Coextruded HDPE and TPU films

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 producing the same, and a method for recycling the same. The HDPE / TPU multilayer sheets described herein comprise a functionalized HDPE (High Density Polyethylene). The methods described herein include co-extruding HDPE, functionalizing HDPE and TPU, and optionally thermally forming the HDPE / TPU multilayer sheet. The HDPE / TPU multilayer sheets described herein have enhanced adhesion and release properties, as well as cold resistance and impact resistance.

Description

Background Art Technical Field

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

[0002] Background Information

[0003] Dunnage pallets are designed to carry heavy machine tools. Dunnage is the name of a durable filling material used in cargo holds and containers to protect packaged goods from moisture, contamination and mechanical damage during transportation (for example, loose materials are placed under or wedged into objects carried by ships or rails to prevent damage due to abrasion or moisture, or to provide ventilation). Pallets are thermoformed into the shape of different machine parts. Therefore, such pallets need to withstand heavy loads under certain environmental conditions and require wear resistance at the surface. Typically, such pallets are prepared by extruding acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) films and then by an overmolding process, where the TPU film is overmolded on top of the ABS film surface and then thermoformed into a shape specific to the object to be carried (for example, tools).

[0004] The use of TPU in automotive cushioning applications is well established. Coextruded sheets of TPU-ABS offer excellent wear resistance, durability, oil resistance, and can protect parts with sharp edges. Despite these properties, TPU-ABS coextruded thermoformed products have some disadvantages. In addition to the higher cost of ABS resin, ABS's poor performance in cold weather and tendency to be brittle during impact can limit the life cycle of cushioning pallets.

[0005] Therefore, there is an urgent need for an alternative to TPU-ABS coextruded sheets for the production of dunnage pallets. This article provides a formulation of HDPE and TPU that was developed to produce a coextruded multilayer sheet with good adhesion between HDPE and TPU. Summary of the invention

[0006] The present invention is based on the groundbreaking discovery that functionalized HDPE can be used to improve its adhesion to TPU to produce coextruded multilayer sheets that can be used to produce highly resistant and recyclable dunnage pallets.

[0007] In one embodiment, the present invention provides a method for producing a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, which comprises coextruding HDPE and TPU, wherein the HDPE comprises unfunctionalized HDPE and functionalized HDPE, thereby producing a HDPE / TPU multilayer sheet.

[0008] In one aspect, the HDPE / TPU multilayer sheet comprises one or more layers of TPU and one or more layers of HDPE. In some aspects, the HDPE / TPU multilayer sheet comprises a layer of HDPE and a layer of TPU or a layer of HDPE and two layers of TPU. In some aspects, the functionalized HDPE comprises grafted maleic anhydride HDPE (HDPE-g-MA). In one aspect, the modified HDPE comprises about 0.1% to 1.5% g-MA. In some aspects, the modified HDPE comprises less than about 0.2% g-MA, about 1% g-MA or about 1.3% g-MA. In another aspect, the HDPE layer comprises about 0.1 wt % to 40 wt % HDPE-g-MA. In some aspects, the HDPE layer comprises about 5 wt %, about 10 wt %, about 15 wt % or about 30 wt % HDPE-g-MA. In one aspect, the HDPE is selected from the group consisting of HDPE, HDPE / NL, HDPE / 04 ​​and HDPE / 05. In another aspect, the TPU is a polyester or a polyether. In various aspects, the TPU is selected from the group consisting of EB 85A 10, EC 90A 10, E 688A 10, E 785A 10, E 685A 10, E 1180A 10, EC 85A 10, and E 1185A 10. In various aspects, the HDPE / TPU multilayer sheet comprises a combination of HDPE and TPU selected from the group consisting of HDPE / EB85A10, HDPE / EB 85A 10, HDPE / EC 90A 13, HDPE / E 688A 10, HDPE / E785A 10, HDPE / E1185A 10, HDPE-NL / EB 85A 10, HDPE-04 / EB 85A10, and HDPE-05 / EB 85A 10. In one aspect, coextruding the HDPE and TPU comprises heating the HDPE and TPU at a temperature in the range of about 150° C. to 250° C. In some aspects, the heating temperature is about 180° C., about 200° C., about 220° C., or about 240° C.

[0009] In another embodiment, the present invention provides a HDPE / TPU multilayer sheet obtained by any of the methods described herein.

[0010] In one aspect, compared with the HDPE / TPU multilayer sheet that does not include functionalized HDPE, the HDPE / TPU multilayer sheet has an increased adhesive strength. In some aspects, the adhesive strength increases with the increase of g-MA content. In another aspect, compared with the HDPE / TPU multilayer sheet that does not include functionalized HDPE, the HDPE / TPU multilayer sheet has an increased t-peel strength. In some aspects, the HDPE / TPU multilayer sheet is non-peelable. In one aspect, the sheet has a thickness in the range of about 1mm to 5mm. In another aspect, the sheet has cold resistance and / or impact resistance.

[0011] In another embodiment, the present invention provides a method of producing a dunnage pallet, the method comprising: producing a HDPE / TPU multilayer sheet, and thermoforming the HDPE / TPU multilayer sheet to produce a dunnage pallet.

