Method for preparing high-strength engineering plastic from recycled PA66 plastic and application thereof

Abstract

This invention discloses a method for preparing high-strength engineering plastics using recycled PA66 plastic and its application, relating to the field of chemical technology. The method includes at least the following steps: homogenizing the recycled PA66 plastic in a silo; crushing the homogenized PA66 plastic, premixing it with a chain extender and antioxidant, and performing a first extrusion process to obtain rPA66; adding a portion of the rPA66, the antioxidant, lubricant, compatibilizer, black sizing agent, and light stabilizer to a high-speed mixer and mixing to obtain a premix; and performing a second extrusion process on the premix, modified carbon fibers, and the remaining rPA66 to obtain a high-strength engineering plastic prepared from the recycled PA66 plastic; wherein the modified carbon fibers are obtained through modification with a silane coupling agent, carbon nanotubes, and polyvinyl alcohol. This application uses grafted silanized carbon nanotubes and polyvinyl alcohol to modify carbon fibers as reinforcing agents for recycled PA66, and combines this with an optimized side-feeding fiber addition process to obtain a high-strength engineering plastic with excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method for preparing high-strength engineering plastics using recycled PA66 plastic and its application. Background Technology

[0002] As society progresses and develops, people have increasingly higher requirements for lightweight and high-performance office chairs and gaming chairs. Components in industries such as automobiles, electronics, and machinery are developing towards lightweighting and miniaturization, and more and more metal materials are being gradually replaced by polymer composite materials.

[0003] Polyamide (PA), commonly known as nylon, is an important thermoplastic engineering plastic. Due to its high strength, good self-lubricating properties, wear resistance, oil resistance, and ease of molding and processing, it is widely used in automobiles, mechanical parts, electronics, and home appliances. However, the presence of hydrogen bonds in the nylon 66 molecule gives it strong water absorption, leading to poor dimensional stability, poor resistance to strong acids and alkalis, and low impact strength in the dry state and at low temperatures, which limits its applications. Therefore, nylon 66 needs to be modified through reinforcement, filling, toughening, and flame retardancy to meet different application requirements.

[0004] Carbon fiber reinforced nylon composites not only retain the inherent advantages of nylon resin, such as chemical resistance, corrosion resistance, and good processability, but also exhibit significantly improved mechanical properties, heat resistance, and dimensional stability. These superior properties have led to the increasing importance of carbon fiber reinforced nylon composites, which are now widely used in cutting-edge fields such as aerospace and civilian applications such as automotive and chemical industries. However, carbon fibers have fewer functional groups on their surface, resulting in surface inertness and poor bonding with nylon 66. Therefore, how to utilize recycled PA66 plastic to prepare high-strength engineering plastics has become an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-strength engineering plastics using recycled PA66 plastic and its application, thereby solving the following technical problems:

[0006] Existing carbon fiber reinforced nylon composites suffer from poor bonding between carbon fiber and nylon and poor mechanical properties of the composite material.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for preparing high-strength engineering plastics using recycled PA66 plastic includes at least the following steps:

[0009] The recycled PA66 plastic is homogenized in the warehouse;

[0010] The homogenized PA66 plastic is crushed, premixed evenly with chain extender and first antioxidant, and subjected to first extrusion process to obtain rPA66.

[0011] A portion of the rPA66, second antioxidant, lubricant, compatibilizer, black sand and light stabilizer are added to a high-speed mixer and mixed evenly to obtain a premix.

[0012] The premix, modified carbon fiber, and remaining rPA66 are subjected to a second extrusion process to obtain a high-strength engineering plastic prepared from recycled PA66 plastic.

[0013] The modified carbon fiber is obtained by modification with silane coupling agent, carbon nanotubes and polyvinyl alcohol.

[0014] Preferably, the high-strength engineering plastic prepared comprises at least the following parts by weight of raw materials:

[0015] rPA66 45.0-50.0;

[0016] Modified carbon fiber 22.0-29.0;

[0017] Graft compatibilizer 3.5-6.0;

[0018] Lubricant 0.2-0.4;

[0019] Second antioxidant 0.1-0.2;

[0020] Black sand 0.08-0.1;

[0021] Light stabilizer 0.2-0.4%.

