Co-extruded film of HDPE and TPU

Abstract

The present invention provides a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, a dunnage tray comprising the HDPE / TPU multilayer sheet, a method for manufacturing the same, and a method for recycling the same. The HDPE / TPU multilayer sheet described herein contains functionalized HDPE. The methods described herein include co-extruding HDPE, functionalized HDPE, and TPU, and optionally thermoforming the HDPE / TPU multilayer sheet. The HDPE / TPU multilayer sheet described herein has enhanced adhesion and delamination properties, as well as cold resistance and impact resistance.

Description

Technical Field

[0001] The present invention generally relates to blends of HDPE and TPU, and more specifically to the coextrusion of multilayer sheets of HDPE and TPU.

Background Art

[0002] Dunnage trays are designed to carry heavy machine tools. Dunnage is the name for a durable stuffing material used to protect packed items from moisture, contamination, and mechanical damage in holds and containers during transportation (e.g., a material placed under or between objects carried by ship or rail to protect against wear or damage from moisture or to provide ventilation). The trays are thermoformed into the shapes of various machine parts. Thus, such trays need to withstand heavy loads under specific environmental conditions and require abrasion resistance on the surface. Conventionally, such trays are manufactured via the extrusion of acrylonitrile butadiene styrene (ABS) films and thermoplastic polyurethane (TPU) films, followed by an overmolding process in which the TPU film is overmolded on top of the ABS film surface, and then thermoformed into a shape specific to the object (e.g., appliance) to be carried.

[0003] The use of TPU in automotive dunnage applications is well established. TPU-ABS coextruded sheets provide excellent abrasion resistance, durability, oil resistance, and can protect parts with sharp edges. Despite these properties, the coextrusion thermoforming of TPU-ABS has several drawbacks. In addition to the high cost of the ABS resin, the poor performance of ABS in cold climates, and the tendency to be brittle upon impact can limit the life cycle of dunnage trays.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Accordingly, there is still an unmet need for an alternative to the co-extruded sheet of TPU-ABS for manufacturing the dunnage tray. Provided herein is a formulation of HDPE and TPU developed to produce a co-extruded multilayer sheet having good adhesion between HDPE and TPU.

Means for Solving the Problems

[0005] Summary of the Invention The present invention is based on the fundamental discovery that the adhesion to TPU can be improved using functionalized HDPE to produce a co-extruded multilayer sheet that can be used to manufacture a highly resistant and recyclable dunnage tray.

[0006] In one embodiment, the present invention provides a method for manufacturing a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, comprising co-extruding HDPE and TPU, wherein the HDPE comprises non-functionalized and functionalized HDPE, thereby producing an HDPE / TPU multilayer sheet.

[0007] In one embodiment, the HDPE / TPU multilayer sheet comprises one or more layers of TPU and one or more layers of HDPE. In some embodiments, the HDPE / TPU multilayer sheet comprises one layer of HDPE and one layer of TPU, or one layer of HDPE and two layers of TPU. In some embodiments, the functionalized HDPE comprises grafted maleic anhydride HDPE (HDPE-g-MA). In one embodiment, the modified HDPE comprises about 0.1 to 1.5% g-MA. In some embodiments, the modified HDPE comprises less than about 0.2% g-MA, about 1% g-MA, or about 1.3% g-MA. In other embodiments, the HDPE layer comprises about 0.1 to 40% by weight of HDPE-g-MA. In some embodiments, the HDPE layer comprises about 5, about 10, about 15, or about 30% by weight of HDPE-g-MA. In one embodiment, the HDPE is selected from the group consisting of HDPE, HDPE / NL, HDPE / 04 and HDPE / 05. In other embodiments, the TPU is polyester or polyether. In various embodiments, the TPU is selected from the group consisting of EB85A10, EC90A10, E688A10, E785A10, E685A10, E1180A10, EC85A10 and E1185A10. In various embodiments, the HDPE / TPU multilayer sheet comprises a combination of HDPE and TPU selected from the group consisting of HDPE / EB85A10, HDPE / EB85A10, HDPE / EC90A13, HDPE / E688A10, HDPE / E785A10, HDPE / E1185A10, HDPE-NL / EB85A10, HDPE-04 / EB85A10, and HDPE-05 / EB85A10. In one embodiment, the coextrusion of HDPE and TPU comprises heating HDPE and TPU at a temperature in the range of about 150°C to 250°C. In some embodiments, the heating temperature is about 180, about 200, about 220 or about 240°C.

[0008] In other embodiments, the present invention provides an HDPE / TPU multilayer sheet obtained by any one of the methods described within the present application.

[0009] In one aspect, the HDPE / TPU multilayer sheet has increased adhesion strength compared to an HDPE / TPU multilayer sheet that does not contain functionalized HDPE. In some aspects, the adhesion strength increases with an increase in the g-MA content. In other aspects, the HDPE / TPU multilayer sheet has increased T-peel strength compared to an HDPE / TPU multilayer sheet that does not contain functionalized HDPE. In some aspects, the HDPE / TPU multilayer sheet cannot be peeled off. In one aspect, the sheet has a thickness in the range of about 1 to 5 mm. In other aspects, the sheet is cold-resistant and / or impact-resistant.