[0012] In one aspect, producing the HDPE / TPU multilayer sheet comprises coextruding HDPE and TPU.

[0013] In another embodiment, the present invention provides a dunnage tray obtained by any of the methods described herein.

[0014] In one aspect, the pallet is cold-resistant and / or impact-resistant.

[0015] In one embodiment, the present invention provides a method for recycling HDPE / TPU pallets, the method comprising: (i) grinding the HDPE / TPU multilayer sheet pallet; 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 pallet.

[0016] In one aspect, the recycled HDPE-TPU / TPU multi-layer sheet has an adhesive strength and a t-peel strength comparable to that of a non-recycled HDPE-TPU / TPU multi-layer sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a graph showing the viscosity matching temperature of different TPU and HDPE.

[0018] Figure 2 It is a schematic diagram of the co-extrusion process.

[0019] Figure 3 Schematic diagram of a method for recycling HDPE / TPU coextruded sheets or thermoformed products.

[0020] Figure 4is a graph showing the adhesion of functionalized HDPE to different TPU grades.

[0021] Figure 5 is a graph showing the adhesion strength of different B 85 grades and C 90A 13 to functionalized HDPE (30% HDPE-g-MA / 70% HDPE).

[0022] Figure 6 is a graph showing the adhesion of different TPU chemistries to functionalized HDPE (ie, 30% HDPE-g-MA / 70% HDPE).

[0023] 7A to 7D is a photograph showing an AFM image showing the interface and the middle phase of the HDPE / TPU co-extruded system.

[0024] FIG. 8A to FIG. 8D is a photograph showing an AFM image of a co-extruded system containing recycled HDPE-05 / B 85A10 and B 85A10.

[0025] FIG. 9A to FIG. 9B is a graph showing the effect of aging on the adhesion between functionalized HDPE and TPU (B 85A 10).

[0026] Fig.10 is a graph showing the T-peel strength of thermoformed TPU (B85A10 and E785A10) / HDPE-04 coextruded sheets. DETAILED DESCRIPTION

[0027] The present invention is based on the groundbreaking discovery that functionalized HDPE can be used to improve its adhesion to TPU to produce coextruded multilayer sheets that can be used to produce highly resistant and recyclable dunnage pallets.

[0028] Before describing the present compositions and methods, it should be understood that the present invention is not limited to the specific compositions, methods and experimental conditions described, as such compositions, methods and conditions may vary. It should also be understood that the terminology used herein is only for the purpose of describing specific embodiments and is not intended to be limiting, as the scope of the present invention will be limited only by the appended claims.

[0029] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "the method" includes one or more methods and / or steps of the type described herein that will become apparent to those skilled in the art upon reading this disclosure and so forth.

[0030] All publications, patents, and patent applications mentioned in this specification are herein 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.

[0031] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those generally understood by those of ordinary skill in the art to which the present invention belongs. Although any methods and materials similar or equivalent to the methods and materials described herein may be used in the practice or testing of the present invention, it is to be understood that modifications and variations are included in the spirit and scope of the present disclosure. Preferred methods and materials are now described.

[0032] In one embodiment, the present invention provides a method for producing a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, which comprises coextruding HDPE and TPU, wherein the HDPE comprises unfunctionalized HDPE and functionalized HDPE, thereby producing a HDPE / TPU multilayer sheet.

[0033] As used herein, "high-density polyethylene," "HDPE," "polyethylene high density," or "PEHD" refers to a thermoplastic polymer produced from the monomer ethylene. When used for HDPE pipe, it is sometimes referred to as "alkathene" or "polyethylene." Due to its high strength-to-density ratio, HDPE is used to produce plastic bottles, corrosion-resistant pipes, geomembranes, and plastic lumber. HDPE is commonly recycled and has the number "2" as its plastic classification designator. HDPE is known for its high strength-to-density ratio. The density of HDPE ranges from 930 kg / m 3 Up to 970kg / m 3 . HDPE has little branching and has stronger intermolecular forces and tensile strength than low-density polyethylene (LDPE) (38 MPa versus 21 MPa). The strength difference exceeds the density difference, giving HDPE a higher specific strength. It is also stiffer and less transparent, and can withstand higher temperatures (120°C / 248°F for short periods of time). Unlike polypropylene, HDPE cannot withstand the autoclave conditions typically required. The absence of branching is ensured by appropriate choice of catalyst (e.g., Ziegler-Natta catalyst) and reaction conditions.

[0034] HDPE is resistant to many different solvents, so it cannot be bonded. The physical properties of HDPE can vary depending on the molding process used to make a particular sample; to some extent, the determining factor is the internationally standardized test methods used to identify these properties for a particular process. For example, in rotational molding, in order to determine the environmental stress cracking resistance of a sample, the notched constant tensile load test (NCTL) is used. Due to these desirable properties, pipes constructed from HDPE are very suitable for drinking water and wastewater (storm water and sewage).