[0022] Preferably, the method for preparing the modified carbon fiber includes at least the following steps:

[0023] Carbon fibers are refluxed in acetone at 60-80℃ for 20-26 hours, rinsed and soaked with deionized water, and dried in a forced-air oven at 80-90℃ for 10-15 hours to obtain desizing carbon fibers.

[0024] The desized carbon fibers are immersed in a 1-3 wt% Michaelis-Müller acid ethanol solution at 20-30°C for 2-4 hours, then rinsed to remove undissolved impurities from the surface, and dried in a forced-air oven at 80-90°C for 10-15 hours to obtain activated carbon fibers.

[0025] Carbon nanotubes were dispersed in a silane coupling agent solution and magnetically stirred for 20-40 min to prepare a carbon nanotube suspension system with a mass fraction of 0.4-0.6%. The activated carbon fibers were immersed in the carbon nanotube suspension system for 5-20 min and then removed and dried in a forced-air oven at 80-90℃ for 3-5 h. The carbon fibers were ultrasonically cleaned with a 1:1 mixture of deionized water and ethanol and then dried in a forced-air oven at 80-90℃ for 3-5 h to obtain carbon fibers grafted with silanized carbon nanotubes.

[0026] Polyvinyl alcohol was dissolved in dichloromethane to prepare a polyvinyl alcohol-dichloromethane solution with a concentration of 0.3-0.6%. The carbon fibers grafted with silanized carbon nanotubes were immersed in the polyvinyl alcohol-dichloromethane solution for 5-30 minutes, drained, and dried in a forced-air oven at 80-90°C for 3-5 hours to obtain the modified carbon fibers.

[0027] Preferably, both the first extrusion process and the second extrusion process are carried out in a co-rotating twin-screw extruder. The premix is ​​fed into the first side feed port of the co-rotating twin-screw extruder, the modified carbon fiber is fed into the second side feed port of the co-rotating twin-screw extruder, and the remaining rPA66 is fed into the main feed port of the co-rotating twin-screw extruder.

[0028] Preferably, the chain extender is a diepoxy group chain extender epoxy resin, and the first antioxidant is antioxidant 1010.

[0029] Preferably, the second antioxidant is any one or more of hindered phenolic antioxidants or phosphite antioxidants, the lubricant is CF-201, the compatibilizer is maleic anhydride-grafted polyolefin elastomer or maleic anhydride-grafted epoxy resin, the black slurry is carbon black or a coupling agent, the light stabilizer is any one or more of hindered phenolic stabilizers, phosphite stabilizers, cuprous halide composite stabilizers or stabilizers containing dimethyl ketone functional groups, and the carbon fiber is a carbon fiber filament with a size of 5-15 mm.

[0030] Preferably, the first extrusion process has a rotation speed of 300-500 rpm and a temperature of 240-270℃.

[0031] Preferably, the second extrusion process has a rotation speed of 300-500 rpm and a temperature of 240-270℃.

[0032] Preferably, before the recycled PA66 plastic is homogenized in the warehouse, it undergoes at least the following processes: unpacking, coarse sorting to remove large impurities, removal of magnetic and non-magnetic metals, manual sorting, wet crushing, hot alkaline water washing to remove oil stains, drying, electrostatic sorting, and infrared and color fine sorting.

[0033] The application of a high-strength engineering plastic obtained by a method for preparing high-strength engineering plastic from recycled PA66 plastic as described in any of the above-mentioned methods in the industries of office chairs, gaming chairs, home appliances, automobiles, or power tools.

[0034] The beneficial effects of this invention are:

[0035] This application utilizes recycled PA66 plastic to prepare high-strength engineering plastics. Silane coupling agents and polyvinyl alcohol-modified carbon fibers are used as reinforcing agents for the recycled PA66, combined with a side-feed fiber-reinforcing process to prepare the high-strength engineering plastics. The resulting high-strength engineering plastics exhibit excellent bending, impact, and tensile properties, meeting the requirements for office chairs or gaming chairs. The high-strength engineering plastics of this application achieve good results in low-carbon environmental protection and green recycling. The process is simple, has certain cost advantages, and is suitable for industrial-scale mass production.

