How to manufacture upgraded used recycled polyethylene

Abstract

Embodiments of a method for producing upgraded used recycled polyethylene (PCR PE) may include melt-blending non-pelletized PCR PE with virgin polyethylene in an extruder to produce a PCR / virgin blend, and melt-filtration of the PCR / virgin blend to remove contaminants to produce upgraded PCR PE.

Description

Technical Field

[0001] (Cross - reference to Related Applications) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 488,873, filed Mar. 07, 2023. The entire contents of the above - mentioned U.S. Provisional Patent Application are hereby incorporated by reference into this specification.

[0002] (Field of the Invention) The present disclosure generally relates to a method for producing upgraded recycled polyethylene, and more particularly to a method for producing upgraded recycled polyethylene, which includes melt - blending and melt - filtering non - pelletized used recycled polyethylene and virgin polyethylene.

Background Art

[0003] Plastic waste is one of the most important sustainability challenges of the 21st century. Almost 400 million tons of plastic waste are produced globally every year. However, only an estimated 9% of plastics are recycled. Unrecycled plastics can be buried in landfill, incinerated, or become litter. In landfill, plastics can take hundreds of years to decompose. Incinerated plastics can pose a danger to the environment and health by releasing toxic substances, heavy metals, and particles into the air. Finally, plastic litter can pose a danger to wildlife, especially when it enters the ocean and rivers.

[0004] Conventional recycling methods can prevent plastics from ending up in landfills, being incinerated, or becoming waste, but many of these methods can be expensive or inefficient. Furthermore, conventional recycling methods involve subjecting recycled plastics to multiple heating and cooling steps, which can degrade the recycled plastics and reduce their durability. Therefore, there is a need for recycling methods that streamline recycling, minimize the number of times recycled plastics are heated, and make the recycling process more energy-efficient and environmentally friendly. [Overview of the Initiative]

[0005] Embodiments of the present disclosure address these and other needs by providing a method for producing upgraded used recycled polyethylene (PCR PE). The method may include melt-blending non-pelletized PCR PE with virgin polyethylene in an extruder to produce a PCR / virgin blend. The method may further include melt-filtration of the PCR / virgin blend to remove contaminants to produce upgraded PCR PE.

[0006] Additional features and advantages are described in the following detailed description and will be readily apparent to those skilled in the art, or will be recognized by carrying out the embodiments described herein, including the following detailed description, claims, and accompanying drawings.

[0007] It should be understood that both the general description above and the detailed description below are intended to describe various embodiments and to provide an overview or framework for understanding the nature and features of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments and are incorporated into and form part of this specification. The drawings illustrate the various embodiments described herein and, together with the descriptions, serve to illustrate the principles and operation of the claimed subject matter. [Brief explanation of the drawing]

[0008] [Figure 1] This document outlines conventional methods for producing upgraded used recycled polyethylene (PCR PE). [Figure 2] This document outlines an exemplary method for producing upgraded PCR PE according to the examples described herein. [Modes for carrying out the invention]

[0009] Herein, we refer in detail to an example of a method for producing upgraded used recycled polyethylene (PCR PE). In the example described herein, a method for producing upgraded PCR PE may include melt-blending non-pelletized PCR PE with virgin polyethylene in an extruder to produce a PCR / virgin blend. The method may also include melt-filtration of the PCR / virgin blend to remove contaminants and produce upgraded PCR PE.

[0010] As used in this disclosure, terms such as “blend” and “polymer blend” mean a composition of two or more polymers. Such a blend may or may not be miscible. Such a blend may or may not be phase-separated. Such a blend may or may not contain one or more domain configurations, as determined by transmission electron spectroscopy, light scattering, X-ray scattering, and any other method known in the art. A blend is not a laminate, but one or more layers of a laminate may contain a blend. Such a blend may be prepared as a dry blend, or formed in situ (e.g., in a reactor), as a molten blend, or by other techniques known to those skilled in the art.

[0011] As used in this disclosure, the term “melt blend” refers to a method by which two or more polymers are heated and mixed to form a polymer blend. A melt blend may be performed using a single-screw extruder, a twin-screw extruder, a Banbury mixer, or other techniques known to those skilled in the art.

