Preparation method, product and application of a polyethylene wax asphalt modifier

Abstract

The present invention relates to the technical field of asphalt pavement materials for road engineering, and particularly to a preparation method, product and application of a polyethylene wax asphalt modifier. The preparation method of the polyethylene wax asphalt modifier comprises the following steps: mixing polyethylene particles and a cracking catalyst to obtain mixture particles; feeding the mixture particles into a twin-screw extruder for extrusion to obtain a micro-cracked liquid glue; subjecting the micro-cracked liquid glue to a high-temperature and high-pressure reaction to obtain the polyethylene wax asphalt modifier. The cracking catalyst is prepared by loading nickel on expanded vermiculite powder. The polyethylene wax asphalt modifier of the present invention not only reduces the viscosity of asphalt but also modifies the asphalt, greatly improving the compatibility and storage stability between asphalt and polyethylene. Compared with ordinary polyethylene cracking technology, it can reduce a large amount of energy consumption, and can increase the recycling degree of waste polyethylene plastics, saving energy and protecting the environment, and making efficient use.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt pavement materials for road engineering, and particularly to a preparation method, product and application of a polyethylene wax asphalt modifier. Background Art

[0002] In recent years, the total mileage of highways has been increasing, which puts forward higher requirements for road quality. To improve the road traffic quality and reduce road diseases, the current mainstream method is to prepare asphalt modifiers with excellent performance and improve the road performance by adding high-performance modifiers. The wax prepared from waste plastic particles, as a new type of modifier, is widely used as an organic viscosity-reducing warm mix agent to reduce the mixing temperature of hot mix mixtures due to its low price and good compatibility with asphalt. However, at present, due to the complex composition of waste plastic particles, which may contain different types of polyethylene, using a single-temperature pyrolysis technology may cause some polyethylene in the waste plastic particles to be over-pyrolyzed or under-pyrolyzed, resulting in poor performance of the produced wax. After adding it to asphalt, it will affect the low-temperature performance of asphalt and cause pavement cracking.

[0003] Recycling waste plastics into pellets is a relatively environmentally friendly plastic recycling method at present. The polyethylene mixed with the original polymer is re-extruded, processed and transformed using a mechanical recycling method to reduce the overall cost. In the early stage of using waste plastics to produce polyethylene wax, its process has been in the exploration stage, and the research on its physical and chemical properties is not in-depth, nor has the wide range of its application fields been recognized, such as its application in fields like cables, coatings, inks, wax products, rubber, etc. Polyethylene wax was only produced as a by-product during the high-temperature preparation of polyethylene. However, the produced products have a large molecular weight difference and uneven quality. Moreover, the production cost is high, which makes the small-scale production ineffective. From this perspective, the further exploration of the polyethylene wax production process is restricted, and it has also become a problem to achieve industrialization and commercialization within a certain period.

[0004] In existing invention patents, using waste polyethylene particles to prepare polyethylene wax mostly adopts a high-temperature and high-pressure reaction kettle and conducts production by controlling a single temperature. This method can achieve good results for pyrolyzing a single type of polyethylene particles. However, at present, the composition of waste plastic particles is complex, mostly a mixture composed of HDPE (high-density polyethylene), LDPE (low-density polyethylene) and LLDPE (linear low-density polyethylene). If the traditional single-temperature pyrolysis method of the reaction kettle is used, it is easy to lead to poor product performance and the inaccurate and uncontrollable pyrolysis of different types of polyethylene. Therefore, it is necessary to further optimize the process of pyrolyzing waste polyethylene particles to prepare a wax modifier to prepare a polyethylene wax asphalt modifier with excellent performance. Summary of the Invention

[0005] Based on the above, the present invention provides a preparation method, product and application of a polyethylene wax asphalt modifier.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is an application of a cracking catalyst in the preparation of a polyethylene wax asphalt modifier, and the preparation method of the cracking catalyst includes the following steps:

[0008] Dry and crush expanded vermiculite to obtain expanded vermiculite powder (particle size 200 - 230 mesh);

[0009] Dissolve nickel salt in water to obtain nickel nitrate solution;

[0010] Immerse the expanded vermiculite powder in the nickel nitrate solution and mix well, then let it precipitate naturally and filter to obtain the impregnated powder;

[0011] Dry the impregnated powder, and then calcine and ashing it at 300 - 350 °C for 2.5 - 3 h to obtain the cracking catalyst;

[0012] The mass ratio of the expanded vermiculite to the nickel salt and water is 30:26:(30 - 50).