[0036] This application utilizes silanized dehydrogenated carbon nanotubes and silane coupling agents grafted onto carbon fibers. The silanized carbon nanotubes are uniformly grafted onto the carbon fiber surface, and the silane-grafted carbon nanotubes have cross-linked network particles formed by silane, which improves the interfacial adhesion between carbon fibers and PA66. On the one hand, the covalent bonding between the silane-grafted carbon nanotubes and carbon fibers enhances the interfacial adhesion between carbon fibers and PA66; on the other hand, the silane coupling agent forms a cross-linked network structure on the carbon fiber surface, improving the wettability between the fiber and PPA66. The carbon fibers with epoxy groups exhibit good interfacial bonding between them and the PA66 matrix. When the composite material is subjected to stress, the PA66 matrix can transfer the stress to the carbon fiber skeleton through the interface, thereby enhancing the mechanical properties of the composite material. Simultaneously, carbon fibers possess good stiffness; when the composite material is subjected to stress, within a certain range, the bending performance of the composite material increases with the increase of carbon fiber content.

[0037] This application utilizes a polyvinyl alcohol (PVA) solution to coat carbon fibers and carbon nanotubes with a thin film of PVA. The interaction between PVA and carbon fibers is physical adhesion, mainly relying on intermolecular forces and physical interlocking. The PVA film further enhances the adhesion of the modified carbon fibers and the compatibility between the modified carbon fibers and PA66, thereby improving the reinforcing effect of the modified carbon fibers on PA66. Before modifying the carbon fibers, this application also uses Michaelis-Menten acid for activation, which effectively introduces polar oxygen-containing functional groups onto the carbon fiber surface, increasing the oxygen-to-carbon ratio and surface roughness, significantly improving the surface energy of the carbon fibers and further enhancing their reinforcing effect.

[0038] In this application, the carbon fiber is a long carbon fiber filament. Using longer carbon fiber raw materials is beneficial for improving the performance of the composite material. Under the main feed fiber addition process, the carbon fiber processing time is longer, subjecting it to stronger shearing action from the screw, resulting in shorter retained fiber length and poorer material mechanical properties. In this application, the premix is ​​fed into the first side feed port of a co-rotating twin-screw extruder, the modified carbon fiber into the second side feed port, and the remaining rPA66 into the main feed port. By optimizing the side feed fiber addition process, the shearing action on the carbon fiber is reduced, and using long carbon fiber filaments as raw material allows for a longer retained fiber length, effectively improving the mechanical properties of the composite material. The side feed fiber addition process effectively reduces the shearing action of the screw on the fiber, increases the retained fiber length, and improves the material's mechanical properties. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] The preparation method of modified carbon fiber includes the following steps:

[0042] The carbon fiber fabric was placed in a reaction vessel and refluxed in acetone at 70°C for 24 h. Then it was rinsed and soaked with deionized water more than 5 times and dried in a forced-air oven at 80°C for 12 h to obtain desized carbon fiber.

[0043] The desized carbon fiber fabric was immersed in a 2wt% Michaelis-Müller acid ethanol solution and soaked at 30°C for 3 hours. After soaking, it was taken out and rinsed with water three to four times to remove undissolved impurities on the surface of the carbon fiber. It was then dried in a forced-air oven at 80°C for 12 hours to obtain activated carbon fiber.

[0044] A mixture of 100 ml anhydrous ethanol and deionized water at a mass ratio of 9:1 was placed in a magnetic stirrer and mixed thoroughly. A certain amount of silane coupling agent was added dropwise to the mixture to prepare a silane coupling agent solution with a mass fraction of 0.5%. The solution was magnetically stirred for 45 min to hydrolyze the silane. A certain amount of hydroxylated multi-walled carbon nanotubes was weighed and dispersed in the silane hydrolysate, and magnetically stirred for 20 min to prepare a carbon nanotube suspension system with a mass fraction of 0.5%. The activated carbon fibers were immersed in the carbon nanotube suspension system for 10 min and then removed. The carbon fibers were then dried in a forced-air oven at 80°C for 4 hours. The carbon fibers were then ultrasonically cleaned with a 1:1 mixture of deionized water and ethanol and then dried in a forced-air oven at 80°C for 4 h to obtain carbon fibers grafted with silanized carbon nanotubes.