[0012] As used in this disclosure, the term “molten filtration” refers to a method by which contaminating plastic particles, such as cross-linked plastics, degraded plastics, or gels, as well as non-plastic particles, such as wood, glass, aluminum, paper, or sand, are removed from molten plastic by filtering the molten plastic.

[0013] As used in this disclosure, the terms “polyethylene” or “ethylene-based polymer” may refer to a polymer containing more than 50 mol% of units derived from ethylene monomers. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers), or blends thereof. The polymer may also be a resin. Common forms of ethylene-based polymers known in the art include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra-low-density polyethylene (ULDPE), very low-density polyethylene (VLDPE), single-site catalyst linear low-density polyethylene (m-LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE), which include both linear low-density resins and substantially linear low-density resins.

[0014] As used in this disclosure, the term “virgin polyethylene” refers to the polyethylene resin materials or blends listed above that have not undergone any further processing or use after their manufacture. For example, virgin polyethylene may refer to manufactured polyethylene that is ready for further processing but has not undergone any processing other than that necessary to form polyethylene.

[0015] Figure 1 shows an overview of a typical recycling method. This method 50 typically begins with collecting plastic 100. The plastic may be collected directly from consumers, businesses, etc., through a recycling program or other means, or it may be obtained indirectly from waste management companies, recycling centers, etc. Next, the used recycled (PCR) plastic is shredded 200 to produce PCR flakes. The PCR flakes may vary in size and shape. The PCR flakes may be sorted to remove contaminants, undesirable types of plastic, undesirable colors of plastic, and other undesirable materials (not shown). Next, the PCR flakes are washed 300 to remove contaminants, including glue, oil, grease, dirt, paper, food residue, or beverage residue. Washing may include washing and drying the PCR plastic.

[0016] Next, the PCR flakes can be further processed. This processing involves melting and mixing the PCR flakes in an extruder or another processing unit. Many plastics, including both high-density and low-density polyethylene, have a distinct microstructure resulting from the repetitive folding of molecular chains. Melting these plastics can disrupt the repetitive folding of molecular chains, which damages and decomposes the microstructure of the plastic. Melting these plastics can also burn contaminants in the plastic and leave residues that discolor the plastic. Furthermore, melting, homogenizing, and pelletizing plastics requires considerable energy, often 0.14 kilowatt-hours (kWh / kg) to 0.31 kWh / kg of energy per kilogram of plastic.

[0017] After the PCR flakes are heated and mixed during processing, the resulting compound can then be melt-filtered to remove contaminants.500 After melt-filtering, the resulting compound can be molded into pellets or other compact forms.600 To mold the resulting compound into pellets, the compound is passed through a die, cooled simultaneously, and cut into pellets. The PCR pellets are typically then transported to a compounder, where the PCR pellets are reheated and combined with virgin plastic.700 In this case as well, this melting damages the microstructure of the plastic and can cause further discoloration as contaminants in the PCR pellets that did not burn previously may burn, leaving further residues. The PCR / virgin blend is then melt-filtered to produce upgraded PCR plastic.800 The upgraded PCR plastic is then molded into pellets or another compact form.900 The upgraded PCR pellets are then transported and can be used to manufacture goods made from recycled plastic.

[0018] While this conventional recycling method prevents plastic from ending up in landfills, avoids environmental pollution from plastic incineration, and helps protect wildlife and waterways, it consumes unnecessary energy and weakens PCR plastic by heating and cooling it multiple times. The method described herein streamlines the PCR plastic recycling process by eliminating unnecessary heating and cooling, thereby protecting the microstructure of the PCR plastic and saving energy in the recycling process.

[0019] Referring here to Figure 2, embodiments of the present disclosure are shown. Similar to conventional recycling methods, method 55 begins with collecting plastic 150. Again, to produce PCR flakes, the PCR plastic is washed 250 and shredded 350. In this case as well, the PCR flakes may be packaged (not shown) if desired for transport. However, unlike conventional recycling methods, the PCR flakes are not processed and melt-filtered on their own, thereby saving a significant amount of energy. Instead, the PCR flakes are heated and mixed with polyethylene 750. The resulting compound is then melt-filtered 850, and the upgraded PCR plastic can be molded into pellets or another compact form 950.

[0020] In some examples, a method for producing upgraded used recycled (PCR) plastics involves melt-blending non-pelletized PCR plastics with virgin plastics in an extruder to produce a PCR / virgin blend. The method may further include melt-filtration of the PCR / virgin blend to remove contaminants to produce upgraded PCR plastics.

