obtain amino-coupled modified PMMA nano-microspheres, and carrying out dispersion and ultrasonic treatment on the amino-coupled modified PMMA nano-microspheres to obtain nano-microsphere dispersion liquid serving as a water phase; s2, heating and melting the matrix asphalt, then adding a plasticizer and an antioxidant, and performing shear mixing to obtain an asphalt phase; s3, mixing the asphalt phase and the water phase, and performing high-speed shearing, ultrasonic treatment, secondary high-speed shearing, sieving and impurity removal to obtain the PMMA nano-microsphere compounded Pickering emulsified asphalt. According to the invention, the PMMA nano-microspheres and the Pickering emulsification technology are combined, so that the stability of the emulsified asphalt can be improved, and the three index performances after demulsification can also be improved.

Description

Technical Field

[0001] This invention belongs to the field of emulsified asphalt technology, specifically relating to a polymethyl methacrylate nanosphere-based Pickering emulsified asphalt and its preparation method. Background Technology

[0002] Emulsified asphalt, as a key binder phase in cold-mix asphalt mixtures and pavement maintenance materials in road engineering, directly determines construction quality and pavement durability. Traditional emulsified asphalt often uses anionic / cationic surfactants as emulsifiers, achieving emulsion stabilization at the oil-water interface through physical adsorption. However, this type of molecular emulsion system has significant limitations. First, the physical adsorption of surfactants at the interface is easily affected by factors such as temperature, shear force, and ionic strength, leading to a short emulsion storage period and susceptibility to demulsification and stratification during transportation. Second, under high-temperature construction conditions, the demulsification rate is difficult to control precisely, easily resulting in insufficient early strength development or excessively rapid demulsification, thus shortening the construction window and affecting construction quality and efficiency.

[0003] In recent years, Pickering emulsification technology has provided a new solution to overcome the above-mentioned bottlenecks. Unlike molecular emulsifiers, solid particles can form a stable steric hindrance layer at the oil-water interface through irreversible adsorption, which can improve the stability of the emulsion by about 2-3 times. Existing research mainly uses layered silicates (such as montmorillonite) or non-metallic oxides (such as nano-SiO2) as stabilizers, but these inorganic particles still have the following shortcomings: (1) High surface energy leads to easy agglomeration in the asphalt phase; (2) The large difference in modulus between rigid inorganic particles and flexible asphalt can easily cause stress concentration under mechanical load, which can accelerate the propagation of microcracks; (3) Strongly polar surfaces have poor compatibility with asphalt, and the interface contact angle is usually greater than 90°, making it difficult to form a dense and stable adsorption layer.

[0004] Polymethyl methacrylate (PMMA) is a synthetic polymer material with excellent transparency, chemical stability, and processability. PMMA nanospheres prepared using controlled polymerization technology exhibit precisely controllable particle size distribution and surface chemical properties. Compared to inorganic particles, PMMA microspheres, being composed of PMMA, have an elastic modulus closer to that of asphalt matrix. Therefore, the application of PMMA microspheres in Pickering emulsified asphalt has significant scientific and engineering potential. Currently, no literature reports the application of PMMA in the preparation of emulsified asphalt. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention aims to provide a polymethyl methacrylate (PMMA) nanosphere-based Pickering emulsified asphalt and its preparation method. This invention combines PMMA nanospheres with Pickering emulsification technology, which not only improves the stability of the emulsified asphalt but also enhances its three key performance indicators after demulsification, meeting the high-performance requirements of road engineering for emulsified asphalt.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a mixture of polymethyl methacrylate nanospheres and Pickering emulsified asphalt includes the following steps: S1. Amino-coupled modified polymethyl methacrylate nanospheres were dispersed in an aqueous solution of a nonionic surfactant and sonicated (40 kHz, 200 W, 10 minutes) to obtain a nanosphere dispersion with a mass concentration of 4%-6%. The nanosphere dispersion was then heated to 80-90 °C and used as the aqueous phase. S2 involves heating the base asphalt to 130-150℃ to melt it, then adding plasticizers and antioxidants, and shearing and mixing to obtain a homogeneous asphalt phase; S3 mixes the asphalt phase and water phase at a weight ratio of 5~6:4~5, performs high-speed shearing, ultrasonication, and secondary high-speed shearing. After removing impurities by passing through a 200-mesh sieve, it is transferred to a closed reaction vessel and matured at 40-50℃ for 6-48 hours to obtain the polymethyl methacrylate nanosphere compound Pickering emulsified asphalt. The amino-coupled modified polymethyl methacrylate nanospheres are obtained by amidation coupling reaction of carboxylated polymethyl methacrylate nanospheres and amino-terminated polyethylene glycol.

[0007] Furthermore, the preparation method of the amino-coupled modified polymethyl methacrylate nanospheres includes: Carboxylated polymethyl methacrylate nanospheres were dispersed in 2-morpholine ethanesulfonic acid (MES) buffer. First, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS) were added and stirred for 15-30 min to activate the mixture. Then, amino-terminated polyethylene glycol was added, and the pH of the system was adjusted to 6.5-7.0. The reaction was carried out for 1-4 h to complete the amidation coupling reaction. After the reaction, the mixture was centrifuged and washed to obtain amino-coupled modified polymethyl methacrylate nanospheres.

[0008] The carboxyl group density of the carboxylated polymethyl methacrylate nanospheres is 0.03-0.3 mmol / g, preferably 0.1-0.3 mmol / g.