[0035] HDPE applications are varied and include, but are not limited to, ropes, disposable suits; nonwoven HDPE fabrics, plastic mailing envelopes, flexible HDPE pipes, corrugated HDPE pipes installed in storm drains, outdoor furniture, bottle boxes, toys and playground equipment, clear plastic bags; blown film shopping bags with handles, strong oil-resistant bottles, jerry cans, 3D printer filaments, arena plates (hockey plates), backpack frames, ballistic plates, banners, bottle caps, boats, chemical containers, chemical-resistant pipes, coaxial cable inner insulators, conduit protectors for electrical or communication cables, corrosion protection for steel pipes, electrical and pipe boxes, far infrared lenses, fireworks, folding chairs and tables, food storage containers, vehicle fuel tanks, geomembranes for hydraulic applications (e.g., canal and embankment reinforcements), geothermal heat transfer piping systems, heat-resistant firework mortars,

[0036] House protection membranes (tyvek), hovercraft (the material is too heavy and dense for such craft, but is still occasionally used), ionizing radiation shielding, laundry detergent jugs, shoe lasts, microwave telescope windows, milk jugs, natural gas distribution piping systems, pipes for fluid, slurry and gas purposes, plastic bags, plastic bottles suitable for recycling or reuse, orthopedics (bone and facial reconstruction), drinking water mains, tree root barriers, shampoo bottles, sewage mains, ski tracks and boxes, stone paper, storage sheds, swimming pool fixtures, track control mats, telecommunications conduit, water pipes for domestic water supply and agricultural processes, wood plastic composites (using recycled polymers). HDPE has a wide range of applications; for applications that fall within the performance range of other polymers, it is usually economical to choose to use HDPE.

[0037] In one aspect, the HDPE is selected from the group consisting of HDPE, HDPE / NL, HDPE / 04 ​​and HDPE / 05.

[0038] As used herein, the terms "HDPE", "HDPE / NL", "HDPE / 04" and "HDPE / 05" refer to various types of HDPE having different functionalities and / or properties such as density, melt flow index (MFI) and melting temperature. The different properties of the HDPE described herein are summarized in Table 1.

[0039] Table 1: HDPE properties

[0040]

[0041] "Thermoplastic polyurethane" or "TPU" is any of a class of polyurethane plastics that possess a variety of properties including elasticity, transparency, oil, grease and abrasion resistance. Technically, they are thermoplastic elastomers composed of linear segmented block copolymers consisting of hard and soft segments. TPU is a block copolymer composed of an alternating sequence of hard and soft segments or domains formed by the reaction of (1) a diisocyanate with a short-chain diol (a so-called chain extender) and (2) a diisocyanate with a long-chain diol. A large number of different TPUs can be produced by varying the ratios, structures and / or molecular weights of the reacting compounds. This allows polyurethane chemists to fine-tune the structure of the polymer to obtain the desired final properties of the material.

[0042] TPU resins consist of linear polymer chains with a block structure. This chain contains relatively long low-polarity segments (called soft segments) alternating with shorter high-polarity segments (called hard segments). The two types of segments are linked together by covalent bonds so that they actually form block copolymers. The miscibility of hard and soft segments in TPU depends on the difference in their glass transition temperatures (Tg), which appear at the beginning of micro-Brownian segment motion and can be identified by dynamic mechanical spectra. For immiscible TPUs, the loss modulus spectrum usually shows a double peak, each peak belonging to the Tg of one component. If the two components are miscible, the TPU is characterized by a single broad peak, which is located between the positions of the two original Tg peaks of the pure components.

[0043] The polarity of the hard blocks creates a strong attraction between them, resulting in a high degree of aggregation and order in this phase, forming crystalline or pseudo-crystalline regions located in a soft and flexible matrix. Depending on the polarity and molecular weight of the flexible chain, production conditions, etc., this so-called phase separation between the two blocks can be more or less important. The crystalline or pseudo-crystalline regions act as physical crosslinks, which explains the high elasticity level of TPU, while the flexible chains will give the polymer elongation properties. However, these "pseudo-crosslinks" disappear under the action of heat, so classic extrusion, injection molding and calendering processing methods are applicable to these materials. Therefore, TPU waste can be reprocessed.

[0044] TPU has many applications, including automotive dashboards, casters, power tools, sporting goods, medical devices, drive belts, footwear, inflatable rafts and various extruded film, sheet and profile uses. TPU is also a common material in flexible housings for devices such as mobile phones and keyboard protectors. It is well known that TPU is used in wire and cable sheathing, hoses and tubing, adhesives and textile coating applications, and as an impact modifier for other polymers. It is also used in high-performance films, such as high-impact resistant glass structures.

[0045] TPU is a thermoplastic elastomer used in fused filament deposition (FFD) 3D printing. Since it does not warp and does not require a primer, TPU is an ideal filament for 3D printers when the object needs to be flexible and elastic. Since TPU is a thermoplastic, it can be melted by the 3D printer's extruder, printed, and then cooled back to a resilient solid. TPU powder is also used in other 3D printing processes such as selective laser sintering (SLS) and 3D inkjet printing. It is also used in large vertical injection molding machines or extrusion molding machines to print directly without the need for intermediate filament extrusion or powder preparation steps. Commercially available TPU has high wear resistance, low temperature performance, high shear strength, high elasticity, transparency, oil resistance, and grease resistance.