[0013] Another technical solution of the present invention is a preparation method of a polyethylene wax asphalt modifier, including the following steps:

[0014] Mix polyethylene particles and the cracking catalyst to obtain mixture particles;

[0015] Feed the mixture particles into a twin-screw extruder for extrusion to obtain a micro-cracked liquid glue;

[0016] Carry out a high-temperature and high-pressure reaction on the micro-cracked liquid glue to obtain the polyethylene wax asphalt modifier.

[0017] A third technical solution of the present invention is a polyethylene wax asphalt modifier prepared according to the above preparation method.

[0018] A fourth technical solution of the present invention is the application of the polyethylene wax asphalt modifier in modified asphalt.

[0019] A fifth technical solution of the present invention is a modified asphalt, the raw materials of which include matrix asphalt and the polyethylene wax asphalt modifier.

[0020] The present invention discloses the following technical effects:

[0021] The preparation methods of the cracking catalyst and the polyethylene wax asphalt modifier of the present invention are simple and easy to be prepared on a large scale industrially.

[0022] The polyethylene wax asphalt modifier prepared by the present invention is a block wax product with a high yield and excellent performance. Using the polyethylene wax asphalt modifier prepared by the present invention to modify the base asphalt, without adding other modifiers, it can effectively reduce the mixing temperature of the asphalt mixture. Compared with the base asphalt, the Brookfield viscosity of the modified asphalt at 135 °C can be reduced by more than 35%. At the same time, the penetration and softening point of the modified asphalt increase significantly, and the penetration index decreases, making the asphalt not only have good high-temperature performance after modification, but also its low-temperature performance is improved. In short, using the polyethylene wax asphalt modifier prepared by the present invention to prepare the modified asphalt, without adding other modifiers, can make the modified asphalt have good high-temperature performance and meet the various performance indicators for road use. Detailed Embodiments

[0023] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0024] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0025] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0026] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention's specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention's specification are obvious to those skilled in the art. The present invention's specification and examples are merely exemplary.

[0027] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0028] The present invention provides a cracking catalyst, which can prepare a polyethylene wax asphalt modifier using waste plastic particles as the main raw material. By using a two-stage gradient cracking technology of a twin-screw extruder + a high-temperature and high-pressure reactor, precise and efficient cracking of different types of polyethylene in waste plastic particles is achieved, and a polyethylene wax asphalt modifier with excellent performance is obtained. The gradient cracking technology of the present invention solves the problem that the traditional reactor affects the performance of polyethylene wax due to excessive cracking of mixed waste plastic particles. The polyethylene wax prepared by the present invention can effectively improve the high and low temperature performance of asphalt without adding other modifiers, and can also significantly reduce the mixing temperature of asphalt.

[0029] The first aspect of the present invention provides an application of a cracking catalyst in the preparation of a polyethylene wax asphalt modifier. The preparation method of the cracking catalyst includes the following steps:

[0030] Dry and crush expanded vermiculite to obtain expanded vermiculite powder (particle size 200-230 mesh);

[0031] Dissolve nickel salt in water to obtain nickel nitrate solution;

[0032] Immerse the expanded vermiculite powder in the nickel nitrate solution and mix well, then naturally precipitate and filter to obtain the impregnated powder;

[0033] Dry the impregnated powder, and then calcine and ashing at 300-350 °C for 2.5-3 h to obtain the cracking catalyst;

[0034] The mass ratio of the expanded vermiculite to the nickel salt and water is 30:26:(30-50).

[0035] In some embodiments of the present invention, the drying is specifically drying at 60 °C for 20-30 min.

[0036] In a preferred embodiment of the present invention, the nickel salt is Ni(NO 3 ) 2 ·6H 2 O.