[0010] In a further embodiment, the present invention provides a method for manufacturing a dunnage tray, comprising manufacturing an HDPE / TPU multilayer sheet and thermoforming the HDPE / TPU multilayer sheet, thereby manufacturing a dunnage tray.

[0011] In one aspect, manufacturing the HDPE / TPU multilayer sheet includes co-extruding HDPE and TPU.

[0012] In a further embodiment, the present invention provides a dunnage tray obtained by any one of the methods described herein.

[0013] In one aspect, the tray is cold-resistant and / or impact-resistant.

[0014] In one embodiment, the present invention provides a method for recycling an HDPE / TPU dunnage tray, comprising (i) grinding a dunnage tray of an HDPE / TPU multilayer sheet and (ii) co-extruding the ground HDPE / TPU multilayer sheet and TPU to produce a recycled HDPE-TPU / TPU multilayer sheet, thereby recycling the HDPE / TPU dunnage tray.

[0015] In one embodiment, the recycled HDPE-TPU / TPU multilayer sheet has an adhesion strength and a T-peel strength equivalent to those of an unrecycled HDPE-TPU / TPU multilayer sheet.

Brief Description of the Drawings

[0016]

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Embodiments for Carrying Out the Invention

[0017] Detailed Description of the Invention The present invention is based on the fundamental discovery that functionalized HDPE can be used to improve the adhesion to TPU in order to produce a coextruded multilayer sheet that can be used to manufacture highly resistant and recyclable dunnage trays.

[0018] Before describing the compositions and methods of the present application, it should be understood that the invention is not limited to the specific compositions, methods, and experimental conditions described, because such compositions, methods, and conditions can vary. It should also be understood that the terms used in the present application are for the purpose of describing specific embodiments only and are not intended to be limiting, because the scope of the present invention is limited only in the appended claims.

[0019] As used in this specification and the appended claims, the singular forms include plural references unless the context clearly dictates otherwise. Thus, for example, references to "a method" include one or more methods and / or steps described herein, which will be apparent to those skilled in the art upon reading this disclosure.

[0020] All publications, patents, and patent applications mentioned in this specification are hereby incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

[0021] Unless defined otherwise, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, modifications and variations are encompassed within the spirit and scope of the present disclosure. Preferred methods and materials are described herein.

[0022] In one embodiment, the present invention provides a method for manufacturing a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, which includes co-extruding HDPE and TPU, wherein the HDPE includes non-functionalized and functionalized HDPE, thereby manufacturing an HDPE / TPU multilayer sheet.

[0023] "High-density polyethylene", "HDPE", "polyethylene high density" or "PEHD", as used within this application, relates to a thermoplastic polymer manufactured from the monomer ethylene. It may be referred to as "alkasene" or "polysene" when used for HDPE pipes. HDPE, having a high strength-to-density ratio, is used in the manufacture of plastic bottles, corrosion-resistant pipes, geomembranes and plastic lumber. HDPE is usually recycled and has the number "2" as its resin identification code. HDPE is known for its high strength-to-density ratio. The density of HDPE ranges from 930 to 970 kg / m 3 . Since HDPE has little branching, it has stronger intermolecular forces and tensile strength than low-density polyethylene (LDPE) (38 MPa vs. 21 MPa). Since the difference in strength exceeds the difference in density, HDPE has a higher specific strength. It is also harder and more opaque and can withstand a somewhat higher temperature (120 °C / 248 °F for a short time). High-density polyethylene, unlike polypropylene, usually cannot withstand the autoclave conditions that are usually required. The lack of branching is ensured by appropriately selecting the catalyst (e.g., Ziegler-Natta catalyst) and reaction conditions.

[0024] Since HDPE is resistant to many different solvents, it cannot be adhered. The physical properties of HDPE can vary depending on the molding process used to produce a particular sample, and to some extent, the elements that specify are the internationally standardized test methods used to identify those properties for a particular process. For example, in rotational molding, a notched constant tensile load test (NCTL) is used to identify the environmental stress crack resistance of a sample. Because of these desirable properties, pipes made of HDPE are ideally applicable for drinking water and wastewater (rainwater and sewage).

[0025] HDPE has a wide variety of uses and is not limited to, ropes, disposable suits; HDPE non-woven fabrics, plastic envelopes, flexible HDPE pipes, corrugated HDPE pipe installations in rainwater drainage pipes, outdoor furniture, bottle crates, toys and play equipment, transparent plastic bags; inflation film shopping bags with handles, oil-resistant strong bottles, jerry cans, filaments for 3D printers, arena boards (pack boards), backpack frames, bulletproof plates, banners, bottle caps, boats, chemical containers, chemical-resistant pipes, internal insulators for coaxial cables, conduit protection devices for electrical or communication cables, corrosion protection for steel pipelines, boxes for electrical and plumbing work, far-infrared lenses, fireworks, folding chairs and tables, food storage containers, fuel tanks for vehicles, geomembranes for hydraulic applications (such as reinforcing canals and levees), geothermal transfer piping systems, heat-resistant fireworks mortar, housewrap (Tyvek), hovercraft (the material is too heavy and too dense for such a craft but is still sometimes used), ionizing radiation shields, washing detergent jugs, shoe molds, windows for microwave telescopes, milk jugs, natural gas distribution piping systems, pipes for fluids, slurries and gases, plastic bags, plastic bottles suitable for both recycling and reuse, reconstructive surgery (skeletal and facial reconstruction), main pipes for drinking water, root barriers, shampoo bottles, main pipes for sewage, rails and boxes for snowboards, stone paper, storage cabinets, equipment for swimming pools, track out control mats, communication ducts, water pipes for household water absorption and agricultural processes, wood plastic composites (utilizing recycled polymers). HDPE has a wide range of applications and for applications corresponding to the properties of other polymers, it is usually economical to select the use of HDPE.

