AU2018293920B2

AU2018293920B2 - Process and system for accelerated degradation of polyolefins

Info

Publication number: AU2018293920B2
Application number: AU2018293920A
Authority: AU
Inventors: Steven Eric BOTTLE; Ian John Dagley; Bronwyn Glenice Laycock; Vanessa Claire LUSSINI; Melissa Anna Louise Nikolić
Original assignee: Integrated Packaging Group Pty Ltd
Current assignee: Integrated Packaging Group Pty Ltd
Priority date: 2017-06-29
Filing date: 2018-06-28
Publication date: 2023-08-24
Anticipated expiration: 2038-06-28
Also published as: WO2019000039A1; AU2018293920A1

Abstract

The invention provides a process for accelerating degradation of a polyolefin, the process comprising: incorporating a transition metal prodegradant in the polyolefin; and applying an inorganic peroxo compound to a surface of the polyolefin.

Description

Process and system for accelerated degradation of polyolefins Technical Field

[1 ] The invention relates to processes for accelerating degradation of a polyolefin. In particular, the processes comprise a step of applying an inorganic peroxo compound to the surface of a polyolefin composition comprising an incorporated transition metal prodegradant. The invention also relates to systems for accelerating degradation of a polyolefin.

Background of Invention

[2] Polyolefin-based compositions are widely used in disposable products such as packaging film and agricultural film. Although discarded polyolefin films do slowly degrade, they generally persist in the environment for many years. Polymer films with enhanced degradability, for example polyesters such as polybutyrate, have been developed, yet are significantly more expensive than polyolefins and still require extended periods (typically greater than 100 days) before they are fully composted.

[3] The need to enhance degradability of waste polymers, and particularly polyolefin films, has led to the incorporation of prodegradants in the polymer matrix of many disposable products. The most widely used prodegradants are metal containing compounds. One group of metal containing prodegradants is the transition metal salts, which catalyse abiotic oxidation of polyolefins by air. US patents 3,454,510 and 5,854,304 thus describe polyolefin compositions with various transition metal salts, including fatty acid salts such as cobalt and manganese salts. Other efforts have focused on photoactive metal oxides such as nanoparticulate titanium dioxide, which enhance light-induced degradation mechanisms. The inclusion of non- ionic surfactants during processing has been shown to enhance the performance of metal-containing prodegradants and to compatibilise different prodegradants in polyolefin films, as reported in WO2013/023247.

[4] Although environmental degradation rates of polymeric products may thus be tailored by both selection of polymer base material and the incorporation of prodegradants during processing, it remains a challenge to provide both acceptable mechanical properties and durability during the required lifetime of the product and suitably rapid degradability after the useful lifetime.

[5] This challenge is evident for degradable films used in agricultural applications. Crop propagation film formed from polyolefins is used to produce a microclimate conducive to plant growth, covering seed or planted seedlings to increase soil and air temperatures, water conservation and rate of plant germination and growth, whilst protecting the crop during early development. The plants should generally be able to break through the film as they mature and the film degrades. Polyolefin films are also used as a mulch, surrounding each plant on top of the ground and thus controlling soil temperature, weed growth, pest infestation and carbon dioxide retention. Polyolefin mulch film may contain pigment to reduce light transmission and resultant weed growth.

[6] Agricultural films incorporating suitable prodegradant packages may provide controlled rates of degradation suitable for the requirements of the cropping cycle, which may be from 1 -24 months. However, the exposed film is typically only embrittled and partially degraded after this time. Furthermore, films used in agriculture are often partially buried for retention against wind and rain. Buried portions of film are protected against degradation induced by exposure to the sun, and may thus remain relatively unaffected by degradation after the useful lifetime of the film.

[7] It is therefore typically necessary to dispose of agricultural film after use.

Current options for disposal on the farm include burying or burning remaining film at the end of the cropping cycle. Alternatively, used films must be removed to off-site locations for landfilling, incineration or recycling alongside other (plastic) waste. Both on-farm and off-site disposal processes add significant cost to farmers and pose environmental challenges, particularly considering that buried/landfilled films may persist in the environment for decades and that used film is already partially degraded and contaminated with biomatter.

[8] In this context, it would be useful if rapid degradation of polymeric materials, and specifically polyolefins, could be initiated, or the natural rate of degradation substantially enhanced, by activating a "trigger" mechanism within the control of a user. For example, triggered post-use degradation of agricultural films would be highly desirable, particularly if the used film would then completely degrade within a relatively short time period (such as less than a year) when buried or aggregated in bundles above the ground. Similarly for packaging materials, it would be useful if rapid degradation of polyolefin-based films disposed of in landfill or by soil burial could be activated at the time of disposal, so as to minimize the volume that such materials occupy.

[9] Triggered degradation of agricultural films has been disclosed in

WO2000/075259. To provide suitable susceptibility to induced degradation, bio- based polymers such as C Ci₂ cellulose esters were employed as the base material of the films. Degradation could thus be triggered by a variety of chemical, enzymatic or microbial agents, for example agricultural lime. The speciality films required for this approach have differing properties, such as mechanical properties and degradation profiles over the cropping cycle, compared with conventional polyolefin-based films, and are substantially more expensive.

[10] There is therefore an ongoing need for improved methods of accelerating or activating the post-use degradation of polymeric materials, particularly polyolefins which are already widely accepted for applications such as agricultural and packaging films. In the case of agricultural films, such methods should preferably be adapted for ready implementation on the farm, thereby avoiding the need to remove the films for off-site disposal.