[0037] The second aspect of the present invention provides a preparation method of a polyethylene wax asphalt modifier, including the following steps:

[0038] Mix polyethylene particles and the cracking catalyst to obtain mixture particles;

[0039] Feed the mixture particles into a twin-screw extruder for extrusion to obtain a micro-cracked liquid glue;

[0040] Perform a high-temperature and high-pressure reaction on the micro-cracked liquid glue to obtain the polyethylene wax asphalt modifier.

[0041] In a preferred embodiment of the present invention, the polyethylene particles include high-density polyethylene, low-density polyethylene, and / or linear low-density polyethylene.

[0042] The polyethylene particles described in the present invention can be waste polyethylene particles such as recycled plastic particles, or can be unused non-recycled polyethylene particles. For cost savings, recycled plastic particles are used in the specific embodiments of the present invention.

[0043] In a preferred embodiment of the present invention, the mass ratio of the polyethylene particles to the cracking catalyst is 100:5.

[0044] In a preferred embodiment of the present invention, the parameter settings of the twin-screw extruder are as follows: the temperature of the first zone is 100 - 120 °C, the temperature of the second zone is 140 - 160 °C, the temperature of the third zone is 170 - 190 °C, the temperature of the fourth zone is 200 - 220 °C, the temperature of the fifth zone is 170 - 190 °C, the temperature of the die head is 120 - 160 °C, and the screw speed is 5 rpm.

[0045] In the present invention, the temperature gradient of the twin-screw extruder is set to ensure partial micro-cracking of polyethylene, so as to cooperate with the precise cracking in the high-temperature and high-pressure reaction. If the temperature of each zone of the twin-screw extruder is too low, the first-stage cracking reaction will be insufficient, and if the temperature is too high, over-cracking will occur.

[0046] In a preferred embodiment of the present invention, the high-temperature and high-pressure reaction is specifically as follows: under an inert atmosphere and a pressure of 0.8 - 1.6 MPa, react at 320 - 360 °C for 15 - 30 min.

[0047] In the present invention, if the temperature of the high-temperature and high-pressure reaction is too low, incomplete cracking of polyethylene will occur, and if the temperature is too high, over-cracking will occur, forming gas or gasoline and affecting the product performance. Therefore, a reaction temperature of 320 - 360 °C is selected.

[0048] Under the protection of an inert gas, the present invention adopts two-stage cracking of a twin-screw extruder and a high-temperature and high-pressure reaction kettle. Under the condition of adding a cracking catalyst, by controlling the temperature, pressure, and reaction time in the high-temperature and high-pressure reaction kettle, a polyethylene wax asphalt modifier with excellent performance is obtained.

[0049] In the present invention, the twin-screw extruder plays a role in mixing and micro-cracking. By cooperating with the specific temperature, pressure, and reaction time in the reaction kettle, an organic whole is formed, preparing a polyethylene wax with performance indicators far superior to those prepared by the existing process. At the same time, it can also shorten the reaction time of the traditional cracking method and greatly reduce the energy consumption problem.

[0050] The third aspect of the present invention provides a polyethylene wax asphalt modifier prepared according to the described preparation method.

[0051] The fourth aspect of the present invention provides the application of the polyethylene wax asphalt modifier described above in modified asphalt.

[0052] The fifth aspect of the present invention provides a modified asphalt, the raw materials of which include matrix asphalt and the polyethylene wax asphalt modifier described above.

[0053] In a further preferred embodiment of the present invention, the addition amount of the polyethylene wax asphalt modifier is 5% of the mass of the matrix asphalt.

[0054] The present invention utilizes the characteristics of expanded vermiculite powder such as porous and strong heat resistance, loads nickel-based compounds on it, prepares an improved cracking catalyst, and blends it with waste polyethylene particles. Under the protection of oxygen isolation, a twin-screw extruder is used to achieve full fusion between polyethylene particles and the catalyst through high temperature and high shear action, and a first-stage gradient micro-cracking product is obtained. The first-stage gradient micro-cracking product is put into a high-temperature and high-pressure reaction kettle, and through high-temperature, high-pressure and short-time cracking, a second-stage gradient deep-cracking product is obtained. By using the gradient cracking technology of a twin-screw extruder + high-temperature and high-pressure reaction kettle, precise control of the cracking degree of waste polyethylene particles is achieved. Compared with ordinary polyethylene wax, the polyethylene wax (polyethylene wax asphalt modifier) prepared by the present invention not only reduces the viscosity of asphalt but also modifies the asphalt, greatly improving the compatibility and storage stability between asphalt and polyethylene. Compared with ordinary polyethylene cracking technology, it can reduce a large amount of energy consumption, increase the recycling degree of waste polyethylene plastics, save energy and protect the environment, and make efficient use.

