Polyethylene recycled PET bottle flakes and preparation method thereof

Abstract

The present invention relates to the technical field of organic synthesis, in particular to a polyethylene recycled PET bottle flake, which is made of the following raw materials by weight: 75-90 parts of PET plastic, 12-30 parts of PE particles, 0.1-0.5 parts of antioxidants, 0.2-0.4 parts of lubricants, 3-8 parts of compatibilizers, 0.1-0.3 parts of ultraviolet absorbers, 0.3-0.5 parts of colorants and 3-5 parts of depolymerizers. In the present invention, the polyethylene recycled PET bottle flakes are prepared by the preparation method, the purity of the recycled raw materials is improved, the quality stability of the recycled products is improved, and in the polyethylene compounding process, the compatibilizer is added to promote the compounding of polyethylene and PET oligomers, and the interface bonding force between the two is enhanced, so that the recycled bottle flakes have good mechanical properties, can be widely used in the fields of plastic packaging, injection molding products, etc., and the added value of the recycled products is improved.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, in particular to a polyethylene recycled PET bottle flake and a preparation method thereof. Background Art

[0002] With the widespread use of plastic products, PET materials are widely used in beverage bottles, food packaging and other fields, while polyethylene is often used in supporting components such as bottle caps and seals. The treatment of discarded plastic bottles has become a serious environmental and resource issue. PET (polyethylene terephthalate) bottles are widely used in beverage, food and other packaging fields, while polyethylene (PE) materials are also commonly used in bottle caps, seals and other parts of plastic bottles. If a large number of discarded PET bottles and related polyethylene parts cannot be effectively recycled, they will not only occupy a large amount of land for landfill, but also cause pollution to the environment.

[0003] Traditional recycling methods often simply crush and clean discarded PET products and then reprocess them. The resulting recycled products have poor performance, such as low mechanical strength and insufficient toughness, which limits their scope of application. Moreover, during the recycling process, there is little research on the composite utilization of PET and polyethylene, and the advantages of both have not been fully utilized.

[0004] Based on this, the present invention provides a polyethylene recycled PET bottle flake and a preparation method thereof to solve the above-mentioned technical problems. Summary of the invention

[0005] The object of the present invention is to provide a polyethylene recycled PET bottle flake and a preparation method thereof to solve the above problems.

[0006] To achieve the above object, the present invention provides the following technical solutions: The invention discloses a polyethylene recycled PET bottle flake, which is prepared from the following raw materials in parts by weight: 75-90 parts of PET plastic, 12-30 parts of PE particles, 0.1-0.5 parts of antioxidant, 0.2-0.4 parts of lubricant, 3-8 parts of compatibilizer, 0.1-0.3 parts of ultraviolet absorber, 0.3-0.5 parts of colorant and 3-5 parts of depolymerizing agent.

[0007] Furthermore, the PE material is selected from one of low-density polyethylene, high-density polyethylene and linear low-density polyethylene, and the antioxidant is selected from one of hindered phenol antioxidants and phosphite antioxidants.

[0008] Furthermore, the lubricant is glyceryl stearate and paraffin, the compatibilizer is maleic anhydride grafted polyethylene, and the depolymerizing agent is ethylene glycol and the catalyst zinc acetate.

