Method for low-temperature carbonization of waste polyolefins and composites thereof

Abstract

The application relates to a low-temperature carbonization method of waste polyolefin and a composite material thereof. First, waste polyolefin is crushed, then mixed with biomass powder to be extruded and granulated, then subjected to a supercritical carbonization reaction at 400-500 DEG C, and finally mixed with polyethylene and processing aids to be extruded and granulated to obtain an antistatic composite material. The application utilizes the synergistic co-degradation effect between biomass and waste polyolefin to reduce the carbonization temperature, utilizes the strong oxidation effect of supercritical water to further reduce the carbonization temperature, improves the carbon conversion efficiency and degree, and extracts tar and oil phase products blocked in pores, so that subsequent acid pickling and industrial wastewater generation are not needed. The carbon material produced by the application can be directly used in antistatic materials, and can be directly used in composite modified polyethylene due to good compatibility with polyethylene, so that comprehensive utilization of waste plastics and agricultural and forestry wastes is realized, and a closed-loop key design of waste plastic recycling and reuse is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plastic processing and solid waste recycling, and particularly relates to a low-temperature carbonization method of waste polyolefin and a composite material thereof. BACKGROUND

[0002] Plastic products have good chemical stability and are difficult to degrade under natural conditions, which has caused serious environmental pollution problems, so the recycling of waste plastics has become the research focus of researchers all over the world. Among numerous plastic products, polyolefin products account for the vast majority. Considering that polyolefin is rich in carbon elements, therefore, it should have great industrial application potential to prepare high-value carbon materials and composite materials thereof from waste polyolefin as raw materials.

[0003] CN102815690A mixes waste plastics with sodium, magnesium and sulfur in a certain proportion, then seals them in a stainless steel autoclave, and reacts for 5-10 hours under high temperature and high pressure conditions to prepare hollow carbon spheres. This method has harsh reaction conditions and low production efficiency, is not suitable for large-scale promotion, and uses inorganic acids such as nitric acid, sulfuric acid and hydrochloric acid in the subsequent treatment of the product, generating a large amount of industrial acid and alkali wastewater, which is not only harmful to environmental protection but also causes subsequent processing to be very troublesome. CN110950318A uses biomass to promote low-temperature carbonization of waste polyester. The intermediate degradation products containing hydroxyl groups generated during the biomass pyrolysis process undergo esterification with carboxylic acid products generated during the degradation of polyester, resulting in the generation of polyester volatile products and the promotion of the crosslinking of polyester, thereby improving the yield of carbon materials. This method ignores the generation of tar during the carbonization of biomass, which adheres to the surface and gaps of the carbon material, seriously affecting the performance of the carbon material and hindering subsequent application. The general method for removing tar is usually inorganic acid washing, but this will generate a large amount of waste acid, so this method still needs to be further improved. CN110817840B uses biomass to promote low-temperature carbonization of waste polyolefin. This method also ignores the presence of tar and oil phase products. Even though the patent does not mention the acid washing step to remove tar, the presence of tar and oil phases affects the performance of the carbon material and the actual application scenario, making it impossible to directly composite with resins such as polyethylene to prepare functional materials. If further application is desired, acid washing and other methods must be used to remove the tar phase. In addition, the muffle furnace only relies on high temperature for carbonization, and the overall carbonization effect is not good. This scheme is carried out in air, and the plastic will burn in the air during the carbonization process and produce corresponding by-products, reducing the carbonization efficiency and carbon conversion degree. CN110592937A uses carbon fibers and carbon nanotubes to composite elastic polyethylene imine and aims to improve the interfacial adhesion of the composite. However, this method has many reaction steps, and the use of concentrated nitric acid and other acid solutions will generate a large amount of waste acid, which is not environmentally friendly. In summary, the current common carbonization processes for waste polyethylene are relatively harsh, often requiring high temperature and high pressure as well as expensive catalysts, resulting in many by-products and complicated subsequent treatment processes of the product. The use of a large amount of acid and alkali solutions poses a problem in the treatment of waste liquid, and there is still a lack of a new technology for carbonizing waste plastics that is mild in conditions, does not require post-treatment, has high controllability of carbonization, and has high reaction efficiency.

