[001] The present invention relates to a thermoplastic resin, a blown film produced from thermoplastic resin and to a medical apron formed from the blown film. The present invention also relates to a method of producing a thermoplastic resin. The present invention further relates to a method of recycling a blown film comprising a thermoplastic resin. The present invention particularly relates to polyethylene resins as the thermoplastic resin.

[002] In a particularly preferred aspect, the present invention relates to the manufacture of polyethylene resins for use in Personnel Protection Equipment (PPE) Individual Use Aprons, also called herein “medical aprons”, and the recovery of recycled polyethylene from waste for incorporation into such products. The recycled polyethylene requires repeated mechanical and thermal processing prior to incorporation into such products and the present invention can incorporate a minimum of 30 wt% recycled polyethylene content into new aprons. The recycled polyethylene content of such products as required to increase progressively in compliance with EU legislated regulations, to meet a minimum threshold of recycled content of 100% by the year 2040.

[003] The global issue of plastic waste from PPE (Personnel Protection Equipment) and recycling continues to challenge both life cycles, carbon footprint, and sustainability in global markets. However, attempts for a quick fix using expensive depolymerization, pyrolysis conversion to fuels and melt casting bricks using isothermal thermal oxidation to slowly melt hospital waste into solid bricks claiming to be utilize such bricks back into school desks for children, chairs, tables, and related plastic toys for both children and animals has created more problems than solutions.

[004] These attempts among others continue to ignore basic issues of stabilization and controlled degradation of all plastics. Post end-of-life and especially fortification of the plastic for its original end use requirements have continued to show deficiencies in the proper levels of stabilization to adjust to changes in manufacturing of the plastic and changes in end use requirements under conditions that have also changed globally. Therefore, little concern has been factored into the original design of the plastic and downstream end-of-life utilization for recycling. These factors have increased the difficulty of recycling and added cost to any solution.

[005] Polyolefins are a large part of the family of plastics used for PPE and packaging globally. The range of polyolefins include polypropylene (e.g. homo- and copolymers) and polyethylene (e g. HOPE, LDPE, MDPE, LLDPE). [006] High density polyethylene (HDPE) is made by a low-pressure method and is linear in structure with few, if any, branches extending from the linear polymer backbone. Such polymers exhibit over 90% crystallinity, and a density typically above 0.95 g/cc. Low-density polyethylene (LDPE) is made by high pressure methods using chain transfer agents to control molecular weights. The crystallinity is low (50-60%), density is typically from 0.91-9.94 g/cc from the reactor. The polymer is highly amorphous, and is highly branched due to chain transfer mechanisms. Subsequently, procedures were developed for producing LDPE at lower pressures involving co-polymerization of higher alpha-olefins, typically having from C3 to C8 carbon chain lengths, with ethylene. These newer LDPEs have increased linearity, with a smaller number of alpha-olefins as co-monomers, and a density range typically from 0.918-0.940 g/cc, and these are referred to as linear low-density polyethylene (LLDPE). The stabilization of all polyolefins influences the overall physical chemical properties of molecular properties, crystallinity, density, rheology, rate of oxidation, mechanical, thermal, and thermo-oxidative rates of degradation. These properties control life cycles, carbon footprint, sustainability, and recycling.

[007] Degradation occurs during compounding, forming and the lifetime of an article. Thus, fortification systems are needed. However, since these substances are expensive, they are added in a quantity just sufficient to protect the polymer during the first melt compounding, heat history, subsequent forming and serving cycles. This occurs at the original equipment manufacturer (OEM) which manufactures pellets from reactor powders. The issue of recycling of OEM materials has never been a design component by resin manufacturing.

[008] The major design optimization has been the end use requirements of the resin being sold. Therefore, in recycling the polymer must be restabilized and adopted to the old system that has been transformed in-situ by melt compounding and fabrication.

[009] The degradative processes may have already changed the macromolecular structure. This occurs at the resin manufacturer, and can result from the use of only nominal levels of fortification. The fortification used is adapted to the limits of the end use requirement, and is not adapted for achieving improved recycling.

[010] Different residual stabilizers, catalyst residues, flow promoters, lubricants, antistatic agents and acid acceptors, and their transformation products may be present in the polyethylene. It is known those skilled in the art that when recycling resins from different sources, those plastic additives and stabilizers may co-react into pro-degradative products and into neutral inert stabilizers while contributing to other adverse side effects depending on the end use applications. Therefore, any new additive system should not react antagonistically with any older system.

[Oi l] In a stressed field, macromolecules are susceptible to bond breakage. This process also generates free radicals that lead to degradative chain reactions. This is especially relevant during shear mechanical conversion of films for further melt compounding into pellets.

[012] In polyolefins, the free radical chain reactions lead to chain scission, grafting, double bond formation (unsaturation). Properties of the structure depend on their concentration of tertiary carbons. Therefore, chain scission is the dominant degradation mechanism of polypropylene, whereas grafting and crosslinking occur in HDPE. During the expansive changes in Ziegler-Natta catalyst technology for HDPE and other polyolefins in the last twenty years, in addition to those known mechanisms noted for HDPE can be added chain scission to those degradative mechanisms for HDPE. Clearly this is dependent on the catalyst used. Those LLDPEs with copolymer structures show more complex behavior caused by the presence of all these reactions. Since chain scission statistically affects the long chain, it reduces molecular weight and narrows molecular weight distribution. The opposite is true for chain branching.

[013] Best practices will allow for upcy cling and supra cycling of recycled polyolefins. However, currently best practices are not practiced in the real world today so alternative innovations are required to adjust to these variables.

[014] Blown films from high density polyethylene homopolymers tend to be very brittle because they lack tie molecules. Low density polyethylene, however, is used to produce flexible materials such as film, while high density polyethylene is used for utility goods such as bottle crates, seats, and containers. Linear low-density polyethylene (LLDPE) has improved physical properties superior to LDPE. In addition, the use of highly active and stereo-specific catalysts, such as Ziegler-Natta catalysts, has enabled product specifications such as cost, linearity, specific density, and melt-flow rates. The linearity in the polymer structure impacts better tear, impact, and tensile properties. Chain branching caused by the alpha-olefinic co-monomers, account for the inherent toughness of the LLDPE and cost performance.

[015] Therefore, the properties of LLDPE confer certain physical attributes more favorable than those associated with LDPE in many applications. LLDPE is tougher and has better tensile and impact properties and stress crack resistance and puncture energy. These properties are contingent on the initial type and level of fortification that will allow for changes in thermo-mechanical processing and residence times in processing equipment and film conversion processes. In addition, LLDPE allows for far better down gauging in thickness of films from 25-35% over LDPE. Finally, LLDPE provides outstanding tear strength in the transverse direction (TD), making the polymer highly suited for stretch film applications.

[016] The blending of LLDPE with HDPE has been utilized to overcome the problem of cutting, die-cutting or punching out thin blown film to produce aprons for hospitals. However, many known blends of LDPE and LLDPE have not been successful, and slow down the process of producing aprons. The major differences have been determined to result from a combination of proper fortification, degradation and resulting lower crystallinity of the blown films prior to post manufacturing of aprons by cutting/punching aprons form very thin blown films (16-18 microns). [017] Furthermore, both blended resins complicate the recycling of individual use PPE aprons. With current legislation having mandated 30 wt% recycled content by April 2022 and further increases in recycled content of 5-10 wt% every five (5) years to 2040 makes this a priority of all PPE and other forms of polyolefin packaging waste including condensation polymers (e.g. thermoplastic polyesters and thermoplastic polyamides), resulting in an urgent problem to be solved.

[018] Polyblends on the other end of the spectrum bring additional risks and complications due to issues of miscibility and molecular structure. It is known in the art that chain branch content is the most important factor to control miscibility of a blended polyethylene or polyolefin like polypropylene. The miscibility decreases with increase in branch content. The branch type also affects the miscibility. The miscibility decreases with increase of branch length.

[019] So, for example, LLDPE with 4.4 mole percent of butene is miscible with high density polyethylene (HDPE) at all compositions. However, LLDPE with 4 mole percent of hexene is immiscible with HDPE when the HDPE fraction is less than 60 weight percent, and LLDPE with 2.1 mole percent of octene is immiscible with HDPE when HDPE fraction is less than 50 wt%.

[020] Additional variables that control miscibility of polyethylene include molecular weight (molecular structure), content of chain branching, and branching type, such as short chain branching (SCB) and long chain branching (LCB), temperature and composition.

[021] In solving such a challenge today, the person skilled in the art requires a full understanding of the end use requirements of the fabricated product, its physical chemical properties, regulatory guidelines (e.g. REACH registration, FDA, GRAS compliance and other environmental compliance issues). This has not been easy when innovative technologies are slower to evolve than environmental regulations.

[022] Accordingly, there is a need in the art for improved thermoplastic resins, in particular polyethylene resin compositions, which can overcome these technical problems.

[023] More specifically, there is a need in the art for thermoplastic resins, in particular polyethylene resin compositions, which can exhibit improved mechanical properties and improved stability and resistance to degradation, and yet can readily be recycled into high value products exhibiting high quality mechanical properties and stability.

[024] There is also a need in the art for products such as medial aprons, fabricated from blown film composed of a thermoplastic resin, in particular a polyethylene resin composition, to be manufactured in a cost effective and reliable manner and to contain a high proportion of recycled thermoplastic resin, such as polyethylene resin, without a reduction, and potentially exhibiting an improvement, in mechanical properties or stability and resistance to degradation as compared to medial aprons composed solely of virgin thermoplastic resin.

[025] The present invention aims to meet these needs in the art and to overcome the problem of achieving improved recycling of thermoplastic resins, in particular polyethylene resin compositions.

[026] In accordance with one aspect of the present invention, there is provided a thermoplastic resin composition comprising a plurality of metal oxide particles dispersed in the thermoplastic resin composition, and wherein the metal oxide particles have molecules of an organic phosphonate salt coupled to surfaces of the metal oxide particles by chemical reaction between phosphonate groups in the molecules of the organic phosphonate salt and oxygen atoms in the metal oxide.

[027] In the preferred embodiments, the metal oxide is an amphoteric metal oxide, and preferably functions as a molecular buffer and synergist within the thermoplastic resin composition.

