Process for producing upgraded post consumer recycle polyethylene

Abstract

Embodiments of a method for producing an upgraded post consumer recycle polyethylene (PCR PE) may include melt blending a non-pelletized PCR PE with a native polyethylene in an extruder to produce a PCR / native blend, and melt filtering the PCR / native blend to remove contaminants and produce the upgraded PCR PE.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 488,873, filed on March 7, 2023, the contents of which are incorporated herein in their entirety. Technical Field

[0003] The present disclosure relates generally to methods for producing upgraded post-consumer recycled polyethylene, and particularly to methods for producing upgraded post-consumer recycled polyethylene that include melt blending and melt filtering non-pelletized post-consumer recycled polyethylene and virgin polyethylene. Background Art

[0004] Plastic waste is one of the most significant sustainability issues of the 21st century. Every year, the world generates nearly 400 million tons of plastic waste. Yet, only an estimated 9% of this plastic is recycled. Unrecycled plastic may end up in landfills, be incinerated, or become trash. In landfills, plastic can take hundreds of years to decompose. Incinerated plastic can cause environmental and health hazards by releasing toxic chemicals, heavy metals, and particles into the air. Finally, plastic waste can harm wildlife, especially when it enters oceans and streams.

[0005] While conventional recycling methods can prevent plastics from ending up in landfills, being incinerated, or becoming trash, many recycling methods can be expensive or inefficient. Furthermore, conventional recycling methods subject 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 recycling methods more energy-efficient and environmentally friendly. Summary of the Invention

[0006] Embodiments of the present disclosure address these and other needs by providing a method for producing upgraded post-consumer 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 filtering the PCR / virgin blend to remove contaminants and produce the upgraded PCR PE.

[0007] Additional features and advantages will be set forth in the detailed description which follows, and in part will become apparent to those skilled in the art from the detailed description or may be learned by practicing the embodiments described herein, which are included in the following detailed description and the accompanying drawings in addition to the claims.

[0008] It should be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein and, together with the description, serve to explain the principles and operation of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 An overview of a conventional process for producing upgraded post-consumer recycled polyethylene (PCR PE) is shown.

[0010] Figure 2 An overview of an example method for producing an upgraded PCR PE according to examples described herein is shown. DETAILED DESCRIPTION

[0011] Reference will now be made in detail to an example of a method for producing upgraded post-consumer recycled polyethylene (PCR PE). In the examples described herein, the 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 filtering the PCR / virgin blend to remove contaminants and produce upgraded PCR PE.

[0012] As used in this disclosure, terms such as "blend," "polymer blend," and the like refer to compositions of two or more polymers. Such blends may or may not be miscible. Such blends may or may not be phase separated. Such blends 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 blends may be prepared as dry blends, in situ formation (e.g., in a reactor), melt blends, or using other techniques known to those skilled in the art.

[0013] As used in this disclosure, the term "melt blending" refers to a process in which two or more polymers are heated and mixed to form a polymer blend. Melt blending can be performed using a single screw extruder, a twin screw extruder, a Banbury mixer, or other techniques known to those skilled in the art.

[0014] As used in this disclosure, the term "melt filtration" refers to a process in which contaminating plastic particles (such as cross-linked plastic, degraded plastic or gel) and non-plastic particles (such as wood, glass, aluminum, paper or sand) are removed from the molten plastic by filtering the molten plastic.

[0015] As used in this disclosure, the term "polyethylene" or "ethylene-based polymer" refers to a polymer comprising greater than 50 mole percent of units derived from ethylene monomer. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers) or blends thereof. The polymer may 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-catalyzed linear low-density polyethylene, including both linear and substantially linear low-density resins (m-LLDPE); medium-density polyethylene (MDPE); and high-density polyethylene (HDPE).

[0016] As used in this disclosure, the term "virgin polyethylene" refers to a material or blend of polyethylene resins, such as those listed above, that has not undergone any additional processing or use after its manufacture. For example, virgin polyethylene may refer to manufactured polyethylene that is ready for further processing but has not undergone any processing beyond that required to form the polyethylene.