[1 1 ] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

Summary of Invention

[12] The inventors have now discovered that application of an inorganic peroxo compound to the surface of a polyolefin composition which incorporates a transition metal prodegradant in the polymeric matrix accelerates the subsequent degradation of the polyolefin. The rate of degradation achieved in accordance with the method of the invention is generally higher than that obtained under the same degradation conditions for an untreated polyolefin composition comprising the transition metal prodegradant, or a polyolefin composition treated with the inorganic peroxo compound but which lacks an incorporated prodegradant. After application of the inorganic peroxo compound, degradation may be allowed to proceed under mild thermo-oxidative conditions (such as by soil burial and/or bundling) or under the influence of irradiation (such as by exposure to sunlight).

[13] Without wishing to be bound by any theory, it is believed that the surface- applied inorganic peroxo compound synergistically cooperates with the incorporated transition metal salt to accelerate polyolefin decomposition. For example, it is considered that the inorganic peroxo compound may oxidise the polyolefin composition to provide oxidic functionalities therein, with further degradation reactions of the oxidic functionalities being promoted by the incorporated transition metal prodegradant.

[14] In accordance with a first aspect the invention provides a process for accelerating degradation of a polyolefin, the process comprising: incorporating a transition metal prodegradant in the polyolefin; and applying an inorganic peroxo compound to a surface of the polyolefin.

[15] In some embodiments, the transition metal prodegradant is incorporated in the polyolefin by melt processing. Melt processing may advantageously disperse the transition metal prodegradant through the polymeric matrix.

[16] In some embodiments, the process further comprises producing and using an object comprising the polyolefin incorporating the transition metal prodegradant, wherein the inorganic peroxo compound is applied to the surface during and/or after use of the object. Certain objects, such as crop propagation films, are required to degrade in use, and the process of the invention may advantageously allow degradation to be initiated or accelerated at a convenient time during this use. Other objects, including various agricultural and packaging films, are required to maintain structural integrity in use, but should degrade rapidly, preferably to extinction, after their beneficial lifetime. The process of the invention may thus be used to initiate or accelerate degradation of a used object to permit its rapid post-use degradation, thereby avoiding or mitigating the economic and environmental costs of disposal. [17] Producing the object may comprise at least one of film blowing, film casting, injection moulding, blow moulding, stretch blow moulding and rotational moulding. In preferred embodiments, the object is a film, which may optionally be produced by film blowing or film casting. The film may be used as an agricultural or a packaging film, and preferably as a mulch film or a crop propagation film.

[18] Although the process of the invention may thus involve a step of incorporating a transition metal prodegradant into the polyolefin, it is also within the scope of the invention that a polyolefin composition already comprising a transition metal prodegradant may be obtained, optionally formed into an object, and degraded according to the invention.

[19] Therefore, in accordance with a second aspect the invention provides a process for accelerating degradation of a polyolefin incorporating a transition metal prodegradant, the process comprising: applying an inorganic peroxo compound to a surface of the polyolefin.

[20] The polyolefin may be obtained from any suitable source, including from commercial sources, and may be, or be formed into, any object (or component thereof). In some preferred embodiments, the polyolefin is in the form of a film. The film may be an agricultural or packaging film, and preferably a mulch film or crop propagation film. The inorganic peroxo compound may be applied to the surface during and/or after use of the film, as described herein.

[21 ] In some embodiments of the first and second aspects, the inorganic peroxo compound is a persulfate salt or a peroxymonosulfate salt. The inorganic peroxo compound may in some embodiments be selected from the group consisting of ammonium persulfate, potassium persulfate, sodium persulfate, ammonium peroxymonosulfate, potassium peroxymonosulfate and sodium peroxymonosulfate, and are preferably selected from the group consisting of ammonium persulfate, potassium persulfate, sodium persulfate and potassium peroxymonosulfate. In other embodiments of the first and second aspects, the inorganic peroxo compound is hydrogen peroxide or a hydrogen peroxide releasing agent such as sodium percarbonate, sodium perborate or urea peroxide. [22] In some embodiments of the first and second aspects, the inorganic peroxo compound is applied to the surface as an aqueous solution. The inorganic peroxo compound may be present in the aqueous solution in an amount of from 0.2 w/v% to 50 w/v%, preferably from 1 w/v% to 20 w/v%, such as from 2 w/v% to 10 w/v%. The aqueous solution may be applied to the surface by spraying, coating or immersion, preferably by spraying. In some embodiments, the inorganic peroxo compound is applied at a loading on the surface of the polyolefin of from 0.1 μιτιοΙ/οιτι² to 75 μιτιοΙ/ατι², preferably from 0.5 μιτιοΙ/οιτι² to 30 μιτιοΙ/οιτι², such as from 1 μιηοΙ/ατι² to 15 μιτιοΙ/οιτι².

[23] In some embodiments of the first and second aspects, the transition metal prodegradant is an organic salt of a transition metal selected from the group consisting of manganese, iron and cobalt. In some preferred embodiments, the transition metal prodegradant is an organic salt of manganese. The organic salt may be a transition metal salt of a C8-C36 fatty acid, such as a stearate. Although organic salts of transition metals are currently preferred, it is envisaged that transition metal oxides, for example nanoparticulate titanium dioxide, may alternatively (or additionally) be incorporated to provide accelerated degradation in accordance with the invention.

[24] In some embodiments of the first and second aspects, the transition metal prodegradant is incorporated in the polyolefin in an amount of from 1 ppm to 1000 ppm of transition metal (i.e. mass of elemental transition metal relative to mass of the total polyolefin composition). The transition metal prodegradant is generally dispersed through the matrix of the polyolefin, and is preferably substantially homogeneously dispersed.