[0021] The PCR plastic may be PCR polyethylene (PCR PE). Polyethylene is commonly used in disposable plastic bottles, disposable condiment containers, milk jugs, shopping bags, garbage bags, soap dispensers, yogurt tabs, frozen foods, furniture, and many other household items. The virgin plastic may be virgin polyethylene. As described above, polyethylene may include LDPE, LLDPE, MDPE, HDPE, and blends thereof. Thus, PCR PE may also include LDPE, LLDPE, MDPE, HDPE, and blends thereof.

[0022] In some examples, the PCR plastic may be processed to separate certain types of plastics. For example, the PCR plastic may pass through a flotation and sedimentation tank that separates polyethylene terephthalate (PET) plastic, polypropylene (PP) plastic, and polyethylene (PE) plastic based on density.

[0023] The non - pelletized PCR PE is PCR PE that has not undergone melting. The non - pelletized PCR PE may be in the form of flakes. Once the PCR PE is collected from consumers, the PCR PE may be cut, shredded, or processed by other means known to those skilled in the art to produce flakes. The flakes may advantageously vary in size and shape. If it is desirable to compress the flakes for transportation, the flakes may be collected in bales.

[0024] Non-pelletized PCR PE can be washed to remove contaminants such as glue, oil, grease, dirt, paper, food residue, or beverage residue. Such washing can be carried out by passing the PCR PE flakes through a water bath, spraying water onto the PCR PE flakes, passing the PCR PE flakes through a mesh screen to remove contaminants, rubbing the PCR PE flakes together, or a combination thereof. Non-pelletized PCR PE can also be dried. Such drying can be carried out by removing water from the PCR flakes using centrifugal force, by heat drying the PCR flakes, or a combination thereof.

[0025] Washing reduces the number of contaminants present in PCR PE, but it rarely removes all of them. Some of the remaining contaminants in PCR PE may burn when the PCR PE is heated during processing and pelletizing. This burning often leaves residue that discolors the PCR PE. Every melting that the PCR PE undergoes can burn further contaminants and cause further discoloration of the PCR PE. Therefore, each additional melting of the PCR PE can result in greater discoloration of the PCR PE. Thus, methods to eliminate melting, such as melting present during processing and pelletizing, can produce PCR PE and PCR PE blends with less discoloration. Pelleting the PCR PE before combining it with virgin polyethylene is a conventional method, but such processing and pelletizing damages the microstructure of the PCR PE, causing further discoloration and offering little benefit.

[0026] In some examples, the melt blending of non - pelletized PCR PE and virgin polyethylene can be carried out in an extruder. The extruder can be a continuous single - screw extruder or a continuous twin - screw extruder. The single - screw extruder can be operated at a processing temperature of 180°C to 265°C, 200°C to 265°C, 225°C to 265°C, 180°C to 250°C, or 180°C to 225°C, and a screw speed of 150 revolutions per minute (rpm) to 250 rpm, 175 rpm to 250 rpm, 200 rpm to 250 rpm, 150 rpm to 225 rpm, or 150 rpm to 200 rpm. The twin - screw extruder can be operated at a processing temperature of 180°C to 265°C, 200°C to 265°C, 225°C to 265°C, 180°C to 250°C, or 180°C to 225°C, and a screw speed of 200 rpm to 450 rpm, 250 rpm to 450 rpm, 300 rpm to 450 rpm, 250 rpm to 400 rpm, or 250 rpm to 350 rpm. The extruder can operate at a rate of 500 pounds per hour (lb / h) to 1000 lb / h, 600 lb / h to 1000 lb / h, 700 lb / h to 1000 lb / h, 500 lb / h to 900 lb / h, or 750 lb / h to 850 lb / h for a given size.

[0027] Without being bound by theory, it is believed that by melt - blending PCR PE with virgin polyethylene, the strength and durability of the upgraded PCR PE can be improved. In some examples, the PCR PE may be melt - blended with virgin polyethylene having the same density as the density of the PCR PE. In some examples, the PCR PE can be melt - blended with virgin polyethylene having a density higher or lower than the density of the PCR PE. In some examples, the melt blending includes homogenization of the PCR PE and the virgin polyethylene. The melt blending mixes the PCR PE and the virgin polyethylene, but the PCR PE and the virgin polyethylene are only homogenized when they spread evenly throughout the resulting PCR / virgin blend. Thus, in examples where the PCR PE and the virgin polyethylene are homogenized, the PCR PE and the virgin polyethylene spread uniformly through the melt blend.