[0017] Figure 1 An overview of a typical recycling process is shown. The process 50 typically begins with collecting plastic 100. The plastic may be collected directly from consumers, businesses, etc., through recycling programs or other means, or may be obtained indirectly from waste management companies, recycling centers, etc. The post-consumer recycled (PCR) plastic is then shredded 200 to produce PCR flakes. The size and shape of the PCR flakes may vary. The PCR flakes may undergo sorting to remove contaminants, unwanted plastic types, unwanted plastic colors, and other unwanted materials (not shown). The PCR flakes are then cleaned 300 to remove contaminants, including glue, oil, grease, dirt, paper, food residue, or beverage residue. Cleaning may include washing and drying the PCR plastic.

[0018] The PCR flakes can then be further processed 400. This processing includes melting and mixing the PCR flakes in an extruder or another processing unit. Many plastics, including both high-density polyethylene and low-density polyethylene, have a well-defined microstructure resulting from repeated folding of the molecular chains. Melting these plastics can disrupt the repeated folding of the molecular chains, which can damage and degrade the plastic's microstructure. Melting these plastics can also cause contaminants in the plastic to burn and leave residues that discolor the plastic. In addition, melting, homogenizing, and pelletizing the plastic requires a large amount of energy, typically as much as 0.14 kilowatt-hours per kilogram of plastic (kWh / kg) to 0.31 kWh / kg.

[0019] After heating and mixing the PCR flakes during processing, the resulting mixture can then be melt filtered 500 to remove contaminants. After melt filtration, the resulting mixture can then be formed into pellets 600 or other compact forms. To form the resulting mixture into pellets, the resulting mixture is passed through a die and simultaneously cooled and cut into pellets. The PCR pellets are then typically transported to a compounder where they are heated again and combined with virgin plastic 700. Again, this melting can damage the microstructure of the plastic and cause additional discoloration, as previously unburned contaminants in the PCR pellets may now burn and leave additional residues. The PCR / virgin blend is then melt filtered 800 to produce upgraded PCR plastic. The upgraded PCR plastic is then formed into pellets 900 or another compact form. The upgraded PCR pellets can then be transported and used to manufacture goods made from recycled plastic.

[0020] While this conventional recycling method helps keep plastics out of landfills, prevents environmental pollution from incinerating plastics, and protects wildlife and waterways, it consumes unnecessary energy and weakens the PCR plastics by heating and cooling them multiple times. The method described herein streamlines the PCR plastic recycling process by eliminating unnecessary heating and cooling, which protects the PCR plastic's microstructure and conserves energy in the recycling process.

[0021] Now refer to Figure 2 , depicting an embodiment according to the present disclosure. As with conventional recycling methods, method 55 begins with collecting plastic 150. Again, the PCR plastic is cleaned 250 and shredded 350 to produce PCR flakes. Again, if transportation is required, the PCR flakes can be packaged (not shown). However, unlike conventional recycling methods, the individual PCR flakes are not processed and melt filtered, which saves a lot of energy. Instead, the PCR flakes are heated and combined with virgin polyethylene 750. The resulting mixture can then be melt filtered 850, and the upgraded PCR plastic can be formed into pellets 950 or another compact form.

[0022] In some examples, a method for producing upgraded post-consumer recycled (PCR) plastic includes melt blending non-pelletized PCR plastic with virgin plastic in an extruder to produce a PCR / virgin blend. The method may further include melt filtering the PCR / virgin blend to remove contaminants and produce upgraded PCR plastic.

[0023] Poly (PCR) plastic can be poly (PCR) polyethylene (PCR PE). Polyethylene is commonly used in disposable plastic bottles, disposable condiment containers, milk jugs, shopping bags, garbage bags, soap dispensers, yogurt tubs, frozen meals, furniture, and many other household items. Virgin plastic can be virgin polyethylene. As mentioned above, polyethylene can include LDPE, LLDPE, MDPE, HDPE, and blends thereof. Therefore, poly (PCR) PE can also include LDPE, LLDPE, MDPE, HDPE, and blends thereof.

[0024] In some examples, PCR plastics can be processed to separate out certain types of plastics. For example, the PCR plastics can be passed through a sink-float separation tank that separates polyethylene terephthalate (PET) plastics, polypropylene (PP) plastics, and polyethylene (PE) plastics based on density.