[0055] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been made public.

[0056] The polyethylene particles used in the examples of the present invention are recycled plastic particles produced by Shenxian Kehuan Renewable Resources Company, and their main components are HDPE, LDPE and LLDPE, and the mass ratio of HDPE, LDPE and LLDPE is between 2:3:5 and 3:4:6.

[0057] The technical solutions provided by the present invention will be described in detail below with reference to the examples, but they should not be construed as limiting the protection scope of the present invention.

[0058] Example 1

[0059] 1. A cracking catalyst, by mass, the raw materials are composed of 26 parts of Ni(NO 3 ) 2 ·6H 2 O, 30 parts of expanded vermiculite and 30 parts of deionized water.

[0060] The preparation method of the above cracking catalyst is as follows:

[0061] (1) Dry the expanded vermiculite at 110 °C for 2 h, crush it with a crusher for 10 min, then grind it with a ball mill for 45 min, and dry it at 110 °C for 1 h to obtain expanded vermiculite powder with a particle size of 200 - 230 mesh.

[0062] (2) Dissolve Ni(NO 3 ) 2 ·6H 2 O in deionized water to obtain a nickel nitrate solution.

[0063] (3) Add the expanded vermiculite powder to the nickel nitrate solution and mix evenly. After waiting for it to naturally precipitate for 2 h, filter it with filter paper to obtain the impregnated expanded vermiculite powder (abbreviation: impregnated powder).

[0064] (4) Dry the impregnated powder at 60 °C for 30 min, then put it into a muffle furnace and calcine it at 350 °C for 3 h to obtain the cracking catalyst.

[0065] 2. A polyethylene wax asphalt modifier, by mass, the raw materials consist of 100 parts of polyethylene particles (20 parts of HDPE + 30 parts of LDPE + 50 parts of LLDPE) and 5 parts of the cracking catalyst.

[0066] The preparation method of the above polyethylene wax asphalt modifier is as follows:

[0067] 1) Put the polyethylene particles and the cracking catalyst into a stirrer and stir well to obtain mixture particles.

[0068] 2) Feed the mixture particles into a twin-screw extruder, and control the temperatures of each zone of the twin-screw extruder as follows: the temperature of the first zone is 100 °C, the temperature of the second zone is 140 °C, the temperature of the third zone is 170 °C, the temperature of the fourth zone is 200 °C, the temperature of the fifth zone is 170 °C, and the temperature of the die head is 120 °C. Control the screw speed at 5 rpm and react in the twin-screw extruder for 10 min to obtain a micro-cracked liquid glue.

[0069] 3) Select a high-temperature and high-pressure reactor with a volume of 1 L, and add the micro-cracked liquid glue to the reactor at an addition amount of 10% of the volume of the high-temperature and high-pressure reactor.

[0070] 4) Open the inlet and exhaust ports of the reactor, and introduce N with a purity of 99.999% into the reactor. 2, introduce for 15 minutes. After purging the air in the reaction kettle, close the exhaust port, use the gas cylinder pressure reducing valve to adjust the pressure in the reaction kettle to 1 MPa. After closing the inlet port, turn on the heating device and raise the temperature to 340 °C at a heating rate of 10 °C / min. After reacting for 10 minutes, wait for the instrument temperature to cool down to room temperature and then discharge the material. And let the product cool naturally to room temperature to obtain the polyethylene wax asphalt modifier.