[028] Preferably, the amphoteric metal oxide comprises zinc oxide, aluminium oxide or gallium oxide, or any combination of any two or more thereof. In particularly preferred embodiments, the metal oxide comprises zinc oxide.

[029] Typically, the organic phosphonate salt comprises an alkyl and/or aryl phosphonate having from 14-25 carbon atoms. [030] In the preferred embodiments, the metal oxide particles have a mean average particle size, by weight, within the range of from 0.05 to less than 1 micron.

[031] Preferably, the metal oxide particles are present in the thermoplastic resin composition in a concentration of from 0.01 to 1 wt%, optionally from 0.05 to 0.5 wt%, based on the total weight of the thermoplastic resin composition.

[032] In the preferred embodiments, the thermoplastic resin composition further comprises a first fortifier, wherein the first fortifier comprises a phenolic antioxidant, and/or a second fortifier, wherein the second fortifier comprises an organic phosphite antioxidant.

[033] Typically, the phenolic antioxidant is a sterically hindered phenolic antioxidant having a molecular weight within the range of from 750 to 2000 g/mol, and the phenolic antioxidant is present in the thermoplastic resin composition at a concentration of from 0.05 to 0.4 wt%, based on the total weight of the thermoplastic resin composition.

[034] Typically, the organic phosphite antioxidant comprises an aryl-substituted phosphite of formula P(OR)s where R comprises an aryl substituent, typically having a molecular weight within the range of from 500 to 1000 g/mol. The organic phosphite antioxidant is present in the thermoplastic resin composition at a concentration of from 0.05 to 0.4 wt%, based on the total weight of the thermoplastic resin composition.

[035] In accordance with preferred embodiments of the present invention, the thermoplastic resin is a polyethylene composition. Preferably, the polyethylene composition has a Melt Flow Rate (MFR) within the range of from 0.175 to 0.250 g/10 minutes measured at 190 °C with a mass of 2.16 kg under ASTM D1238-20. In accordance with the preferred embodiments of the present invention, the polyethylene composition has a Melt Index Ratio, which is a ratio of the Melt Flow Rate (MFR) measured at 190 °C with a mass of 2.16 kg under ASTM D1238-20 to the Melt Flow Rate (MFR) measured at 190 °C with a mass of 21.6 kg under ASTM D1238-20, of from 60 to 90. [036] In a second aspect of the present invention, there is provided a blown film produced from the thermoplastic resin composition, preferably a polyethylene composition, according to the first aspect of the present invention.

[037] Preferably, the blown film has a dart impact strength of at least 50 grams, typically at least 100 grams, for a 16 micron thickness of the blown film.

[038] In preferred embodiments, the polyethylene composition in the blown film has a crystallinity of at least 50%, typically from 50 to 55%. [039] In a third aspect of the present invention, there is provided a medical apron formed from the blown film of the second aspect of the present invention.

[040] In a fourth aspect of the present invention, there is provided a method of producing a thermoplastic resin material, the method comprising the steps of:

(i) providing a first thermoplastic resin component;

(ii) providing a second thermoplastic resin component, wherein the second thermoplastic resin component comprises a thermoplastic resin composition according to the first aspect of the present invention, and preferably the second thermoplastic resin component has been mechanically ground, melt compounded and pelletized; and

(iii) blending the first and second thermoplastic resin components to form a thermoplastic resin material.

[041] Typically, the thermoplastic resin material comprises from 30 to 70 wt% of the first thermoplastic resin component and from 30 to 70 wt% of the second thermoplastic resin component, each based on the based on the total weight of the thermoplastic resin material.

[042] In some embodiments, the first thermoplastic resin component comprises a thermoplastic resin composition according to the first aspect of the present invention.

[043] Typically, the first thermoplastic resin component further comprises a primary or secondary antioxidant, optionally at least one of which primary or secondary antioxidants comprises an organophosphorous compound, further optionally which organophosphorous compound comprises an organophosphite, organophosphinate, organophosphonate or any combination of two or more thereof.

[044] In alternative embodiments, the first thermoplastic resin composition comprises a thermoplastic resin constituent which is a virgin thermoplastic resin.

[045] Typically, the virgin thermoplastic resin further comprises a primary or secondary antioxidant, optionally at least one of which primary or secondary antioxidants comprises an organophosphorous compound, further optionally which organophosphorous compound comprises an organophosphite, organophosphinate or organophosphonate, or any combination of two or more thereof.

[046] Preferably, the first and second thermoplastic resin components comprise, or consist of, polyethylene resin as the thermoplastic resin. [047] In a fifth aspect of the present invention, there is provided a method of recycling a blown film comprising a thermoplastic resin material, preferably a polyethylene resin material, the method comprising the steps of

(i) providing a blown film comprising a thermoplastic resin material;

(ii) mechanically and thermally processing the thermoplastic resin material in the blown film to form a plurality of pellets;

(iii) during or after step (ii), dispersing a plurality of metal oxide particles in the thermoplastic resin material, wherein the metal oxide particles have molecules of an organic phosphonate salt coupled to surfaces of the metal oxide particles by chemical reaction between phosphonate groups in the molecules of the organic phosphonate salt and oxygen atoms in the metal oxide to form a recycled thermoplastic resin material comprising the dispersed metal oxide particles;

(iv) blending the recycled thermoplastic resin material with a non-recycled thermoplastic resin material to form a final thermoplastic resin material which comprises, as a proportion of the weight of the final thermoplastic resin material, recycled thermoplastic resin; and

(v) blowing the final thermoplastic resin material to form a blown film comprising the final thermoplastic resin material.

[048] In this specification, the term “non-recycled” applied to a thermoplastic resin material is to be construed as meaning that thermoplastic resin material has not been directly obtained from a recycling operation, and may comprise or consist of a virgin thermoplastic resin; however, the “non-recycled” thermoplastic resin material may comprise, as a fraction thereof, thermoplastic resin material which had been previously recycled in a previous recycling operation and has been previously blended into the thermoplastic resin material.

[049] Typically, the final thermoplastic resin material comprises from 30 to 70 wt% of the nonrecycled thermoplastic resin material and from 30 to 70 wt% of the recycled thermoplastic resin material, each based on the based on the total weight of the final thermoplastic resin material.

[050] Preferably, the recycled thermoplastic resin material comprises a thermoplastic resin composition, preferably a polyethylene composition, according to the first aspect of the present invention. [051] In some embodiments, the non-recycled thermoplastic resin material comprises a thermoplastic resin composition, preferably a polyethylene composition, according to the first aspect of the present invention.

[052] In some embodiments, the non-recycled thermoplastic resin composition comprises or consists of a thermoplastic resin constituent which is a virgin thermoplastic resin, preferably polyethylene.

[053] Typically, any one or more of (a) the thermoplastic resin material of the blown film, (b) the non-recycled thermoplastic resin material and the (c) the virgin thermoplastic resin further comprises a primary or secondary antioxidant, optionally at least one of which primary or secondary antioxidants comprises an organophosphorous compound, further optionally which organophosphorous compound comprises an organophosphite, organophosphinate or organophosphinite, or any combination of two or more thereof.

[054] Preferably, the blown film produced in step (v) has a dart impact strength of at least 50 grams, more preferably at least 100 grams, for a 16 micron thickness of the blown film.

[055] Typically, the thermoplastic resin composition is polyethylene, and more preferably in the blown film produced in step (v) the polyethylene has a crystallinity of at least 50%, preferably from 50 to 55%.

[056] The preferred embodiments of the present invention can solve the problems in the prior art as discussed above by achieving the technical effects and advantages that blown films composed of polyethylene, such as blown films used for individual single use PPE aprons, can be recycled back into a polyethylene recycle stream multiple times without compromising mechanical properties, such dart impact strength representing puncture resistance, and without altering major changes in molecular properties during multiple mechanical and thermo-mechanical melt processing cycles. Such enhanced ability for recycling to achieve high quality mechanical properties in a recycled product is referred to herein as “Supra Cycling”.

[057] Without being bound by any theory, it is believed by the present inventor that these technical effects and advantages were achieved by altering the molecular properties in-situ of the original base resin fortification present in the virgin resin manufactured by the original equipment manufacturer (OEM). In particular, a molecular buffer, and optionally additional fortifier(s), are added to the polyethylene resin to achieve a balanced ratio of components to achieve synergisms in fortification and eliminate antagonisms against fortification. The molecular buffer, and optionally additional fortifier(s), can also be added to post-recycled polyethylene produced from blown film products, such as aprons, during mechanical and thermal reprocessing of the recycled polyethylene into pellets. The molecular buffer, and optionally additional fortifier(s), are preferably added to the polyethylene resin using a masterbatch formulation. The molecular buffer, and optionally additional fortifier(s), function as a modified version of the original fortification ingredients by pretreatment and or in-situ conversion processes, during masterbatch production and/or during blown film production, to stop both branching, cross-linking and chain scission mechanisms, thereby controlling molecular properties and physical properties of the thin blown film.

[058] The molecular buffer, which comprises a metal oxide, preferably zinc oxide, has been modified by coupling with an orgonic phosphonate salt. It is believed that this modification allows for interaction between the aryl phosphonate and any primary or secondary antioxidant in the thermoplastic resin to control rates of free radical consumption and formation of in situ chromphores while stabilizing the aryl phosphonate from in-situ hydrolysis.

[059] The preferred embodiments of the present invention can achieve both intermolecular and intramolecular control in polyethylene resin which in turn can result in life cycle extensions of the polyethylene. The preferred embodiments can enhance polyethylene recycling, and therefore can reduce the carbon footprint and energy costs, and can provide for recycling, upcy cling and “Supracycling” of polyethylene resins, while extending life cycles, lowering carbon footprint and mitigating physical chemical limitations that currently exist in the market globally.

[060] The preferred embodiments of the present invention can achieve enhanced properties in recycled PPE aprons and other PPE products produced from polyethylene. The preferred embodiments of the present invention can allow for the repeat recycling of individual use polyethylene aprons while retaining the physical and chemical properties of the downstream aprons containing recycled polyethylene. This allows significant reduction in the current carbon footprint, increased sustainability of the plastic, environmental compliance in use and after end- of-life by complementing the existing fortification systems in both HDPE and LLDPE resins.