[0028] Non-pelletized PCR PE may have densities of 0.870 g / cm³ (g / cc) to 0.965 g / cc, 0.880 g / cc to 0.955 g / cc, or 0.890 g / cc to 0.945 g / cc, 0.900 g / cc to 0.945 g / cc, 0.910 g / cc to 0.930 g / cc, 0.915 g / cc to 0.925 g / cc, or 0.918 g / cc to 0.922 g / cc.

[0029] Non-pelletized PCR PE may contain melt indices (I2) of 0.3g / 10 min to 5.0g / 10 min, 0.5g / 10 min to 2.0g / 10 min, 0.25g / 10 min to 5.0g / 10 min, 0.1g / 10 min to 10g / 10 min, 0.75g / 10 min to 1.75g / 10 min, or 1.0g / 10 min to 1.5g / 10 min.

[0030] Virgin polyethylene can have densities of 0.870 g / cm³ to 0.965 g / cc, 0.880 g / cc to 0.955 g / cc, or 0.890 g / cc to 0.945 g / cc. In some examples, virgin polyethylene may include low-density polyethylene (LDPE) having densities of 0.900 g / cc to 0.945 g / cc, 0.910 g / cc to 0.930 g / cc, 0.915 g / cc to 0.925 g / cc, or 0.918 g / cc to 0.922 g / cc.

[0031] Non-pelletized PCR PE can be obtained from various sources. Non-pelletized PCR PE may include spent recycled materials derived from single-layer flexible films, multi-layer flexible films, and combinations thereof. Single-layer and multi-layer flexible films may have a thickness of 10 mil or less.

[0032] In one embodiment, the upgraded PCR PE does not undergo any additional blending steps downstream of melt filtration. Conventional recycling methods often involve melt filtration after processing the PCR PE flakes. The melt-filtered PCR PE is then formed into pellets, which are then combined with virgin polyethylene and subsequently subjected to additional melt filtration. However, the method described herein does not subject the PCR PE to any melting before it is combined with virgin polyethylene. After combining the PCR PE with virgin polyethylene and melt filtration, no additional blending steps are required. In some examples, filtration of the melt is performed downstream of homogenization. Conventional recycling methods often involve melt filtration of the PCR PE flakes before the PCR PE is melt-blended with virgin polyethylene, but the present invention eliminates any melting of the PCR flakes before blending with virgin polyethylene. While melt filtration helps remove contaminants, it can weaken the microstructure of the PCR PE, and because melt filtration requires heating the PCR PE, it can cause further discoloration due to the combustion of contaminants. By homogenizing the PCR / virgin blend and then performing melt filtration, the PCR PE can be subjected to fewer melt filtration steps, which can reduce damage to the upgraded PCR PE microstructure and reduce the amount of color change in the upgraded PCR PE.

[0033] Melt filtration may include at least one or at least two filtration steps. The filtration steps may include passing the heated plastic through a laser filter (a continuous filtration technique in which a screen is made by precisely drilling holes using a laser beam, and collected contaminants are continuously scraped off and removed without the need to remove the filter screen), a surface filter (e.g., a mesh filter, a woven screen filter, etc.), a depth filter (e.g., a sintered powder filter, a superplate filter, a random fiber filter, etc.), a combination thereof, or other types of filters known in the art. Each filtration step may use the same filter in each step, or it may use different filters in each step. In some examples, multiple melt filtration steps may include melting the plastic to be filtered only once, and then performing multiple filtration steps using the molten plastic.

[0034] In some examples, the first melt filtration step may include passing the plastic through a first filter having a screen opening size of 50 μm to 250 μm, 70 μm to 200 μm, 75 μm to 175 μm, 80 μm to 150 μm, or 80 μm to 120 μm. In some examples, the second melt filtration step may include passing the plastic through a second filter located downstream of the first filter. The second filter may have a screen opening size of 10 μm to 300 μm, 25 μm to 250 μm, 35 μm to 200 μm, 40 μm to 150 μm, or 50 to 100 μm.