[25] In some embodiments of the first and second aspects, the polyolefin further incorporates a non-ionic surfactant. The non-ionic surfactant may be an alkoxylated ethylenically saturated surfactant compound with an HLB of less than 12, such as an ethoxylated C12-C30 fatty alcohol. The non-ionic surfactant and the transition metal prodegradant are preferably melt blended together in the polyolefin. The inventors have surprisingly discovered that accelerated degradation of polyolefins in accordance with the present invention may also be further enhanced in at least some embodiments by the incorporation of the non-ionic surfactant. The inclusion of the surfactant may be particularly useful, for example, in accelerating the degradation of compositions comprising low levels of transition metal prodegradant or containing other additives, such as pigments, which render the polyolefin more resistant to degradation.

[26] In some embodiments of the first and second aspects, the polyolefin further incorporates a pigment, such as carbon black. Pigments may be required for products such as mulch films to reduce transmission of sunlight. The process of the invention may be particularly useful to accelerate the degradation of pigmented polyolefins, which may otherwise be especially resistant to degradation.

[27] In some embodiments of the first and second aspects, the polyolefin is blended with a further polymer and/or the polyolefin and a further polymer are both components of an object. Where the polyolefin and the further polymer are a blend, the polyolefin may comprise at least 20% of the blend, preferably at least 60% of the blend and most preferably at least 80% of the blend. Where the polyolefin and the further polymer are separate components of an object, the further polymer may optionally also incorporate a transition metal prodegradant. Degradation of the further polymer may also be accelerated by application of the inorganic peroxo compound. Advantageously, the degradation of objects comprising multiple polymeric materials may thus be accelerated according to the invention. Examples of such objects may include films comprising a blend of polyolefin and the further polymer, or films having a polyolefin and the further polymer as adjacent layers of a laminate multi -layered structure. In some embodiments, the further polymer is a polyester, preferably a biodegradable polyester such as polybutyrate.

[28] In some embodiments of the first and second aspects, the polyolefin is selected from the group consisting of polyethylene, polypropylene and blends and copolymers thereof. In some preferred embodiments, the polyolefin is polyethylene. Suitable polyethylene grades for film applications include linear low density polyethylene, low density polyethylene and ultra-low density polyethylene.

[29] In some embodiments of the first and second aspects, the process further comprises heating the polyolefin during and/or after applying the inorganic peroxo compound to the surface of the polyolefin. In these or other embodiments of the first and second aspects, the process may further comprise contacting the polyolefin with water and/or water vapour after applying the inorganic peroxo compound to the surface of the polyolefin. In some embodiments of the first and second aspects, the process further comprises burying and/or bundling the polyolefin after applying the inorganic peroxo compound to the surface of the polyolefin. Burying and/or bundling the polyolefin may assist with heating and/or humidifying the polyolefin to enhance degradation thereof, and may advantageously reduce the space occupied by the polyolefin during degradation.

[30] The invention also provides a system for accelerated degradation of polyolefins, and for performing the processes of the invention.

[31 ] In accordance with a third aspect the invention provides a system for accelerating degradation of a polyolefin, the system comprising: a polyolefin incorporating a transition metal prodegradant; an inorganic peroxo compound; and an applicator configured to apply the inorganic peroxo compound to a surface of the polyolefin.

[32] In some embodiments, the polyolefin is in the form of a film, including an agricultural or packaging film, and preferably a mulch film or crop propagation film.

[33] In some embodiments, the inorganic peroxo compound is present in an aqueous solution.

[34] In some embodiments, the applicator comprises a sprayer for spraying the aqueous solution onto the surface. Suitable sprayers may include spraying equipment already available on farms, such as spraying equipment for irrigation or the application of fertiliser or pesticides.

[35] Where the terms "comprise", "comprises" and "comprising" are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[36] Further aspects of the invention appear below in the detailed description of the invention. Detailed Description

[37] The present invention provides for the accelerated degradation of polyolefins comprising a transition metal prodegradant, via application of an inorganic peroxo compound to a surface of the polyolefin. The invention encompasses either i) incorporating a transition metal prodegradant into the polyolefin composition, or ii) the use of a polyolefin composition which already incorporates a transition metal prodegradant. The invention is presently considered to be of particular utility for accelerated degradation of polyolefin films, such as agricultural or a packaging film.

Transition metal prodegradant

[38] The transition metal pro-degradant may comprise a transition metal salt, a transition metal oxide or a combination of transition metal salt and a transition metal oxide. The preferred choice of transition metal prodegradant may depend at least in part on the intended application of the polyolefin. For example, the prodegradant may be selected to produce a suitable rate of degradation over the useful lifetime of a polyolefin product, for example over the cropping cycle with agricultural films. As such, it will be appreciated that the acceleration of post-use polyolefin degradation in accordance with the invention may be only one of several considerations when incorporating a prodegradant in a polyolefin composition, or if selecting a suitable polyolefin composition which already incorporates a transition metal prodegradant. Alternatively, however, the prodegradant may be added only for the purposes of accelerated degradation in accordance with the invention, for example where a polyolefin product is not required to degrade in use, or is envisaged to have only a short useful lifetime.

