Polymer reclamation from multilayer polymeric materials having barrier structures

Abstract

Disclosed herein are methods for recovering polymers from a multilayer polymeric material. The method includes contacting the multilay er polymeric material with a barrier solvent for a time and at a temperature to selectively dissolve a layer of barrier material, thereby forming a barrier-material solution, and separating the barrier-material solution from an undissolved first polymer layer and an undissolved second polymer layer. The multilayer polymeric material comprises a first polymeric layer, a second polymeric layer, and the layer of a barrier material positioned between the first polymeric layer and the second polymeric layer.

Description

[0001] POLYMER RECLAMATION FROM MULTILAYER POLYMERIC MATERIALS HAVING BARRIER STRUCTURES

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] Priority is hereby claimed to U.S. provisional application Ser. No. 63 / 620,489, filed January 12, 2024, which is incorporated herein by reference.

[0004] FEDERAL FUNDING STATEMENT

[0005] This invention was made with government support under Grant No. 2132093 as awarded by the National Science Foundation (NSF). The government has certain rights in the invention.

[0006] BACKGROUND

[0007] Multilayer plastics are widely used in various industries, particularly for packaging applications, due to their ability to combine the advantageous properties of different materials into a single structure. Annually, over 100 million tons of multilayer thermoplastics are manufactured worldwide (D. Lithner, A. Larsson, G. Dave, “Environmental and health hazard ranking and assessment of plastic polymers based on chemical composition.” Sci. Total Environ. 2011, 409: 3309-3324).

[0008] These multilayer constructions often include layers of barrier materials, such as ethylene vinyl alcohol (EV OH) or polyamide (PA), which enhance the performance of the plastic by providing resistance to gas, vapor, or liquid transmission. This makes multilayer plastics ideal for preserving food, pharmaceuticals, and other perishable products. Despite their functional benefits, the complex structure of multilayer plastics presents significant challenges for recycling. Multilayer plastics are less likely to be recycled. Traditional recycling methods, which often involve mechanical grinding or melting, can be inadequate for multilayer plastics, and lead to poor-quality recycled products. When multilayer plastic barrier structures are recycled, the barrier material is incorporated into the stream of the majority component (e.g. a polyolefin or polyethylene terephthalate) resulting in a loss of barrier properties.

[0009] As the global demand for sustainable materials and waste reduction increases, there is a pressing need for efficient and environmentally friendly methods to recycle multilayer polymeric materials. In particular, methods that can effectively recover and reuse barrier materials hold great promise for reducing landfill waste, conserving resources, and enhancing the circularity of plastic products. Chemical recycling of multilayer food packaging plastics has been explored in recent years. One notable approach is the Solvent-Targeted Recover}' and Precipitation (STRAP) method, which uses staged dissolution to recycle polymers in multilayer plastics. See T. W. Walker, N. Frelka, Z. Shen, A. K. Chew, J. Banick, S. Grey, M. S. Kim, J. A. Dumesic, R. C. Van Lehn, and G. W. Huber, “Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation.” Sci. Adv. 2020, 6: eaba7599. However, the STRAP method currently faces significant challenges, including excessive solvent consumption, lengthy processing times, and high costs, which limit its practical application.

[0010] The present disclosure addresses these challenges by providing an efficient method for separately recycling valuable barrier layers and abundant polyolefins from multilayer plastics, facilitating their recovery and reuse while maintaining the quality and integrity of the recycled materials.

[0011] SUMMARY

[0012] Disclosed herein is a method that enables the dissolution of barrier materials in multilayer polymer constructions. The method utilizes solvents that selectively dissolve the barrier material layer and a process for enhancing the dissolution through the application of heat and shear. The process may result in two products. The first product comprising undissolved polymers such as polyolefins that can be further processed using traditional polymer melt processing techniques. The second product comprising polymer-loaded solvent containing high-value barrier materials such as an ethylene vinyl alcohol (EV OH) or a polyamide (PA). The polymer from this second product can be recovered from the solvent. The method has advantages over existing recycling technologies for multi-layer polymer constructions in that high-cost processes such as dissolution and drying are applied to the higher value materials such as EV OH and PA. Lower cost processes may be applied to lower value materials such as polyolefins.

[0013] Specifically, disclosed and claimed herein is a method of recovering polymers from a multilayer polymeric material. The method includes contacting a multilayer polymeric material with barrier solvent for a time and at a temperature to selectively dissolve a layer of barrier material, thereby forming a barrier-material solution. The multilayer polymeric material comprises a first polymeric layer, a second polymeric layer, and the barrier material disposed between the first polymeric layer and the second polymeric layer. The undissolved layers of the first polymeric layer and second polymeric layer remain and can be readily separated from the barrier-material solution.

[0014] In some embodiments, the method includes contacting the multilayer polymeric material with the barrier solvent at the temperature of about 20 °C to about 200 °C. In some embodiments, contacting the multilayer polymeric material with the barrier solvent may comprise applying shear force when contacting the plastic film with the solvent. The barrier material may comprise an ethylene vinyl alcohol (EV OH) or a polyamide (PA). Non-limiting examples of the barrier-recovery solvent include formic acid and other carboxylic acids such as acetic acid, dimethyl sulfoxide (DMSO), ethylene glycol, methanol, ethanol, and dimethylformamide (DMF).

[0015] In one embodiment, the barrier material comprises EV OH, and the barrier solvent comprises formic acid.

[0016] In another embodiment, the barrier material comprises EV OH, and the barrier solvent comprises DMSO.

[0017] In another embodiment, the barrier material comprises EV OH, and the barrier solvent comprises ethylene glycol.

[0018] In another embodiment, the barrier material comprises PA, and the barrier solvent comprises formic acid.

[0019] The first polymeric layer and second polymeric layer may comprise polyolefins, and the method may further comprise melting and extruding the first and / or second polymenc layer without addition of solvent.

[0020] The objects and advantages of the disclosure will appear more fully from the following detailed description of the preferred embodiments of the disclosure made in conjunction with the accompanying drawings.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1. Exemplary workflow of recycling multilayer plastics according to the present disclosure.

[0023] Figs. 2A-2B. Characterization of EV OH extracted from commercial plastic waste using DMSO at 100 °C for about 1 day. Fig. 2A shows FTIR spectra of the extracted EVOH compared to two grades of neat EVOH, “G” grade (48 mol% EC EVOH) and “L” grade (27 mol% EC EVOH). Fig. 2B shows DSC analysis of the extracted EVOH compared to “H’’ grade EVOH.

[0024] Figs. 3A-3C. Characterization of EVOH extracted from multilayer plastic packaging using DMSO at 50 °C for 3 hours or 3 days. Fig. 3A shows FTIR spectra of the extracted EVOH compared to a commercially available EVOH (G176B). Fig. 3B shows Raman spectra of the extracted EVOH compared to G176B EVOH. Fig. 3C shows DSC analysis results of the EVOH from the 3-hour and 3-day extractions.

[0025] Figs. 4A-4D. Chip percentage during the dissolution of Sargento cheese packaging films by DMSO at 75 °C and with high-shear impeller operated at different RPMs. Fig. 4A shows results of the experiment using 0.5"xl" plastic chips with a stirring speed of 30 RPM. Fig. 4B shows results of the experiment using 0.5"* 1" plastic chips with a stirring speed of 150 RPM. Fig. 4C shows results of the experiment using 0.75" plastic circles with a stirring speed of 30 RPM. Fig. 4D shows the combined results from Figs. 4A-4C.