[0046] Based on the soft segment chemistry, currently available TPUs can be divided into two main categories: polyester-based TPUs (mainly derived from adipate esters) and polyether-based TPUs (mainly based on tetrahydrofuran (THF) ethers).

[0047] In one aspect, the TPU is a polyester or a polyether. In various aspects, the TPU is selected from the group consisting of EB 85A10, EC 90A 10, E688A 10, E 785A 10, E 685A 10, E 1180A 10, E C85A 10, and E 1185A 10.

[0048] As used herein, the terms "EB 85A 10", "EC 90A 10", "E 688A 10", "E 785A 10", "E685A 10", "E1180 A 10", "EC 85A 10" and "E1185A 10" refer to various types of TPUs having different formulations. The different formulations of the TPUs described herein are summarized in Tables 2-6.

[0049] Table 2: E1180A10 formulation

[0050]

[0051] Table 3: E785A10 formulation

[0052]

[0053] Table 4: EB85A10 formulation

[0054]

[0055] Table 5: EC85A10 formulation

[0056]

[0057] Table 6: E685A10 formulation

[0058]

[0059] In various aspects, the HDPE / TPU multilayer sheet comprises a combination of HDPE and TPU selected from the group consisting of HDPE / EB 85A 10, HDPE / EB 85A 10, HDPE / EC 90A 13, HDPE / E 688A 10, HDPE / E 785A 10, HDPE / E 1185A 10, HDPE-NL / EB 85A 10, HDPE-04 / EB 85A 10, and HDPE-05 / EB 85A 10.

[0060] The present invention provides a method for producing a HDPE / TPU multilayer sheet. "HDPE / TPU multilayer sheet" or "HDPE / TPU multilayer film" refers to a composite plastic material comprising one or more layers of HDPE and / or TPU, wherein one layer is stacked on top of another layer. 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. These layers may alternate between HDPE and TPU in any order.

[0061] Traditionally, TPU and HDPE do not adhere to each other, but the addition of functionalized HDPE improves the interfacial adhesion between the two. Much work has been done to improve the adhesion between HDPE containing polar polymers. In most cases, the improvement of HDPE adhesion focuses on functionalizing HDPE to reduce the polarity difference at the interface. HDPE grafted with functional groups such as maleic anhydride, alkylated maleic anhydride and / or amines adheres better to TPU than pure HDPE. In addition, the coextrusion process also improves interfacial adhesion due to tensile and compressive flow, which helps reactive species penetrate the interface.

[0062] As used herein, the term "functionalized HDPE" refers to a HDPE polymer modified with functional groups to change its properties (eg, improve its adhesion to TPU). In some aspects, the functionalized HDPE includes grafted maleic anhydride HDPE (HDPE-g-MA).

[0063] The method described herein includes coextruding HDPE and TPU. "Coextrusion" means extruding HDPE and TPU together to form an extrudate composed of different layers of HDPE and TPU respectively by combining molten HDPE and TPU layers.

[0064] In one aspect, the HDPE / TPU multilayer sheet comprises one or more layers of TPU and one or more layers of HDPE.

[0065] In some aspects, the HDPE / TPU multilayer sheet comprises 1, 2, 3, 4 or more layers of HDPE and 1, 2, 3, 4 or more layers of TPU. In one aspect, the HDPE / TPU multilayer sheet comprises a layer of HDPE and a layer of TPU.

[0066] In another aspect, the HDPE / TPU multilayer sheet comprises a layer of HDPE and two layers of TPU. In various aspects, the HDPE layer is surrounded by two layers of TPU (e.g., a layer of TPU is arranged on the top of the HDPE layer and a layer of TPU is arranged below the HDPE layer).

[0067] In another aspect, the HDPE layer comprises a blend of unfunctionalized HDPE and functionalized HDPE.

[0068] The incorporation of functionalized HDPE in the HDPE / TPU multilayer sheet is partial, i.e., not all of the HDPE is modified to be functionalized HDPE, but a portion of the total amount of HDPE is functionalized. Therefore, the HDPE content in the HDPT / TPU multilayer sheet is a blend comprising unmodified (or unfunctionalized) HDPE and functionalized HDPE. The content of functionalized HDPE in the HDPT / TPU multilayer sheet can be measured as a ratio of functionalized HDPE: unfunctionalized HDPE, or as the total content of functionalized HDPE in the HDPT / TPU multilayer sheet. For example, the ratio of functionalized HDPE: unfunctionalized HDPE can be in the range of about 1:1000 to 1:20. Alternatively, the amount of functionalized HDPE can be measured as a percentage of modified HDPE relative to the total content of HDPE.

[0069] In one aspect, the modified HDPE comprises about 0.1% to 1.5% g-MA. In some aspects, the modified HDPE comprises less than about 0.2% g-MA, about 1% g-MA, or about 1.3% g-MA.

[0070] In another aspect, the HDPE layer comprises about 0.1 wt% to 40 wt% HDPE-g-MA.

[0071] In some aspects, the HDPE layer comprises about 5 wt%, about 10 wt%, about 15 wt%, or about 30 wt% HDPE-g-MA.