[39] In some embodiments, the prodegradant comprises a transition metal salt, such as any of the transition metal salts disclosed in the art to promote the degradation of polyolefins. Organic salts of transition metals are particularly preferred. It is generally believed in the art that organic salts of transition metal salts promote polyolefin degradation under thermo-oxidative conditions, including in the absence of sunlight, by catalysing the rate-limiting decomposition of hydroperoxide species. [40] Transition metal organic salts may thus be preferred for agricultural films which are partially buried in use, yet where partial degradation over the lifetime of the film is desired. Accelerated further degradation of the film, preferably to extinction, may then be accomplished after the use, in accordance with the invention. Alternatively, degradation may be triggered in use for certain applications, as will be described in greater detail hereafter. Without wishing to be bound by any theory, it is believed that the oxidising action of a surface-applied inorganic peroxo compound synergistically cooperates with the hydroperoxide decomposition action of an incorporated transition metal salt to accelerate polyolefin decomposition. It is further believed that this cooperative degradation process does not require photo-initiation, such that the peroxo treated film may potentially be buried or bundled during the accelerated degradation provided by the invention.

[41 ] The transition metal salt may be a transition metal salt of a carboxylic acid, amide or dithiocarbamate and is preferably a metal salt of a fatty acid. Suitable transition metal salts comprise transition metal ions selected from the group consisting of manganese, cobalt, nickel, cerium, copper and iron and mixtures thereof. Preferably, the transition metal salt prodegradant is an organic salt of a transition metal selected from the group consisting of manganese, iron and cobalt. A particularly preferred transition metal salt prodegradant is an organic salt of manganese.

[42] Suitable examples of transition metal salt prodegradants include transition metal salts of a fatty acids with a carbon number ranging from C₄ to C36, in particular from Cs to C36 is preferred. Transition metal salts formed with saturated fatty acids are preferred. Particularly preferred examples are metal carboxylates of palmitic acid (C16) , stearic acid (C-is), 12-hydroxy stearic acid (ds) and naphthenic acid. C₄-C36 carboxylate salts, in particular stearate, palmitate or naphthenate salts of Fe, Ce, Co, Mn, Ni or mixtures thereof are of particular interest. Particularly preferred are Fe- stearate, Mn-stearate and Co-stearate. It is, however, also possible to use mixtures of the aforementioned metal carboxylates.

[43] The transition metal salt prodegradant, such as metal carboxylate, is typically present in an amount of from 0.001 wt% to 10 wt%, such as 0.001 wt% to 1 .6 wt%, 0.01 wt% to 1 wt% or from 0.06 wt% to 0.5 wt%, based on the weight of the polyolefin.

[44] The transition metal prodegradant may alternatively comprise a transition metal oxide, such as any of the photoactive transition metal oxides disclosed in the art to promote the degradation of polyolefins. Photoactive transition metal oxides may be preferred for agricultural films which are exposed to sunlight in use and where partial degradation over the lifetime of the film is desired. Accelerated further degradation of the film, preferably to extinction, may then be accomplished after the use, in accordance with the invention.

[45] The photoactive metal oxide prodegradant is preferably nanoparticulate titanium oxide. TiO₂ may be in the form of Rutile or Anatase, preferred is Anatase. Mixtures of Anatase and Rutile may also be used; preferably such mixtures contain 50% to 90% by weight of Anatase, based on the weight of the mixture. A commercially available form of T1O2 that fits this description is supplied by Evonik Industries as "Aeroxide" TiO₂ P 25 ("Aeroxide" is a trademark).

[46] The titanium oxide may also be doped, wherein at least a portion of the titanium dioxide particles comprise, in their crystal lattice, metal ions selected from the group consisting of copper, manganese, nickel, cobalt, iron, and zinc. Furthermore, the titanium dioxide may be surface-treated with compatibilisers to improve dispersibility in the polyolefin, for example organosilanes.

[47] The photoactive titanium dioxide may be produced by combustion or thermal decomposition via spray or aerosol, atomizing from a starting colloidal solution or precursor to prepare particles in the required size range. The photoactive titanium dioxide may also be produced via spray pyrolysis of a solution or precursor or by thermal decomposition of precursors from a solution or by thermal deposition in vacuum, such as chemical vapour deposition and plasma processing methods. As another alternative, the photoactive titanium dioxide may be produced by melting or rapid quenching, by microwave processing, by ultrasonic processing, by electrochemical and mechanochemical methods or by cryochemical (freeze-drying) methods so that the particle size of the metal oxides is within the range required. [48] The titanium dioxide useful in accordance with the present invention preferably has a particle size such that the largest dimension of the particle is less than 200 nm, more preferably from 1 nm to 100 nm, most preferably from 1 nm to 30 nm. The transition metal oxide prodegradant, such as nano-scaled T1O2, is typically present in an amount of from 0.05 wt% to 10 wt% by weight, preferably 0.2 wt% to 10 wt%, most preferably from 0.5 wt% to 3 wt% based on the weight of the polyolefin.

[49] The transition metal pro-degradant may comprise a combination of transition metal salt and a transition metal oxide. Although antagonistic effects between such prodegradants have been reported, some of the inventors have previously disclosed that these effects may be beneficially overcome by melt processing the two prodegradants into a polyolefin composition in the presence of an non-ionic surfactant, for example as described in WO 2013/023247.

[50] The transition metal prodegradants, including transition metal salt prodegradants such as metal carboxylates and transition metal oxide prodegradants such as nano-scaled titanium dioxide, are items of commerce and may be used in their various commercial grades. Furthermore, polyolefin products, such as films, which incorporate various transition metal prodegradants are also items of commerce, and may be used as supplied in accordance with the invention.

Incorporating the prodegradant

[51 ] In an aspect, the invention includes a step of incorporating a transition metal prodegradant in a polyolefin. The incorporation of the prodegradant and any optional additives into the polyolefin is carried out by known methods such as melt blending, dry blending in the form of a powder, or wet mixing in the form of solutions, dispersions or suspensions, for example in an inert solvent, water or oil, or by addition of the prodegradants in the form of a spray or solution to the polymer following formation of an article. If a plurality of components is added, these can be premixed or added individually.