[0025] Non-granulated PCR PE is PCR PE that has not undergone any melting. Non-granulated PCR PE may be in the form of flakes. Once collected from the consumer, the PCR PE may be cut, shredded, or otherwise processed by methods known to those skilled in the art to produce flakes. The size and shape of the flakes can vary significantly. If compaction of the flakes is required for shipping, the flakes may be collected into bundles.

[0026] The non-granulated PCR PE can be washed to remove contaminants such as glue, oil, grease, dirt, paper, food residue, or beverage residue. Such washing can be performed by passing the PCR PE sheet through a water bath, spraying the PCR PE sheet with water, passing the PCR PE sheet through a mesh screen to remove contaminants, rubbing the PCR PE sheets against each other, or a combination thereof. The non-granulated PCR PE can also be dried. Such drying can be performed by using centrifugal force to remove water from the PCR sheet, by heat drying the PCR sheet, or a combination thereof.

[0027] Although washing reduces the number of contaminants present in PCR PE, it rarely eliminates all of the contaminants. When PCR PE is heated during processing and pelletizing, some of the remaining contaminants in the PCR PE may burn. This burning typically leaves a residue that discolors the PCR PE. Each melting that the PCR PE undergoes may cause additional contaminants to burn and may cause additional PCR PE discoloration. Therefore, each additional melting of PCR PE may result in greater discoloration of the PCR PE. Therefore, methods that exclude melting (such as melting present during processing and pelletizing) can produce PCR PE and PCR PE blends with less discoloration. Although it may be conventional to pelletize the PCR PE before combining it with virgin polyethylene, such processing and pelletizing can damage the microstructure of the PCR PE and cause additional discoloration while providing little benefit.

[0028] In some examples, blending the non-pelletized PCR PE with the virgin polyethylene melt can be performed in an extruder. The extruder can be a single-screw extruder or a 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 revolutions per minute (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. For a given size, the extruder can be operated 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.

[0029] Without wishing to be bound by theory, it is believed that melt blending PCR PE with virgin polyethylene can enhance the strength and durability of the upgraded PCR PE. In some examples, the PCR PE can be melt blended with a virgin polyethylene having the same density as the PCR PE. In some examples, the PCR PE can be melt blended with a virgin polyethylene having a density that is higher or lower than the density of the PCR PE. In some examples, melt blending involves homogenizing the PCR PE and the virgin polyethylene. Although melt blending combines the PCR PE with the virgin polyethylene, the PCR PE and the virgin polyethylene are only homogenized if they are uniformly dispersed 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 are uniformly dispersed throughout the melt blend.

[0030] Non-pelletized PCR PE can have a density of 0.870 grams per cubic centimeter (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.

[0031] The non-pelletized PCR PE can comprise a melt index (I2) of 0.3 g / 10 min to 5.0 g / 10 min, 0.5 g / 10 min to 2.0 g / 10 min, 0.25 g / 10 min to 5.0 g / 10 min, 0.1 g / 10 min to 10 g / 10 min, 0.75 g / 10 min to 1.75 g / 10 min, or 1.0 g / 10 min to 1.5 g / 10 min.

[0032] The virgin polyethylene may have a density of 0.870 grams per cubic centimeter (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. In some examples, the virgin polyethylene may include a low density polyethylene (LDPE) having a density 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.

[0033] Non-granulated PCR PE can be obtained from a variety of sources. Non-granulated PCR PE can include post-consumer recycled materials derived from single-layer flexible films, multi-layer flexible films, and combinations thereof. Single-layer flexible films and multi-layer flexible films can have a thickness of less than or equal to 10 mils.

[0034] In one embodiment, the upgraded PCR PE does not undergo an additional compounding step downstream of melt filtration. Conventional recycling methods typically melt filter the PCR PE flakes after they have been processed. The melt-filtered PCR PE is then formed into pellets, and the pellets are then combined with virgin polyethylene and then subjected to additional melt filtration. However, the method described herein does not subject the PCR PE to any melting before combining it with the virgin polyethylene. No additional compounding step is required after the PCR PE has been combined with the virgin polyethylene and melt filtered. In some examples, melt filtration occurs downstream of homogenization. Although conventional recycling methods typically subject the PCR PE flakes to melt filtration before melt blending them with virgin polyethylene, the present invention excludes any melting of the PCR flakes before blending them with the virgin polyethylene. Although melt filtration helps remove contaminants, melt filtration may weaken the microstructure of the PCR PE and may cause additional discoloration due to burning of contaminants because melt filtration requires heating the PCR PE. By melt filtering the PCR / virgin blend after it has been homogenized, the PCR PE may be subjected to fewer melt filtration steps, which may reduce damage to the upgraded PCR PE microstructure and may reduce the amount of discoloration of the upgraded PCR PE.

