Degradable polymer composition

Abstract

The present invention relates to a degradable polymer composition comprising: (a) a polyolefin; (b) one or more transition metal compounds in a total amount of from 0.03 to 0.6wt%, based on the total weight of the polymer composition, (c) one or more non-coordinated, saturated C14-C24 carboxylic acid or an ester, anhydride or amide thereof, in an amount of from 0.01 to 0.6wt%, based on the total weight of the polymer composition; (d) a rubber in an amount of from 0.02 to 0.65wt%, based on the total weight of the composition; (e) an antioxidant stabilizer composition in an amount of from 0.005 to 0.48 wt%, based on the total weight of the composition; wherein the one or more transition metal compounds comprises iron, manganese, copper, cobalt or cerium, and wherein the antioxidant stabiliser composition comprises a phenolic antioxidant, a non-phenolic antioxidant and a mineral acid scavenger.

Description

Degradable Polymer Composition The present invention relates to a degradable polymer composition and, in particular, to a masterbatch and / or final polymer formulation with optimal service life in hot climates. Polymer materials, and particularly polyolefins, have many uses and can provide strong, inert materials at low cost. However, plastic waste builds up in the environment and causes damage to ecosystems, and human and animal health. The problem of plastic waste build-up in the environment, both on land and in water, is a widely known problem. Various attempts have been made to tackle this problem over the years. Compostable plastics (made from compostable polymers) have been developed but these have drawbacks in that they tend to be of lower strength and have lower barrier properties than conventional polyolefin materials. In addition, compostable polymers often require high temperature industrial composting facilities for breakdown, and recent research has shown that they can be a source of microplastics when the composting process is incomplete. Therefore, compostable plastics / polymers are not a viable option, particularly in regions without advanced waste collection schemes. Formulations have been developed and disclosed in WO 2018 / 095905 A1 which can be combined with polyolefins to create a degradable polyolefin composition that is suitable for use as a packaging material, and which maintains its strength and functionality for a period of time, before then biodegrading. While these products have proven to offer an improvement in the environmental impact of traditional polyolefins, some drawbacks have been identified. Firstly, the service life, particularly the service life in hot climates, can be limited. In particular, in regions that are in tropical and arid climate zones, the plastics are subjected to high temperatures during transportation and storage which could result in a non-optimal service life.  Furthermore, when trying to produce transparent plastics, such as for packaging purposes, the formulation incorporated into the polyolefin product can result in a yellow tint on the resulting polymer product, which is undesirable for both the transparency properties of the plastic and is also disliked by consumers due to its visual appearance. Consumers tend to prefer clear plastics with good optical properties (i.e. clear / see-through plastic), as a yellow tint is aesthetically displeasing. Lastly, HDPE-based plastic products are a major market in the polymer industry, and are widely used to make plastic bottles, milk jugs, shampoo bottles, cleaning product bottles, chopping boards, piping, waste bins, toys, etc. In internal studies, the masterbatch formulation of WO 2018 / 095905 was found to be less effective in plastics with a high concentration of HDPE, resulting in slower breakdown of high-concentration HDPE plastic products that might not be conducive to market needs.  Therefore, the inventors have been trying to overcome these difficulties and meet a market need for a degradable polymer composition with a longer service life before degradation begins (particularly in hotter climates), which is not susceptible to yellowing during production or during the service life, and which has an effective degradation rate even when the polymer composition has a high concentration of HDPE. It is also a feature of the present invention that polyolefin-based plastics incorporating the masterbatch technology, before the onset of degradation, can be recycled in existing polyolefin recycling streams.  Accordingly, it is desirable to provide an improved degradable polymer composition (or an improved intermediate masterbatch), or one which addresses problems in the prior art, or at least provides a commercially viable alternative thereto. According to the first aspect of the present invention there is provided a degradable polymer composition comprising:(a) a polyolefin;(b) one or more transition metal compounds in a total amount of from 0.03 to 0.6wt% based on the total weight of the polymer composition, (c) one or more non-coordinated, saturated C14-C24 carboxylic acid or an ester, anhydride or amide thereof, in an amount of from 0.01 to 0.6wt% based on the total weight of the polymer composition; (d) a rubber in an amount of from 0.02 to 0.65wt% based on the total weight of the polymer composition;(e) an antioxidant stabilizer composition in an amount of from 0.005 to 0.48 wt% based on the total weight of the polymer composition;wherein the one or more transition metal compounds comprises iron, manganese, copper, cobalt or cerium, andwherein the antioxidant stabiliser composition comprises a phenolic antioxidant, a non-phenolic antioxidant and a mineral acid scavenger.  