[0004] Due to the immaturity of the waste polyolefin carbonization process, the application research of the carbon material is also very few, and the current research is only limited to the carbon material itself, such as preparing a simple adsorption carbon for adsorbing heavy metal ions, but limited by the cost and other problems, it is doomed to be unable to popularize. Some scholars also made the carbon material into lithium and sodium ion battery anode, but limited by the cycle stability and other problems, it also cannot realize commercialization, so the existing technology lacks effective and high value-added application process scheme. In contrast, the carbon material prepared from waste polyolefin is melt blended with polyethylene and other raw materials to prepare antistatic composite modified material, which is undoubtedly of historical significance. At present, the research on carbon / polyethylene composite material mainly selects carbon nanotubes and carbon fibers as carbon materials, which are not only expensive, but also have poor compatibility with polyethylene and are prone to agglomeration. The carbon material prepared from waste polyolefin contains a large amount of residues, which can act as a natural compatibilizer and exhibit better compatibility with polyethylene. In addition, the carbon material prepared from waste polyolefin is used as a composite modified raw material, and the composite modified material can be prepared into carbon material again after being discarded, which realizes the closed cycle design of waste plastic recycling and reuse. SUMMARY

[0005] One of the purposes of the present application is to provide a low-temperature carbonization method of waste polyolefin, which comprises the following steps: first, crushing the waste polyolefin, then mixing and extruding granulation with biomass, and performing a supercritical carbonization reaction, to obtain carbon material with excellent performance without subsequent treatment. The blending extrusion granulation can ensure that the biomass is uniformly dispersed in the polyethylene matrix, and the use of biomass as a synergistic catalytic degradation agent can reduce the carbonization temperature of polyolefin. With the strong oxidation effect of supercritical water, the carbonization temperature can be further reduced, and the carbon conversion efficiency and degree of carbon conversion can be improved. The supercritical water can also extract tar and oil phase products blocked in the pores, avoiding subsequent complex and high-cost acid washing treatment. The prepared carbon material can be directly used as an antistatic material to composite modify polyethylene.

[0006] Further, the waste polyolefin is at least one selected from waste high-density polyethylene, waste low-density polypropylene, waste low-density linear polyethylene, waste medium-density polyethylene, waste polypropylene, waste poly-1-butene, waste poly-2-butene, waste 1,3-butadiene, waste poly-1-pentene, waste 1,4-pentadiene, waste poly-1-hexene, waste cis, cis-2,4-hexadiene, waste (2Z,4Z)-2,4-hexadiene, waste poly-1-octene, waste poly-1-heptene, waste cyclohexene, and waste 3-methylcyclopentene.

[0007] Further, the waste polyolefin is crushed into small pieces or particles of 2-4 mm by a crusher for standby use.

[0008] Further, the biomass is selected from at least one of sunflower seed shell, corn stalk, rice husk, jute, bamboo, wood chips, flax, wheat straw, coconut shell, reed.

[0009] Further, the biomass is added in the form of powder, and the particle size is 200-400 meshes.

[0010] Further, the biomass is added in the form of powder, and the particle size is 200-400 meshes.

[0011] Further, the device used for extruding and granulating is a single or double screw extruder, the blending temperature is set to 170-190 DEG C, the extrusion temperature is set to 160-170 DEG C, and the screw extrusion speed is 100-200 r / min.

[0012] Further, the device used for supercritical carbonization reaction is a supercritical carbonization reactor, and the reaction process is as follows: the material is added into the supercritical carbonization reactor, the temperature is raised to 400-500 DEG C at a temperature rising speed of 5-10 DEG C / min, during which the temperature reaches 200 DEG C, the horizontal flow pump is started, the water flow rate is set to 5-10 mL / min, the pressure in the reactor is controlled to 25-35 MPa, and the carbonization time is 15-30 min.

[0013] Further, the supercritical carbonization reaction is naturally cooled to room temperature, then the product is dried at 60-80 DEG C, and then ground to 800-1000 meshes, and finally the carbon material is obtained.

[0014] The second object of the present application is to provide a carbon material obtained based on waste polyolefin supercritical carbonization.

[0015] Further, the average particle size of the carbon material is 0.80-1.70 mu m, the specific surface area is 200-270 m 2 g -1 .