[0009] A method for preparing polyethylene recycled PET bottle flakes comprises the following steps: Ⅰ. Raw material preparation: Collect discarded PET plastic bottles and PE material parts, perform preliminary screening on the collected raw materials, remove impurities therein, and obtain mixed raw materials; Ⅱ. Raw material pretreatment: crush the mixed raw materials into fragments with a size of 3 to 5 cm by crushing equipment, and then wash and dry the fragments to obtain mixed fragments; III. Density separation: the mixed fragments are put into a separation device filled with a density separation liquid, and the density of the density separation liquid is adjusted to be between the densities of polyethylene and PET. The density separation liquid is a saline solution. Under stirring, the mixed fragments are fully dispersed in the density separation liquid. Since the density of polyethylene is less than that of the separation liquid, and the density of PET is greater than that of the separation liquid, after a period of standing, the polyethylene fragments will float on the liquid surface, and the PET fragments will sink to the bottom. The floating polyethylene fragments and the sinking PET fragments are collected separately; IV. PET purification: The collected PET fragments are further purified by combining high-temperature cooking and chemical cleaning. The PET fragments are placed in a high-temperature cooking device and cooked at a temperature of 120 to 150°C for 30 to 60 minutes to remove residual glue and pigment impurities. The cooked PET fragments are then soaked in an alkaline solution, wherein the alkaline solution is a sodium hydroxide solution with a concentration of 3 to 5%, and the soaking time is 2 to 4 hours to further remove surface dirt and a small amount of residual polyethylene; V. PET depolymerization: The purified PET fragments are subjected to depolymerization reaction. The PET fragments are added to a depolymerization reactor, and an appropriate amount of depolymerizing agent is added at the temperature of 180-220°C for 2-4 hours to depolymerize PET into oligomers. VI. Polyethylene treatment: The collected polyethylene fragments are cleaned and dried. First, the polyethylene fragments are rinsed with clean water to remove the salt and residual impurities on the surface, and then dried at a temperature of 80-100°C to constant weight; Ⅶ. Polyethylene compounding: Compounding the treated polyethylene fragments with the depolymerized PET oligomers, adding the polyethylene fragments to the PET oligomers, and adding appropriate amounts of antioxidants, lubricants, compatibilizers, ultraviolet absorbers and colorants, wherein the amount of the compatibilizer added is 3-5% of the total mass of the polyethylene and PET oligomers, and extruding the mixture by high-speed stirring and extruder, and controlling the extrusion temperature at 200-240° C. to uniformly disperse the polyethylene in the PET oligomers to form a composite material; VIII. Granulation and molding: The composite material is granulated by a granulator. The screw speed of the granulator is controlled at 80-120 r / min. The temperature of each section is set as follows: zone 1 180-200°C, zone 2 200-220°C, zone 3 220-240°C, zone 4 240-260°C, head temperature 230-250°C, cooling water temperature 20-30°C, to prepare polyethylene recycled PET bottle flakes with uniform particle size.

[0010] Further, in step III, the separation device includes a stirring mechanism and a separation mechanism, the top of the stirring mechanism is fixedly connected to the bottom of the separation mechanism, the separation mechanism includes a separation frame, a top plate, a fixed plate, a screw motor, a screw, a support plate, a telescopic frame and a movable plate, the bottom of the fixed plate is fixedly installed on the top of the separation frame, and one end of the fixed plate is rotatably installed on one end of the top plate, a sliding groove is provided on the top of the fixed plate, the output end of the screw motor is fixedly connected to one end of the screw, a movable block is threadedly engaged with the outer wall of the screw, a connecting plate is fixedly connected to the bottom of the movable block, two ends of the support plate are fixedly installed on the inner wall of the bottom end of the separation frame, two ends of the movable plate are slidably installed on the inner wall of the bottom end of the separation frame, the bottom end of the connecting plate passes through the sliding groove and is fixedly connected to the top of the movable plate, a separation net is provided between the support plate and the movable plate, one end of the telescopic frame is rotatably connected to the two ends of the support plate, and the other end of the telescopic frame is rotatably connected to the two ends of the movable plate.

[0011] Furthermore, the bottom end of the screw motor is fixedly connected to the top of the fixed plate, the outer side of the connecting plate is slidably connected to the inner wall of the sliding groove, a pull rod is fixedly installed on the top of the top plate, and a feeding pipe is fixedly connected to the top of the top plate.

[0012] Furthermore, the stirring mechanism includes a stirring tank, a support frame, a stirring rod, a fixed rod, an annular frame and a motor, the top of the stirring tank is fixedly connected to the bottom of the separation frame, and the bottom end of the stirring tank is fixedly connected to the top of the annular frame, the output end of the motor is fixedly connected to the bottom end of the stirring rod, the outer wall of the stirring rod is symmetrically fixedly connected with a plurality of stirring blades, and the bottom end of the stirring rod is symmetrically fixedly connected with two scrapers.