The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. The method of the present invention is for the manufacture of a degradable polymer composition. The term degradable polymer (composition) refers to synthetic polymer compositions which break down into CO2, H2O, biomass and inorganic salts under aerobic terrestrial conditions. The degradable polymer composition comprises a polyolefin, preferably a copolymer or homopolymer of polyethylene and / or polypropylene. The degradable polymer composition can comprise more than one copolymer and / or homopolymer of polyethylene and / or polypropylene. The degradable polymer composition may, in addition, include other types of polymer that are not ethylene-based or propylene-based. The copolymer or homopolymer of polyethylene and / or polypropylene forms the majority of the composition, such as preferably at least 50wt%, more preferably at least 60 wt.%, and even more preferably at least 70 wt.%. When the degradable polymer composition is a masterbatch, preferably the copolymer or homopolymer of polyethylene and / or polypropylene forms less than 90 wt.%, preferably less than 80 wt.% of the composition.  The term “Polymer” means a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term “polymer” embraces the terms “homopolymer,” “copolymer,” “terpolymer” as well as “interpolymer”. The polymers employed in the invention comprise repeat units of the general formula –[CH2CRR’]-, preferably wherein R and R’ are individual selected from the list comprising hydrogen, methyl, ethyl, acetate, methyl methacrylate, vinyl alcohol and acrylic acid. A “homopolymer” means that the polymer is prepared by the polymerization of only one type of monomer. “Interpolymer” means a polymer prepared by the polymerization of at least two different types of monomers. The generic term “interpolymer” includes the term “copolymer”. A “copolymer” refers to a polymer prepared from two different monomers. Non-limiting examples of homopolymers and copolymers of polyethylene include ultralow, low, linear low, medium, high and ultrahigh density polyethylene (i.e. ULDPE, LDPE, LLDPE, MDPE, HDPE, UHDPE). Equivalent homopolymers and copolymers of polypropylene, such as ULDPP, LDPP etc. are available. Preferably the polyolefin is selected from LDPE, LLDPE, HDPE, MDPE, VLDPE, EVA, EVOH, EMMA, PVA, PVOH, PMA and EAA, and optionally any other polymers containing a saturated C-C backbone, hydrocarbon resins, Fischer Tropsch and olefin waxes. Preferably the polyolefin comprises at least 40wt% HDPE, preferably at least 60wt%, more preferably at least 80wt% and most preferably is HDPE. Preferably the polyolefin comprises ethylene and / or propylene monomers and, optionally, further comprises monomers selected from the group consisting of acetate, vinyl acetate, methyl methacrylate, vinyl alcohol and acrylic acid.  The copolymers of polyethylene comprise a majority amount of ethylene monomers, and the copolymers of polypropylene comprise a majority amount of propylene monomers. By majority amount, it is meant at least 50 wt.%, preferably at least 60 wt%, more preferably at least 70, or 80 wt.%, and most preferably at least 90 wt.%. Homopolymers are the most preferred polymers. Preferably, the copolymer or homopolymer of polyethylene and / or polypropylene forms the balance of the degradable polymer composition along with the listed components. That is, preferably the degradable polymer composition consists of the copolymer or homopolymer of polyethylene and / or polypropylene and the listed components. However, the degradable polymer composition may further include up to 5 wt.% of other organic ingredients, more preferably less than 1 wt.%, most preferably the degradable polymer composition is essentially free of further organic ingredients or impurities. The degradable polymer composition may further include up to 50wt% inorganic material such as inert filler materials, preferably less than 10 wt.%, more preferably less than 1wt%, and most preferably the degradable polymer composition is essentially free of further inorganic ingredients or impurities. The presence of fillers is particularly likely when considering the final polymer product and not a masterbatch. In particular, the degradable polymer composition preferably consists of the homopolymer or copolymer of polyethylene and / or polypropylene, and components (b) to (e) (and (f) when present).  The degradable polymer composition comprises a component, (b), which is one or more transition metal compounds, wherein the transition metal is selected from iron, manganese, copper, cobalt and cerium, preferably wherein the compound is a transition metal stearate.  The following description uses the term transition metal to refer to any of the metallic elements of groups IVB–VIII, IB, and IIB, or 4–12 in the periodic table. Preferred transition metals are iron, manganese, copper, cobalt and cerium. These compounds catalyse the degradation of the polymer composition.  