PET (Polyethylene Terephthalate) plastic recycling method, modified PET plastic wire and application

Abstract

The invention provides a PET (Polyethylene Terephthalate) plastic recycling method, a modified PET plastic wire and application. The method comprises the following steps: mixing PET plastic with a chain extender, a flexibilizer and fibers to obtain a mixed material; wherein the mass ratio of the PET plastic to the chain extender to the flexibilizer to the fiber is 1: (0.8-1.2): (1.5-2.2): (1.5-2.2); the mixed material obtained in the burdening step is subjected to wire extrusion treatment, and a wire is obtained; and cooling the obtained wire material to obtain the modified PET plastic wire material. According to the PET plastic recovery method provided by the invention, the PET plastic is mixed with the modified material toughening agent, the fiber and the chain extender, and then wire extrusion molding treatment is performed, so that the modified PET plastic wire which has excellent mechanical properties and melt viscosity and can be used as a 3D printing wire is obtained.

Description

Technical Field

[0001] This invention belongs to the field of plastic recycling technology, specifically relating to a method for recycling PET plastic, a modified PET plastic filament and its application. Background Technology

[0002] Plastics have brought numerous conveniences to humankind, and global demand for them is steadily increasing. However, the disposal of waste plastics remains a challenge, as their excellent chemical stability allows them to persist in the natural environment for hundreds of years. Currently, the total amount of global plastic waste has reached 6.3 billion tons, and it is projected to reach hundreds of millions of tons by 2050.

[0003] Currently, the main methods of disposing of waste plastics are incineration and landfill, accounting for over 70%, with only less than 15% being truly recycled. Direct landfilling of untreated plastics releases various toxic and harmful substances during natural degradation, causing irreversible damage to the ecosystem. Even after treatment, many plastics are difficult to decompose in the natural environment; over time, some plastics gradually decompose into microplastics and nanoplastics, polluting groundwater and soil and disrupting the ecosystem. Microplastics can enter the food chain, thus harming human health. While incineration can recover energy, it causes severe environmental pollution, producing large amounts of harmful chemicals such as carbon monoxide, sulfur dioxide, dioxins, toxic fumes, and ash, posing serious threats to human health and the natural environment.

[0004] Currently, some new plastic recycling methods have gradually emerged for the recycling of waste plastics, including physical recycling methods (such as mechanical recycling), chemical recycling methods under high temperature and high pressure (such as pyrolysis, catalytic pyrolysis, hydrolysis and alcoholysis), chemical upgrading recycling methods under normal temperature and pressure conditions (such as electrocatalysis, photocatalysis and solvent catalysis), and biological recycling methods.

[0005] For polyester plastics (PET), the most common recycling method is mechanical recycling. However, during mechanical recycling of PET, grinding and melting processes cause the PET molecular chains to break down, leading to a deterioration of the material structure. Therefore, the performance of the recycled product is significantly lower than that of the original PET. Biological recycling of PET offers advantages such as low energy consumption and environmental friendliness. This method primarily utilizes microorganisms, enzymes, or other bioactive substances to decompose PET into smaller molecules or monomers, allowing it to re-enter the material cycle or be reused. While some microorganisms can completely degrade PET using biological recycling methods, the efficiency is extremely low. Chemical upgrading recycling methods, as a cutting-edge direction in the resource utilization of PET, demonstrate unique technological advantages in the field of depolymerization and conversion. This method precisely breaks down polyester molecular chains to depolymerize polyester macromolecules into monomers. These monomers can either be used to rebuild high-performance polymer materials through polymerization reactions or to prepare high-value-added fine chemicals through selective catalytic conversion. However, chemical upgrading recycling methods for PET, whether photocatalysis, electrocatalysis, or solvent catalysis, are still developing technologies and generally suffer from low precision and operational difficulties.