[0072] When co-extruding HDPE and TPU, the two polymers are fed into an extruder and heated at a temperature at least as high as the melting point of the polymers so that the polymers melt. Therefore, the co-extrusion step of the method described herein includes a heating step. To ensure melting of the polymers, the heating temperature is at least about 100°C and at most about 400°C. For example, the heating temperature is in the range of about 100°C-200°C, about 200°C-300°C, about 300°C-400°C, about 100°C-300°C, about 200°C-400°C, about 150°C-250°C, about 250°C-350°C, or about 150°C-300°C.

[0073] In one aspect, coextruding the HDPE and TPU comprises heating the HDPE and TPU at a temperature in the range of about 150° C. to 250° C. In some aspects, the heating temperature is about 180° C., about 200° C., about 220° C., or about 240° C.

[0074] In another embodiment, the present invention provides a HDPE / TPU multilayer sheet obtained by any of the methods described herein.

[0075] In one aspect, the HDPE / TPU multilayer sheet has increased bond strength compared to a HDPE / TPU multilayer sheet that does not include a functionalized HDPE.

[0076] As used herein, the term "adhesive strength" refers to a measure of the strength of the bond between two materials. This can be achieved by the load, stress, energy or work required to destroy the intermediate phase. Adhesive strength can be measured by: a tensile test, a conventional mechanical test that measures the resistance of a material to a gradually applied uniaxial strain; a peel test, a technique often used to measure the adhesive strength between two materials (different peel test configurations can be used by changing the crack opening angle); and / or interface fracture fundamental work (EWIF), a method derived from fundamental fracture work (EWF), which has been successfully used to determine the fracture behavior of many ductile polymer systems. As used herein, interfacial adhesive strength is characterized as a function of the concentration of TPU chemicals and functionalized HDPE in the layered system. In some aspects, adhesive strength increases with the increase of g-MA content.

[0077] In one aspect, the HDPE / TPU multilayer sheet has an increased adhesive strength compared to a HDPE / TPU multilayer sheet that does not contain a functionalized HDPE. In another aspect, the HDPE / TPU multilayer sheet has an increased t-peel strength compared to a HDPE / TPU multilayer sheet that does not contain a functionalized HDPE.

[0078] For example, a HDPE / TPU multilayer sheet having a HDPE layer containing about 30 wt% HDPE-g-MA has increased bonding strength compared to a HDPE / TPU multilayer sheet containing 0 wt%, about 5 wt%, about 10 wt%, or about 15 wt% HDPE-g-MA.

[0079] For example, a HDPE / TPU multilayer sheet having a HDPE layer containing about 30 wt% HDPE-g-MA has increased t-peel strength compared to a HDPE / TPU multilayer sheet containing 0 wt%, about 5 wt%, about 10 wt%, or about 15 wt% HDPE-g-MA.

[0080] In some aspects, the t-peel strength of the HDPE / TPU multilayer sheet is so strong that it is virtually impossible to peel the HDPE layer from the TPU layer regardless of the strength applied. In this case, the t-peel strength cannot be measured. In some aspects, the HDPE / TPU multilayer sheet is non-peelable.

[0081] The thickness of the sheet may vary depending on the thickness of each layer (HDPE and TPU, respectively) and depending on the number of layers (e.g., for a given thickness of one layer, a multilayer sheet comprising three layers may be thicker than a multilayer sheet comprising two layers). One polymer layer (e.g., a HDPE layer or a TPU layer) may have a thickness in the range of about 100 μm to 2 mm. For example, the polymer layer may 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 may include 2 or more layers and have a thickness of about 200 μm to 5 mm. For example, the HDPE / TPU multilayer sheet may 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 aspects, the sheet has a thickness in the range of about 1 mm to 5 mm. In one aspect, the sheet has a thickness of about 2 mm.

[0082] In another embodiment, the present invention provides a method of producing a dunnage pallet, the method comprising producing a HDPE / TPU multilayer sheet, and thermoforming the HDPE / TPU multilayer sheet to produce a dunnage pallet.

[0083] As used herein, the term "dungaree pallet" refers to a pallet designed for transporting, handling and / or processing parts or products for various applications. These pallets are specifically designed to protect the parts during transport, handling and / or processing.

[0084] In one aspect, the production of the HDPE / TPU multilayer sheet comprises coextruding HDPE and TPU. In another aspect, the production of the dunnage tray does not include overmolding. The method of using the HDPE / TPU multilayer sheet described herein does not require an injection molding step to produce the dunnage tray. Instead, the multilayer sheet is thermoformed, which allows the dunnage tray to be produced. During the thermoforming step, the HDPE / TPU multilayer sheet is heated to its softening point, and then the sheet is stretched and manipulated on a single-sided mold. It is then cooled to a desired shape (e.g., the shape of the product portion to be maintained in the dunnage tray).

[0085] In another embodiment, the present invention provides a dunnage tray obtained by any of the methods described herein.

[0086] In one aspect, the pallet is cold-resistant and / or impact-resistant.