[0013] Furthermore, a discharge pipe is fixedly connected to the bottom of the annular frame, and a control valve is fixedly connected to the bottom end of the discharge pipe. Both ends of the fixed rod are fixedly installed on the inner wall of the stirring tank, and the bottom of the fixed rod is rotatably connected to the top end of the stirring rod.

[0014] Beneficial effects of the present invention: 1. Polyethylene recycled PET bottle flakes are prepared by the preparation method of the present invention. In the density separation process, the PET and polyethylene in the discarded PET bottles can be effectively separated by a separation device and a density separation technology, thereby improving the purity of the recycled raw materials and laying a foundation for the subsequent preparation of high-quality recycled bottle flakes. In the PET purification process, a series of treatment steps such as high-temperature cooking, chemical cleaning and depolymerization can be used to completely remove impurities in the PET fragments, and the PET fragments can be depolymerized into oligomers, which are convenient for compounding with polyethylene, thereby improving the quality stability of the recycled products. In the polyethylene compounding process, antioxidants are added to enhance the antioxidant effect. By adding ultraviolet absorbers, the recycled bottle flakes can be prevented from aging and discoloring under ultraviolet irradiation, thereby improving the use effect of the recycled bottle flakes. The addition of a compatibilizer promotes the compounding of polyethylene and PET oligomers, enhances the interface bonding force between the two, and enables the recycled bottle flakes to have good mechanical properties. At the same time, the preparation method of the present invention has a relatively simple process and strong operability, and can realize large-scale industrial production.

[0015] 2. In the present invention, by setting a separation device, the density of the density separation liquid is adjusted to be between the densities of polyethylene and PET, and then the mixed fragments and the density separation liquid are added to the stirring tank through the feeding pipe, and the liquid level of the density separation liquid is located in the middle of the separation frame. Under the stirring action, the mixed fragments are fully dispersed in the density separation liquid. Since the density of polyethylene is less than the density of the separation liquid, and the density of PET is greater than the density of the separation liquid, after a period of standing, the polyethylene fragments will float on the liquid surface, and the polyethylene fragments and the PET fragments are separated by the separation net, and the density separation liquid and the PET fragments at the bottom are discharged through the discharge pipe, and finally the polyethylene fragments located on the separation net can be taken out. Through the separation device, the mixed fragments can be separated and taken out conveniently and quickly, without manual separation, thereby improving the separation effect and separation efficiency of the mixed fragments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of a separation device in a method for preparing polyethylene recycled PET bottle flakes of the present invention; Figure 2 It is a schematic diagram of the top view of the structure of a separation device in a method for preparing polyethylene recycled PET bottle flakes of the present invention; Figure 3 It is a schematic diagram of the internal structure of the stirring mechanism of the separation device in the method for preparing polyethylene recycled PET bottle flakes of the present invention; Figure 4 It is a front cross-sectional view of a stirring mechanism of a separation device in a method for preparing polyethylene recycled PET bottle flakes of the present invention; Figure 5It is a structural schematic diagram of a separation mechanism of a separation device in a method for preparing polyethylene recycled PET bottle flakes of the present invention; Figure 6 The present invention is a schematic diagram of the internal structure of a separation mechanism of a separation device in a method for preparing polyethylene recycled PET bottle flakes.