[0006] In short, the current problems with waste plastic disposal are as follows:

[0007] 1. Plastics have a stable structure and a long natural degradation time: The main component of plastics is a high molecular polymer. Its molecules are formed by a large number of repeating monomer units connected by covalent bonds to form long chains. The covalent bonds have high bond energy and strong stability. Water, oxygen or microorganisms commonly found in nature have difficulty breaking these chemical bonds, which makes the molecular chains of plastics not easy to break.

[0008] 2. Low plastic recycling rate: Plastic recycling is difficult. Existing plastic recycling methods have high requirements for operational precision and conditions, which are not easy to meet, so plastic recycling methods have not been able to replace traditional landfill and incineration methods.

[0009] 3. The high value of plastics has not been significantly improved: the value of recycled plastics is not high and has not generated the expected commercial value.

[0010] 4. Poor mechanical properties of waste PET plastic filaments: Filaments obtained by direct extrusion of waste PET plastic have a certain degree of bending and unstable molding. The elongation after fracture and tensile strength, which can reflect plasticity and toughness, are only about 1.2% and 6 MPa, respectively. Waste PET plastic filaments have poor mechanical properties.

[0011] In conclusion, new methods for recycling PET plastics are still needed to achieve high-value recycling and reuse of waste PET plastics. Summary of the Invention

[0012] The purpose of this invention is to provide a technical solution that enables the high-value recycling and reuse of waste PET plastics.

[0013] To achieve the above objectives, the present invention provides the following three technical solutions.

[0014] In a first aspect, the present invention provides a method for recycling PET plastic, wherein the method includes:

[0015] Ingredient preparation steps: PET plastic is mixed with chain extender, toughening agent and fiber to obtain a mixture; wherein, the mass ratio of PET plastic to chain extender, toughening agent and fiber is 1:(0.8-1.2):(1.5-2.2):(1.5-2.2);

[0016] Filament extrusion molding steps: The mixture obtained in the batching step is subjected to filament extrusion to obtain filaments; the obtained filaments are cooled to obtain modified PET plastic filaments.

[0017] The PET plastic recycling method provided by this invention involves mixing PET plastic with a modifier, toughening agent, fiber, and chain extender, followed by filament extrusion molding to obtain modified PET plastic filaments that can be used as 3D printing filaments. The modified PET plastic filaments prepared by this PET plastic recycling method possess excellent mechanical properties and melt viscosity, meeting the requirements of 3D printing.

[0018] In 3D printing, filaments are molten at high temperatures, then adhere and stack together to form a three-dimensional product. During recycling and processing (such as extrusion and melting), PET plastic undergoes molecular chain breakage due to thermal oxidation and mechanical shearing. To ensure the melt viscosity of PET plastic filaments used in 3D printing, chain extenders are added. These chain extenders contain active functional groups that react chemically with the hydroxyl and carboxyl groups at the ends of the PET molecular chains, reconnecting the broken chains to form longer chains. This repaired chain increases the melt viscosity of PET and improves the material's thermal stability.

[0019] PET plastic filaments used in 3D printing require excellent mechanical properties, primarily plasticity and toughness. This is because products used for extended periods must withstand various impacts from the external environment, and good plasticity and toughness are essential for long-term use. Toughening agents and fibers are selected to improve the mechanical properties of PET plastic filaments. Toughening agents enhance the tensile properties of PET plastic filaments. During the recycling process, the molecular chains of PET plastic may be damaged to some extent, leading to a decrease in the material's flexibility and toughness. Toughening agent molecules can insert into the molecular chains of PET plastic, making it more resilient and improving its impact resistance. Fibers themselves possess high strength and rigidity; when uniformly dispersed in PET plastic, they can withstand external forces, significantly improving the material's tensile strength, flexural strength, and elastic modulus.

[0020] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the PET plastic is selected from waste PET plastic.

