Method for synergistically modifying asphalt through nitrogen-doped biomass carbon dots and SBS and modified asphalt

Abstract

The invention discloses a method for synergistically modifying asphalt through nitrogen-doped biomass carbon dots and SBS and modified asphalt, and relates to the technical field of preparation of asphalt for road engineering. The method comprises the following steps: preparing a carbon dot precursor by taking biomass waste as a raw material, and then adding a nitrogen-containing micromolecular dopant for hydrothermal reaction to prepare nitrogen-doped biomass carbon dots; carbon dots and SBS form composite master batches, and the composite master batches are introduced into matrix asphalt to be mixed and modified to prepare the modified asphalt. According to the invention, asphalt oxidation and SBS degradation are inhibited through excellent free radical capture and ultraviolet shielding capabilities of the carbon dots; polyphenols / hydroxyl / carboxyl and other polar functional groups on the surfaces of the carbon dots are subjected to chemical reaction or pi-pi interaction and hydrogen-bond interaction with SBS styrene blocks and asphalt aromatic components, a multi-phase interpenetrating network is constructed, and compatibility and dispersion are improved; through a technical path of biomass carbon dot preparation, nitrogen doping, an SBS composite master batch method and asphalt synergistic modification, synergistic improvement of high-temperature performance, aging resistance and storage stability is realized.

Description

Technical Field

[0001] This invention relates to the field of asphalt materials technology for road engineering, specifically to a method for synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS, and the modified asphalt. Background Technology

[0002] In recent years, with the continuous growth of traffic demand and the expansion of the highway network, asphalt pavement has become the main pavement form in global highway construction due to its advantages such as simple construction, good driving comfort, and short maintenance cycle. Statistics show that asphalt pavement now accounts for over 90% of all pavements in my country. However, petroleum asphalt, the core material of asphalt pavement, relies on non-renewable petrochemical resources, and its production process involves high energy consumption and large amounts of pollution emissions, necessitating the development of green and sustainable alternative or modification technologies.

[0003] To address the problems of petroleum asphalt's susceptibility to rutting at high temperatures, cracking at low temperatures, and insufficient anti-aging properties during service, polymer modification technology is widely used both domestically and internationally. Among these, SBS (styrene-butadiene-styrene block copolymer) modifiers are widely applied due to their excellent elastic recovery and network reinforcement properties. SBS-modified asphalt exhibits good resistance to rutting and cracking at high temperatures and has been widely used in highways and heavy-duty road systems.

[0004] However, there are still a series of problems to be solved in the practical engineering application of SBS modified asphalt: (1) High cost: SBS is a petrochemical-based polymer material, which is expensive and significantly affected by the fluctuation of crude oil prices, which greatly restricts its large-scale promotion and application. (2) Poor storage stability: SBS and asphalt have limited compatibility. During thermal storage, they are prone to phase separation or aggregation, resulting in uneven distribution of modifiers, which affects the quality of pavement construction and long-term performance. (3) Insufficient aging resistance: Under the combined action of ultraviolet radiation, oxidation and thermal environment, SBS molecular chain segments (especially the polybutadiene part) are prone to breakage, cross-linking or degradation, resulting in asphalt hardening and embrittlement, and shortening its service life.

[0005] Studies have shown that under storage conditions of 160-180℃, the mechanical properties of SBS-modified asphalt decrease significantly over time, and its network structure is gradually destroyed, indicating that the existing system still has shortcomings in long-term durability. To overcome the above problems, researchers have proposed a variety of improvement strategies, including introducing additives, copolymers or nano-reinforcing agents into the SBS-asphalt system. For example: (1) Inorganic nanomaterials: such as nano-clay, silica, etc., are used to improve the dispersibility and thermal stability of SBS, but their compatibility with organic asphalt is limited. (2) Carbon nanomaterials: such as carbon nanotubes, graphene, which enhance the mechanical properties and anti-aging properties of asphalt by strengthening interfacial forces. However, the preparation process of such materials is complicated and expensive, and it is difficult to promote them in large-scale engineering. (3) Organic additives: such as plasticizers and compatibilizers, which can delay phase separation to a certain extent, but there are problems such as environmental unfriendliness or unstable effects.

[0006] Building upon the aforementioned research on modifiers, carbon dots (CDs) have gradually attracted attention as a novel type of carbon nanomaterial. Carbon dots possess characteristics such as small particle size (<10 nm), excellent fluorescence properties, abundant polar functional groups (hydroxyl, carboxyl, and polyphenolic groups) on their surface, and UV absorption and free radical scavenging capabilities. These properties make them show significant application potential in optoelectronic materials, sensors, catalysis, and polymer composites. Existing studies have shown that carbon dots can effectively inhibit the degradation process of polymer materials under light and oxidation conditions and improve the interfacial bonding between the polymer matrix and the modifier.

[0007] In the field of asphalt modification, there have been a few exploratory research attempts, such as: combining graphene quantum dots (GQDs) or petroleum-based carbon dots (CQDs) with SBS, which showed that they could improve the high-temperature performance and storage stability of asphalt; using the Pickering emulsion method to disperse GQDs in the SBS phase and incorporate them into asphalt, which significantly improved the high-temperature modulus and compatibility; and using CQDs / SBS modified asphalt, which demonstrated its advantages in rutting resistance and aging resistance.

[0008] However, these studies still have the following prominent problems: (1) Unsustainable carbon source: Most of the carbon dots reported so far come from graphite, petrochemical products, etc. The preparation process is energy-intensive and costly, which is not conducive to the large-scale application of road engineering. (2) Blank in biomass carbon dot research: Although the preparation of carbon dots using by-products such as straw, lignin, tea residue, and coffee grounds has been successfully applied in catalysis, optoelectronics, medicine and other fields, the surface of these carbon dots is rich in polar groups, showing excellent antioxidant and interfacial activity. However, there has been no systematic research in the field of asphalt modification, and its research mechanism is still unclear.

[0009] For example, Chinese patent application CN120271901A discloses a biomass-activated waste rubber powder material and its preparation method and application. It uses a mixture of bio-oil, biochar, biomass carbon dots, and waste rubber powder, which is then microwave-activated to obtain biomass-activated waste rubber powder. This biomass-activated waste rubber powder is then mixed into waste asphalt to obtain recycled asphalt. CN117487370A discloses a carbon dot antibacterial composite material and its modified asphalt preparation method. It uses a hydrothermal method with DTAC and CTAB as carbon and nitrogen sources to prepare carbon dots, and separates and purifies the CDs solution. Then, zinc oxide in different proportions is dissolved in the purified CDs solution, and the mixture is reacted in a reactor to obtain a ZnO-CDs composite solution, which is then applied to asphalt pavement antibacterial treatment. The above solutions all involve the application of biomass carbon dots in asphalt modification, but none of them have yet achieved the use of biomass waste to prepare carbon dots and synergistically use them with SBS for asphalt modification to improve the high-temperature performance and aging resistance of asphalt.