[0087] "Cold resistance" means that the properties of the dunnage pallet (e.g., which reflect the properties of the HDPE / TPU multilayer sheet) will not change due to temperature changes, especially due to exposure of the pallet to low temperatures. For example, if the pallet is exposed to low temperatures, the adhesion strength and t-peel strength of the pallet will not change. "Change" means that the properties of the pallet either do not change, and change to a degree that is not sufficient to make the pallet unusable, or have properties that make it ineffective. "Low temperature" refers to temperatures below room temperature. For example, low temperature includes temperatures in the range of about -20°C to 20°C, for example, -20°C, -18°C, -16°C, -14°C, -12°C, -10°C, -8°C, -6°C, -4°C, -2°C, 0°C, 2°C, 4°C, 6°C, 8°C, 10°C, 12°C, 14°C, 16°C, 18°C ​​and 20°C.

[0088] "Impact resistance" means that if subjected to any kind of impact, the HDPE / TPU multilayer sheet does not have a tendency to become brittle, which would limit the life cycle of the sheet (and therefore limit the products derived therefrom, such as HDPE / TPU multilayer sheet dunnage pallets). Therefore, the impact-resistant HDPE / TPU multilayer sheets described herein and the dunnage pallets produced therefrom have an extended life cycle compared to conventional HDPE / TPU multilayer sheets and dunnage pallets (e.g., those formed without HDPE / TPU, where the HDPE is a blend of unfunctionalized HDPE and functionalized HDPE).

[0089] In one embodiment, the present invention provides a method for recycling HDPE / TPU pallets, the method comprising: (i) grinding the HDPE / TPU multilayer sheet pallet; 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 pallet.

[0090] As used herein, the term "recycling" refers to converting preformed materials into base materials or elements that can then be used to produce "recycled" materials. In the methods described herein, "recycling" HDPE / TPU dunnage pallets generally refers to converting previously formed ("preformed") HDPE / TPU dunnage pallets or materials (e.g., preformed HDPE / TPU multilayer sheets) into HDPE / TPU dunnage pallets or multilayer sheet fragments that can be used to produce recycled HDPE / TPU dunnage pallets or materials, such as recycled HDPE / TPU multilayer sheets.

[0091] Any previously formed HDPE / TPU dunnage pallet or multilayer sheet can be used as the preform material, including those used for a previously intended purpose or those not originally used for any intended purpose (i.e., virgin material, such as waste or unused commercial products, etc.). HDPE / TPU dunnage pallet or multilayer sheet scraps are a base material that can be used in the production of any HDPE / TPU dunnage pallet or multilayer sheet regardless of the type of HDPE / TPU combination from which it is derived.

[0092] The term "recycled" as used hereinafter in the phrase "recycled article" generally refers to the use of a previously formed ("preformed") object or material. In other words, any previously formed object or material may be used, including those used for a previously intended purpose or those not originally used for any intended purpose. In other words, for an HDPE / TPU article to be considered a "recycled HDPE / TPU article" as used herein, the only requirement is that it is a preformed object or material and is ready for use now. The recycled HDPE / TPU article may be in the form of a multilayer sheet or a thermoformed dunnage tray and any combination thereof.

[0093] As used herein, the term "grinding" of an HDPE / TPU article refers to any process applied to an 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 HDPE / TPU articles include, but are not limited to, grinding, compacting, compacting, grinding, crushing, extrusion, and the like. In various aspects, processing and / or grinding includes the use of a grinder, a processor, a shredder, a granulator, a crusher, a compactor, or a mill. In another aspect, processing of the HDPE / TPU article produces shredded HDPE / TPU article fragments. Increasing the density of the HDPE / TPU article or reducing the volume of the HDPE / TPU article (e.g., grinding) includes producing HDPE / TPU article fragments that are smaller in size than the initial HDPE / TPU sheet.

[0094] In one aspect, the recycled HDPE-TPU / TPU multi-layer sheet has an adhesive strength and a t-peel strength comparable to that of a non-recycled HDPE-TPU / TPU multi-layer sheet.

[0095] Given below are examples of coextruded HDPE / TPU multilayer sheets that are intended for use in the applications discussed. The following examples are provided to further illustrate embodiments of the present invention, but are not intended to limit the scope of the invention. Although they are typical methods that may be used, other procedures, methods or techniques known to those skilled in the art may also be used.

[0096] Example

[0097] Example 1

[0098] Materials and methods

[0099] Material

[0100] Table 7 lists the materials used in this paper.

[0101] Table 7 :

[0102]

[0103] Co-extrusion process

[0104] Coextrusion of HDPE and TPU was performed using a Collin extrusion line equipped with an ABA feed block. The composition of the coextruded layers in the film can be controlled by the volume melt flow of the polymers. To ensure uniform layer integrity, the processing temperature is determined based on the viscosity match of the two polymers when melted. A melt flow indexer is used to measure the apparent viscosity of both HDPE and TPU. Figure 1As shown in Figure 2, the viscosity matching temperature of different formulations of HDPE and TPU was evaluated. Figure 2 As shown, the coextrusion process allows the production of three-layer HDPE and TPU coextruded sheets. 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 by coextrusion technology. Table 8 lists the list of coextruded layered systems of HDPE / TPU produced.

