Polyethylene rotomolding composition having improved adhesion properties to polyurethane

Abstract

A rotomolding composition and a method of rotational molding are disclosed. The rotomolding composition can include (a) 85 wt. % to 99 wt. %, based on the total weight of the rotomolding composition, of a first particulate polyethylene composition having an average particle size of 300 microns to 1500 microns; and (b) 1 wt. % to 15 wt. %, based on the total weight of the rotomolding composition, of a second particulate polyethylene composition that includes 500 ppm to 5000 ppm, based on the total weigh of the second particulate polyethylene composition, of a transition metal stearate, and at least 100 parts per million (ppm), based on the total weight of the second particulate polyethylene composition, of an antioxidant, where the second particulate polyethylene composition has an average particle size of 300 microns to 1500 microns.

Description

[0001] POLYETHYLENE ROTOMOLDING COMPOSITION HAVING IMPROVED ADHESION PROPERTIES TO POLYURETHANE

[0002] TECHNICAL FIELD

[0003] The invention generally concerns a rotomolding composition that includes two particulate polyethylene compositions. In one aspect, a metal stearate can be used in at least one of the particulate compositions, which can improve the adhesion properties of the rotomolding composition to polyurethane.

[0004] BACKGROUND ART

[0005] Rotational molding, also known as rotomolding, is a process which is widely used to produce hollow plastic parts such as, for example, gasoline containers, garbage cans, agricultural storage vessels, septic tanks, sporting goods (e.g., kayaks or boats), etc. The process is undertaken by loading a charge of particulate plastic resin into the mold “shell” and then rotating the mold shell (usually on two axes) while heating it to a temperature above the melting point of the particulate plastic resin. The melted plastic flows through the mold shell cavity under the forces caused by the rotation. The rotation continues for a sufficient time to allow the molten plastic to cover the surface of the mold. The mold is then cooled to permit the plastic to solidify. Then the rotomolded article is removed from the mold.

[0006] Rotomolded polyethylene (PE) articles oftentimes have internal cavities. For example rotomolded PE coolers, totes, or containers include cavities. These cavities are then filled with insulation (e.g., polyurethane (PU) foam). Due to the differing polarity of PE and PU, there can be poor interfacial adhesion between the PE container surface and the PU foam. However, adequate adhesion is desired to ensure sufficient thermal insulation. As a result, the rotomolded PE compositions and / or the rotomolded PE articles obtained from the compositions are often treated with ozone or plasma to cause oxidation to the PE surface. This oxidation step then allows for interfacial bonding to dissimilar polymers like PU.

[0007] A disadvantage of ozone or plasma treatment of the PE is the complexity and costs associated with such treatments. Still further, such treatments can result in the use of excess energy and / or produce unwanted waste.

[0008] SUMMARY OF INVENTION

[0009] A discovery has been made that provides a solution to at least one or more of the aforementioned problems associated with rotomolding polyethylene compositions and ensuring sufficient adhesion between the rotomolded polyethylene article and a dissimilar polymer such as polyurethane. In one aspect, the solution leverages a discovery that transition metal stearates (e.g., manganese stearate, cobalt stearate, or iron stearate, or any combination or all thereof) can act as a pro-degradant when used in rotomolding compositions of the present invention. Without wishing to be bound by theory, it is believed that a transition metal stearate can catalyze the thermo-oxidative reactions occurring within the rotomolding polyethylene compositions of the present invention, which can facilitate the formation of polar oxygenated groups at a surface of a rotomolded article. This can lead to improved adhesion of the polyethylene surface of the rotomolded article and insulation such as polyurethane foam insulation. Notably, this improved PE-PU adhesion can be obtained without having to use the more traditional ozone or plasma surface treatment methods. Still further, it was also discovered that any one of or both of the rotomolding polyethylene compositions of the present invention can include antioxidants to increase the shelf-life of the rotomolding compositions without having a detrimental effect on the ability of the rotomolding compositions to form polar oxygenated groups at an inside surface of a rotomolded article.

[0010] In one aspect of the present invention, there is disclosed a rotomolding composition. The composition can include 85 wt. % to 99 wt. %, based on the total weight of the rotomolding composition, of a first particulate polyethylene composition and 1 wt. % to 15 wt. %, based on the total weight of the rotomolding composition, of a second particulate polyethylene composition. The first particulate polyethylene composition can include a melt index (12) of 0.5 to 10 grams / 10 minutes, as measured by ASTM D 1238 at 190°C using a 2.16 kg load, a density of 0.920 to 0.950 g / cc, as measured by ASTM D792, and / or an average particle size of 300 microns to 1500 microns. The second particulate polyethylene composition can include 500 ppm to 5000 ppm, based on the total weigh of the second particulate polyethylene composition, of a transition metal stearate, and at least 100 ppm, based on the total weight of the second particulate polyethylene composition, of an antioxidant. The second particulate polyethylene composition can include a high load melt index (121) of 2 to 20 grams / 10 minutes, as measured by ASTM D 1238 at 190°C using a 21.6 kg load, a density of 0.950 to 0.965 g / cc, as measured by ASTM D792, and / or an average particle size of 500 microns to 3000 microns. In one aspect, the polyethylene in the first particulate polyethylene composition can be stabilized polyethylene. The first particulate polyethylene composition can be stabilized with a primary antioxidant and / or a secondary antioxidant in an amount(s) of 250 ppm to 1500 ppm, by total weight of the first particulate polyethylene composition. In another aspect, the polyethylene in the second particulate polyethylene composition can be stabilized polyethylene. The second particulate polyethylene composition can be stabilized with the antioxidant and / or with a secondary antioxidant in an amount(s) of 250 ppm to 1500 ppm, by total weight of the first particulate polyethylene composition. In one aspect, the transition metal stearate can comprise a manganese stearate, a cobalt stearate, or an iron stearate, or any combination or all thereof. In yet another aspects, the second particulate polyethylene composition can comprise 2000 ppm to 3000 ppm, based on the total weigh of the second particulate polyethylene composition, of the transition metal stearate. In a preferred aspect, the transition metal stearate comprises manganese stearate. In another aspect, the first particulate polyethylene composition can have an average particle size of 300 microns to 700 microns, or preferably 400 microns to 600 microns, and the second particulate polyethylene composition can have an average particle size of 1200 microns to 1600 microns, or preferably 1300 microns to 1600 microns. In still another aspect, the rotomolding composition can include 90 wt. % to 99 wt. %, preferably 93 wt. % to 97 wt. %, based on the total weight of the rotomolding composition, of the first particulate polyethylene composition, and 1 wt. % to 10 wt. %, preferably 3 wt. % to 7 wt. %, based on the total weight of the rotomolding composition, of the second particulate polyethylene composition. In one preferred aspect, the first particulate polyethylene composition can have an 12 of 2 to 8 grams / 10 minutes, and a density of 0.933 to 0.942 g / cc, and the second particulate polyethylene composition can have an 121 of 2 to 10 grams / 10 minutes, and a density of 0.953 to 0.956 g / cc. In still another aspect, the average particle size of the first particulate polyethylene composition can be smaller than the average particle size of the second particulate polyethylene composition. In some aspects, the first and second particulate polyethylene compositions are mixed together to form a mixture. The mixture can then be added to a rotomolding tool and used to make a rotomolded article. In other aspects, the first particulate polyethylene composition is separated from the second particulate polyethylene composition (e.g., in separate containers), which can be helpful for using a drop box rotomolding technique where the two compositions can be added to the rotomolding tool at different time points. In an aspect of the present invention, the transition metal stearate can be capable of oxidizing and / or degrading the polyethylene in the second particulate polyethylene composition when the rotomolding composition is subjected to rotational molding and / or a temperature of 250°C to 400°C. In yet another aspect, the first particulate polyethylene composition can comprise at least 95 wt. % polyethylene, based on the total weight of the first particulate polyethylene composition, and the second particulate polyethylene composition can comprise at least 95 wt. % polyethylene, based on the total weight of the second particulate polyethylene composition. Also disclosed in the context of the present invention is a rotational molded article of manufacture. The article of manufacture can comprise or be formed of any one of the rotomolding compositions of the present invention. The article of manufacture can comprise an outer surface, an inner surface, and a volume defined at least partially by the inner surface. The inner surface can be at least partially oxidized and / or comprises carbonyl groups. In some aspects, a polyurethane (e.g., polyurethane foam) is in contact with at least a portion of the inner surface and / or is comprised in at least a portion of the volume. In one particular aspect, the inner surface of the article of manufacture can comprise (i) a carbonyl index of at least 0.35 and / or (ii) a polyurethane adhesion strength of at least 25.0 Ib-ft.