[0035] Melt filtration may involve at least one or at least two filtration steps. The filtration step may include passing the heated plastic through a laser filter (a continuous filtration technique in which a screen is made by drilling precision holes using a laser beam, and the collected contaminants are continuously scraped and removed without removing the filter screen), a surface filter (e.g., a mesh filter, a woven mesh filter, etc.), a depth filter (sintered powder filter, super pate filter, 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 a different filter may be used in each filtration step. In some examples, multiple melt filtration steps may include melting the plastic to be filtered only once, and then subjecting the molten plastic to multiple filtration steps.

[0036] In some examples, the first melt filtering step may include passing the plastic through a first filter having a mesh 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 filtering step may include passing the plastic through a second filter located downstream of the first filter. The second filter may have a mesh size of 10 μm to 300 μm, 25 μm to 250 μm, 35 μm to 200 μm, 40 μm to 150 μm, or 50 μm to 100 μm.

[0037] Upgraded PCR PE may include 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 an antioxidant package, a slip agent, a filler, a polymer processing aid, a coupling agent, an odor absorber, a flame retardant, or a dye. The antioxidant package may include a primary antioxidant, a secondary antioxidant, or a combination thereof. The antioxidant package may include a hindered phenol, a phosphite, a thioether, an aromatic amine, a hydroxylamine, or a combination thereof. The filler may include calcium carbonate, talc, or a combination thereof. The slip agent may include an amide. The coupling agent may include a silane, a maleic anhydride grafted polymer, a stearate, an organic titanate, or a combination thereof. The dye may include an organic dye, titanium oxide, carbon black, or a combination thereof. The polymer processing aid may include a fluoropolymer.

[0038] Upgraded PCR PE

[0039] In one or more embodiments, upgraded PCR PE can be produced from the non-granulated PCR PE described herein and virgin polyethylene. The upgraded PCR PE can be used in pellets, resins, or films, such as monolayer films or multilayer films. The upgraded PCR PE comprising films can be used in non-rigid packaging, such as garbage bags, shopping bags, flexible packaging, pouches, stand-up pouches, and the like. The upgraded PCR PE can also be used in rigid packaging, such as trash cans, compost bins, plastic bottles, condiment containers, milk jugs, soap dispensers, yogurt tubs, frozen meals, and the like. The upgraded PCR PE can also be used in furniture, paneling, lumber, landscaping ties, floor tiles, and the like.

[0040] The upgraded PCR PE may have a density 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.

[0041] Upgraded PCR PE can contain 1% to 99% virgin polyethylene, 10% to 90% virgin polyethylene, 20% to 80% virgin polyethylene, 25% to 75% or 30% to 60% virgin polyethylene. The amount of virgin polyethylene used can affect the color, durability and stain level of the upgraded PCR PE.

[0042] Test Method

[0043] Melt Index (190°C, 2.16 kg, "I2") Test Method: ASTM D1238-13 "Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Platometer" (the entire protocol of which is hereby incorporated by reference), using conditions of 190°C / 2.16 kilograms (kg). Results are reported in grams eluted per 10 minutes (g / 10 min).

[0044] Density measurements were performed according to ASTM D4703, the entire protocol of which is hereby incorporated herein by reference. Measurements were performed according to ASTM D792, Method B, the entire protocol of which is hereby incorporated herein by reference, within one hour of sample pressing.

[0045] Color change measurements can be made by evaluating the yellowness index according to ASTM D6290 (the complete protocol of which is hereby incorporated by reference).

[0046] Number average molecular weight (MW) can be determined according to ASTM D4274 (the entire protocol of which is hereby incorporated by reference).

[0047] Example

[0048] The following examples are provided by way of illustration and are presented in a manner that one skilled in the art will recognize and are not meant to limit the disclosure as a whole or the appended claims.

