Waste rubber and plastic modified asphalt and preparation method thereof

Abstract

The application provides a waste rubber-plastic modified asphalt and a preparation method thereof. In the application, waste rubber is activated by double screw shearing extrusion at 250-270 DEG C, part of crosslinking structure is broken, and active reaction sites are exposed; under the initiation of dicumyl peroxide, waste polypropylene is subjected to controllable degradation and generates grafting sites; relying on the chemical bonding grafting effect of castor oil, the interface compatibility of waste rubber and polypropylene is effectively improved, the phase separation problem of the two phases is inhibited, and the dispersion uniformity of the waste rubber-plastic modifier in the asphalt is improved; meanwhile, the unreacted castor oil can be used as a plasticizing component to reduce the viscosity of the system and optimize the workability. The waste rubber-plastic modifier can effectively reduce the high-temperature storage segregation problem of the modified asphalt, significantly improve the interface adhesion strength of the asphalt and aggregate, and optimize the comprehensive road performance of the asphalt at high and low temperatures. The application realizes the resource utilization of waste rubber-plastic solid waste, has simple process, green economy, and good engineering application prospect.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment and road asphalt materials, and particularly to a waste rubber and plastic modified asphalt and its preparation method. Background Technology

[0002] Waste rubber and waste plastics are two types of solid waste generated in huge quantities. Using waste rubber and waste plastics for asphalt modification can not only realize the resource utilization of solid waste, but also improve the road performance of asphalt, and has become a research hotspot in the field of road materials.

[0003] Currently, the common method for using waste rubber and waste plastics in asphalt modification is physical blending. This method typically involves directly adding waste rubber and plastic powder (such as waste rubber and / or waste plastic) to molten base asphalt in a certain proportion, and then dispersing the waste rubber and plastic particles in the asphalt through high-speed shearing or stirring, thus producing waste rubber and plastic modified asphalt. However, due to significant differences in polarity, solubility parameters, and surface properties between waste rubber and plastic and base asphalt, the waste rubber and plastic modified asphalt prepared by physical blending suffers from obvious interfacial compatibility problems, leading to uneven dispersion and easy agglomeration of waste rubber and plastic particles in the asphalt. More importantly, the waste rubber and plastic modified asphalt prepared by the above-mentioned physical blending method generally suffers from insufficient interfacial adhesion strength with aggregates. When using pull-out tests to quantitatively evaluate the interfacial bonding force between modified asphalt and aggregates, the pull-out strength value is usually low, and the failure mode is mostly adhesion failure at the asphalt-aggregate interface, rather than cohesive failure within the asphalt itself. This indicates that the interfacial adhesion between waste rubber and plastic modified asphalt and aggregates is weaker than the cohesive force of the asphalt itself. The fundamental reason is that the surface of waste rubber and plastic particles lacks sufficient polar functional groups, making it difficult to form strong chemical bonds or strong physical adsorption with the active sites on the aggregate surface, which makes the asphalt-aggregate interface prone to peeling under the action of moisture or load.

[0004] Therefore, how to improve the interfacial adhesion strength between waste rubber and plastic modified asphalt and aggregates is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem of poor interfacial adhesion between waste rubber and plastic modified asphalt and aggregates in the prior art, and to provide a waste rubber and plastic modified asphalt and its preparation method, which can effectively improve the interfacial adhesion strength between waste rubber and plastic modified asphalt and aggregates.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing waste rubber and plastic modified bitumen, comprising the following steps:

[0008] Waste rubber is fed into a twin-screw extruder and extruded at a temperature of 250~270℃ under the shearing action of the screw to obtain surface-activated waste rubber;

[0009] The surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and fed into a twin-screw extruder. After extrusion by the twin-screw extruder, the mixture is granulated to obtain a waste rubber and plastic modifier.

[0010] Waste rubber and plastic modifiers are mixed with molten base asphalt to obtain waste rubber and plastic modified asphalt.

[0011] Preferably, in the step of feeding waste rubber into a twin-screw extruder and extruding it at a temperature of 250~270℃ and under the shearing action of the screw, the screw speed of the twin-screw extruder is 100~130 rpm.

[0012] Preferably, the mass ratio of the surface-activated waste rubber, waste polypropylene, dicumyl peroxide, and castor oil is (60~120):(80~140):(0.6~0.7):(5~6).

[0013] Preferably, the surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and then extruded in a twin-screw extruder at 170~190°C and granulated to obtain a waste rubber and plastic modifier.

[0014] Preferably, the surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and fed into a twin-screw extruder. After extrusion by the twin-screw extruder, the mixture is granulated to obtain a waste rubber and plastic modifier. The screw speed of the twin-screw extruder is 100~130 rpm.

[0015] Preferably, the particle size of the waste rubber and plastic modifier is ≤3mm.