[0035] Upgraded PCR PE may contain additional additives. In some examples, additional additives may be added when non-pelletized PCR PE is melt-blended with virgin polyethylene. These additional additives may impart additional strength and durability to the upgraded PCR PE. In some examples, these additives may include antioxidant packages, slips, fillers, polymer processing aids, coupling agents, odor absorbers, flame retardants, or dyes. Antioxidant packages may include primary antioxidants, secondary antioxidants, or combinations thereof. Antioxidant packages may include hindered phenols, phosphites, thioethers, aromatic amines, hydroxylamines, or combinations thereof. Fillers may include calcium carbonate, talc, or combinations thereof. Slips may include amides. Coupling agents may include silanes, maleic anhydride graft polymers, stearates, organic titanates, or combinations thereof. Dyes may include organic dyes, titanium dioxide, carbon black, or combinations thereof. Polymer processing aids may include fluoropolymers.

[0036] Upgraded PCR PE In one or more embodiments, upgraded PCR PE may be produced from non-pelletized PCR PE and virgin polyethylene as described herein. Upgraded PCR PE may be used in pellets, resins, or films, such as single-layer or multi-layer films. Upgraded PCR PE incorporating films may be used in non-rigid packaging such as garbage bags, shopping bags, flexible packaging, pouches, and stand-up pouches. Upgraded PCR PE may also be used in rigid packaging such as trash cans, compost bins, plastic bottles, condiment containers, milk jugs, soap dispensers, yogurt tubs, and frozen foods. Upgraded PCR PE may also be used in furniture, panels, lumber, landscaping sleepers, floor tiles, and the like.

[0037] The upgraded PCR PE may have densities of 0.876 g / cc to 0.961 g / cc, 0.880 g / cc to 0.955 g / cc, 0.885 g / cc to 0.950 g / cc, 0.888 g / cc to 0.945 g / cc, or 0.902 g / cc to 0.942 g / cc.

[0038] Upgraded PCR PE may contain 1%–99% virgin polyethylene, 10%–90% virgin polyethylene, 20%–80% virgin polyethylene, 25%–75% or 30%–60% virgin polyethylene. The amount of virgin polyethylene used may affect the color, durability, and contamination level of the upgraded PCR PE.

[0039] Test method Melt Index (190°C, 2.16 kg, "I2") Test Method: Using the conditions of 190°C / 2.16 kilograms (kg), ASTM D1238-13, Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer. The entire protocol is incorporated herein by reference. Results are reported in units of elution grams per 10 minutes (g / 10 min).

[0040] Density measurements were performed in accordance with ASTM D4703. The entire protocol is incorporated herein by reference. Measurements were performed within one hour of sample pressing in accordance with ASTM D792, Method B. The entire protocol is incorporated herein by reference.

[0041] Discoloration measurements were performed by evaluating the yellowness index according to ASTM D6290. The entire protocol is incorporated herein by reference.

[0042] The average molecular weight (MW) may be determined according to ASTM D4274. The entire protocol is incorporated herein by reference. [Examples]

[0043] The following examples are provided for illustrative purposes and are presented in a manner that will be recognized by those skilled in the art, and are not intended to limit the entire disclosure or the scope of the appended claims.

[0044] Example 1 Commercially available from Avangard Innovative, with melt index I2 of 0.6736–0.9521 g / 10 min and 0.921–0.933 g / cm³. 3Washed used recycled polyethylene (PCR PE) AVG 150 flakes with a density of 150 were fed into a preconditioning unit along with virgin low-density polyethylene (LDPE) 132I pellets, commercially available from Dow Inc, Midland, MI, in an INTAREMA 1108 TVE Plus single-screw extruder equipped with two in-line filtration systems, an Erema laser filter, and an Erema backflush filter, commercially available from Erema. The PCR PE flakes and virgin LDPE pellets were then melt-blended in the single-screw extruder to produce a homogenization blend. The extruder had an extrusion rate of 943 pounds / hour (lbs / h), a screw speed of 190 revolutions / minute (rpm), a torque of 91%, and a melt pressure of 764 pounds / square inch (psi) at the die. The PCR PE flakes constituted 70% by weight of the homogenization blend, and the virgin LDPE pellets constituted 30% by weight of the homogenization blend. The method involved two melt filtration unit operations to remove contaminants. The melt temperature before pre-filtration was 402°F. The melt pressure before filtration was 2311 psi. The homogenized blend was first passed through a laser filter per filter to screen for contaminants between 90 micrometers (μm) and 110 μm or larger. The homogenized blend was then passed through a microfilter to screen for contaminants larger than 50 μm. The upgraded PCR PE was formed into pellets by passing it through a die, followed by simultaneous water cooling, and cutting the upgraded PCR PE into pellets.