[0026] In one aspect, the HDPE is selected from the group consisting of HDPE, HDPE / NL, HDPE / 04 and HDPE / 05.

[0027] As used herein, the terms "HDPE", "HDPE / NL", "HDPE / 04", and "HDPE / 05" relate to various types of HDPE having various functionalities and properties such as density, melt flow index (MFI), and melt temperature. The various properties of the HDPE described herein are summarized in Table 1.

[0028]

Table 1

[0029] "Thermoplastic polyurethane" or "TPU" is any class of polyurethane plastics having many properties including elasticity, transparency, and resistance to oil, grease, and abrasion. Technically, they are thermoplastic elastomers consisting of linear segmented block copolymers composed of hard segments and soft segments. TPU is a block copolymer consisting of an alternating arrangement of hard and soft segments or domains formed by the reaction of (1) a diisocyanate with a short-chain diol (so-called chain extender) and (2) a diisocyanate with a long-chain diol. By varying the ratio, structure, and / or molecular weight of the reaction compounds, a wide variety of different TPUs can be produced. This enables urethane chemists to fine-tune the structure of the polymer to the desired final properties of the material.

[0030] TPU resin consists of linear polymer chains in a block structure. Such chains alternately contain somewhat long low-polarity segments (referred to as soft segments) and shorter high-polarity segments (referred to as hard segments). Both types of segments are bonded together by covalent bonds, and they actually form a block copolymer. The miscibility between the hard segments and the soft segments in TPU depends on the difference in their glass transition temperatures (Tg) that occurs at the onset of micro-Brownian motion, which can be identified by the dynamic mechanical spectrum. For immiscible TPU, the loss modulus spectrum typically shows a double peak, each of which is assigned to the Tg of one component. When the two components are miscible, the TPU is characterized by a single broad peak located between the two original Tg peaks of the pure components.

[0031] The polarity of the hard parts creates strong attractive forces between them, which causes a high degree of aggregation and order in this phase, forming crystalline or pseudo-crystalline regions located in a soft and flexible matrix. This so-called phase separation between the two blocks may be more or less important depending on the polarity and molecular weight of the flexible chains, manufacturing conditions, etc. The crystalline or pseudo-crystalline regions act as physical cross-links, which is the cause of the high elastic level of TPU, while the flexible chains impart elongation properties to the polymer. However, since their "pseudo-cross-links" disappear under the influence of heat, conventional extrusion, injection molding, and calendering processes are applicable to these materials. As a result, TPU scraps can be reprocessed.

[0032] TPU has many applications, including automotive instrument panels, caster wheels, power tools, sports goods, medical devices, drive belts, footwear, inflatable rafts, and various extruded films, sheets, and profiles. TPU is also a popular material for flexible outer cases of devices such as mobile phones and as keyboard protectors. TPU is well known for use in wire and cable jacketing, in adhesives and textile coatings in hoses and tubes, and as an impact modifier for other polymers. It is also used in high-performance films, such as in highly impact-resistant glass structures.

[0033] TPU is a thermoplastic elastomer used in fused filament deposition (FFD) 3D printing. Due to its lack of warping and the need for no primer, it is an ideal filament for 3D printers when the object needs to be flexible and elastic. Since TPU is thermoplastic, it can be melted and printed by the extruder of a 3D printer and then cooled back into an elastic solid. TPU powder is also used for other 3D printing methods, such as selective laser sintering (SLS) and 3D inkjet printing. It is also used in large vertical injection or extrusion molding machines for direct printing without an intermediate step of filament extrusion or powder preparation. Commercially available TPU has high abrasion resistance, low-temperature performance, high shear strength, high elasticity, transparency, and oil and grease resistance.

[0034] Currently available TPU can be mainly divided into two groups, polyester-based TPU (mainly derived from adipic acid esters) and polyether-based TPU (mainly based on tetrahydrofuran (THF) ethers), based on the chemical properties of the soft segments.

[0035] In one aspect, the TPU is polyester or polyether. In various aspects, the TPU is selected from the group consisting of EB85A10, EC90A10, E688A10, E785A10, E685A10, E1180A10, EC85A10 and E1185A10.

[0036] As used within this application, the terms "EB85A10", "EC90A10", "E688A10", "E785A10", "E685A10", "E1180A10", "EC85A10" and "E1185A10" relate to various types of TPU having various formulations. The various formulations of the TPU described within this application are summarized in Tables 2-6.