[0049] Example 1

[0050] Commercially available from Avangard Innovative, the melt index I2 is 0.6736 g / 10 min to 0.9521 g / 10 min and the density is 0.921 g / cm 3 to 0.933g / cm 3Washed post-consumer recycled polyethylene (PCRPE) AVG 150 flakes were fed together with virgin low-density polyethylene (LDPE) 132I pellets, commercially available from Dow Inc. in Midland, Michigan, into a preconditioning unit in a single-screw extruder, an INTAREMA 1108TVE plus, commercially available from Eema, equipped with two inline filtration systems: an Eema laser filter and an Eema backwash filter. The PCR PE flakes and virgin LDPE pellets were then melt blended in the single-screw extruder to produce a homogenized blend. The extruder throughput was 943 pounds per hour (lbs / h), the screw speed was 190 revolutions per minute (rpm), the torque was 91%, and the melt pressure at the die was 764 pounds per square inch (psi). The PCR PE flakes comprised 70% by weight of the homogenized blend, and the virgin LDPE pellets comprised 30% by weight of the homogenized blend. The process includes two melt filtration unit operations to remove contaminants. The melt temperature before the prefilter is 402°F. The melt pressure before the filter is 2311 psi. The homogenized blend is first passed through a laser filter prefilter, which screens for contaminants ranging from 90 microns (μm) to 110 μm or larger. The homogenized blend is then passed through a fine filter, which screens for contaminants larger than 50 μm. The upgraded PCR PE is formed into pellets by passing it through a die, followed by simultaneous water cooling and cutting into pellets.

[0051] Comparative Example 2

[0052] Commercially available from Avangard Innovative, the melt index I2 is 0.6736 g / 10 min to 0.9521 g / 10 min and the density is 0.921 g / cm 3 to 0.933g / cm 3Washed post-consumer recycled polyethylene (PCRPE) AVG 150 flakes were melt blended in an INTAREAMA 1108TVE plus single-screw extruder (available from Eema) equipped with two inline filtration systems: an Eema laser filter and an Eema backwash filter, to produce PCR PE pellets. The extruder had a throughput 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 the pre-filter was 397°F. The melt pressure before the filter was 2049 psi. The PCR PE was first passed through a pre-filter, which screened for contaminants ranging from 90 microns (μm) to 110 μm or larger. It was then passed through a fine filter, which screened for contaminants larger than 50 μm. The resulting PCR PE pellets were formed by passing it through a die, followed by simultaneous water cooling and pelletizing. 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 40mm Coperion twin-screw extruder. The PCR PE pellets accounted for 70% by weight of the resulting mixture, and the virgin LDPE pellets accounted for 30% by weight of the resulting mixture. The extruder throughput was 200 lbs / h, the screw speed was 250 rpm, and the melt pressure at the die was 1503 psi. The PCR / virgin blend was then melt filtered. The melt pressure before the filter was 2375 psi. The PCR / virgin blend was passed through a filter that screened for contaminants larger than 149 μm. The resulting upgraded PCR PE was formed into pellets by passing the upgraded PCR PE through a die, followed by simultaneous water cooling and cutting of the upgraded PCR PE into pellets.

[0053] Comparative Examples 3 to 5

[0054] Commercially available from Avangard Innovative, the melt index I2 is 0.6736 g / 10 min to 0.9521 g / 10 min and the density is 0.921 g / cm 3 to 0.933g / cm 3Washed post-consumer recycled polyethylene (PCRPE) AVG 150 flakes were melt blended in an INTAREAMA 1108TVE plus single-screw extruder (available from Eema) equipped with two inline filtration systems: an Eema laser filter and an Eema backwash filter, to produce PCR PE pellets. The extruder had a throughput 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 the pre-filter was 397°F. The melt pressure before the filter was 2049 psi. The PCR PE was first passed through a pre-filter, which screened for contaminants ranging from 90 microns (μm) to 110 μm or larger. It was then passed through a fine filter, which screened for contaminants larger than 50 μm. The resulting PCR PE pellets were formed by passing it through a die, followed by simultaneous water cooling and pelletizing. The PCR PE pellets were then compounded with virgin low-density polyethylene (LDPE) 132I pellets commercially available from The Dow Chemical Company in a separate Banbury mixer equipped with a single-screw extruder. The Banbury mixer was operated with a batch size of 390 to 420 lbs, a mixing time of 65 to 150 seconds, and a drop temperature of 145 to 150°C. The processing temperature of the single-screw extruder was 180 to 240°C, and the extruder speed was 25 to 50 rpm. The PCR PE pellets accounted for 70% by weight of the resulting compound, and the virgin LDPE pellets accounted for 30% by weight of the resulting compound. The resulting upgraded PCR PE was formed into pellets by passing the upgraded PCR PE through a die, followed by simultaneous water cooling and cutting of the upgraded PCR PE into pellets.