[0016] The third object of the present application is to provide a preparation method of a carbon material / polyethylene antistatic composite material, mainly comprising the following steps: the prepared carbon material is uniformly mixed with polyethylene, a compatibilizer, a dispersing agent and an antioxidant, and then extruding and granulating.

[0017] Further, the polyethylene is high-density polyethylene, and the adding amount is 60%-80% of the mass of waste polyolefin.

[0018] Further, the compatibilizer is selected from at least one of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, ethylene-acrylate-succinic anhydride copolymer, ethylene-glycidyl methacrylate copolymer, and the adding amount is 4%-6% of the waste polyolefin.

[0019] Further, the dispersant is selected from at least one of paraffin, polyethylene wax, stearic acid, zinc stearate, calcium stearate, butyl stearate, and the adding amount is 1%-3% of the waste polyolefin.

[0020] Further, the antioxidant is selected from at least one of antioxidant DLTDP, antioxidant BHT, antioxidant 168, antioxidant 626, antioxidant 1010, antioxidant 1075, antioxidant 2246, and the adding amount is 0.5%-2% of the waste polyolefin.

[0021] Further, the equipment used for extrusion granulation is a single screw extruder or a double screw extruder, the blending temperature is 170-190 DEG C, the extrusion temperature is 160-170 DEG C, and the screw extrusion rotation speed is 100-200 r / min.

[0022] Further, the material obtained by extrusion granulation needs to be fully dried at 60-80 DEG C.

[0023] The principle of the present application is as follows: biomass has a synergistic co-degradation effect with waste polyolefin, the carbonization temperature of biomass is lower than that of polyolefin, the formed biomass carbon can act as a catalyst, the free radical macromolecules formed by the degradation of polyolefin are dissolved on the surface of carbon material and attached to the biomass carbon skeleton to grow, which promotes the carbonization process and reduces the carbonization temperature. In addition, the intermediate products of biomass degradation can react with the free radical macromolecules produced by the degradation of waste polyolefin, capture the macromolecular free radicals generated by the degradation of polyolefin, avoid their further decomposition into smaller molecular fragments and volatilization, and promote the subsequent crosslinking reaction of macromolecular free radicals, thereby improving the carbonization reaction efficiency and the yield of carbon material, effectively avoiding the generation of by-products and inducing the production of aromatic hydrocarbons, and aromatic hydrocarbons are more likely to form amorphous carbon. In fact, there are multiple branch reactions in the thermal decomposition process of polyolefin plastics, so different decomposition products will be produced. The addition of biomass in the present application actually induces a certain reaction to occur (i.e. the reaction of generating aromatic hydrocarbon compounds), and then amorphous carbon is prepared.

[0024] Supercritical water has strong oxidizing property and catalytic effect, which can further reduce the carbonization temperature of waste polyolefin, realize low-temperature carbonization, and supercritical water has high permeability and high diffusivity, extracts tar and oil phase products blocked in the pores, forms more microporous structure, and improves the application potential of carbon materials. The residues of waste polyolefin carbon and polyethylene raw materials have better compatibility, and a small amount of compatibilizer is added and melt reactive blending is adopted to prepare carbon / polyethylene antistatic composite materials with good compatibility, which realizes the comprehensive utilization of waste plastics and agricultural and forestry wastes, and also realizes the closed loop key design of waste plastic recycling and reuse.

[0025] The progressiveness and beneficial effects of the present application mainly reflect in the following points:

[0026] (1) The present application first uses waste polyolefin to prepare amorphous carbon material, which not only improves the conversion efficiency of carbon material and simplifies the process, but also reduces the cost, and then the carbon material is melt blended with polyethylene and other raw materials to prepare a composite material with better compatibility. The mechanical properties of the composite material are excellent, and it can be applied in the field of antistatic materials.

[0027] (2) The present application uses biomass as a synergistic degradation catalyst to prepare carbon materials under supercritical water conditions, which is simpler in process and does not need subsequent treatment, and the whole process is more safe and environmentally friendly.