[0045] Polyvinyl alcohol was dissolved in dichloromethane to prepare a 0.5% polyvinyl alcohol-dichloromethane solution. The carbon fibers grafted with silanized carbon nanotubes were immersed in the polyvinyl alcohol-dichloromethane solution for 20 min, drained, and dried in a forced-air oven at 80°C for 4 h to obtain modified carbon fibers.

[0046] A method for preparing high-strength engineering plastics using recycled PA66 plastic includes the following steps:

[0047] The recycled car radiators containing PA66 plastic are unpacked, coarsely sorted to remove large impurities, magnetic metals and non-magnetic metals, then manually sorted, wet crushed, washed with hot alkaline water to remove oil stains, dried, electrostatically sorted, and finely sorted by infrared and color, and then put into the warehouse for homogenization.

[0048] The homogenized crushed car water tank material was premixed with 1.8 parts by weight of epoxy resin, a chain extender with diepoxy groups, and 0.2 parts by weight of antioxidant 1010. The mixture was then added to a co-rotating twin-screw extruder. After the first extrusion process, the compound was granulated to obtain chain-extended and thickened rPA66. The co-rotating twin-screw extruder had a rotation speed of 400 rpm and a temperature of 260℃.

[0049] The above-mentioned 25 parts by weight of rPA66, 0.2 parts by weight of hindered phenolic antioxidant 1098, 0.4 parts by weight of lubricant CF-201, 5 parts by weight of compatibilizer maleic anhydride grafted polyolefin elastomer, 0.1 parts by weight of black shale carbon black and 0.3 parts by weight of hindered amine light stabilizer 944 are added into a high-speed mixer and mixed evenly to obtain a premix.

[0050] The remaining 25 parts by weight of rPA66 were fed into the main feed port of a co-rotating twin-screw extruder using a loss-in-weight balance. The premix was fed into the first side feed port, and 28 parts by weight of modified carbon fiber was fed into the second feed port. The second extrusion process was carried out to obtain a high-strength engineering plastic made from recycled PA66 plastic. The rotation speed of the co-rotating twin-screw extruder was 400 rpm and the temperature was 260°C.

[0051] Example 2

[0052] The preparation method of modified carbon fiber includes the following steps:

[0053] The carbon fiber fabric was placed in a reaction vessel and refluxed in acetone at 70°C for 24 h. Then it was rinsed and soaked with deionized water more than 5 times and dried in a forced-air oven at 80°C for 12 h to obtain desized carbon fiber.

[0054] The desized carbon fiber fabric was immersed in a 2wt% Michaelis-Müller acid ethanol solution and soaked at 30°C for 3 hours. After soaking, it was taken out and rinsed with water three to four times to remove undissolved impurities on the surface of the carbon fiber. It was then dried in a forced-air oven at 80°C for 12 hours to obtain activated carbon fiber.

[0055] A mixture of 100 ml anhydrous ethanol and deionized water at a mass ratio of 9:1 was placed in a magnetic stirrer and mixed thoroughly. A certain amount of silane coupling agent was added dropwise to the mixture to prepare a silane coupling agent solution with a mass fraction of 0.5%. The solution was magnetically stirred for 45 min to hydrolyze the silane. A certain amount of hydroxylated multi-walled carbon nanotubes was weighed and dispersed in the silane hydrolysate, and magnetically stirred for 20 min to prepare a carbon nanotube suspension system with a mass fraction of 0.4%. The activated carbon fibers were immersed in the carbon nanotube suspension system for 10 min and then removed. The carbon fibers were then dried in a forced-air oven at 80°C for 4 hours. The carbon fibers were then ultrasonically cleaned with a 1:1 mixture of deionized water and ethanol and then dried in a forced-air oven at 80°C for 4 hours to obtain carbon fibers grafted with silanized carbon nanotubes.

[0056] Polyvinyl alcohol was dissolved in dichloromethane to prepare a 0.3% polyvinyl alcohol-dichloromethane solution. The carbon fibers grafted with silanized carbon nanotubes were immersed in the polyvinyl alcohol-dichloromethane solution for 20 min, drained, and dried in an 80°C forced-air oven for 4 h to obtain modified carbon fibers.

[0057] The composition and method for preparing high-strength engineering plastics using recycled PA66 plastic are the same as in Example 1.

