A method for recycling post-consumer polyethylene film and applications thereof

Abstract

The application discloses a recycling method of post-consumer polyethylene film and application thereof, and belongs to the technical field of plastic film recycling. The recycling method of the application first makes the post-consumer polyethylene film into a flattened single film, then places the film in an electric field, and then makes the film pass through a transmission gap between a group of reverse grounding rollers to obtain a purified polyethylene film, and then melts, extrudes and cuts the purified film to obtain regenerated polyethylene particles. The polyethylene particles prepared by the recycling method have the advantages of low haze and high impact.

Description

Technical Field

[0001] This invention belongs to the field of plastic film recycling, specifically relating to a method for recycling post-consumer polyethylene film and its application. Background Technology

[0002] Driven by policy initiatives and rising demand for resource recycling, China's polyethylene film recycling market continues to expand. Taking polyethylene as an example, my country's apparent consumption of recycled polyethylene reached 8.5 million tons in 2024, with high-end applications accounting for over 18%. It is estimated that polyethylene film recycling volume was approximately 3.5 million tons in 2023, and is projected to increase by 6.8% year-on-year in 2024, reaching approximately 3.738 million tons.

[0003] Post-consumer polyethylene (PCE) films are characterized by their soft texture, complex shape, and multiple layers. During recycling, they tend to curl and stack, easily trapping fine particulate contaminants such as silt, dust, and paper scraps within the multiple layers, leading to increased haze and reduced mechanical properties. Therefore, targeted treatment is necessary. However, improper treatment methods can also result in decreased mechanical properties. How to reduce the haze of post-consumer polyethylene films while maintaining good mechanical properties as much as possible is a pressing issue that needs to be addressed in this field. Summary of the Invention

[0004] To address the processing problems inherent in existing post-consumer polyethylene film recycling processes, this invention provides a method for recycling post-consumer polyethylene film. The recycled polyethylene particles prepared using this method exhibit advantages such as low haze and high impact strength.

[0005] Another object of the present invention is to provide recycled polyethylene particles prepared by the above-described recycling method.

[0006] Another object of the present invention is to provide articles prepared from the above-mentioned recycled polyethylene particles.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for recycling post-consumer polyethylene film includes the following steps: Flattening: The process of flattening post-consumer polyethylene film into a single sheet; Purification: The monolithic film is placed in an electric field, and then the monolithic film is passed through the conveying gap between two reverse grounding rollers to obtain a purified polyethylene film; Regeneration: The purified polyethylene film is melted, extruded, and pelletized to obtain recycled polyethylene particles; in: The moisture content of the single-piece film is no higher than 5‰, and the size is 100~400mm; The voltage of the electric field is not less than 50kV; The rotational speed of the grounding roller is no higher than 20 m / min.

[0008] A method for purifying post-consumer polyethylene film includes the following steps: Flattening: The process of flattening post-consumer polyethylene film into a single sheet; Purification: The monolithic film is placed in an electric field, and then the monolithic film is passed through the conveying gap between a set of reverse grounding rollers to obtain a purified polyethylene film. in: The moisture content of the single-piece film is no higher than 5‰, and the size is 100~400mm; The voltage of the electric field is not less than 50kV; The rotational speed of the reverse grounding roller is no higher than 20 m / min.

[0009] Preferably, the moisture content of the monolithic film is 1-5‰. Within this range, the moisture content of the monolithic film allows the recycled polyethylene particles to exhibit superior impact resistance.

[0010] Preferably, the voltage of the electric field is 50~70 kV. A voltage within this range allows the recycled polyethylene particles to exhibit superior impact resistance.

[0011] Preferably, the rotational speed of the reverse grounding roller is 5~20 m / min. Within this range, the rotational speed of the reverse grounding roller allows the recycled polyethylene particles to exhibit superior impact resistance.

[0012] The electric field described in this invention can be achieved using common methods in the art. This invention obtains the electric field by placing a metal electrode plate on each of the upper and lower sides of the thin film and applying a DC voltage to the metal electrode plates.

[0013] The reverse grounding rollers of this invention consist of two rollers as a group, both of which are grounded. The axes of the two rollers are parallel and their rotation directions are opposite, thereby allowing a flattened monolithic film to pass through the transfer gap between the two rollers under the influence of inertia, gravity, or other conventional methods in the art. The transfer gap between the two grounding rollers of this invention is <1mm, which is greater than the thickness of the flattened monolithic film.

[0014] Specifically, the flattening process involves: separating the stacked post-consumer polyethylene films through vibration to obtain individual single films; and passing the individual single films through the conveying gap of a set of reverse rollers to obtain flattened single films.