[0026] Fig. 5. Chip percentage during the dissolution of Sargento cheese packaging chips by DMSO at 75 °C with a stirring speed of 30, 150, 800, and 1200 RPM.

[0027] Fig. 6. DSC chart of Sargento cheese packaging chips before dissolution and after 5- hour and 6-hour dissolution periods.

[0028] Fig. 7. NMR spectra of virgin nylon in formic acid and nylon extracted from the sausage wrapper in formic acid.

[0029] Fig. 8. Microscopic image of the cross-section of the regrind multilayer sheet structure.

[0030] Fig. 9. Weight percent of regrind multilayer sheet versus dissolution time at 25 °C, 50 °C, and 75 °C using formic acid.

[0031] Fig.10. Cross-sectional images of the regrind multilayer sheet as a function of dissolution time under the conditions of 75 °C, 88% formic acid concentration, and a stirring speed of 300 RPM: (a) 0 h, (b) 0.5 h, (b) 1 h, (dl) 1.5 h (upper part), and (d2) 1.5 h (lower part).

[0032] Fig. 11A-11B. DSC curves of the regrind multilayer sheet before and after EV OH dissolution under the conditions of 75 °C, 88% formic acid concentration, and a stirring speed of 500 rpm: (Fig. 11A) crystallization curves and (Fig. 1 IB) melting curves.

[0033] Fig. 12. Weight percent of regrind multilayer sheet versus dissolution time at 135 °C using ethylene glycol.

[0034] Fig. 13A-13B. DSC curves of EVOH-based Berry Global multilayer films before and after dissolution: (Fig. 13 A) crystallization curves and (Fig. 13B) melting curves.

[0035] Fig. 14A-14B. DSC curves of nylon-based Berry Global multilayer films before and after dissolution: (Fig. 14A) crystallization curves and (Fig. 14B) melting curves.

[0036] Fig. 15. Post-consumer multilayer products: (a) Dole fruit bottle, (b) Dole fruit cup, (c) coffee K-Cup, (d) baby food tub, and (e) pet food container.

[0037] Fig. 16. Cross-sectional macroscopic images of post-consumer multilayer structures before and after formic acid dissolution: (al) Dole fruit bottle, (bl) Dole fruit cup, (cl) coffee K-Cup, (dl) baby food tub, and (el) pet food container. Images labeled al, bl, cl, dl, and el represent the structures before dissolution. Images labeled a2, b2, c2, d2, e2 and a3, b3, c3, d3, e3 correspond to parts one and two of the respective multilayer structures after dissolution.

[0038] DETAILED DESCRIPTION

[0039] Abbreviations and Definitions

[0040] DMF = Dimethylformamide; DMSO = Dimethyl sulfoxide; DSC = Differential scanning calorimetry; EVOH = Ethylene vinyl alcohol; FTIR = Fourier-transform infrared spectroscopy; HDPE = High-density polyethylene; LDPE = Low-density polyethylene; LLDPE = Linear low-density polyethylene; MLPs = Multilayer plastics; NMR = Nuclear Magnetic Resonance; PA = Poly amide; PP = Poly propylene.

[0041] Numerical ranges as used herein are intended to include every number and subset of numbers contained within that range, whether specifically disclosed or not. Further, these numerical ranges should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 2 to 8, from 3 to 7, from 5 to 6, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

[0042] As used herein, the singular forms “a,” “an,” and ‘'the” include plural referents unless the content clearly dictates otherwise.

[0043] As used herein, the term “or” is an inclusive “or” operator and is equivalent to the term “and / or” unless the context clearly dictates otherwise.

[0044] As used herein, the term “about” refers to ±10% of the variable referenced.

[0045] The elements and method steps described herein can be used in any combination whether explicitly described or not, unless otherwise specified or clearly implied to the contrary' by the context in which the referenced combination is made.

[0046] All combinations of method steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

[0047] The systems and methods of the present disclosure can comprise, consist of, or consist essentially of the essential elements and limitations described herein, as well as any additional or optional components, or limitations described herein or otherwise useful in the art. The disclosure provided herein suitably may be practiced in the absence of any element which is not specifically disclosed herein.

[0048] It is understood that the disclosure is not confined to the particular elements and method steps herein illustrated and described, but embraces such modified forms thereof as come within the scope of the claims.

[0049] As used herein, the term “polyolefin” refers to a class of polymers derived from one or more olefin monomers (also known as alkenes), such as ethylene, propylene, butene, pentene, or higher a-olefins. Polyolefins include, but are not limited to, homopolymers such as polyethylene (e.g., low-density polyethylene (LDPE), high-density polyethylene (HDPE)) and polypropylene (PP), as well as copolymers such as ethylene-propylene copolymers, linear low-density polyethylene (LLDPE), and other blends or alloys thereof. As used herein, the term “barrier material’’ refers to any material incorporated into a multilayer material to reduce or prevent the penneation of gases, vapors, liquids, or other substances through the plastic. Barrier materials are typically used to enhance the performance of packaging and containers by improving properties such as gas retention, moisture resistance, or flavor preservation. Examples of barrier materials include, but are not limited to, ethylene vinyl alcohol (EV OH) and polyamide (nylon).

[0050] EV OH is a copolymer comprised of ethylene and vinyl alcohol, known for its excellent gas barrier properties. EV OH undergoes plasticization when exposed to water, making it particularly suitable for use in multilayer plastics.

[0051] EVOH

[0052] Polyamide is a class of synthetic polymers characterized by the presence of amide groups (-CONH-) in the polymer backbone. Polyamides are commonly referred to as nylons and are widely used in the production of plastics due to their excellent mechanical properties, thermal stability , and resistance to wear and chemicals. In the context of the present disclosure, polyamide may include, but is not limited to, nylons including aliphatic nylons (e.g., nylon-6; nylon-6, 6; nylon 6,12; nylon 4,6; and nylon 12), semi-aromatic nylons, and aromatic nylons.

[0053] As used herein, the term “multilayer polymeric material” or “multilayer plastic” refers to any composite material made by combining at least tw o or more distinct layers, typically of different types of polymeric materials, to achieve enhanced properties that a single layer cannot provide. In the case of multilayer plastic materials, these layers are often chosen for their specific functions, such as improved barrier properties, mechanical strength, heat resistance, and sealing capabilities. Multilayer polymeric materials are commonly used in packaging applications, such as food, pharmaceuticals, and consumer goods, these materials may comprise polymers such as polyethylene, polypropylene, or polyvinyl chloride to offer benefits like better protection against oxygen, moisture, and light while also being flexible and durable. Multilayer polymeric materials are not limited to two or three layers; they can comprise as many layers as needed, depending on the intended use and the specific manufacturing process. Multilayer polymeric materials may include 2, 3, 4, 5, 6, 7. 8, 9, or more than 9 layers. Multilayer polymeric materials may have a number of different uses such as in food packaging, construction materials, or landscaping materials for oxygen and moisture barriers, or advanced medical packaging to ensure sterility and protect against contaminants. The barrier material can be applied in multiple layers within the structure to provide enhanced protective performance when you have many layers of polymeric material. The presently disclosed methods provide for selective dissolution of the barrier material while retaining the surrounding layers substantially undissolved. As used herein, the term “barrier solvent7’ refers to a solvent or solvent system used to dissolve the barrier material in a multilayer plastic structure, such as ethylene vinyl alcohol (EV OH) or polyamide (PA), without substantially affecting the other polymeric layers, including but not limited to polyolefins. The barrier solvent is used in the recycling or reprocessing of multilayer polymeric materials, allowing for the separation or recovery of the barrier material while preserving the integrity of the surrounding layers, thus enabling the re-use or repurposing of the material. These solvents often include polar protic and aprotic solvents or cosolvent systems that can selectively dissolve barrier materials while leaving the surrounding polymeric layers substantially undissolved. Examples of solvents that could be used to recover EV OH or PA include, without limitation, carboxylic acids (e.g., formic acid and acetic acid), alcohols (e.g., methanol or ethanol), diols (e.g., ethylene glycol), sulfoxides (e.g., dimethyl sulfoxide (DMSO)), or formamides (e.g., dimethylformamide (DMF)).