[0009] The 2-morpholine ethanesulfonic acid buffer solution has a concentration of 0.05 mol / L and a pH of 6.0-6.2. The molar ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to N-hydroxysuccinimide is 1:1; the molar ratio of the total carboxyl group of the carboxylated polymethyl methacrylate nanospheres to the molar ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:1.5. The amine value of the amino-terminated polyethylene glycol is 0.6-0.8 mmol / g by titration; preferably, the ratio of the total amount of amine groups in the amino-terminated polyethylene glycol to the total amount of carboxyl groups in the carboxylated polymethyl methacrylate nanospheres is 2:1.

[0010] The nonionic surfactant is poloxamer, and its aqueous solution has a concentration of 0.1-0.2 wt%.

[0011] The nonionic surfactant is at least one of poloxamer 407, poloxamer 188, poloxamer 64, poloxamer 108, and poloxamer 64.

[0012] Furthermore, the mass concentration of the nanosphere dispersion is 5%.

[0013] Further, step S3 is as follows: the asphalt phase and the water phase are mixed at a weight ratio of 5~6:4~5, and sheared at high speed at 12,000±500 rpm for 3-5 minutes; after the system is cooled to 80-90℃, it is ultrasonicated (20kHz, power 400W) for 3 minutes; after the system is cooled to 50-60℃, it is sheared at high speed at 5,000 rpm for 3-5 minutes; after impurities are removed by passing through a 200-mesh sieve, it is transferred to a closed reaction vessel and matured at 40-50℃ for 6-48 hours to obtain the polymethyl methacrylate nanosphere compound Pickering emulsified asphalt.

[0014] Preferably, the mass fraction of amino-coupled modified polymethyl methacrylate nanospheres in the mixture obtained by mixing the asphalt phase and the aqueous phase is 2%-3%, more preferably 2.5%.

[0015] Furthermore, in step S2, the base asphalt is at least one of 70# base asphalt and 90# base asphalt.

[0016] Furthermore, in step S2, the plasticizer accounts for 3%-5% of the mass of the base asphalt, and the plasticizer is at least one of epoxidized soybean oil, epoxidized linseed oil, epoxidized rapeseed oil, epoxidized palm oil, and epoxidized fatty acid methyl ester.

[0017] Further, in step S2, the antioxidant accounts for 0.05%-0.1% of the mass of the base asphalt, and the antioxidant is at least one selected from pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3,5-di-tert-butyl-4-hydroxyphenylpropionate, N,N′-hexamethylenebis-3,5-di-tert-butyl-4-hydroxyphenylpropionamide, and thiodipropionate.

[0018] The functions of each added substance in the preparation of amino-coupled modified polymethyl methacrylate nanospheres are described below: 2-Morpholine ethanesulfonic acid (MES) buffer: provides a suitable weakly acidic buffer environment for the system to maximize the EDC / NHS activation efficiency of carboxyl groups and maintain the stable dispersion of nanospheres.

[0019] Amino-terminated polyethylene glycol (PEG): Amino-terminated PEG is an amphiphilic polymer whose terminal primary amine group allows it to covalently couple with a carboxyl group. In this invention, the amino-terminated PEG plays a role in surface modification of carboxylated PMMA nanospheres. By covalently grafting PEG molecules onto the surface of the microspheres, a flexible hydrophilic layer is imparted to them. This PEG chain significantly improves the dispersion stability of the microspheres in the aqueous phase (preventing aggregation between microspheres) and provides additional steric hindrance and hydrophobic-hydrophilic balance at the emulsion interface, allowing the microspheres to be more firmly positioned at the oil-water interface.

[0020] 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC): EDC acts as a coupling agent in this system to covalently bond amino-terminated polyethylene glycol to the carboxyl groups on the surface of the microspheres. Specifically, EDC activates the carboxyl groups to form an active O-acylisourea intermediate, allowing the carboxyl groups to undergo a condensation reaction with the amine groups. However, this intermediate has a short lifespan in water and is easily hydrolyzed, thus requiring the assistance of NHS. In general, the role of EDC is to initiate and promote the coupling reaction between the carboxyl and amine groups, ensuring the successful grafting of PEG onto the PMMA microspheres. After EDC treatment, a large number of PEG chains are firmly fixed on the surface of the microspheres, giving the microspheres a lasting hydrophilic modification effect. EDC itself transforms into a urea-like byproduct after the reaction and dissolves in water, being removed by subsequent steps and therefore not remaining in the final asphalt system. However, its role is crucial for constructing the functionalized microsphere support system required by this invention.

[0021] N-Hydroxysuccinimide (NHS): In this invention, NHS is used in conjunction with EDC as a promoter of the coupling reaction. After the EDC activates the carboxyl group, NHS reacts with the activated carboxyl group to form an NHS ester, making the intermediate more stable and possessing higher amine reactivity. Thus, when amino-terminated polyethylene glycol is added, the amine group on the PEG can efficiently replace the NHS ester, forming a stable amide bond and attaching the PEG chain to the microsphere surface.

[0022] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: This invention applies amino-coupled modified PMMA nanospheres to the preparation of emulsified asphalt. When the amino-coupled modified PMMA nanospheres are within a reasonable particle content range (accounting for 2%-3% of the mass of emulsified asphalt), the 1-day and 5-day storage stability of the emulsified asphalt of this invention is significantly better than that of traditional emulsified asphalt and nano-SiO2-Pickering emulsified asphalt systems, and is far below the standard limits. It can maintain a good dispersion state under static conditions for a long time, and basically does not undergo stratification and sedimentation.