[0015] The reverse rollers of this invention consist of two rollers as a group, with parallel axes and opposite rotation directions, allowing an individual monolithic film to pass through the transfer gap between the two rollers under the influence of inertia, gravity, or other conventional methods in the art. The transfer gap between the two grounded rollers of this invention is narrower than the thickness of the individual monolithic film.

[0016] The individual monolithic films obtained by vibration separation are often in a loose and fluffy state. The fluffy films are passed through the transmission gap of two reverse rollers. Under the clamping, traction and reverse straightening action of the reverse rollers, the wrinkles, curls and deformed areas on the film surface are gradually stretched and straightened, and finally a fully stretched, flat and wrinkle-free monolithic polyethylene film is obtained.

[0017] Specifically, the microparticle contaminants mentioned in this invention can be microparticle contaminants that are commonly present on polyethylene films, including but not limited to silt, dust and / or paper scraps, whose particle size is usually less than 500 micrometers, and which are easily encapsulated in multiple layers of film and cannot be effectively removed.

[0018] The recycling method of the present invention is applicable to commonly used transparent or semi-transparent polyethylene films in the field. The post-consumer polyethylene films include, but are not limited to, one or more of industrial packaging films, agricultural films, supermarket packaging films, and household product packaging films. The materials include, but are not limited to, one or more of LDPE, LLDPE, and HDPE.

[0019] Preferably, the haze of the polyethylene particles is <90.

[0020] Preferably, the impact strength of the polyethylene particles is ≥40 MPa.

[0021] The above method is applied in the preparation of recycled polyethylene products, including but not limited to disposable packaging bags, disposable packaging films, plastic pipes, and furniture.

[0022] Compared with the prior art, the present invention has the following beneficial effects: The recycling method of the present invention purifies the post-consumer polyethylene film by flattening it into a single sheet, placing it in an electric field, and passing it through the conveying gap between a set of reverse grounding rollers.

[0023] The polyethylene particles prepared by this invention have the advantages of low haze and high impact. Detailed Implementation

[0024] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0025] The reagents used in the various embodiments and comparative examples of this invention are described below: Post-consumer polyethylene film 1: Material: LLDPE, Source: Packaging stretch film, Haze 96, Impact 30; Post-consumer polyethylene film 2: Material LDPE, source: clothing packaging bags, haze 97, impact 32.

[0026] Except for Comparative Examples 1 and 2, the recycling methods of each embodiment and comparative example of the present invention include the following steps: 1. Crushing: The collected post-consumer polyethylene film is crushed, and water is introduced during the crushing process to obtain polyethylene film of a specific size.

[0027] 2. Dehydration: Take out the broken polyethylene film and put it into a centrifugal dehydrator to remove surface moisture.

[0028] 3. Drying: Take out the broken polyethylene film and put it into a hot air dryer to remove moisture and obtain a dried polyethylene film with a specific moisture content.

[0029] 4. Flattening: The stacked dry polyethylene film is separated by a vibrating feeder and evenly conveyed onto a rubber roller. After passing through the conveying gap of a set of reverse rollers, a flattened single polyethylene film is obtained.

[0030] 5. Ionization: Place the above-mentioned single polyethylene film on the conveyor belt and set metal electrode plates on the upper and lower sides. Apply DC high voltage to ionize air molecules into positive and negative ions, which attach to the surface of tiny particulate pollutants and make them charged.

[0031] 6. Adsorption: A charged single-piece polyethylene film is passed through a conveying gap (<1mm) between two grounded adsorption rollers that rotate in opposite directions and have parallel axes. Tiny particulate pollutants are adsorbed onto the roller surface and thus removed.

[0032] 7. Repeat the above ionization and adsorption process 5 times to obtain a purified polyethylene film.

[0033] 8. Extrusion granulation: The purified polyethylene film is added to an extruder and melt-extruded into pellets to obtain recycled polyethylene particles.

[0034] The recovery method for Comparative Example 1 is the same as the steps described above, except that step 4 (flattening) is not included.

[0035] The recovery method of Comparative Example 2 is the same as the above steps, except that: Step 6 adsorption is: a 10kV cationic positive electrode plate parallel to the second conveyor belt is set 1 cm directly above the second conveyor belt, and a charged single polyethylene film is sent to the belt. The negatively charged particles are attracted by the positive charge and thus adsorbed.

[0036] The recycling method for Comparative Example 3 is the same as the steps described above, except that the adsorption in step 6 is as follows: the second track is grounded, and a charged single-piece polyethylene film is sent onto the track, whereby the fine particulate pollutants are adsorbed onto the track surface and thus removed.