[0105] Table 8. List of coextruded HDPE / TPU systems .

[0106]

[0107]

[0108] Recycling process

[0109] In order to develop a recycling process for extruded HDPE / TPU sheets, regrind was produced to produce sheets. This means that the HDPE / TPU coextruded sheet was processed three times to produce three regrinds, each time the regrind replaced the HDPE core layer with regrind, while keeping the same TPU layer as a limiting layer for the regrind instead of HDPE. Figure 3 The recycling process is described. Table 9 provides a list of the regrind material produced for the recycling study.

[0110] Table 9. List of produced HDPE / TPU regrind materials .

[0111] Regrinding materials definition TPU layer Core layer HDPE / TPU co-extruded sheet-R0 Produced sheets EB 85A 10 HDPE-05 1st regrind material - R1 Grinding of produced sheets EB 85A 10 R1 Second regrind material - R2 R1 grinding EB 85A 10 R2 3rd regrind material - R3 R2 grinding EB 85A 10 R3

[0112] Adhesion strength

[0113] Compression molding was performed on different HDPE / TPU systems to determine the HDPE and TPU pairs for coextrusion studies. Films of HDPE and TPU were compressed at a viscosity matching temperature determined by a melt flow indexer to prepare t-peel samples. Samples were prepared according to ASTM D1876 and tested in a mechanical testing machine. Similarly, the interfacial strength of the coextruded samples was also analyzed.

[0114] AFM (Atomic Force Microscope)

[0115] Standard AFM analysis was performed to observe the morphology at the interface of the coextruded sheets.

[0116] DSC (Differential Scanning Calorimetry)

[0117] DSC was performed on each of the coextruded sheets to understand the effect of the coextrusion process on their thermal transitions.

[0118] Mechanical properties

[0119] The abrasion loss of coextruded HDPE / TPU sheets was measured according to DIN53516.

[0120] Additionally, tensile strength was measured according to ASTM D412, and tear strength of the coextruded sheets was measured using ASTM D624.

[0121] Thermoforming

[0122] The coextruded samples were thermoformed on a Formech 508DT vacuum thermoformer. This was a process that produced approximately 300 mm 2 The temperature is adjusted to allow the material to form around the mold without melting out of the frame or tearing.

[0123] Example 2

[0124] Evaluation of interfacial strength of compression molded sheets

[0125] like Figure 4 As shown in Figure 1, the effect of the concentration of HDPE-g-MA in the blends of HDPE / HDPE-g-MA on the adhesion of different TPU grades was evaluated. It can be observed that the bond strength of non-functionalized HDPE and TPU is very low, which is expected due to the absence of polarity in HDPE. On the other hand, the bond strength increases with the increase of the content of HDPE-g-MA in the blend. At 30 wt% HDPE-g-MA content in the blend, E 785A 10 shows the highest bond strength. Although the adhesion of TPU to ABS is still stronger than that to functionalized HDPE, TPU and functionalized HDPE have considerable interfacial strength for use in padding applications.

[0126] The bond strength of various B 85 grades and C 90 grades was also tested. Figure 5 As shown, the t-peel strength of HDPE blends containing 30% HDPE-g-Ma with different TPUs was measured. The C 90A10 grade showed improved bond strength with the functionalized HDPE.

[0127] Example 3

[0128] Evaluation of interfacial strength of coextruded HDPE / TPU sheets

[0129] like Figure 6As shown, coextruded sheets of functionalized HDPE (i.e., 30% HDPE-g-MA / 70% HDPE) were evaluated for adhesion strength to different polyester and polyether grades. C 85A 10 showed the best adhesion strength. However, all TPU grades showed good t-peel strength with the functionalized HDPE.

[0130] Table 10 summarizes the T-peel strength of TPU / HDPE-g-MA (varying MA%) as a function of the adhesion strength of the coextruded sheets. Due to very strong adhesion, the samples with HDPE-05 and HDPE-04 were not peelable, so there is no t-peel data for these samples. Therefore, functionalized HDPE can also be used as the core layer of a coextruded system with TPU. 7A to 7D The interphase between the functionalized HDPE and TPU is very strong as observed in the AFM images shown.

[0131] Table 10. T-peel strength of maleic anhydride functionalized HDPE / TPU coextrusion system

[0132] Coextrusion system MA% (in HDPE-g-Mas) T peel strength (lbf / in) HDPE-NL <0.2 282.80±85.93 HDPE-04 1.0 TBD HDPE-05 1.3 347.67±48.85

[0133] Example 4

[0134] Evaluation of Adhesion of Coextruded TPU / HDPE-05 Recycled Sheets

[0135] Table 11 shows the t-peel strength of the recycled coextruded TPU / HDPE-05 sheets. All recycled coextruded sheets showed very good adhesion as reported in the table. It should be noted that the bond strength decreases with increasing number of recycling. This may be due to the reduction of reactive species in the recycled core layer of the coextruded system. However, the bond strength is higher than that of the extruded sheet. Therefore, all recycled systems maintained the bond strength very well. This is also attributed to the fact that FIG. 8A to FIG. 8D There is a clear interphase between the TPU layer and the recycled core layer as seen in the AMF image of Figure 5.