[0016] The particle size of the waste rubber and plastic is 30-50 mesh;

[0017] The mass ratio of the waste rubber and plastic modifier to the base asphalt is (15~30):300.

[0018] Preferably, the waste rubber and plastic modifier is mixed with molten base asphalt at 150~170℃ for 60~100min to obtain waste rubber and plastic modified asphalt;

[0019] The base asphalt is heated at 150~170℃ for 60~80 minutes to obtain molten base asphalt.

[0020] Preferably, the waste rubber and plastic modifier and molten base asphalt are stirred and mixed at a temperature of 150~170℃ and a shear rate of 200~1500r / min for 30~50min, and then stirred and mixed at a temperature of 150~170℃ and a shear rate of 2500~4000r / min for 40~60min to obtain waste rubber and plastic modified asphalt.

[0021] Secondly, the present invention also provides a waste rubber and plastic modified asphalt, which is prepared by the aforementioned preparation method.

[0022] The waste rubber and plastic modified asphalt and its preparation method of the present invention have the following advantages compared with the prior art:

[0023] The method for preparing waste rubber-modified asphalt of the present invention first involves feeding waste rubber into a twin-screw extruder and extruding it at a temperature of 250-270°C under screw shear. During extrusion, the waste rubber undergoes partial decrosslinking due to heat and shear, exposing active reaction sites to obtain surface-activated waste rubber. Subsequently, under the initiation of dicumyl peroxide and high-temperature shear, the waste polypropylene undergoes moderate degradation, providing grafting sites for the grafting reaction of castor oil. Some castor oil is chemically grafted onto the polypropylene molecular chain, significantly improving the compatibility between waste rubber and waste polypropylene and reducing phase separation. The degree of dispersion of waste rubber and plastic modifiers in asphalt is significantly improved; ungrafted castor oil acts as a plasticizing component, effectively reducing the viscosity of the system and improving workability; through the synergistic effect of the above extrusion process on the compatibilization and viscosity reduction of the waste rubber and plastic system, the degree of segregation of the waste rubber and plastic modified asphalt is significantly reduced during high-temperature storage, and the overall road performance is effectively improved; the waste rubber and plastic modifier can effectively improve the interfacial adhesion strength between the modified asphalt and aggregates when used to prepare modified asphalt; this method uses waste rubber and plastic as the main raw material to prepare asphalt modifiers for asphalt road construction, realizing the large-scale development and resource utilization of waste rubber and plastic. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a reaction mechanism diagram of the preparation method of waste rubber and plastic modified bitumen of the present invention;

[0026] Figure 2 These are scanning electron microscope (SEM) images of the waste rubber and plastic modifiers in Examples 4-6 of the present invention, the waste polypropylene in Comparative Example 1, and the polypropylene modifiers in Comparative Example 2.

[0027] Figure 3 These are pull-out section diagrams of modified asphalt and base asphalt in Examples 4-6 and Comparative Examples 1-4. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0030] This invention provides a method for preparing waste rubber and plastic modified bitumen, comprising the following steps:

[0031] S1. Waste rubber is fed into a twin-screw extruder and extruded at a temperature of 250~270℃ and under the shearing action of the screw to activate the surface of the waste rubber and plastic, thereby obtaining surface-activated waste rubber.

[0032] S2. Surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide and castor oil, and fed into a twin-screw extruder. After extrusion by the twin-screw extruder, the mixture is granulated to obtain waste rubber and plastic modifier.

[0033] S3. Mix the waste rubber and plastic modifier with the molten base asphalt to obtain waste rubber and plastic modified asphalt.

[0034] The method for preparing waste rubber-modified asphalt of the present invention first involves feeding waste rubber into a twin-screw extruder and extruding it at a temperature of 250-270°C under screw shearing action. During the extrusion process, the waste rubber undergoes partial decrosslinking through heat and shearing, exposing active reaction sites to obtain surface-activated waste rubber. Subsequently, dicumyl peroxide (also known as vulcanizing agent DCP, chemical formula C...) is used to prepare the modified asphalt. 18 H 22 Under the initiation of O2 and high-temperature shearing, polypropylene undergoes moderate degradation, providing grafting sites for the grafting reaction of castor oil. Some castor oil is chemically grafted onto the polypropylene molecular chain, significantly improving the compatibility between waste rubber and polypropylene, reducing phase separation, and significantly enhancing the uniform dispersion of the waste rubber modifier in asphalt. The ungrafted castor oil acts as a plasticizer, effectively reducing system viscosity and improving workability. Through the synergistic effect of the above extrusion process on the compatibility and viscosity reduction of the waste rubber system, the resulting waste rubber modified asphalt exhibits significantly reduced segregation during high-temperature storage, effectively improving its overall road performance. The waste rubber modifier of this invention, used in the preparation of modified asphalt, can effectively improve the interfacial adhesion strength between modified asphalt and aggregates. This method uses waste rubber as the main raw material to prepare an asphalt modifier for asphalt road construction, realizing the large-scale development and resource utilization of waste rubber, while significantly reducing the economic costs incurred in road construction.