[0023] Compared with unmodified PMMA nanospheres or traditional inorganic nanoparticle emulsified asphalt systems, the amino-coupled modified PMMA nanospheres used in this invention can effectively improve the overall stiffness and high-temperature deformation resistance of the asphalt system after demulsification, significantly reduce the penetration of emulsified asphalt residues and significantly increase the softening point, thereby significantly improving high-temperature rutting resistance.

[0024] While improving high-temperature performance, the emulsified asphalt of this invention still maintains good low-temperature ductility. The flexible characteristics of the grafted PEG segments and the uniform dispersion of nanospheres in the asphalt enable the system to still have good strain coordination and energy dissipation capabilities under low-temperature conditions. The ductility of the residue after demulsification is significantly higher than that of traditional emulsified asphalt and inorganic nanoparticle Pickering emulsified asphalt, which is beneficial to improving the low-temperature crack resistance of road materials. Attached Figure Description

[0025] Figure 1 The image shows a fluorescence micrograph of the emulsified asphalt prepared in Example 1.

[0026] Figure 2 The image shows a fluorescence micrograph of the emulsified asphalt prepared in Example 2.

[0027] Figure 3 The image shows a fluorescence micrograph of the emulsified asphalt prepared in Example 3.

[0028] Figure 4 Fluorescence micrograph of the emulsified asphalt prepared in Comparative Example 1.

[0029] Figure 5Fluorescence micrograph of the emulsified asphalt prepared in Comparative Example 2.

[0030] Figure 6 Fluorescence micrograph of the emulsified asphalt prepared in Comparative Example 3. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] Unless otherwise specified, all raw materials used in the embodiments are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0033] The raw materials used in the following embodiments and comparative examples are described below: The carboxylated polymethyl methacrylate nanospheres have a particle size of 50-200 nm (as measured by dynamic light scattering DLS) and a carboxyl density of 0.1 mmol / g.

[0034] The amino-terminated polyethylene glycol has the following properties: purity > 95% (HPLC), amine value: 0.6 mmol / g (titration method), and moisture content: < 1% (Karl Fischer method).

[0035] The epoxidized soybean oil has an epoxy value of 6.4-6.6% (ASTM D1652), an iodine value of ≤3gI2 / 100g (ASTM D1959), and a refractive index (25℃) of 1.470-1.473 (ASTM D1218).

[0036] The volatile matter content of Irganox 1010 (105°C, 2h): ≤0.5% (ASTM D4571).

[0037] Example 1: A method for preparing a mixture of polymethyl methacrylate nanospheres and Pickering emulsified asphalt, comprising the following steps: (1) Amino coupling modification of polymethyl methacrylate nanospheres Take 4.0 g of carboxylated polymethyl methacrylate nanospheres (total carboxyl group of 0.4 mmol) and disperse them in 100 mL of 2-morpholine ethanesulfonic acid (MES) buffer (0.05 mol / L, pH 6.15). Stir magnetically at room temperature (500 rpm, 15 min) to form a dispersion system.

[0038] 0.069 g (0.60 mmol) of N-hydroxysuccinimide (NHS) and 0.115 g (0.60 mmol) of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) were added sequentially to the above dispersion. The molar ratio of EDC:COOH was controlled to be ≈1.5:1 and the molar ratio of NHS:EDC was controlled to be 1:1. The mixture was stirred at 500 rpm at 25 °C for 30 min to activate the nanospheres, thereby converting the carboxyl groups on the surface of the nanospheres into active NHS ester intermediates.

[0039] Subsequently, 1.33 g of amino-terminated polyethylene glycol was added to the system, bringing the amino group dosage to approximately 0.80 mmol (approximately twice the molar amount of the carboxyl group). The pH of the system was adjusted and maintained at neutral conditions of 7.0 by adding 0.01 mol / L NaOH solution dropwise to improve the nucleophilic reaction efficiency of the amino group with the active NHS ester intermediate. The reaction was continued at room temperature for 2 h to complete the amidation coupling reaction between the carboxyl and amino groups, yielding amino-coupled modified PMMA nanospheres with PEG segments grafted onto the surface.

[0040] After the reaction was completed, the modified PMMA nanospheres were first removed by centrifugation at 3,000×g for 10 min; then, they were recovered by centrifugation at 10,000×g for 30 min. The resulting precipitate was washed twice (50 mL each time) with a 0.15 wt% poloxamer 407 aqueous solution to remove unreacted small molecule byproducts and to prevent irreversible aggregation of the modified PMMA nanospheres during the washing process.

[0041] Finally, the washed modified PMMA nanospheres were redispersed in 100 mL of poloxamer 407 aqueous solution (concentration of 0.15 wt%) and ultrasonically treated (40 kHz, 10 min) to obtain an amino-coupled modified PMMA nanosphere dispersion with a mass fraction of 4 wt%.