[0054] As used herein, the term “barrier-material solution” refers to a mixture consisting of a barrier solvent and the barrier material (such as ethylene vinyl alcohol (EV OH) or polyamide (PA)) that is being dissolved or recovered from a multilayer polymeric material. This solution enables the selective removal of the barrier material while leaving the other polymeric layers substantially intact. Substantially intact means that less than 10% of the material has been dissolved by the barrier solvent. This solution is used in processes such as recycling or reprocessing of multilayer polymeric materials, allowing for the recover}' and reuse of the barrier materials.

[0055] As used herein, the term “first polymeric layer” refers to a layer in a multilayer polymeric material that is not targeted by the barrier solvent, meaning it remains substantially intact during the dissolution process of the barrier material. In some instances, less than 5% , less than 2%, or less than 1% of the first polymeric layer is dissolved by the barrier solvent. This layer could be made from a variety of polymers, such as polyolefins (e.g., polyethylene or polypropylene), and is ty pically chosen for its mechanical properties, flexibility, or sealing capabilities.

[0056] Similarly, a “second polymeric layer” is another layer in the multilayer polymeric material that also remains substantially intact during the dissolution process of the barrier material. In some instances, less than 5%, less than 2% or less than 1% of the second polymeric layer is dissolved by the barrier solvent. Like the first polymeric layer, it could be made of the same material or a different material, depending on the specific requirements of the product. These layers are designed to complement the barrier material and enhance the overall performance of the multilayer polymeric material. Both layers are retained in the recycling or reprocessing process, with only the barrier material being dissolved or removed. The multilayer polymeric material comprises a layer of barrier material disposed between a first and second layer of polymeric material that is different than the barrier material. The multilayer polymeric material may have an A1-B-A2 multilayer structure where Al and A2 are the first and second layers of polymeric material and B is the barrier material layer. Al and A2 may be composed of the same material but need not be. The choice of layers Al, B, and A2 may be selected for the desired use. The multilayer polymeric material may also have an A1-C1-B-C2-A2 multilayer structure where Al and A2 are the first and second layers of polymeric material, B is the barrier material layer, and Cl and C2 are tie layers for adhering Al and A2 to B, respectively. Such a multilayer structure is illustrated in Fig. 1 A. Al and A2 may be composed of the same material but need not be and Cl and C2 may be composed of the same material but need not be. The choice of layers Al, Cl, B, C2, and A2 may be selected for the desired use. Multilayer polymeric materials may have one or more additional layers opposite Al or A2 from B, e.g., D1-A1-B-A2, A1-B-A2-D2, D1-A1-B-A2-D2, D1-A1-C1-B- C2-A2. A1-C1-B-C2-A2-D2, D1-A1-C1-B-C2-A2-D2 where DI and D2 are the one or more additional layers of material.

[0057] Multilayer polymeric materials may have more than one barrier layer. The multilayer polymeric material may have an A1-B1-A2-B2-A3 multilayer structure where Al, A2, and A3 are first, second, and third layers of polymeric material and Bl and B2 are barrier material layers. Al, A2, and A3 may be composed of the same material but need not be and Bl and B2 may be composed of the same material but need not be. The choice of layers Al, Bl, A2, B3, and A3 may be selected for the desired use. The multilayer polymeric material may have an A1-C1-B1-C2-A2-C3-B2-C4-B3 multilayer structure where Al, A2, and A3 are the first, second, and third layers of polymeric material, Bl and B2 are barn er material layers, and Cl, C2, C3, and C4 are tie layers for adhering Al and A2 to Bl and A2 and A3 to B2. Al, A2, and A3 may be composed of the same material but need not be; Bl and B2 may be composed of the same material but need not be; and Cl, C2, C3, and C4 may be composed of the same material but need not be. The choice of layers Al, Cl, Bl, C2, A2. C3, B2, C4, and A3 may be selected for the desired use. Multilayer polymeric materials may have one or more additional layers of material opposite Al from Bl or A3 from B2, e.g., D1-A1-B1-A2-B2-A3, A1-B1-A2-B2-A3-D2, D1-A1-B1-A2-B2-A3-D2, D1-A1-C1-B1-C2-A2-C3-B2-C4-A3, Al- C1-B1-C2-A2-C3-B2-C4-A3-D2, DI- A1-C1-B1-C2-A2-C3-B2-C4-A3-D2 where DI and D2 are the one or more additional layers of material.

[0058] As used herein, the term “flexible materials” refers to materials that can bend, stretch, or conform to various shapes without breaking under typical use conditions. These materials are A pically thin, lightweight, and adaptable, making them suitable for applications where ease of manipulation, sealing, and flexibility are required. Films, made from polymers including but not limited to polyolefins, polyethylene, polypropylene, polyvinyl chloride, or polyethylene terephthalate, are examples of flexible packaging materials. Films can be used for a wide range of packaging, including food, medical products, and consumer goods, due to their ability to wrap around products, offer protective barriers, and often provide transparency. Sheets can also be flexible, depending on the thickness and type of polymer. Thin plastic sheets made from materials like polyolefins or other flexible plastics are often used in packaging applications where the material must bend and conform, such as in shrink wraps or flexible packaging pouches. These materials are lightweight, cost-effective, and capable of being sealed tightly to protect against moisture, oxygen, and light.

[0059] As used herein, the term “rigid materials” refers to materials that are stiff and retain their shape under typical use conditions. These materials are thicker and provide more structural integrity than flexible materials. Sheets in the rigid category are typically thicker than flexible sheets and made from polymers including but not limited to polystyrene, polypropylene, polyethylene terephthalate, or polyvinyl chloride, offering stability and protection. These rigid sheets are commonly used for applications where the packaging must maintain a specific shape, such as in the manufacture of blister packs, trays, or certain types of food containers. Additionally, rigid structures can refer to molded packaging, such as bottles, jars, and boxes, which are made from polymers including but not limited to polyethylene, polypropylene, or polyethylene terephthalate. These materials provide enhanced protection, durability, and support for products requiring more robust barriers against physical damage, moisture, and external contaminants. Rigid packaging is preferred in cases where stability, stackability, and protection are important for maintaining the integrity of the product inside.

[0060] As used herein, the term “scrap” refers to excess, leftover, or waste material generated during the manufacturing or processing of multilayer polymeric films. This includes but is not limited to unused or cut-off portions of multilayer polymeric materials during production, packaging, and processing. Scrap encompasses all material waste that is discarded or left over before use by an end user. As used herein, the term ‘'post-consumer waste” refers to the multilayer polymeric materials that have been used by the consumer and are discarded after the product’s useful life, representing the waste generated after the consumer has finished using the product. In the context of multilayer polymeric films, this could include packaging materials from food (e.g., meat packaging films, snack bags, and barrier films), as well as other consumer goods such as cosmetic packaging, landscape barrier materials, or balloons. These materials are collected after they are disposed of by consumers, often through recycling programs or waste disposal. Post-consumer waste reflects the lifecycle of products after they have been used and discarded, and it plays a significant role in recycling efforts and the development of circular economies in packaging and other industries.