[0011] In yet another aspect of the present invention, there is disclosed a melt-blended polymeric composition comprising any one of the rotomolding compositions of the present invention. A surface of the melt-blended polymeric composition can be in contact with a polyurethane composition (e.g., a polyurethane foam). In one aspect, the melt-blended polymeric composition can have a surface having a carbonyl index of greater than 0, at least 0.1, at least 0.2, at least 0.3, at least 0.4, at least 0.5, at least 0.6, at least 0.7, at least 0.8, at least 0.9, or more or any range or number therein (e.g, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5., 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or more or any range or number therein). In some preferred aspects, the melt-blended polymeric composition can have a surface having a carbonyl index of at least 0.2 or preferably at least 0.35. In certain aspects, the melt-blended polymeric composition can have a polyurethane adhesion strength (Ib-ft) of greater than 0, at least 5, at least 10, at least 15, at least 20, at least 25, at least 30 Ib-ft, or more or any range or number therein (e.g., 01, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 Ib-ft, or more or any range or number therein). In certain aspects, the relationship between the carbonyl index and the adhesion strength are such that an increase in the carbonyl index can be associated with an increase in the adhesion strength, and / or an increase in the adhesion strength can be associated with an increase in the carbonyl index.

[0012] In still another aspect of the present invention, there is disclosed a method of making a rotomolded article of manufacture. The method can include subjecting any one of the rotomolding compositions of the present invention to rotational molding to obtain the article of manufacture. In one aspect, the rotational molding can be performed at a temperature of 250°C to 400°C. In another aspect, the produced rotomolded article of manufacture can comprise an outer surface, an inner surface, and a volume defined at least partially by the inner surface. In a particular aspect, the first particulate polyethylene composition and the second particulate polyethylene composition can be mixed together prior to subjecting the rotomolding composition to rotational molding. The mixture can then be added to a rotomolder to make a rotomolded article. In another aspect, the first particulate polyethylene composition and the second particulate polyethylene composition can be added to a rotomolder at separate times during the rotational molding process, such as by a drop box rotomolding method. By way of example, the first particulate polyethylene composition can be added to the rotomolder first followed by the addition of the second particulate polyethylene composition. Alternatively, the second particulate polyethylene composition can be added to the rotomolder first followed by the addition of the first particulate polyethylene composition. In a particular aspect, the method can include the use of a rotational mold drop box to allow the rotomolding composition to be rotationally molded into an article.

[0013] Other aspects or embodiments (aspects and embodiments can be used interchangeably) of the invention are discussed throughout this specification. Any aspects discussed with respect to one aspect of the invention applies to other aspects of the invention as well and vice versa. Each aspect described herein is understood to be aspects of the invention that are applicable to other aspects of the invention. It is contemplated that any aspect discussed herein can be combined with other aspects discussed herein and / or implemented with respect to any method or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

[0014] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

[0015] BRIEF DESCRIPTION OF DRAWINGS

[0016] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings. Figure 1A and IB ARM impact testing of CC3 (Control), IE1 (5% W555 MnSt2), and CE2 (5% W555). Compositions were rotationally molded for indicated cure times at 560°F oven temperature to 0. 125 inch thickness.

[0017] Figure 2A and 2B Inside mold color of CC3 (Control), IE1 (5% W555 MnSt2), and CE2 (5% W555). Compositions were rotationally molded for indicated cure times at 560°F oven temperature to 0. 125 inch thickness.

[0018] Figure 3 Outside mold color of CC3 (Control), IE1 (5% W555 MnSt2), and CE2 (5% W555). Compositions were rotationally molded for indicated cure times at 560°F oven temperature to 0. 125 inch thickness.

[0019] Figure 4 Surface FTIR spectra for the rotomolded compositions CC3 (Control), IE1 (5% W555 MnSt2), and CE2 (5% W555) at indicated cure times. Note the significant carbonyl peak growing at -1718 cm'1indicating surface oxidation.

[0020] Figure 5 PE-PU adhesion testing results for IE1 (5% W555 MnSt2) and CE2 (5% W555). Higher max load indicates stronger adhesion between PE-PU.

[0021] Figure 6A and 6B Photos of PE-PU adhesion testing samples after tensile testing. Figure 6A top, left to right: CE2 (5% W555) at 14 min, 18 min, and 22 min. Figure 6B left to right: IE1 (5% W555 MnSt2) at 14 min, 18 min, and 22 min.

[0022] Figure 7 provides a graph illustrating the carbonyl index (x-axis) relationship to the adhesion strength (Ib-ft) of IE1 (5% W555 MnSt2) and CE2 (5% W555) compositions.

[0023] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

[0024] DESCRIPTION OF EMBODIMENTS

[0025] A discovery has been made that provides a solution to at least one or more of the aforementioned problems associated with rotomolding polyethylene compositions. The solution can include the use of a transition metal stearate in either the first and / or second polyethylene compositions of the present invention. The transition metal stearate can help to oxidize a surface of an article of manufacture produced by any one of the rotomolding compositions of the present invention. In particular, and without wishing to be bound by theory, it is believed that a transition metal stearate can catalyze the thermo-oxidative reactions occurring within the rotomolding polyethylene compositions of the present invention, which can facilitate the formation of polar oxygenated groups at a surface (e.g., inside surface) of a rotomolded article. Notably, this can be done in the presence of antioxidants. A benefit of the compositions of the present invention is that they can help to improve adhesion of polyethylene surfaces of the rotomolded article to other polymeric materials (e.g., polyurethane materials such as foam insulation).

[0026] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

[0027] Definitions

[0028] The following includes definitions of various terms and phrases used throughout this specification.

[0029] “HDPE” refers to high density polyethylene, which generally has a density of greater or equal to 0.941 g / cm3, or for example, from 0.941 to 0.97 g / cm3. HDPE has a low degree of branching. HDPE may be produced using chromium / silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. HDPE, and the other polyethylenes described herein, typically contain additives.

[0030] “LDPE” refers to low density polyethylene, which is a polyethylene with a high degree of branching with long chains. Often, the density of a LDPE will range from 0.910 g / cm3to 0.940 g / cm3. LDPE is created by free radical polymerization under conditions of high ethylene pressure.

[0031] “LLDPE” refers to linear low density polyethylene, which is a polyethylene with significant numbers of short branches resulting from copolymerization of ethylene with at least one C3-12 a-olefin comonomer, e.g., butene, hexene or octene. Typically, LLDPE has a density in the range of 0.915 g / cm3to 0.925 g / cm3. In some embodiments, the LLDPE is an ethylene hexene copolymer, or an ethylene octene copolymer, or an ethylene butene copolymer. The amount of comonomer incorporated can be from 0.5 to 12 mole %, or in some embodiments from 1.5 to 10 mole %, and in other embodiments from 2 to 8 mole % relative to ethylene. LLDPE may be produced using a wide variety of catalysts, including Ziegler Natta catalysts and single site / metallocene catalysts, and in a wide variety of processes, including gas phase, slurry and solution processes.

[0032] “MDPE” refers to medium density polyethylene, which is a polyethylene with some branching and a density in the range of 0.926 g / cm3to 0.940 g / cm3. MDPE can be produced using chromium / silica catalysts, Ziegler-Natta catalysts or single site / metallocene catalysts and in a wide variety of processes, including gas phase, slurry and solution processes.

[0033] “VLDPE” refers to very low density polyethylene, which is a polyethylene with high levels of short chain branching with a typical density in the range of 0.88 g / cm3to 0.915 g / cm3. In some embodiments, VLDPE is a substantially linear polymer. VLDPE is typically produced by copolymerization of ethylene with short-chain alpha-olefins (e.g., 1 -butene, 1 -hexene, or 1 -octene). VLDPE is most commonly produced using metallocene catalysts in a solution process.