[061] Without being bound by any theory, it is believed by the present inventor that, when incorporated into a polyethylene composition already or additionally containing fortifier(s) comprising phosphinite and/or phosphinate functional groups, the molecular buffer component will synergize with any phosphinite and phosphinate transformation products present in the polyethylene composition. This process harmonizes both the ingredients in the OEM resins and complements additional enhancement to control the mechanical and thermo-mechanical properties after multiple recycling processing cycles, but without significant changes in the molecular weight and rheology of the polyethylene composition. In addition, it is believed that the molecular buffer component can function to stabilize the primary stabilization system from in-situ conversion during storage and during melt processing, and during repeated use for recycling.

[062] It is believed that the molecular buffer component provides radical termination to both mechanical stress and thermal stress oxidation during processing of the thermoplastic resin. The rate of crystallization and percent crystallinity from thermal analysis indicates a secondary contribution, which can be described as stress-induced oriented nucleation, by the interaction of the molecular buffer and the phosphonite and phosphonate to cause eventually an in-situ reaction forming a hetero-homogeneous nucleating agent or metal phosphonate.

[063] Polyethylene is kinetically one of the fastest polymers to crystallize from the melt to the solid state. The crystal growth rate of polyethylene is also fast. However, it has been found that as a result of the temperature dependence of nucleation and growth rates of polyethylene, at any given temperature below the melting point, the rate of crystal growth is always higher than the nucleation rate. The overall crystallization rate is a product of these two processes. Nucleating agents can increase the rate of nucleation to compete more effectively with the higher crystal growth rate. It is believed that shear-induced homogeneous/heterogeneous nucleation is enhanced or caused by the metal phosphonate formed in-situ, which can cause an increase in crystallinity and rate of nucleation of an orientated film during a blown film process.

[064] The Examples and Comparative Examples described hereinafter show the unexpected enhanced properties of both the OEM polyethylene resin systems and post recycled polyethylene produced from blown film such as in aprons by the addition of the molecular buffer component, optionally with additional fortifiers, which can achieve enhanced recycling of the polymeric waste, because the polyethylene properties are profoundly changed by the molecular buffer, optionally in combination with a phosphinite mixture of known constituents. This change is reflected in the increase and maintenance of crystallinity of the aprons produced. In addition, such a molecular buffer component/additional fortifier system has broad applicability in other polyolefins including polypropylene homopolymers and copolymers and thermoplastic polyolefins (TPO) and thermoplastic elastomers (TPE). The utility of this system goes beyond polyolefins, and in general has application to all thermoplastic resins. It will provide the same degree of control of recycled plastics from condensation polymers to other addition thermoplastic polymers, including polystyrene and acrylonitrile-butadiene-styrene (ABS) polymers.

[065] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[066] Figure 1 schematically illustrates the chemical structure of a molecular buffer, comprising a metal oxide with organic phosphonate coupled thereto, which is incorporated into a polyethylene composition according to a first embodiment of the present invention.

[067] As described above, the present invention has general applicability to thermoplastic resins, including but not limited to polyolefins. However, the following specific description discusses the technical features, advantages and effects when the thermoplastic resin is polyethylene, which is the preferred thermoplastic resin in the context of the present invention. However, the person skilled in the art would readily be able to utilize the present disclosure to incorporate the technical features, advantages and effects when the thermoplastic resin is polyethylene into other thermoplastic resins, including other polyolefins, such as polypropylene homopolymers and copolymers, thermoplastic elastomers, polystyrene, acrylonitrile-butadiene-styrene, etc.

[068] In accordance with the preferred embodiments of the present invention, a polyethylene composition is provided. The polyethylene composition may comprise a single polyethylene polymer, for example a high-density polyethylene (HDPE) or a linear low-density polyethylene (LLDPE), or any blend of two or more polyethylenes. Each polyethylene component may comprise a homopolymer or a copolymer. In preferred embodiments, the polyethylene composition comprises a blend of a high-density polyethylene (HDPE) and a linear low-density polyethylene (LLDPE). Any suitable weight ratio may be used for the different components of the blend, depending on the desired properties and end use of the polyethylene composition. For example, an HDPE resin and an LLDPE resin may be blended to produce a first polymer blend comprising 70 wt% HDPE and 30 wt% LLDPE, or a second polymer blend comprising 60 wt% HDPE and 40 wt% LLDPE each wt% being based on the total weight of the polyethylene in the blend.

[069] Each polyethylene component typically comprises one or more antioxidants and/or any other additives known for incorporation into polyethylenes to improve the properties of the polyethylene resin, for example to provide protection against thermos-oxidative degradation and the provide reduced discoloration. [070] Typically, each polyethylene component comprises a primary or secondary antioxidant, and preferably at least one of the primary or secondary antioxidants comprises an organophosphorous compound. The organophosphorous compound preferably comprises an organophosphite, organophosphinate or organophosphonate, or any combination of two or more thereof.

[071] Preferably, in an HDPE/LLDPE blend, the HDPE resin and the LLDPE resin each comprise primary and secondary antioxidants.

[072] In one example, the primary antioxidant may comprise pentaerythritol tetrakis(3-(3,5-di- tert-butyl-4-hydroxyphenyl)propionate), which has CAS No. 6683-19-8. The primary antioxidant is available in commerce under the product name “Irganox ® 1010” from BASF. This primary antioxidant is commercially available to those skilled in the art as a non-discoloring, sterically hindered primary phenolic antioxidant stabilizer that protects organic substrates against thermo- oxidative degradation.

[073] In this example, the secondary antioxidant may comprise an additive which has CAS No. 119345-01-6 and is known in the art as the “Reaction products of phosphorous trichloride, with 1,1 '-biphenyl and 2,4-bis(l,l-dimethylethyl)phenol” and also “Tetrakis(2,4-di-tert-butylphenyl) 4,4-biphenyldiphosphonite tech”. The secondary antioxidant is available in commerce from various manufacturers/suppliers, for example under the product name “Irgafos ® P-EPQ” from BASF. This secondary antioxidant is commercially available to those skilled in the art as a hydrolytically stable organic phosphonite processing stabilizer and a secondary antioxidant, which reacts during processing with hydroperoxides formed by autoxidation of polymers preventing process-induced degradation and widening the performance of primary antioxidants, to prevent discoloration and give the polymer long-term protection against thermo-oxidative degradation.

[074] In both the HDPE resin and the LLDPE resin, these primary and secondary antioxidants may be present in known concentrations, as recommended by the manufacturer, and for example each in the range of 0.05 to 0.5 wt%, and in known weight ratios.

[075] These primary and secondary antioxidants may be present in a weight ratio of 1 part of primary antioxidant (Irganox ® 1010): 2 parts of secondary antioxidant (Irgafos ® P-EPQ).

[076] In accordance with a first aspect of the present invention, the polyethylene composition is modified by the addition of a modifier in the form of a metal oxide. In the preferred embodiments, the metal oxide is an amphoteric metal oxide, and preferably functions as a molecular buffer within the thermoplastic resin composition. Preferably, the amphoteric metal oxide comprises zinc oxide, aluminium oxide or gallium oxide, or any combination of any two or more thereof. In particularly preferred embodiments, the metal oxide comprises zinc oxide.

[077] The metal oxide is provided in particulate form, and a plurality of metal oxide particles is dispersed in the polyethylene composition. The metal oxide particles typically have a prismatic, spherical, pyramidal or cubic morphology.

[078] The metal oxide particles have a mean average particle size, by weight, within the range of from 0.05 to less than 1 micron. In this specification, the particle size is measured using laser diffraction, for example by a particle size analyzer available in commerce from Microtrac. The metal oxide particles typically have a mean surface area (by weight) of from 8 to 11 m ² /gm, for example 9 to 10 m ² /gm.

[079] Typically, the metal oxide particles are present in the polyethylene composition in a concentration of from 0.01 to 1 wt%, for example from 0.05 to 0.5 wt%, based on the total weight of the polyethylene composition.

[080] When the metal oxide comprises zinc oxide, the zinc oxide is preferably produced by the French process, which is well known to those skilled in the art as an indirect process for making zinc oxide, in which metallic zinc is vaporized and reacts with atmospheric oxygen to produce ZnO, and which is used to manufacture most of the zinc oxide produced worldwide. The resultant zinc oxide is chemically pure, and substantially free of any impurities such as Pb, Fe or sulphates. Preferably, the zinc oxide has a purity of at least 99.9 wt%.

[081] The metal oxide particles, preferably zinc oxide particles, have molecules of an organic phosphonate salt coupled to the surface of the metal oxide by chemical reaction between phosphonate groups, present in the corresponding phosphonic acid which reacts with the metal oxide, and oxygen atoms in the metal oxide. Typically, the organic phosphonate salt comprises an akyl and/or aryl phosphonate having from 14-25 carbon atoms.

[082] The chemical structure of the preferred molecular buffer added to the polyethylene resin is illustrated in Figure 1.

[083] The amphoteric metal oxide, for example zinc oxide, is untreated by any chemicals prior to coupling the molecules of the organic phosphonate salt to the surface of the metal oxide, which in turn is conducted prior to blending into the polyethylene resin, for example the HDPE and LLDPE resins. Consequently, the metal oxide particles have no deliberately-applied coatings thereon prior to coupling the molecules of the organic phosphonate salt to the surface of the metal oxide.

[084] Preferably, the amphoteric metal oxide, for example zinc oxide, in particulate form is added to a carrier, for comprising an LLDPE-hexene co-monomer carrier resin to form a masterbatch composition. Typically, the zinc oxide comprises 5 wt% of the masterbatch composition based on the total weight of the masterbatch composition. Then the masterbatch composition is blended into the respective polyethylene resin or resin blend. For example, the masterbatch composition may provide 2 wt% of the total weight of the final composition, to provide a concentration of 0.1 wt% zinc oxide, based on the total weight of the individual HDPE and LLDPE resins or resin blends.

[085] The pretreatment of the molecular buffer base component, i.e. the metal oxide particulate, with the aryl -substituted phosphonic acid is carried out prior to compounding the molecular buffer component with the polyethylene resin, and the aryl-substituted phosphonic acid is added at a concentration so that in the final molecular buffer component the aryl-substituted phosphonic acid is at a concentration no more than 3000 ppm by weight, based on the total weight of the final molecular buffer component.