The one or more transition metal compounds are included in such an amount of 0.03 to 0.6wt%, preferably 0.1 to 0.6wt%, preferably 0.2 to 0.5wt% and more preferably 0.3 to 0.4wt%, so as to provide the desired degradation properties. However, including large amounts of transition metal increases the cost of the degradable composition. Additionally, since the transition metal plays a catalytic role in the degradation process, increasing the transition metal content above these amounts has a decreasing impact on the degradation rate. Preferably, only one transition metal compound is present. When two or more transition metal compounds are present, they are selected from iron, manganese, copper, cobalt and cerium compounds and the transition metals in the two or more transition metal compounds are preferably different.  By ‘transition metal compounds’ it is meant the transition metal compound when formed as a salt (i.e. with one or more ligands). For example, iron could be provided as iron stearate (i.e. the salt of Iron and stearic acid). Further references to the amount of the transition metal compound (in wt.%) refer to the amount when in a salt.  Preferably, the ligands of the metal compounds are inorganic ligands and / or saturated organic ligands. Preferably the organic ligands are C6-C20 and are mono- or di-functional. Examples include carboxylic acids, acetylacetone, triazacyclononane and the like. Preferably the transition metal compounds comprise moieties selected from stearate, carboxylate, acetylacetonate, triazacyclononane or combinations of two or more thereof.  Certain non-ionic ligands that play an active role in the degradation may also be included. Where present, the non-ionic ligands are preferably selected from amines, imines, amides, phosphites, phosphines, and carbenes. Such non-ionic ligands can have an advantageous effect on the degradation rate of the composition whilst maintaining the essential material properties. When present, non-ionic ligands preferably constitute at least 5% of the ligands and preferably up to 50% of the ligands, preferably 10 to 40% of the ligands. Preferably, the transition metal ligands are chosen in order to make the transition metal physically and chemically compatible with the polymer. Ligand selection may affect the transition metal’s catalytic activity. The ligands may be chosen to make the metal compatible with the particular polymer used and to control the degradation rate of the polymer composition.  The temperature of the polymer composition as well as its exposure to light may also affect its degradation rate. The choice of transition metal can be used to further tune these effects to suit the end purpose. For example, iron is a more efficient photo catalyst whilst manganese is a more efficient thermal catalyst of the degradation process. The transition metal component may, therefore, be selected to tune the degradation rate depending on the expected exposure to heat and light of a particular product.  Specific transition metals may have effects on the properties of the polymer composition. For example, iron compounds may colour the polymer composition.  Additionally, other metals such as copper advantageously increase the degradation rate but may make the polymer composition unsuitable for certain applications such as use as a food wrap, due to its toxicity. Accordingly, if the product is for use in the food industry copper may be avoided. The selection of one or more appropriate transition metal compounds depends on the final product that is to be made. The degradable polymer composition comprises a component (c) which is one or more non-coordinated saturated C14-C24 (preferably C16 -C20) carboxylic acid, or an ester, anhydride or amide thereof. The carboxylic acid or an ester, anhydride or amide components are “free” or “non-coordinated”, in the sense that they do not form a part of a transition metal compound. The non-coordinated, saturated C14-C24 carboxylic acid or an ester, anhydride or amide thereof, is present in an amount of from 0.01 to 0.6wt%, preferably 0.01 to 0.3wt%, preferably 0.02 to 0.2wt%, preferably 0.04 to 0.15wt%, more preferably 0.06 to 0.12wt%. The following description uses the term carboxylic acid to refer to the range of molecules containing a carboxylic acid –(COOH) moiety. The carboxylic acid of the present invention are saturated (i.e. have only single carbon-carbon bonds). It has a carbon backbone containing between 14 and 24 (preferably 16 and 20) carbon atoms. The carbon backbone of the carboxylic acid may be linear, branched or aromatic. Preferably the saturated carboxylic acid is a C16-C20 carboxylic acid. Preferred carboxylic acids are palmitic, stearic and behenic .  Alternatively, the degradable polymer composition comprises an ester, anhydride or amide of a saturated C14-C24 (preferably C16-C20) carboxylic acid. Where the degradable polymer composition comprises an ester of a saturated carboxylic acid the alcohol component preferably comprises a C1-C30 alcohol, more preferably a saturated straight chain C1-C30 alcohol.  