[0010] Based on the above, this invention aims to provide a method for preparing modified asphalt by synergistic modification of nitrogen-doped biomass carbon dots with SBS, which can introduce biomass carbon dots into the SBS-modified asphalt system. This method aims to reduce the dependence of the existing SBS-asphalt system on petroleum products, achieve high-value utilization of waste biomass, and improve the high-temperature performance and aging resistance of asphalt. Summary of the Invention

[0011] The technical problem to be solved by this invention is to provide a method for synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS, and the modified asphalt itself. The aim is to reduce the cost of asphalt modification by synergistically preparing modified asphalt with biomass carbon dots and SBS, while simultaneously achieving resource utilization of waste biomass and reducing dependence on petrochemical products. Furthermore, it addresses the technical problems of poor storage stability and insufficient aging resistance of traditional SBS-modified asphalt, improving the high-temperature performance and aging resistance of the modified asphalt.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0013] In a first aspect, the present invention provides a method for synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS, specifically comprising the following steps:

[0014] S1. Preparation of biomass carbon dot precursor: After crushing biomass waste, mix it with deionized water, stir and extract, and collect the filtrate as biomass carbon dot precursor.

[0015] S2, Nitrogen Doping and Premixing: Add nitrogen-containing small molecule dopant to the filtrate of S1 and stir until homogeneous;

[0016] S3. Preparation of nitrogen-doped biomass carbon dots by hydrothermal reaction: Transfer the solution of S2 to the reaction vessel and hydrothermally react at 160~220℃ for 4~12h. After the reaction is completed, cool and filter, collect the filtrate, concentrate and purify it to obtain the product.

[0017] S4. Preparation of composite masterbatch: The biomass carbon dots from S3 are sheared and mixed evenly with SBS and rubber additives in a specific ratio. The mixed material is then granulated to obtain the composite masterbatch. The mass ratio of biomass carbon dots to SBS is 1:(4~10), and the amount of rubber additives is 10~30 wt% of the mass of SBS.

[0018] S5. Asphalt Modification: Add the composite masterbatch of S4 to the base asphalt, control the temperature at 160℃~180℃, the rotation speed at 3000~5000rpm, and shear for 15~30min to make the modifier evenly dispersed, thus obtaining the modified asphalt.

[0019] Furthermore, in S1, the mass-to-volume ratio of biomass waste to deionized water is (1~5) g : (20~100) mL. Preferably, the mass-to-volume ratio of biomass waste to deionized water is 3 g : 50 mL.

[0020] Furthermore, in S1, the stirring extraction conditions are: stirring extraction at 60~100℃ for 10~60 min. Preferably, the stirring extraction temperature is 70~90℃; and the stirring extraction time is 20~40 min.

[0021] Furthermore, the biomass waste in S1 includes at least one of tea residue, straw, coffee grounds, and fruit shells. Preferably, the biomass waste is tea residue, which includes green tea residue and black tea residue.

[0022] Furthermore, the nitrogen-containing small molecule dopants in S2 include at least one of DETA (diethylenetriamine) and TETA (triethylenetetramine).

[0023] Furthermore, relative to the volume of the biomass carbon dot precursor solution, the amount of nitrogen-containing small molecule dopant added in S2 is 0.5~5 vol%. Preferably, it is 1~3%.

[0024] Furthermore, the nitrogen-doped biomass carbon dots obtained by S3 have a particle size of 2~6nm, and their surface is rich in -OH (hydroxyl), -COOH (carboxyl), phenolic hydroxyl groups, etc. They have the ability to absorb ultraviolet light in the range of 280~400nm and have a certain DPPH free radical scavenging ability.

[0025] Furthermore, the rubber additives in S4 include silica as a reinforcing filler for the rubber, mixed with sulfur (S), BR-g-MAH (maleic anhydride-grafted cis-butadiene rubber), and Si69 (silane coupling agent). Preferably, based on 100 parts of SBS, it includes: SiO2: 8-15 parts; sulfur: 0.5-2 parts; BR-g-MAH: 1-5 parts; Si69: 1-5 parts.

[0026] Furthermore, the concentration and purification process in S3 is as follows: The collected filtrate (i.e., the crude biomass carbon dot solution) is concentrated using a rotary evaporator and dialyzed for 24-72 hours using a dialysis membrane with NWCO=1000Da to remove small molecule impurities, thereby obtaining the purified biomass carbon dot solution. Preferably, the dialysis time is 48-72 hours.

[0027] Furthermore, in S4, the shear mixing conditions are: shear mixing for 5-15 minutes at a temperature of 160-190℃ and a rotation speed of 3000-5000 rpm. Preferably, it is shear mixing for 10 minutes at 180℃ and 4000 rpm.

[0028] Furthermore, in S4, the granulation process is carried out in a twin-screw extruder, with the extrusion temperature controlled at 160℃~200℃.

[0029] Furthermore, in S4, the particle size of the composite masterbatch is controlled to be 1~5nm by extrusion granulation to ensure metering and subsequent dispersion efficiency.

[0030] Furthermore, in S5, the amount of composite masterbatch added is 2wt% to 6wt% of the base asphalt. Preferably, it is 3wt% to 5wt%.

[0031] Secondly, the present invention provides modified asphalt prepared by the above-mentioned method of synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS.

[0032] The inventive concept and modification principle of this invention are as follows:

[0033] To address the problems of high cost, poor storage stability, and easy aging associated with existing SBS-modified asphalt, the core idea of ​​this invention is as follows: The method uses biomass waste as raw material, incorporating nitrogen-containing small molecules through a hydrothermal reaction to prepare biomass carbon dots. The excellent free radical capture and UV shielding capabilities of these carbon dots inhibit asphalt oxidation and SBS degradation. Then, the biomass carbon dots are introduced into the matrix asphalt in the form of a composite masterbatch formed by the biomass carbon dots and SBS. Simultaneously, the polar functional groups such as polyphenols, hydroxyl groups, and carboxyl groups on the carbon dot surface react chemically with the SBS styrene blocks and asphalt aromatic components, or engage in π-π interactions and hydrogen bonding, improving compatibility and dispersion, and constructing a multi-interpenetrating network of "asphalt-SBS-carbon dots." Through the technical path of "biomass carbon dot preparation, nitrogen incorporation, SBS composite masterbatch method, and asphalt synergistic modification," a synergistic improvement in high-temperature performance, aging resistance, and storage stability can be achieved, while also considering environmental friendliness and cost.