[0037] The performance testing methods and standards for polyethylene particles prepared by the recycling methods of the various embodiments and comparative examples of the present invention are as follows: Haze: Tested according to standard GB / T 2410-2008, with 5 samples tested in parallel for each sample.

[0038] Impact strength: Tested according to standard ISO 180, with 10 samples tested in parallel for each sample.

[0039] Examples and Comparative Examples The process parameters for the recovery methods of each embodiment and comparative example are shown in Table 1.

[0040] Table 1

[0041] Continued from Table 1

[0042] Continued from Table 1

[0043] As can be seen from Table 1, the polyethylene particles prepared in each embodiment have the advantages of low haze and high impact strength, with haze <90 and impact strength not less than 40 MPa.

[0044] Comparative Example 1 was not flattened, and fine particulate pollutants could not be effectively removed, resulting in high fog and low impact.

[0045] Comparative Example 2 uses a cation positive electrode plate for adsorption, but its adsorption effect is poor, resulting in high haze and low impact.

[0046] Comparative Example 3 used a grounded track for adsorption, but the adsorption effect was insufficient, and the resulting polyethylene particles did not meet the requirements for haze and impact strength.

[0047] The moisture content of the film in Comparative Example 4 was too high, and the resulting polyethylene particles did not meet the requirements for haze and impact strength.

[0048] The voltage of Comparative Example 5 was too low, and the resulting polyethylene particles did not meet the requirements for haze and impact strength.

[0049] The fragment size of Comparative Example 6 was too small, and the fragment size of Comparative Example 7 was too large, resulting in polyethylene particles whose haze and impact strength did not meet the requirements.

[0050] The adsorption roller speed of Comparative Example 8 was too high, and the resulting polyethylene particles did not meet the requirements for haze and impact strength.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for recycling post-consumer polyethylene film, characterized in that, Includes the following steps: Flattening: The process of flattening post-consumer polyethylene film into a single sheet; Purification: The monolithic film is placed in an electric field, and then the monolithic film is passed through the conveying gap between a set of reverse grounding rollers to obtain a purified polyethylene film. Regeneration: The purified polyethylene film is melted, extruded, and pelletized to obtain recycled polyethylene particles; in: The moisture content of the single-piece film is no higher than 5‰, and the size is 100~400mm; The voltage of the electric field is not less than 50kV; The rotational speed of the grounding roller is no higher than 20 m / min.

2. A method for purifying post-consumer polyethylene film, characterized in that, Includes the following steps: Flattening: The process of flattening post-consumer polyethylene film into a single sheet; Purification: The monolithic film is placed in an electric field, and then the monolithic film is passed through the conveying gap between two reverse grounding rollers to obtain a purified polyethylene film; in: The moisture content of the single-piece film is no higher than 5‰, and the size is 100~400mm; The voltage of the electric field is not less than 50kV; The rotational speed of the grounding roller is no higher than 20 m / min.

3. The recycling method according to claim 1 or the purification method according to claim 2, characterized in that, The moisture content of the single-piece film is 1-5‰.

4. The recycling method according to claim 1 or the purification method according to claim 2, characterized in that, The voltage of the electric field is 50~70 kV.

5. The recycling method according to claim 1 or the purification method according to claim 2, characterized in that, The rotational speed of the reverse grounding roller is 5~20m / min.

6. The recycling method according to claim 1 or the purification method according to claim 2, characterized in that, The specific steps of the flattening are as follows: the stacked post-consumer polyethylene films are separated by vibration to obtain independent single films; the independent single films are passed through the conveying gap of a set of reverse rollers to obtain flattened single films.

7. The recycling method according to claim 1 or the purification method according to claim 2, characterized in that, The post-consumer polyethylene film includes one or more of industrial packaging films, agricultural films, supermarket packaging films, and household goods packaging films; and / or, the polyethylene is one or more of LDPE, LLDPE, and HDPE.

8. The recycling method according to claim 1 or the purification method according to claim 2, characterized in that, The polyethylene particles have a haze of <90; and / or the polyethylene particles have an impact strength of ≥40MPa.

9. The recycling method according to claim 1 or the purification method according to claim 2, characterized in that, The transmission gap is <1mm.

10. The application of the recycling method according to any one of claims 1, 3 to 9 or the purification method according to any one of claims 2 to 9 in the preparation of recycled polyethylene products, wherein the recycled polyethylene products include disposable packaging bags, disposable packaging films, plastic pipes, and furniture.

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