Where the degradable polymer composition comprises an anhydride of a saturated carboxylic acid, the anhydride may or may not be symmetrical. The second carboxylic acid component preferably comprises a C1-C30 carboxylic acid, more preferably a saturated straight chain C1-C30 carboxylic acid. Where the degradable polymer composition comprises an amide of a saturated carboxylic acid the amide may be a primary, secondary or tertiary amide. Where a secondary or tertiary amide is present, each of the carbon chains preferably comprises from 1 to 30 carbon atoms, more preferably each carbon chain is a C1-C30 alkyl group. Unless otherwise specified, where features of the carboxylic acid are discussed in this description it is intended to also encompass the ester, anhydride or amide thereof. In addition to the component (c) there may also be a component (f) which is one or more non-coordinated mono or poly-unsaturated C14-C24 (preferably C16 -C20) carboxylic acid, or an ester, anhydride or amide thereof. All the discussion of the component (c) above applies equally, by analogy, except that the component (f) may have one or more unsaturated double bonds. When component (f) is present, the total amount of (c) and (f) is 0.01 to 0.6wt%, preferably 0.01 to 0.3wt%, preferably 0.02 to 0.2wt%, preferably 0.04 to 0.15wt%, more preferably 0.06 to 0.12wt%. That is, it is essential that there is a saturated component (and this is the preferred species), but some of this may be substituted for an unsaturated equivalent. When both (c) and (f) are present, preferably the component (c) is present in an amount at least equal to component (f), and preferably in a weight ratio of at least 2:1, preferably at least 4:1. The degradable polymer composition comprises a component (d) which is a rubber, preferably a synthetic rubber. The rubber is present in an amount of rubber in an amount of from 0.02 to 0.65wt%, preferably 0.02 to 0.4wt%, preferably 0.02 to 0.2wt%, preferably 0.03 to 0.2wt%, preferably 0.05 to 0.15wt% and more preferably 0.08 to 0.12wt%. The following description uses the term rubber to refer to viscous, elastic polymers. Rubbers are amorphous polymers which exist at temperatures above their glass transition temperature. Preferably, the rubber of the present invention is an unsaturated rubber. Preferably, the unsaturated rubber is one or more copolymers of isobutene and isoprene, and / or a polybutadiene and / or styrene-butadiene-styrene, and / or a natural rubber.  Natural rubber is generally supplied as a latex emulsion that requires evaporation of the liquid to remove the solvent. Natural rubber can be sticky and difficult to extrude, so can be blended with other synthetic rubbers or appropriate additives to overcome this difficulty. The natural rubber can be cis or trans natural rubber, and preferably the natural rubber comprises, or consists of trans natural rubber. Natural rubber is often called ‘Indian rubber’, ‘latex’, or ‘Amazonian rubber’, and consists of polymers of the isoprene, with minor impurities of other organic compounds. It can be harvested from various natural sources, such as the Gutta-percha tree or the Pará rubber tree, or other appropriate sources. In contrast, synthetic rubber is ‘human-made’.  Preferably, the rubber of the present invention is a synthetic rubber that comprises polyisoprene, styrene-isoprene (SI), styrene-isoprene-styrene (SIS), or a blend of two or more thereof. The rubber content may improve the mechanical properties of the polymer composition. Additionally, rubbers are generally less chemically stable than the bulk polyolefin. Accordingly, the rubber content may improve the degradation rate without adversely affecting the physical properties of the polymer. In this way it seems to act as a co-catalyst. Advantageously, the presence of the rubber in the polymer composition improves the elasticity. This may help to counteract the embrittlement of the polymer composition caused by the other ingredients.  The degradable polymer composition comprises a component (e) which is an antioxidant stabilizer composition in an amount of from 0.005 to 0.48wt%, preferably 0.005 to 0.45 wt%, preferably 0.005 to 0.35wt%, preferably 0.01 to 0.25wt% and more preferably 0.05 to 0.15wt%. The antioxidant stabiliser composition comprises a phenolic antioxidant, a non-phenolic antioxidant and a mineral acid scavenger. Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. Antioxidants act as radical scavengers and remove peroxy radicals, as well as alkoxy radicals, hydroxyl radicals and alkyl radicals. They can also act to remove organic hydroperoxides formed during the degradation process. The inclusion of one or more antioxidants may delay the onset of degradation increasing the shelf-life of a product. Phenolic antioxidant stabilisers are well known in the art and include, for example, Irganox 1076 (octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate). Phenolic antioxidant stabilisers are generally known to be primary antioxidants, and remove free radicals to slow down degradation of the polymer composition.  