[0034] The core mechanism of this invention lies in the fact that biomass carbon dots in SBS-modified asphalt systems can simultaneously achieve multiple synergistic functions, including promoting chemical crosslinking, regulating interfacial compatibility, and protecting against UV aging. Its core improvement mechanism can be summarized in three points:

[0035] (1) Interfacial interaction enhancement mechanism: The polar groups of carbon dots form multi-point crosslinks with SBS, which improves the interfacial bonding force and the density of the system. At the same time, they combine with the aromatic components of asphalt through hydrogen bonding and π-π conjugation structure to form a crosslinked phase.

[0036] (2) Anti-aging mechanism: Carbon dots scavenge free radicals and absorb ultraviolet light, slowing down the oxidative breakage and degradation of SBS and asphalt molecular chains.

[0037] (3) Structural stability mechanism: The masterbatch method ensures uniform carbon point distribution and good compatibility, which significantly improves storage stability.

[0038] Specifically,

[0039] First, at the chemical structure level, the biomass carbon dots prepared in this invention are rich in active functional groups such as carboxyl groups (—COOH), hydroxyl groups (—OH), phenolic hydroxyl groups (—ArOH), and amino groups (—NH2). These polar groups can chemically react with the double bonds (—C=C—) on the SBS molecular chain under sulfurization conditions, promoting sulfurization crosslinking and bond bridging between SBS segments, thereby improving the network density and structural stability of the system. Simultaneously, the π–π conjugated system of the biomass carbon dots can undergo non-covalent interactions (π–π stacking) with aromatic compounds in asphalt. The hydroxyl and carboxyl groups on their surface can also form hydrogen bonds or van der Waals forces with the polar components of asphalt, thus constructing a stable interfacial coupling layer between the SBS and asphalt phases. This interfacial layer effectively reduces the interfacial tension between SBS and asphalt, inhibits phase separation, and transforms the modified system from a physical blending to a chemical-physical synergistic network structure, significantly improving the system's storage stability and resistance to high-temperature deformation.

[0040] Secondly, regarding anti-aging, the unique electronic structure of the biomass carbon dots prepared in this invention endows them with excellent photochemical stability and free radical scavenging ability. The polyphenolic hydroxyl, amino, and carboxyl groups on the surface of the biomass carbon dots can scavenge reactive free radicals generated during thermo-oxidative aging and ultraviolet aging (such as...) through hydrogen donor reactions. (etc.), terminate the free radical chain reaction, and delay the oxidative chain scission and cross-linking curing of SBS and asphalt molecules. In addition, the π-conjugated structure of carbon dots can effectively absorb and scatter ultraviolet light in the 280~400nm wavelength range, playing a composite role of "ultraviolet absorption-energy dissipation-oxidation blocking", significantly reducing the rate of ultraviolet-induced molecular degradation reaction, thereby achieving long-term protection against photo-oxidative aging.

[0041] Finally, nitrogen doping is also a key step in the preparation of carbon dots in this invention. Adding nitrogen-containing dopants (such as DETA or TETA) to the hydrothermal reaction system allows some nitrogen atoms to be incorporated into the carbon dot framework or surface functional groups in the form of pyrrole nitrogen, graphitic nitrogen, or amino nitrogen. This structural modification not only increases the electron density and polarity of the carbon dots but also endows them with a stronger density of active sites and chemical reactivity, making it easier for them to form chemical bonds with SBS during sulfur crosslinking. Simultaneously, nitrogen doping also enhances the free radical scavenging ability of the carbon dots (by forming stable N–O or N–H bond intermediates) and ultraviolet absorption capacity (due to the increased π-conjugated electron mobility of graphitic nitrogen).

[0042] The present invention has the following beneficial effects:

[0043] The method for synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS provided by this invention specifically involves preparing a carbon dot precursor using biomass waste such as tea residue as raw material, then preparing nitrogen-doped biomass carbon dots through a hydrothermal reaction by adding a nitrogen-containing small molecule dopant; subsequently, introducing the nitrogen-doped biomass carbon dots into an SBS-modified asphalt system for synergistic modification with SBS to prepare modified asphalt. In the mixing modification process, nitrogen-doped biomass carbon dots and SBS are first extruded and granulated to obtain carbon dot / SBS composite masterbatch, which is then added to the matrix asphalt for mixing modification to obtain modified asphalt.

[0044] Compared with the prior art, the present invention has the following technical advantages:

[0045] (1) It adopts green and low-cost carbon sources and the preparation process is simple and controllable, which can reduce production costs and energy consumption.

[0046] This invention utilizes readily available and extremely low-cost biomass waste such as tea residue, straw, lignin, and coffee grounds as carbon sources to prepare biomass carbon dots via a hydrothermal method. This method uses water as the reaction medium, with a low reaction temperature (160~200℃) and short reaction time (4~8h), requiring no high-pressure pyrolysis or complex catalytic conditions. Compared with the preparation of traditional petroleum-based carbon dots or graphene quantum dots, the equipment requirements are simpler, energy consumption is reduced by more than 40%, and the overall preparation cost is only 1 / 5 to 1 / 10 of that of traditional carbon nanomaterials.

[0047] Therefore, this invention achieves high-performance modification while significantly reducing raw material and energy costs, meeting the technological development trend of green, low-carbon, and scalable production.

[0048] (2) Introducing biomass carbon dots and SBS to form a synergistic modification system significantly improves storage stability and dispersion uniformity.

[0049] This invention proposes for the first time a synergistic modification pathway of "carbon dots-SBS composite masterbatch". This involves first combining carbon dots with SBS under high-temperature shear conditions (180±5℃, 3000~5000rpm) before introducing them into the matrix asphalt. This innovative step allows the carbon dots to form primary dispersion nuclei within the SBS phase. The polar functional groups (hydroxyl, carboxyl, phenolic hydroxyl groups) on the carbon dot surface then form π–π interactions and hydrogen bonds with the styrene segments of SBS and the aromatic molecules of the asphalt, enhancing interfacial bonding.

[0050] This "masterbatch preparation followed by asphalt blending" process effectively suppresses phase separation between SBS and asphalt during thermal storage, significantly improving the thermodynamic stability of the system. Experiments show that the biomass carbon dot / SBS synergistic modified asphalt prepared using this invention exhibits a softening point stratification difference of only 0.8–1.9 mm after storage at 180°C for 48 hours, while the stratification difference of traditional SBS modified asphalt is as high as 2.7–4.6 mm. Comprehensive comparison shows that the storage stability of the system proposed in this invention is improved by more than 60–80%, demonstrating significant thermal storage uniformity and phase separation suppression capabilities.