[0034] The term “stabilized polyethylene” broadly refers to a polyethylene (which may be a heterogeneous polyethylene or a homogeneous polyethylene) that contains a “stabilizer”' package to protect the polyethylene against degradation / oxidation during the rotomolding process. The stabilizer package can include a primary antioxidant (which can scavenge free radicals) and a secondary antioxidant (which can quench hydroperoxides).

[0035] The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0036] The terms “wt. %”, “% by weight”, “vol.%”, “% by volume”, “mol.%”, or “% by mol.” refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, which includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt. % of component.

[0037] The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and / or the specification includes any measurable decrease or complete inhibition to achieve a desired result.

[0038] The term “effective,” as that term is used in the specification and / or claims, means adequate to accomplish a desired, expected, or intended result.

[0039] The use of the words “a” or “an” when used in conjunction with any of the terms “comprising,” “including,” “containing,” or “having” in the claims, or the specification, may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one”.

[0040] The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0041] The rotomolding compositions of the present invention can “comprise”, “consist essentially of’, or “consist of’ particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phrase “consisting essentially of,” in one non-limiting aspect, a basic and novel characteristic of the rotomolding compositions of the present invention is that they can be rotomolded and at least one of their surfaces can have sufficient adhesion to other polymers (e.g., polyurethane polymers).

[0042] Rotomolding Compositions

[0043] The rotomolding compositions of the present invention may include i) 85 wt. % to 99 wt. % (e.g., 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt. % or any number or range therein), based on the total weight of the rotomolding composition, of a first particulate polyethylene composition having a melt index (12) of 0.5 to 10 grams / 10 minutes, as measured by ASTM D 1238 at 190°C using a 2.16 kg load; a density of 0.920 to 0.950 g / cc, as measured by ASTM D792; and an average particle size of 300 microns to 1500 microns; and ii) 1 wt. % to 15 wt. % (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 wt. % or any number or range therein), based on the total weight of the rotomolding composition, of a second particulate polyethylene composition comprising: 500 parts per million (ppm) to 5000 ppm, based on the total weight of the second particulate polyethylene composition, of a transition metal stearate; and at least 100 ppm, based on the total weight of the second particulate polyethylene composition, of an antioxidant, the second particulate polyethylene composition having: a high load melt index (121) of 2 to 20 grams / 10 minutes, as measured by ASTM D 1238 at 190°C using a 21.6 kg load; a density of 0.950 to 0.965 g / cc, as measured by ASTM D792; and an average particle size of 500 microns to 3000 microns.

[0044] In some aspects, the first particulate polyethylene composition in the rotomolding composition has a melt index (12) of at least equal to any one of, or between any two of 0.5, 1, 1.5, 2.0, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 grams / 10 minutes, as measured by ASTM D 1238 at 190°C using a 2.16 kg load. In some aspects, the first particulate polyethylene composition in the rotomolding composition has a density of at least equal to any one of, or between any two of 0.920, 0.921, 0.922, 0.923, 0.924, 0.925, 0.926, 0.927, 0.928, 0.929, 0.930, 0.931, 0.932, 0.933, 0.934, 0.935, 0.936, 0.937, 0.938, 0.939, 0.940,, 0.941, 0.942, 0.943, 0.944, 0.945, 0.946, 0.947, 0.948, 0.949, or 0.950 g / cc, as measured by ASTM D792. In some aspects, the first particulate polyethylene composition in the rotomolding composition has an average particle size of at least equal to any one of, or between any two of 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500 microns.

[0045] In some aspects, the second particulate polyethylene composition in the rotomolding composition has 500 to 5000 ppm or at least equal to any one of, or between any two of 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, or 5000 ppm of transition metal stearate, based on the total weight of the second particulate polyethylene composition. In some aspects, the second particulate polyethylene composition in the rotomolding composition has at least 100 ppm an antioxidant, based on the total weight of the second particulate polyethylene composition. The antioxidant can be a primary antioxidant (which can scavenge free radicals) or a secondary antioxidant (which can quench hydroperoxides), or a combination thereof. In some aspects, the second particulate polyethylene composition in the rotomolding composition has a high load melt index (121) of at least equal to any one of, or between any two of 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 grams / 10 minutes, as measured by ASTM D1238 at 190°C using a 21.6 kg load. In some aspects, the second particulate polyethylene composition in the rotomolding composition has a density of at least equal to any one of, or between any two of 0.950, 0.951, 0.952, 0.953, 0.954, 0.955, 0.960, 0.961, 0.962, 0.963, 0.964, or 0.965 g / cc, as measured by ASTM D792. In some aspects, the second particulate polyethylene composition in the rotomolding composition has an average particle size of at least equal to any one of, or between any two of 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 2050, 2100, 2150, 2200, 2250, 2300, 2350, 2400, 2450, 2500, 2550, 2600, 2650, 2700, 2750, 2800, 2850, 2900, 2950, or 3000 microns.

[0046] In some particular aspects, the rotomolding compositions of the present invention can include, based on the total weight of the rotomolding composition, at least 85 wt. %, 86 wt. %, 87 wt. %, 88 wt. %, 89 wt. %, 90 wt. %, 91 wt. %, 92 wt. %, 93 wt. %, 94 wt. %, 95 wt. %, 96 wt. % , 97 wt. %, 98 wt. %, or 99 wt.% of a first particulate polyethylene composition or any range or number therein. In some particular aspects, the rotomolding compositions of the present invention can include, based on the total weight of the rotomolding composition, at least 1 wt. %, 2 wt. %, 3 wt. %, 4 wt. %, 5 wt. %, 6 wt. %, 7 wt. %, 8 wt. %, 9 wt. %, 10 wt. %, 11 wt. %, 12 wt. %, 13 wt. %, 14 wt. %, or 15 wt.% of a second particulate polyethylene composition or any range or number therein.

[0047] In some aspects, the rotomolding compositions having PE in the first particulate polyethylene composition is stabilized polyethylene. In some aspects, the rotomolding compositions having PE in the second particulate polyethylene composition is stabilized polyethylene. Stabilized PE can include PE having a primary and / or a secondary antioxidant.

[0048] In some aspects, the first particulate polyethylene compositions may include 250 to 1500 ppm or at least equal to any one of, or between any two of 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, or 1500 ppm of a primary antioxidant and a secondary antioxidant based on the total weight of the rotomolding composition.

[0049] In some aspects, transition metal stearate in the second particulate polyethylene composition of the rotomolding composition may include manganese stearate, cobalt stearate, or iron stearate, or any combination thereof. In some aspects, the transition metal stearate is manganese stearate in the rotomolding composition.

[0050] In some aspects, the average particle size of the first particulate polyethylene composition is smaller than the average particle size of the second particulate polyethylene composition in a rotomolding composition.

[0051] 1. Polyethylene

[0052] Polyethylene is a commonly used plastic resin for the manufacture of rotomolded parts. Polyethylene copolymer (which is generally prepared by the copolymerization of ethylene with a C4to 10 alpha olefin in the presence of a chromium catalyst or a Ziegler Natta catalyst) is typically used, although it is also known to use polyethylene homopolymer. The alpha olefin comonomer produces “short chain branches” (SCB) in the copolymer. These SCB reduce the crystallinity of the copolymer (in comparison to a linear ethylene homopolymer) and the copolymers typically have improved impact resistance in comparison to homopolymers. These conventional polyethylenes may be referred to as “heterogeneous” in the sense that the polyethylene is actually a mixture of different polyethylene chains having significantly different molecular weights and comonomer distributions. Most notably, a conventional heterogeneous polyethylene generally contains three fractions: i) a low molecular weight fraction having a high comonomer content (or high level of SCB) - this fraction is often referred to as “wax” or “extractables”; ii) a very high molecular weight fraction having little or no comonomer this fraction is often referred to as “homopolymer”; and iii) a fraction of intermediate molecular weight and SCB content.

[0053] These conventional polyethylenes are well suited for rotomolding. For example, while not wishing to be bound by theory, it has been postulated that the high molecular weight “homopolymer” fraction may enhance the stiffness or modulus of the rotomolded part. More recently, homogeneous polyethylenes have become commercially available. These homogenous polyethylenes have a uniform (or narrow) molecular weight distribution and a uniform comonomer distribution. This, in turn, causes the homogeneous polyethylenes to have a well-defined melting point (in comparison to the heterogeneous polyethylenes which have a melting point “range”, or even multiple melting points). It is also known to use “homogeneous” polyethylene in a rotomolding process.