[0045] Comparative Example 2 Commercially available from Avangard Innovative, with melt index I2 of 0.6736–0.9521 g / 10 min and 0.921–0.933 g / cm³. 3Washed used recycled polyethylene (PCR PE) AVG 150 flakes with a density of 150 were melt-blended in an INTAREMA 1108 TVE Plus single-screw extruder equipped with two in-line filtration systems: an Erema laser filter and an Erema backflush filter, commercially available from Erema, to produce PCR PE pellets. The extruder had an extrusion rate of 900 lbs / h, a screw speed of 190 rpm, a torque of 92%, and a melt pressure of 645 psi at the die. The PCR PE was then melt-filtered. The melt temperature before pre-filtration was 397°F. The melt pressure before filtration was 2049 psi. The PCR PE was first passed through a per-filter to screen for contaminants between 90 micrometers (μm) and 110 μm or larger. The homogenized blended PCR PE was then passed through a microfilter to screen for contaminants larger than 50 μm. The obtained PCR PE was passed through a die, followed by simultaneous water cooling, and then the PCR PE was cut into pellets to form the PCR PE. The PCR PE pellets were then compounded with virgin low-density polyethylene (LDPE) 132I pellets, commercially available from Dow Chemical, in a separate mixer using a 40 mm Coperion twin-screw extruder. The PCR PE pellets constituted 70% by weight of the resulting compound, and the virgin LDPE pellets constituted 30% by weight of the resulting compound. The extruder had an extrusion rate of 200 lbs / h, a screw speed of 250 rpm, and a melt pressure of 1503 psi at the die. The PCR / virgin blend was then subjected to melt filtration. The melt pressure before filtration was 2375 psi. The PCR / virgin blend was then filtered to screen for contaminants larger than 149 μm. The upgraded PCR PE obtained was passed through a die, then simultaneously cooled in water, and the upgraded PCR PE was cut into pellets to form the upgraded PCR PE into pellets.

[0046] Comparative Examples 3-5 Commercially available from Avangard Innovative, with melt index I2 of 0.6736–0.9521 g / 10 min and 0.921–0.933 g / cm³. 3 Washed used recycled polyethylene (PCR PE) AVG 150 flakes with a density of 150 were melt-blended in an INTAREMA 1108 TVE Plus single-screw extruder equipped with two in-line filtration systems: an Erema laser filter and an Erema backflush filter, commercially available from Erema, to produce PCR PE pellets. The extruder had an extrusion rate of 900 lbs / h, a screw speed of 190 rpm, a torque of 92%, and a melt pressure of 645 psi at the die. The PCR PE was then melt-filtered. The melt temperature before pre-filtration was 397°F. The melt pressure before filtration was 2049 psi. The PCR PE was first passed through a per-filter to screen for contaminants between 90 micrometers (μm) and 110 μm or larger. The homogenized blended PCR PE was then passed through a microfilter to screen for contaminants larger than 50 μm. The obtained PCR PE was passed through a die, followed by simultaneous water cooling, and the PCR PE was cut into pellets to form the PCR PE into pellets. The PCR PE pellets were then compounded with virgin low-density polyethylene (LDPE) 132I pellets, commercially available from Dow Chemical, in a separate Banbury mixer equipped with a single-screw extruder. The Banbury mixer was operated with a batch size of 390–420 lbs, a mixing time of 65–150 seconds, and a dropping temperature of 145°C–150°C. The single-screw extruder had a method temperature of 180°C–240°C and an extruder speed of 25 rpm–50 rpm. The PCR PE pellets constituted 70 wt% of the obtained compound, and the virgin LDPE pellets constituted 30 wt% of the obtained compound. The obtained upgraded PCR PE was passed through a die, followed by simultaneous water cooling, and the upgraded PCR PE was cut into pellets to form the upgraded PCR PE into pellets.