[0051] (3) The multifunctional groups on the surface of carbon dots promote the vulcanization reaction of SBS, construct a three-way interpenetrating network of "asphalt-SBS-carbon dots", and enhance the structural strength.

[0052] The structural formula of biomass carbon dots is shown in formula (I) below, and its surface is rich in various functional groups such as –OH, –COOH, and –NH2:

[0053]

[0054] These polar functional groups on the surface of biomass carbon dots can act as chemically active centers during the shearing stage of the composite masterbatch, participating in the vulcanization and cross-linking reactions of SBS. On the one hand, they promote the vulcanization rate of the polybutadiene segment and increase the cross-linking density; on the other hand, through π-π interactions and hydrogen bond bridging, they realize the construction of a three-phase synergistic network of "carbon dots-SBS-asphalt". This network can effectively disperse applied stress, uniformly transfer load, and form a multi-scale structure with synergistic effects of "elasticity-viscosity-toughness".

[0055] (4) The free radical scavenging and ultraviolet shielding effects of carbon dots significantly delay thermo-oxidative and photo-aging, and improve the durability of materials.

[0056] This invention utilizes the natural polyphenols and nitrogen-doped structure in the carbon dots of tea residue to give them excellent antioxidant and free radical scavenging capabilities: the polyphenols and amide groups on the surface of the carbon dots can provide hydrogen / electron transfer channels to capture free radicals generated during the thermo-oxidative aging of asphalt, thereby terminating the chain oxidation reaction; the π-conjugated structure of the carbon dots has a strong absorption peak, which can shield ultraviolet light and reduce photoaging-induced polymer chain breakage.

[0057] (5) Multi-scale dispersion and interfacial synergy significantly improve high-temperature rutting resistance and low-temperature crack resistance.

[0058] The biomass carbon dots prepared by the method of this invention have a small particle size (2~6nm) and can be uniformly distributed at the interface between SBS and asphalt, playing a role in "energy buffering" and "crack passivation" at the microscopic level. When the temperature rises or under load, the carbon dots can quickly disperse stress and prevent the accumulation of local plastic deformation, thereby improving the high-temperature rutting resistance; at low temperatures, the elastic recovery ability of the carbon dot-SBS network can effectively delay crack initiation.

[0059] (6) It takes into account both environmental benefits and engineering applicability, and can be promoted on a large scale.

[0060] The raw materials for this invention are derived from renewable biomass waste. Water is used as a solvent during the production process, eliminating the need for organic solvents such as toluene and DMF, and resulting in virtually no harmful gas emissions. It is compatible with traditional SBS modification processes and can be implemented directly on existing equipment without additional investment.

[0062] In summary, this invention achieves a unified approach to greening raw materials, stabilizing structure, enhancing performance durability, and reducing carbon emissions through "carbon dot-SBS composite synergistic modification technology." The synergistic effects of these improvements result in materials that significantly outperform existing SBS-modified asphalt in terms of high-temperature stability, storage stability, aging resistance, and mechanical properties, demonstrating clear scientific rationale and engineering application value. This invention utilizes a quadruple synergistic effect of "chemical crosslinking enhancement + interface structure optimization + free radical scavenging + UV shielding" to construct a highly stable, highly compatible, and highly aging-resistant "SBS-carbon dot-asphalt three-phase network structure," thereby comprehensively improving the performance of modified asphalt under high-temperature, low-temperature, and long-term service conditions. Attached Figure Description

[0063] Figure 1 A schematic flowchart illustrating the method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS, provided in this embodiment of the invention.

[0064] Figure 2 This is an electron microscope image of nitrogen-doped biomass carbon dots obtained in an embodiment of the present invention.

[0065] Figure 3 This is a particle size distribution diagram of nitrogen-doped biomass carbon dots obtained in an embodiment of the present invention.

[0066] Figure 4 The infrared spectrum of nitrogen-doped biomass carbon dots obtained in an embodiment of the present invention is shown.

[0067] Figure 5 The image shows the ultraviolet spectrum of nitrogen-doped biomass carbon dots obtained in an embodiment of the present invention. Detailed Implementation

[0068] As used in this article:

[0069] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0070] When a parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1~5” is disclosed, the described range should be interpreted as including ranges “1~4”, “1~3”, “1~2”, “1~2 and 4~5”, “1~3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In these embodiments, unless otherwise specified, portions and percentages are expressed by mass.

[0071] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0072] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0073] like Figure 1 As shown, this invention provides a method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS, the method specifically including the following steps:

[0074] S1. Preparation of biomass carbon dot precursor: After crushing the biomass waste, mix it with deionized water, stir and extract, and collect the filtrate as the biomass carbon dot precursor. The mass-volume ratio of biomass waste to deionized water is (1~5) g : (20~100) mL; the stirring extraction conditions are: 60~100℃ for 10~60 min.

[0075] The biomass waste in this invention includes at least one of tea residue, straw, coffee grounds, and fruit shells. In the following preferred embodiments, tea residue is used as an example, including green tea residue and black tea residue. The green tea residue and black tea residue in the following specific embodiments are byproducts of tea processing or beverage preparation, and their main components include cellulose, hemicellulose, lignin, and polyphenols. Their aromatic skeletons and phenolic hydroxyl groups are conducive to the formation of multifunctional carbon dot structures.

[0076] S2, Nitrogen Doping and Premixing: Add nitrogen-containing small molecule dopant to the filtrate of S1 and stir until homogeneous; relative to the volume of the biomass carbon dot precursor solution, the amount of nitrogen-containing small molecule dopant added in S2 is 0.5~5 vol%, preferably 1~3%.

[0077] The nitrogen-containing small molecule dopant in this invention includes at least one of diethylenetriamine and TETA (triethylenetetramine). In the following preferred embodiments, DETA is used as an example dopant.

[0078] S3. Preparation of nitrogen-doped biomass carbon dots by hydrothermal reaction: The solution of S2 is transferred to a polytetrafluoroethylene (PTFE) lined reactor and hydrothermally reacted at 160~220℃ for 4~12h. After the reaction is completed, the solution is cooled, filtered, and the filtrate is collected to obtain a crude carbon dot solution. The collected crude biomass carbon dot solution is concentrated by rotary evaporator and dialyzed with a dialysis membrane of NWCO=1000Da for 24~72h, preferably 48~72h, to remove small molecule impurities and obtain a purified biomass carbon dot solution.

[0079] The obtained nitrogen-doped biomass carbon dots have a particle size of 2-6 nm and are rich in -OH (hydroxyl), -COOH (carboxyl), phenolic hydroxyl groups, etc. on their surface. They have the ability to absorb ultraviolet light in the range of 280-400 nm and have a certain DPPH free radical scavenging ability.