[0058] Example 3

[0059] The preparation method of modified carbon fiber includes the following steps:

[0060] The carbon fiber fabric was placed in a reaction vessel and refluxed in acetone at 70°C for 24 h. Then it was rinsed and soaked with deionized water more than 5 times and dried in a forced-air oven at 80°C for 12 h to obtain desized carbon fiber.

[0061] The desized carbon fiber fabric was immersed in a 2wt% Michaelis-Müller acid ethanol solution and soaked at 30°C for 3 hours. After soaking, it was taken out and rinsed with water three to four times to remove undissolved impurities on the surface of the carbon fiber. It was then dried in a forced-air oven at 80°C for 12 hours to obtain activated carbon fiber.

[0062] A mixture of 100 ml anhydrous ethanol and deionized water at a mass ratio of 9:1 was placed in a magnetic stirrer and mixed thoroughly. A certain amount of silane coupling agent was added dropwise to the mixture to prepare a silane coupling agent solution with a mass fraction of 0.5%. The solution was magnetically stirred for 45 min to hydrolyze the silane. A certain amount of hydroxylated multi-walled carbon nanotubes was weighed and dispersed in the silane hydrolysate, and magnetically stirred for 20 min to prepare a carbon nanotube suspension system with a mass fraction of 0.5%. The activated carbon fibers were immersed in the carbon nanotube suspension system for 10 min and then removed. The carbon fibers were then dried in a forced-air oven at 80°C for 4 hours. The carbon fibers were then ultrasonically cleaned with a 1:1 mixture of deionized water and ethanol and then dried in a forced-air oven at 80°C for 4 h to obtain carbon fibers grafted with silanized carbon nanotubes.

[0063] Polyvinyl alcohol was dissolved in acetone to prepare a 0.3% polyvinyl alcohol-acetone solution. The carbon fibers grafted with silanized carbon nanotubes were immersed in the polyvinyl alcohol-dichloromethane solution for 20 min, drained, and dried in a forced-air oven at 80°C for 4 h to obtain the desired carbon fibers.

[0064] A method for preparing high-strength engineering plastics using recycled PA66 plastics includes the following steps.

[0065] Example 4

[0066] A method for preparing high-strength engineering plastics using recycled PA66 plastic includes the following steps:

[0067] The recycled car radiators containing PA66 plastic are unpacked, coarsely sorted to remove large impurities, magnetic metals and non-magnetic metals, then manually sorted, wet crushed, washed with hot alkaline water to remove oil stains, dried, electrostatically sorted, and finely sorted by infrared and color, and then put into the warehouse for homogenization.

[0068] The homogenized crushed car water tank material was premixed with 1.8 parts by weight of epoxy resin, a chain extender with diepoxy groups, and 0.2 parts by weight of antioxidant 1010. The mixture was then added to a co-rotating twin-screw extruder. After the first extrusion process, the compound was granulated to obtain chain-extended and thickened rPA66. The co-rotating twin-screw extruder had a rotation speed of 400 rpm and a temperature of 260℃.

[0069] The above-mentioned 20 parts by weight of rPA66, 0.2 parts by weight of hindered phenolic antioxidant 1098, 0.4 parts by weight of lubricant CF-201, 6 parts by weight of compatibilizer maleic anhydride grafted polyolefin elastomer, 0.1 parts by weight of black shale carbon black and 0.4 parts by weight of hindered amine light stabilizer 944 are added into a high-speed mixer and mixed evenly to obtain a premix.

[0070] The remaining 25 parts by weight of rPA66 were fed into the main feed port of a co-rotating twin-screw extruder using a loss-in-weight balance. The premix was fed into the first side feed port, and 29 parts by weight of modified carbon fiber was fed into the second feed port. The second extrusion process was carried out to obtain a high-strength engineering plastic made from recycled PA66 plastic. The rotation speed of the co-rotating twin-screw extruder was 400 rpm and the temperature was 260°C.

[0071] The composition and preparation method of the modified carbon fiber are the same as in Example 1.

[0072] Comparative Example 1

[0073] The preparation method of modified carbon fiber includes the following steps:

[0074] The desizing process is the same as in Example 1, resulting in desizing carbon fibers.