[0061] As used herein, the term “chip” or '‘chips” refers to small, pre-cut pieces of multilayer polymeric materials that are substantially two-dimensional. Substantially two-dimensional refers to multilayer polymeric materials that have dimensions in two directions that are an order of magnitude or greater than in a third dimension. Chips can come in a variety of shapes and sizes. Common dimensions include 0.5" xl" (1.27 cmx2.54 cm) for rectangular chips or 0.75" (1.91 cm) in diameter for circular chips, but chips can also be made in larger or smaller sizes depending on the application. For instance, chips can range up to 2" (5.08 cm) in length or width for larger rectangular shapes, or up to 1.5" (3.81 cm) in diameter for circular chips. These plastic pieces can be cut into a variety of other shapes, such as squares, triangles, hexagons, or irregular forms.

[0062] As used herein, the term “chip percentage” refers to the proportion of the chips that have been converted into smaller chips during a dissolution process, expressed as a percentage of the total material. Over time, as the barrier material in the multilayer plastic chips dissolves, each chip typically breaks down into multiple thinner chips, increasing the chip percentage. For example, a single chip may split into two thinner chips as the barrier material between the two plastic layers dissolves. As the dissolution process continues, this fragmentation leads to a higher chip percentage, indicating the extent to which the material has been broken down into smaller components. This metric helps to assess the efficiency and progression of the dissolution process, with higher chip percentages signifying a greater degree of breakdow n.

[0063] Polymer Reclamation from Multilayer Plastics

[0064] Multilayer plastics are extensively used across various industries, particularly in packaging applications. They are typically composed of polyolefin polymers that sandwich a barrier polymer, with tie layers serving as adhesives to bond the layers together. The left side of Fig. 1 shows a representative multilayer plastic packaging structure, comprising inner and outer layers of polyolefins, a barrier layer of EVOH or nylon, and tie layers that bond the different layers together. Polyolefins are commonly used for the inner and outer layers due to their moisture resistance, sealability, and mechanical strength. The barrier layer comprising EV OH or nylon commonly serves as an oxygen barrier to prevent food spoilage. Typical tie layer materials include, but are not limited to, maleic anhydride grafted polypropylene (PP) or polyethylene (PE).

[0065] Disclosed herein is a method for separately recycling valuable barrier layers and abundant polyolefins from multilayer plastics. The present disclosure provides a method for recovering a barrier material that includes contacting a multilayer polymeric material with barrier solvent for a time and at a temperature to selectively dissolve the barrier material, thereby forming a barrier-material solution, wherein the multilayer polymeric material comprises a first polymeric layer, a second polymeric layer, and the barrier material disposed between the first polymeric layer and the second polymeric layer.

[0066] In some embodiments, the suitable dissolution temperature typically ranges from about 20 °C to about 200 °C, although temperatures outside this range are also contemplated within this disclosure. In some instances, the dissolution temperature is greater than 20 °C, 30 °C, 40 °C, 50 °C, or 60 °C and less than 200 °C, 190 °C, 180 °C, 170 °C, 160 °C, 150 °C, or 140 °C.

[0067] The dissolution time may vary from about 0.5 hour to 3 days, with durations shorter or longer than this range also being encompassed by this disclosure. In some instances, the dissolution time is between 0.5 hour and 72 hours, 0.5 hour and 48 hours, 0.5 hour and 24 hours, 0.5 hour and 12 hours, 0.5 hour and 6 hours, 0.5 hour and 3 hours, 0.5 hour and 2 hours, or 0.5 hour and 1 hour.

[0068] In some embodiments, the barrier material includes EV OH or PA. Any solvent capable of selectively dissolving the barrier material without dissolving the polyolefins and tie layers is suitable for use in the dissolution process. Exemplary solvents include, but are not limited to, formic acid, acetic acid, DMSO, ethylene glycol, methanol, ethanol, and DMF. Other solvents with similar properties are also encompassed within the scope of this disclosure.

[0069] In one embodiment of the method, the solvent is formic acid. The formic acid may be used as an aqueous solution with a concentration of about 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 88%, or 90%. The dissolution time increases with lower concentration of formic acid.

[0070] In some embodiments, cosolvents are introduced. Cosolvents work in tandem with the primary barrier solvent to modify its solvation or to facilitate the dissolution of more complex or resistant barrier materials. For instance, combining a solvent like DMSO with a cosolvent such as water, ethanol, or methanol can increase the overall efficacy of the solvent system. Cosolvent systems can also be designed to optimize the solubility of the barrier material while minimizing the effect on other polymeric layers within the multilayer polymeric material.

[0071] The method may also involve separating the barrier-material solution from undissolved first polymer layer and undissolved second polymer layer. Any method or equipment suitable for the mechanical separation of solids and liquids may be used, including, but not limited to, filtration. The undissolved polymeric layers may primarily comprise polyolefins, which can be further recovered using low-cost conventional methods, such as melting and extrusion, to produce finished pellets.

[0072] In some cases, the method includes recovering at least a portion of the barrier material from the barrier-material solution. Recovering the barrier material from solution may be accomplished by techniques known in the art for separating the barrier material from the solvent.

[0073] An exemplary method for separating the barrier material from the solvent is evaporation of the solvent. Suitably the barrier-material solution may be allowed to dry, heated, and / or subjected to vacuum to evaporate solvent.

[0074] The recovery7can happen when an anti-solvent is added to recover at least a portion of the barrier material. Antisolvents are substances used to recover a solute from a solution by reducing its solubility. When applied to polymeric materials antisolvents effectively disrupt the solvation process. These substances are typically chosen based on their ability to selectively interact with specific polymers without affecting other components of the mixture. Common antisolvents for EV OH or PA include alcohols like ethanol or isopropanol, ketones like acetone. Antisolvents can be used in various processes such as polymer recovery and film processing, where they help separate the dissolved polymer from other components or solvents in the solution.

[0075] Temperature reduction is another method used to recover the barrier material from the barrier solvent by lowering the temperature, which decreases the solubility of the barrier material in the barrier solvent. As the temperature drops, the barrier material becomes less soluble and begins to solidify. In some cases, an anti-solvent in combination with a controlled reduction in temperature, can be used to selectively solidify' the barrier material while leaving the other polymeric layers undissolved.

[0076] Another technique used to recover the barrier material is referred to as a pressureswing process. This technique is used to separate or recover the barrier material from the barrier solvent by varying the pressure, which affects the barrier material's solubility. This method is useful for barrier materials that exhibit changes in solubility with pressure variations. Beyond recovery of the barrier material, the disclosure also provides methods for recovering the undissolved first polymeric layer and undissolved second polymer layer.

[0077] The multilayer polymeric material can be composed of either flexible or rigid materials, as previously described. Flexible materials typically include thin films, such as those used in packaging, which can be bent or folded without breaking, while rigid materials are more solid and inflexible, often used in applications like containers or structural components. The multilayer polymeric material may originate from scrap or from postconsumer waste. Both sources are valuable for recycling and repurposing into new products, offering a sustainable approach to the reuse of multilayer polymeric materials.

[0078] In some embodiments, the method includes applying shear force when the multilayer polymeric materials come into contact with the barrier solvent. This shear force can assist in breaking down the multilayer polymeric material, facilitating the interaction between the barrier solvent and the individual layers. The application of shear force can be achieved through various methods, such as stirring, mixing, or even mechanical agitation.