[0080] S4. Preparation of composite masterbatch: The biomass carbon dots of S3 are sheared and mixed evenly with SBS and rubber additives in a high-speed shearing apparatus in proportion. The shearing and mixing conditions are: temperature 160~190℃, speed 3000~5000rpm for 5~15min.

[0081] The mass ratio of biomass carbon dots to SBS is 1:(4~10), and the total amount of rubber additives is 10~30wt% of the mass of SBS. As a preferred embodiment, the rubber additives include silica as a reinforcing filler for the rubber, mixed with sulfur, BR-g-MAH, and silane coupling agent Si69. Based on 100 parts of SBS, the additives include: SiO2: 8~15 parts; sulfur: 0.5~2 parts; BR-g-MAH: 1~5 parts; Si69: 1~5 parts.

[0082] The mixed material is then granulated using a twin-screw extruder to obtain composite masterbatch. The extrusion temperature is controlled at 160℃~200℃, and the particle size of the composite masterbatch is controlled at 1-5nm to ensure metering and subsequent dispersion efficiency.

[0083] S5. Asphalt Modification: Add the composite masterbatch of S4 to the base asphalt. The amount of composite masterbatch added is 2wt%~6wt% of the base asphalt. Control the temperature at 160℃~180℃, the rotation speed at 3000~5000rpm, and shear for 15~30min to ensure uniform dispersion of the modifier, thus obtaining the modified asphalt. The following examples use 70# asphalt as an example for illustration.

[0084] The following detailed explanation uses specific examples:

[0085] Example 1

[0086] This embodiment provides a method for synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS, the method specifically including the following steps:

[0087] S1. Preparation of biomass carbon dot precursor: 3.0g of green tea residue was crushed, mixed with 50ml of deionized water, and extracted by stirring at 80℃ for 30min. The filtrate was then collected as the biomass carbon dot precursor.

[0088] S2, Nitrogen doping and premixing: Add nitrogen-containing small molecule dopant DETA to the biomass carbon dot precursor (filtrate) in S1. In this example, 1.0 ml of DETA is added and premixed for 5 min with stirring until homogeneous. The amount of DETA added is 2% relative to the volume of the biomass carbon dot precursor solution.

[0089] S3. Preparation of nitrogen-doped biomass carbon dots by hydrothermal reaction: The solution of S2 was transferred to a polytetrafluoroethylene (PTFE) lined reactor and hydrothermally reacted at 180℃ for 6 hours. After the reaction was completed, the solution was cooled, filtered, and the filtrate was collected to obtain a crude carbon dot solution. The collected crude biomass carbon dot solution was concentrated by rotary evaporator and dialyzed for 72 hours using a dialysis membrane with NWCO=1000Da to remove small molecule impurities and obtain a purified biomass carbon dot solution.

[0090] like Figure 2 , 3 As shown, the nitrogen-doped biomass carbon dots prepared by this invention have a uniform particle size distribution, ranging from 2 to 6 nm. Infrared spectroscopy measurements yielded the following results: Figure 4 As shown, based on the structural formula of biomass carbon dots, it can be seen that the surface of the prepared biomass carbon dots is rich in -OH (hydroxyl groups), -COOH (carboxyl groups), phenolic hydroxyl groups, etc. Figure 5As shown in the ultraviolet spectrum, the biomass carbon dots prepared in this embodiment have good absorption capacity for 280-400nm ultraviolet light, and therefore have a certain DPPH free radical scavenging ability.

[0091] S4. Preparation of composite masterbatch: 20 parts of the biomass carbon dot solution from S3, 100 parts of SBS, and rubber additives are mixed uniformly in a high-speed shear apparatus at 180°C, 4000 rpm, and for 10 minutes. The mass ratio of biomass carbon dots to SBS is 1:5. The rubber additives in this invention include silica as a reinforcing filler for rubber, mixed with sulfur (S), BR-g-MAH (maleic anhydride-grafted cis-butadiene rubber), and Si69 (silane coupling agent). As a preferred embodiment, in this embodiment, the rubber additives include: 10 parts of silica, 1.2 parts of sulfur, 3 parts of BR-g-MAH, and 3 parts of Si69.

[0092] The mixed material is then granulated using a twin-screw extruder. The twin-screw extruder barrel consists of a feed section, three intermediate sections, and a discharge section. The temperature of each section is controlled at 160 / 170 / 180 / 190 / 190℃, so that the overall extrusion temperature is controlled within the range of 160℃~200℃, resulting in composite masterbatch. The particle size of the composite masterbatch is controlled to be 1~5 mm to ensure metering and subsequent dispersion efficiency.

[0093] S5. Asphalt Modification: The composite masterbatch of S4 is added to 70# base asphalt, with the amount of composite masterbatch added being 4 wt% of the base asphalt. The temperature is controlled at 170℃, the rotation speed at 4000 rpm, and shearing is performed for 20 minutes to ensure uniform dispersion of the modifier, thus obtaining modified asphalt.

[0094] Example 2

[0095] The difference between this embodiment and Embodiment 1 is that the amount of nitrogen-containing small molecule dopant DETA used in step S2 is 0.5 ml, and the amount of nitrogen-containing dopant added is 1% of the volume of the biomass carbon dot precursor solution.

[0096] The effect of nitrogen doping on the antioxidant capacity of asphalt was verified by adjusting the nitrogen doping amount.

[0097] Example 3

[0098] The difference between this embodiment and Embodiment 1 is that the hydrothermal reaction temperature in step S3 is adjusted to 220°C, the reaction time remains 6 hours, and the other conditions are the same as in Embodiment 1.

[0099] By adjusting the reaction temperature for preparing nitrogen-doped biomass carbon dots via hydrothermal reaction, the feasibility of preparing biomass carbon dots under the upper limit of hydrothermal reaction temperature was verified.

[0100] Example 4

[0101] The difference between this embodiment and Embodiment 1 is that the hydrothermal reaction temperature in step S3 is adjusted to 160°C, the reaction time remains 6 hours, and the other conditions are the same as in Embodiment 1.

[0102] The feasibility of preparing nitrogen-doped biomass carbon dots under the lower limit of hydrothermal reaction temperature was verified by adjusting the reaction temperature of hydrothermal reaction.

[0103] Example 5

[0104] The difference between this embodiment and Embodiment 1 is that the hydrothermal reaction time in step S3 is adjusted to 12 hours, while the reaction temperature remains at 180°C. All other conditions are the same as in Embodiment 1.

[0105] The feasibility of preparing nitrogen-doped biomass carbon dots under the upper limit of hydrothermal reaction time was verified by adjusting the reaction time of the hydrothermal reaction.