[0054] The polyethylene used in the first particulate polyethylene composition and / or the second particulate polyethylene composition of the present invention can be HDPE, LDPE, LLDPE, MDPE, and / or VLDPE, or blends thereof. The polyethylene can be a polyethylene copolymer or a polyethylene homopolymer or a blend thereof.

[0055] The polyethylene used in the first particulate polyethylene composition and / or the second particulate polyethylene composition can be stabilized polyethylene. In general, any stabilizer package that is currently used in a rotomolding application is potentially suitable for use with the compositions of the present invention. In some aspects, the stabilizer package can include a primary antioxidant and / or a secondary antioxidant. Non-limiting examples of primary antioxidants include hindered phenols, hydroxylamines, and / or lactones. Nonlimiting examples of secondary antioxidants include phosphites and phosphinites.

[0056] In some aspects, a Hindered Amine Light Stabilizer (HALS) can be used in the compositions of the present invention. Amounts can range from 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, or 3000 ppm, based on the total weight of the first and second particulate polyethylene compositions, respectively, or any number or range therein.

[0057] In some aspect, a zinc oxide can be used in the compositions of the present invention. Amounts can range from 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, or 5000 ppm, based on the total weight of the first and second particulate polyethylene compositions, respectively, or any number or range therein.

[0058] In some aspect, an ultralight violet (UV) light absorber can be used in the compositions of the present invention. Amounts can range from 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, or 5000 ppm, based on the total weight of the first and second particulate polyethylene compositions, respectively, or any number or range therein. In one aspect of the present invention, the stabilizer package can include: (1) from 250 to 1500 ppm of at least one primary antioxidant that includes a hindered phenol and / or a hydroxylamine; and (2) 100 to 1000 ppm of at least one secondary antioxidant that includes a phosphite, a phosphinite, 100 to 3000 ppm of a HALS, and 0 to 5000 ppm of zinc oxide.

[0059] Many other additives can be used in the compositions of the present invention, some of which are described in the Additives section below. The additives may be incorporated into the first and / or second particulate polyethylene compositions using mixing equipment such as an extruder, or internal batch mixer (also known as a banbury mixer). The additives may be added “neat” (i.e. directly to the resin); as a “masterbatch” (i.e. by premixing the additives with a small amount of polyethylene which is subsequently mixed with the bulk of the composition); or as “preblends” (i.e., mixtures of the additives).

[0060] 2, Antioxidants

[0061] The rotomold compositions of the present invention may include an antioxidant. In some aspects, rotomold compositions may include more than one antioxidant. In some aspects, antioxidants can be primary and / or secondary antioxidants. Non-limiting examples of antioxidants include alkylated mono-phenols (also described herein as “hindered phenol primary antioxidants”). Non-limiting examples of hindered phenols include 2,6-di-tert-butyl- 4-methylphenol; 2-tert-butyl-4,6-dimethylphenol; 2,6-di-tert- butyl-4-ethylphenol; 2,6-di- tert-butyl-4-n-butylphenol; 2,6-di-tert-butyl-4-isobutylphenol; 2,6-dicyclopentyl-4- methylphenol; 2-(alpha.-methylcyclohexyl)-4,6 dimethylphenol; 2,6-di- octadecyl-4- methylphenol; 2,4,6,-tricyclohexyphenol; and 2,6-di-tert-butyl-4- methoxy methylphenol. Suitable hindered phenolic antioxidants which can be used in embodiments of the disclosure, are sold under the trademarks IRGANOX® 1010 (CAS Registry number 6683-19-8) and IRGANOX 1076 (CAS Registry number 2082-79-3) by BASF Corporation.

[0062] In some embodiments, antioxidants can include alkylated hydroquinones. Nonlimiting examples of alkylated hydroquinones include 2,6-di-tert-butyl-4-methoxyphenol; 2,5-di-tert- butylhydroquinone; 2,5-di-tert-amyl-hydroquinone; and 2,6-diphenyl-4- octadecyloxyphenol .

[0063] Other non-limiting examples of antioxidants include thiodiphenyl ethers. Nonlimiting examples of thiodiphenyl ethers include: 2,2'-thio-bis-(6-tert-butyl-4- methylphenol); 2,2'-thio-bis-(4-octylphenol); 4,4'-thio-bis-(6-tertbutyl-3-methylphenol); and 4, 4'-thio-bis-(6-tert-butyl-2 -methylphenol).

[0064] In some aspects, an antioxidant can include alkylidenebisphenols. Non-limiting examples of alkylidenebisphenols can include 2,2'-methylene-bis-(6-tert-butyl-4- methylphenol); 2,2'- methylene-bis-(6-tert-butyl-4-ethylphenol); 2,2'-methylene-bis-(4- methyl-6-(alpha- methylcyclohexyl)phenol); 2,2'-methylene-bis-(4-methyl-6- cyclohexylphenol); 2,2'- methylene-bis-(6-nonyl-4-methylphenol); 2,2'-methylene-bis-(6- nonyl-4-methylphenol); 2,2'-methylene-bis-(6-(alpha-methylbenzyl)-4-nonylphenol); 2,2'- methylene-bis-(6-(alpha, alpha-dimethylbenzyl)-4-nonyl-phenol); 2,2'-methylene-bis-(4,6- di-tert-butylphenol); 2,2'-ethylidene-bis-(6-tert-butyl-4-isobutylphenol); 4,4'-methylene-bis- (2,6-di-tert-butylphenol); 4,4'-methylene-bis-(6-tert-butyl-2-methylphenol); l,l-bis-(5-tert- butyl-4-hydroxy-2- methylphenol)butane 2,6-di-(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4- methylphenol; l,l,3-tris-(5-tert-butyl-4-hydroxy-2-methylphenyl)butane; l,l-bis-(5-tert-butyl- 4-hydroxy-2- methylphenyl)-3-dodecyl-mercaptobutane; ethylene glycol-bis-(3,3,-bis-(3'- tert-butyl-4'- hydroxyphenyl)-butyrate)-di-(3-tert-butyl-4-hydroxy-5-methylpenyl)- dicyclopentadiene; di- (2-(3 '-tert-butyl -2 'hydroxy-5 'methylbenzyl)-6-tert-butyl-4- methylphenyl)terephthalate; and other phenolics such as monoacrylate esters of bisphenols such as ethylidene bis-2,4-di-t- butylphenol monoacrylate ester.

[0065] In certain aspects, antioxidants can include benzyl compounds. Non-limiting examples of benzyl compounds include: l,3,5-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-2,4,6- trimethylbenzene; bis-(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide; isooctyl 3,5-di-tert-butyl- 4-hydroxybenzyl-mercaptoacetate; bis-(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)dithiol- terephthalate; l,3,5-tris-(3,5-di-tert-butyl-4,10 hydroxybenzyl)isocyanurate; l,3,5-tris-(4- tert- butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate; dioctadecyl 3,5-di-tert-butyl-4- hydroxybenzylphosphonate; calcium salt of monoethyl 3, 5 -di -tertbutyl -4- hydroxybenzylphosphonate; and l,3,5-tris-(3,5-dicyclohexyl-4- hydroxybenzyl)isocyanurate.

[0066] Non-limiting examples of an acyl aminophenol antioxidant can include: 4-hydroxy- lauric acid anilide; 4-hydroxy-stearic acid anilide; 2,4-bis-octyhnercapto-6-(3,5-tert-butyl-4- hydroxyanilino)-s-triazine; and octyl- N-(3,5-di-tert-butyl-4-hydroxyphenyl)-carbamate.