[0037] [Table 2]

[0038] [Table 3]

[0039] [Table 4]

[0040] [Table 5]

[0041] [Table 6]

[0042] In various embodiments, the HDPE / TPU multilayer sheet comprises a combination of HDPE and TPU selected from the group consisting of HDPE / EB85A10, HDPE / EB85A10, HDPE / EC90A13, HDPE / E688A10, HDPE / E785A10, HDPE / E1185A10, HDPE-NL / EB85A10, HDPE-04 / EB85A10, and HDPE-05 / EB85A10.

[0043] The present invention provides a method for manufacturing an HDPE / TPU multilayer sheet. The "HDPE / TPU multilayer sheet" or "HDPE / TPU multilayer film" means a composite plastic material comprising one or more layers of stacked HDPE and TPU. For example, the composite plastic material may include one or more layers (e.g., 1, 2, 3, 4 or more layers) of HDPE and / or one or more layers (e.g., 1, 2, 3, 4 or more layers) of TPU. The layers can be alternating in any order between HDPE and TPU.

[0044] Conventionally, TPU and HDPE do not adhere to each other, but the addition of functional HDPE improves the interfacial adhesion between the two. There have been numerous studies on improving the adhesion between HDPE and polar polymers. In most cases, the improvement of HDPE adhesion focuses on functionalizing HDPE to reduce the polarity difference at the interface. Functional groups, such as maleic anhydride, alkylated maleic anhydride, and / or amine-grafted HDPE, adhere to TPU better than pure HDPE. Furthermore, the coextrusion process improves the interfacial adhesion due to the extensional flow and compression flow, which helps the reactive species to pass through the interface.

[0045] As used within the present application, the term "functionalized HDPE" relates to an HDPE polymer that has been modified by a functional group to change its properties, for example, to improve its adhesion to TPU. In some embodiments, the functionalized HDPE includes grafted maleic anhydride HDPE (HDPE-g-MA).

[0046] The method described within this application involves co-extruding HDPE and TPU. "Co-extruding" means extruding HDPE and TPU together and combining the layers of melted HDPE and TPU to form an extrudate composed of various layers of each of HDPE and TPU.

[0047] In one aspect, the HDPE / TPU multilayer sheet includes one or more layers of TPU and one or more layers of HDPE.

[0048] In some aspects, the HDPE / TPU multilayer sheet includes one, two, three, four or more layers of HDPE and one, two, three, four or more layers of TPU. In one aspect, the HDPE / TPU multilayer sheet includes one layer of HDPE and one layer of TPU.

[0049] In other aspects, the HDPE / TPU multilayer sheet includes one layer of HDPE and two layers of TPU. In various aspects, the HDPE layer is surrounded by two layers of TPU (e.g., one layer of TPU is on top of the HDPE layer and one TPU layer is beneath the HDPE layer).

[0050] In other aspects, the HDPE layer includes a blend of non-functionalized HDPE and functionalized HDPE.

[0051] The incorporation of functionalized HDPE into the HDPE / TPU multilayer sheet is partial, i.e., not all of the HDPE is modified to functionalized HDPE. Rather, only a portion of the total HDPE amount is functionalized. Thus, the content of HDPE in the HDPT / TPU multilayer sheet is a blend containing unmodified (or non-functionalized) HDPE and functionalized HDPE. The content ratio of functionalized HDPE in the HDPT / TPU multilayer sheet can be measured as the ratio of functionalized HDPE:non-functionalized HDPE or as the total content ratio functionalized in the HDPT / TPU multilayer sheet. For example, the ratio of functionalized HDPE:non-functionalized HDPE can be in the range of about 1:1000 to 1:20. Alternatively, the amount of functionalized HDPE can be measured as the percentage of modified HDPE compared to the total content of HDPE.

[0052] In one embodiment, the modified HDPE contains about 0.1 - 1.5% of g-MA. In some embodiments, the modified HDPE contains less than about 0.2% of g-MA, about 1% of g-MA, or about 1.3% of g-MA.

[0053] In other embodiments, the HDPE layer contains about 0.1 - 40% by mass of HDPE-g-MA.

[0054] In some embodiments, the HDPE layer contains about 5, about 10, about 15, or about 30% by mass of HDPE-g-MA.

[0055] When co-extruding HDPE and TPU, both polymers are fed into an extruder and heated to at least the height of the melting point of the polymers to melt the polymers. Accordingly, the co-extrusion step of the method described in the present application includes a heating step. To ensure melting of the polymers, the heating temperature is at least about 100°C and up to about 400°C. For example, the heating temperature ranges from about 100 - 200°C, about 200 - 300°C, about 300 - 400°C, about 100 - 300°C, about 200 - 400°C, about 150 - 250°C, about 250 - 350°C, or about 150 - 300°C.

[0056] In one embodiment, the co-extrusion of HDPE and TPU includes heating HDPE and TPU at a temperature in the range of about 150°C - 250°C. In some embodiments, the heating temperature is about 180, about 200, about 220, or about 240°C.