[0079] In some embodiments, the first polymeric layer and second polymeric layer include polyolefins, as these materials are commonly used in packaging, or other robust polymers. In some embodiments, the first and second polymeric layers are made from the same material, while in others, they may consist of different materials. The method may where the first and second polymeric layers are the same, the method may further involve melting and extruding the first and second polymeric layers to yield a second recovered polymer. This process allow s the recovered material to be reshaped or reused.

[0080] Fig. 1A and IB shows an exemplary workflow of recycling multilayer plastics according to the present disclosure. A multilayer plastic film comprising, e.g., EV OH or PA as the barrier layer, undergoes a dissolution process using a selective solvent under stirring and heating. Following dissolution, filtration is performed to separate the polymer solution from the undissolved polyolefins. The undissolved polymeric layers can then be recycled using conventional techniques. Prior to dissolution, the multilayer polymeric material may be processed into smaller components than the original starting material. For example, the multilayer polymeric material may be cut, chopped, ground, or milled prior to dissolution.

[0081] The methods disclosed herein addresses the current shortage of barrier plastics, such as EV OH and PA. by enabling their reclamation and reuse from industrial scrap. Although these barrier materials typically constitute only about 5% to 20% of the volume in multilayer plastics, they are significantly more expensive than polyolefins or other robust polymers commonly used in the first and second polymeric layer. The disclosed technology may reduce material costs for converters, as the higher-cost steps, such as dissolution and recovery, are applied to the high-value barrier materials, while the lower-value first and second polymeric layer can be recycled using more cost-effective processes. Additionally, the process can greatly enhance the recycling rate of post-consumer multilayer food packaging. Selective removal of the barrier layer simplifies the processing of polyolefin materials present in the structure.

[0082] EXAMPLES

[0083] In the following examples, selective removal of barrier layer material EV OH and nylon from multilayer polymeric materials, which may be referred to as multilayer plastics (MLPs), were evaluated using different solvents. Various MLPs were tested, including flexible and rigid structures, extrusion blow-molded structures, and thermoformed trays. It is demonstrated that the methods disclosed herein are effective at recovering barrier materials such as EV OH and nylon from various MLP sources.

[0084] General Experimental Protocol

[0085] Sample Preparation of MLPs

[0086] MLPs were rinsed with water, dried, and cut into approximately 0.5" xO.5" (1.27cmxl.27cm) chips using scissors, avoiding any labels on the outside of the MLPs.

[0087] Dissolution and Recovery of EVOH from MLPs

[0088] The dissolution of EVOH from the prepared MLPs was carried out in a reactor flask flushed with an inert gas at a controlled flow rate. The condenser tubing was pre-cooled before initiating the dissolution process. The dissolution was performed under stirring and heating at 100 °C, with varying time frames to evaluate the impact of dissolution time on yield.

[0089] After dissolution, the reaction flask was allowed to cool to room temperature, and the solvent solution was drained into a storage vial or beaker for further characterization. The undissolved plastics remaining in the reactor flask were rinsed thoroughly with excess water.

[0090] Precipitation of EVOH from solution was completed by adding antisolvent (water) by 3x the volume of DMSO used (i.e., 100 ml DMSO, 300 ml water). The solution was placed on a hot plate at 70 °C until total volume was less than 25 ml. Then the solution was placed in a vacuum oven at 70 °C under full vacuum overnight or until sample was completely dried. The resultant sample was weighted to determine recovery yield compared to theoretical yield based on cross-sectional analysis of the initial MLP.

[0091] Validation of EVOH The recovered EV OH was validated by characterization from FTIR, Raman spectroscopy, and DSC analysis. The presence of characteristic C-O, -CH2, and -OH peaks were confirmed in FTIR spectra. The presence of EV OH melting and crystallization peaks were also noted in DSC thermograms.

[0092] Example 1. Selective Extraction of EVOH from MLPs by DMSO

[0093] In this Example, multilayer films comprising EVOH as the barrier material were subjected to dissolution by DMSO. Various temperatures, dissolution durations, and stirring speeds were evaluated.

[0094] In one test, EVOH was extracted from commercial plastic waste using DMSO at 100 °C for about 1 day. The extracted EVOH residues were characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and melt rheology.

[0095] Fig. 2A shows FTIR spectra of the extracted EVOH compared to two grades of neat EVOH. FTIR provides information about chemical bonding, purity, and species in the samples. Key characteristic peaks of EVOH include: (1) CH2 and CH3 deformations at 2800 to 3000 cm'1; (2) OH groups arising from vinyl alcohol at -3300 cm'1; and (3) series of peaks below -1500 cm'1which are associated with various C-0 and C-H deformations. As shown in the figure, the FTIR spectra of the extracted EVOH matched the two grades of neat EVOH (G176 and L171). The peak formation around 1730 cm'1, associated with C=O bonds from carbonyl groups, may result from thermal degradation of EVOH.

[0096] DSC was used to evaluate the presence of residual polyolefins or other contaminants in the extracted EVOH. As shown in Fig. 2B, the melting and crystallization peaks of the extracted EVOH are consistent with the "‘H” grade EVOH, indicating that thermal properties of the extracted EVOH were comparable to the commercially available materials.

[0097] In another test, EVOH was extracted from multilayer plastic packaging using DMSO at 50 °C for 3 hours or 3 days. The extracted EVOH residues were characterized by FTIR, Raman spectroscopy, and DSC. As shown in Figs. 3A-3C, the properties of the extracted EVOH w ere comparable to the commercially available material G176B EVOH. The FTIR and Raman spectra of the EVOH resulted from both the 3-hour and 3-day extractions show profiles consistent with those of the G176B EVOH (Figs. 3 A and 3B).

[0098] In another test, EVOH was extracted from Sargento cheese packaging films (Sargento Foods Inc., Plymouth, WI, U.S.) using DMSO at 75 °C with stirring. A high-shear impeller driven by a high-shear motor was used, with varying revolutions per minute (RPM). The plastic films were cut into rectangular 0.5"xl" (1.27cm><2.54 cm) chips or 0.75" (1.91 cm) diameter circles. Mass was measured before and after each experiment conducted at different stirring speeds. Plastic chips were counted before and after the dissolution process to determine if full dissolution was achieved. Full dissolution was determined to be when the chip count doubled.

[0099] Fig. 4A shows results of a baseline experiment for the dissolution of the plastic chips with a stirring speed of 30 RPM. The chip percentage doubled with a run time of 120 min or longer. Fig. 4B shows results of the experiment with a stirring speed of 150 RPM. The chip percentage reached about 190% with a run time of about 90 min. Fig. 4C shows results of the experiment using the plastic circles with a stirring speed of 30 RPM. The chip percentage reached about 190% with a run time of about 240 min. Fig. 4D shows the combined results from Figs. 4A-4C. Overall, the results indicate that a higher stirring speed (RPM) enhances dissolution of the plastic films, and that chip-shape particles dissolve more easily than circular ones.

[0100] The effect of stirring speed was further examined by comparing dissolution of the plastic chips with a stirring speed of 30, 150, 800, and 1200 RPM. As shown in Fig. 5, the dissolution run at 800 RPM had a significantly shorter dissolution time compared to runs at 30 and 150 RPM. However, increasing the speed to 1200 RPM did not further reduce the dissolution time.