[0067] Non-limiting examples of other antioxidants can include esters of beta-(5-tert-butyl- 4-hydroxy-3-methylphenyl)-propionic acid with monohydric or polyhydric alcohols. Nonlimiting examples of such compounds include: methanol; diethyleneglycol; octadecanol; triethyleneglycol; 1,6-hexanediol; pentaerythritol; neopentylglycol; tris -hydroxy ethyl isocyanurate; tridiethyleneglycol; and dihydroxy ethyl oxalic acid diamide. In embodiments of the disclosure, a primary antioxidant is selected from amides of beta-(3,5-di-tert-butyl-4- hydroxyphenol)-propionic acid, such as for example, N,N'-di-(3,5- di-tert-butyl-4- hydroxyphenylpropionyl)-hexamethylendiamine ; N,N'-di-(3 ,5 -di-tert-butyl- 4- hydroxyphenylpropionyl) trimethylenediamine; and N,N'-di(3,5-di-tert-butyl-4- hydroxyphenylpropionyl) -hydrazine .

[0068] Non-limiting examples of other antioxidants can include phosphites and phosphonites (also described herein as “phosphorus containing secondary antioxidants”), such as, for example, triphenyl phosphite; diphenylalkyl phosphites; phenyldialkyl phosphites; tris (nonyl -phenyl)phosphite [WESTON® 399, available from SI Group]; phosphorous acid, mixed 2,4-bis(l,l-dimethylpropyl)phenyl and 4-( 1 , 1- dimethylpropyl)phenyl triesters [WESTON 705, CAS Reg. No. 939402-02-5, available from SI Group]; trilauryl phosphite; trioctadecyl phosphite; distearyl pentaerythritol diphosphite; tris(2,4-di-tert- butylphenyl)phosphite [IRGAFOS® 168, available from BASF]; diisodecyl pentaerythritol diphosphite; 2,4,6-tri-tert-butylphenyl-2-butyl-2-ethyl-l,3-propanediol phosphite; bis(2,4-di- tert-butyl-6-methylphenyl) ethyl phosphite [IRGAFOS 38, available from BASF]; 2, 2', 2"- nitrilo[triethyltris(3,3'5,5'-tetra-tert-butyl-l,r-biphenyl- 2,2'-diyl) phosphite [IRGAFOS 12, available from BASF]; bis(2,4-di-tert- butylphenyl)pentaerythritol diphosphite tristearyl sorbitol triphosphite; tetrakis(2,4-di-tert- butylphenyl)4,4'-biphenylene diphosphonate; 6-[3- (3 -tert-butyl -4-hydroxy-5- methylphenyl)propoxy]-2,4,8, 10-tetra-tert-butyldibenzo[d,f] [1,3,2] dioxaphospepin [SUMILIZER® GP]; bis(2,4,6-tri-tert-butylphenyl) pentaerythritol diphosphate; bis(2,4- dicumylphenyl)pentaerythritol diphosphate; distearyl pentaerythritol diphosphate; diisodecyl pentaerythritol diphosphate; bis(2,4 di-tert-butylphenyl) pentaerythritol diphosphite [UETRANOX® 626, available from SI Group]; bis(2,6-di-tert- butyl-4-methylpenyl) pentaerythritol diphosphite; bisisodecyloxy-pentaerythritol diphosphite; bis(2,4-di-tert-butyl-6-methylphenyl) pentaerythritol diphosphite; bis(2,4,6-tri- tert- butylphenyl) pentaerythritol diphosphite; tetrakis(2,4-di-tert-butylphenyl)4,4'- bipheylene-diphosphonite [IRGAFOS P-EPQ, available from BASF]; bis(2,4- dicumylphenyl)pentaerythritol diphosphite [DOVERPHOS® S9228-T or DOVERPHOS S9228-CT] and P-EPQ® (CAS Reg. No. 119345-01-06) a commercially available diphosphonate; or a mixture thereof. In embodiments of the disclosure, a secondary antioxidant is selected from DOVERPHOS LGP-11, DOVERPHOS LGP-12 and DOVERPHOS LGP-12LV. In some embodiments, alkylphenol free, polymeric polyphosphites, can be used. Non-limiting examples of which are disclosed in U.S. Pat. No. 8,563,637.

[0069] Antioxidants can also include hydroxylamines and amine oxides. Non-limiting examples of hydroxylamines and amine oxides can include N,N-dibenzylhydroxylamine; N,N- diethylhydroxylamine; N,N-dioctylhydroxylamine; N,N-dilaurylhydroxylamine; N,N- ditetradecylhydroxylamine; N,N-dihexadecylhydroxylamine; N,N- dioctadecylhydroxylamine ; N-hexadecy-l-N-octadecylhydroxylamine; N-heptadecyl-N- octadecylhydroxylamine; and N,N-dialkylhydroxylamine derived from hydrogenated tallow amine. The analogous amine oxides are also suitable. A commercially available example of hydroxylamine which may be used in embodiments of the disclosure is the N,N- di(alkyl)hydroxylamine sold as IRGASTAB® 042 (by BASF) and which is reported to be prepared by the direct oxidation of N,N - di (hydrogenated) tallow amine.

[0070] In embodiments an antioxidant can include a nitrone. Non-limiting examples of nitrones include N-benzyl-alpha-phenyl nitrone; N-ethyl-alpha- methyl nitrone; N- octyl- alpha-heptyl nitrone; N-lauryl-alpha-undecyl nitrone; N-tetradecyl-alpha-tridecyl nitrone; N- hexadecyl-alpha-pentadecyl nitrone; N-octadecyl-alpha-heptadecylnitrone; N- hexadecyl- alpha-heptadecyl nitrone; N-octadecyl-alpha-pentadecyl nitrone; N-heptadecyl- alphaheptadecyl nitrone; N-octadecyl- alpha-hexadecyl nitrone; and nitrone derived from N, N- dialkylhydroxylamine derived from hydrogenated tallow amine.

[0071] 3 , Additives

[0072] The rotomold compositions of the present invention may include an additive or multiple additives, fdlers, pigments, and the like. Non-limiting examples of additives include the antioxidants, light stabilizers, ultra-violet (UV) light absorbers, and zinc oxide discussed above, as well as other additives (e.g., a co-stabilizer, a nucleating agent, a metal deactivator, a slip agent, an anti-blocking agent, a colorant, an antistatic agent), or mixtures or additive packages thereof. The first particulate polyethylene composition and / or the second particulate polyethylene composition of the present invention can include an additive in an amount of, based on the total weight of each of the first and second particulate compositions, respectively, 0 and 5 wt. % (e.g., 0, 1, 2, 3, 4, or 5 wt. % or any number or range therein), preferably 0.01 wt% to 1 wt. % (e.g., 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1 wt. % or any number or range therein).