[0057] In other embodiments, the present invention provides an HDPE / TPU multilayer sheet obtained by any one of the methods described in the present application.

[0058] In one embodiment, the HDPE / TPU multilayer sheet has increased adhesion strength compared to an HDPE / TPU multilayer sheet that does not contain functionalized HDPE.

[0059] As used herein, the term "adhesion strength" relates to a measure of how strong the bond is between two materials. This can be done in terms of the load, stress, energy, or work required to break the interface. Adhesion strength can be measured by tensile testing (a conventional mechanical test that measures the resistance of a material to the gradually applied uniaxial strain), peel testing (a technique frequently used to measure the adhesion strength between two materials (various configurations of peel tests can be used by varying the crack opening angle)), and / or the Essential Work of Interfacial Fracture (EWIF) (a method derived from the Essential Work of Fracture (EWF) methodology used to adequately characterize the fracture behavior of many ductile polymer systems). As used herein, the interfacial adhesion strength was characterized depending on the chemical nature of the TPU and the concentration of the functionalized HDPE in the layered system. In some embodiments, the adhesion strength increases with an increase in the g-MA content.

[0060] In one embodiment, the HDPE / TPU multilayer sheet has an increased adhesion strength compared to an HDPE / TPU multilayer sheet that does not contain functionalized HDPE. In other embodiments, the HDPE / TPU multilayer sheet has an increased T-peel strength compared to an HDPE / TPU multilayer sheet that does not contain functionalized HDPE.

[0061] For example, an HDPE / TPU multilayer sheet having an HDPE layer containing about 30 wt% HDPE-g-MA has an increased adhesion strength compared to an HDPE / TPU multilayer sheet containing 0 wt%, about 5 wt%, about 10 wt%, or about 15 wt% HDPE-g-MA.

[0062] For example, an HDPE / TPU multilayer sheet having an HDPE layer containing about 30 wt% HDPE-g-MA has an increased T-peel strength compared to an HDPE / TPU multilayer sheet containing 0 wt%, about 5 wt%, about 10 wt%, or about 15 wt% HDPE-g-MA.

[0063] In some embodiments, the T-peel strength of the HDPE / TPU multilayer sheet is so strong that, regardless of the applied strength, the HDPE layer cannot be substantially peeled from the TPU layer. In such cases, the T-peel strength cannot be measured. In some embodiments, the HDPE / TPU multilayer sheet cannot be peeled.

[0064] The thickness of the sheet can vary depending on the thickness of each layer (of the individual HDPE and TPU) and on the number of layers (e.g., for one layer of a particular thickness, a multilayer sheet containing three layers can be thicker than a multilayer sheet containing two layers). A single layer of polymer (e.g., an HDPE layer or a TPU layer) can have a thickness in the range of about 100 μm to 2 mm. For example, the polymer layer can have a thickness of about 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1,000 μm, 1,250 μm, 1,500 μm, 1,750 μm, or 2,000 μm. The HDPE / TPU multilayer sheet can include two or more layers and can have a thickness in the range of about 200 μm to 5 mm. For example, the HDPE / TPU multilayer sheet can have a thickness of about 200 μm, 400 μm, 500 μm, 600 μm, 750 μm, 800 μm, 1,000 μm, 1,250 μm, 1,500 μm, 1,750 μm, 2,000 μm, 2,500 μm, 3,000 μm, 3,500 μm, 4,000 μm, 4,500 μm, or 5,000 μm. In some embodiments, the sheet has a thickness in the range of about 1 to 5 mm. In one embodiment, the sheet has a thickness of about 2 mm.

[0065] In a further embodiment, the present invention provides a method for manufacturing a dunnage tray, the method comprising manufacturing an HDPE / TPU multilayer sheet and thermoforming the HDPE / TPU multilayer sheet, thereby manufacturing a dunnage tray.

[0066] As used herein, the term "dunnage tray" relates to trays designed for the transport, handling, and / or processing of parts or products for various applications. These trays are designed to protect the parts, particularly during transport, handling, and / or processing.

[0067] In one aspect, manufacturing an HDPE / TPU multilayer sheet involves co-extruding HDPE and TPU. In other aspects, manufacturing the dunnage tray does not include overmolding. The methods described herein use an HDPE / TPU multilayer sheet and do not require an injection molding step to produce the dunnage tray. Instead, the multilayer sheet is thermoformed, thereby enabling the production of the dunnage tray. During the thermoforming step, the HDPE / TPU multilayer sheet is heated to its softening point and then stretched and manipulated across a mold on one side. It is then cooled into the desired shape (e.g., the shape of the parts of the product to be held within the dunnage tray).

[0068] In a further embodiment, the invention provides a dunnage tray obtained by any one of the methods described herein.

[0069] In one aspect, the tray is cold-resistant and / or impact-resistant.