Non-phenolic antioxidants include Phosphite antioxidant stabilisers which are also well known in the art and include, for example, Irgafos 168 (Tris(2,4-di-tert-butylphenyl) phosphite). Phosphite antioxidant stabilisers are generally known as secondary antioxidants, and remove the organic hydroperoxides. Preferably the non-phenolic antioxidant is a phosphite or phosphonite antioxidant. Preferably the antioxidant stabiliser composition comprises (i) the phenolic antioxidant and (ii) the non-phenolic antioxidant in a weight ratio of (i) to (ii) of from 2:1 to 1:3, more preferably 1:1 to 1:2. An acid scavenger is a chemical added to remove or deactivate impurities and unwanted reaction products. An acid scavenger neutralizes acid residues which may delay the onset of degradation increasing the shelf-life of a product and the period in which the product may be recycled in existing polyolefin recycling streams. The acid scavenger together with the one or more antioxidant stabilisers forms the stabilising system that acts to delay degradation and enable it to be balanced so that the product has a desired shelf life, and can have appropriate durability and functionality before the onset of degradation.  Examples of suitable acid scavengers include metal oxides such as calcium oxide, magnesium oxide, and zinc oxide, layered hydroxide minerals such as hydrotalcites, or metal salts such as calcium, magnesium and zinc stearate. Preferably the mineral acid scavenger is a hydrotalcite. The following description uses the term calcium oxide to refer to the crystalline solid with the chemical formula CaO. Advantageously calcium oxide reacts with and immobilises water in the composition. This stabilises the composition during processing and may reduce the occurrence of blemishes and discoloration of the final product. The present inventors have also found that increasing the calcium oxide content of the polymer composition may increase the degradation rate.  When the degradable polymer described herein is provided as a final product, preferably the degradable polymer is a film having a thickness of 0.55 microns to 1.2mm, preferably 1 micron to 0.5mm. A film may be composed of a single polymer or multi-component composition made up of a single layer or multi-layer through co-extrusion, it may blown, cast extruded or biaxially extruded. Other possible forms include a fibre which may be melt-blown, spun or extruded filament, and, 3-D articles may be made through processes such as thermoforming, injection moulding or extrusion blow moulding. In all embodiments the thickness is preferably 0.55 microns to 1.2mm. According to another aspect there is provided a masterbatch formulation for forming the degradable polymer composition described herein in combination with a further polyolefin, the masterbatch formulation comprising:the polyolefin as a carrier polymer,the one or more transition metal compounds, the one or more saturated C14-C24 carboxylic acid or ester, anhydride or amide thereof (and optionally one or more mono- or poly-unsaturated C14-C24 carboxylic acid or ester, anhydride or amide thereof), the rubber andthe antioxidant stabiliser composition,wherein the masterbatch formulation is for dilution in the further polyolefin in an amount of from 0.5 to 20wt% of the masterbatch formulation in the degradable polymer composition, preferably 0.5 to 4 wt%, more preferably 0.5 to 2wt%. The inventors surprisingly found that they could provide a degradable polymer composition which was able to overcome the drawbacks of the prior art. The inventors have found that for the degradable polymer composition to have the desired product features as well as a long service life (especially in hotter climates), effective degradation rate in HDPE-containing formulations, and a reduced susceptibility to yellowing during production and storage, it is critical to have a specific stabiliser system (component (e)), in combination with specific components (b) to (d) in the recited amounts.  The antioxidant stabiliser composition (e) comprises a phenolic antioxidant, a non-phenolic antioxidant and an acid scavenger. A blend of a phenolic antioxidant with a non-phenolic antioxidant together with an acid scavenger was advantageously found to delay the onset of decomposition at hotter temperatures sufficiently, whilst still enabling effective degradation after an appropriate service life in both HDPE-free polymer compositions and polymer compositions having a high HDPE concentration. Minimal discolouration was observed during heating cycles performed during manufacturing.  With regard to component (b), it was found that the use of multiple TM compounds could exacerbate discolouration. Surprisingly, the use of only one TM compound was found to reduce undesirable yellowing during heating cycles that are performed during manufacturing, while maintaining the desirable degradation properties.  With regard to component (c), it was surprisingly found that using a saturated C14-C24 carboxylic acid or an ester, anhydride or amide or a blend thereof, instead of a mono- or poly- unsaturated C14-C24 carboxylic acid or an ester, anhydride or amide thereof, was more compatible with the stabiliser system, whilst still providing the desired degradation effect and sufficiently long service life in hotter climate conditions. It was also observed that switching to a saturated oil, reduced discoloration that was associated with oxidation of the unsaturated C=C bonds. Surprisingly the formulation is also suitable for inclusion in HDPE-rich blends which are generally difficult to decompose. HDPE is a versatile material that can provide greater strength and stiffness than LDPE. It is also easy to fabricate, and has many applications in food-related products, such as cutting boards and food packaging. However, different polyethylenes have different degradability properties. Although HDPE, LDPE and LLDPE are all based on polyethylene, they have very different degrees of crystallinity and crystal density. The rate of degradation is linked to the amorphous fraction of the polymer, and so degradation for HDPE is typically much slower than for LLDPE and LDPE. The specific blend of components (b) to (e) (and optionally (f)) in the recited amounts have shown to be surprisingly effective at enabling the breakdown of HDPE-rich compositions, whilst maintaining a long service life and avoiding yellowing.  