[0106] Example 6

[0107] The difference between this embodiment and Embodiment 1 is that the hydrothermal reaction time in step S3 is adjusted to 4 hours, while the reaction temperature remains at 180°C. All other conditions are the same as in Embodiment 1.

[0108] The feasibility of preparing nitrogen-doped biomass carbon dots under the lower limit of hydrothermal reaction time was verified by adjusting the reaction time of the hydrothermal reaction.

[0109] Example 7

[0110] The difference between this embodiment and Embodiment 1 is that the purification time of carbon dots in S3 is adjusted from 72h to 48h; all other conditions are the same as in Embodiment 1. This is to verify the effect of purification time on asphalt properties.

[0111] Example 8

[0112] The difference between this embodiment and Embodiment 1 is that the amount of composite masterbatch added in S5 is adjusted from 4 wt% of the base asphalt mass to 5 wt%; the carbon point purification time remains 72 h, the shear speed is 4000 rpm, and the other conditions are the same as in Embodiment 1. This verifies the effect of the change in masterbatch dosage on asphalt properties.

[0113] Example 9

[0114] The difference between this embodiment and Example 1 is that the shear speed in step S5 is adjusted to 4500 rpm; the carbon point purification time remains 72 h; the composite masterbatch dosage is 4 wt%; and the other conditions are the same as in Example 1. This is to verify the effect of shear speed on asphalt properties during asphalt modification.

[0115] Example 10

[0116] The difference between this embodiment and Embodiment 1 is that the biomass waste green tea residue in step S1 is replaced with black tea residue, while the other conditions are the same as in Embodiment 1. This is to verify the effect of different carbon point sources on asphalt performance.

[0117] To verify the overall technical effect of the present invention and the synergistic effect between the various steps, the present invention also provides the following comparative examples:

[0118] Comparative Example 1: SBS Single Modification

[0119] The difference between this comparative example and Example 1 is that steps S1-S4 are omitted, and in S5, 4 wt% of SBS is directly added to the 70# base asphalt. The modification conditions are the same as those in S5 of Example 1.

[0120] Comparative Example 2: Nitrogen-doped biomass carbon dot single modification

[0121] The difference between this comparative example and Example 1 is that the biomass carbon dot solution obtained in step S3 is directly added to the matrix bitumen at 0.3 wt%, and the other modification conditions are the same as in S5 of Example 1.

[0122] Comparative Example 3: Biomass carbon dots without nitrogen source doping

[0123] The difference between this comparative example and Example 1 is that the process of adding the nitrogen-containing small molecule dopant DETA is omitted, and the biomass carbon dot precursor of S1 is directly introduced into the hydrothermal reaction of S3. Other aspects are the same as in Example 1.

[0124] Comparative Example 4: Biomass carbon dot solution without purification

[0125] The difference between this comparative example and Example 1 is that the biomass carbon dot solution obtained by the hydrothermal reaction in S3 is not purified and is directly mixed with SBS and rubber additives in S4 to prepare masterbatch. The parameters and conditions of S4 and S5 are the same as in Example 1.

[0126] Comparative Example 5: SBS was modified after being prepared into masterbatch with other rubber additives, without the addition of nitrogen-doped biomass carbon dots.

[0127] The difference between this comparative example and Example 1 is that the process of preparing nitrogen-doped biomass carbon dots in S1-S3 is omitted. Instead, the process in S4 is followed. The masterbatch formulation contains only SBS and other rubber additives, including SiO2, S, BR-g-MAH, and Si69, and the mass fractions are the same as in Example 1. The parameters and conditions in S5 are also the same as in Example 1.

[0128] Comparative Example 6:

[0129] The difference between this comparative example and Example 1 is that the carbon dots, SBS, and rubber additives (including 10 parts silica, 1.2 parts sulfur, 3 parts BR-g-MAH, and 3 parts Si69) are not granulated from the composite masterbatch in S4, but are directly incorporated into the base asphalt.

[0130] The modified asphalts prepared in the above embodiments and comparative examples were subjected to performance tests. The test methods for each performance test were carried out in accordance with the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering". The test results are shown in Table 1 below.

[0131]

[0132] The data in Table 1 clearly demonstrate that the method of synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS of the present invention can significantly improve the dispersion uniformity and interfacial stability of carbon dots in the asphalt system, thereby greatly improving the high-temperature rutting resistance, low-temperature crack resistance, UV aging resistance, and long-term storage stability of the modified asphalt. The analysis is based on the data from various embodiments and comparative examples as follows:

[0133] 1. As shown in Table 1, the softening points of Examples 1-10 of the present invention are all within the range of 82.0-90.2℃, significantly higher than the 64.1-73.0℃ of Comparative Examples 1-6, with an overall improvement exceeding 15-25℃. Among them,

[0134] In Example 1, under the conditions of hydrothermal reaction at 180℃ for 6 hours, appropriate nitrogen doping, and thorough purification, the softening point reached 89.6℃. This indicates that under the optimal preparation conditions (hydrothermal reaction at 180℃ for 6 hours + nitrogen doping + thorough dialysis), tea residue carbon dots have higher reactivity and a more complete surface functional group structure, which can form stable cross-linking bonds on SBS segments, thereby improving the system's heat resistance and deformation resistance.

[0135] Example 2, with its lower nitrogen doping content, resulted in fewer amino sites on the carbon dot surface compared to Example 1, leading to a slight decrease in cross-linking degree. This resulted in a reduction in antioxidant capacity and free radical scavenging ability, and a slightly weaker UV shielding. However, it still exhibited superior performance compared to the comparative scheme. This demonstrates that the amount of nitrogen doping in the present invention affects the performance of the prepared modified asphalt. However, within the preferred range of 1-3 vol% of the biomass carbon dot precursor solution volume, the modified asphalt still possesses superior material properties.

[0136] The solutions in Examples 3 and 4 are located at the upper limit (220°C) and lower limit (160°C) of the hydrothermal reaction temperature, respectively. Their softening points are both lower than those in Example 1, indicating that high temperatures lead to the carbonization and deactivation of some functional groups, while low temperatures result in insufficient carbonization, neither of which is conducive to the formation of the optimal cross-linked structure. Therefore, the hydrothermal reaction temperature affects the performance of the modified asphalt prepared, but within the hydrothermal reaction temperature range (160~220°C) of this invention, the modified asphalt still exhibits superior material properties.