[086] Accordingly, preferably, the organic phosphonate salt is present in a concentration of up to 3000 ppm by weight, optionally from 500 to 3000 ppm by weight, further optionally from 1000 to 3000 ppm by weight, based on the total weight of the metal oxide particles and the organic phosphonate salt.

[087] The molecular buffer component, and the aryl phosphonate therein, exhibit high temperature stability, and molecular buffer component can be subjected to temperatures up to 290 °C and still provide the desired fortification of the thermoplastic resin, typically polyethylene. The aryl phosphonate also exhibits high solubility in a variety of thermoplastic resins, such as polyethylene, for example HDPE, LLDPE or LDPE. The solubility of the aryl phosphonate in the thermoplastic resin determines the processing stability of the resultant thermoplastic resin product, for example cast and blown films, and of the recycled thermoplastic resin. The aryl phosphonate is soluble at typical thermoplastic resin densities within a range of from 0.96 to 0.84 g/cc. This broad density range allows for enhanced interactions between the molecular modifier, whether coupled to the metal oxide or not coupled. [088] In the preferred embodiments of the polyethylene composition of the first aspect of the present invention, the polyethylene composition further comprises a first fortifier and/or a second fortifier.

[089] Preferably, the first fortifier comprises a phenolic antioxidant.

[090] Typically, the phenolic antioxidant is a sterically hindered phenolic antioxidant having a molecular weight within the range of from 750 to 2000 g/mol, and the phenolic antioxidant is present in the polyethylene composition at a concentration of from 0.05 to 0.4 wt%, based on the total weight of the polyethylene composition.

[091] Preferably, the second fortifier comprises an organic phosphite antioxidant, and more preferably comprises an aryl -substituted phosphite of formula P(OR)s where R comprises an aryl substituent.

[092] Typically, the organic phosphite antioxidant comprises tris(2,4-ditert-butylphenyl) phosphite having Cas No. 31570-04-4 and a molecular weight of 647 g/mol. The organic phosphite antioxidant is present in the polyethylene composition at a concentration of from 0.05 to 0.4 wt%, based on the total weight of the polyethylene composition.

[093] In the preferred embodiments of the present invention, the molecular buffer component, and optionally additional fortifier(s), are preferably added to the polyethylene to complement the loading and type of existing additive(s), particularly fortification(s) such as antioxidants, to achieve the best synergisms between the added components to maximize both mechanical and thermo-mechanical processing at elevated temperatures from 230 °C to 260 °C and residence time for the fabrication of blown film composed of polyethylene.

[094] The molecular buffer component, and the additional fortifier(s), are REACH and EP A registered additives that meet all environmental regulations and food contact approval.

[095] In accordance with preferred embodiments of the present invention, the polyethylene composition has a Melt Flow Rate (MFR) within the range of from 0.175 to 0.250 g/10 minutes measured at 190 °C with a mass of 2.16 kg under ASTM D1238-20.

[096] In accordance with preferred embodiments of the present invention, the polyethylene composition has a Melt Index Ratio, which is a ratio of the Melt Flow Rate (MFR) measured at 190 °C with a mass of 2.16 kg under ASTM D1238-20 to the Melt Flow Rate (MFR) measured at 190 °C with a mass of 21.6 kg under ASTM D1238-20, of from 60 to 90. [097] In accordance with a second aspect of the present invention, a blown film is produced from the polyethylene composition described above.

[098] The blown film is produced by a conventional film blowing process and apparatus, to form a biaxially oriented film. The film may comprise known additives such as pigments or dyes. The blown film has any suitable thickness desired for any given end application. A typical thickness is within the range of 10 to 20 microns. In preferred embodiments of the present invention, the blown film is intended to be die-cut to form medical aprons, which are for single use and are therefore intended to be disposable and recyclable. A preferred thickness of the blown film to manufacture the medical aprons is 16 microns.

[099] In accordance with the present invention, it has been found that the addition of the molecular buffer, and preferably also the first and/or second fortifiers, to the polyethylene composition can increase both the dart strength and the crystallinity of the blown film.

[100] Preferably, the blown film has a dart impact strength of at least 50 grams, typically at least 100 grams, for a 16 micron thickness of the blown film.

[101] In preferred embodiments, the polyethylene composition in the blown film has a crystallinity of at least 50%, typically from 50 to 55%.

[102] In a third aspect of the present invention, there is therefore provided a medical apron formed from the blown film of the second aspect of the present invention.

[103] In a fourth aspect of the present invention, there is provided a method of producing a polyethylene resin material.

[104] The method comprises providing a first polyethylene component and a second polyethylene component. The second polyethylene composition comprises recycled polyethylene which comprises a polyethylene composition as described above according to the first aspect of the present invention. Preferably, the second polyethylene component has been mechanically ground, melt compounded and pelletized. The first and second polyethylene components are blended to form the polyethylene resin material.

[105] Typically, the polyethylene resin material comprises from 30 to 70 wt% of the first polyethylene component and from 30 to 70 wt% of the second polyethylene component, each based on the based on the total weight of the polyethylene composition.

[106] In some embodiments, the first polyethylene component comprises a polyethylene composition according to the first aspect of the present invention. [107] In alternative embodiments, the first polyethylene component comprises a polyethylene constituent which is a virgin polyethylene.

[108] Typically, the polyethylene composition of the first polyethylene component, and optionally any virgin polyethylene therein, further comprises a primary or secondary antioxidant, optionally at least one of which primary or secondary antioxidants comprises an organophosphorous compound, further optionally which organophosphorous compound comprises an organophosphite, organophosphinate or organophosphonate, or any combination of two or more thereof.

[109] In a fifth aspect of the present invention, there is provided a method of recycling a blown film comprising a polyethylene resin material.

[110] In this method, a blown film comprising a polyethylene resin material is provided, and the polyethylene resin material in the blown film is mechanically and thermally processed to form a plurality of pellets.

[111] During or after the mechanically and thermally processing, a plurality of metal oxide particles are dispersed in the polyethylene resin material. The metal oxide particles have molecules of an organic phosphonate salt coupled to the surface of the metal oxide by chemical reaction between phosphonate groups and oxygen atoms in the metal oxide to form a recycled polyethylene resin material comprising the dispersed metal oxide particles.

[112] As described above with respect to the first aspect of the present invention, the metal oxide may comprise zinc oxide, and the metal oxide particles form a molecular buffer in the recycled polyethylene resin material. The recycled polyethylene resin material may also comprise the first and/or second fortifiers, as described above.

[113] Thereafter, the recycled polyethylene resin material is blended with a non-recycled polyethylene resin material to form a final polyethylene resin material which comprises, as a proportion of the weight of the final polyethylene resin material, recycled polyethylene.

[114] Finally, the final polyethylene resin material is blown to form a blown film comprising the final polyethylene resin material.

[115] Typically, the final polyethylene resin material comprises from 30 to 70 wt% of the nonrecycled polyethylene resin material and from 30 to 70 wt% of the recycled polyethylene resin material, each based on the based on the total weight of the final polyethylene resin material. [116] Preferably, the recycled polyethylene resin material comprises a polyethylene composition according to the first aspect of the present invention.

[117] In some embodiments, the non-recycled polyethylene resin material comprises a polyethylene composition according to the first aspect of the present invention

[118] In alternative embodiments, the non-recycled polyethylene composition comprises or consists of a polyethylene constituent which is a virgin polyethylene.

[119] Typically, any one or more of (a) the thermoplastic resin material of the blown film, (b) the non-recycled thermoplastic resin material and the (c) the virgin thermoplastic resin further comprises a primary or secondary antioxidant. At least one of the primary or secondary antioxidants may comprise an organophosphorous compound. Typically, the organophosphorous compound comprises an organophosphite, organophosphinate or organophosphonate or any combination of two or more thereof.

[120] Preferably, the blown film has a dart impact strength of at least 50 grams, more preferably at least 100 grams, for a 16 micron thickness of the blown film.

[121] Typically, the polyethylene composition in the blown film has a crystallinity of at least 50%, preferably from 50 to 55%.

[122] The present invention will now be described in greater detail with reference to the following non-limiting Examples and Comparative Examples.

Comparative Example 1

[123] In this Comparative Example, two commercially available polyolefin resins were provided and the individual resins, and blend of the resins, were subject to processing at elevated temperature. The processing was repeated multiple times to simulate the effect of a recycle loop on the rheological properties of the polyolefin resins.

[124] In particular, a high-density polyethylene (HDPE) resin was provided. The HDPE resin is available in commerce from Lyondel Basell under the trade name Alathon L5485. Also, a linear low-density polyethylene (LLDPE) resin was provided. The LLDPE resin is available in commerce from Dow Chemical under the trade name DOWLEX 2045. The HDPE resin and the LLDPE resin each comprised primary and secondary antioxidants.

[125] The primary antioxidant comprised pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyljpropionate), which has CAS No. 6683-19-8. The primary antioxidant is available in commerce under the product name “Irganox ® 1010” from BASF. This primary antioxidant is commercially available to those skilled in the art as a non-discoloring, sterically hindered primary phenolic antioxidant stabilizer that protects organic substrates against thermo-oxidative degradation.

[126] The secondary antioxidant comprised an additive which has CAS No. 119345-01-6 and is known in the art as the “Reaction products of phosphorous trichloride, with 1,1 '-biphenyl and 2,4- bis(l,l-dimethylethyl)phenol” and also “Tetrakis(2,4-di-tert-butylphenyl) 4,4- biphenyldiphosphonite tech”. The secondary antioxidant is available in commerce from various manufacturers/suppliers, for example under the product name “Irgafos ® P-EPQ” from BASF. This secondary antioxidant is commercially available to those skilled in the art as a hydrolytically stable organic phosphonite processing stabilizer and a secondary antioxidant, which reacts during processing with hydroperoxides formed by autoxi dation of polymers preventing process-induced degradation and widening the performance of primary antioxidants, to prevent discoloration and give the polymer long-term protection against thermo-oxidative degradation.