The invention will now be described further in relation to the following non-limiting examples. Example 1 A Masterbatch Composition A was prepared as described in Table 1.  Table 1: Masterbatch Composition AComponentWeight %Polyethylene 76Cobalt stearate10Palmitic acid4styrene-isoprene-styrene rubber4Calcium stearate3octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate1tris(2,4-di-tert-butylphenyl) phosphite2 The Masterbatch Composition A was used to produce: 1a) A low density polyethylene cast extruded film (90 micrometers thick) containing a masterbatch composition A dosed at 2 wt%. 1b) A polypropylene homopolymer cast extruded film (90 micrometers thick) containing masterbatch composition A dosed at 2 wt%. The films were artificially aged using a QUV weatherometer for 14 days using a cycle of 1h UV light (0.8 W / m2 at 60 °C) and 23 h dark (60 °C) which simulates real world conditions of up to 4 months in South Florida. After 14 days the Molecular weight of the samples were measured and, as shown in Table 2, the polymer backbone had degraded significantly .  Table 2: Molecular Weight of Inventive and Control Samples After Accelerated AgingExampleMn(Da)Mw(Da)Mz(Da)1a2,2174,6578,1681b1,5475,07510,053Control PE45,553136,642281,778Control PP27,840142,119386,571  Example 2 A Masterbatch Composition B was prepared as described in Table 3. Table 3: Masterbatch Composition BComponentWeight %Polyethylene 72Cobalt stearate10Stearic Acid4Behenic Acid4styrene-isoprene-styrene rubber4Calcium stearate3octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate1tris(2,4-di-tert-butylphenyl) phosphite2 The Masterbatch Composition B was used to produce: 2a) A low density polyethylene cast extruded film (90 micrometers thick) containing a masterbatch composition B dosed at 2 wt%. 2b) A polypropylene homopolymer cast extruded film (90 micrometers thick) containing masterbatch composition B dosed at 2 wt%. The films were artificially aged using a QUV weatherometer for 14 days using a cycle of 1h UV light (0.8 W / m2 at 60 °C) and 23 h dark (60 °C) which simulates real world conditions of up to 4 months in South Florida. After 14 days the Molecular weight of the samples were measured and, as shown in Table 4, the polymer backbone had degraded significantly.   Table 4:Molecular Weight of Inventive and Control Samples After Accelerated AgingCompositionMn(Da)Mw(Da)Mz(Da)2a1,8413,8156,9742b1,9716,79313,511Control PE46,990147,007313,635Control PP31,543145,279387,902 Example 3 A Masterbatch Composition C was prepared as described in Table 5. Table 5: Masterbatch Composition CComponentWeight %Polyethylene 72Cobalt stearate10Behenic Acid4styrene-isoprene-styrene rubber4Calcium stearate3octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate1tris(2,4-di-tert-butylphenyl) phosphite2 The Masterbatch Composition C was used to produce: 3a) A low density polyethylene cast extruded film (90 micrometers thick) containing a masterbatch composition B dosed at 2 wt%. 3b) A polypropylene homopolymer cast extruded film (90 micrometers thick) containing masterbatch composition B dosed at 2 wt%. The films were artificially aged using a QUV weatherometer for 14 days using a cycle of 1h UV light (0.8 W / m2 at 60 °C) and 23 h dark (60 °C) which simulates real world conditions of up to 4 months in South Florida. After 14 days the Molecular weight of the samples were measured and, as shown in Table 6, the polymer backbone had degraded significantly.  Table 6:Molecular Weight of Inventive and Control Samples After Accelerated AgingCompositionMn(Da)Mw(Da)Mz(Da)3a2,2914,7108,2583b1,9396,25312,275Control PE49,330146,216315,374Control PP30,735143,032383,674 Example 4  Yellowness Improvements While the invention described in WO 2018 / 095905 A1 can be used to degrade polyolefins, when incorporated into the polymer, a level of discolouration may be imparted to the resultant packaging product that can be perceived negatively by consumers. Surprisingly, the inventors found that compositions prepared according to the current invention generated products which had much improved yellowness index.  Yellowness Index measurements of cast sheets prepared using inventive compositions 1a, 2a, and 3a are shown in Table 7 and compared with the yellowness index for a Cast Sheet made according to WO 2018 / 095905 (in particular using an unsaturated organic acid and a blend of TMs). A high yellowness index is indicative of a material with higher yellow colour which is not preferred by consumers. As seen in the table, the yellowness index of the inventive samples is very similar to that of the control sample (this is the best possible achievement – that the product matches the non-degradable pure carrier polymer), whereas the yellowness index of the material made according to the prior art is over 5x that of the control sample.  