[0035] In some embodiments, waste rubber is extruded at a high temperature of 250~270℃, resulting in the severing of sulfur bonds and carbon chains to generate a large number of rubber free radicals, thus activating the rubber. Then, the activated waste rubber, waste PP (waste polypropylene), castor oil, and DCP are mixed and extruded: the decomposition of DCP initiates the degradation of polypropylene to generate PP free radicals; castor oil acts as a bridge, covalently grafting rubber free radicals and polypropylene free radicals through double bond addition; finally, rubber-castor oil-polypropylene graft copolymer particles (waste rubber and plastic modifier) ​​are obtained; after this graft copolymer is added to the matrix asphalt, its compatibility is greatly improved, it can be uniformly swollen and dispersed, and the high and low temperature performance of the asphalt is significantly improved.

[0036] Further reference Figure 1 As shown, this is the main reaction mechanism of the preparation method of waste rubber and plastic modified asphalt of the present invention:

[0037] First, the activation of waste rubber powder (i.e., waste rubber): Waste rubber is cross-linked vulcanized rubber, and its molecular chain contains polysulfide bonds RS. x -R', monosulfide bond RS-R', polyisoprene carbon-carbon double bond; under high-temperature shearing of a twin-screw extruder at 250~270℃, thermal decomposition occurs to produce free radicals, thereby achieving surface activation;

[0038] (1-1) Homolytic cleavage of polysulfide crosslinks

[0039] RS crosslinking point of vulcanized rubberx -R' breaks down upon heating, releasing two sulfur radicals RS. y ·、·S z -R' disrupts the original three-dimensional cross-linked network, causing a large number of active sites to be generated on the rubber surface.

[0040] (1-2) Monosulfide bond cleavage

[0041] The monosulfide bonds within the rubber molecule are further broken, generating carbon free radicals R· and sulfur free radicals ·S-R', which further increases the concentration of free radicals on the rubber surface.

[0042] (1-3) Chain breakage at the double bond of the carbon chain in polyisoprene

[0043] The isoprene double bond sites of the rubber backbone are homogenized by heat, and the long rubber macromolecule is broken down into two short-chain carbon free radicals, which greatly reduces the molecular weight of rubber and improves its compatibility with asphalt and polypropylene.

[0044] (1-4) Carbon free radicals absorb oxygen to generate peroxy free radicals

[0045] Rubber carbon free radicals combine with trace amounts of oxygen in the system to generate peroxy free radicals ROO·.

[0046] (1-5) Hydrogen abstraction by peroxy radicals to form hydrogen peroxides

[0047] ROO· removes hydrogen atoms from the molecular chains of rubber, castor oil, and polypropylene to generate hydrogen peroxide ROOH, while simultaneously producing new carbon free radicals R'·, and the chain reaction continuously proliferates active sites.

[0048] (1-6) Secondary cracking of hydroperoxides

[0049] ROOH undergoes bond breakage again at high temperature, generating alkoxy radicals RO· and hydroxyl radicals ·OH, which continuously replenish the active free radicals in the system, thus completing the surface activation of waste rubber.

[0050] High-temperature shearing breaks down the rubber crosslinking network, generating a large number of carbon free radicals on the surface of rubber molecules, providing reaction sites for subsequent grafting with polypropylene and castor oil.

[0051] DCP initiates the degradation of waste polypropylene, generating free radicals.

[0052] Dicumyl peroxide (DCP) is the high-temperature free radical initiator in this system. It decomposes at the extrusion temperature, inducing polypropylene chain scission and producing polypropylene macromolecular free radicals.

[0053] (2-1) Thermal decomposition of DCP

[0054] The peroxy bond within the DCP molecule is homolytically cleaved, generating two kurtoid oxygen free radicals, which are the initial source of free radicals in the system.

[0055] (2-2) Hydrogen abstraction reaction of polypropylene

[0056] The cumyl oxygen free radical takes a hydrogen atom from the tertiary carbon of polypropylene: the polypropylene molecule generates a polypropylene carbon free radical, and the oxygen free radical combines with hydrogen to form cumyl alcohol.

[0057] (2-3) Polypropylene β-Cleavage (Degradation and Chain Breaking)

[0058] The tertiary carbon radical of polypropylene is unstable and undergoes β-fracture, splitting a long polypropylene molecule into a large polypropylene radical (short chain radical on the left) and a small polypropylene molecule containing terminal double bonds, reducing the viscosity of the polypropylene melt and providing active radicals that can be grafted.

[0059] DCP decomposition triggers polypropylene chain scission, generating polypropylene free radicals, enabling controlled degradation of polypropylene, while providing active sites that can couple with rubber.