[0017] In the figure: 1. stirring mechanism; 2. separation mechanism; 11. stirring tank; 12. support frame; 13. stirring rod; 14. fixed rod; 15. stirring blade; 16. scraper; 17. ring frame; 18. discharge pipe; 19. control valve; 110. motor; 21. separation frame; 22. top plate; 23. fixed plate; 24. screw motor; 25. pull rod; 26. feeding pipe; 27. screw; 28. movable block; 29. ​​sliding groove; 210. support plate; 211. separation net; 212. connecting plate; 213. telescopic frame; 214. movable plate. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Embodiment 1: This embodiment provides a polyethylene recycled PET bottle flake, which is made of the following raw materials in parts by weight: 90 parts of PET plastic, 30 parts of PE particles, 0.5 parts of antioxidant, 0.4 parts of lubricant, 8 parts of compatibilizer, 0.3 parts of ultraviolet absorber, 0.5 parts of colorant and 5 parts of depolymerizing agent, the PE material is low-density polyethylene, the antioxidant is a hindered phenol antioxidant, the lubricant is stearic acid glyceryl ester and paraffin, the compatibilizer is maleic anhydride grafted polyethylene, and the depolymerizing agent is ethylene glycol and the catalyst zinc acetate; The method for preparing polyethylene recycled PET bottle flakes comprises the following steps: Ⅰ. Raw material preparation: Collect discarded PET plastic bottles and PE material parts, perform preliminary screening on the collected raw materials, remove impurities therein, and obtain mixed raw materials; Ⅱ. Raw material pretreatment: crush the mixed raw materials into fragments with a size of 3 to 5 cm by crushing equipment, and then wash and dry the fragments to obtain mixed fragments; III. Density separation: put the mixed fragments into a separation device filled with density separation liquid, adjust the density of the density separation liquid to between the density of polyethylene and PET, and select saline solution as the density separation liquid. Under stirring, the mixed fragments are fully dispersed in the density separation liquid. Since the density of polyethylene is less than that of the separation liquid, and the density of PET is greater than that of the separation liquid, after a period of standing, the polyethylene fragments will float on the liquid surface, while the PET fragments will sink to the bottom. Collect the floating polyethylene fragments and the sinking PET fragments separately. IV. PET purification: The collected PET fragments are further purified by combining high-temperature cooking and chemical cleaning. The PET fragments are placed in a high-temperature cooking device and cooked at 120°C for 30 minutes to remove residual glue and pigment impurities. The cooked PET fragments are then soaked in an alkaline solution with a concentration of 3% sodium hydroxide solution for 2 hours to further remove surface dirt and a small amount of residual polyethylene. V. PET depolymerization: The purified PET fragments are subjected to depolymerization reaction. The PET fragments are added to a depolymerization reactor, and an appropriate amount of depolymerizing agent is added at the temperature of 180°C for 2 hours to depolymerize PET into oligomers. VI. Polyethylene treatment: The collected polyethylene fragments are cleaned and dried. First, the polyethylene fragments are rinsed with clean water to remove the salt and residual impurities on the surface, and then dried at 80°C to constant weight; VII. Polyethylene compounding: Compounding the treated polyethylene fragments with the depolymerized PET oligomers, adding the polyethylene fragments to the PET oligomers, and adding appropriate amounts of antioxidants, lubricants, compatibilizers, ultraviolet absorbers and colorants, wherein the amount of the compatibilizer added is 3% of the total mass of the polyethylene and PET oligomers, and extruding the mixture by high-speed stirring and extruder, with the extrusion temperature controlled at 200°C, so that the polyethylene is uniformly dispersed in the PET oligomers to form a composite material; VIII. Granulation: The composite material is granulated by a granulator. The screw speed of the granulator is controlled at 80r / min. The temperature of each section is set as follows: 180°C for zone 1, 200°C for zone 2, 220°C for zone 3, 240°C for zone 4, 230°C for die head, and 20°C for cooling water to produce polyethylene recycled PET bottle flakes with uniform particle size.