[0028] (3) The production efficiency of the method of the present application is high, and it can be mass produced, which provides a new solution for the recycling and reuse of waste olefins. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The scanning electron microscope graph of the carbon material prepared in Example 4. DETAILED DESCRIPTION

[0030] In order for those skilled in the art to fully understand the technical solutions and beneficial effects of the present application, the following will be further described in combination with specific embodiments and drawings.

[0031] In order to fully understand the properties of raw materials, intermediate products and final products, the present application tests each sample according to the following method:

[0032] 1. Average particle size test

[0033] The prepared carbon material is carefully ground into powder, then an appropriate amount is placed in anhydrous ethanol for ultrasonic dispersion, then a small amount of mixture is dropped on a silicon wafer, and after the alcohol evaporates, the silicon wafer is stuck on the sample stage, and the morphology is observed with a scanning electron microscope, and the average particle size of the particles in the morphology photo is measured with a computer.

[0034] 2. Specific surface area test

[0035] The prepared carbon material was carefully ground, and the nitrogen adsorption and desorption amount was determined by a specific surface area analyzer, thereby obtaining the specific surface area data of the carbon material.

[0036] 3. Volume resistance test

[0037] The composite material was compression molded at 180°C and 10MPa for 10min, and the pressure was maintained for cooling to obtain a sheet with a size of 120mmx100mmx2mm. The volume resistivity was measured at room temperature by using a high resistance meter, and 5 groups were tested in parallel. The average value of the 5 groups of data was taken as the result.

[0038] 4. Tensile property test

[0039] The composite material was compression molded at 180°C and 10MPa for 10min, and the pressure was maintained for cooling to obtain a sheet with a thickness of 1mm. The sheet was cut into a dumbbell shape with a size of 20mmx4mmx1mm, and tested according to ASTM D63-2014 by using a universal tensile testing machine with a tensile speed of 50mm / min. 5 groups were tested in parallel, and the average value of the 5 groups of data was taken as the result.

[0040] Example 1

[0041] First, 100 parts by weight of waste low-density polyethylene was crushed into small pieces of about 2mm by using a crusher. Then, the crushed particles were transferred to a high-speed mixer, and 20 parts by weight of 200 mesh sunflower seed shell powder was added. The obtained mixture was mixed at room temperature for 5min at a speed of 500rpm. The mixed material was extruded and granulated by using a single screw extruder, with a blending temperature of 170°C and an extrusion temperature of 160°C, and a screw extrusion speed of 100rpm. The granulated material was added to a supercritical carbonization reactor, and the temperature was increased from room temperature to 400°C at a rate of 5°C / min. When the temperature reached 200°C, a horizontal flow pump was started, with a water flow rate of 5mL / min. The pressure in the reactor was controlled at 25MPa, and the carbonization time was 15min. After carbonization, the material was naturally cooled to room temperature in the oven, and then dried at 60°C. Finally, the material was ground to 800 mesh in a ball mill, thereby obtaining a carbon material powder.

[0042] The ground carbon powder was added to a high-speed mixer, and 60 parts by weight of polyethylene, 4 parts by weight of maleic anhydride grafted polyethylene, 1 part by weight of paraffin, and 0.5 parts by weight of antioxidant DLTDP were added. The obtained mixture was mixed at room temperature for 10min at a speed of 600rpm. The mixed material was extruded and granulated by using a single screw extruder, with a blending temperature of 170°C and an extrusion temperature of 160°C, and a screw extrusion speed of 100rpm. The granulated material was dried at 60°C, thereby obtaining a carbon material / polyethylene composite material.

[0043] The average particle size of the carbon material prepared was 0.92 μm, the specific surface area was 214.84 m 2 g -1 The volume resistance of the composite material prepared was 4.42 x 10 7 Ω / sq., and the tensile properties were as shown in Table 1.

[0044] Example 2

[0045] First, 100 parts by weight of waste polypropylene was crushed into small pieces of about 2.5 mm using a crusher, and the crushed particles were then transferred to a high-speed mixer. Then, 22 parts by weight of 250 mesh corn straw powder was added, and the resulting mixture was mixed at room temperature for 6 minutes at a speed of 550 rpm. The mixed material was then added to a twin-screw extruder, and the blending temperature was set to 175°C, the extrusion temperature was set to 162°C, and the screw extrusion speed was set to 125 rpm. The granulated material was then added to a supercritical carbonization reactor, and the temperature was increased from room temperature to 425°C at a rate of 6°C / min. When the temperature reached 200°C, a laminar flow pump was started, and the water flow rate was set to 6 mL / min. The pressure was controlled at 27.5 MPa, and the carbonization time was 18 minutes. After carbonization, the material was naturally cooled to room temperature in the furnace, and then the material was removed and dried at 65°C. The dried material was then ground to 850 mesh in a ball mill, thereby obtaining a carbon material powder.