[0060] Castor oil bridging grafting reaction

[0061] Castor oil molecular structure: The main chain contains a large number of hydroxyl (-OH), unsaturated carbon-carbon double bonds, and long fatty acid ester chains, which act as a compatibility bridging agent to covalently link rubber free radicals and polypropylene free radicals to form rubber-plastic graft copolymers (the core effective component of the modifier).

[0062] The system contains three types of reactive free radicals:

[0063] Polypropylene free radical: (polypropylene tertiary carbon free radical)

[0064] Rubber free radicals: (activated rubber carbon free radicals)

[0065] Dual reactive sites of castor oil:

[0066] The hydroxyl groups on fat molecules provide active hydrogen, which participates in free radical hydrogen abstraction chain reactions;

[0067] The C=C unsaturated double bonds on the carbon chain of oils and fats can undergo addition grafting with polypropylene and rubber free radicals.

[0068] Castor oil double bonds undergo addition coupling with polypropylene free radicals and rubber free radicals simultaneously, generating a ternary grafted macromolecule with castor oil as the intermediate skeleton, one side attached to a polypropylene chain and the other side attached to a rubber chain, ultimately yielding rubber-castor oil-polypropylene graft copolymer particles (i.e. waste rubber and plastic modifier).

[0069] In some embodiments, in the step of feeding waste rubber into a twin-screw extruder and extruding it at a temperature of 250~270°C under screw shearing action, the screw speed of the twin-screw extruder is 100~130 rpm.

[0070] In some embodiments, the mass ratio of surface-activated waste rubber, waste polypropylene, dicumyl peroxide, and castor oil is (60~120):(80~140):(0.6~0.7):(5~6).

[0071] In some embodiments, surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and then fed into a twin-screw extruder for extrusion at 170~190°C and granulation to obtain a waste rubber and plastic modifier.

[0072] In some embodiments, surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and fed into a twin-screw extruder. After extrusion by the twin-screw extruder, the mixture is granulated to obtain a waste rubber and plastic modifier. The screw speed of the twin-screw extruder is 100~130 rpm.

[0073] In some embodiments, surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, fed into a twin-screw extruder, granulated after extrusion, crushed and sieved to obtain waste rubber and plastic modifier with a particle size ≤3mm.

[0074] In some embodiments, the waste rubber is waste tire rubber;

[0075] The particle size of waste rubber and plastic is 30-50 mesh;

[0076] The mass ratio of waste rubber and plastic modifier to base asphalt is (15~30):300.

[0077] In some embodiments, waste rubber and plastic modifier is mixed with molten base asphalt at 150-170°C for 60-100 min to obtain waste rubber and plastic modified asphalt.

[0078] In some embodiments, the base asphalt is heated at 150~170°C for 60~80 minutes to obtain molten base asphalt.

[0079] In some embodiments, waste rubber and plastic modifier and molten base asphalt are placed in a shearing device and first stirred and mixed at a temperature of 150~170°C and a shear rate of 200~1500 r / min for 30~50 min, and then stirred and mixed at a temperature of 150~170°C and a shear rate of 2500~4000 r / min for 40~60 min to obtain waste rubber and plastic modified asphalt.

[0080] Based on the same inventive concept, the present invention also provides a waste rubber and plastic modified asphalt, which is prepared by the above-described preparation method.

[0081] The following detailed embodiments further illustrate the waste rubber and plastic modified bitumen and its preparation method of this application. This section, in conjunction with specific embodiments, further explains the content of the present invention, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in the art.

[0082] In the following examples and comparative examples, the waste rubber came from Dujiangyan Huayi Rubber Co., Ltd.; the matrix asphalt used was Donghai brand Grade A 70 road petroleum matrix asphalt provided by Maoming Branch of China Petroleum & Chemical Corporation; the waste polypropylene was from Qingyuan Randian New Material Technology Co., Ltd.; and the limestone aggregate used in the pull-out test was limestone provided by Shandong Dashixiong Engineering Technology Co., Ltd.

[0083] Example 1

[0084] This embodiment provides a method for preparing waste rubber and plastic modified asphalt, including the following steps:

[0085] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 260℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder is 120 rpm during extrusion.

[0086] S2. Mix 60g of surface-activated waste rubber, 140g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide evenly, and feed the mixture into a twin-screw extruder. Extrude the mixture at 180℃. The extrudate is then granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0087] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0088] 15g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, the mixture was stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain waste rubber and plastic modified asphalt.

[0089] Example 2

[0090] This embodiment provides a method for preparing waste rubber and plastic modified asphalt, including the following steps:

[0091] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 260℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder is 120 rpm during extrusion.

[0092] S2. 90g of surface-activated waste rubber, 110g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide are mixed evenly and fed into a twin-screw extruder. The mixture is extruded at a temperature of 180℃. The extrudate is granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0093] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0094] 15g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, the mixture was stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain waste rubber and plastic modified asphalt.