[0021] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the PET plastic recycling method further includes:

[0022] Crushing step: PET plastic is crushed before the batching step to obtain PET plastic fragments, which are then mixed with chain extenders, toughening agents, and fibers in the batching step;

[0023] More preferably, the particle size of the PET plastic fragments does not exceed 5 mm;

[0024] PET plastic fragments with a particle size of no more than 5mm are more conducive to mixing with chain extenders, toughening agents, and fibers for filament extrusion molding.

[0025] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the chain extender includes at least one of pyromellitic dianhydride (PMDA), phthalic anhydride (PA), and maleic anhydride (MAH);

[0026] More preferably, the chain extender is pyromellitic dianhydride (PMDA).

[0027] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the toughening agent may include, but is not limited to, at least one of ethylene octene copolymer toughening agents (e.g., copolymers of ethylene octene with a degree of polymerization of 935-945) and PE toughening agents.

[0028] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the fiber includes at least one of carbon fiber and glass fiber.

[0029] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the fiber size satisfies the following: diameter of 5-30 μm (e.g., 14 μm) and length of 0.1-1 mm (e.g., 0.5 mm).

[0030] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the mass ratio of PET plastic to chain extender, toughening agent and fiber is 1:1:2:2.

[0031] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, in the process of extruding the mixture obtained in the batching step to obtain filaments, the mixture is first softened at a temperature of 190-210°C (e.g., 200°C), the softened material is then melted and mixed at a temperature of 230-250°C (e.g., 240°C), and the melted and mixed material is then extruded into filaments at a temperature of 180-200°C (e.g., 190°C) to obtain filaments; in this preferred technical solution, by controlling the temperature during the filament extrusion process, the filaments can be formed more effectively;

[0032] More preferably, the process of extruding the mixture obtained in the batching step to obtain filaments is carried out using an extruder. The feed temperature (i.e., cooling and softening temperature) of the extruder is set to -℃ (e.g., 200℃), the mixing temperature (i.e., barrel heating temperature) is set to 230-250℃ (e.g., 240℃), and the discharge temperature (i.e., die heating temperature) is set to 180-200℃ (e.g., 190℃). The screw speed of the extruder is set to no more than 20 rpm. A water-cooling unit is provided at the discharge port of the extruder. The water-cooling unit includes a water tank and a sponge placed in the water tank. The sponge is immersed in the water in the water tank and is in contact with the extruder. The extruder outlet is contacted, and the outlet is cooled by a sponge. The water temperature in the water tank is 0-20℃ (e.g., 20℃). The feed temperature (i.e., cooling and softening temperature) and mixing temperature (i.e., barrel heating temperature) of the extruder can usually reach the set temperature. However, the discharge temperature is difficult to reach the set temperature and usually appears to be close to the mixing temperature (i.e., barrel heating temperature). In order to make the discharge temperature reach the set temperature of 180-200℃ (e.g., 190℃), in this preferred technical solution of the present invention, an external water cooling unit is provided to assist the discharge temperature in reaching the set temperature of 180-200℃ (e.g., 190℃).

[0033] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the cooling process of the obtained filament is carried out by immersing the filament in cold water at 0-20°C.

[0034] According to a specific embodiment of the PET plastic recycling method provided by the present invention, preferably, the diameter of the filament is 1.70-1.80 mm (e.g., 1.75 mm).

[0035] Secondly, the present invention provides a modified PET plastic filament that can be prepared by the PET plastic recycling method provided in the first aspect of the present invention.

[0036] Thirdly, the present invention provides the use of the modified PET plastic filament provided in the second aspect of the present invention as a 3D printing filament in 3D printing.

[0037] The technical solution provided by this invention involves mixing PET plastic with modified toughening agents, fibers, and chain extenders, followed by filament extrusion molding to obtain modified PET plastic filaments with excellent mechanical properties and melt viscosity that meet the requirements of 3D printing, which can be used as 3D printing filaments. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the extruder in Example 1.

[0039] Figure 2 This is a schematic diagram of the extruder and cooling unit in Example 1.

[0040] Figure 3 This is a schematic diagram of the extruder and cooling unit in Example 1.