[0046] The ground carbon powder was then added to a high-speed mixer, and 65 parts by weight of polyethylene, 4.5 parts by weight of maleic anhydride grafted polypropylene, 1.5 parts by weight of polyethylene wax, and 0.9 parts by weight of antioxidant BHT were added. The resulting mixture was mixed at room temperature for 15 minutes at a speed of 650 rpm. The mixed material was then added to a twin-screw extruder, and the blending temperature was set to 175°C, the extrusion temperature was set to 163°C, and the screw extrusion speed was set to 125 rpm. The granulated material was then dried at 65°C, thereby obtaining a carbon material / polyethylene composite material.

[0047] The average particle size of the carbon material prepared was 1.05 μm, the specific surface area was 223.82 m 2 g -1 The volume resistance of the composite material prepared was 4.99 x 10 7 Ω / sq., and the tensile properties were as shown in Table 1.

[0048] Example 3

[0049] First, 50 parts by weight of waste high-density polyethylene, 50 parts by weight of poly-1-butene were crushed into small pieces of about 3 mm by a crusher, and then the crushed particles were transferred to a high-speed stirrer, 12 parts by weight of wheat straw powder with a particle size of 300 mesh, 13 parts by weight of rice husk powder were added, and the obtained mixture was mixed at room temperature for 7 min at a speed of 600 rpm. The mixed material was added to a twin-screw extruder for extrusion and granulation, the blending temperature was set to 180°C, the extrusion temperature was set to 165°C, and the screw extrusion speed was 150 rpm. The granulated material was added to a supercritical carbonization reactor, and the temperature was raised from room temperature to 450°C at a rate of 7°C / min. When the temperature reached 200°C, a horizontal flow pump was started, the water flow rate was set to 7 mL / min, the pressure was controlled at 30 MPa, and the carbonization time was 22 min. After carbonization, the material was naturally cooled to room temperature in the furnace, and then the material was taken out and dried at 70°C. Then the material was ground to 900 mesh in a ball mill, and thus a carbon material powder was obtained.

[0050] The ground carbon powder was added to a high-speed stirrer, and 70 parts by weight of polyethylene raw material, 5 parts by weight of ethylene-acrylic acid ester-succinic anhydride copolymer, 2 parts by weight of zinc stearate, and 1.2 parts by weight of antioxidant 168 were added. The obtained mixture was mixed at room temperature for 20 min at a speed of 700 rpm. The mixed material was added to a twin-screw extruder for extrusion and granulation, the blending temperature was set to 180°C, the extrusion temperature was set to 165°C, and the screw extrusion speed was 150 rpm. The granulated material was dried at 70°C to obtain a carbon material / polyethylene composite material.

[0051] The test results showed that the average particle size of the prepared carbon material was 1.29 μm, the specific surface area was 238.15 m 2 g -1 The volume resistance of the prepared composite material was 5.78 x 10 7 Ω / sq., and the tensile properties were as shown in Table 1.

[0052] Example 4

[0053] Firstly, 50 parts by weight of waste polypropylene and 50 parts by weight of 1, 3-butadiene were crushed into small pieces of about 3.5 mm by a crusher, and then the crushed particles were transferred to a high-speed stirrer, 14 parts by weight of coconut shell powder and 14 parts by weight of flax powder with a mesh size of 350 were added, and the obtained mixture was mixed at room temperature for 8 min at a speed of 650 r / min. The mixed material was added to a twin-screw extruder for extrusion and granulation, the blending temperature was set to 185°C, the extrusion temperature was set to 168°C, and the screw extrusion speed was 175 r / min. The granulated material was added to a supercritical carbonization reactor, and the temperature was raised from room temperature to 475°C at a rate of 8°C / min. When the temperature reached 200°C, the horizontal flow pump was started, the water flow rate was set to 9 mL / min, the pressure was controlled at 32.5 MPa, and the carbonization time was 26 min. After carbonization, the material was naturally cooled to room temperature in the furnace, and then the material was taken out and dried at 75°C. Then the material was ground to 950 mesh in a ball mill, thereby obtaining a carbon material powder.