[0095] Example 3

[0096] This embodiment provides a method for preparing waste rubber and plastic modified asphalt, including the following steps:

[0097] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 260℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder is 120 rpm during extrusion.

[0098] S2. Mix 120g of surface-activated waste rubber, 80g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide evenly, and feed the mixture into a twin-screw extruder. Extrude the mixture at a temperature of 180℃. The extrudate is then granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0099] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0100] 15g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, the mixture was stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain waste rubber and plastic modified asphalt.

[0101] Example 4

[0102] This embodiment provides a method for preparing waste rubber and plastic modified asphalt, including the following steps:

[0103] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 260℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder is 120 rpm during extrusion.

[0104] S2. Mix 60g of surface-activated waste rubber, 140g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide evenly, and feed the mixture into a twin-screw extruder. Extrude the mixture at 180℃. The extrudate is then granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0105] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0106] 30g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, they were stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain waste rubber and plastic modified asphalt.

[0107] Example 5

[0108] This embodiment provides a method for preparing waste rubber and plastic modified asphalt, including the following steps:

[0109] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 260℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder is 120 rpm during extrusion.

[0110] S2. 90g of surface-activated waste rubber, 110g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide are mixed evenly and fed into a twin-screw extruder. The mixture is extruded at a temperature of 180℃. The extrudate is granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0111] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0112] 30g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, they were stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain waste rubber and plastic modified asphalt.

[0113] Example 6

[0114] This embodiment provides a method for preparing waste rubber and plastic modified asphalt, including the following steps:

[0115] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 260℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder is 120 rpm during extrusion.

[0116] S2. Mix 120g of surface-activated waste rubber, 80g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide evenly, and feed the mixture into a twin-screw extruder. Extrude the mixture at a temperature of 180℃. The extrudate is then granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0117] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0118] 30g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, they were stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain waste rubber and plastic modified asphalt.

[0119] Comparative Example 1

[0120] This comparative example provides a method for preparing modified asphalt (this comparative example is used to investigate the effect of direct physical blending of polypropylene on the properties of modified asphalt, and to compare its effect with that of the modifier prepared by the reactive extrusion method of this invention), including the following steps:

[0121] S1. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0122] S2. Place 30g of waste polypropylene and 300g of molten base asphalt in a shearing device, first stir and mix at a temperature of 160℃ and a shear rate of 500r / min for 30min, and then stir and mix at a temperature of 160℃ and a shear rate of 4000r / min for 40min to obtain modified asphalt.

[0123] Comparative Example 2

[0124] This comparative example provides a method for preparing modified asphalt (this comparative example is used to examine the contribution of waste rubber components to the comprehensive performance of the modifier, and to compare its effect with that of the modifier prepared by synergistic extrusion of waste rubber and polypropylene of the present invention), including the following steps:

[0125] S1. Mix 200g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide evenly, and feed it into a twin-screw extruder. Extrude the mixture at a temperature of 180℃. The extrudate is then granulated and crushed to obtain a polypropylene modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0126] S2. Heat 300g of base bitumen at 160℃ for 70min to obtain molten base bitumen;

[0127] 30g of polypropylene modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, they were stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain modified asphalt.

[0128] Comparative Example 3

[0129] This comparative example provides a method for preparing modified asphalt (this comparative example is used to investigate the effect of activation temperature change on the activation effect of waste rubber, and compares its performance with that of a waste rubber and polypropylene synergistic reaction extrusion modifier prepared using the specific activation temperature of this invention), including the following steps:

[0130] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 200℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder is 120 rpm during extrusion.

[0131] S2. Mix 60g of surface-activated waste rubber, 140g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide evenly, and feed the mixture into a twin-screw extruder. Extrude the mixture at 180℃. The extrudate is then granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0132] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0133] 30g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, the mixture was stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain modified asphalt.

[0134] Comparative Example 4

[0135] This comparative example provides a method for preparing modified asphalt (this comparative example is used to investigate the effect of activation temperature change on the activation effect of waste rubber, and compares its performance with that of a waste rubber and polypropylene synergistic reaction extrusion modifier prepared using the specific activation temperature of this invention), including the following steps:

[0136] S1. 30-mesh waste rubber is fed into a twin-screw extruder and extruded at a temperature of 300℃ under the shearing action of the screw to activate the surface of the waste rubber and obtain surface-activated waste rubber; wherein, the screw speed of the twin-screw extruder during extrusion is 120 rpm;

[0137] S2. Mix 60g of surface-activated waste rubber, 140g of waste polypropylene, 5g of castor oil and 0.6g of dicumyl peroxide evenly, and feed the mixture into a twin-screw extruder. Extrude the mixture at 180℃. The extrudate is then granulated and crushed to obtain a waste rubber and plastic modifier with an average particle size of 2mm. The screw speed of the twin-screw extruder during extrusion is 120 rpm.