[0070] "Cold-resistant" means that the properties of the dunnage tray (e.g., which reflect the properties of the HDPE / TPU multilayer sheet) do not change due to temperature changes, particularly when the tray is exposed to low temperatures. For example, the adhesion strength and T-peel strength of the tray do not change even when the tray is exposed to low temperatures. "Do not change" means that the properties of the tray do not change to the extent that they render the tray unusable or have properties that invalidate it. "Low temperature" means a temperature lower than room temperature. For example, low temperatures include temperatures in the range of about -20°C to 20°C, such as -20, -18, -16, -14, -12, -10, -8, -6, -4, -2, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20°C.

[0071] "Impact resistance" means that when exposed to any type of impact, the HDPE / TPU multilayer sheet does not have a tendency to embrittle that could limit the life cycle of the sheet (and thus the products derived therefrom, such as the dunnage tray of the HDPE / TPU multilayer sheet). Accordingly, the HDPE / TPU multilayer sheets and dunnage trays having impact resistance described herein have an extended life cycle compared to conventional HDPE / TPU multilayer sheets and dunnage trays (for example, those not formed using HDPE / TPU where HDPE is a blend of non-functionalized HDPE and functionalized HDPE).

[0072] In one embodiment, the present invention provides a method for recycling an HDPE / TPU dunnage tray, comprising: (i) grinding the dunnage tray of the HDPE / TPU multilayer sheet; and (ii) co-extruding the ground HDPE / TPU multilayer sheet and TPU to produce a recycled HDPE-TPU / TPU multilayer sheet, thereby recycling the HDPE / TPU dunnage tray.

[0073] The term "recycle" as used herein relates to converting a pre-formed material into a base material or element that can be used for the production of a "recycled" material. In the methods described herein, "recycling" an HDPE / TPU dunnage tray generally relates to converting a previously formed ( "pre-formed") HDPE / TPU dunnage tray or material (such as a pre-formed HDPE / TPU multilayer sheet) into a fragment of an HDPE / TPU dunnage tray or multilayer sheet that can be used for the production of a recycled HDPE / TPU dunnage tray or material, such as a recycled HDPE / TPU multilayer sheet.

[0074] Previously formed HDPE / TPU dunnage trays or multilayer sheets, including those that have been used for their intended purpose or otherwise not used for their intended purpose (i.e., unused materials such as scrap or commercially available products that have not been used), can be used as preformed materials. Fragments of HDPE / TPU dunnage trays or multilayer sheets are base materials that can be used in the manufacture of any HDPE / TPU dunnage tray or multilayer sheet, regardless of the type of HDPE / TPU combination from which they are derived.

[0075] The term "recycled", when used in the phrase "recycled article" within this application, generally relates to the use of previously formed ("preformed") objects or materials. In other words, any previously formed object or material can be used, including those that have been used for their intended purpose or otherwise not used for their intended purpose. In other words, the only requirement for an HDPE / TPU article to be considered a "recycled HDPE / TPU article" when used within this application is that it is a preformed HDPE / TPU object or material and is now usable. Recycled HDPE / TPU articles can be in the form of multilayer sheets or thermoformed dunnage trays, or any combination thereof.

[0076] As used herein, the term "crushing" an HDPE / TPU article refers to any process applied to the article that results in an increase in the density of the HDPE / TPU article, a decrease in the volume of the HDPE / TPU article, or a combination thereof. Examples of methods for increasing the density of an HDPE / TPU article include, without limitation, crushing, densification, compression, milling, shredding, squeezing, etc. In various embodiments, processing and / or crushing may involve the use of a crusher, processor, shredder, granulator, pulverizer, consolidator, or mill. In other embodiments, processing of the HDPE / TPU article results in shredded HDPE / TPU article pieces. Increasing the density of an HDPE / TPU article, or decreasing the volume of an HDPE / TPU article (e.g., crushing), involves producing pieces of the HDPE / TPU article that are smaller in size than the original HDPE / TPU pieces.

[0077] In one embodiment, the recycled HDPE-TPU / TPU multilayer sheet has an adhesion strength and a T-peel strength equivalent to that of an unrecycled HDPE-TPU / TPU multilayer sheet.

[0078] Examples discussing coextruded HDPE / TPU multilayer sheets contemplated for the uses discussed are provided below. The following examples are provided to further illustrate embodiments of the invention but are not intended to limit the scope of the invention. They are typically what can be used, but other procedures, methodologies, or techniques known to those skilled in the art can be used alternatively.

Examples

[0079] Example 1 Materials and Methods Materials Table 7 shows a list of the materials used herein.

[0080]

Table 7

[0081] Coextrusion Process The coextrusion of HDPE and TPU was carried out using a Collin extrusion line equipped with an ABA feed block. The composition of the coextruded layer in the film can be controlled by the volume melt flow of the polymers. To ensure the integrity of the homogeneous layer, the processing temperature is determined based on the viscosity match of the two polymers during melting. The apparent viscosities of both HDPE and TPU were measured using a melt flow indexer. As shown in Figure 1, the viscosity match temperatures were evaluated for various formulations of HDPE and TPU. Furthermore, as shown in Figure 2, the coextrusion process enabled the production of a three-layer coextruded sheet of HDPE and TPU. A three-layer system of TPU / HDPE / TPU with a composition of 15 / 70 / 15 (v / v) and a thickness of 2 mm was produced via the coextrusion technique. Table 8 shows a list of the produced HDPE / TPU coextruded layered systems.