[0054] The ground carbon powder was added to a high-speed stirrer, 75 parts by weight of polyethylene raw material, 2 parts by weight of ethylene-glycidyl methacrylate, 2.5 parts by weight of maleic anhydride grafted polyethylene, 1 part by weight of paraffin wax, 1.5 parts by weight of calcium stearate, 0.8 parts by weight of antioxidant 168, and 0.8 parts by weight of antioxidant 626 were added, and the obtained mixture was mixed at room temperature for 25 min at a speed of 750 r / min. The mixed material was added to a twin-screw extruder for extrusion and granulation, the blending temperature was set to 185°C, the extrusion temperature was set to 168°C, and the screw extrusion speed was 175 r / min. The granulated material was dried at 75°C to obtain a carbon material / polyethylene composite material.

[0055] The microstructure of the prepared carbon material was tested as shown in Figure 1 The average particle size was 1.50 μm, and the specific surface area was 262.37 m 2 g -1 The volume resistance of the prepared composite material was 6.28 x 10 7 Ω / sq., and the tensile properties were as shown in Table 1.

[0056] Example 5

[0057] First, 30 parts by weight of waste low-density linear polyethylene, 30 parts by weight of poly-1-hexene and 40 parts by weight of cyclohexene were crushed into small pieces of about 4 mm with a crusher, and then the crushed particles were transferred to a high-speed mixer, 15 parts by weight of jute powder with a particle size of 400 mesh and 15 parts by weight of sunflower shell powder were added, and the obtained mixture was mixed at room temperature for 10 min at a speed of 700 rpm. The mixed material was added to a twin-screw extruder for extrusion and granulation, the blending temperature was set to 190°C, the extrusion temperature was set to 170°C, and the screw extrusion speed was 200 rpm. The granulated material was added to a supercritical carbonization reactor, and the temperature was raised from room temperature to 500°C at a rate of 10°C / min. When the temperature reached 200°C, a horizontal flow pump was started, the water flow rate was set to 10 mL / min, the pressure was controlled at 35 MPa, and the carbonization time was 30 min. After carbonization, the material was naturally cooled to room temperature in the furnace, and then the material was taken out and dried at 80°C. Then the material was ground to 1000 mesh in a ball mill, and thus a carbon material powder was obtained.

[0058] The ground carbon powder was added to a high-speed mixer, and then 80 parts by weight of polyethylene, 3 parts by weight of ethylene-acrylate-succinic anhydride copolymer, 3 parts by weight of ethylene-glycidyl methacrylate copolymer, 1.5 parts by weight of zinc stearate, 1.5 parts by weight of stearic acid, 1 part by weight of antioxidant 1010 and 1 part by weight of antioxidant 1075 were added, and the obtained mixture was mixed at room temperature for 30 min at a speed of 800 rpm. The mixed material was added to a twin-screw extruder for extrusion and granulation, the blending temperature was set to 190°C, the extrusion temperature was set to 170°C, and the screw extrusion speed was 200 rpm. The granulated material was dried at 80°C to obtain a carbon material / polyethylene composite material.

[0059] The average particle size of the prepared carbon material was 1.62 μm, the specific surface area was 259.25 m 2 g -1 The volume resistance of the prepared composite material was 8.54 x 10 7 Ω / sq., and the tensile properties were as shown in Table 1.