[0075] The activation steps are the same as in Example 1, resulting in activated carbon fibers;

[0076] A mixture of 100 ml anhydrous ethanol and deionized water at a mass ratio of 9:1 was placed in a magnetic stirrer and mixed thoroughly. A certain amount of silane coupling agent was added dropwise to the mixture to prepare a silane coupling agent solution with a mass fraction of 0.5%. The solution was magnetically stirred for 45 min to hydrolyze the silane. A certain amount of hydroxylated multi-walled carbon nanotubes was weighed and dispersed in the silane hydrolysate, and magnetically stirred for 20 min to prepare a carbon nanotube suspension system with a mass fraction of 0.5%. The activated carbon fibers were immersed in the carbon nanotube suspension system for 10 min and then removed. The carbon fibers were then dried in a forced-air oven at 80°C for 4 hours. After that, the carbon fibers were ultrasonically cleaned with a 1:1 mixture of deionized water and ethanol and then dried in a forced-air oven at 80°C for 4 hours to obtain carbon fibers grafted with silanized carbon nanotubes, which are modified carbon fibers.

[0077] The composition and method for preparing high-strength engineering plastics using recycled PA66 plastic are the same as in Example 1.

[0078] Comparative Example 2

[0079] The preparation method of modified carbon fiber includes the following steps:

[0080] The desizing process is the same as in Example 1, resulting in desizing carbon fibers.

[0081] The activation steps are the same as in Example 1, resulting in activated carbon fibers;

[0082] Polyvinyl alcohol was dissolved in dichloromethane to prepare a 0.5% polyvinyl alcohol-dichloromethane solution. The activated carbon fibers were then immersed in the polyvinyl alcohol-dichloromethane solution for 20 minutes, drained, and dried in a forced-air oven at 80°C for 4 hours to obtain carbon fibers covered with a thin layer of polyvinyl alcohol, which are modified carbon fibers.

[0083] The composition and method for preparing high-strength engineering plastics using recycled PA66 plastic are the same as in Example 1.

[0084] Comparative Example 3

[0085] The steps for preparing modified carbon fibers are omitted.

[0086] A method for preparing high-strength engineering plastics using recycled PA66 plastic includes the following steps:

[0087] The recycled car radiators containing PA66 plastic are unpacked, coarsely sorted to remove large impurities, magnetic metals and non-magnetic metals, then manually sorted, wet crushed, washed with hot alkaline water to remove oil stains, dried, electrostatically sorted, and finely sorted by infrared and color, and then put into the warehouse for homogenization.

[0088] The homogenized crushed car water tank material was premixed with 1.8 parts by weight of epoxy resin, a chain extender with diepoxy groups, and 0.2 parts by weight of antioxidant 1010. The mixture was then added to a co-rotating twin-screw extruder. After the first extrusion process, the compound was granulated to obtain chain-extended and thickened rPA66. The co-rotating twin-screw extruder had a rotation speed of 400 rpm and a temperature of 260℃.

[0089] The above-mentioned 25 parts by weight of rPA66, 0.2 parts by weight of hindered phenolic antioxidant 1098, 0.4 parts by weight of lubricant CF-201, 5 parts by weight of compatibilizer maleic anhydride grafted polyolefin elastomer, 0.1 parts by weight of black shale carbon black and 0.3 parts by weight of hindered amine light stabilizer 944 are added into a high-speed mixer and mixed evenly to obtain a premix.

[0090] The remaining 25 parts by weight of rPA66 were fed into the main feed port of a co-rotating twin-screw extruder using a loss-in-weight balance. The premix was fed into the first side feed port, and 28 parts by weight of carbon fiber was fed into the second feed port. The second extrusion process was carried out to obtain a high-strength engineering plastic made from recycled PA66 plastic. The rotation speed of the co-rotating twin-screw extruder was 400 rpm and the temperature was 260°C.