[0020] Example 2: This example provides a polyethylene recycled PET bottle flake and a preparation method thereof. The above steps are repeated, with the following differences: high-density polyethylene is selected as the PE material, a phosphite antioxidant is selected as the antioxidant, the PET fragments are cooked at 140°C for 30 min, soaked in 5% sodium hydroxide solution for 2 h, the depolymerization temperature is 210°C, the reaction time is 2.5 h, the polyethylene drying temperature is 85°C, the compatibilizer addition amount is 3.5%, the extrusion temperature is 230°C, the granulator screw speed is 90 r / min, the temperature of each section is set to: 200°C for zone 1, 220°C for zone 2, 240°C for zone 3, 260°C for zone 4, 250°C for die head, and 22°C for cooling water.

[0021] Example 3: This example provides polyethylene recycled PET bottle flakes and a preparation method thereof. The basic steps are repeated again, with the following differences: linear low-density polyethylene is selected as the PE material, a phosphite antioxidant is selected as the antioxidant, the PET cooking temperature is 150°C, the cooking time is 60 min, the sodium hydroxide solution concentration is 3%, the soaking time is 4 h, the depolymerization temperature is 180°C, the reaction time is 4 h, the polyethylene drying temperature is 100°C, the compatibilizer addition amount is 5%, the extrusion temperature is 200°C, the granulator screw speed is 120 r / min, the temperature of each section is set as: 190°C for zone 1, 210°C for zone 2, 230°C for zone 3, 250°C for zone 4, the head temperature is 240°C, and the cooling water temperature is 20°C.

[0022] Example 4: Please refer to Figure 1 - Figure 6As shown, this embodiment provides a method for preparing polyethylene recycled PET bottle flakes. In step III, the separation device includes a stirring mechanism 1 and a separation mechanism 2. The top of the stirring mechanism 1 is fixedly connected to the bottom of the separation mechanism 2. The separation mechanism 2 includes a separation frame 21, a top plate 22, a fixed plate 23, a screw motor 24, a screw 27, a support plate 210, a telescopic frame 213 and a movable plate 214. The bottom of the fixed plate 23 is fixedly installed with the top of the separation frame 21, and one end of the fixed plate 23 is rotatably installed with one end of the top plate 22. The top of the fixed plate 23 is connected to the top of the separation frame 21. A sliding groove 29 is provided, the output end of the screw motor 24 is fixedly connected to one end of the screw 27, the outer wall of the screw 27 is threadedly engaged with a movable block 28, the bottom of the movable block 28 is fixedly connected to a connecting plate 212, the two ends of the support plate 210 are fixedly installed with the bottom inner wall of the separation frame 21, the two ends of the movable plate 214 are slidably installed with the bottom inner wall of the separation frame 21, the bottom end of the connecting plate 212 passes through the sliding groove 29 and is fixedly connected to the top of the movable plate 214, a separation net 211 is provided between the support plate 210 and the movable plate 214, and a telescopic frame 213 is provided. One end of the support plate 210 is rotatably connected to the two ends of the telescopic frame 213, and the other end of the telescopic frame 213 is rotatably connected to the two ends of the movable plate 214. The bottom end of the screw motor 24 is fixedly connected to the top of the fixed plate 23, the outer side of the connecting plate 212 is slidably connected to the inner wall of the sliding groove 29, the top of the top plate 22 is fixedly installed with a pull rod 25, and the top of the top plate 22 is fixedly connected with a feeding pipe 26. The stirring mechanism 1 includes a stirring tank 11, a support frame 12, a stirring rod 13, a fixing rod 14, an annular frame 17 and a motor 110. The top of the stirring tank 11 is connected to the separation frame 21 The bottom of the stirring tank 11 is fixedly connected, and the bottom end of the stirring tank 11 is fixedly connected to the top of the annular frame 17, the output end of the motor 110 is fixedly connected to the bottom end of the stirring rod 13, the outer wall of the stirring rod 13 is symmetrically fixedly connected with a plurality of stirring blades 15, the bottom end of the stirring rod 13 is symmetrically fixedly connected with two scrapers 16, the bottom of the annular frame 17 is fixedly connected with a discharge pipe 18, and the bottom end of the discharge pipe 18 is fixedly connected with a control valve 19, both ends of the fixed rod 14 are fixedly installed with the inner wall of the stirring tank 11, and the bottom of the fixed rod 14 is rotatably connected to the top of the stirring rod 13.