[0042] (2) Preparation of emulsified asphalt S1 Preparation of aqueous phase: Take 4 wt% of the amino-coupled modified PMMA nanosphere dispersion obtained in step (1), heat it to 80°C, stir for 10 minutes to form an aqueous phase; S2 Preparation of Asphalt Phase: Take 100g of 70# base asphalt and heat it to 140℃ to melt it. Then add 5g of epoxidized soybean oil and 0.10g of Irganox1010. Shear the mixture at 3,000rpm for 10min at 140℃ using a high-shear emulsifier (IKAT25) to obtain a homogeneous asphalt phase. S3 Emulsification: Take 100g each of the asphalt phase obtained in step S2 and the aqueous phase obtained in step S1 and inject them into a high-shear emulsifier (IKAT25). Shear at 12,000 rpm for 3 minutes. After the system cools down to 90°C, perform ultrasonic treatment (20kHz, 400W) for 3 minutes. After the system cools down to 60°C, shear at 5,000 rpm for 5 minutes to obtain the emulsion. S4 Post-processing: The emulsion is passed through a 200-mesh metal sieve to remove impurities, then transferred to a sealed reactor and matured at 50°C for 48 hours. This allows the PEG segments grafted onto the PMMA nanospheres to form a stable composite interface layer at the oil-water interface through physical adsorption, molecular entanglement, and polar interactions with the polar components and epoxidized soybean oil in the asphalt. This further improves the storage stability of the emulsified asphalt, ultimately yielding the finished product of Pickering emulsified asphalt compounded with polymethyl methacrylate nanospheres. The finished product should be stored in a cool, dark environment, avoiding temperatures above 50°C.

[0043] Example 2: A method for preparing a mixture of polymethyl methacrylate nanospheres and Pickering emulsified asphalt, comprising the following steps: (1) Amino coupling modification of polymethyl methacrylate nanospheres Take 5.0 g of carboxylated polymethyl methacrylate nanospheres (total carboxyl group of 0.50 mmol) and disperse them in 100 mL of 2-morpholine ethanesulfonic acid (MES) buffer (0.05 mol / L, pH=6.15). Stir magnetically at room temperature (500 rpm, 15 min) to form a dispersion system.

[0044] 0.086 g (0.75 mmol) of N-hydroxysuccinimide (NHS) and 0.144 g (0.75 mmol) of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) were added sequentially to the above dispersion. The molar ratio of EDC to carboxyl groups was controlled to be approximately 1.5:1, and the molar ratio of NHS to EDC was 1:1. The mixture was stirred at 500 rpm at 25 °C for 30 min to activate the nanospheres, thereby converting the carboxyl groups on the surface of the nanospheres into active NHS ester intermediates.

[0045] Subsequently, 1.67 g of amino-terminated polyethylene glycol was added to the system, corresponding to an amino group dosage of approximately 1.00 mmol, resulting in a molar ratio of amino to carboxyl groups of approximately 2:1. The pH of the system was adjusted and maintained at neutral conditions of 7.0 by adding 0.01 mol / L NaOH solution dropwise to improve the nucleophilic reaction efficiency of the amino group with the active NHS ester intermediate. The reaction was continued at room temperature for 2 h to complete the amidation coupling reaction between the carboxyl and amino groups, yielding amino-coupled modified PMMA nanospheres with PEG segments grafted onto their surface.

[0046] After the reaction was completed, the modified PMMA nanospheres were first removed by centrifugation at 3,000×g for 10 min, and then recovered by centrifugation at 10,000×g for 30 min. The resulting precipitate was washed twice (50 mL each time) with a 0.15 wt% poloxamer 407 aqueous solution to remove unreacted small molecule byproducts and to avoid irreversible aggregation of the modified PMMA nanospheres during the washing process.

[0047] Finally, the washed modified PMMA nanospheres were redispersed in 100 mL of poloxamer 407 aqueous solution (concentration of 0.15 wt%) and ultrasonicated (40 kHz, 10 min) to obtain a dispersion of amino-coupled modified PMMA nanospheres with a mass fraction of 5 wt%.

[0048] (2) Preparation of emulsified asphalt This step is exactly the same as the preparation step of emulsified asphalt in Example 1. The only difference is that the mass fraction of the amino-coupled modified PMMA nanosphere dispersion used is different, which is 5 wt%.

[0049] Example 3: A method for preparing a mixture of polymethyl methacrylate nanospheres and Pickering emulsified asphalt, comprising the following steps: (1) Amino coupling modification of polymethyl methacrylate nanospheres Take 6.0 g of carboxylated polymethyl methacrylate nanospheres (total carboxyl group of 0.60 mmol) and disperse them in 100 mL of 2-morpholine ethanesulfonic acid (MES) buffer (0.05 mol / L, pH=6.15). Stir magnetically at room temperature (500 rpm, 15 min) to form a dispersion system.

[0050] 0.104 g (0.90 mmol) of N-hydroxysuccinimide (NHS) and 0.173 g (0.90 mmol) of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) were added sequentially to the above dispersion. The molar ratio of EDC to carboxyl groups was controlled to be approximately 1.5:1, and the molar ratio of NHS to EDC was 1:1. The mixture was stirred at 500 rpm at 25 °C for 30 min to activate the nanospheres, thereby converting the carboxyl groups on the surface of the nanospheres into active NHS ester intermediates.

[0051] Subsequently, 2.00 g of amino-terminated polyethylene glycol was added to the system, corresponding to an amino group dosage of approximately 1.20 mmol, resulting in a molar ratio of amino to carboxyl groups of approximately 2:1. The pH of the system was adjusted and maintained at neutral conditions of 7.0 by adding 0.01 mol / L NaOH solution dropwise to improve the nucleophilic reaction efficiency of the amino group with the active NHS ester intermediate. The reaction was continued at room temperature for 2 h to complete the amidation coupling reaction between the carboxyl and amino groups, yielding amino-coupled modified PMMA nanospheres with PEG segments grafted onto their surface.

[0052] After the reaction was completed, the modified PMMA nanospheres were first removed by centrifugation at 3,000×g for 10 min, and then recovered by centrifugation at 10,000×g for 30 min. The resulting precipitate was washed twice (50 mL each time) with a 0.15 wt% poloxamer 407 aqueous solution to remove unreacted small molecule byproducts and to avoid irreversible aggregation of the modified PMMA nanospheres during the washing process.