[0060] Comparative Example 1

[0061] Firstly, 100 parts by weight of waste low-density polyethylene was crushed into small pieces of about 2 mm by a crusher, and then the crushed particles were transferred to a high-speed stirrer, 20 parts by weight of 200 mesh sunflower seed shell powder was added, and the obtained mixture was mixed at room temperature for 5 min at a speed of 500 r / min. The mixed material was added to a single-screw extruder for extrusion and granulation, the blending temperature was set to 170°C, the extrusion temperature was set to 160°C, and the screw extrusion speed was 100 r / min. The granulated material was added to a high-temperature carbonization furnace, and the temperature was raised from room temperature to 400°C at a rate of 5°C / min, the cavity atmosphere was high-purity argon atmosphere, and the carbonization time was 20 min. After carbonization, the furnace was naturally cooled to room temperature, the material was taken out and dried at 60°C, and then ground to 800 mesh in a ball mill, thereby obtaining a carbon material powder.

[0062] The ground carbon powder was placed in a high-speed stirrer, and 60 parts by weight of polyethylene, 4 parts by weight of maleic anhydride grafted polyethylene, 1 part by weight of paraffin, and 0.5 parts by weight of antioxidant DLTDP were added. The obtained mixture was mixed at room temperature for 10 min at a speed of 600 r / min. The mixed material was added to a twin-screw extruder for extrusion and granulation, the blending temperature was set to 170°C, the extrusion temperature was set to 160°C, and the screw extrusion speed was 100 r / min. The granulated material was dried at 60°C to obtain a carbon material / polyethylene composite material.

[0063] After testing, the average particle size of the prepared carbon material was 1.52 μm, the specific surface area was 155.77 m 2 g -1 The volume resistance of the prepared composite material was 4.19 x 10 9 Ω / sq., and the tensile properties were as shown in Table 1.

[0064] Comparative Example 2

[0065] Firstly, 100 parts by weight of waste low-density polyethylene was crushed into small pieces of about 2 mm by a crusher, and then added to a high-temperature carbonization furnace, and the temperature was raised from room temperature to 400°C at a rate of 5°C / min, the cavity atmosphere was high-purity argon atmosphere, and the carbonization time was 20 min. After carbonization, the furnace was naturally cooled to room temperature, the material was taken out and dried at 60°C, and then ground to 800 mesh in a ball mill, thereby obtaining a carbon material powder.

[0066] The ground carbon powder was placed in a high-speed blender, and 60 parts by weight of polyethylene, 4 parts by weight of maleic anhydride grafted polyethylene, 1 part by weight of paraffin wax, and 0.5 parts by weight of antioxidant DLTDP were added. The mixture was mixed at room temperature for 10 min at a speed of 600 rpm. The mixed material was then added to a twin-screw extruder for extrusion and granulation. The blending temperature was set to 170°C, the extrusion temperature was set to 160°C, and the screw extrusion speed was 100 rpm. The granulated material was dried at 60°C to obtain a carbon material / polyethylene composite material.

[0067] The average particle size of the prepared carbon material was 5.32 μm, the specific surface area was 33.14 m 2 g -1 The volume resistance of the prepared composite material was 4.59 x 10 15 Ω / sq., and the tensile properties are shown in Table 1.

[0068] Comparative Example 3

[0069] The test sample was the polyethylene raw material without any treatment, and the volume resistance was 3.67 x 10 16 Ω / sq., and the tensile properties are shown in Table 1.

[0070] Comparative Example 4

[0071] This comparative example was basically the same as Comparative Example 1, except that the high-temperature carbonization furnace was replaced by a muffle furnace, and the atmosphere was changed from high-purity argon to air.

[0072] The average particle size of the prepared carbon material was 1.93 μm, the specific surface area was 132.54 m 2 g -1 The volume resistance of the prepared composite material was 6.47 x 10 9 Ω / sq., and the tensile properties are shown in Table 1.

[0073] Table 1 Performance Comparison of Different Samples

[0074]

[0075] From the above table and other performance test results, it can be seen that the method according to the present application can prepare carbon materials with high specific surface area and high carbonization degree, and the composite material formed by blending the carbon materials with polyethylene has a lower volume resistance value, which indicates that the carbon materials can be used as antistatic materials. As can be seen from the tensile properties of the samples, the carbon materials provided by the present application exhibit good compatibility with polyethylene, because a certain amount of free radicals is retained on the surface of the carbon materials, which increases the compatibility with polyethylene and improves the mechanical properties of polyethylene. In addition, compared with the supercritical reaction carbonization described in the present application, the carbon materials prepared by using a common high-temperature carbonization furnace are weaker in various performances, because the carbonization effect of the carbonization furnace itself is poor and the tar and oil phase in the carbon materials are not removed. As can be seen from Comparative Example 4, the carbonization process needs to be controlled, otherwise the prepared material will be worse. If the biomass for synergistic catalytic degradation is removed, polyethylene cannot be carbonized at low temperature, and therefore cannot be used as an antistatic modification material for compounding with polyethylene and the like.