Table 7: Yellowness Index Measurements for Control, Inventive Samples, and Prior ArtSample Yellowness IndexControl Blank PE 0.841a0.332a0.463a0.30WO 2018 / 0959055.3 Example 5  Service Life / Shelf Life Penetration of other degradable polymers (such as compostable polymers) into developing world markets have been limited due to premature material degradation in the supply chain. Technologies that combine Masterbatch with polyolefins to deliver a degradable plastic can offer improvements in this space through careful formulation. Table 8 shows the average service life for 5-15 prototypes of each sample type. Service life was measured in an accelerated manner as per ASTM-D3045 and the results were extrapolated to ambient conditions.  Sample types 5a and 5b were prepared using Masterbatches formulated according to the current invention (i.e. containing a saturated organic acid and a three-component stabilizer system), while sample types 5c and 5d were prepared from a Masterbatch formulated with an unsaturated organic acid and a two-component stabilizer system. As seen in Table, the average service life for the products prepared according to the current invention was approximately twice that of the other samples.  Table 8: Sample TypeProductAverage Service Life (Months)5aPE Cast Sheet135bPP Cast Sheet225cPE Cast Sheet7.55dPP Cast Sheet11 Examples 6  HDPE The highly efficient packing encountered in HDPE often results in exclusion of foreign materials from the crystal domain. To date, no Masterbatch technology has been able to completely overcome this phenomenon and degrade 100% HDPE structures. Surprisingly, the inventors found that formulations prepared according to the invention was successfully able to degrade 100% HDPE as shown in Table 9.  9a) A high density polyethylene thermoformed container was prepared using masterbatch (MB) made with a combination of unsaturated and saturated organic acid and a polyethylene carrier resin; 9b) A high density polyethylene thermoformed container was prepared using MB made with saturated organic acid (only) and a polypropylene carrier; 9c) A high density polyethylene thermoformed container was prepared using MB made with unsaturated organic acid (only) and a polypropylene carrier; The products were artificially aged using a QUV weatherometer for 14 days using a cycle of 1h UV light (0.8 W / m2 at 60 °C) and 23 h dark (60 °C) or a QSUN Xenon-Arc weatherometer for 28 days using a cycle of 8h of light calibrated at 340 nm with irradiance of 0.35 W / m2 and temperature of 60 °C which simulates real world conditions of up to 4 months in South Florida. After 14 days the Molecular weight of the samples were measured and, as shown in Table 9, the polymer backbone had degraded significantly where a MB formulation containing a saturated organic acid had been used (9a or 9b). On the other hand, when a MB was formulated with an unsaturated organic acid (9c) the HDPE polymer backbone was not significantly impacted.  Table 9: Molecular Weight of Inventive and Control Samples After Accelerated Aging CompositionMn (Da)Mw (Da)Mz (Da)9a3,7938,94427,5309b4,6468,12724,0009c3,73043,540279,087Control HDPE for 9a and 9b9,226 96,658446,582 As used herein, the singular form of “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. The use of the term “comprising” is intended to be interpreted as including such features but not excluding other features and is also intended to include the option of the features necessarily being limited to those described. In other words, the term also includes the limitations of “consisting essentially of” (intended to mean that specific further components can be present provided they do not materially affect the essential characteristic of the described feature) and “consisting of” (intended to mean that no other feature may be included such that if the components were expressed as percentages by their proportions, these would add up to 100%, whilst accounting for any unavoidable impurities), unless the context clearly dictates otherwise. Unless otherwise indicated, all percentages are by weight. Furthermore, all percentages are by total weight of the degradable polymer composition, unless indicated otherwise. It will be understood that, although the terms "first", "second", etc. may be used herein to describe various elements, layers and / or portions, the elements, layers and / or portions should not be limited by these terms. These terms are only used to distinguish one element, layer or portion from another, or a further, element, layer or portion. It will be understood that the term “on” is intended to mean “directly on” such that there are no intervening layers between one material being said to be “on” another material. Spatially relative terms, such as “under”, "below", "beneath", "lower", “over”, "above", "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s). It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device as described herein is turned over, elements described as "under” or “below" other elements or features would then be oriented “over” or "above" the other elements or features. Thus, the example term "under" can encompass both an orientation of over and under. The device may be otherwise oriented and the spatially relative descriptors used herein interpreted accordingly. The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.  