[0073] In addition to the UV absorbers and / or light stabilizers discussed above, non-limiting examples may include 2-(2'-hydroxyphenyl)-benzotriazoles, such as, for example, the 5'- methyl-; 3',5'-di-tert- butyl-; 5 '-tert-butyl-; 5'(l,l,3,3-tetramethylbutyl)-; 5-chloro-3',5'-di-tert- butyl-; 5-chloro-3'- tert-butyl-5 '-methyl-; 3'-sec-butyl-5'-tert-butyl-; 4'-octoxy-3',5'-di-tert- amyl-; and 3',5'-bis- (alpha, alpha - dimethylbenzyl) derivatives. In some aspects, the UV absorber or light stabilizer can include 2 -hydroxy-benzophenones. Non-limiting examples of benzophenones include: the 4-hydroxy-; 4-methoxy-; 4-octoxy; 4- decyloxy-; 4-dodecyloxy- ; 4-benzyloxy-; 4,2',4'-trihydroxy-; and 2'-hydroxy-4,4'-dimethoxy derivative. In some aspects, the UV absorber or light stabilizer can be a sterically hindered amines. Non-limiting examples of sterically hindered amines include: bis (2,2,6,6-tetramethylpiperidyl)-sebacate; bis-5(l,2,2,6,6-pentamethylpiperidyl)-sebacate; n-butyl-3,5-di-tert-butyl-4- hydroxybenzyl malonic acid bis(l,2,2,6,6,-pentamethylpiperidyl)ester; condensation product of 1- hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxy-piperidine and succinic acid; condensation product of N,N'-(2,2,6,6-tetramethylpiperidyl)-hexamethylendiamine and 4- tert-octylamino- 2,6-dichloro-l,3,5-s-triazine; tris-(2,2,6,6-tetramethylpiperidyl)- nitrilotriacetate, tetrakis- (2,2,6,6-tetramethyl-4-piperidyl)-l,2,3,4butane-tetra-arbonic acid; and l,l'(l,2-ethanediyl)-bis- (3,3,5,5-tetramethylpiperazinone). These amines are typically called HALS (Hindered Amines Light Stabilizing) and include butane tetracarboxylic acid 2,2,6,6-tetramethyl piperidinol esters. Such amines include hydroxylamines derived from hindered amines, such as di(l -hydroxy-2, 2, 6, 6-tetramethylpiperidin-4-yl) sebacate; 1- hydroxy 2, 2,6,6- tetramethyl-4-benzoxypiperidine; 1 -hydroxy-2, 2, 6, 6-tetramethyl-4-(3,5-di- tert-butyl -4- hydroxy hydrocinnamoyloxy) -piperdine; and N-(l-hydroxy-2, 2,6,6- tetramethyl-piperidin-4- yl)-epsiloncaprolactam. Suitable commercially available HALS which may be used in embodiments ofthe disclosure include those sold underthe trademarks CHIMASSORB® 119; CHIMASSORB 944; CHIMASSORB 2020; TINUVIN® 622 and TINUVIN 770 from BASF, and CYASORB® UV 3346, CYASORB UV 3529, CYASORB UV 4801, and CYASORB UV 4802 from Solvay. In other embodiments, the use of mixtures of more than one HALS are also contemplated. Other examples of UV absorbers or light stabilizers are substituted and unsubstituted benzoic acids. Non-limiting examples of benzoic acids can include: phenyl salicylate; 4-tertbutylphenyl-salicylate; octylphenyl salicylate; dibenzoylresorcinol; bis-(4- tert- butylbenzoyl)-resorcinol; benzoylresorcinol; 2, 4-di-tert-butyl-phenyl-3, 5 -di -tert-butyl - 4- hydroxybenzoate; and hexadecyl-3, 5 -di -tert-butyl -4-hydroxybenzoate. In some embodiments, a UV absorber or light stabilizer can be an acrylates. Non-limiting examples of acrylates can include: alpha-cyano-beta,beta-diphenylacrylic acid-ethyl ester or isooctyl ester; alpha-carbomethoxy-cinnamic acid methyl ester; alpha-cyano-beta-methyl-p- methoxy-cinnamic acid methyl ester or butyl ester; alpha-carbomethoxy-p-methoxy- cinnamic acid methyl ester; and N-(beta-carbomethoxy-beta-cyano-vinyl)-2-methyl- indoline.

[0074] Non-limiting examples of co-stabilizers can include melamine; polyvinylpyrrolidone; dicyandiamide; triallyl cyanurate; urea derivatives; hydrazine derivatives; amines; polyurethanes; alkali metal salts and alkaline earth metal salts of higher fatty acids, for example, Ca stearate, calcium stearoyl lactate, calcium lactate, Zn stearate, Mg stearate, Na ricinoleate and K palmitate; antimony pyrocatecholate or zinc pyrocatecholate, including neutralizers such as hydrotalcites and synthetic hydrotalcites; and Li, Na, Mg, Ca, Al hydroxy carbonates. Hydrotalcites which may be used in embodiments of the present invention can, include materials commercially available under the general tradenames DHT®-4 (A, C, or V), ZHT-4V®, HYCITE® 713, and AC-207®.

[0075] Non-limiting examples of nucleating agents can include 4-tert-butylbenzoic acid; adipic acid; diphenylacetic acid; sodium salt of methylene bis-2,4-dibutylphenyl; cyclic phosphate esters; sorbitol tris-benzaldehyde acetal; and sodium salt of bis(2,4-di-t- butylphenyl) phosphate or Na salt of ethylidene bis(2,4-di-t-butyl phenyl)phosphate. Nucleating agents may improve stiffness of a rotomolded part.

[0076] In some embodiments, slip agents can be used. Non-limiting examples of slip agents can include oleamide, erucamide, stearamide, and behenamide.

[0077] In some aspects, metal deactivators can be used. Non-limiting examples of metal activators can include N,N'-diphenyloxalic acid diamide, N-salicylal-N'-salicyloylhydrazine, N,N'-bis-salicyloylhydrazine, N,N'-bis-(3,5-di-tert-butyl-4-hydrophenylpropionyl)-2- hydrazine, salicyloylamino-l,2,4-triazole, and bis-benzyliden-oxalic acid dihydrazide.

[0078] Other additives can include plasticizers, epoxidized vegetable oils, such as epoxidized soybean oils, lubricants, emulsifiers, pigments, optical brighteners, flameproofing agents, anti-static agents, blowing agents and thiosynergists, such as dilaurythiodipropionate or distearylthiodipropionate .

[0079] Non-limiting examples of fillers and reinforcing agents can include calcium carbonate, silicates, glass fibers, asbestos, talc, kaolin, mica, barium sulfate, metal oxides and hydroxides, carbon black, and graphite. If present, then in some embodiments of the present invention, fillers may be incorporated into the thermoplastic polyolefin (e.g., the linear polyethylene) in amounts up to about 50 weight percent, or up to about 30 weight percent, or up to about 20 weight percent, or up to about 10 weight percent (based on the weight of the thermoplastic polyolefin).

[0080] Method of Making the Rotomolding Composition and Rotomolded Article

[0081] The rotomolding compositions of the present invention can be made by various methods known in the art. For example, first particulate polyethylene composition and second particulate polyethylene composition can be mixed together prior to subjecting the rotomolding composition into rotational molding. In some aspects, the first particulate polyethylene composition and the second particulate polyethylene composition can be added to a rotomolder at separate intervals during the rotational molding. In some aspects, the method can further include a rotational mold drop box to allow the rotomolding composition to rotational molding. In some aspects of the present invention can be method of making a rotomolded article.

[0082] Rotational molding is a well-known process which is undertaken by loading a charge of finely divided plastic resin into the mold “shell”, then rotating the mold (usually, on two axes) while heating it to a temperature above the melting point of the plastic resin. The melted plastic flows through the mold cavity under the forces caused by the rotation of the apparatus. The rotation continues for sufficient time to allow the molten plastic to cover the surface of the mold. The mold can then cooled to permit the plastic to freeze or solidify into a solid. The plastic can then be removed from the rotomolding machine. In some aspects, the time used to complete the molding cycle is a function of the bulk properties of the plastic which is being molded, the size of the part being molded, and / or the molding temperature. In addition, the plastic resin which is charged into the mold can be particularized (e.g., ground into a powder or pellets). In some aspects, the particularized compositions can have narrow particle size distributions (for each of the first and second particulate polyethylene compositions) to facilitate the “free flow” of the resin. It will also be appreciated that the physical properties of the rotomolded part can be influenced by the use of a molding cycle time with “undercooked” rotomolded parts having poor strength properties and “overcooked” rotomolded parts suffering from poor appearance (a "burnt" color) and / or a deterioration of strength properties.

[0083] In certain aspects, it is desirable to have a shorter molding cycle (so as to improve the productivity of the expensive rotomolding machinery) and a broader “processing window” (e.g., the rotomolding composition can be “properly cooked” rotomolded parts in a relatively short period of time but does not become “overcooked”). In addition, the properties of the rotomolded part can be affected by the molecular structure of the polymer used to prepare the part. Physical properties of the polymer compositions can include stiffness (as indicated by the modulus of the part) environmental stress crack resistance (or “ESCR”), impact resistance, and / or resistance to warpage. Non-limiting examples of conditions for rotomolding the compositions of the present invention are illustrated in the examples.

[0084] The rotomolding compositions of the present invention can be shaped into a variety of articles and shapes by using a variety of methods (e.g., rotation molding, melt spinning, and the like). It offers much in the way of design flexibility and scale of products, with products ranging from simple bulk storage containers to sophisticated automotive, medical, and aerospace applications. Rotational molding lends itself to hollow, complex forms like no other process. Small parts, such as medical pipette bulbs can be made in essentially the same manner as large boats. Intricate parts, such as fuel tanks and components for aircraft ducting. Non-limiting examples of articles include consumer goods, packaging products, pharmaceutical containers, bottles, caps, closures, liners, trash bags, food packaging film and / or materials, laminations, toys, tanks, wire sheathing, cable sheathing, pipes, hoses, or fittings.