[52] The transition metal prodegradants and optional further additives can also be added to the polyolefin in the form of a masterbatch ("concentrate") which contains the components in a concentration of, for example, about 1 % to about 40% and preferably 2% to about 20% by weight incorporated in a polymer. The masterbatch polymer need not necessarily be of identical composition to the base polyolefin with which it is combined, though preferably it is sufficiently compatible for blending during the subsequent processing. The polymer of the masterbatch can be used in the form of powder, granules, solutions, or suspensions. A desired level of prodegradant and other additives can be provided in the polyolefin composition by combining appropriate quantities of masterbatch composition and base polyolefin resin.

[53] The melt blended or dried mixture of polyolefin, transition metal prodegradant and any other additives may be added directly into processing apparatus equipped with a mixing mechanism (e.g. extruders, internal mixers, etc). The processing equipment may include a closed apparatus such as a kneader, mixer or stirred vessel. Processing may optionally take place in an inert atmosphere or in the presence of oxygen. Particularly preferred processing machines are single-screw extruders, contra-rotating and co-rotating twin-screw extruders, planetary-gear extruders, ring extruders or co-kneaders. It is also possible to use processing machines. In some cases it may be beneficial to have at least one gas removal compartment to which a vacuum can be applied.

[54] Suitable extruders and kneaders are described, for example, in Handbuch der Kunststoff extrusion, Vol. 1 Grundlagen, Editors F. Hensen, W. Knappe, H. Potente, 1989, pp. 3-7, ISBN:3-446-14339-4 (Vol. 2 Extrusionsanlagen 1986, ISBN 3- 446 14329-7).

[55] In preferred embodiments, the transition metal prodegradant is incorporated into the matrix of the polymer in a melt processing step, whether initially when combining the materials in a melt blending step or subsequently when extruding or otherwise melt processing the mixture of materials into pellets or a shaped product. Preferably, the incorporated transition metal prodegradant is dispersed throughout the polymeric matrix after the melt processing step.

Surfactant

[56] The polyolefin may further incorporate a non-ionic surfactant, which in some embodiments may be an alkoxylated ethylenically saturated compound. It was previously disclosed by some of the inventors in WO2013/023247 that the incorporation of such surfactants together with transition metal prodegradants may enhance the transition metal mediated degradation of polyolefin compositions under the influence of natural weathering conditions. The inventors have now discovered that accelerated degradation of polyolefins in accordance with the present invention may also be further enhanced in at least some embodiments by the incorporation of surfactant. The inclusion of a surfactant may be particularly useful, for example, in accelerating the degradation of compositions comprising low levels of transition metal prodegradant or containing other additives, such as pigments like carbon black, which render the polyolefin more resistant to degradation.

[57] The term "saturated" with reference to the surfactant means that the compound has no double, triple bonds or aromatic moieties. The presence of unsaturation in the carbon-carbon system is not desirable as this makes the system highly susceptible to oxidation during and after processing, significantly reducing the shelf-life of the film. The non-ionic surfactant generally comprises carbon, oxygen and hydrogen and typically will not comprise other heteroatoms such as nitrogen, sulfur, phosphorus, silicon or the like. The incorporation of surfactants or other additives that are unhindered amines, into the polyolefin film are not desirable as they cause film discolouration, are unstable during processing and produce a strong odour.

[58] In some embodiments, the alkoxylated ethylenically saturated non-ionic surfactant contains at least one alkylene glycol unit and at least one saturated hydrocarbon chain having at least eight carbon atoms. The hydrophillic-lipophillic balance (HLB) of the surfactant is generally less than 12, preferably no more than 10, more preferably no more than 8 and most preferably no more than 7. Generally the HLB will be at least 2 and preferably at least 3. Accordingly, a particularly preferred HLB range is from 3 to 7.

[59] The HLB of a surfactant is a measure of the balance between the size and strength of hydrophilic portion of the surfactant and the lipophilic group(s). The hydrophilic portion of the alkoxylated ethylenically saturated non-ionic surfactant comprises the alkylene glycol groups and the lipophilic group comprises the saturated hydrocarbon chain. Generally speaking, surfactants which are more lipophilic in character have a lower HLB than surfactants which are hydrophilic. HLB may be calculated using the method of Griffin referred to in "Schick Non-Ionic Surfactants", Suf. Sci. Series Vol 1 . Chapter 18. The HLB is frequently reported by manufacturers such as reported in McCutcheon's Emulsifiers and Detergents 2010. In the absence of information of a definitive structure or information from the manufacturer, HLB may be experimentally determined as described in "The HLB System a time-saving guide to emulsifier selection" ICI Americas Inc. March 1980, Chapter 7.

[60] The surfactant contains at least one carbon chain which can be linear or branched. The saturated carbon chain generally contains at least 8 carbons, preferably at least 12 carbons and more preferably at least 16 carbons. Generally the carbon chain length will be no more than 40 carbons, such as no more than 36 carbons, no more than 30 carbons, no more than 26 carbons or no more than 22 carbons. Accordingly useful ranges include Cs-C₄o, such as Cs to C26, preferably C12 to C30, more preferably C12 to C26, and most preferably C16-C18.

[61 ] The surfactant typically contains at least one alkoxylate (alkylene glycol) unit which can be derived from ethylene oxide, propylene oxide, butylene oxide or combinations thereof. Most preferably it is derived from ethylene oxide. The surfactant may contain more than one alkoxylate unit which may be an alkylene glycol dimer or polyalkyleneglycol.