[0023] In this embodiment, by setting a separation device, the density of the density separation liquid is adjusted to be between the densities of polyethylene and PET, and then the mixed fragments and the density separation liquid are added to the stirring tank 11 through the feeding pipe 26, and the liquid level of the density separation liquid is located in the middle of the separation frame 21, and the motor 110 is turned on, and the motor 110 drives the stirring rod 13 and the plurality of stirring blades 15 to rotate, so as to stir the mixed fragments. Under the stirring action, the mixed fragments are fully dispersed in the density separation liquid. After stirring for a period of time, the motor 110 is turned off, and the stirring rod 13 and the plurality of stirring blades 15 stop rotating. Since the density of polyethylene is less than the density of the separation liquid, and the density of PET is greater than the density of the separation liquid, after a period of standing, the polyethylene fragments will float on the liquid surface, and the PET fragments will sink to the bottom (in the annular frame 17). At this time, the screw motor 24 is turned on, and the screw motor 24 drives the screw 27 to rotate, so that the movable block 28 moves along the screw 27, and the movable block 28 drives the connecting plate 21 2 and the movable plate 214 move, the movable plate 214 slides along the inner wall of the separation frame 21 until the movable plate 214 moves to the end of the separation frame 21, and the screw motor 24 is turned off. At this time, the separation net 211 between the movable plate 214 and the support plate 210 is unfolded, and the polyethylene fragments floating on the liquid surface are located on the top of the separation net 211. The polyethylene fragments and the PET fragments are separated by the separation net 211. At this time, the motor 110 and the control valve 19 are turned on, and the density separation liquid in the stirring tank 11 and the PET fragments located at the bottom are discharged through the discharge pipe 18. At the same time, the motor 110 drives the scraper 16 to rotate along the annular frame 17, so that all the PET fragments in the annular frame 17 are discharged from the discharge pipe 18. Finally, the top plate 22 is opened to take out the polyethylene fragments on the separation net 211. Through the separation device, the mixed fragments can be separated and taken out conveniently and quickly without manual separation, thereby improving the separation effect and separation efficiency of the mixed fragments.

[0024] Test: The polyethylene recycled PET bottle flakes provided in Examples 1 to 3 are marked as Example 1 to 3 groups, and the relevant properties (heat resistance, tensile strength, hardness) of the polyethylene recycled PET bottle flakes obtained by the preparation methods of Examples 1 to 3 are tested respectively:

[0025]

[0026] By comparing and analyzing the relevant data in Table 1, it can be seen that the differences in heat resistance, tensile strength and hardness between Example 1 to Example 3 are not obvious, and each group has excellent heat resistance, tensile strength and hardness; In the present invention, 90 parts of PET plastic, 30 parts of PE particles, 0.5 parts of antioxidant, 0.4 parts of lubricant, 8 parts of compatibilizer, 0.3 parts of ultraviolet absorber, 0.5 parts of colorant and 5 parts of depolymerizing agent are used as raw materials. First, discarded PET plastic bottles and PE material parts are collected, and the collected raw materials are preliminarily screened to remove impurities therein to obtain mixed raw materials. The mixed raw materials are crushed into fragments with a size of 3 to 5 cm by crushing equipment, and the fragments are then cleaned and dried to obtain mixed fragments. In the density separation process, the PET and polyethylene in the discarded PET bottles can be effectively separated by the separation device and the density separation technology, thereby improving the purity of the recycled raw materials and laying a foundation for the subsequent preparation of high-quality recycled bottle flakes. In the PET purification process, a series of treatments such as high-temperature cooking, chemical cleaning and depolymerization are performed. The processing steps can completely remove impurities in the PET fragments and depolymerize them into oligomers, which are convenient for compounding with polyethylene, thereby improving the quality stability of the recycled product. In the polyethylene compounding process, by adding an antioxidant, the antioxidant effect is enhanced. By adding an ultraviolet absorber, the recycled bottle pieces can be prevented from aging and discoloring under ultraviolet irradiation, thereby improving the use effect of the recycled bottle pieces. The addition of a compatibilizer promotes the compounding of polyethylene and PET oligomers, enhances the interface bonding force between the two, and makes the recycled bottle pieces have good mechanical properties. The recycled bottle pieces can be widely used in the fields of plastic packaging, injection molding products, etc., thereby improving the added value of the recycled products. At the same time, the preparation method of the present invention has a relatively simple process and strong operability, and can realize large-scale industrial production, which is conducive to promoting the development of the recycling and reuse industry of waste plastic bottles, and has significant economic and environmental benefits.