[0053] Finally, the washed modified PMMA nanospheres were redispersed in 100 mL of poloxamer 407 aqueous solution (concentration of 0.15 wt%) and ultrasonicated (40 kHz, 10 min) to obtain an amino-coupled modified PMMA nanosphere dispersion with a mass fraction of 6 wt%.

[0054] (2) Preparation of emulsified asphalt This step is exactly the same as the preparation step of emulsified asphalt in Example 1. The only difference is that the mass fraction of the amino-coupled modified PMMA nanosphere dispersion used is different, which is 6 wt%.

[0055] Comparative Example 1 This comparative example provides a nano-SiO2-Pickering emulsified asphalt. Its preparation method includes the following steps: (1) Hydrophobic modification of nano-SiO2 5.0 g of nano-SiO2 (average particle size 50 nm) was added to 200 mL of anhydrous ethanol and ultrasonically treated at room temperature (40 kHz, 10 min) to form a dispersion system. Then, 0.50 g of KH-570 silane coupling agent (nano-SiO2 to KH-570 mass ratio 10:1) was added to the system and mixed evenly under magnetic stirring.

[0056] The above mixture was heated to 60°C and stirred continuously under reflux for 2 hours to allow KH-570 to undergo a condensation reaction with the hydroxyl groups on the surface of nano-SiO2, thereby introducing hydrophobic organosilanes onto the surface of nano-SiO2.

[0057] After the reaction was completed, the product was cooled to room temperature and collected by centrifugation. The product was then washed twice with anhydrous ethanol to remove unreacted silane coupling agent and byproducts. The resulting solid was then vacuum dried at 60°C for 12 hours to obtain 5.0 g of hydrophobically modified nano-SiO2 particles for later use.

[0058] (2) Preparation of nano-SiO2-Pickering emulsified asphalt S1 Preparation of aqueous phase: Take 90g of deionized water and heat it to 70-80℃. Stir mechanically at 500rpm for 10min. Then add 1.0g of 37wt% hydrochloric acid and 4.0g of Span-80. Continue stirring at 70-80℃ for 10min to obtain the aqueous phase system. Adjust the pH of the aqueous phase to 2-3.

[0059] S2 Preparation of Asphalt Phase: Take 100g of 70# base asphalt and heat it to 140℃ to melt it, and obtain an asphalt phase with good fluidity.

[0060] S3 Emulsification: Start the high-shear emulsifier (IKAT25) and set the shear speed to 15,000 rpm. Slowly inject the 140℃ molten asphalt phase obtained in step S2 into the aqueous phase of step S1 at an oil-water mass ratio of 1:1; at the same time, add 5.0 g of hydrophobic modified nano-SiO2 prepared in step (1). Continue emulsification under high shear conditions for 15 min, control the system temperature at 80-90℃ during the emulsification process, and maintain the system pH at 2-3, so that the hydrophobic modified nano-SiO2 is adsorbed at the oil-water interface to form a Pickering stable layer, and obtain the emulsified asphalt emulsion.

[0061] S4 Post-processing: While the emulsion is still warm, filter it through a 200-mesh metal sieve to remove impurities and large particles. After cooling to room temperature, the nano-SiO2-Pickering emulsified asphalt product is obtained. The finished product should be stored in a cool, dark environment, avoiding temperatures above 50°C.

[0062] Comparative Example 2 This comparative example provides a conventional emulsified asphalt material. Its preparation method includes the following steps: Preparation of the aqueous phase (S1): Add 90g of deionized water to a heat-resistant reaction vessel and heat to 60℃. Under mechanical stirring (500rpm), add 6.0g of CTAB and 2.0g of calcium chloride sequentially, and continue stirring for 10min until completely dissolved. Then add 2.0g of 37wt% hydrochloric acid to adjust the pH of the aqueous phase to 2-3, and continue stirring at 60℃ for 5min to obtain an acidic aqueous phase system.

[0063] S2 Preparation of Asphalt Phase: Take 100g of 70# base asphalt and heat it to 140℃ until it is completely melted and kept at a constant temperature to obtain an asphalt phase with good fluidity.

[0064] S3 Emulsification: The aqueous phase obtained in step S1 is maintained at 60°C. The molten asphalt phase obtained in step S2 at 140°C is slowly added to the aqueous phase at a mass ratio of oil phase to aqueous phase of 1:1. The mixture is then transferred to a colloid mill and emulsified for 5 minutes under high-speed shear conditions (2500 rpm). This allows the asphalt droplets to form a dispersion system under the stabilizing effect of cationic emulsifiers and inorganic salts, resulting in an emulsified asphalt emulsion.

[0065] S4 Post-treatment: After emulsification, cool the resulting emulsion to room temperature. If necessary, filter it through a 200-mesh metal sieve to remove impurities, obtaining the traditional cationic emulsified asphalt product. Store the finished product in a cool, dark environment, avoiding temperatures above 50°C.

[0066] Comparative Example 3: A method for preparing a polymethyl methacrylate nanosphere-based Pickering emulsified asphalt Compared to Example 1, this comparative example omits step (1) and directly uses carboxylated polymethyl methacrylate nanospheres to prepare emulsified asphalt. The steps for preparing emulsified asphalt are exactly the same as those in Example 1, except that the steps for preparing the aqueous phase are different, specifically: 4 g of carboxylated polymethyl methacrylate nanospheres (total carboxyl group of 0.4 mmol) were dispersed in 100 mL of poloxamer 407 aqueous solution (concentration of 0.15 wt%) and ultrasonically treated (40 kHz, 10 min) to obtain a carboxylated PMMA nanosphere dispersion with a mass fraction of 4 wt%. The 4 wt% carboxylated PMMA nanosphere dispersion was then heated to 80 °C and stirred for 10 min to obtain an aqueous phase.