[0041] Figure 4 This is a comparison chart of the set temperature and the actual temperature of the extruder in Example 1.

[0042] Figure 5 This is a graph showing the temperature change of the discharge material after the cooling unit is placed close to the discharge port.

[0043] Figure 6 This is a comparison chart of temperature changes after the filament was immersed in water in Example 1.

[0044] Figure 7 This is a thermal image of the filament after it is immersed in water in Example 1.

[0045] Figure 8 The stress-time curve is shown in Comparative Example 1 for the commercial 3D printed filament.

[0046] Figure 9 The graph shows the melt viscosity of the commercial 3D printing filament in Comparative Example 1.

[0047] Figure 10 This is a stress-time curve of the modified PET plastic filament in Example 1.

[0048] Figure 11This is a melt viscosity curve of the modified PET plastic filament in Example 1.

[0049] Figure 12 The stress-time curve of the PET plastic filament in Comparative Example 2 is shown.

[0050] Figure 13 The stress-time curve of the PET plastic filament in Comparative Example 3 is shown.

[0051] Figure 14 The stress-time curve of the PET plastic filament in Comparative Example 4 is shown.

[0052] Figure 15 The image shows the finished product obtained by 3D printing using the modified PET plastic filaments from Example 1. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0054] Comparative Example 1

[0055] The mechanical properties of commercially available 3D printed filaments were tested using a universal tensile testing machine, including elongation after fracture and tensile strength, which best reflect plasticity and toughness. The results are shown in Table 1. Figure 8 As shown.

[0056] Table 1

[0057]

[0058] As shown in Table 1, the tensile strength of commercial 3D printing filaments is 553 MPa and the elongation after fracture is 89.32%. Commercial 3D printing materials exhibit good plasticity and toughness.

[0059] The melt viscosity of commercial 3D printing filaments was tested using a capillary rheometer. Pressure was applied to allow the molten material to flow in a capillary, and the viscosity was calculated based on the pressure drop and flow rate. This simulates the shear flow state during processing, with the shear rate γ = 4·Q÷(π·R). 2 Shear stress τ=ΔP·L÷(2·π·R) 2 The viscosity η = τ ÷ γ, R is the capillary radius, Q is the volumetric flow rate, ΔP is the pressure difference across the capillary, and L is the filament length. The results are shown in Table 2. Figure 9 As shown.

[0060] Table 2

[0061]

[0062] Commercial 3D printing filaments exhibit apparent viscosity ranging from 28 Pa·s to 0.085 Pa·s at 190℃ and under different shear rates and shear stresses. The high-speed shearing significantly improves the fluidity of the filaments, which is beneficial for the extrusion of 3D printing filaments.

[0063] Example 1

[0064] This embodiment provides a modified PET plastic filament.

[0065] The modified PET plastic filament is prepared by the following PET plastic recycling method, wherein the method includes:

[0066] 1. Crushing steps: Put waste PET plastic into a crusher for crushing. The crushed product is passed through a 5mm sieve to obtain PET plastic fragments.

[0067] 2. Ingredient preparation steps: PET plastic fragments are mixed with chain extender PMDA, toughening agent ethylene octene copolymer (in this example, a copolymer of ethylene octene with a degree of polymerization of about 940) and fibers (size: diameter 14μm, length 0.5mm) at a mass ratio of 1:1:2:2 to obtain a mixture.

[0068] 3. Filament extrusion molding step: The mixture obtained in the batching step is extruded using an extruder (e.g., ...). Figure 1 The filaments were extruded to obtain filaments; the obtained filaments were cooled to obtain modified PET plastic filaments; wherein the diameter of the filaments was 1.75 mm.