[0071] Use the polyethylene wax asphalt modifier prepared in this example to modify asphalt: Preheat 70# base asphalt to 120 °C in a container, put the polyethylene wax asphalt modifier with a mass percentage of 5% (referring to the mass percentage of 70# base asphalt) into the asphalt. After it is fully dissolved in the asphalt, stir for 15 minutes to obtain modified asphalt Example 1.

[0072] Example 2

[0073] 1. A cracking catalyst, calculated by mass parts, the raw materials are composed of 26 parts of Ni(NO 3 ) 2 ·6H 2 O, 30 parts of expanded vermiculite and 40 parts of deionized water.

[0074] The preparation method of the above cracking catalyst is as follows:

[0075] (1) The same as step (1) of Example 1.

[0076] (2) The same as step (2) of Example 1.

[0077] (3) The same as step (3) of Example 1.

[0078] (4) Dry the impregnated powder at 60 °C for 30 minutes, then put it into a muffle furnace and calcine and ashing at 320 °C for 3 hours to obtain the cracking catalyst.

[0079] 2. A polyethylene wax asphalt modifier, calculated by mass parts, the raw materials are composed of 100 parts of polyethylene particles (20 parts of HDPE + 30 parts of LDPE + 50 parts of LLDPE) and 5 parts of cracking catalyst.

[0080] The preparation method of the above polyethylene wax asphalt modifier is as follows:

[0081] 1) The same as step 1) of Example 1.

[0082] 2) Feed the mixture particles into a twin-screw extruder, and control the temperatures of each zone of the twin-screw extruder as follows: the temperature of zone 1 is 110 °C, the temperature of zone 2 is 150 °C, the temperature of zone 3 is 180 °C, the temperature of zone 4 is 210 °C, the temperature of zone 5 is 180 °C, and the temperature of the die head is 130 °C. Control the screw speed at 5 rpm. After reacting in the twin-screw extruder for 10 min, a micro-cracked liquid glue is obtained.

[0083] 3) Select a high-temperature and high-pressure reactor with a volume of 1 L, and add the micro-cracked liquid glue to the reactor at an addition amount of 10% of the volume of the high-temperature and high-pressure reactor.

[0084] 4) Open the inlet and exhaust ports of the reactor, and introduce N with a purity of 99.999% into the reactor. 2 , the introduction time is 15 min. After exhausting the air in the reactor, close the exhaust port. Use a cylinder pressure reducing valve to adjust the pressure in the reactor to 1.2 MPa. After closing the inlet port, turn on the heating device and raise the temperature to 320 °C at a heating rate of 10 °C / min. After reacting for 15 min, wait for the instrument temperature to cool down to room temperature and then discharge the material. And let the product cool naturally to room temperature, then a polyethylene wax asphalt modifier can be obtained.

[0085] Use the polyethylene wax asphalt modifier prepared in this example to modify asphalt: Preheat 70# base asphalt to 120 °C in a container, add 5% by mass of the polyethylene wax asphalt modifier to the asphalt. After it is fully dissolved in the asphalt, stir for 15 min to obtain modified asphalt Example 2.

[0086] Example 3

[0087] 1. A cracking catalyst, by mass, the raw materials are composed of 26 parts of Ni(NO 3 ) 2 ·6H 2 O reagent, 30 parts of expanded vermiculite and 50 parts of deionized water.

[0088] The preparation method of the above cracking catalyst is as follows:

[0089] (1) The same as step (1) of Example 1.

[0090] (2) The same as step (2) of Example 1.

[0091] (3) The same as step (3) of Example 1.

[0092] (4) Dry the impregnated powder at 60 °C for 30 min, and then put it into a muffle furnace and calcine and ashing at 300 °C for 2.5 h to obtain the cracking catalyst.

[0093] 2. A polyethylene wax asphalt modifier, by mass, the raw materials are composed of 100 parts of polyethylene particles (20 parts of HDPE + 30 parts of LDPE + 50 parts of LLDPE) and 5 parts of cracking catalyst.

[0094] The preparation method of the above polyethylene wax asphalt modifier is as follows:

[0095] 1) The same as step 1) of Example 1.