[0067] Comparative Example 4: A method for preparing a polymethyl methacrylate nanosphere-based Pickering emulsified asphalt, comprising the following steps: (1) Amino coupling modification of polymethyl methacrylate nanospheres Take 2.0 g of carboxylated polymethyl methacrylate nanospheres (total carboxyl group of 0.20 mmol) and disperse them in 100 mL of 2-morpholine ethanesulfonic acid (MES) buffer (0.05 mol / L, pH 6.15). Stir magnetically at room temperature (500 rpm, 15 min) to form a dispersion system.

[0068] 0.035 g (0.30 mmol) of N-hydroxysuccinimide (NHS) and 0.058 g (0.30 mmol) of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) were added sequentially to the above dispersion, with the molar ratio of EDC:COOH controlled at approximately 1.5:1 and the molar ratio of NHS:EDC at 1:1. The mixture was stirred at 500 rpm at 25 °C for 30 min to activate the nanospheres, thereby converting the carboxyl groups on the surface of the nanospheres into active NHS ester intermediates.

[0069] Subsequently, 0.67 g of amino-terminated polyethylene glycol was added to the reaction system, bringing the amino group dosage to approximately 0.40 mmol (approximately twice the molar amount of the carboxyl group). The pH of the system was adjusted and maintained at neutral conditions of 7.0 by adding 0.01 mol / L NaOH solution dropwise to promote the nucleophilic reaction efficiency of the amino group with the active NHS ester intermediate. The reaction was continued at room temperature for 2 h to complete the amidation coupling reaction between the carboxyl and amino groups, yielding amino-coupled modified PMMA nanospheres with PEG segments grafted onto their surface.

[0070] After the reaction was completed, the modified PMMA nanospheres were first removed by centrifugation at 3,000×g for 10 min, and then recovered by centrifugation at 10,000×g for 30 min. The resulting precipitate was washed twice (50 mL each time) with a 0.15 wt% poloxamer 407 aqueous solution to remove unreacted small molecule byproducts and to prevent irreversible aggregation of the modified PMMA nanospheres during the washing process.

[0071] Finally, the washed modified PMMA nanospheres were redispersed in 100 mL of poloxamer 407 aqueous solution (concentration of 0.15 wt%) and ultrasonically treated (40 kHz, 10 min) to obtain a 2 wt% amino-coupled modified PMMA nanosphere dispersion.

[0072] (2) Preparation of emulsified asphalt This step is exactly the same as the preparation step of emulsified asphalt in Example 1. The only difference is that the mass fraction of the amino-coupled modified PMMA nanosphere dispersion used is different, which is 2wt%.

[0073] Test case The properties of the emulsified asphalt in each embodiment and comparative example were tested, and the test indicators were storage stability, penetration, softening point, ductility, and microstructure. The test methods are as follows: Storage stability: The storage stability of emulsified asphalt was tested using the storage stability test of emulsified asphalt (T0655-1993) in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTGE20-2011).

[0074] Penetration (25℃): According to the asphalt penetration test (T0604-2011) in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTGE20-2011), the penetration of the evaporation residue after emulsification of emulsified asphalt was determined under the conditions of 25℃, 100g load and 5 seconds penetration time (unit: 0.1mm).

[0075] Softening point (ring and ball method): Referring to the asphalt softening point test (T0606-2011), the high-temperature stability of the residue after emulsified asphalt demulsification is characterized by the temperature (unit: °C) at which a steel ball sinks 25.4 mm.

[0076] Ductility (5℃): According to the asphalt ductility test (T0605-2011) in the specification, the elongation fracture length (unit: cm) of the residue after the emulsified asphalt is broken is determined in a constant temperature water bath at 5℃ with a tensile rate of 5cm / min to evaluate the low-temperature plasticity and crack resistance of asphalt.

[0077] Fluorescence microscopy experiments: Emulsified asphalt samples from Examples 1-3 and Comparative Examples 1-3 were selected and stored at room temperature for 5 days before sampling. The samples were stained with Nile Red (final concentration 0.5 μg / mL) and allowed to stand in the dark for 10 minutes. A clean glass slide was placed with a 150 μm thick spacer to form a shallow cavity. 5-10 μL of the staining emulsion was gently added, covered with a coverslip, and sealed with clear nail polish. The morphology and distribution of the emulsified asphalt were observed and imaged using a fluorescence microscope (10× objective, 40× eyepiece, excitation wavelength 540-560 nm).

[0078] The test results are shown in Table 1.