[0069] The extruder's feed temperature (i.e., cooling and softening temperature) is set to 200℃, mixing temperature (i.e., barrel heating temperature) to 240℃, and discharge temperature (i.e., mold heating temperature) to 190℃. The extruder's screw speed is set to 10-20 revolutions per minute. A water-cooled cooling unit (e.g., [missing information]) is installed at the extruder's discharge port. Figure 2 , Figure 3 As shown), the water-cooling unit includes a water tank and a sponge placed in the water tank. The sponge is immersed in the water in the water tank and is in contact with the extruder outlet. The sponge cools the extruder outlet. The water temperature in the water tank is 20°C. Thus, the mixture is first softened at 200°C, then melted and mixed at 240°C, and then extruded into filaments at 190°C at a speed of 0 m / s to obtain filaments.

[0070] The temperature of an extruder consists of three parts: the feed temperature (i.e., the cooling and softening temperature), the mixing temperature (i.e., the barrel heating temperature), and the discharge temperature (i.e., the die heating temperature). While the feed temperature (i.e., the cooling and softening temperature) and the mixing temperature (i.e., the barrel heating temperature) can reach the set temperatures, the discharge temperature often fails to do so. The temperature at the extruder's discharge port (i.e., the die heating temperature) is easily affected by the mixing temperature (i.e., the barrel heating temperature), appearing close to the barrel heating temperature. This causes a discrepancy between the set and actual die heating temperature. The temperatures at various points within the extruder, such as... Figure 4 As shown; to achieve the set discharge temperature of 190℃, a water-cooled unit is installed at the discharge port of the extruder. The screw speed of the extruder is adjusted to 0, and then a sponge is placed against the discharge port. Because the sponge in the water-cooled unit is immersed in water for a long time, its temperature is close to the water temperature, around 20℃. The discharge port temperature is close to the barrel heating temperature, around 240℃. Therefore, heat exchange occurs between the two. Initially, due to the large temperature difference, the discharge port temperature drops rapidly. As the temperature difference gradually decreases, the cooling rate slows down. Due to the presence of water, the sponge reaches a heat dissipation balance, and eventually, the temperature at the discharge port slowly drops to around 190℃ (e.g., Figure 5 (As shown), thus achieving the goal of reaching the set temperature of 190℃ through the water-cooled cooling unit;

[0071] In the cooling process, the obtained filament is cooled by immersing it in cold water at 20°C. Initially, the temperature difference between the water and the filament is large, resulting in rapid cooling. As the temperature difference decreases, the cooling rate slows down. However, due to the large volume of water and the small size of the filament, the cooling rate will decrease to some extent (e.g., ...). Figure 6 , Figure 7 As shown in the figure, the filament cools rapidly after being immersed in water, thereby achieving stable molding and completing temperature control.

[0072] The mechanical properties of the modified PET plastic filaments prepared in this embodiment were tested using a universal tensile testing machine, including elongation after fracture and tensile strength, which best reflect plasticity and toughness. The results are shown in Table 3. Figure 10 As shown.

[0073] Table 3

[0074]

[0075] As can be seen from Table 3, the modified PET plastic filament prepared in this embodiment has a tensile strength of 453 MPa and an elongation after fracture of 86.04%, which is very close to the commercial 3D printing material in Comparative Example 1. It has good plasticity and toughness and can meet the mechanical performance requirements for use as a 3D printing material.

[0076] The melt viscosity of the modified PET plastic filaments prepared in this embodiment was tested using a capillary rheometer. Pressure was applied to allow the molten material to flow in a capillary tube, and the viscosity was calculated based on the pressure drop and flow rate. This simulates the shear flow state during processing, with a shear rate γ = 4·Q÷(π·R). 2 Shear stress τ=ΔP·L÷(2·π·R) 2 The viscosity η = τ ÷ γ, R is the capillary radius, Q is the volumetric flow rate, ΔP is the pressure difference across the capillary, and L is the filament length. The results are shown in Table 4. Figure 11 As shown.