[0101] Fig. 6 shows DSC chart of chips before dissolution and after 5-hour and 6-hour dissolution periods. The small peak observed on the far right, at about 180 °C on the curve before dissolution, represents the EVOH peak. The peak is absent in the curves after 5 and 6 hours of dissolution, indicating that EVOH was removed from the multilayer structure during the dissolution process.

[0102] In another test, EVOH was extracted from K-Cups using DMSO at 75 °C with the high-shear impeller operated at 350 RPM or 0 RPM. The K-Cups were cut into rectangular 0.5"xl" (1.27cm><2.54 cm) chips. As shown in Table 1, operating the high-shear impeller at 350 RPM significantly enhances the dissolution of the plastic chips compared to no stirring.

[0103] Table 1. Mass of K-Cup chips before and after dissolution using DMSO at 75 °C.

[0104] Example 2. Dissolution of nylon from multilayer sausage wrapper packaging film by formic acid

[0105] Experimental procedure

[0106] The commercial multilayer sausage wrapper packaging film, with nylon as the barrier layer, was contacted with formic acid to selectively dissolve nylon from the multilayer structure. The results indicated that nylon was successfully dissolved by formic acid. The detailed experimental steps are as follows:

[0107] The labels on the commercial sausage wrapper were manually removed. The wrapper was then rinsed with deionized water to eliminate any post-consumer residues. Afterward, the wrapper was dried at 50 °C overnight. The dried sausage wrapper was cut into chips measuring approximately 20 mm * 10 mm using scissors.

[0108] One gram of the sausage wrapper chips was placed into a 50 mL three-neck flask containing 100 mL of 88% formic acid. The flask was heated in a water bath on a hotplate, and the temperature of the formic acid was maintained at 75 °C. The dissolution process was conducted at a stirring speed of 300 rpm using a magnetic stir bar. The experiment was performed under a nitrogen inert atmosphere and within a fume hood. The mass of the sample was measured every 30 minutes as a function of dissolution time. The process continued until the sample mass stabilized, indicating the complete dissolution of nylon. After dissolution, both the sausage wrapper remnants and the formic acid solution were collected and stored for further characterization.

[0109] Results

[0110] The sample mass was observed to decrease continuously with increasing dissolution time. After 4 hours, the mass stabilized, indicating the complete dissolution of nylon in formic acid. The sample mass was reduced by 20% over the 4-hour dissolution period.

[0111] After dissolution, the collected formic acid solution was placed in a beaker and left under a fume hood at room temperature to allow evaporation. The solution was reduced to approximately 10 mL. This 10 mL solution was analyzed using Nuclear Magnetic Resonance (NMR) to detect the presence of dissolved nylon. For companson. formic acid containing virgin nylon was also analyzed using NMR. The NMR spectra of virgin nylon in formic acid and extracted nylon from the sausage wrapper in formic acid are show n in Fig. 7. The spectrum of the extracted nylon closely matched that of the virgin nylon, confirming that nylon was successfully dissolved in formic acid. Example 3. Dissolution of EVOH from regrind multilayer plastic packaging sheet by formic acid

[0112] Experimental procedure

[0113] The regrind multilayer plastic packaging sheet, with EVOH as the barrier layer, was contacted with formic acid to selectively dissolve EVOH from the multilayer structure. The results indicated that EVOH was successfully dissolved by formic acid. The detailed experimental steps are as follows:

[0114] The regrind multilayer sheet is composed of polyolefin outer layers and an EVOH barrier layer, wi th tie layers bonding them together. A microscopic image of the cross-section of the regrind multilayer sheet structure is presented in Fig. 8.

[0115] Five regrind multilayer plastic packaging sheets were immersed in 30 mL of 88% formic acid for dissolution at a temperature of 25 °C, with a stirring speed of 500 rpm. The mass change of the regrind multilayer sheets was recorded as a function of dissolution time. Microscopic images were captured each time the samples were removed for mass measurements.

[0116] Two additional experiments were conducted under the same dissolution conditions, except the temperatures were set to 50 °C and 75 °C, respectively. The remaining polyolefins, after the EVOH had dissolved, were collected for characterization.

[0117] Results

[0118] The weight percent of the regrind multilayer sheets as a function of dissolution time is shown in Fig. 9. At a dissolution temperature of 25 °C, the weight percent decreased steadily with increasing dissolution time, indicating the gradual dissolution of EVOH. After 4 hours of dissolution, the weight percent stabilized at approximately 89%, closely matching the calculated value for the regrind sheets excluding the EVOH layer, based on the density and thickness of each layer. This result indicates that EVOH was nearly completely dissolved in 88% formic acid within 4 hours at 25 °C with a stirring speed of 500 rpm.

[0119] For dissolution at higher temperatures of 50 °C and 75 °C, the weight percent also reached 89%, but stabilization occurred much faster, within 1.5 hours. These results indicate that at both 50 °C and 75 °C, the regrind multilayer sheets were successfully dissolved in 88% formic acid within 1.5 hours under a stirring speed of 500 rpm.

[0120] To verify the complete dissolution of EVOH, the cross-section of the regrind multilayer sheet was examined under a microscope. Representative microscopic images are shown in Fig. 10 for the regrind multilayer sheet dissolved under the conditions of 75 °C, 88% formic acid concentration, and a stirring speed of 500 rpm.

[0121] As the dissolution time increased, the EV OH layer gradually diminished and became visually undetectable after 1 hour. By 1.5 hours, the regrind multilayer sheet had separated into two distinct parts, with the tie layers still adhered to the polyolefin layers. This observation suggests that the EV OH layer was completely dissolved under these conditions.

[0122] Moreover, the remaining layer after the dissolution of the EV OH layer was analyzed using DSC to examine changes in composition. An undissolved regrind multilayer sheet was also analyzed for comparison. The DSC curves are presented in Fig. 11A-1 IB. A small peak at 189 °C in the melting curve of the undissolved regrind multilayer sheet corresponds to the melting temperature of EV OH. Similarly, a small peak at 163 °C in the crystallization curve corresponds to the crystallization temperature of EV OH. These peaks confirm the presence of EV OH in the regrind multilayer sheet. After dissolution under the conditions of 75 °C, 88% formic acid concentration, and a stirring speed of 500 rpm for 1.5 hours, both peaks disappeared from the DSC curves. This result indicates that the EVOH layer was completely dissolved.

[0123] Example 4. Dissolution of EVOH from regrind multilayer plastic packaging sheet by ethylene glycol

[0124] Experimental procedure

[0125] The regrind multilayer plastic packaging sheet, with EVOH as the barrier layer, was contacted with ethylene glycol to selectively dissolve EVOH from the multilayer structure. The results indicated that EVOH was successfully dissolved by ethylene glycol. The detailed experimental steps are as follows:

[0126] Similar to the dissolution of EVOH using formic acid, five regrind multilayer sheets were prepared and dissolved in ethylene glycol. The ethylene glycol used for dissolution had a concentration of 99%, with the process conducted at a temperature of 135 °C and a stirring speed of 500 rpm. The mass change of the regrind multilayer sheets was recorded as a function of dissolution time.

[0127] Results

[0128] The weight percent of the regrind multilayer sheets as a function of dissolution time is shown in Fig. 12. The weight percent decreased to 89% at 1.5 hours, after which the sample mass remained unchanged despite continued dissolution time. This result indicates that the dissolution of EVOH was completed within 1.5 hours under the conditions of 99% ethylene glycol concentration, 135 °C, and a stirring speed of 500 rpm.