[62] The at least one carbon chain and the at least one alkoxylate unit may be linked by either an ether or ester linkage. Thus the surfactant may be the product of condensing preformed alkyleneglycol, alkylene glycol dimer or polyalkyleneglycol with one or more saturated alcohols or saturated carboxylic acids. Alternatively the surfactant can be the product of alkoxylation of a saturated alcohol or saturated carboxylic acid. The non-ionic surfactant can be a diblock or multiblock structure, including an ABA structure (for example a copolymer formed by the condensation reaction of a polyethylene glycol with two or more mole equivalents of 12- hydroxystearic acid). The non-ionic surfactant may also be terminally blocked, for example by alkylation of a terminal hydroxyl group. [63] In preferred embodiments, the surfactant is an alkoxylated ethylenically saturated alcohol. Such surfactants are generally produced from alcohols having linear or branched alkyl chains with between 8 and 40 carbons, preferably 12 to 30, more preferably from 16 to 18. Alkylene oxide is then chemically added to the alcohol in molar ratios ranging from 1 to 9, generally resulting in a range of molecules having a statistically distributed number of additions. Surfactant molecules of the form R-O- (AO)n-H are thus produced, where R is the saturated alkyl chain, A is a C2-C₄ alkylene group and n is an integer ranging from 1 to 9. Preferably the alkylene oxide is selected from ethylene oxide and propylene oxide, and is most preferably ethylene oxide. Preferably n is from 1 to 5, and is particularly selected such that the HLB is less than 12. It will be understood by those skilled in the art that the HLB may be determined by the choice of appropriate lengths of the ethylenically saturated chain and average number of alkylene glycol additions. For example, generally a non-ionic surfactant comprising an ethylenically saturated alcohol of at least eight carbon atoms and having on average from 1 to 5 alkylene glycol units will have an HLB of less than 12. Increasing the number of carbon atoms in the saturated alcohol will reduce the HLB and increasing the extent of alkoxylation will increase HLB.

[64] The surfactant, if added, may be incorporated in the polyolefin before, simultaneously or after incorporating the transition metal prodegradant. Preferably it is present while melt processing the transition metal prodegradant in the polyolefin composition.

Polyolefin

[65] The process of the invention is for accelerating the degradation of a polyolefin. Suitable polyolefins may include polymers of monoolefins and diolefins, for example polyethylene, polypropylene, polyisobutylene, polybut-1 -ene, poly-4- methylpent-1 -ene, polyvinylcyclohexane, polyisoprene or polybutadiene, as well as polymers of cycloolefins, for instance of cyclopentene or norbornene. Any of the polyolefins, including polyethylene, may optionally be crosslinked. Suitable classes of polyethylene may include, for example, high density polyethylene (HDPE), high density and high molecular weight polyethylene (HDPE-HMW), high density and ultrahigh molecular weight polyethylene (HDPE-UHMW), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE) and ultra-low density polyethylene (ULDPE).

[66] Polyolefins, specifically the polymers of monoolefins exemplified in the preceding paragraph, preferably polyethylene and polypropylene, can be prepared by different, and especially by the following, methods: a) radical polymerisation (normally under high pressure and at elevated temperature); and b) catalytic polymerisation using a catalyst that normally contains one or more than one metal of groups IVb, Vb, Vlb or VIII of the Periodic Table. The catalytic metals usually have one or more than one ligand, typically oxides, halides, alcoholates, esters, ethers, amines, alkyls, alkenyls and/or aryls that may be either ττ- or σ-coordinated. These metal complexes may be in the free form or fixed on substrates, typically on activated magnesium chloride, titanium(lll) chloride, alumina or silicon oxide. The catalysts may be soluble or insoluble in the polymerisation medium. The catalysts can be used by themselves in the polymerisation or further activators may be used, typically metal alkyls, metal hydrides, metal alkyl halides, metal alkyl oxides or metal alkyloxanes, said metals being elements of groups la, lla and/or Ilia of the Periodic Table. The activators may be modified conveniently with further ester, ether, amine or silyl ether groups. These catalyst systems are usually termed Phillips, Standard Oil Indiana, Ziegler-Natta, TNZ (DuPont), metallocene or single site catalysts (SSC).

[67] Mixtures of any of the polyolefins described herein may also be used, such as mixtures of polypropylene with polyisobutylene, polypropylene with polyethylene (for example PP/HDPE, PP/LDPE) and mixtures of different types of polyethylene (for example LDPE/HDPE or LDPE/LLDPE).

[68] Copolymers of monoolefins and diolefins with each other or with other vinyl monomers may also be used, for example ethylene/propylene copolymers, linear low density polyethylene (LLDPE), propylene/but-1 -ene copolymers, propylene/isobutylene copolymers, ethylene/but-1 -ene copolymers, ethylene/hexene copolymers, ethylene/methylpentene copolymers, ethylene/heptene copolymers, ethylene/octene copolymers, ethylene/vinylcyclohexane copolymers, ethylene/cycloolefin copolymers (e.g. ethylene/norbornene like COC), ethylene/1 - olefins copolymers, where the 1 -olefin is generated in-situ; propylene/butadiene copolymers, isobutylene/isoprene copolymers, ethylene/vinylcyclohexene copolymers, ethylene/alkyl acrylate copolymers, ethylene/alkyl methacrylate copolymers, ethylene/vinyl acetate copolymers or ethylene/acrylic acid copolymers and their salts (ionomers) as well as terpolymers of ethylene with propylene and a diene such as hexadiene, dicyclopentadiene or ethylidene-norbornene. Mixtures of such copolymers with one another and with polyolefin homopolymers are also contemplated, for example polypropylene/ethylene-propylene copolymers, LDPE/ethylene-vinyl acetate copolymers (EVA), LDPE/ethylene-acrylic acid copolymers (EAA), LLDPE/EVA, LLDPE/EAA and alternating or random polyalkylene/carbon monoxide copolymers and mixtures thereof with other polymers, for example polyamides.