Claims

1. A degradable polymer composition comprising: (a) a polyolefin; (b) one or more transition metal compounds in a total amount of from 0.03 to 0.6wt%, based on the total weight of the polymer composition, (c) one or more non-coordinated, saturated C14-C24 carboxylic acid or an ester, anhydride or amide thereof, in an amount of from 0.01 to 0.6wt%, based on the total weight of the polymer composition; (d) a rubber in an amount of from 0.02 to 0.65wt%, based on the total weight of the composition;(e) an antioxidant stabilizer composition in an amount of from 0.005 to 0.48 wt%, based on the total weight of the composition; wherein the one or more transition metal compounds comprises iron, manganese, copper, cobalt or cerium, andwherein the antioxidant stabiliser composition comprises a phenolic antioxidant, a non-phenolic antioxidant and a mineral acid scavenger.

2. A degradable polymer composition according to claim 1, wherein the polyolefin comprises ethylene and / or propylene monomers and, optionally, further comprises monomers selected from the group consisting of acetate, vinylacetate, methyl methacrylate, vinyl alcohol and acrylic acid.

3. A degradable polymer composition according to claim 1 or claim 2, wherein the polyolefin is selected from LDPE, LLDPE, HDPE, MDPE, VLDPE, EVA, EVOH, EMMA, PVA, PVOH, PMA and EAA.

4. A degradable polymer composition according to claim 3, wherein the polyolefin comprises at least 40wt% HDPE, preferably at least 60wt%, more preferably at least 80wt% and most preferably is HDPE.

5. A degradable polymer composition according to any of the preceding claims, wherein the transition metal compound comprises coordinated moieties selected from stearate, carboxylate, acetylacetonate, triazacyclononane or combinations of two or more thereof.

6. A degradable polymer composition according to any of the preceding claims, wherein the polymer comprises only one transition metal.

7. A degradable polymer composition according to any of the preceding claims, wherein the antioxidant stabiliser composition comprises (i) the phenolic antioxidant and (ii) the non-phenolic antioxidant in a weight ratio of (i) to (ii) of from 2:1 to 1:3.

8. A degradable polymer composition according to any of the preceding claims, wherein the non-phenolic antioxidant is a phosphite or phosphonite antioxidant.

9. A degradable polymer composition according to any of the preceding claims, wherein the mineral acid scavenger is a hydrotalcite.

10. A degradable polymer composition according to any of the preceding claims, wherein the rubber is a synthetic rubber and comprises an unsaturated polymer, such as polyisoprene, polybutadiene, or copolymer, such as styrene-butadiene-styrene, styrene-butadiene, but preferably styrene-isoprene-styrene, more preferably a blend of a styrene-isoprene-styrene and a styrene-isoprene copolymer.

11. A degradable polymer composition according to any of the preceding claims, further comprising (f) one or more non-coordinated, mono- or poly-unsaturated C14-C24 carboxylic acid or an ester, anhydride or amide thereof, wherein the total amount of components (c) and (f) is from 0.01 to 0.6wt%, based on the total weight of the composition.

12. The degradable polymer of any of the preceding claims as:(a) a film having a thickness of 0.55 microns to 1.2mm,(b) an extruded-cast sheet having a thickness of up to 1200 microns, or(c) an injection moulded plastic product.

13. An masterbatch formulation for forming the degradable polymer composition of any of claims 1 to 12 in combination with a further polyolefin, the masterbatch formulation comprising:the polyolefin as a carrier polymer,the one or more transition metal compounds, the one or more saturated C14-C24 carboxylic acid or ester, anhydride or amide thereof, the rubber andthe antioxidant stabiliser composition,wherein the masterbatch formulation is for dilution in the further polyolefin in an amount of from 0.5 to 20wt% of the masterbatch formulation in the degradable polymer composition, preferably 0.5 to 4 wt%.