[0082]

Table 8

[0083] Recycling process To develop a recycling process for the extruded HDPE / TPU sheet, shredded recycled materials were produced to manufacture the sheet. This means that the HDPE / TPU coextruded sheet was processed three times to produce three shredded recycled materials, and in each pass, the shredded recycled material replaced the core HDPE layer with the shredded recycled material while the same TPU layer was retained as the sealing layer for the shredded recycled material in place of HDPE. Figure 3 illustrates the recycling process. Table 9 provides a list of the shredded recycled materials produced for the recycling study.

[0084]

Table 9

[0085] Adhesion strength Various HDPE / TPU compression moldings were carried out to identify pairs of HDPE and TPU for coextrusion studies. Films of HDPE and TPU were compressed at the viscosity matching temperature identified by a melt flow indexer to prepare T-peel samples. Specimens were prepared according to ASTM D1876 and tested on a mechanical tester. Similarly, the coextruded samples were also analyzed for interfacial strength.

[0086] AFM (Atomic Force Microscope) Standard AFM analysis was performed to observe the morphology at the interface of the coextruded sheet.

[0087] DSC (Differential Scanning Calorimetry) DSC was performed on each coextruded sheet to understand the effect of the coextrusion process on their thermal transitions.

[0088] Mechanical properties The abrasion loss of the coextruded HDPE / TPU sheet was measured according to DIN53516.

[0089] Furthermore, the tensile properties were measured according to ASTM D412, and the tear strength of the coextruded sheet was measured using ASTM D624.

[0090] Thermoforming The coextruded samples were thermoformed on a Formech 508DT vacuum thermoforming machine. This is a small benchtop unit that can form samples of about 300 mm 2 The temperature was adjusted so that the material could be formed around the mold without melting out of the frame or being torn.

[0091] Example 2 Evaluation of the interfacial strength of the compression molded sheet As shown in Fig. 4, the influence of the concentration of HDPE-g-MA in the blend of HDPE / HDPE-g-MA on the adhesion of various TPU grades was evaluated. The adhesion strength between non-functionalized HDPE and TPU was observed to be very low, which was predicted due to the absence of polarity in HDPE. On the other hand, the adhesion strength increased with the increase in the HDPE-g-MA content in the blend. E785A10 showed the highest adhesion strength at a 30 wt% HDPE-g-MA content in the blend. The adhesion between TPU and ABS is even stronger than that with functionalized HDPE, but TPU and functionalized HDPE have significant interfacial strength for dunnage applications.

[0092] The adhesion strengths of various B85 grades and C90 grades were also tested. As shown in Fig. 5, the T-peel strengths of blends of 30% HDPE-g-Ma-containing HDPE with various TPUs were measured. The C90A13 grade showed improved adhesion strength with functionalized HDPE.

[0093] Example 3 Evaluation of the interfacial strength of co-extruded HDPE / TPU sheets As shown in Fig. 6, the adhesion strengths of co-extruded sheets of functional HDPE (i.e., 30% HDPE-g-MA / 70% HDPE) against various polyester and polyether grades were evaluated. C85A10 showed the best adhesion strength. However, all TPU grades showed good T-peel strength with functional HDPE.

[0094] The T-peel strengths of TPU / HDPE-g-MA (various MA%) in the adhesion strength of co-extruded sheets are summarized in Table 10. Samples using HDPE-05 and HDPE-04 had very strong adhesion and could not be peeled, so T-peel data for these samples were not available. Therefore, functionalized HDPE can also be used as the core layer in a co-extrusion system with TPU. The interface between functional HDPE and TPU was very strong as observed in the AFM images shown in Figs. 7A - 7D.

[0095]

Table 10

[0096] Example 4 Evaluation of the Adhesion of Recycled Sheets of Co - extruded TPU / HDPE - 05 Table 11 shows the T - peel strength of the recycled co - extruded TPU / HDPE - 05 sheets. As reported in the table, all the recycled co - extruded sheets showed very good adhesion. It is noted that the adhesion strength decreases with an increase in the number of recycling. This may be due to the decrease in reactive species in the recycled core layer of the co - extrusion system. However, the adhesion strength was higher than that of the sheet during extrusion. Therefore, the adhesion strength was well maintained in all the recycled systems. This is also due to the sharp interface between the TPU layer and the recycled core layer as can be seen in the AFM images of Figures 8A - 8D.

[0097]

Table 11

[0098] Example 5 Evaluation of the Effect of Aging on the Adhesion Strength of HDPE / TPU As shown in Figures 9A - 9B, the effect of aging in air on the adhesion strength between functional HDPE (HDPE - g - MA / HDPE blend) and EB85A10 was evaluated. The co - extruded samples were placed in an oven at room temperature and 70 °C for 7 days. Due to the further diffusion of reactive species in HDPE into TPU, the peel strength increases with time. Furthermore, when treated at 70 °C, the increase in peel strength is higher. Similarly, the peel strength also increased when the samples were aged in hot water for 7 days. This further shows that the co - extruded samples do not lose their adhesion over time. This phenomenon can provide additional benefits by allowing the use of less functional polymer (e.g., FUSABOUND (trademark)) in the formulation or by providing a superior product with exceptional durability.