[0138] S3. Heat 300g of base asphalt at 160℃ for 70min to obtain molten base asphalt;

[0139] 30g of waste rubber and plastic modifier and 300g of molten base asphalt were placed in a shearing device and stirred for 30 minutes at a temperature of 160℃ and a shear rate of 500r / min. Then, the mixture was stirred for 40 minutes at a temperature of 160℃ and a shear rate of 4000r / min to obtain modified asphalt.

[0140] Performance testing

[0141] Figure 2 The images are scanning electron microscope (SEM) images of the waste rubber and plastic modifiers in Examples 4-6, the waste polypropylene in Comparative Example 1, and the polypropylene modifier in Comparative Example 2.

[0142] from Figure 2As can be seen, the waste polypropylene is in a uniform block shape; after the addition of castor oil and dicumyl peroxide, the matrix shows a filamentous structure, indicating that the polypropylene has degraded and its plastic deformation ability has been enhanced due to the grafting of castor oil; with the further addition of activated rubber, the rubber is wrapped by polypropylene at low content, and a clear island structure with rubber as islands and polypropylene as sea is formed at high content. When modifiers with this structure are used for asphalt modification, their fibrous polypropylene continuous phase can construct a fibrous network skeleton in the asphalt, directly bearing and dispersing tensile stress, significantly improving tensile strength. More importantly, the high-strength interfacial bonding between the rubber island phase and the polypropylene sea phase, as well as between the entire modifier and the asphalt matrix, is achieved through chemical bridging and molecular entanglement of castor oil graft chains. This effectively prevents crack initiation and propagation along the interface during the pull-out process, forcing the failure to occur in the material body in a higher-energy cohesive mode, thereby significantly improving the pull-out failure work and overall anti-peeling ability. However, when the activated rubber content is too high, the excess rubber phase will dilute and break the fibrous network skeleton of the polypropylene continuous phase, causing it to degenerate from a load-bearing body into a discontinuous dispersed unit. In addition, the limited reactive groups are consumed by the competition of excess rubber, the interfacial chemical bridging density decreases, causing cracks to re-initiate and propagate along the interface during the pull-out process, and the adhesion performance is reduced. In summary, after waste polypropylene is reacted and blended with castor oil, dicumyl peroxide and activated rubber, its structure gradually evolves from a uniform block shape to a filamentous plastic network. Finally, when the activated rubber is in an appropriate amount, a fiber skeleton-island synergistic structure is formed, while when the activated rubber is in an excessive amount, the skeleton is broken.

[0143] Softening point test

[0144] Softening point: According to the test method T 0606 in the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), the softening point of the modified asphalt and base asphalt in Examples 1-6 and Comparative Examples 1-5 was tested using the ring and ball method. The test results are shown in Table 1. Specific test procedure: (1) Place the sample ring containing the asphalt sample along with the sample base plate in a constant temperature water bath containing water at 5℃±0.5℃ for at least 15 minutes; (2) Pour freshly boiled and cooled water to 5℃ into the beaker, with the water level slightly lower than the depth mark on the pole; (3) Place the sample ring containing the asphalt sample in step (1) into the round hole of the middle plate of the support, put on the positioning ring and put it into the beaker, and keep the water temperature at 5℃±0.5℃; (4) Place the steel ball in the center of the sample in the middle of the positioning ring, immediately turn on the electromagnetic oscillation stirrer to make the water oscillate slightly, and start heating, so that the water temperature in the cup is adjusted to maintain a rise of 5℃±0.5℃ per minute within 3 minutes; (5) The asphalt sample softens and gradually falls when heated, and the temperature is read immediately when it comes into contact with the surface of the lower base plate.

[0145] Penetration test

[0146] Penetration: According to the test method T 0604 in the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), the penetration of modified asphalt and base asphalt in Examples 1-6 and Comparative Examples 1-5 was tested at an experimental temperature of 25℃. The test results are shown in Table 1. Specific test procedure: (1) The asphalt sample heated to a fluid state was injected into the sample container. The height of the sample should exceed the expected penetration value by more than 10 mm. The sample container was covered to prevent dust from falling in. (2) After the sample container containing the sample was cooled at room temperature of 15-30℃ for 1.5-2 hours, it was moved into a constant temperature water bath with the temperature controlled at (25±0.1)℃ and kept warm for 1.5-2 hours. Take out the sample dish and place it on the needle penetration tester platform. Adjust the standard needle tip so that it just contacts the sample surface. (3) Under standard test conditions (test temperature 25℃, total mass of standard needle, needle rod and additional weight (100±0.05)g, penetration time 5s), release the standard needle so that it can freely and vertically penetrate the sample. Record the penetration depth in units of 0.1mm. (4) Perform at least 3 parallel measurements on the same sample. The distance between each test point and the distance between the test point and the edge of the sample dish should not be less than 10mm. Take the arithmetic mean as the needle penetration measurement result of the sample.