[0085] EXAMPLES

[0086] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results. Example 1 (Materials Used)

[0087] A first particulate polyethylene composition (PEI) (Major Component), a second particulate polyethylene composition (PE2) (Minor Component), and manganese stearate (MnSt2) were used to form a rotomolding composition.

[0088] The first particulate polyethylene composition (PEI) was SURPASS® RMs341-U, which is commercially available from NOVA Chemicals (Calgary, Canada). SURPASS RMs341-U is an octene copolymer HDPE rotational molding resin having the following properties: a melt index of 3.5 grams / 10 minutes (as measured by ASTM D 1238, condition 190°C / 2.16 kg); a density of 0.9410 g / cm3(as measured by ASTM D 792); a melting point (DSC) of 126°C; a flexural modulus of 827 MPa (as measured by ASTM D 790); a yield strength of 20.2 MPa (as measured by ASTM D 638, Type IV specimen, 2" (50.8 mm) per minute test speed, 0.075" (1.9 mm) thickness compression molded samples); an elongation at yield of 12% (as measured by ASTM D 638, Type IV specimen, 2" (50.8 mm) per minute test speed, 0.075" (1.9 mm) thickness compression molded samples); an ESCR, (Fso) of greater than 1000 h (as measured by ASTM D 1693, Condition A & B, 100% IGEPAL, 50°C, F50 values. From compression molded specimens), a heat distortion temperature of 62°C (as measured by ASTM D 648, 66 psi (4.64 kg / cm2)) and 43°C (264 psi (18.56 kg / cm2); and an ARM low temperature impact of 67 J (as measured by ARM Method, -40°C on rotomolded samples, 0.125" (3.17 mm) and 230 J (as measured by ARM Method, -40°C on rotomolded samples, 0.250" (6.35 mm). PEI included a processing antioxidant and a UV stabilizer (> UV 22). PEI was pulverized to a powder free flow state using a 35 US mesh screen size, which equates to an average particle size of about 500 microns. The second particulate polyethylene composition (PE2) was NOVAPOL® HB-W555- A, which is commercially available from NOVA Chemicals (Calgary, Canada). NOVAPOL HB-W555-A is a hexene copolymer HDPE blow molding resin having the following properties: a high load melt index of 5.0 grams / 10 minutes (as measured by ASTM D 1238, condition 190°C / 21.6 kg); a density of 0.955 g / cm3(as measured by ASTM D 792); a yield strength of 28 MPa (as measured by ASTM D 638; an elongation of 830% (as measured by ASTM D 638); a flexural modulus of 1400 MPa (as measured by ASTM D 790); a tensile impact of 42 J / cm2(as measured by ASTM D 1822), a low temperature brittleness point of < -70°C (as measured by ASTM D 746), an ESCR, (Fso) of greater than 500 h (as measured by ASTM D 1693, environmental stress crack resistance, Condition A, 100% IGEPAL®), and an Izod impact of 7.2 J / cm (3.2 mm (0.125 in) thick specimen). PE2 included a process stabilizer. PE2 was pulverized to a powder free flow state using a 35 US mesh screen size, which equates to an average particle size of about 500 microns.

[0089] Manganese stearate (MnSt2) was used as the transition metal stearate. MnSt2 was obtained from American Elements (Los Angeles, USA).

[0090] Example 2 (Preparation of a Rotomoldable Composition)

[0091] Inventive Example Composition 1 (IE1) was prepared by first compounding PE2 with 2500 ppm MnSt2, followed by grinding to a powder free flow state using a 35 US mesh screen size (PE2 + MnSt2). PE2 + MnSt2 (5 wt. %) and PEI (95 wt. %) were mixed together in a tumbler to obtain IE I, which can then be used in a rotomolder machine. Alternatively, the PEI and PE2 components can be added to a rotomolder machine as individual components (not first mixed together), and the rotational process of the rotomolder machine could mix the components together. Whether in the form of a pre-mixed mixture or added as individual components to the rotomolder machine, the components are capable of separating during the rotomolding process based on their particle size. IE1 is also referred to as “5% W555 MnSt2”.

[0092] Comparative Example Composition 2 (CE2) was prepared by grinding PE2 to a powder free flow state using a 35 US mesh screen size. MnSt2 was not added. PE2 (5 wt. %) and PE 1 (95 wt. %) were mixture together in a tumbler to obtain CE2, which can then be used in a rotomolder machine. CE2 is also referred to as “5% W555”.

[0093] Control Composition 3 (CC3) was prepared by obtaining PEI. CC3 is 100 wt. % PEI. CC3 is also referred to as “Control”.

[0094] Example 3 (Preparation of Rotomolded Parts)

[0095] Rotomolded parts were prepared from the IE1 (5% W555 MnSt2), CE2 (5% W555), and CC3 (Control). IE1, CE2, and CC3 were each subjected to rotational molding. In particular, each of IE1, CE2, and CC3 were placed into test cube molds as described below. IE1, CE2, and CC3 were each then rotationally molded at temperature of 293.3°C (560°F) to a thickness of 0.125 inches for various times (12 min, 14 min, 16 min, 18 min, 20 min, and 22 min) on a Rotospeed RS3-160 rotomolder machine (commercially available from Ferry Industries Inc. (Stow, Ohio, USA)) to evaluate the process window for the blends.

[0096] The Rotospeed RS3-160 rotomolder machine has two arms which rotate about a central axis. Each arm is fitted with a plate which rotates on an axis that is roughly perpendicular to the axis of rotation of the arm. Each plate is fitted with three cast aluminum molds that produce plastic cubes having dimensions of 12.5 inches (31.8 cm) x 12.5 inches x 12.5 inches. These molds produce parts having a nominal thickness of about 0.25 inches (0.64 cm) when initially filled with a standard charge of about 3.7 kg of polyethylene resin. A gas fired furnace which is capable of providing 2 million British thermal units (Btu) per hour is used to provide hot air that is circulated about the molds by a fan. In general, the temperature within the enclosed oven is maintained at a selected temperature (e.g., 250°C and 400°C) for specified periods of time while the machine rotates the arms (typically, at about 8 revolutions per minute (rpm) and the plate (typically, at about 2 rpm). Specific molding conditions for the different compositions are reported in Table 1. The “cooked parts” are then cooled by opening the oven. Water spray may also be used to facilitate cooling. “Cook times”, rotation speed, temperatures and cooling cycles are computer controlled with appropriate software which also includes a data acquisition system.

[0097] TABLE 1

[0098] Example 4 (Results)

[0099] As can be seen in Figure 1A and Figure 1 B, each composition IE1 (5% W555 MnSt2), CE2 (5% W555), and CC3 (Control) traverses a region where the impact performance drops significantly. This is a phenomenon sometimes referred to as the “impact knee” and is a known issue with various rotational molding resins, from NOVA Chemicals and others. After this drop in performance, the impact properties recover for each of the formulations at 22 min. Figure 2 demonstrates the visual appearance of the IE1 (5% W555 MnSt2), CE2 (5% W555), and CC3 (Control) compositions. The color is essentially the same for each, whereas there is a notably lower gloss for the IE1 (5% W555 MnSt2) and CE2 (5% W555) compositions. Gloss is typically used as an indicator for cure state, where an increase typically indicates “over-cure”. That is, the “optimal cure” for each formulation is about 14 min. However, this serves only as a guide, as the present case may be an example of where overcure may be desirable to preserve physical properties and improve PU adhesion.

[0100] Figure 3 demonstrates that the outside or inside surface of the molded parts are not significantly different in the presence of MnSt2.

[0101] FTIR spectroscopy can be used to evaluate relative degree of oxidation of film and molded part surfaces through semi-quantitative analysis of the diagnostic carbonyl peak at -1718 cm'1by integrating the peaks area. Figure 4 shows the surface FTIR spectra for the inside and outside surface of the molded parts at indicated cure times. Clearly, there is essentially no carbonyl peak on the outside surface for any sample. At 18 min cure time, carbonyl peaks are clearly evident on the inside surface of both of the IE1 (5% W555 MnSt2) and CE2 (5% W555) compositions. However, at 22 min, it is clear there is a significantly higher amount of carbonyl present with the IE1 (5% W555 MnSt2) composition, which indicates the activity of the MnSt2 to catalyze surface oxidation. Table 2 provides the carbonyl index on the inside surface of molded parts via integration of peaks at -1718 cm'1shown in Figure 4.