[0099] Example 6 Evaluation of the Influence of Thermoforming on Adhesion Strength Table 12 reports the qualitative evaluation of the thermoformed samples. As shown in Figure 10, the T-peel strength of the thermoformed samples of the co-extruded HDPE / TPU system was evaluated. The thermoformed samples showed better adhesion compared to the samples during co-extrusion due to the diffusion of the layer induced by the elongation stress. This indicates that thermoforming maintains good adhesion between the layers in the co-extruded sheet of HDPE and TPU.

[0100] [Table 12]

[0101] Although the present invention has been described with reference to the above examples, it is understood that modifications and changes within the spirit and scope of the present invention are included. Therefore, the present invention is limited only by the following claims.

Claims

1. A method for manufacturing a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, comprising co-extruding HDPE and TPU, wherein the HDPE includes non-functionalized HDPE and functionalized HDPE, whereby an HDPE / TPU multilayer sheet is manufactured.

2. The method according to claim 1, wherein the HDPE / TPU multilayer sheet includes one or more layers of TPU and one or more layers of HDPE.

3. The method according to claim 2, wherein the HDPE / TPU multilayer sheet includes one layer of HDPE and one layer of TPU, or one layer of HDPE and two layers of TPU.

4. The method according to claim 1, wherein the functionalized HDPE includes grafted maleic anhydride HDPE (HDPE-g-MA).

5. The method according to claim 4, wherein the modified HDPE includes about 0.1 to 1.5% of g-MA.

6. The method according to claim 5, wherein the modified HDPE includes less than about 0.2% of g-MA, about 1% of g-MA, or about 1.3% of g-MA.

7. The method according to claim 3, wherein the HDPE layer includes about 0.1 to 40% by mass of HDPE-g-MA.

8. The method according to claim 7, wherein the HDPE layer includes about 5% by mass, about 10% by mass, about 15% by mass, or about 30% by mass of HDPE-g-MA.

9. The method according to claim 1, wherein the HDPE is selected from the group consisting of HDPE, HDPE / NL, HDPE / 04, and HDPE / 05.

10. The method according to claim 1, wherein the TPU is polyester or polyether.

11. The method according to claim 10, wherein the TPU is selected from the group consisting of EB85A10, EC90A10, E688A10, E785A10, E685A10, E1180A10, EC85A10 and E1185A10.

12. The method according to claim 1, wherein the HDPE / TPU multilayer sheet comprises a combination of HDPE and TPU selected from the group consisting of HDPE / EB85A10, HDPE / EB85A10, HDPE / EC90A13, HDPE / E688A10, HDPE / E785A10, HDPE / E1185A10, HDPE-NL / EB85A10, HDPE-04 / EB85A10, and HDPE-05 / EB85A10.

13. The method according to claim 1, wherein the coextrusion of HDPE and TPU comprises heating HDPE and TPU at a temperature in the range of about 150°C to 250°C.

14. The method according to claim 13, wherein the heating temperature is about 180, about 200, about 220 or about 240°C.

15. A high density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet obtained by the method according to any one of claims 1 to 14.

16. The HDPE / TPU multilayer sheet according to claim 15, having increased adhesion strength as compared to an HDPE / TPU multilayer sheet not containing functionalized HDPE.

17. The HDPE / TPU multilayer sheet according to claim 15, wherein the adhesion strength increases with an increase in the g-MA content.

18. The HDPE / TPU multilayer sheet according to claim 15, having increased T-peel strength as compared to an HDPE / TPU multilayer sheet not containing functionalized HDPE.

19. The HDPE / TPU multilayer sheet according to claim 18, wherein the HDPE / TPU multilayer sheet cannot be peeled off.

20. The HDPE / TPU multilayer sheet according to claim 15, wherein the sheet has a thickness in the range of about 1 to 5 mm.

21. The HDPE / TPU multilayer sheet according to claim 15, wherein the sheet has cold resistance and / or impact resistance.

22. A method for manufacturing a dunnage tray, comprising: (i) manufacturing a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, and (ii) thermoforming the HDPE / TPU multilayer sheet to thereby manufacture a dunnage tray.

23. The method according to claim 22, wherein manufacturing the HDPE / TPU multilayer sheet includes co-extruding HDPE and TPU.

24. A dunnage tray obtained by the method according to claim 22 or 23.

25. The dunnage tray according to claim 24, wherein the tray has cold resistance and / or impact resistance.

26. A method for recycling a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) dunnage tray, comprising: (i) pulverizing a dunnage tray of an HDPE / TPU multilayer sheet, and (ii) co-extruding the pulverized HDPE / TPU multilayer sheet and TPU to produce a recycled HDPE-TPU / TPU multilayer sheet to thereby recycle the HDPE / TPU dunnage tray.

27. The method according to claim 26, wherein the recycled HDPE-TPU / TPU multilayer sheet has an adhesion strength and a T-peel strength equivalent to those of an unrecycled HDPE-TPU / TPU multilayer sheet.

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