[0147] Viscosity test

[0148] Viscosity: According to the test method T 0625 in the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), the viscosity of modified asphalt and base asphalt in Examples 1-6 and Comparative Examples 1-4 was tested at a test temperature of 135℃. The test results are shown in Table 1. Specific test procedure: (1) Place the asphalt sample in the viscosity test container and keep it warm for 1.5h; (2) Insert the selected rotor into the asphalt liquid surface in the container to the specified height and continue to keep it warm for more than 15min; (3) Start the viscosity test, observe the change in viscosity value, read the value after it stabilizes and record it, and determine the average value of 3 readings.

[0149] Table 1 - Softening point, penetration, and viscosity of modified asphalt prepared in different embodiments and comparative examples

[0150]

[0151] As shown in Table 1, the modified asphalt prepared in Examples 1-6 generally exhibited higher softening point, lower penetration, and increased viscosity compared to the base asphalt. This indicates that the waste rubber and plastic modifier has a positive effect on the high-temperature performance of asphalt and significantly influences its workability, meeting the requirements for asphalt road construction materials. Furthermore, the amount of waste rubber and plastic modifier added in Examples 1-3 was 5% of the base asphalt, while in Examples 4-6 it was 10%. The performance improvement effect of the modified asphalt prepared in Examples 1-3 was not as significant as that in Examples 4-6. When the amount of waste rubber and plastic modifier added was 10% of the base asphalt, the softening point of the modified asphalt increased significantly, the penetration decreased, and the viscosity increased. Further, a comparison between Example 5 and Comparative Examples 1-2 shows that the addition of waste rubber and plastic modifier resulted in a significant increase in penetration of the modified asphalt (compared to Comparative Examples 1-2). Increased viscosity and decreased viscosity improved workability and ease of construction. Simultaneously, the softening point was significantly increased compared to the base asphalt, enhancing high-temperature performance. In Comparative Example 3, compared to Example 5, the waste rubber activation temperature (200℃) was lower, resulting in less activation and a slight increase in the softening point of the prepared modified asphalt. In Comparative Example 4, compared to Example 5, the waste rubber activation temperature (300℃) was too high, leading to excessive activation and a significant decrease in the softening point of the prepared modified asphalt. This indicates that both excessively high and low activation levels of waste rubber are detrimental to the stable control of the modified asphalt's softening point, suggesting the existence of an optimal activation temperature range. Pull-out test.

[0152] Pull-out test method: A clean limestone slab was bonded to a stainless steel substrate, with custom-made metal gaskets on both sides to strictly control the asphalt film thickness to 0.2 mm. Modified asphalt from Examples 1-6 and Comparative Examples 1-4, preheated to a fluid state (heating temperature 165℃), and base asphalt were coated onto the limestone slab surface, respectively. The stainless steel substrate was then pressed onto it at 165℃ to form a sandwich-type specimen (limestone slab + 0.2 mm asphalt + stainless steel substrate), ensuring the gap between the two surfaces was completely filled with asphalt. The resulting specimens were first cured at room temperature for 4 hours, then left to stand at a constant temperature of 20℃ for 4 hours. Pull-out tests were conducted at a constant temperature of 25℃, with a displacement rate of 5 mm / min until specimen failure. The maximum load was recorded and the pull-out strength was calculated to evaluate the bonding performance of the asphalt-aggregate interface. The results are shown in Table 2.

[0153] Table 2 - Bonding properties of modified asphalt prepared in different embodiments and comparative examples

[0154] In Table 2, a peeling area ≤ 10% is defined as minor; a peeling area > 10% and ≤ 30% is defined as moderate; and a peeling area > 30% is defined as severe.

[0155] As can be seen from Table 2, the modified asphalt prepared in Examples 1-6 showed a significant increase in maximum stress and fracture energy density compared to the base asphalt, and the pull-out performance increased with the increase of the amount of waste rubber and plastic modifier. In Examples 4-6, the amount of waste rubber and plastic modifier added was 10% of the base asphalt. After pull-out, the surface state of the asphalt was honeycomb structure with less peeling and enhanced adhesion compared to the base asphalt. From the comparison of Comparative Examples 3-4 and Example 5, it can be seen that the maximum stress, maximum strain, and fracture energy density of the modified asphalt showed a trend of first increasing and then decreasing with the increase of the activation temperature of the waste rubber. This indicates that the activation degree of the waste rubber needs to be controlled within a suitable range and reaches the optimum under moderate decrosslinking conditions in order to obtain the best mechanical properties.

[0156] As can be seen from Tables 1 and 2, the waste rubber-plastic modified asphalt prepared in Example 4 has the best comprehensive performance.

[0157] Figure 3 The figures show pull-out sections of modified asphalt and base asphalt in Examples 4-6 and Comparative Examples 1-4.