[69] The homopolymers and copolymers disclosed herein may have any stereostructure including syndiotactic, isotactic, hemi-isotactic or atactic; where atactic polymers are preferred. Stereoblock polymers are also included.

[70] For example, in one embodiment the polyolefin comprises at least one selected from the group consisting of polyethylene, polypropylene, polyethylene copolymers, polypropylene copolymers and blends of any of the aforementioned. Blends of the aforementioned may be blends of one or more of the aforementioned with other polymers, where preferably at least 20% by weight is a polyolefin, preferably at least 60% and most preferably at least 80% by weight is a polyolefin, or blends of two or more of the polymers. Low density and linear low density polyethylene may be particularly preferred for some agricultural film applications.

[71 ] It will be understood by those skilled in the art that the polyolefin composition may contain the types of processing aids and additives used in the art. Examples of suitable additional additives include:

• pigments, such as carbon black;

• antioxidants such as alkylated monophenols, alkylthiomethylphenols, hydroquinones and alkylated hydroquinones, tocopherols hydroxylated thiodiphenyl ethers, alkylidenebisphenols, O-, N- and S-benzyl compounds, hydroxybenzylated malonates, aromatic hydroxybenzyl compounds, triazine compounds, benzylphosphonates, acylaminophenols, esters of p-(3,5-di-tert-butyl- 4-hydroxyphenyl)propionic acid with mono- or polyhydric alcohols, esters of β-(5- tert-butyl-4-hydroxy-3-methylphenyl)propionic acid with mono- or polyhydric alcohols, esters of p-(3,5-dicyclohexyl-4-hydroxyphenyl)propionic acid with mono- or polyhydric alcohols, esters of p-3,5-di-tert-butyl-4-hydroxyphenyl acetic acid, amides of p-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, ascorbic acid (vitamin C) and mimic antioxidants;

• UV absorbers and light stabilizers such as 2-(2'-hydroxyphenyl)benzotriazoles, 2- hydroxybenzophenones, esters of substituted and unsubstituted benzoic acids, acrylates, nickel compounds, sterically hindered amines, oxamides and 2-(2- hydroxyphenyl)-1 ,3,5-triazines;

• metal deactivators;

• phosphites and phosphonites;

• hydroxylamines;

• nitrones;

• thiosynergists;

• peroxide scavengers;

• the polyamide class of stabilizers;

• basic co-stabilizers;

• nucleating agents;

• fillers and reinforcing agents;

• benzofuranones and indolinones;

• materials that reduce or eliminate whitening of the film following aging, particularly in those films that contain metal oxide prodegradants (e.g. photoactive titanium dioxide), such as materials having a refractive index approximately matching that of the bulk material. Such materials could include, but are not limited to, oils and waxes. Waxes can include animal, vegetable, mineral and synthetic waxes, for example petrolatum, polyolefin waxes, such as polybutene and polyethylene waxes, wool wax and its derivatives, such as wool wax alcohols, and silicone waxes. Oils can include vegetable oils, animal oils, mineral oils, silicone oils or their mixtures. In particular, hydrocarbon oils, such as paraffin oils, isoparaffin oils, squalane, oils from fatty acids and polyols are preferred. Hydrocarbon oils, especially mineral oils (paraffinum liquidum), are especially preferred, in particular Mobil DTE Heavy oil. Further examples of such additives are provided in International Patent Publication WO2009/021270;

• other additives, for example plasticisers, lubricants, emulsifiers, rheology additives, catalysts, flow-control agents, optical brighteners, flame-proofing agents, antistatic agents and blowing agents.

[72] It will be appreciated that the type and amounts of any additional additives may depend on the required properties of the polyolefin composition, both before and after application of the inorganic peroxo compound. For example, it is considered that incorporation of increased amounts of anti-oxidants or other stabilisers in the polyolefin may advantageously prolong the useful lifetime of a polyolefin composition, but then reduce or inhibit the acceleration of degradation afforded by applying the inorganic peroxo compound. A balance between the durability before, and degradability after, application of the inorganic peroxo compound may thus be required. The skilled person, with the benefit of this disclosure, will be able to determine an appropriate additive package for a given application with no more than routine experimentation.

[73] The additional additives are, for example, present in the composition in an amount of 0.001 to 10% by weight, preferably 0.001 to 5% by weight, relative to the weight of the polyolefin. Additional additives, if incorporated in the polyolefin, may be incorporated before, simultaneously or after incorporating the transition metal prodegradant.

Products

[74] The polyolefin to be degraded in accelerated manner according to the invention may be, or be a component of, a product which has already performed a function and reached the end of its useful lifetime. Optionally, the polyolefin is already partially degraded as a result of the usage. Accelerated degradation of a used product may be advantageous for a number of reasons, including the avoidance of disposal costs incurred via transportation and/or landfilling and the minimisation of environment impacts of discarded polyolefins. [75] Although the method of the invention is considered to be particularly useful for composting objects after the end of their beneficial lifetime, it will be appreciated the method may also be used to achieve a targeted degradation rate or degradation profile of an object during its functional lifetime. It is thus envisaged that the method of the invention may be useful to allow faster degradation of a polyolefin film in uses requiring such degradation than could be achieved with a particular type of prodegradant by itself, or to achieve a target rate of degradation while reducing the amount of prodegradant incorporated. Furthermore, the triggered acceleration of degradation according to the invention may advantageously allow different rates of degradation to be achieved during the lifetime of a product (i.e. an initial nonaccelerated degradation phase and a later, accelerated degradation phase).