[0077] Table 4

[0078]

[0079]

[0080] The modified PET plastic filaments prepared in this embodiment have an apparent viscosity ranging from 35 Pa·s to 0.012 Pa·s at 190°C, different shear rates, and shear stresses. Both the maximum apparent viscosity and the decrease in viscosity at these temperatures, shear rates, and shear stresses are better than the commercial 3D printing material in Comparative Example 1, and can meet the melt viscosity performance requirements for use as a 3D printing material.

[0081] Comparative Example 2

[0082] This comparative example provides a PET plastic filament.

[0083] The only difference between this PET plastic filament and the modified PET plastic filament provided in Example 1 is that the preparation process does not involve a batching step, but directly uses PET plastic fragments for filament extrusion molding.

[0084] The mechanical properties of the PET plastic filaments prepared in this comparative example were tested using a universal tensile testing machine, including elongation after fracture and tensile strength, which best reflect plasticity and toughness. The results are as follows: Figure 12 As shown.

[0085] The PET plastic filament prepared in this comparative example has a tensile strength of 6 MPa and an elongation after fracture of 1.2%, which are significantly lower than those of the commercial 3D printing material in Comparative Example 1. The stress-time curve of the PET plastic filament prepared in this comparative example differs from that of the commercial 3D printing filament in Comparative Example 1 by approximately 100 times, a substantial difference. Furthermore, the stress-time curve of the PET plastic filament prepared in this comparative example lacks the rapid rise, slow rise, and rapid fall phases. Therefore, the PET plastic filament prepared in this comparative example does not meet the mechanical performance requirements for use as a 3D printing material.

[0086] Comparative Example 3

[0087] This comparative example provides a modified PET plastic filament.

[0088] The only difference between this PET plastic filament and the modified PET plastic filament provided in Example 1 is that during the batching step in the preparation process, PET plastic fragments are mixed with fibers at a mass ratio of 1:1, without adding chain extender PMDA and toughening agent.

[0089] The mechanical properties of the modified PET plastic filaments prepared in this comparative example were tested using a universal tensile testing machine, including elongation after fracture and tensile strength, which best reflect plasticity and toughness. The results are shown in Table 5. Figure 13 As shown.

[0090] Table 5

[0091]

[0092]

[0093] The PET plastic filament prepared in this comparative example has a tensile strength of 82 MPa and an elongation after fracture of 3.26%. Its tensile strength is approximately 15 times higher than that of the PET plastic filament provided in Comparative Example 2, but the change in elongation after fracture is not significant. Both its elongation after fracture and tensile strength are significantly lower than those of the commercial 3D printing material in Comparative Example 1. The stress-time curve of the modified PET plastic filament prepared in this comparative example shows a similar initial rising phase to that of the commercial 3D printing material, but it lacks the subsequent slow rising phase and extrusion falling phase. Therefore, the modified PET plastic filament prepared in this comparative example does not meet the mechanical performance requirements for use as a 3D printing material.

[0094] Comparative Example 4

[0095] This comparative example provides a modified PET plastic filament.

[0096] The only difference between this PET plastic filament and the modified PET plastic filament provided in Example 1 is that during the preparation process, the PET plastic fragments are mixed with the toughening agent at a mass ratio of 1:1 during the batching step, without adding the chain extender PMDA and fibers.

[0097] The mechanical properties of the modified PET plastic filaments prepared in this comparative example were tested using a universal tensile testing machine, including elongation after fracture and tensile strength, which best reflect plasticity and toughness. The results are shown in Table 6. Figure 14 As shown.

[0098] Table 6

[0099]

[0100] The PET plastic filament prepared in this comparative example has a tensile strength of 7 MPa and an elongation after fracture of 439.76%. Its elongation after fracture is significantly increased compared to the PET plastic filament provided in Comparative Example 2, but the tensile strength remains almost unchanged. Its tensile strength is significantly lower than that of the commercial 3D printing material in Comparative Example 1. The stress-time curve of the modified PET plastic filament prepared in this comparative example shows a plateau. The material, a mixture of toughening agent and waste PET plastic in equal proportions, exhibits a "broken yet connected" phenomenon, meaning the filament diameter decreases after stretching. This trend is approaching a slow upward phase, but it still shows significant deficiencies compared to commercial 3D printing materials. The modified PET plastic filament prepared in this comparative example does not meet the mechanical performance requirements for use as a 3D printing material.