[0096] 2) Feed the mixture particles into a twin-screw extruder, and control the temperatures of each zone of the twin-screw extruder as follows: the temperature of the first zone is 120 °C, the temperature of the second zone is 160 °C, the temperature of the third zone is 190 °C, the temperature of the fourth zone is 220 °C, the temperature of the fifth zone is 190 °C, and the temperature of the die head is 140 °C. Control the screw speed at 5 rpm. After reacting in the twin-screw extruder for 10 min, a micro-cracked liquid glue is obtained.

[0097] 3) Select a high-temperature and high-pressure reactor with a volume of 1 L, and add the micro-cracked liquid glue to the reactor at an addition amount of 10% of the volume of the high-temperature and high-pressure reactor.

[0098] 4) Open the inlet and outlet valves of the reactor, and introduce N with a purity of 99.999% into the reactor. 2 , the introduction time is 15 min. After exhausting the air in the reactor, close the outlet valve, use a cylinder pressure reducing valve to adjust the pressure in the reactor to 0.8 MPa, close the inlet valve, then turn on the heating device, and raise the temperature to 360 °C at a heating rate of 10 °C / min. After reacting for 10 min, wait for the instrument temperature to cool down to room temperature and then discharge the material. And let the product cool naturally to room temperature, then the polyethylene wax asphalt modifier can be obtained.

[0099] Use the polyethylene wax asphalt modifier prepared in this example to modify asphalt: Preheat 70# base asphalt to 120 °C in a container, put 5% of the cracked wax modifier by mass percentage into the asphalt. After it is fully dissolved in the asphalt, stir for 15 min to obtain Modified Asphalt Example 3.

[0100] Example 4

[0101] The difference from Example 1 is only that the reaction temperature of the reactor in step 4) is 320 °C, and the other steps and parameters are the same as those in Example 1.

[0102] Example 5

[0103] The difference from Example 1 is only that the reaction temperature of the reactor in step 4) is 300 °C and the reaction time is 20 min, and the other steps and parameters are the same as those in Example 1.

[0104] Comparative Example 1

[0105] The difference from Example 1 is only that in the process of preparing the polyethylene wax asphalt modifier, step 2) is omitted, and the reaction time in the reaction kettle in step 4) is 20 min.

[0106] Comparative Example 2

[0107] The difference from Example 1 is only that in the process of preparing the polyethylene wax asphalt modifier, step 2) is omitted, and the air pressure in the reaction kettle in step 4) is 1.2 MPa, the reaction temperature is 320 °C, and the reaction time is 25 min.

[0108] Comparative Example 3

[0109] The difference from Example 1 is only that in the process of preparing the polyethylene wax asphalt modifier, step 2) is omitted, and the air pressure in the reaction kettle in step 4) is 0.8 MPa, the reaction temperature is 360 °C, and the reaction time is 20 min.

[0110] Comparative Example 4

[0111] The difference from Example 1 is only that in the process of preparing the polyethylene wax asphalt modifier, step 2) is omitted, and the reaction temperature in the reaction kettle in step 4) is 320 °C, and the reaction time is 20 min.

[0112] Comparative Example 5

[0113] The difference from Example 1 is only that in the process of preparing the polyethylene wax asphalt modifier, step 2) is omitted, and the reaction temperature in the reaction kettle in step 4) is 300 °C, and the reaction time is 30 min.

[0114] The penetration, softening point, ductility and viscosity changes of the modified asphalt prepared in the above examples and comparative examples were analyzed and detected. The analysis and detection tests were carried out strictly in accordance with the specific requirements and steps of "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTGE20 - 2011). The results are shown in Table 1.

[0115] Table 1

[0116]

[0117]

[0118] As can be seen from Table 1, the penetration of Examples 1-5 decreased significantly compared with the base asphalt, and the softening point increased significantly compared with the base asphalt, indicating that the polyethylene wax modifier prepared by using the gradient controllable technology of the present invention (two-stage gradient cracking technology of twin-screw extruder + high-temperature and high-pressure reactor) has a great improvement effect on the high-temperature performance of asphalt. The ductility at 10 °C increased to a certain extent compared with the base asphalt, indicating that it has an improvement effect on the low-temperature performance of asphalt. The Brookfield viscosity at 135 °C decreased significantly compared with the base asphalt, indicating that it has a great effect on the warm mixing of asphalt.