[0091] Comparative Example 4

[0092] A method for preparing high-strength engineering plastics using recycled PA66 plastic includes the following steps:

[0093] The recycled automotive water tanks containing PA66 plastic are unpacked, and large impurities, magnetic metals, and non-magnetic metals are removed through coarse sorting. Then, manual sorting, wet crushing, degreasing with hot alkaline water washing, drying, electrostatic sorting, and fine sorting by infrared and color are carried out, and then stored in the warehouse for homogenization;

[0094] The homogenized crushed automotive water tank materials are premixed evenly with 1.8 parts by weight of the chain extender epoxy resin with double epoxy groups and 0.2 parts by weight of antioxidant 1010, and then added into a co-rotating twin-screw extruder. Through the first extrusion process, pelletized rPA66 with chain extension and viscosity increase is obtained. Among them, the rotational speed of the co-rotating twin-screw extruder is 400 rpm, and the temperature is 260 °C;

[0095] 20 parts by weight of the above rPA66, 0.2 parts by weight of the hindered phenol type 1098 antioxidant, 0.4 parts by weight of the lubricant CF-201, 6 parts by weight of the compatibilizer maleic anhydride grafted polyolefin elastomer, 0.1 part by weight of black sand carbon black, and 0.4 parts by weight of the hindered amine type 944 light stabilizer are put into a high-speed mixer and mixed evenly to obtain a premixed material;

[0096] The remaining 25 parts by weight of the above rPA66, the above premixed material, and 29 parts by mass of the modified carbon fiber are added into a co-rotating twin-screw extruder for the second extrusion process to obtain a high-strength engineering plastic prepared from recycled PA66 plastic. Among them, the rotational speed of the co-rotating twin-screw extruder is 400 rpm, and the temperature is 260 °C.

[0097] The components and preparation method of the modified carbon fiber are the same as those in Example 1.

[0098] Performance testing

[0099] Tensile property test: Test according to GB / T 1040—2006. Use a universal testing machine to apply a load of 50 N to the sample, set the crosshead speed to 5 mm / min, and test the tensile strength, tensile modulus, and elongation at break of the PA66 / CF composite material. Each group of samples has 5 replicates, and the results are averaged; a tensile strength of ≥110 MPa is considered qualified. The test results are shown in the following table:

[0100] Flexural property test: Test according to GB / T 9341—2008. Set the load to 5 N and test the flexural strength and flexural modulus of the PA66 / CF composite material. Each group of samples has 5 control groups, and the results are averaged. The test results are shown in the following table:

[0101] Izod impact strength test: Test according to GB / T 1843—2008. Set the pendulum to 2.75 J and test the impact strength of the PA66 / CF composite material. Each group of samples has 5 replicates, and the results are averaged. The test results are shown in Table 1:

[0102] Table 1: Statistical Table of Mechanical Property Test Data for Examples 1-4 and Comparative Examples 1-4

[0103] Tensile strength (MPa) Flexural modulus (MPa) Bending strength (MPa) Impact strength (MPa) Example 1 168.1 7800 189.5 93 Example 2 172.3 7824 190.2 91 Example 3 164.0 7942 179.6 95 Example 4 158.3 7763 184.1 92 Comparative Example 1 114.2 5746 122.5 80 Comparative Example 2 122.9 5981 134.1 85 Comparative Example 3 88.6 4000 73.4 64 Comparative Example 4 134.0 6102 134.9 85

[0104] As shown in the table above, the high-strength engineering plastics prepared from recycled PA66 plastic in Examples 1-4 of this invention exhibit high tensile strength, flexural strength, and impact strength, demonstrating excellent mechanical properties that meet the testing requirements of the office chair industry. In Comparative Example 1, the step of immersion in a polyvinyl alcohol-dichloromethane solution was omitted, meaning no polyvinyl alcohol layer was formed on the carbon fibers grafted with silanized carbon nanotubes. In Comparative Example 2, the carbon nanotube suspension system was not immersed, meaning no silanized carbon nanotubes were grafted onto the carbon fibers.

[0105] In Comparative Example 3, no treatment was performed on the carbon fiber, and PA66 was directly reinforced with carbon fiber. In Comparative Example 4, the tensile strength, flexural strength, and impact strength were significantly reduced in the second extrusion process without distinguishing between main / side feeding, and the reduction was more significant in Comparative Example 3. This indicates that modifying carbon fiber by grafting silanized carbon nanotubes and forming a polyvinyl alcohol film can have an excellent reinforcing effect on PA66, improving the mechanical properties of the obtained high-strength engineering plastic. Furthermore, optimizing the side feeding fiber addition process can also improve the reinforcing effect of carbon fiber on PA66.