[0047] The characteristics of the pellets obtained in Examples 1 to 5 are shown in Tables 1 and 2.

[0048] [Table 1]

[0049] [Table 2]

[0050] As shown in Table 1, the pellets of Example 1 had a lower yellowness index than those of Examples 3-5. Therefore, despite both pellets having the same composition, the pellets containing upgraded PCR PE produced by the method of Example 1 showed less discoloration than the pellets containing upgraded PCR PE produced by the conventional method.

[0051] Furthermore, as shown in Table 2, the average transparency of Example 1 is higher than that of Example 3, which further demonstrates that the method of Example 1 causes less clouding than the conventional method.

[0052] Furthermore, as shown in Table 2, the upgraded PCR PE of Example 1 and the upgraded PCR PE of Example 3 show only slight differences in tensile properties. Therefore, it appears that preparing upgraded PCR PE using the method of Example 1 provides upgraded PCR PE with tensile properties similar to upgraded PCR PE prepared by conventional methods.

[0053] The subject matter of this disclosure is described in detail with reference to specific embodiments. Any detailed description of the components or features of the embodiments should be understood not to mean that such components or features are essential to the specific embodiment or any other embodiment. Furthermore, it will be apparent to those skilled in the art that various modifications and changes can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter.

[0054] Note that one or more of the following claims utilize the term “wherein” as a transitional clause. Note that, for the purpose of defining the art, this term is introduced into the claims as an unrestricted transitional clause used to introduce an enumeration of a set of structural features, and should be interpreted similarly to the more commonly used unrestricted preamble term “comprising.”

[0055] Where a first component is described as "comprising" a second component, it should be understood that in embodiments, the first component is intended to "consist" or "consist essentially of" its second component. Where a first component is described as "comprising" a second component, it should be further understood that in embodiments, the first component is intended to contain at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or even more than 99% of its second component (where % can be by weight or by moles).

[0056] It should also be noted that the use of the term "at least one" in this specification for constituent elements, etc., should not be used to infer that the alternative use of the article "a" or "an" should be limited to a single constituent element, etc.

Claims

1. A method for producing upgraded used recycled polyethylene (PCR PE), The process involves producing a PCR / virgin blend by melt-blending non-pelletized PCR PE with virgin polyethylene in an extruder, and A method comprising: melt-filtration of the PCR / virgin blend to remove contaminants and produce the upgraded PCR PE.

2. The method according to claim 1, wherein the virgin polyethylene has a density of 0.870 g / cc to 0.965 g / cc.

3. The method according to claim 2, wherein the virgin polyethylene has a density of 0.910 g / cc to 0.930 g / cc.

4. The method according to any one of claims 1 to 3, wherein the non-pelletized PCR PE comprises spent recycled material derived from a single-layer flexible film, a multilayer flexible film, and a combination thereof, and the single-layer flexible film and the multilayer flexible film have a thickness of 10 mils or less.

5. The aforementioned non-pelletized PCR PE has a density of 0.900 g / cc to 0.945 g / cc and a melt index (I) of 0.5 g / 10 min to 2.0 g / 10 min. ２ The method according to any one of claims 1 to 4, comprising LDPE having )

6. The method according to any one of claims 1 to 5, wherein there is no additional blending step downstream of the melt filtration.

7. The method according to any one of claims 1 to 6, wherein the extruder is a single-screw extruder.

8. The method according to claim 1, wherein the melted blend includes homogenization of the PCR and the virgin polyethylene.

9. The method according to claim 8, wherein the melt filtration is performed downstream of the homogenization.

10. The method according to any one of claims 1 to 9, wherein the non-pelletized PCR PE and the virgin polyethylene include additional additives.

11. The method according to any one of claims 1 to 10, wherein the melt filtration comprises at least two filtration steps.

12. The method according to claim 11, wherein the melt filtration comprises a first filter having a screen opening size of 70 to 200 μm, and a second downstream filter having a screen opening size of 25 to 250 μm or 50 to 100 μm.

13. Upgraded PCR PE, manufactured by the method according to any one of claims 1 to 12.

14. The upgraded PCR PE according to claim 13, wherein the upgraded PCR PE has a density of 0.876 g / cc to 0.961 g / cc.

15. The upgraded PCR PE according to claim 13 or 14, wherein the upgraded PCR PE comprises 20% to 80% of the virgin polyethylene.

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