[0027] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0028] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A polyethylene recycled PET bottle flake, characterized in that: The polyethylene recycled PET bottle flakes are prepared from the following raw materials in parts by weight: 75-90 parts of PET plastics, 12-30 parts of PE particles, 0.1-0.5 parts of antioxidants, 0.2-0.4 parts of lubricants, 3-8 parts of compatibilizers, 0.1-0.3 parts of ultraviolet absorbers, 0.3-0.5 parts of colorants and 3-5 parts of depolymerizing agents.

2. The polyethylene recycled PET bottle flakes according to claim 1, characterized in that: The PE material is selected from one of low-density polyethylene, high-density polyethylene and linear low-density polyethylene, and the antioxidant is selected from one of hindered phenol antioxidants and phosphite antioxidants.

3. The polyethylene recycled PET bottle flakes according to claim 1, characterized in that: The lubricant is glyceryl stearate and paraffin, the compatibilizer is maleic anhydride grafted polyethylene, and the depolymerizing agent is ethylene glycol and catalyst zinc acetate.

4. A method for preparing polyethylene recycled PET bottle flakes, characterized in that: The polyethylene recycled PET bottle flakes according to any one of claims 1 to 3 are used, comprising the following steps: Ⅰ. Raw material preparation: Collect discarded PET plastic bottles and PE material parts, perform preliminary screening on the collected raw materials, remove impurities therein, and obtain mixed raw materials; Ⅱ. Raw material pretreatment: crush the mixed raw materials into fragments with a size of 3 to 5 cm by crushing equipment, and then wash and dry the fragments to obtain mixed fragments; III. Density separation: the mixed fragments are put into a separation device filled with a density separation liquid, and the density of the density separation liquid is adjusted to be between the densities of polyethylene and PET. The density separation liquid is a saline solution. Under stirring, the mixed fragments are fully dispersed in the density separation liquid. Since the density of polyethylene is less than that of the separation liquid, and the density of PET is greater than that of the separation liquid, after a period of standing, the polyethylene fragments will float on the liquid surface, and the PET fragments will sink to the bottom. The floating polyethylene fragments and the sinking PET fragments are collected separately; IV. PET purification: The collected PET fragments are further purified by combining high-temperature cooking and chemical cleaning. The PET fragments are placed in a high-temperature cooking device and cooked at a temperature of 120 to 150°C for 30 to 60 minutes to remove residual glue and pigment impurities. The cooked PET fragments are then soaked in an alkaline solution, wherein the alkaline solution is a sodium hydroxide solution with a concentration of 3 to 5%, and the soaking time is 2 to 4 hours to further remove surface dirt and a small amount of residual polyethylene; V. PET depolymerization: The purified PET fragments are subjected to depolymerization reaction. The PET fragments are added to a depolymerization reactor, and an appropriate amount of depolymerizing agent is added at the temperature of 180-220°C for 2-4 hours to depolymerize PET into oligomers. VI. Polyethylene treatment: The collected polyethylene fragments are cleaned and dried. First, the polyethylene fragments are rinsed with clean water to remove the salt and residual impurities on the surface, and then dried at a temperature of 80-100°C to constant weight; Ⅶ. Polyethylene compounding: Compounding the treated polyethylene fragments with the depolymerized PET oligomers, adding the polyethylene fragments to the PET oligomers, and adding appropriate amounts of antioxidants, lubricants, compatibilizers, ultraviolet absorbers and colorants, wherein the amount of the compatibilizer added is 3-5% of the total mass of the polyethylene and PET oligomers, and extruding the mixture by high-speed stirring and extruder, and controlling the extrusion temperature at 200-240° C. to uniformly disperse the polyethylene in the PET oligomers to form a composite material; VIII. Granulation and molding: The composite material is granulated by a granulator. The screw speed of the granulator is controlled at 80-120 r / min. The temperature of each section is set as follows: zone 1 180-200°C, zone 2 200-220°C, zone 3 220-240°C, zone 4 240-260°C, head temperature 230-250°C, cooling water temperature 20-30°C, to prepare polyethylene recycled PET bottle flakes with uniform particle size.