[0137] Examples 5 and 6 fall within the upper (12h) and lower (4h) limits of the hydrothermal reaction time, respectively, and their performance is lower than that of Example 1. This indicates that the formation of biomass carbon dots mainly occurs in the initial stage of the reaction, with carbon dots possessing basic structure and function forming in approximately 4 hours. As the reaction time is extended to 6 hours, the number and activity of functional groups on the carbon dot surface reach a relatively optimal state. When the reaction time is further extended to 12 hours, the carbon core structure of the carbon dots tends to stabilize, but some oxygen- and nitrogen-containing functional groups on the surface undergo rearrangement or removal, resulting in a slight decrease in their antioxidant and interface regulation capabilities. Therefore, in the macroscopic asphalt performance test, the modification effects exhibited by carbon dots prepared under 4h and 12h conditions are similar, while the comprehensive performance under the 6h condition is optimal. Thus, the hydrothermal reaction temperature affects the performance of the modified asphalt, but within the hydrothermal reaction time range (4~12h) of this invention, the modified asphalt still possesses superior material properties.

[0138] Examples 7, 8, and 9 respectively adjusted the carbon point purification time in S3, the amount of composite masterbatch added in S5, and the rotation speed of shear mixing modification in S5. The modified asphalt materials obtained still maintained high softening point and ductility. This indicates that the carbon point purification time, the amount of composite masterbatch added, and the rotation speed of shear mixing modification all affect the performance of modified asphalt. However, within the controllable range of the present invention, the modified asphalt obtained can still have superior material properties.

[0139] Example 10 (black tea residue) uses a different type of carbon source than Example 1 (green tea residue), yet it still maintains excellent performance. A comparison between Example 10 and Example 1 demonstrates that the biomass carbon source of the present invention has a wide adaptability range, facilitates local sourcing and cost reduction, and exhibits good universality and stability. This also shows that the carbon dots from tea residue, after hydrothermal preparation, are rich in hydroxyl, carboxyl, and amino groups on their surface, which can undergo cross-linking reactions with the SBS double bond structure. Simultaneously, through π–π conjugation, they combine with the aromatic components of pitch to form a "carbon dot–SBS–pitch" triple interpenetrating network, improving the high-temperature stability of the system at the molecular level.

[0140] 2. By comparing Comparative Examples 1 and 2 with Example 1, it is shown that the synergistic modification of nitrogen-doped biomass carbon dots and SBS is important. The modification effect cannot be well improved by modifying SBS alone or by modifying nitrogen-doped biomass carbon dots alone. If nitrogen-doped biomass carbon dots are not combined with SBS, the dispersion / interface construction will be insufficient, most carbon dots will remain in the bitumen phase, it will be difficult to form a stable network, and the performance will be significantly degraded.

[0141] Comparison of Example 3 and Example 1 shows that the lack of nitrogen source doping in biomass carbon dots leads to a decrease in the free radical scavenging and bridging ability of the prepared modified asphalt due to the absence of nitrogen-containing functional groups.

[0142] The comparison between Comparative Example 4 and Example 1 shows that if biomass carbon dots are not purified by dialysis, low-molecular-weight byproducts will remain, and impurities will cause unstable interfacial activity / agglomeration, resulting in impaired storage stability and aging resistance. This demonstrates the necessity of purifying biomass carbon dots in the solution.

[0143] The comparison between Comparative Example 5 and Example 1 shows that traditional vulcanization and SBS granulation modification alone cannot achieve the comprehensive performance level of the modified asphalt prepared in Example 1 of this invention. This indicates that the triple synergistic effect of CDs' free radical scavenging, cross-linking structure, and ultraviolet shielding is necessary to improve the comprehensive performance of the modified asphalt.

[0144] To further verify the necessity of the step of "preparing a composite masterbatch of biomass carbon dots and SBS before blending it into asphalt" in this invention, Comparative Example 6 was set up: carbon dots and SBS were directly blended into the base asphalt without pretreatment of the composite masterbatch and mixed under high shear. The experimental results in Table 1 show that simply blending carbon dots and SBS directly into asphalt, while improving high and low temperature performance and anti-aging properties to some extent, cannot achieve the comprehensive modification effect of the composite masterbatch process of this invention. On the one hand, under direct blending conditions, carbon dots are prone to agglomeration in the high-viscosity asphalt system, making it difficult to fully penetrate the SBS phase or uniformly distribute at the SBS / asphalt interface. The functional groups on the surface of carbon dots cannot fully participate in the SBS chain vulcanization and interfacial crosslinking reaction, resulting in an incomplete crosslinking network. The high-temperature stability and low-temperature toughness are significantly weaker than in the examples. On the other hand, since the carbon dots were not fixed in the SBS phase by the composite masterbatch, their dispersion and spatial position in the asphalt were unstable. During high-temperature storage, they still showed a tendency to migrate and aggregate, making it difficult to form a stable "carbon dot-SBS-asphalt three-way interpenetrating network." Therefore, their storage stability and resistance to UV aging were significantly lower than in Example 1. In contrast, in Example 1, the carbon dots and SBS were first prepared into a composite masterbatch in a molten state, allowing the carbon dots to be preferentially anchored to the SBS segments and achieve sufficient and stable nano-dispersion within the masterbatch. Subsequently, the composite masterbatch was incorporated into the asphalt, which rapidly constructed a uniform "carbon dot-SBS-asphalt" synergistic crosslinking structure in the asphalt medium, resulting in significant improvements in high-temperature performance, low-temperature performance, UV aging resistance, and storage stability. These comparative results fully demonstrate that adding biomass carbon dots and SBS to the matrix asphalt in the form of a composite masterbatch is one of the key steps in achieving excellent comprehensive performance in the technical solution of this invention and cannot be simply omitted.

[0145] 3. A comparison of the overall data shows that Examples 1-10 are significantly superior to Comparative Examples 1-6 in terms of softening point, ductility at 5°C, penetration ratio after UV aging, and storage stability difference. This indicates that the key technical path of this invention (i.e., "nitrogen-doped biomass carbon dot preparation + composite masterbatch incorporation + interfacial reaction network construction") is the decisive factor in performance improvement. The method provided by this invention can produce modified asphalt with the following performance advantages:

[0146] (1) High temperature stability (softening point)

[0147] The softening points of Examples 1-10 of the present invention are generally between 82-90°C, which is about 15-20°C higher than that of Comparative Examples 1-6 (64-73°C). This is because the carbon dots participate in the chemical crosslinking reaction of SBS, significantly improving the crosslinking density and interfacial adhesion of the system. In particular, the nitrogen-doped carbon dots in Example 1 provide -NH2 active sites, promoting the vulcanization reaction of SBS to form a high-strength network structure, which makes the asphalt exhibit stronger deformation resistance under high-temperature shear and loading. In contrast, Comparative Example 1 (SBS only) and Comparative Example 2 (CDs directly incorporated into asphalt) lack effective chemical bonding, and the carbon dots or SBS are prone to agglomeration and stratification, resulting in significantly lower high-temperature modulus and softening points of the system.