Claims

1. A method for low temperature carbonization of waste polyolefins, characterized in that The method comprises the following steps: firstly, crushing waste polyolefin, then mixing and extruding granulation with biomass, and finally supercritical carbonization reaction to obtain carbon material; wherein the supercritical carbonization reaction uses a supercritical carbonization reactor, and the reaction process is as follows: the material is added into the supercritical carbonization reactor, the temperature is raised to 400-500℃ at a temperature rising rate of 5-10℃ / min, during which the temperature reaches 200℃, the laminar pump is started, the water flow rate is set to 5-10mL / min, the pressure in the reactor is controlled to 25-35MPa, and the carbonization time is 15-30min; after the supercritical carbonization reaction, the reactor is naturally cooled to room temperature, then dried at 60-80℃, and then ground to 800-1000 mesh to obtain the carbon material.

2. The method of claim 1, wherein: The waste polyolefin is at least one of waste high-density polyethylene, waste low-density polypropylene, waste low-density linear polyethylene, waste medium-density polyethylene, waste polypropylene, waste poly-1-butene, waste poly-2-butene, waste 1,3-butadiene, waste poly-1-pentene, waste 1,4-pentadiene, waste poly-1-hexene, waste cis,cis-2,4-hexadiene, waste (2Z,4Z)-2,4-hexadiene, waste poly-1-octene, waste poly-1-heptene, waste cyclohexene, and waste 3-methylcyclopentene.

3. The method of claim 1, wherein: The biomass is at least one of sunflower seed shell, corn straw, rice husk, jute, bamboo, wood chips, flax, wheat straw, coconut shell, and reed, and the addition amount is 20%-30% of the mass of the waste polyolefin.

4. The method of claim 1, wherein: The waste polyolefin is added in the form of small pieces or particles with a size of 2-4mm, and the biomass is added in the form of powder with a size of 200-400mesh.

5. The method of claim 1, wherein: The device used for extrusion granulation is a single or double screw extruder, the blending temperature is 170-190℃, the extrusion temperature is 160-170℃, and the screw extrusion speed is 100-200r / min.

6. A carbon material based on supercritical low-temperature carbonization of waste polyolefins, characterized by: The carbon material is prepared according to any one of claims 1-5, and has an average particle size of 0.80-1.70 μm, a specific surface area of 200-270 m 2 g -1 .

7. A method for producing a carbon material / polyethylene antistatic composite material, characterized by The method comprises the following steps: mixing the carbon material, polyethylene, compatibilizer, dispersant, and antioxidant uniformly, and then extruding and granulating, wherein the carbon material is prepared by any one of the methods in claims 1-5.

8. The method of claim 7, wherein: The polyethylene is specifically high-density polyethylene, and the addition amount is 60%-80% of the mass of the waste polyolefin; the compatibilizer is at least one of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, ethylene-propylene-acrylate-succinic anhydride copolymer, and ethylene-glycidyl methacrylate copolymer, and the addition amount is 4%-6% of the mass of the waste polyolefin; the dispersant is at least one of paraffin wax, polyethylene wax, stearic acid, zinc stearate, calcium stearate, and butyl stearate, and the addition amount is 1%-3% of the mass of the waste polyolefin; and the antioxidant is at least one of antioxidant DLTDP, antioxidant BHT, antioxidant 168, antioxidant 626, antioxidant 1010, antioxidant 1075, and antioxidant 2246, and the addition amount is 0.5%-2% of the mass of the waste polyolefin.

9. The method of claim 7, wherein: The equipment used for the extrusion granulation is a double-screw extruder, the blending temperature is set to 170-190 DEG C, the extrusion temperature is set to 160-170 DEG C, the screw extrusion rotating speed is 100-200 r / min; the material obtained by the extrusion granulation also needs to be fully dried at 60-80 DEG C.

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