[0129] Example 5. Dissolution of EVOH from Berry Global multilayer film by formic acid Experimental procedure

[0130] A typical five-layer commercial multilayer film was provided by Berry Global, Inc. (Evansville, IN, U.S.). This multilayer film comprises two low-density polyethylene (LDPE) outer layers, an EVOH barrier middle layer, and two maleic anhydride grafted linear low- density polyethylene (MA-g-LLDPE) tie layers, which bond the LDPE and EVOH layers into a cohesive multilayer structure with a total thickness of 60 pm. The film was cut into circular samples with a 1-inch (2.54 cm) diameter. The circular samples were placed in a 250 mL three-neck flask containing 50 mL of formic acid for EVOH dissolution. The stirring speed was maintained at 300 rpm. Dissolution experiments were conducted using three formic acid concentrations (88%, 50%, and 20%) and three temperatures (75 °C, 50 °C, and room temperature). The mass reduction of the multilayer film was measured every 30 minutes as a function of dissolution time until the mass stabilized, indicating the complete dissolution of EVOH.

[0131] Results

[0132] The dissolution times required for the multilayer film mass to decrease and stabilize under each condition are summarized in Table 2. These dissolution times indicate the time needed to completely dissolve EVOH from the Berry Global multilayer. The weight percent of dissolved EVOH was calculated based on the decreased mass of the multilayer film after dissolution.

[0133] Among these dissolution conditions, the combination of 88% formic acid concentration, 75 °C, and a stirring speed of 300 rpm showed the highest dissolution efficiency, achieving complete EVOH dissolution in 0.5 h. The dissolution efficiency dramatically decreased with decreasing formic acid concentration and dissolution temperature.

[0134] Table 2. Dissolution time and weight percent of dissolved EVOH in formic acid under varying solvent concentrations and dissolution temperatures.

[0135] To confirm the dissolution of EV OH. a multilayer film sample dissolved under the conditions of 88% formic acid concentration, 75 °C, and a stirring speed of 300 rpm was analyzed using DSC. For comparison, an undissolved multilayer film was also examined. The DSC cry stallization and melting curves are shown in Fig. 13A-13B.

[0136] In the undissolved multilayer film, two major peaks were observed in both the melting and crystallization curves, corresponding to LDPE and EVOH. The melting peak temperatures of LDPE and EVOH were 114 °C and 178 °C, respectively, while the crystallization peak temperatures were 100 °C and 153 °C. After dissolution, both the melting and crystallization peaks associated with EVOH disappeared, confirming that EVOH was completely dissolved from the Berry Global multilayer film by formic acid.

[0137] Example 6. Dissolution of nylon from Berry Global multilayer film by formic acid Experimental procedure

[0138] Another typical five-layer commercial multilayer film was provided by Berry Global, Inc. (Evansville, IN, U.S.), where nylon serves as the barrier layer instead of EVOH. The outer layers and tie layers are still LDPE and MA-g-LLDPE, respectively. This nylon-based multilayer film w as dissolved under the conditions of 88% formic acid concentration, 75 °C, and a stirring speed of 300 rpm to evaluate the ability' of formic acid to dissolve nylon from the multilayer film. The multilayer film samples, both before and after dissolution, were analyzed using DSC.

[0139] Results

[0140] The crystallization and melting curves are shown in Fig. 14A-14B. Peaks observed at 158 °C and 195 °C correspond to the crystallization and melting temperatures of nylon, respectively. These peaks were no longer detectable after the multilayer film was subjected to dissolution using formic acid. This result confirms that nylon was successfully dissolved by formic acid.

[0141] Example 7. Dissolution of barrier layers from several post-consumer multilayers by formic acid

[0142] Experimental procedure

[0143] Several common post-consumer multilayer products were collected and dissolved using formic acid. These products included a Dole fruit bottle, Dole fruit cup, coffee K-Cup, baby food tub, and pet food container. Images of these multilayer products are presented in Fig. 15.

[0144] Several square samples, each smaller than 10 mm x 10 mm, were cut from the multilayer products and dissolved in 30 mL of 88% formic acid at 75 °C with a stirring speed of 300 rpm for 4 hours. Cross-sectional images of the multilayer products were captured using a microscope both before and after dissolution to visually evaluate the removal of the barrier layers from the multilayer structures.

[0145] Results

[0146] The cross-sectional macroscopic images of these multilayer products are presented in Fig. 16, with arrows pointing to the barrier layers in the multilayer structures. After 4 hours of dissolution in 88% formic acid at 75 °C and a stirring speed of 300 rpm, the multilayer structures of all tested post-consumer products separated into two parts, and the barrier layers were no longer visible. This confirms that the barrier layers were successfully dissolved by formic acid.

[0147] Example 8. Additional experimental procedure for plastic film recovery by formic acid and characterization

[0148] Films used to seal the package were removed from Dole* fruit cup (Dole food Company, Thousand Oaks, CA) packaging. The empty cups were rinsed thoroughly using tap water, followed by rinsing with deionized (DI) water. The rims and thick bottoms of the cups were removed using scissors and discarded. The remaining plastic was cut into rectangular specimens measuring approximately 0.5" * 1" (1.27cm*2.54cm).

[0149] A total of ten grams, measured using a digital scale, of prepared rectangular specimens were added to a 500 mL round-bottom flask stabilized with a cork base. Separately, 150 mL of formic acid was measured using a 250 mL graduated cylinder, under a fume hood. The formic acid was then added to the flask, along with a magnetic stirring rod. The flask was placed on a stirring hot plate equipped with a round-bottom heating mantle. A condenser was attached to the flask, and the setup was sealed with a 2"x4" piece of Parafilm. Cooling water circulated through the condenser. The temperature was set to 50 °C, and the stirring speed was adjusted to 400 RPM for a duration of 4 hours.

[0150] A filter funnel was used to pour a solution into a beaker, retaining the undissolved material specimens in the flask. The specimens were removed, spread evenly on a glass pan, and left to dry overnight.

[0151] The beaker containing the filtered solution was placed on a stirring hot plate set to 65 °C and 450 RPM to concentrate the mixture. Once the volume was reduced to approximately 100 mL or less, the solution was transferred to a vacuum oven to remove any remaining liquid. The polymer residue at the bottom of the flask was collected and stored in a labeled bag.

[0152] The experiment was repeated under the following conditions: a. Dissolution times of 2 hours and 4 hours, keeping all other parameters constant. b. Plastic film specimen sizes of 0.5"x0.5" (1.27cmx f .27cm), with a dissolution time of 4 hours.

[0153] The recovered plastic film specimens from the 4-hour and 6-hour dissolution experiments were analyzed for ethylene-vinyl alcohol (EV OH) content using Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, and Nuclear Magnetic Resonance (NMR) spectroscopy which confirmed the presence of EV OH in the dissolved solution.

[0154] Experiments

[0155] Experiments #1 & #2

[0156] Dole fruit jars (Dole pic, Dublin, Ireland) were used as the MLP source. The jars were rinsed with water, dried, and cut into approximately 0.5"x0.5" (1.27cmx 1.27cm) chips using scissors, avoiding any labels on the outside of the jars.

[0157] The procedure followed the general protocol with minor variations: a. Two runs were performed with dissolution times of 2 hours and 4 hours, respectively, under mixing at 100 °C. b. The input MLP mass was 10 g for both runs. c. The input solvent volume was 150 mL for both runs. d. An anti-solvent was not used because the relatively low concentration prevented particle agglomeration. Instead, the samples were placed on a hot plate at 70 °C to concentrate to approximately 25 ml for both runs. e. After concentrating, the samples were placed into vacuum oven under full vac. at 70 °C overnight. f. Yields were calculated after samples were completely dried. g. FTIR spectroscopy and DSC were used to verify the presence of EV OH as the selectively recovered polymer.