[0158] from Figure 3 As can be seen, the pull-out fracture surface of the matrix asphalt is smooth, exhibiting typical interfacial adhesion and delamination characteristics. The waste polypropylene modified asphalt has sparse particles but high fracture energy, due to the huge frictional energy consumption during fiber pull-out. After introducing dicumyl peroxide and castor oil, dicumyl peroxide both degrades and embrittles the polypropylene and induces castor oil grafting to enhance interfacial anchoring. The combination of these two factors forces the fiber to change from pull-out to low-energy brittle fracture, resulting in denser particles on the fracture surface and a decrease in fracture energy. Further introduction of 260℃ activated rubber transforms the fracture surface into a honeycomb structure, indicating that the energy consumption mode has shifted from brittle fracture of polypropylene fibers to deformation tearing of the rubber phase and shear yielding of the matrix. With the increase of the proportion of activated waste rubber, the honeycomb pores enlarge and the edges become finer, due to the expansion of the rubber phase volume, which expands the deformation tearing zone. At the same time, excessive rubber dilutes and breaks the continuous polypropylene skeleton, resulting in a thinning of the load-bearing structure of the pore walls. Comparison of different activation temperatures revealed that rubber activated at 200℃ had low surface reactivity due to insufficient temperature, resulting in weak interfacial bonding with the polypropylene matrix. Under stress, only a small amount of rubber participated in deformation and tearing, forming sporadic honeycomb structures, while a large amount of insufficiently activated rubber was pulled out entirely or fractured brittlely, leaving behind large granular fracture surfaces. Conversely, over-activation at 300℃ caused the waste rubber to degrade and release excessive oil, weakening the rubber's bulk strength and interfacial bonding. Under stress, the honeycomb structure collapsed and caved in, leaving only a small number of granular fracture surfaces. In conclusion, the introduction of activated waste rubber is a crucial turning point in the fracture morphology, shifting from granular brittle fracture to honeycomb shear yielding. The degree of activation directly dominates the contribution of rubber to the toughening and energy-dissipating mechanism relative to the matrix, thus influencing the bonding properties of the modified asphalt.

[0159] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0160] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for preparing waste rubber and plastic modified asphalt, characterized in that, Includes the following steps: Waste rubber is fed into a twin-screw extruder and extruded at a temperature of 250~270℃ under the shearing action of the screw to obtain surface-activated waste rubber; The surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and fed into a twin-screw extruder. After extrusion by the twin-screw extruder, the mixture is granulated to obtain a waste rubber and plastic modifier. Waste rubber and plastic modifiers are mixed with molten base asphalt to obtain waste rubber and plastic modified asphalt.

2. The method for preparing waste rubber-plastic modified asphalt as described in claim 1, characterized in that, In the step of feeding waste rubber into a twin-screw extruder and extruding it at a temperature of 250~270℃ under the shearing action of the screw, the screw speed of the twin-screw extruder is 100~130 rpm.

3. The method for preparing waste rubber and plastic modified bitumen as described in claim 1, characterized in that, The mass ratio of the surface-activated waste rubber, waste polypropylene, dicumyl peroxide, and castor oil is (60~120):(80~140):(0.6~0.7):(5~6).

4. The method for preparing waste rubber and plastic modified bitumen as described in claim 1, characterized in that, The surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and then extruded in a twin-screw extruder at 170~190℃ and granulated to obtain a waste rubber and plastic modifier.

5. The method for preparing waste rubber-plastic modified bitumen as described in claim 1, characterized in that, The surface-activated waste rubber is mixed with waste polypropylene, dicumyl peroxide, and castor oil, and fed into a twin-screw extruder. After extrusion by the twin-screw extruder, the mixture is granulated to obtain a waste rubber and plastic modifier. The screw speed of the twin-screw extruder is 100~130 rpm.

6. The method for preparing waste rubber and plastic modified bitumen as described in claim 1, characterized in that, The particle size of the waste rubber and plastic modifier is ≤3mm.

7. The method for preparing waste rubber-plastic modified bitumen as described in claim 1, characterized in that, The particle size of the waste rubber is 30-50 mesh; The mass ratio of the waste rubber and plastic modifier to the base asphalt is (15~30):

300.

8. The method for preparing waste rubber-plastic modified bitumen as described in claim 1, characterized in that, Waste rubber and plastic modifiers are mixed with molten base asphalt at 150-170℃ for 60-100 minutes to obtain waste rubber and plastic modified asphalt. The base asphalt is heated at 150~170℃ for 60~80 minutes to obtain molten base asphalt.

9. The method for preparing waste rubber and plastic modified bitumen as described in claim 8, characterized in that, Waste rubber and plastic modifiers are mixed with molten base asphalt at a temperature of 150-170℃ and a shear rate of 200-1500 r / min for 30-50 min, and then mixed at a temperature of 150-170℃ and a shear rate of 2500-4000 r / min for 40-60 min to obtain waste rubber and plastic modified asphalt.

10. A waste rubber-plastic modified asphalt, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.

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