[0079] Table 1 According to the data in Table 1, the 1-day and 5-day storage stability of Examples 1-3 were significantly better than those of Comparative Examples 1-3, while the storage stability of Comparative Example 4 deteriorated significantly. Specifically, the 1-day storage stability of Examples 1-3 was 0.2%-0.3%, and the 5-day storage stability was 0.4%-0.8%, both far below the standard requirements of 1-day ≤1% and 5-day ≤5%, with Example 3 showing the lowest 5-day stability (0.4%), indicating that no significant stratification or sedimentation occurred during long-term storage. In contrast, the 1-day storage stability of Comparative Examples 1-3 was 0.6%-0.9%, and the 5-day storage stability was 3.1%-4.3%, both significantly higher than those of Examples 1-3, and close to or near the upper limit of the standard, indicating that traditional emulsified systems and nano-SiO2-Pickering emulsified asphalt are prone to stratification and sedimentation during standing. Although Comparative Example 3 introduced carboxylated PMMA nanospheres, its 1-day and 5-day storage stability decreased (by 0.6% and 3.1%, respectively). Adding only unmodified PMMA nanospheres could mitigate stratification to some extent, but the improvement was limited. Comparative Example 4 achieved 1.9% and 5.7% storage stability at 1-day and 5-day, respectively, significantly higher than Examples 1-3 and Comparative Examples 1-3. Furthermore, its 5-day stability exceeded the specification limit of 5%, indicating that when the amount of amino-coupled modified PMMA nanospheres was reduced to the level of Comparative Example 4, the particle coverage at the oil-water interface was insufficient, making it difficult to form a continuous and dense Pickering stable layer, thus leading to a significant decrease in system stability. In summary, within a reasonable particle dosage range (Examples 1-3), the storage stability of the amino-coupled modified PMMA nanosphere-based Pickering emulsion system was improved. However, when the particle dosage was too low (Comparative Example 4), the system stability not only failed to improve but also deteriorated, further demonstrating that the present invention has a clearly defined suitable particle dosage range.

[0080] Regarding post-demulsification performance, the penetration of Examples 1-3 was significantly lower than that of Comparative Examples 1-3. The penetration of Examples 1-3 was 59-63, while the penetration of Comparative Examples 1 and 2 was 72 and 76, respectively. This indicates that the traditional emulsified asphalt system without added PMMA nanospheres is relatively soft and more prone to permanent deformation at high temperatures. Comparative Example 3, due to the addition of carboxylated PMMA nanospheres, reduced its penetration to 70, showing some improvement over Comparative Examples 1-2, but still significantly higher than the Examples 1-3. This indicates that the participation of carboxylated PMMA nanospheres alone cannot sufficiently improve the high-temperature deformation resistance of asphalt. Example 3 had the lowest penetration (59), corresponding to the best high-temperature rutting resistance, proving the effectiveness of grafted PMMA nanospheres in enhancing the stiffness of asphalt. The penetration of Comparative Example 4 was 74, even higher than Comparative Examples 1 and 3, and close to Comparative Example 2. This indicates that when the particle dosage is low and the emulsion system is unstable, the grafted PMMA nanospheres are unable to construct an effective spatial skeleton and interfacial reinforcement structure in the continuous phase of asphalt, resulting in the failure to demonstrate high-temperature stiffness and rutting resistance. This further demonstrates that the expected reinforcement effect of this invention cannot be achieved when there is only a "grafted structure" but insufficient particle dosage.

[0081] The softening point results also reflect the above trend. The softening points of Examples 1-3 were 57-62℃, which is about 4-10℃ higher than that of Comparative Examples 1-2 (52-53℃), indicating that amino-coupled modified PMMA nanospheres significantly improve the high-temperature resistance of asphalt. Among them, Example 3 had the highest softening point (62℃), which corresponds to its lowest penetration, indicating that the system has the best deformation resistance under high-temperature conditions. The softening point of Comparative Example 3 was 56℃, which is between that of the conventional Comparative Examples 1-2 and the Examples, indicating that using only unmodified carboxylated PMMA nanospheres can improve the softening point to a certain extent, but the improvement is significantly smaller than that of Examples 1-3. The softening point of Comparative Example 4 was 54℃, which is only slightly higher than that of Comparative Examples 1-2, but significantly lower than that of Examples 1-3 and Comparative Example 3, indicating that when the amount of grafted PMMA nanospheres is too low, a stable composite interface layer and particle skeleton structure cannot be fully constructed, and the gain on the high-temperature resistance of asphalt is extremely limited, even approaching the level of conventional emulsified asphalt.

[0082] From the perspective of ductility, the ductility of Examples 1-3 after demulsification remained at 19-22 cm, a significant improvement compared to 12-15 cm in Comparative Examples 1-2. This indicates that the amino-coupled modified PMMA nanospheres not only improved the high-temperature stiffness of asphalt but also maintained good ductility and crack resistance at low temperatures. Example 1 exhibited the highest ductility, achieving good low-temperature flexibility while ensuring sufficient high-temperature stability. Comparative Examples 1 and 2, which did not use PMMA nanospheres, had lower ductility and were more prone to brittle cracking at low temperatures. The ductility of Comparative Example 3 was approximately 17 cm, showing some improvement over Comparative Examples 1-2, but still lower than Examples 1-3, indicating that the unmodified PMMA nanospheres had a limited effect on improving low-temperature toughness. The ductility of Comparative Example 4 was 16 cm, which was only slightly higher than that of Comparative Example 2, but lower than that of Examples 1-3 and Comparative Example 3. This further indicates that under the conditions of insufficient particle dosage and poor stability of the emulsion itself, PMMA nanospheres grafted with PEG segments are difficult to form a continuous flexible network structure, and their improvement effect on low-temperature toughness and crack resistance is also significantly weakened.