[0119] The penetration of Comparative Examples 1-5 increased significantly compared with the base asphalt, and the softening point increased compared with the base asphalt but the effect was not obvious, indicating that the polyethylene wax modifier prepared by the traditional reactor cracking technology has little effect on improving the high-temperature performance of asphalt. The ductility at 10 °C decreased to a certain extent compared with the base asphalt, indicating that it has an adverse effect on the low-temperature performance of asphalt.

[0120] From the above results, it can be concluded that since the waste plastic particles used in the examples are mixed by three different types of polyethylene (HDPE+LDPE+LLDPE), when using a traditional high-temperature and high-pressure reactor to crack them, there will be a phenomenon of over-cracking of some polyethylene particles. Due to over-cracking, it will cause the phenomenon that the polyethylene wax modifier produced has an adverse effect on the performance of asphalt. The modified asphalt prepared by using the polyethylene wax asphalt modifier of the present invention can effectively improve the high-temperature performance of asphalt while the mixing temperature is effectively reduced and meets the "Technical Specification for Highway Asphalt Pavement Construction", and the low-temperature performance is also improved to a certain extent. Therefore, by using the method of gradient cracking of polyethylene particles with a twin-screw extruder + high-temperature and high-pressure reactor, it is possible to achieve precise and controllable full cracking of waste polyethylene particles mixed with various polyethylenes, so as to prepare a polyethylene wax modifier with good appearance and excellent performance.

[0121] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. Use of a cracking catalyst in the preparation of a polyethylene waxy asphalt modifier, characterized in that: The preparation method of the cracking catalyst comprises the following steps: Drying and crushing the expanded vermiculite to obtain expanded vermiculite powder; Dissolving a nickel salt in water to obtain a nickel nitrate solution; The expanded vermiculite powder is immersed in a nickel nitrate solution and mixed evenly, and then naturally precipitated and filtered to obtain an immersed powder; The impregnated powder is dried, and then calcined at 300-350° C. for 2.5-3 hours to obtain the cracking catalyst; The mass ratio of the expanded vermiculite to the nickel salt and water is 30:26:(30-50).

2. The use of the cracking catalyst according to claim 1 in the preparation of a polyethylene waxy asphalt modifier, characterized in that: The nickel salt is Ni(NO3)2·6H2O.

3. A method for preparing a polyethylene waxy asphalt modifier, characterized in that: The following steps are involved: Mixing polyethylene particles and the cracking catalyst described in claim 1 or 2 to obtain mixture particles; The mixture particles are fed into a twin-screw extruder for extrusion to obtain a micro-cracked liquid glue; The micro-cracked liquid gum is subjected to a high temperature and high pressure reaction to obtain the polyethylene waxy asphalt modifier.

4. The method for preparing the polyethylene waxy asphalt modifier according to claim 3, characterized in that: The polyethylene particles include high-density polyethylene, low-density polyethylene and / or linear low-density polyethylene.

5. The method for preparing the polyethylene waxy asphalt modifier according to claim 3, characterized in that: The mass ratio of the polyethylene particles to the cracking catalyst is 100:

5.

6. The method for preparing the polyethylene waxy asphalt modifier according to claim 3, characterized in that: The parameters of the twin-screw extruder are set as follows: zone 1 temperature 100-120°C, zone 2 temperature 140-160°C, zone 3 temperature 170-190°C, zone 4 temperature 200-220°C, zone 5 temperature 170-190°C, die head temperature 120-160°C, and screw speed 5rpm.

7. The method for preparing the polyethylene waxy asphalt modifier according to claim 3, characterized in that: The high temperature and high pressure reaction is specifically: reacting at 320-360° C. for 15-30 minutes under an inert atmosphere and a pressure of 0.8-1.6 MPa.

8. The polyethylene waxy asphalt modifier prepared according to the preparation method according to any one of claims 3 to 7.

9. Use of the polyethylene waxy asphalt modifier as claimed in claim 8 in modified asphalt.

10. A modified asphalt, characterized in that: The raw materials include base asphalt and the polyethylene waxy asphalt modifier described in claim 8.

Images