[0101] Comparative Example 5

[0102] This comparative example provides a modified PET plastic filament.

[0103] The only difference between this PET plastic filament and the modified PET plastic filament provided in Example 1 is that during the preparation process, the PET plastic fragments are mixed with the chain extender PMDA at a mass ratio of 1:1 during the batching step, without adding toughening agents and fibers, ultimately resulting in filament failure.

[0104] Experimental Example 1

[0105] This experimental example uses the modified PET plastic filament provided in Example 1 for 3D printing.

[0106] The 3D printer was instructed to print a small fan. The modified PET plastic filament provided in Example 1 did not experience any jamming or filament sticking issues throughout the entire 3D printing process, and ultimately successfully printed a structurally stable and usable small fan. Figure 15 As shown.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recycling PET plastic, wherein, The method includes: Ingredient preparation steps: PET plastic is mixed with chain extender, toughening agent and fiber to obtain a mixture; wherein, the mass ratio of PET plastic to chain extender, toughening agent and fiber is 1:(0.8-1.2):(1.5-2.2):(1.5-2.2); Filament extrusion molding steps: The mixture obtained in the batching step is subjected to filament extrusion to obtain filaments; the obtained filaments are cooled to obtain modified PET plastic filaments.

2. The PET plastic recycling method according to claim 1, wherein, PET plastic recycling methods also include: Crushing step: PET plastic is crushed before the batching step to obtain PET plastic fragments, which are then mixed with chain extenders, toughening agents, and fibers in the batching step; Preferably, the particle size of the PET plastic fragments does not exceed 5 mm.

3. The PET plastic recycling method according to claim 1, wherein, Chain extenders include at least one of pyromellitic dianhydride, phthalic anhydride, and maleic anhydride; The toughening agent includes at least one of the following: a copolymer toughening agent of ethylene octene and a PE toughening agent; The fiber includes at least one of carbon fiber and glass fiber.

4. The PET plastic recycling method according to claim 1, wherein, The fiber dimensions meet the following requirements: diameter 5-30μm and length 0.1-1mm.

5. The PET plastic recycling method according to claim 1, wherein, The mass ratio of PET plastic to chain extender, toughening agent and fiber is 1:1:2:

2.

6. The PET plastic recycling method according to claim 1, wherein, In the process of extruding the mixture obtained from the batching step into filaments, the mixture is first softened at a temperature of 190-210℃, then melted and mixed at a temperature of 230-250℃, and then extruded into filaments at a temperature of 180-200℃ to obtain filaments. Preferably, the process of extruding the mixture obtained in the batching step to obtain filaments is carried out using an extruder. The feed temperature of the extruder is set to 190-210℃, the mixing temperature is set to 230-250℃, and the discharge temperature is set to 180-200℃. The screw speed of the extruder is set to no more than 20 revolutions per minute. A water-cooling unit is provided at the discharge port of the extruder. The water-cooling unit includes a water tank and a sponge placed in the water tank. The sponge is immersed in the water in the water tank and is in contact with the discharge port of the extruder. The sponge cools the discharge port of the extruder. The temperature of the water in the water tank is 0-20℃.

7. In the PET plastic recycling method according to claim 1, the cooling process of the obtained filaments is carried out by immersing the filaments in cold water at 0-20°C.

8. The PET plastic recycling method according to claim 1, wherein the diameter of the filament is 1.70-1.80 mm.

9. A modified PET plastic filament, which can be prepared by the PET plastic recycling method according to any one of claims 1-8.

10. The use of the modified PET plastic filament of claim 9 as a 3D printing filament in 3D printing.

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