[0083] Based on the results of fluorescence microscopy experiments ( Figures 1-6 As can be seen, after 5 days, the emulsified asphalt droplets of Examples 1-3 remained uniformly dispersed in the aqueous phase, with a narrow particle size distribution. No obvious agglomeration or large-scale aggregation was observed, and the interface structure was stable, confirming its excellent storage stability. In contrast, the droplet distribution of Comparative Examples 1 and 2 was uneven, with large differences in particle size. Obvious droplet aggregation and fusion occurred in local areas, indicating that traditional emulsification systems are prone to severe particle aggregation and stratification during standing. Although Comparative Example 3 contained carboxylated PMMA nanospheres, some droplet aggregation and particle size increase could still be observed in the fluorescence microscopy. The interface structure stability was significantly weaker than that of the examples, indicating that the emulsification system constructed solely by PMMA nanospheres without amino coupling modification is insufficient to achieve the stability required for long-term storage. Based on the combined storage stability data and microscopic morphology, it can be inferred that the amidation coupling of amino-terminated polyethylene glycol and carboxyl groups on the surface of PMMA nanospheres achieved through the EDC / NHS system in the examples is the key factor that significantly improves storage stability and overall road performance.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing polymethyl methacrylate nanospheres compounded with Pickering emulsified asphalt, characterized in that, Includes the following steps: S1. Amino-coupled modified polymethyl methacrylate nanospheres are dispersed in an aqueous solution of a nonionic surfactant and sonicated to obtain a nanosphere dispersion with a mass concentration of 4%-6%. The nanosphere dispersion is then heated to 80-90℃ and used as the aqueous phase. S2 involves heating the base asphalt to 130-150℃ to melt it, then adding plasticizers and antioxidants, and shearing and mixing to obtain a homogeneous asphalt phase; S3 mixes the asphalt phase and water phase at a weight ratio of 5~6:4~5, performs high-speed shearing, ultrasonication, and secondary high-speed shearing. After removing impurities by passing through a 200-mesh sieve, it is transferred to a closed reaction vessel and matured at 40-50℃ for 6-48 hours to obtain the polymethyl methacrylate nanosphere compound Pickering emulsified asphalt. The amino-coupled modified polymethyl methacrylate nanospheres are obtained by amidation coupling reaction of carboxylated polymethyl methacrylate nanospheres and amino-terminated polyethylene glycol.

2. The preparation method according to claim 1, characterized in that, The preparation method of the amino-coupled modified polymethyl methacrylate nanospheres includes: Carboxylated polymethyl methacrylate nanospheres were dispersed in 2-morpholine ethanesulfonic acid buffer. First, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added and stirred for 15-30 min to activate the mixture. Then, amino-terminated polyethylene glycol was added, and the pH of the system was adjusted to 6.5-7.

0. The reaction was carried out for 1-4 h to complete the amidation coupling reaction. After the reaction was completed, the mixture was centrifuged and washed to obtain amino-coupled modified polymethyl methacrylate nanospheres.

3. The preparation method according to claim 2, characterized in that, The carboxyl group density of the carboxylated polymethyl methacrylate nanospheres is 0.03-0.3 mmol / g, preferably 0.1-0.3 mmol / g; and / or The 2-morpholine ethanesulfonic acid buffer solution has a concentration of 0.05 mol / L and a pH of 6.0-6.2; and / or The molar ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to N-hydroxysuccinimide is 1:1; the molar ratio of the total carboxyl groups of the carboxylated polymethyl methacrylate nanospheres to the molar ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:1.5; and / or The amine value of the amino-terminated polyethylene glycol is 0.6-0.8 mmol / g by titration; preferably, the ratio of the total amount of amine groups in the amino-terminated polyethylene glycol to the total amount of carboxyl groups in the carboxylated polymethyl methacrylate nanospheres is 2:

1.

4. The preparation method according to claim 1, characterized in that, The nonionic surfactant is poloxamer, and its aqueous solution has a concentration of 0.1-0.2 wt%.

5. The preparation method according to claim 4, characterized in that, The nonionic surfactant is at least one of poloxamer 407, poloxamer 188, poloxamer 64, poloxamer 108, and poloxamer 64.

6. The preparation method according to claim 1, characterized in that, The mass concentration of the nanosphere dispersion is 5%.

7. The preparation method according to claim 1, characterized in that, Step S3 is as follows: mix the asphalt phase and the water phase at a weight ratio of 5~6:4~5, and shear at high speed of 12,000±500 rpm for 3-5 minutes; after the system cools down to 80-90℃, sonicate for 3 minutes; after the system cools down to 50-60℃, shear at high speed of 5,000 rpm for 3-5 minutes; after passing through a 200-mesh sieve to remove impurities, transfer it to a closed reaction vessel and mature at 40-50℃ for 6-48 hours to obtain the polymethyl methacrylate nanosphere compound Pickering emulsified asphalt.

8. The preparation method according to claim 7, characterized in that, asphalt In the mixture obtained by mixing the aqueous phase and the aqueous phase, the mass fraction of amino-coupled modified polymethyl methacrylate nanospheres is 2%-3%, preferably 2.5%.

9. The preparation method according to claim 1, characterized in that, The base asphalt is at least one of 70# base asphalt and 90# base asphalt.

10. The preparation method according to claim 1, characterized in that, The plasticizer accounts for 3%-5% of the mass of the base asphalt, and the plasticizer is at least one of epoxidized soybean oil, epoxidized linseed oil, epoxidized rapeseed oil, epoxidized palm oil, and epoxidized fatty acid methyl ester. The antioxidant accounts for 0.05%-0.1% of the mass of the base asphalt, and the antioxidant is at least one selected from pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3,5-di-tert-butyl-4-hydroxyphenylpropionate, N,N′-hexamethylenebis-3,5-di-tert-butyl-4-hydroxyphenylpropionamide, and thiodipropionate.

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