[0148] (2) Low temperature flexibility (5℃ ductility)

[0149] Examples 1-10 exhibit ductility between 36-50 cm, significantly superior to the 11-20 cm of Comparative Examples 1-6, demonstrating that the method of this invention improves high-temperature performance without sacrificing the system's low-temperature flexibility. The carbon dots, with a particle size of 2-6 nm, can be uniformly distributed at the interface between the SBS and asphalt phases, forming a flexible "stress buffer layer." This effectively disperses stress concentration during low-temperature tensile testing, delaying the initiation and propagation of microcracks. Conversely, Comparative Examples 1-3 lack the interface control structure involving carbon dots, resulting in significant interface defects between SBS and asphalt. Under low-temperature conditions, stress concentration easily occurs, leading to a significant reduction in ductility.

[0150] (3) UV aging resistance (penetration retention rate)

[0151] In Example 1, the penetration ratio reached 88% after UV aging, while in Comparative Example 1 it was only 58%. This is because carbon dots have a dual function of free radical scavenging and UV shielding in the system. Their surface phenolic hydroxyl, carboxyl, and amino groups can rapidly react with free radicals generated during aging to terminate chain oxidation; simultaneously, the π-conjugated electronic structure of carbon dots can effectively absorb UV light, reducing photo-oxidation reactions. In Comparative Example 2, the carbon dots were directly incorporated into the asphalt without forming a stable binding layer with SBS, making them prone to agglomeration, and the effective specific surface area participating in the anti-aging reaction was limited. Comparative Example 3 did not undergo nitrogen doping, resulting in a significant decrease in free radical scavenging ability, and its penetration retention rate after aging was significantly lower than that of Example 1, fully demonstrating the crucial role of nitrogen doping in the anti-aging function of carbon dots.

[0152] (4) Storage stability (stratification difference)

[0153] The storage stability difference of Examples 1-10 was controlled within 0.8-1.6 mm, significantly better than the 2.7-4.6 mm of Comparative Examples 1-6. In particular, the stratification difference of Example 1 was only 0.8 mm, indicating that the system maintained high homogeneity even under long-term high-temperature storage conditions. This is because the present invention employs a composite masterbatch process, which ensures stable anchoring and uniform dispersion of carbon dots during the melt mixing stage with SBS, and fixes them in the polymer phase through chemical crosslinking and interfacial interactions, thereby preventing migration and phase separation in the asphalt. In contrast, in Comparative Example 6, carbon dots and SBS were directly incorporated into the asphalt, lacking the pre-construction in the masterbatch stage. The carbon dots were prone to agglomeration and migration in the high-viscosity asphalt system, making it difficult to form a stable three-phase network structure, resulting in significantly inferior storage stability compared to the examples.

[0154] In summary, this invention achieves significant performance improvements through a technical path of "tea residue carbon dot preparation → nitrogen-containing admixture → SBS composite masterbatch method → ​​asphalt synergistic modification". Therefore, the biomass carbon dot synergistic modification technology proposed in this invention exhibits excellent comprehensive performance under high temperature, low temperature and UV aging conditions, and has broad engineering application and ecological value.

[0155] Based on the same inventive concept, asphalt concrete prepared by mixing modified asphalt obtained using the method of this invention with mineral aggregates has the same technical effects as the modified asphalt of this invention. Therefore, it should also be within the protection scope of this invention.

[0156] The above description is only a part of the preferred embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS, characterized in that, Specifically, the steps include the following: S1. Preparation of biomass carbon dot precursor: After crushing biomass waste, mix it with deionized water, stir and extract, and collect the filtrate as biomass carbon dot precursor. S2, Nitrogen Doping and Premixing: Add nitrogen-containing small molecule dopant to the filtrate of S1 and stir until homogeneous; S3. Preparation of nitrogen-doped biomass carbon dots by hydrothermal reaction: Transfer the solution of S2 to the reaction vessel and hydrothermally react at 160~220℃ for 4~12h. After the reaction is completed, cool and filter, collect the filtrate, concentrate and purify it to obtain the product. S4. Preparation of composite masterbatch: The biomass carbon dots from S3 are sheared and mixed evenly with SBS and rubber additives in a certain proportion. The mixed material is then granulated to obtain composite masterbatch. The mass ratio of biomass carbon dots to SBS is 1:(4~10), and the amount of rubber additives is 10~30wt% of the mass of SBS. S5. Asphalt Modification: Add the composite masterbatch of S4 to the base asphalt, control the temperature at 160℃~180℃, the rotation speed at 3000~5000rpm, and shear for 15~30min to make the modifier evenly dispersed, thus obtaining the modified asphalt.

2. The method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, The mass-to-volume ratio of biomass waste to deionized water in S1 is (1~5) g : (20~100) mL; the extraction conditions are: 60~100℃ for 10~60 min.

3. The method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, Biomass waste in S1 includes at least one of tea dregs, straw, coffee grounds, and fruit shells.

4. The method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, The nitrogen-containing small molecule dopants in S2 include at least one of DETA and TETA.

5. The method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, The amount of nitrogen-containing small molecule dopant added in S2 is 0.5~5 vol relative to the volume of the biomass carbon dot precursor solution.

6. The method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, The rubber additives in S4 include silica as a reinforcing filler for rubber, mixed with sulfur, BR-g-MAH, and silane coupling agent Si69; based on 100 parts of SBS, it includes SiO2: 8~15 parts; sulfur: 0.5~2 parts; BR-g-MAH: 1~5 parts; Si69: 1~5 parts.

7. The method for synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, The concentration and purification process in S3 is as follows: The collected filtrate is concentrated by a rotary evaporator and dialyzed for 24-72 hours using a dialysis membrane with NWCO=1000Da to remove small molecule impurities and obtain a purified biomass carbon dot solution.

8. The method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, The shear mixing conditions in S4 are: shear mixing for 5 to 15 minutes at a temperature of 160~190℃ and a rotation speed of 3000~5000rpm; the granulation process is carried out in a twin-screw extruder, with the extrusion temperature controlled at 160℃~200℃ and the particle size of the composite masterbatch controlled at 1~5nm.

9. The method for synergistic modification of bitumen with nitrogen-doped biomass carbon dots and SBS according to claim 1, characterized in that, The amount of composite masterbatch added in S5 is 2wt% to 6wt% of the base asphalt.

10. Modified asphalt prepared by the method of synergistic modification of asphalt with nitrogen-doped biomass carbon dots and SBS as described in any one of claims 1 to 9.

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