[0055] The properties of the pellets obtained in Examples 1 to 5 are shown in Tables 1 and 2.

[0056] Table 1: Pellets properties

[0057]

[0058] Table 2: Comparison of differences

[0059]

[0060] As shown in Table 1, the pellets of Example 1 have a lower yellowness index than Examples 3 to 5. Therefore, the pellets containing upgraded PCR PE prepared by the method of Example 1 exhibit less discoloration than the pellets containing upgraded PCR PE prepared by the conventional method, even though the two pellets have the same composition.

[0061] In addition, as shown in Table 2, the average transparency of Example 1 is higher than the average transparency of Example 3, which further indicates that the method of Example 1 causes less turbidity than the conventional method.

[0062] In addition, as shown in Table 2, the upgraded PCR PE of Example 1 and the upgraded PCR PE of Example 3 showed only minor differences in tensile properties. Therefore, it appears that preparing upgraded PCR PE using the method of Example 1 provides upgraded PCR PE having similar tensile properties to upgraded PCR PE prepared by conventional methods.

[0063] The subject matter of the present disclosure has been described in detail and by reference to specific embodiments. It will be understood that any detailed description of a component or feature of an embodiment does not necessarily imply that component or feature is essential to that particular embodiment or any other embodiment. Further, it will be apparent to those skilled in the art that various modifications and changes may be made to the described embodiments without departing from the spirit and scope of the claimed subject matter.

[0064] It should be noted that one or more of the appended claims utilize the term "wherein" as a transitional expression. For purposes of defining the present technology, it should be noted that this term is introduced in the claims as an open transition phrase that is used to introduce a recitation of a series of features of a structure and should be interpreted in a manner similar to the more commonly used open-ended term "comprising."

[0065] It is to be understood that where a first component is described as "comprising" a second component, it is contemplated that, in embodiments, the first component "consists of" or "consists essentially of" the second component. It is also to be understood that where a first component is described as "comprising" a second component, it is contemplated that, in embodiments, the first component may comprise 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 at least 99% of the second component (where % may be by weight or mole).

[0066] It should also be noted that reference herein to "at least one" component, element, etc. should not be used to create an inference that the alternative use of the article "a" should be limited to a single component, element, etc.

Claims

1. A method for producing upgraded post-consumer recycled polyethylene (PCR PE), the method comprising: melt blending non-pelletized PCR PE with virgin polyethylene in an extruder to produce a PCR / virgin blend, and The PCR / virgin blend is melt filtered to remove contaminants and produce the upgraded PCR PE.

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

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

4. The method of any preceding claim, wherein the non-granulated PCR PE comprises post-consumer recycled material derived from single-layer flexible films, multi-layer flexible films, and combinations thereof, wherein the single-layer flexible films and the multi-layer flexible films have a thickness less than or equal to 10 mils.

5. The method of any preceding claim, wherein the non-pelletized PCR PE comprises LDPE having a density of 0.900 to 0.945 g / cc and a melt index (I2) of 0.5 to 2.0 g / 10 min.

6. A method according to any preceding claim, wherein there is no additional compounding step downstream of the melt filtration.

7. A method according to any preceding claim, wherein the extruder is a single screw extruder.

8. A method according to any preceding claim, wherein the melt blending involves homogenisation of the PCR and the virgin polyethylene.

9. The method of claim 8, wherein the melt filtration occurs downstream of the homogenization.

10. A method according to any preceding claim, wherein the non-pelletised PCR PE and the virgin polyethylene comprise additional additives.

11. A method according to any preceding claim, wherein the melt filtration involves at least two filtration steps.

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

13. An upgraded PCR PE produced by the method according to any preceding claim.

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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