[127] In both the HDPE resin and the LLDPE resin, these primary and secondary antioxidants were present in a weight ratio 1 part of primary antioxidant (Irganox ® 1010): 2 parts of secondary antioxidant (Irgafos ® P-EPQ).

[128] The HDPE resin comprised 277 ppm of the mixture of these primary and secondary antioxidants and the LLDPE resin comprised 300 ppm of the mixture of these primary and secondary antioxidants.

[129] The HDPE resin and the LLDPE resin were blended to produce two polymer blends; Blend #1 comprised 70 wt% HDPE and 30 wt% LLDPE, and Blend #2 comprised 60 wt% HDPE and 40 wt% LLDPE each wt% being based on the total weight of the polyethylene in the blend.

[130] Each of the HDPE resin, the LLDPE resin, Blend #1 and Blend #2 were subjected to a resin processing which simulates recycling of the polymer resin. The processing comprised extrusion of the resin at a temperature of 240 °C using a conventional twin screw extruder having a screw diameter of 21 mm for each screw.

[131] The extruded resin was then tested to measure the effect of the processing on the rheological properties of the polymer resin. In particular, the Melt Flow Rate (MFR), hereinafter also referred to as the “Melt Index”, of the polymer resin was measured using the test protocol of ASTM DI 238-20 (entitled “Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer”), Procedure A, using the test parameters of a temperature of 190 °C and a mass of 2.16 kg.

[132] The MFR of each of the tested resins after the “first pass” of the tested polymer resin through the extrusion processing was measured and the results are shown in Table 1.

[133] Table 1 shows that after the “first pass”, the HDPE resin, the LLDPE resin, Blend #1 and Blend #2 had the following respective Melt Index values: 0.85, 1.10, 1.6 and 1.5 g/10 minutes.

[134] The four tested polymer resins were then subjected to a plurality of successive extrusion processing steps in order to simulate further recycling processing. The MFR of each of the tested resins was determined after three (3X), five (5X) and ten (10X) passes of the tested polymer resin through the extrusion processing. The results are shown in Table 1.

Table 1

[135] Table 1 shows that with an increase in the number of passes, the MFR of each of the tested resins, namely the HDPE resin, the LLDPE resin, Blend #1 and Blend #2, exhibited a significant change, either a decrease in MFR for the HDPE resin, Blend #1 and Blend #2 and an increase in MFR for the LLDPE resin.

[136] The data in Table 1 shows that the known antioxidants, comprising the primary and secondary antioxidants in typical known concentrations when used in polyolefins, were not capable of maintaining the rheological properties of the polyolefin resins, which properties are represented by the MFR, as a result of successive resin processing treatments which simulates the treatments of resins during a recycling process. The data in Table 1 therefore shows that known antioxidants are not able to provide polyolefin resins which can maintain the desired rheological properties during multiple successive recycle loops. Example 1

[137] In this Example, the same HDPE and LLDPE resins as used in Comparative Example 1, both the individual resins and blends of the resins, were subject to processing at elevated temperature using the same processing as employed in Comparative Example 1.

[138] However, in Example 1 the HDPE and LLDPE resins were each modified by the addition to the resin, prior to the extrusion processing, of a modifier in the form of zinc oxide. The zinc oxide was provided in particulate form, and the particles were in a sub-micron particle size range with a mean average particle size (by weight) of 0.11 microns and D90 of 0.11 microns, DIO of 0.8 microns measured using laser diffraction by a particle size analyzer available in commerce from Microtrac. The particles had a mean surface area (by weight) of 9 m ² /gm. The zinc oxide was produced by the French process, which is well known to those skilled in the art as an indirect process for making zinc oxide, in which metallic zinc is vaporized and reacts with atmospheric oxygen to produce ZnO, and which is used to manufacture most of the zinc oxide produced worldwide. The resultant zinc oxide is chemically pure 99.9 wt% minimum and substantially free of any impurities such as Pb, Fe or sulphates. Levels of Pb, Fe, Cu, below 2 ppm. The zinc oxide added to the HDPE and LLDPE resins was untreated by any chemicals prior to coupling the molecules of the organic phosphonate salt to the surface of the metal oxide, which in turn is conducted prior to blending into the HDPE and LLDPE resins

[139] Conventionally, metal oxide particulates for use in thermoplastic resins, for example for use as conventional fillers, are typically coated with propionic acid or a carboxylic acid to allow uniform dispersion of the metal oxide particles throughout the thermoplastic resin.

[140] However, in accordance with the present invention, the metal oxide particles are not coated with such conventional acid coating but instead are coated by an organic phosphonic acid, so that the surface of the metal oxide particles are coupled to organic phosphonate molecules.

[141] Zinc oxide produced by the French process, and which has not been coated with chemicals such as propionic acid which are conventionally used to limit agglomeration, has a charge density on the surface of the particles that causes agglomeration. Treatment of the zinc oxide with low levels of an organic phosphonic acid, for example an aryl phosphonic acid, creates a metastable particle state, i.e. particle instability but which is sufficiently long-lived as to be stable for practical purposes when used as a modifier for the thermoplastic resin. The charge density on the metal oxide surface allows for coupling of the organic phosphonic acid on the surface of the particles, thereby lowering charge density and reversing agglomeration. Such coupling allows for formation of both zinc phosphate and reactive nanoparticles with transformation products from any phosphorous-containing fortifiers, such as aryl phosphonite, which are additionally present in the thermoplastic resin. Such formation can occur in-situ during the melt compounding of the masterbatch and subsequently during the production of the thermoplastic resin material or any product thereof, for example during blown film production. In addition, aryl phosphonates contain trace amounts of phosphite and both transform in-situ with hydroperoxides and alkoxy radicals to form phosphonates and phosphates. Phosphites have low solubility in thermoplastic resins such as polyethylene, while phosphonites have significantly higher solubility.

[142] Without being bound by any theory, it is believed by the present inventor that metal phosphonates which are formed act to increase the crystallinity of HDPE and HDPE-LLDPE polyblends by a nucleation mechanism. The zinc oxide molecular buffer component is also believed to increase hydrolytic stability and reduce hygroscopicity of the aryl phosphonite fortifier while altering the free radical mechanism and transformation properties of the primary antioxidant thereby controlling initial and post storage discoloration of the thermoplastic resin/fortification system. It is also believed that the molecular buffer also acts as an anti-fungal agent, an antimicrobial agent and a molecular tag. The amphoteric character of the molecular buffer is believed also to balance out the stabilization system by providing an acid and base balance. Such an amphoteric balance also reduces free radical stability and reduces the formation of hydroperoxides by adjusting the system on the basic side thereby reducing free radical formation and dissociating alkyl radicals into inert non-reactive species.

[143] The zinc oxide was added to the HDPE and LLDPE resins at a concentration of 0.1 wt%, based on the total weight of the individual HDPE and LLDPE resins or blends of those resins containing the zinc oxide. The zinc oxide in particulate form was added to a carrier comprising an LLDPE-hexene co-monomer carrier resin to form a masterbatch composition, the zinc oxide comprising 5 wt% of the masterbatch composition based on the total weight of the masterbatch composition. Then the masterbatch composition was blended into the respective resin or resin blend, to provide 2 wt% of masterbatch composition based on the total weight of the final composition, which provided the required concentration of 0.1 wt% zinc oxide, based on the total weight of the individual HDPE and LLDPE resins or resin blends. [144] Each of the HDPE resin, the LLDPE resin, Blend #1 and Blend #2, all of which comprised the added zinc oxide, were subjected to the same resin processing as described above for Comparative Example 1 which simulates recycling of the polymer resin. The processing again comprised extrusion of the resin at a temperature of 240 °C using a conventional twin screw extruder having a screw diameter of 21 mm for each screw.

[145] The extruded resin was then tested to measure the Melt Flow Rate (MFR) as described for Comparative Example

[146] The MFR of each of the tested resins after three (3X), five (5X) and ten (10X) passes of the tested polymer resin through the extrusion processing, were measured and the results are shown in Table 2.

Table 2

[147] A comparison of Tables 1 and 2 shows the effect of adding the zinc oxide to the polyolefin resins. The data in Table 2 shows that the addition of zinc oxide tends to stabilize the MFR of each of the tested resins as the number of passes is increased. The HDPE resin, the LLDPE resin, Blend #1 and Blend #2, exhibited reduced changes, either a reduced decrease in MFR for the HDPE resin, Blend #1 and Blend #2 and or a reduced increase in MFR for the LLDPE resin.

[148] The data in Table 2 shows that the addition of the zinc oxide modifier to polyolefins comprising known antioxidants, in particular the known primary and secondary antioxidants in typical known concentrations, can provide the technical effect of maintaining the rheological properties of the polyolefin resins, which properties are represented by the MFR, as a result of successive resin processing treatments which simulates the treatments of resins during a recycling process. The data in Table 1 therefore shows that addition of the zinc oxide modifier to polyolefin resins comprising known antioxidants can maintain the desired rheological properties during multiple successive recycle loops.

Example 2

[149] In this Example, the same HDPE and LLDPE resins as used in Comparative Example 1, both the individual resins and blends of the resins, were subject to processing at elevated temperature using the same processing as employed in Comparative Example 1, but at two different temperatures, in particular at 240 °C as in Comparative Example 1 and also at 260 °C.

[150] In addition, in Example 2 the HDPE and LLDPE resins were each modified by the addition to the resin, prior to the extrusion processing, of two fortifier components to the resin.

[151] The first fortifier comprises a phenolic antioxidant, preferably a high molecular wight sterically hindered phenolic antioxidant, for example which are well known for use as antioxidants in polyolefins. The molecular weight of the sterically hindered phenolic antioxidant is typically within the range of from 750 to 2000 g/mol, for example from 1000 to 1500 g/mol. The phenolic antioxidant is typically present in the polyethylene at a concentration of from 0.05 to 0.4 wt%, based on the weight of the polyethylene.

[152] In the Examples, the first fortifier was the same as the primary antioxidant in the resins, and comprised pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), which has CAS No. 6683-19-8, and is available in commerce under the product name “Irganox ® 1010” from BASF. This phenolic antioxidant is a high molecular wight sterically hindered phenolic antioxidant, well known for use as an antioxidant in polyolefins, having a molecular weight of 1178 g/mol.