[0102] TABLE 2

[0103] Polyurethane adhesion testing is conducted by spraying foamed PU and sandwiching between two pieces of the PE sample and allowing to cure. After curing, the samples are evaluated by pulling the PE and measuring the relative load required to separate the samples: higher loads indicate stronger interfacial adhesion between the PE and PU. Furthermore, the samples are then visually examined to assess the failure mode, with a PU cohesive failure indicating a strong PE-PU bond. Table 3 provides PE-PU Adhesion testing studies. TABLE 3

[0104] Figure 5 includes the PE-PU adhesion testing results for the IE1 (5% W555 MnSt2) and CE2 (5% W555) compositions. Higher max load indicates stronger adhesion between PE-PU. The IE1 (5% W555 MnSt2) composition has a stronger max load when compared with the CE2 (5% W555) composition at cook times of greater than 18 min.

[0105] Figures 6A-6B provide photos of PE-PU adhesion testing samples after tensile testing. Figure 6A left to right: rotomolding composition of CE2 (5% W555) at 14 min, 18 min, and 22 min; Figure 6B, left to right: rotomolding composition of IE1 (5% W555 MnSt2) at 14 min, 18 min, and 22 min.

[0106] Figure 7 provides a graph illustrating the carbonyl index (x-axis) relationship to the adhesion strength (Ib-ft) of IE1 (5% W555 MnSt2) and CE2 (5% W555) compositions.

[0107] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. INDUSTRIAL APPLICABILITY

[0108] Provided is a rotomolding composition comprising two particulate polyethylene compositions. Rotomolded articles prepared from the rotomolding composition include at least one surface having sufficient adhesion to polyurethane polymers.

Claims

CLAIMS1. A rotomolding composition comprising:(a) 85 wt. % to 99 wt. %, based on the total weight of the rotomolding composition, of a first particulate polyethylene composition having: a melt index (12) of 0.5 to 10 grams / 10 minutes, as measured by ASTM D 1238 at 190°C using a 2. 16 kg load; a density of 0.920 to 0.950 g / cc, as measured by ASTM D792; and an average particle size of 300 microns to 1500 microns; and(b) 1 wt. % to 15 wt. %, based on the total weight of the rotomolding composition, of a second particulate polyethylene composition comprising:500 parts per million (ppm) to 5000 ppm, based on the total weigh of the second particulate polyethylene composition, of a transition metal stearate; and at least 100 ppm, based on the total weight of the second particulate polyethylene composition, of an antioxidant, the second particulate polyethylene composition having: a high load melt index (121) of 2 to 20 grams / 10 minutes, as measured by ASTM D 1238 at 190°C using a 21.6 kg load; a density of 0.950 to 0.965 g / cc, as measured by ASTM D792; and an average particle size of 500 microns to 3000 microns.

2. The rotomolding composition of claim 1, wherein polyethylene in the first particulate polyethylene composition is stabilized polyethylene.

3. The rotomolding composition of any one of claims 1 to 2, wherein polyethylene in the second particulate polyethylene composition is stabilized polyethylene.

4. The rotomolding composition of any one of claims 1 to 3, wherein the first particulate polyethylene composition comprises a primary antioxidant and a secondary antioxidant in an amount of 250 ppm to 1500 ppm, by total weight of the rotomolding composition.

5. The rotomolding composition of any one of claims 1 to 4, wherein the transition metal stearate comprises manganese stearate, cobalt stearate, or iron stearate, or any combination thereof.

6. The rotomolding composition of any one of claims 1 to 5, wherein the second particulate polyethylene composition comprises 2000 ppm to 3000 ppm, based on thetotal weigh of the second particulate polyethylene composition, of the transition metal stearate.

7. The rotomolding composition of claim 6, wherein the transition metal stearate comprises manganese stearate.

8. The rotomolding composition of any one of claims 1 to 7, wherein: the first particulate polyethylene composition has an average particle size of 300 microns to 700 microns, or preferably 400 microns to 600 microns; and the second particulate polyethylene composition has an average particle size of 1200 microns to 1600 microns, or preferably 1300 microns to 1600 microns.

9. The rotomolding composition of any one of claims 1 to 8, comprising:90 wt. % to 99 wt. %, preferably 93 wt. % to 97 wt. %, based on the total weight of the rotomolding composition, of the first particulate polyethylene composition; and1 wt. % to 10 wt. %, preferably 3 wt. % to 7 wt. %, based on the total weight of the rotomolding composition, of the second particulate polyethylene composition.

10. The rotomolding composition of any one of claims 1 to 9, wherein: the first particulate polyethylene composition has: an 12 of 2 to 8 grams / 10 minutes; and a density of 0.933 to 0.942 g / cc; and the second particulate polyethylene composition has: an 121 of 2 to 10 grams / 10 minutes; and a density of 0.953 to 0.956 g / cc.

11. The rotomolding composition of any one of claims 1 to 10, wherein the average particle size of the first particulate polyethylene composition is smaller than the average particle size of the second particulate polyethylene composition.

12. The rotomolding composition of any one of claims 1 to 11, wherein the first and second particulate polyethylene compositions are mixed together.13 The rotomolding composition of any one of claims 1 to 11, wherein the first particulate polyethylene composition is separated from the second particulate polyethylene composition.

14. The rotomolding composition of any one of claims 1 to 13, wherein the transition metal stearate is capable of oxidizing and / or degrading the polyethylene in the second particulate polyethylene composition when the rotomolding composition is subjected to rotational molding and / or a temperature of 250°C to 400°C.

15. The rotomolding composition of any one of claims 1 to 14, wherein: the first particulate polyethylene composition comprises at least 95 wt. % polyethylene, based on the total weight of the first particulate polyethylene composition; and the second particulate polyethylene composition comprises at least 95 wt. % polyethylene, based on the total weight of the second particulate polyethylene composition.

16. A rotational molded article of manufacture comprising the rotomolding composition of any one of claims 1 to 15.

17. The rotational molded article of manufacture of claim 16, wherein the article of manufacture comprises an outer surface, an inner surface, and a volume defined at least partially by the inner surface.

18. The rotational molded article of manufacture of claim 17, wherein the inner surface is at least partially oxidized and / or comprises carbonyl groups.

19. The rotational molded article of manufacture of any one of claims 17 to 18, wherein a polyurethane is in contact with at least a portion of the inner surface and / or is comprised in at least a portion of the volume.

20. The rotational molded article of manufacture of any one of claims 17 to 19, wherein the inner surface comprises (i) a carbonyl index of at least 0.2, preferably at least 0.35 and / or (ii) a polyurethane adhesion strength of at least 19.0 Ib-ft, preferably at least 25.0 Ib-ft.

21. A melt-blended polymeric composition comprising the rotomolding composition of any one of claims 1 to 15.

22. The melt-blended polymeric composition of claim 21, further comprising a surface in contact with a polyurethane composition.

23. The melt-blended polymeric composition of any one of claims 21 to 22, further comprising a surface having (i) a carbonyl index of at least 0.2, preferably at least 0.35, and / or (ii) a polyurethane adhesion strength of at least 19.0 Ib-ft, preferably at least 25.0 Ib-ft.

24. A method of making a rotomolded article of manufacture, the method comprising subjecting the rotomolding composition of any one of claims 1 to 15 to rotational molding to obtain the article of manufacture.

25. The method of claim 24, wherein the rotational molding is performed at a temperature of 250°C to 400°C.

26. The method of any one of claims 24 to 25, wherein the rotomolded article of manufacture comprises an outer surface, an inner surface, and a volume defined at least partially by the inner surface.

27. The method of any one of claims 24 to 26, wherein the first particulate polyethylene composition and the second particulate polyethylene composition are mixed together prior to subjecting the rotomolding composition to rotational molding.

28. The method of any one of claims 24 to 27, wherein the first particulate polyethylene composition and the second particulate polyethylene composition are added to a rotomolder at separate times during the rotational molding.

29. The method of any one of claims 24 to 28, wherein the method further comprises a rotational mold drop box to allow the rotomolding composition to rotational molding.

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