[0158] The recovered mass was 0.2116 g for the 2-hour run and 0.2046 g for the 4-hour run. Given the similar yields for both run times, it is likely that the yield has plateaued. A shorter duration, such as 1 hour, may be sufficient. However, cross-sectional analysis indicates that approximately 5% of the total structure is EV OH. corresponding to 0.5 g of EV OH. This suggests that significantly longer run times could be employed to recover more EV OH, optimizing the balance between yield and run time.

[0159] Experiment #3

[0160] Used K-Cups (Keurig Dr Pepper Inc., Burlington, MA and Frisco, TX, U.S.) were collected as MLP waste. The aluminum and filters of the K-Cups were stripped out and the plastic containers were rinsed in DI water to remove residual coffee grounds and contaminants. The K-Cup plastic was cut into approximately 0.5"x0.5" (I.27cmxl.27cm) chips using scissors.

[0161] The procedure followed the general protocol with minor variations: a. The dissolution time was about 22 hours under mixing at 100 °C. b. The input MLP mass was 12.6 g. c. The input solvent volume was 120 mL. d. After dissolution, the mixture was filtered through an 1 1 pm Whatman filter paper to collect the EV OH solution and left the polyolefins atop the filter. e. The EV OH was recovered by slowly evaporating the solvent off at 50 °C overnight (approximately 18 hours). The recovered mass was 0.342g. f. FTIR spectroscopy, Raman spectroscopy, and DSC were used to verify the presence of EV OH as the selectively recovered polymer. Rheology was also done to compare to neat EV OH.

[0162] Experiment #4

[0163] Multilayer films supplied by Berry Global Inc. (Evansville, IN, U.S.) were used. The films were cut into strips ranging in size but were generally about 0.5"xl" (1.27cmx2.54cm).

[0164] The procedure followed the general protocol with minor variations: a. The dissolution time was about 47 hours under mixing at 70 °C. b. The input MLP mass was 3.0 g. c. The solvent was 70% ethanol, and the input volume was 120 mL. d. After dissolution, the mixture was filtered through an 11 pm Whatman filter paper to collect the EV OH solution and left the polyolefins atop the filter. e. The EVOH was recovered by slowly evaporating the solvent off at 50 °C overnight (approximately 18 hours). The recovered mass was 0.182 g. f. EVOH was confirmed by FTIR spectroscopy.

[0165] Experiment #5

[0166] Multilayer regrind sheets were supplied by Berry Global Inc. (Evansville, IN, U.S.).

[0167] The procedure followed the general protocol with minor variations: a. The dissolution time was about 20 hours under mixing at 100 °C. b. The input MLP mass was 30.68 g. c. The input solvent volume was 120 mL. d. After dissolution, the mixture was filtered through an 11 pm Whatman filter paper to collect the EVOH solution and left the polyolefins atop the filter. e. The EVOH was recovered by centrifuging the solution at 4000 RPM for 40 minutes and then 4500 RPM for 30 minutes. The top fraction was discarded, and the bottom fraction was slowly evaporated on a hot plate overnight at 50 °C. The recovered mass was 1.67 g. f. EVOH was confirmed by FTIR spectroscopy and DSC.

[0168] Experiment #6

[0169] Multilayer regrind sheets were supplied by Berry Global Inc. (Evansville, IN, U.S.).

[0170] The procedure followed the general protocol with minor variations: a. The dissolution time was about 1 hour under mixing at 100 °C. b. The input MLP mass was 14.5 g. c. The input solvent volume was 100 mL. d. After dissolution, the mixture was filtered through an 11 pm Whatman filter paper to collect the EVOH solution and left the poly olefins atop the filter. e. The solids were removed and vacuum dried overnight.

[0171] Experiment #7

[0172] Used K-Cups (Keurig Dr Pepper Inc., Burlington, MA and Frisco, TX, U.S.) were collected as MLP waste. The aluminum and filters of the K-Cups were stripped out and the plastic containers were rinsed in DI water to remove residual coffee grounds and contaminants. The K-Cup plastic was cut into approximately 0.5" x 0.5" (1.27 cm x 1.27 cm) chips using scissors.

[0173] The procedure followed the general protocol with minor variations: a. The dissolution time was about 23.5 hours under mixing at 100 °C. b. The input MLP mass was 11.4 g. c. The input solvent volume was 140 m . d. After dissolution, the mixture was filtered through an 11 pm Whatman filter paper to collect the EV OH solution and left the polyolefins atop the filter. e. The EV OH was recovered by precipitation through the addition of excess DI water. f. The solids were removed and vacuum dried overnight.

Claims

CLAIMSWhat is claimed is:

1. A method for recovering polymers from a multilayer polymeric material, the method comprising: contacting the multilayer polymeric material, the multilayer polymeric material comprising a first polymeric layer, a second polymeric layer, and a layer of a barrier material positioned between the first polymeric layer and the second polymeric layer, with a barrier solvent for a time and at a temperature to selectively dissolve the layer of barrier material, thereby forming a barrier-material solution, and separating the barrier-material solution from an undissolved first polymer layer and an undissolved second polymer layer.

2. The method of claim 1, wherein the barrier material comprises an ethylene vinyl alcohol (EV OH) or a polyamide (PA).

3. The method of claim 2, wherein the barrier solvent is selected from the group consisting of formic acid, acetic acid, dimethyl sulfoxide (DMSO), ethylene glycol, methanol, ethanol, and dimethylformamide (DMF).

4. The method of claim 2, wherein the barrier material comprises EV OH. and the barrier solvent comprises formic acid.

5. The method of claim 2, wherein the barrier material comprises EV OH, and the barrier solvent comprises DMSO.

6. The method of claim 2, wherein the barrier material comprises EV OH, and the barrier solvent comprises ethylene glycol.

7. The method of claim 2. wherein the barrier material comprises PA, and the barrier solvent comprises formic acid.

8. The method of any one of claims 1-7, wherein the first polymeric layer and / or the second polymeric layer comprises a polyolefin.

9. The method of claim 8 further comprising recovering a portion of the barrier material from the barrier-material solution.

10. The method of claim 9. wherein an anti-solvent is added to the barrier-material solution to recover the portion of the barrier material.

11. The method of claim 9, wherein the temperature of the barrier-material solution is reduced to recover the portion of the barrier material.

12. The method of claim 9, wherein the portion of the barrier material is recovered by a pressure-swing process.

13. The method of claim 8 further comprising recovering the undissolved first polymeric layer and / or the undissolved second polymer layer, optionally further comprising recovering a portion of the barrier material from the barrier-material solution.

14. The method of claim 13, wherein the first polymeric layer and / or the second polymeric layer comprise a polyolefin.

15. The method of claim 14, further comprising melting and extruding the first polymeric layer and / or the second polymeric layer without addition of solvent to yield a second recovered polymer.

16. The method of any one of claims 1-15, wherein the multilayer polymeric material is flexible.

17. The method of any one of claims 1-17. wherein the multilayer polymeric material is rigid.

18. The method of any one of claims 1-17, wherein the multilayer polymeric material is scrap or post-consumer waste.

19. The method of any one of claims 1-18, wherein the multilayer polymeric material is contacted with the barrier solvent at the temperature of about 20 °C to about 200 °C.

20. The method of any one of claims 1-19, wherein a shear force is applied to the multilayer polymeric material when contacting the multilayer polymeric material with the barrier solvent.

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