[153] The second fortifier comprised an organic phosphite, having the formula Tris(2,4-ditert- butylphenyl) phosphite and Cas No. 31570-04-4. This fortifier is commercially available as an antioxidant, in particular a secondary antioxidant, under the trade name Irgafos ® 168 from BASF, Omnistab AN 168 from Partners in Chemicals or Westco AO 168 from Western Reserve Chemicals.

[ 154] The first fortifier was added to the HDPE and LLDPE resins at a concentration of 0.1 wt%, and the second fortifier was added to the HDPE and LLDPE resins at a concentration of 0.4 wt%, each based on the total weight of the individual HDPE and LLDPE resins or blends of those resins containing the first and second fortifiers. The first and second fortifiers were added to a carrier comprising an LLDPE-hexene co-monomer carrier resin to form a masterbatch composition, the first fortifier comprising 5 wt% of the masterbatch composition and the second fortifier comprising 20 wt% of the masterbatch composition, each based on the total weight of the masterbatch composition. Then the masterbatch composition was blended into the respective resin or resin blend, to provide 2 wt% of masterbatch composition based on the total weight of the final composition, which provided the required concentration of 0.1 wt% first fortifier and 0.4 wt% second fortifier, based on the total weight of the individual HDPE and LLDPE resins or resin blends.

[155] Each of the HDPE resin, the LLDPE resin, Blend #1 and Blend #2, all of which comprised the added first and second fortifiers, were subjected to the same resin processing as described above for Comparative Example 1 which simulates recycling of the polymer resin. A first processing sequence again comprised extrusion of the resin at a temperature of 240 °C using a conventional twin screw extruder having a screw diameter of 21 mm for each screw, and an alternative second processing sequence used a higher temperature of 260 °C.

[156] The extruded resin was then tested to measure the Melt Flow Rate (MFR) as described for Comparative Example 1.

[157] The MFR of each of the tested resins after a first pass of the tested polymer resin through the extrusion processing at 240 °C, was measured and the results are shown in Table 3.

[158] The MFR of each of the tested resins after three (3X), five (5X) and ten (10X) passes of the tested polymer resin through the extrusion processing at 240 °C and 260 °C, were measured and the results are shown in Table 3.

Table 3

[159] A comparison of Tables 1 and 3 shows the effect of adding the first and second fortifiers to the polyolefin resins.

[160] The data in Table 3 shows that, for the same extrusion processing temperature of 240 °C, the addition of the first and second fortifiers tends to stabilize the MFR of each of the tested resins as the number of passes is increased. The HDPE resin, the LLDPE resin, Blend #1 and Blend #2, exhibited reduced changes, either a reduced decrease in MFR for the HDPE resin, Blend #1 and Blend #2 and or a reduced increase in MFR for the LLDPE resin. The data in Table 3 also shows that a similar effect is achieved at a higher extrusion processing temperature of 260 °C, which would be expected to cause even greater degradation of the rheological properties of the resin with successive processing cycles.

[161] The data in Table 3 shows that the addition of the first and second fortifiers to polyolefins comprising known antioxidants, in particular the known primary and secondary antioxidants in typical known concentrations, can provide the technical effect of maintaining the rheological properties of the polyolefin resins, which properties are represented by the MFR, as a result of successive resin processing treatments which simulates the treatments of resins during a recycling process. The data in Table 3 therefore shows that addition of the first and second fortifiers to polyolefin resins comprising known antioxidants can maintain the desired rheological properties during multiple successive recycle loops.

Example 3

[162] In this Example, the same HDPE and LLDPE resins as used in Example 2, both the individual resins and blends of the resins, were subject to processing at elevated temperature using the same processing as employed in Example 2 at two different temperatures, in particular at 240 °C and at 260 °C. [163] In addition, in Example 3 the HDPE and LLDPE resins were each modified by the addition to the resin, prior to the extrusion processing, of (i) the zinc oxide modifier as used in Example 1 and (ii) the first and second fortifier components as used in Example 2.

[164] The zinc oxide was added to the HDPE and LLDPE resins at a concentration of 0.1 wt%, the first fortifier was added to the HDPE and LLDPE resins at a concentration of 0.1 wt%, and the second fortifier was added to the HDPE and LLDPE resins at a concentration of 0.4 wt%, each based on the total weight of the individual HDPE and LLDPE resins or blends of those resins containing the zinc oxide and first and second fortifiers. The zinc oxide and the first and second fortifiers were added using a masterbatch composition as described above in Examples 1 and 2.

[165] Each of the HDPE resin, the LLDPE resin, Blend #1 and Blend #2, all of which comprised the added zinc oxide and first and second fortifiers, were subjected to the same resin processing as described above for Comparative Example 1 which simulates recycling of the polymer resin. A first processing sequence again comprised extrusion of the resin at a temperature of 240 °C using a conventional twin screw extruder having a screw diameter of 21 mm for each screw, and an alternative second processing sequence used a higher temperature of 260 °C.

[166] The extruded resin was then tested to measure the Melt Flow Rate (MFR) as described for Comparative Example 1.

[167] The MFR of each of the tested resins after a first pass of the tested polymer resin through the extrusion processing at 240 °C, was measured and the results are shown in Table 4.

[168] The MFR of each of the tested resins after three (3X), five (5X) and ten (10X) passes of the tested polymer resin through the extrusion processing at 240 °C and 260 °C, were measured and the results are shown in Table 4.

[169]

Table 4

[170] A comparison of Tables 1, 3 and 4 shows the effect of adding zinc oxide and the first and second fortifiers to the polyolefin resins.

[171] The data in Table 4 shows that, for the same extrusion processing temperature of 240 °C, the addition of the zinc oxide and the first and second fortifiers tends even further to stabilize the MFR of each of the tested resins as the number of passes is increased. The HDPE resin, the LLDPE resin, Blend #1 and Blend #2, exhibited significantly reduced changes, either a reduced decrease in MFR for the HDPE resin, Blend #1 and Blend #2 and or a reduced increase in MFR for the LLDPE resin. The data in Table 4 also shows that a similar effect is achieved at a higher extrusion processing temperature of 260 °C, which would be expected to cause even greater degradation of the rheological properties of the resin with successive processing cycles.

[172] The data in Table 4 shows that the addition of the zinc oxide and the first and second fortifiers to polyolefins comprising known antioxidants, in particular the known primary and secondary antioxidants in typical known concentrations, can provide the technical effect of enhanced maintenance of the rheological properties of the polyolefin resins, which properties are represented by the MFR, as a result of successive resin processing treatments which simulates the treatments of resins during a recycling process. The data in Table 4 therefore shows that addition of the zinc oxide and the first and second fortifiers to polyolefin resins comprising known antioxidants can maintain the desired rheological properties during multiple successive recycle loops.

Example 4

[173] In this Example, the same HDPE and LLDPE resins as used in Example 3, both the individual resins and blends of the resins, were subject to processing at elevated temperature using the same processing as employed in Example 3 at two different temperatures, in particular at 240 °C and at 260 °C. [174] In addition, in Example 4 the HDPE and LLDPE resins were each modified by the pretreatment of the zinc oxide modifier, as used in Example 1, prior to the zinc oxide being incorporated into the masterbatch as described above in the preceding Examples 1 and 3. The zinc oxide was pretreated by contact with both H3PO3 phosphorous acid and aryl phosphonic acid constitutents having the formula R-P0(0H)2, and R00-P0-(0R)2 where R is an unsubstituted aryl substituent having 14-25 carbon atoms, such as mono-Phosphonite, 4,4’-phosphonite, 3,3’ phosphonite; 4, 3 ’-phosphonite as shown below. Phosphorous acid activation of the amphoteric metal oxide, such as zinc oxide, allows interaction with the phosphonite structures in the second fortifier, i.e. secondary antioxidant, such as P-EPQ. There are four principal isomers identified in the P-EPQ secondary antioxidant, and all or some will interact depending on the in-situ hydrolysis reaction controlled by the amphoteric metal oxide. The balance in the synergism allows selective isomers noted to form and extends the life and performance of the secondary antioxidant more effectively than without out the treated or untreated oxide.

[176] As shown above, the P-EPQ comprises mono-P-EPQ and di-P-EPQ constituents. The mono-P-EPQ will react like the phosphorus acid activation, whereas the di-P-EPQ constituents provide greater synergisms with the phenolic antioxidant. In accordance with the preferred embodiments of the present invention, the P-EPQ is effectively altered in-situ to work more effectively. This effect is also achieved by triphenyl phosphite interactions for the Irgafos ® 168 secondary antioxidant. However, triphenyl phosphites are not very thermally stable and consume faster than P-EPQ due to the simple chemistry of phosphite to phosphate, while phosphonites transform to phosphonates via a more complex set of mechanisms and appear to alter more with various environmental changes in the system.

[177] The zinc oxide particles were pretreated by contact with phosphorous acid and the aryl phosphonic acid, and the -OH and =0 groups of the aryl phosphonic acid react with the oxide groups of the zinc oxide, or with -OH groups of hydrated zinc oxide, to provide a phosphonate- containing “molecular buffer” layer on the surface of the zinc oxide particles. The reaction and structure are shown in Figure 1, which shows the organic phosphonate salt coupled to the surface of the metal oxide.

[178] The organic phosphonate salt typically comprises from one to two P atoms. The treatment acid has one phosphorous atom (i.e. IP) but the secondary reaction by the phosphonite transformation products and isomer mix of constituents forms products with two phosphorous atoms (i.e. 2P). The concentration of the phosphorous acid is typically initially about 500 ppm, and then the phosphorous acid initiates in-situ phosphonite interactions during melt compounding while controlling the reaction and synergisms with the metal oxide and the primary and secondary antioxidants.

[179] The resultant pretreated zinc oxide particles comprised 500 ppm by weight of the aryl phosphonate and 100 ppm phosphorous acid based on the total weight of the pretreated zinc oxide particles.