[0106] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing high-strength engineering plastics using recycled PA66 plastic, characterized in that, At least the following steps are included: The recycled PA66 plastic is homogenized in the warehouse; The homogenized PA66 plastic is crushed, premixed evenly with chain extender and first antioxidant, and subjected to first extrusion process to obtain rPA66. A portion of the rPA66, second antioxidant, lubricant, compatibilizer, black sand and light stabilizer are added to a high-speed mixer and mixed evenly to obtain a premix. The premix, modified carbon fiber, and remaining rPA66 are subjected to a second extrusion process to obtain a high-strength engineering plastic prepared from recycled PA66 plastic. The method for preparing the modified carbon fiber includes at least the following steps: Carbon fibers are refluxed in acetone at 60-80℃ for 20-26 hours, rinsed and soaked with deionized water, and dried in a forced-air oven at 80-90℃ for 10-15 hours to obtain desizing carbon fibers. The desized carbon fibers are immersed in a 1-3 wt% Michaelis-Müller acid ethanol solution at 20-30°C for 2-4 hours, then rinsed to remove undissolved impurities from the surface, and dried in a forced-air oven at 80-90°C for 10-15 hours to obtain activated carbon fibers. Carbon nanotubes were dispersed in a silane coupling agent solution and magnetically stirred for 20-40 min to prepare a carbon nanotube suspension system with a mass fraction of 0.4-0.6%. The activated carbon fibers were immersed in the carbon nanotube suspension system for 5-20 min and then removed and dried in a forced-air oven at 80-90℃ for 3-5 h. The carbon fibers were ultrasonically cleaned with a 1:1 mixture of deionized water and ethanol and then dried in a forced-air oven at 80-90℃ for 3-5 h to obtain carbon fibers grafted with silanized carbon nanotubes. Polyvinyl alcohol is dissolved in dichloromethane to prepare a polyvinyl alcohol-dichloromethane solution with a concentration of 0.3-0.6%. The carbon fibers grafted with silanized carbon nanotubes are immersed in the polyvinyl alcohol-dichloromethane solution for 5-30 minutes, drained, and dried in a forced-air oven at 80-90°C for 3-5 hours to obtain the modified carbon fibers. Both the first extrusion process and the second extrusion process are carried out in a co-rotating twin-screw extruder. The premixed material is fed into the first side feed port of the co-rotating twin-screw extruder, the modified carbon fiber is fed into the second side feed port of the co-rotating twin-screw extruder, and the remaining rPA66 is fed into the main feed port of the co-rotating twin-screw extruder.

2. The method for preparing high-strength engineering plastics using recycled PA66 plastic according to claim 1, characterized in that, The high-strength engineering plastic prepared comprises at least the following parts by weight of raw materials: rPA66 45.0-50.0; Modified carbon fiber 22.0-29.0; Graft compatibilizer 3.5-6.0; Lubricant 0.2-0.4; Second antioxidant 0.1-0.2; Black sand 0.08-0.1; Light stabilizer 0.2-0.4%.

3. The method for preparing high-strength engineering plastics using recycled PA66 plastic according to claim 1, characterized in that, The chain extender is a diepoxy group chain extender epoxy resin, and the first antioxidant is antioxidant 1010.

4. The method for preparing high-strength engineering plastics using recycled PA66 plastic according to claim 1, characterized in that, The first extrusion process has a rotation speed of 300-500 rpm and a temperature of 240-270℃.

5. The method for preparing high-strength engineering plastics using recycled PA66 plastic according to claim 1, characterized in that, The second extrusion process has a rotation speed of 300-500 rpm and a temperature of 240-270℃.

6. The method for preparing high-strength engineering plastics using recycled PA66 plastic according to claim 1, characterized in that, Before being homogenized in the warehouse, the recycled PA66 plastic undergoes at least the following processes: unpacking, coarse sorting to remove large impurities, removal of magnetic and non-magnetic metals, manual sorting, wet crushing, hot alkaline water washing to remove oil stains, drying, electrostatic sorting, and infrared and color fine sorting.

7. The application of a high-strength engineering plastic obtained by a method for preparing high-strength engineering plastics using recycled PA66 plastics as described in any one of claims 1-6 in the industries of office chairs, gaming chairs, home appliances, automobiles, or power tools.