5. The method for preparing polyethylene recycled PET bottle flakes according to claim 4, characterized in that: In step III, the separation device comprises a stirring mechanism (1) and a separation mechanism (2), the top end of the stirring mechanism (1) is fixedly connected to the bottom end of the separation mechanism (2), the separation mechanism (2) comprises a separation frame (21), a top plate (22), a fixed plate (23), a screw motor (24), a screw (27), a support plate (210), a telescopic frame (213) and a movable plate (214), the bottom of the fixed plate (23) is fixedly mounted to the top of the separation frame (21), and one end of the fixed plate (23) is rotatably mounted to one end of the top plate (22), a sliding groove (29) is formed through the top of the fixed plate (23), and the output end of the screw motor (24) is fixedly connected to one end of the screw (27), The outer wall of the screw rod (27) is threadedly engaged with a movable block (28); the bottom of the movable block (28) is fixedly connected to a connecting plate (212); the two ends of the support plate (210) are fixedly mounted on the inner wall of the bottom end of the separation frame (21); the two ends of the movable plate (214) are slidably mounted on the inner wall of the bottom end of the separation frame (21); the bottom end of the connecting plate (212) passes through a sliding groove (29) and is fixedly connected to the top of the movable plate (214); a separation net (211) is provided between the support plate (210) and the movable plate (214); one end of the telescopic frame (213) is rotatably connected to the two ends of the support plate (210), and the other end of the telescopic frame (213) is rotatably connected to the two ends of the movable plate (214).

6. The method for preparing polyethylene recycled PET bottle flakes according to claim 5, characterized in that: The bottom end of the screw motor (24) is fixedly connected to the top of the fixed plate (23), the outer side of the connecting plate (212) is slidably connected to the inner wall of the sliding groove (29), a pull rod (25) is fixedly installed on the top of the top plate (22), and a feeding pipe (26) is fixedly connected to the top of the top plate (22).

7. The method for preparing polyethylene recycled PET bottle flakes according to claim 5, characterized in that: The stirring mechanism (1) comprises a stirring tank (11), a support frame (12), a stirring rod (13), a fixing rod (14), an annular frame (17) and a motor (110); the top end of the stirring tank (11) is fixedly connected to the bottom of the separation frame (21), and the bottom end of the stirring tank (11) is fixedly connected to the top of the annular frame (17); the output end of the motor (110) is fixedly connected to the bottom end of the stirring rod (13); a plurality of stirring blades (15) are symmetrically fixedly connected to the outer wall of the stirring rod (13); and two scrapers (16) are symmetrically fixedly connected to the bottom end of the stirring rod (13).

8. The method for preparing polyethylene recycled PET bottle flakes according to claim 7, characterized in that: The bottom of the annular frame (17) is fixedly connected to a discharge pipe (18), and the bottom end of the discharge pipe (18) is fixedly connected to a control valve (19). Both ends of the fixed rod (14) are fixedly mounted to the inner wall of the stirring tank (11), and the bottom of the fixed rod (14) is rotatably connected to the top end of the stirring rod (13).

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