[180] In the preferred embodiments of the present invention, therefore, the metal oxide, preferably amphoteric metal oxide, and more preferably zinc oxide, is activated by coupling with an organic phosphonate salt. Such activation preferably additionally uses phosphorous acid H3PO3, but since the phosphorous acid undergoes tautomerism the following reversible reaction occurs:

[181] [182] Phosphorous acid activates the metal (e.g. zinc) oxide structure. The formation in-situ of metal (e.g. zinc) phosphate, metal (e.g. zinc) oxide phosphate and potentially tertiary metal (e.g. zinc) phosphate is rate determining and dependant on the concentration of phosphorous acid utilized. The formation of the metal phosphate has a crystalline reaction product matrix, which can allow diffusion and leakage of small molecules to further react. No all of the amphoteric metal oxide is reacted with the phosphorous acid and the organic phosphonate salt, which therefore provides some residual amphoteric metal oxide to interact with secondary antioxidants and any isomers of the secondary antioxidant, such as the isomers of the secondary antioxidant P-EPQ discussed above, thereby forming synergistic reactive products which can achieve or enable the rheological and molecular changes in the final thermoplastic polymers, for example polyolefins such as polyethylene or polypropylene. These rheological outcomes are also related to changes in molecular weight and molecular weight distribution. For example, the following reaction scheme may occur:

[184] The activation of the amphoteric metal oxide can function to improve the antioxidant function of phosphites and phosphonites present in, or resulting from, secondary antioxidants. By activation of the amphoteric metal oxide, in-situ performance of the secondary antioxidants can be enhanced by inducing new synergisms and control of the rates of reaction and improving on the ROOH radical mechanism.

[185] Again, the pretreated zinc oxide was added to the HDPE and LLDPE resins at a concentration of 0.1 wt%, based on the total weight of the individual HDPE and LLDPE resins or blends of those resins containing the zinc oxide and first and second fortifiers. Again, the first fortifier was added to the HDPE and LLDPE resins at a concentration of 0.1 wt%, and the second fortifier was added to the HDPE and LLDPE resins at a concentration of 0.4 wt%, each based on the total weight of the individual HDPE and LLDPE resins or blends of those resins containing the zinc oxide and first and second fortifiers. The zinc oxide and the first and second fortifiers were added using a masterbatch composition as described above in Example 3. [186] Each of the HDPE resin, the LLDPE resin, Blend #1 and Blend #2, all of which comprised the added pretreated zinc oxide and first and second fortifiers, were subjected to the same resin processing as described above for Comparative Example 1 which simulates recycling of the polymer resin. A first processing sequence again comprised extrusion of the resin at a temperature of 240 °C using a conventional twin screw extruder having a screw diameter of 21 mm for each screw, and an alternative second processing sequence used a higher temperature of 260 °C.

[187] The extruded resin was then tested to measure the Melt Flow Rate (MFR) as described for Comparative Example 1.

[188] The MFR of each of the tested resins after three (3X), five (5X) and ten (10X) passes of the tested polymer resin through the extrusion processing at 240 °C and 260 °C, were measured and the results are shown in Table 5.

Table 5

[189] A comparison of Tables 1, 3 and 5 shows the effect of adding pretreated zinc oxide and the first and second fortifiers to the polyolefin resins.

[190] The data in Table 5 shows that, for the same extrusion processing temperature of 240 °C, the addition of the pretreated zinc oxide and the first and second fortifiers tends even further to stabilise the MFR of each of the tested resins as the number of passes is increased. [191] Comparing Table 5 to Table 4, it can be seen that pretreating the zinc oxide particles with a phosphonate-containing “molecular buffer” layer on the surface of the zinc oxide even further provides the technical effect of enhanced maintenance of the rheological properties of the polyolefin resins as a result of successive resin processing treatments. The data in Table 5 therefore shows that addition of the pretreated zinc oxide and the first and second fortifiers to polyolefin resins comprising known antioxidants can maintain the desired rheological properties during multiple successive recycle loops.

Comparative Example 2

[192] In this Comparative Example, a typical commercial polyethylene composition used for the manufacture of blown films was provided. The polyethylene composition comprised 62 wt% of HDPE, 33 wt% of an LLDPE/butene-1 copolymer, 3 wt% of a titanium dioxide inorganic particle filler and 2 wt% of a masterbatch comprising a process aid in a conventional carrier, each wt% value being based on the total weight of the polyethylene composition.

[193] The polyethylene composition was tested to measure the MFR, using the same test method as described above for Comparative Example 1. The initial polyethylene composition had an MFR of 0.2933 g/10 minutes.

[194] A portion of the initial polyethylene composition was blown into a film with a thickness of 16 microns, which is a thickness suitable for making medical aprons. Then the blown film was mechanically ground, formed into pellets and melt compounded at a temperature of 230 °C. These steps of mechanical grinding, pellet forming and melt compounding simulated a typical polyolefin recycling process and formed a simulated-recycled polyethylene composition called herein “Rl”, i.e. the polyethylene had been “recycled” through one recycle loop.

[195] The simulated-recycled polyethylene composition Rl was tested to measure the MFR, using the same test method as described above for Comparative Example 1, and the MFR was 0.2333 g/10 minutes.

[196] It will be noted that the MFR of the polyethylene composition was significantly reduced as a result of the polyethylene composition being passed through the simulated recycle loop.

[197] Then, the simulated-recycled polyethylene composition Rl was formed into face cut pellets, by mechanical grinding at high shear followed by melt compounding in air at a temperature of 230 °C to form the pellets, and accordingly was subjected to high shear conditions. The MFR of the resin in the pellets was measured using the same test method as described above for Comparative Example 1, and the MFR was found to have increased to 17.19 g/10 minutes as a result of the high shear conditions.

[198] The simulated-recycled polyethylene composition R1 was then again tested to measure the MFR, but this time using a modification of the test method as described above for Comparative Example 1, the modification being that the temperature of 230 °C, rather than 190 °C, was used in the MFR test. The MFR, measured at 230 °C, was found to have increased to 0.2597 g/10 minutes.

[199] Then, the MFR of the resin in the pellets was measured using the higher test temperature of 230 °C, and the MFR was found to have increased to 26.778 g/10 minutes as a result of the high shear conditions. The higher test temperature corresponds to the temperature used to compound the pellets.

[200] Without being bound by any theory, these MFR results are believed to show that when the unfortified resin is subjected to high shear, which is typically used when manufacturing a blown film, such as for use in making medial aprons, high chain scission of the polyethylene molecules occurs. The high chain scission reduces the average length of the polyethylene molecules, and consequently the melt flow rate is significantly increased.

[201] A portion of the initial polyethylene composition was then blended with a portion of the simulated-recycled polyethylene composition R1 to represent a typical commercial use of recycled polyolefins, in which “virgin” polyolefin is blended with “recycled” polyolefin to utilize recycled polymer material while trying to maintain the desired rheological properties, and other desired material properties, of the polyolefin composition. In particular, a blend comprising 60 wt% of the initial polyethylene composition and 40 wt% of the simulated-recycled polyethylene composition R1 was formed. This blend was again used to form a blown film of a thickness suitable for making medical aprons. The MFR of the blend was measured, using the same test method as described above for Comparative Example 1, and the MFR was 4.3072 g/10 minutes. The MFR of the blend has significantly increased as compared to the MFR of the virgin resin, which results in the blend exhibiting poor rheological and other properties.

[202] The blown film of 16 microns thickness formed from the initial polyethylene composition was tested to determine the impact strength of the blown film. In particular, the blown film was subjected to a dart impact test as specified in ISO7765-E2004. One known threshold applied by one medical organization for the minimum dart impact strength acceptable for medical aprons is a dart impact strength of greater than 30 grams. The average dart impact strength for a sample of 16 micron thick typical medical aprons sold commercially in the UK was found to be 47.1 grams.

[203] The blown film of 16 microns thickness formed from the initial polyethylene composition was determined to have a dart impact strength of 110 grams. The crystallinity of this blown film was also measured by a conventional thermal analysis, calibrated to a value of 293 Joules for 100% polyethylene crystallinity, and the crystallinity was measured as 53.53%. This compares to an average crystallinity of 48.2 % for a sample of 16 micron thick typical medical aprons sold commercially in the UK.

[204] The blown film of 16 microns thickness formed from the blend comprising 60 wt% of the initial polyethylene composition and 40 wt% of the simulated-recycled polyethylene composition R1 was determined to have a dart impact strength of 107 grams. The crystallinity of this blown film was also measured as described above, and the crystallinity was measured as 52.77%. Accordingly, the crystallinity was reduced by incorporating the recycled polyethylene.

[205] It will therefore be noted that the incorporation of “recycled” polyethylene into the “virgin” polyethylene reduced the dart impact strength of the blown film. Even though the dart impact strength in each case was above the minimum threshold specified by one medical organization for the minimum dart impact strength acceptable for medical aprons, nevertheless any drop in dart impact strength as a result of incorporating recycled polymer is undesirable, and the drop in dart impact strength would decrease even further as a result of plural recycling loops.

[206] The MFR of the blend comprising 60 wt% of the initial polyethylene composition and 40 wt% of the simulated-recycled polyethylene composition Rl, which was 4.3072 g/10 minutes as described above, was again measured, using the same test method as described above for Comparative Example 1, at a temperature of 190 °C, but with an applied mass of 21.6 kg rather than an applied mass of 2.16 kg. The MFR value when using the 21.6 kg mass was 14,4899 g/10 minutes, and therefore the Melt Index Ratio, which is defined at the ratio of the MFR values measured at 21.6 kg and 2.16 kg, was 3.3641.

[207] The MFR of the simulated-recycled polyethylene composition Rl, which was 0.2333 g/10 minutes as described above, was again measured, using the same test method as described above for Comparative Example 1, at a temperature of 190 °C, but with an applied mass of 21.6 kg rather than an applied mass of 2.16 kg. The MFR value when using the 21.6 kg mass was 17,1900 g/10 minutes, and therefore the Melt Index Ratio was 73.682. Example 5

[208] In this Example, as compared to Comparative Example 2, the polyethylene composition used for the manufacture of the blown films comprised a modified polyethylene composition additionally comprising the pretreated zinc oxide, and the first and second fortifiers, as described in Example 4.