[0136] Table 11. T-peel strength of recycled HDPE-05 / TPU coextrusion system .

[0137]

[0138] Example 5

[0139] Evaluation of the effect of aging on the bond strength of HDPE / TPU

[0140] like FIG. 9A to FIG. 9BAs shown in Figure 1, the effect of aging in air on the bond strength of functionalized HDPE (HDPE-g-MA / HDPE blend) and EB 85A 10 was evaluated. The coextruded samples were placed in an oven at room temperature and 70°C for 7 days. The peel strength increased over time due to further diffusion of reactive species in the HDPE into the TPU. In addition, the increase in peel strength was higher when treated at 70°C. Similarly, the peel strength also increased when the samples were aged in hot water for 7 days. This further indicates that the coextruded samples do not lose adhesion over time. This phenomenon can be explained by allowing the use of less functionalized polymers in the formulation (such as FUSABOUND TM ), or provide additional benefits by delivering a premium product with excellent durability.

[0141] Example 6

[0142] Evaluation of the effect of thermoforming on bond strength

[0143] Table 12 reports the qualitative evaluation of the thermoformed samples. Fig.10 As shown in Figure 1, the T-peel strength of thermoformed samples of coextruded HDPE / TPU systems was evaluated. Due to the tensile stress-induced layer diffusion, the thermoformed samples showed good adhesion strength compared to the coextruded samples. This indicates that thermoforming will maintain good adhesion between the layers in the HDPE and TPU coextruded sheets.

[0144] Table 12 :

[0145]

[0146] Although the present invention has been described with reference to the above embodiments, it will be understood that modifications and variations are encompassed within the spirit and scope of the present invention. Accordingly, the present invention is limited only by the following claims.

Claims

1. A method for producing a high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheet, the method comprising coextruding HDPE and TPU, wherein the HDPE comprises unfunctionalized HDPE and functionalized HDPE, thereby producing a HDPE / TPU multilayer sheet.

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

4. The method of claim 1, wherein the functionalized HDPE comprises grafted maleic anhydride HDPE (HDPE-g-MA).

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

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

7. The method of claim 3, wherein the HDPE layer comprises about 0.1 wt% to 40 wt% HDPE-g-MA.

8. The method of claim 7, wherein the HDPE layer comprises about 5 wt%, about 10 wt%, about 15 wt%, or about 30 wt% HDPE-g-MA.

9. The method of 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 of claim 10, wherein the TPU is selected from the group consisting of EB 85A 10, EC 90A 10, E 688A 10, E 785A 10, E 685A 10, E 1180A 10, EC85A 10, and E 1185A 10.

12. The method of claim 1, wherein the HDPE / TPU multilayer sheet comprises a combination of HDPE and TPU selected from the group consisting of HDPE / EB 85A10, HDPE / EB 85A 10, HDPE / EC 90A 13, HDPE / E 688A 10, HDPE / E 785A 10, HDPE / E 1185A10, HDPE-NL / EB 85A 10, HDPE-04 / EB 85A 10, and HDPE-05 / EB 85A 10.

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

14. The method of claim 13, wherein the heating temperature is about 180°C, about 200°C, about 220°C, 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 multi-layer sheet according to claim 15, wherein the HDPE / TPU multi-layer sheet has increased bonding strength compared to a HDPE / TPU multi-layer sheet not comprising functionalized HDPE.

17. The HDPE / TPU multi-layer sheet according to claim 15, wherein the bonding strength increases with increasing g-MA content.

18. The HDPE / TPU multi-layer sheet according to claim 15, wherein the HDPE / TPU multi-layer sheet has increased t-peel strength compared to a HDPE / TPU multi-layer sheet not comprising a functionalized HDPE.

19. The HDPE / TPU multi-layer sheet according to claim 18, wherein the HDPE / TPU multi-layer sheet is non-peelable.

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

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

22. A method of producing a dunnage pallet, the method comprising: (i) producing high density polyethylene (HDPE) / thermoplastic polyurethane (TPU) multilayer sheets, and (ii) thermoforming the HDPE / TPU multilayer sheet, Thus a dunnage pallet is produced.

23. The method of claim 22, wherein producing the HDPE / TPU multilayer sheet comprises coextruding HDPE and TPU.

24. A dunnage pallet obtainable by a method according to any one of claims 22 to 23.

25. A dunnage pallet according to claim 24, wherein the pallet is cold and / or impact resistant.

26. A method for recycling high-density polyethylene (HDPE) / thermoplastic polyurethane (TPU) pallet, the method comprising: (i) Grinding HDPE / TPU multi-layer sheet pallet; as well as (ii) co-extruding the ground HDPE / TPU multilayer sheet and TPU to produce a recycled HDPE-TPU / TPU multilayer sheet, The HDPE / TPU dunnage tray is thus recycled.

27. The method of claim 26, wherein the recycled HDPE-TPU / TPU multi-layer sheet has an adhesive strength and a t-peel strength comparable to those of a non-recycled HDPE-TPU / TPU multi-layer sheet.

Images