[209] The polyethylene composition therefore comprised 62 wt% of HDPE, 33 wt% of an LLDPE/butene-1 copolymer, 3 wt% of a titanium dioxide inorganic particle filler and 2 wt% of the same masterbatch comprising the same process aid in the same carrier as in Comparative Example 2, and additionally the masterbatch comprised the pretreated zinc oxide, and the first and second fortifiers to provide 0.1 wt% of the pretreated zinc oxide, 0.1 wt% of the first fortifier and 0.4 wt% of the second fortifier, each wt% value being based on the total weight of the polyethylene composition.

[210] The modified polyethylene composition was tested to measure the MFR, using the same test method as described above for Comparative Example 1. The initial modified polyethylene composition had an MFR of 0.2233 g/10 minutes.

[211] Therefore, the addition of the pretreated zinc oxide, and the first and second fortifiers to the initial polyethylene composition caused the modified polyethylene composition to exhibit an MFR which was 20.46% lower than the MFR for the “unmodified” polyethylene composition having an MFR of 0.2933 g/10 minutes.

[212] This shows that the addition of the pretreated zinc oxide, and the first and second fortifiers to the initial polyethylene composition significantly alters the rheological properties of the polyethylene composition.

[213] A portion of the initial modified polyethylene composition was blown into a film with a thickness of 16 microns.

[214] The blown film of 16 microns thickness formed from the initial “modified” of the polyethylene composition was tested to determine the impact strength of the blown film, which was found to be a dart impact strength of 118 grams. The crystallinity of this blown film was also measured as described above, and the crystallinity was measured as 52.28%.

[215] In other words, the dart impact strength of the initial “modified” polyethylene composition was higher than the dart impact strength of the initial “unmodified” polyethylene composition of Comparative Example 2 and the dart impact strength of the “unmodified” blend of the “virgin” and “simulated recycled” polyethylene composition of Comparative Example 2.

[216] Then the blown film was mechanically ground, formed into pellets and melt compounded at a temperature of 230 °C. These steps of mechanical grinding, pellet forming and melt compounding again simulated a typical polyolefin recycling process and formed a simulated- recycled polyethylene composition called herein “modified Rl”, i.e. the modified polyethylene had been “recycled” through one recycle loop.

[217] A portion of the initial “unmodified” polyethylene composition as described above in Comparative Example 2, having an MFR of 0.2933 g/10 minutes, was then blended with a portion of the simulated-recycled polyethylene composition “modified Rl”. In particular, a blend comprising 60 wt% of the initial “unmodified” polyethylene composition and 40 wt% of the simulated-recycled polyethylene composition “modified Rl” was formed. This blend was again used to form a 16 micron blown film of a thickness suitable for making medical aprons. The MFR of the blend was measured, using the same test method as described above for Comparative Example 1, and the MFR was 0.1851 g/10 minutes. The MFR of the blend has slightly decreased as compared to the MFR of the virgin resin, which results in the “modified” blend exhibiting acceptable rheological and other properties. The Melt Index Ratio of the blend, which is defined at the ratio of the MFR values measured at 21.6 kg and 2.16 kg, was 80.443.

[218] The blown film of 16 microns thickness formed from the “modified” blend of the polyethylene composition was again tested to determine the impact strength of the blown film. The blown film of 16 microns thickness formed from the blend comprising 60 wt% of the initial polyethylene composition and 40 wt% of the simulated-recycled polyethylene composition “modified Rl” was determined to have a dart impact strength of 123 grams. The crystallinity of this blown film was also measured as described above, and the crystallinity was measured as 53.98%. Accordingly, the crystallinity was increased by incorporating the modified recycled polyethylene.

[219] Therefore, the use of the added components of the pretreated zinc oxide, and the first and second fortifiers, can increase the crystallinity of the polyethylene used for medical aprons from a current typical average value of about 48% to a value of about 53% in a medical apron comprising no recycled polyethylene and in a medical apron comprising 40 wt% recycled polyethylene.

[220] These results of Comparative Example 2 and Example 5 are summarised in Table 6. Table 6

[221] The MFR test is variable shear test based on a constant weight, and the Melt Index Ratio is a relative measure of the molecular weight distribution of the polymer. The 60 wt% “Modified” PE blend/40 wt% recycled “modified” PE blend of Example 5 has a higher Melt Index Ratio than the Recycled “unmodified” PE blend of Comparative Example 2. Without being bound by any theory, these Melt Index Ratio results are believed to show that when the fortified “modified” resin is subjected to high shear, which is typically used when manufacturing a blown film, such as for use in making medial aprons, although high chain scission of the polyethylene molecules occurs, the added components of the pretreated zinc oxide, and the first and second fortifiers, increase the tendency of the HDPE portion to cross-link. This results in improved mechanical properties of the 60 wt% “Modified” PE blend/40 wt% recycled “modified” PE blend of Example 5.

[222] The preferred embodiments of the present invention enable the polyethylene composition from disposable products such as aprons to be recycled through up to twenty recycle loops. The addition of the molecular buffer component, and optionally the first and/or second fortifiers, achieves control of short and long chain branching, crosslinking and particularly chain scission in the thermoplastic resin, typically polyethylene. With respect to polyethylene, HDPE is a linear polyethylene resin, and when blended with LLDPE, the blended resin responds differently as compared to each resin constituent individually. For example, HDPE can either crosslink by increasing viscosity or undergo chain scission thereby decreasing viscosity. Viscosity is reflected in the Melt Flow Rate (MFR) value; as the viscosity increases, the MFR decreases, and vice versa.

[223] From rheological data at 190 °C and 230 °C and at mass loads of 2.16 and 21.6 kg in the MFR test, the molecular weight distribution of the polymer and the effect of chain scission can be observed, and in particular to determine whether the MWD is broad, as a result of chain scission, or narrow, and to determine the stabilization of the thermoplastic resin system. The physical properties of ISO dart impact and thermal analysis for thermal profiles show changes in melt character and recrystallization behaviour, and these parameters all reflect the state of the thermoplastic resin system and changes in molecular architecture.

[224] It will be also noted that the incorporation of “modified recycled” polyethylene into the “virgin” polyethylene increased the dart impact strength of the blown film. In other words, modifying the polyethylene composition by the to the initial polyethylene composition, provides that when recycled polyethylene is incorporated into virgin polyethylene, the mechanical properties of the polyethylene can be maintained, or even enhanced as compared to the use of “unmodified” polyethylene. The result is that recycled polyethylene can be reliably incorporated into products such as blown films, for example for in medical aprons, without compromising the mechanical properties of the blown film.

[225] Therefore, the use of the added components of the pretreated zinc oxide, and the first and second fortifiers, can increase the crystallinity and impact resistance of the polyethylene used for medical aprons, when the medical apron comprises no recycled polyethylene, and, alternatively, particularly when the medical apron comprises recycled polyethylene comprising 40 wt% recycled polyethylene. [226] The use of the added components of the pretreated zinc oxide, and the first and second fortifiers, can overcome degradation of the properties of polyethylene resins which otherwise would occur by the incorporation of recycled polyethylene into a polyethylene blend. Products made from blown films such as medical aprons can comprised a recycled polyethylene content of at least 40 wt% without a degradation in properties, which may even exhibit enhanced properties as a result of incorporating “modified” recycled polyethylene.

Example 6 and Comparative Example 3

[227] In this Example and Comparative Example, the effect of the pretreated zinc oxide, and the first and second fortifiers, as described in the preceding Examples was investigated for polypropylene compositions. The polypropylene compositions have a variety of end uses, such as for the manufacture of fibres, woven blankets, surgical mesh and injection moulded syringes.

[228] In this Example and Comparative Example, the polypropylene resin was LyondellBassell Montel 6501, which is a polypropylene flake available in commerce from LyondellBassell. The polypropylene flake had a density of 0.900 g/cc. The Melt Flow Rate (MFR) of the polypropylene flake, using the test protocol of ASTM D1238-20 measured at 230 °C with a mass of 2.16 kg, was 4.0 g/10 minutes. This resin, without addition of any antioxidants or any zinc oxide, comprised a Control resin.

[229] Various resin formulations were prepared by adding first and second fortifiers, as described in the preceding Examples, in particular Irganox ® 1010 as a primary antioxidant and Irgafos ® P-EPQ or Irgafos ® 168 as a secondary antioxidant, each at a respective concentration of 0.1 wt% based on the total weight of the polypropylene composition.

[230] In some further resin formulations, the polypropylene resin comprised a modified polypropylene composition additionally comprising the untreated zinc oxide or pretreated zinc oxide, and the first and second fortifiers. The base zinc oxide was the same zinc oxide used in the preceding Examples.

[231] As in the previous examples, the polypropylene resin formulations were subjected to a resin processing which simulates recycling of the polymer resin. The processing comprised extrusion of the resin at a temperature of 260 °C using a conventional twin screw extruder having a screw diameter of 21 mm for each screw. [232] After each extrusion test, the Melt Flow Rate (MFR) of the polypropylene composition was measured, using the test protocol of ASTM D1238-20 measured at 230 °C with a mass of 2.16 kg-

[233] The results are shown in Table 7.

Table 7 [234] It may be seen that the modified polypropylene composition, which additionally comprised the pretreated zinc oxide, and the first and second fortifiers, exhibited a rather stable rheology, evidenced by the rather stable MFR values, even after the modified polypropylene composition has been subjected to a number of passes through the extruder, representing a plurality of successive recycling loops.

[235] It may be seen from Table 7 that for conventional unmodified polypropylenes, containing conventional fortifiers, and optionally untreated zinc oxide, the MFR values changed significantly when subjected to degradation as a result of recycling. These significant changes in MFR values show that the rheology and molecular structure of the unmodified polypropylenes had suffered significant degradation. In particular, the significant increase in the MFR values indicates that the unmodified polypropylene resins had undergone significant chain scission.

[236] In contrast, Example 6 shows that the relatively stable MFR values for the modified polypropylene composition evidence that chain scission has been minimized by the addition of the pretreated zinc oxide, and the first and second fortifiers.

[237] This experimental data shows that the addition of the pretreated zinc oxide, and the first and second fortifiers to the polypropylene compositions can significantly alter the rheological properties of the polyethylene composition, and can achieve enhanced properties and performance of polypropylene compositions which can be used to make a variety of different products using a variety of different manufacturing techniques. Again, these enhanced properties enable polypropylene to be passed through a number of successive recycle loops without losing the desired performance of the polypropylene resin system.