[76] In some embodiments, the process of the invention may include steps of producing and using an object which comprises a polyolefin having incorporated transition metal prodegradant. In this case, the prodegradant may be incorporated while producing the object as described in greater detail hereafter, or the object may be produced from a polyolefin resin which already incorporates the prodegradant. In an alternative embodiment, an object which includes a polyolefin component incorporating transition metal prodegradant may be obtained, and used as supplied. Such objects may be obtained from any source, including by purchase from commercial suppliers. In any of these cases, the step of applying an inorganic peroxo compound to a surface of the polyolefin may be performed to accelerate degradation of at least the polyolefin component of the product, and potentially also other components, such as non-polyolefinic polymers.

[77] In some embodiments, the object comprises polyolefin in the form of a film, for example an agricultural or a packaging film. In some preferred embodiments, the film is a mulch film or a crop propagation film, as will be described in greater detail hereafter.

[78] In another embodiment, the film is a packaging film for temporary packaging, such for the purpose of retaining or protecting articles temporarily. One example of such packaging is the protection of material such as mail, commercial products or correspondence during delivery to customers. Another example is shopping bags required to merely maintain strength for a period sufficient to allow them to be dispensed to customers in shops at the point of sale of goods and to transport the goods to the point of use.

[79] Films that can be degraded according to the invention may include both single layer and multi-layer films. In the case of a single-layer film, the layer comprises the polyolefin and the transition metal prodegradant, optionally blended with other polymers and further additives. In the case of multi-layer films, at least one layer comprises the polyolefin with incorporated transition metal prodegradant. Each layer comprising polyolefin may have a different package of transition metal prodegradants and other additives. One or more of the other layers may comprise other polymeric materials, and may indeed be substantially free of polyolefin. Polyolefin-free layers may also incorporate a transition metal prodegradant. However, where the constituent polymers are inherently more susceptible to degradation than polyolefins, it may be unnecessary to incorporate a prodegradant in the matrix. These materials, for example biodegradable polyesters such as polybutyrate, may already have an acceptable degradation profile. Furthermore, it has been found that the application of the inorganic peroxo compound to such materials, which may be done simultaneously to applying the compound to the polyolefin surface, can accelerate polymer degradation substantially even when a prodegradant is not included.

[80] Polyolefin films or other polyolefin-based products incorporating transition metal prodegradant may be produced by conventional processing techniques, including film blowing, film casting, injection moulding, blow moulding, stretch blow moulding and rotational moulding.

[81 ] In forming the polyolefin composition into suitable film for crop propagation it may be preferred to use the procedures described in US 6168840. Polyolefins are thus stretched in at least localised regions along a length of the film to beyond the yield point of the film to achieve a reduced thickness in the stretched region or regions, whereby in use the film will deteriorate to allow passage of a germinated seedling through the film. Indeed the film may be completely stretched beyond its yield point. In one embodiment the film is completely stretched biaxially. The film is preferably stretched at its point of extrusion, that is, in-line stretching of the film during the extrusion process. The polyolefin film may also be stretched at a secondary out of line stretching process.

[82] The polyolefin film, such as for agricultural or packaging applications, may have a thickness of from 1 to 500 microns and preferably from 2 to 200 microns. In the case of film for plant propagation, the stretching of the film may provide areas of thickness of less than 10 microns or the thickness of the whole film may be reduced to less than 10 microns. The polyolefin film may optionally be perforated with multiple perforations, which may advantageously further increase the degradation rate due to the enhanced contact with the inorganic peroxo compound and/or oxygen.

Inorganic peroxo compound

[83] The process of the invention involves a step of applying an inorganic peroxo compound to a surface of the polyolefin. Peroxo compounds are compounds containing an oxygen-oxygen single bond, i.e. a peroxo group. The inorganic peroxide compounds of the invention are thus compounds, salts or adducts comprising a moiety having the formula R¹-O-O-R², where R¹ and R² are independently inorganic groups or hydrogen.

[84] The inorganic peroxo compound may be a persulfate salt (also known as a peroxydisulfate salt) or a peroxymonosulfate salt. Suitable examples of persulfate salts may include, but are not limited to, ammonium persulfate, potassium persulfate and sodium persulfate. Suitable examples of peroxymonosulfate salts may include, but are not limited to, ammonium peroxymonosulfate, potassium peroxymonosulfate and sodium peroxymonosulfate. As an alternative to the salt form, it is envisaged that peroxydisulfuric acid or peroxymonosulfuric acid could in principle be used instead, although this may in practice be less preferred due to stability and explosive risks.

[85] The inorganic peroxo compound may alternatively be hydrogen peroxide or a hydrogen peroxide releasing agent. Suitable hydrogen peroxide releasing agents may include sodium percarbonate (2Na2CO3.3H₂O2), sodium perborate or urea peroxide. These compounds release H2O2 in aqueous solution, and may be a more convenient source of hydrogen peroxide for triggering degradation according to the invention than solutions of un-complexed hydrogen peroxide solutions, which are relatively unstable.

[86] Other suitable inorganic peroxo compounds may include: peroxide salts (O2^", such as sodium peroxide and its hydrates), hydroperoxide salts (HO2 ), peroxophosphates, and the like.

Applying the inorganic peroxo compound

[87] The inorganic peroxo compound may be applied to the surface of the polyolefin in any form. In preferred embodiments, it is applied in the form of a solution, most preferably an aqueous solution.

[88] The inventors have found that the application of aqueous solutions having inorganic peroxo compounds concentrations in the range of 0.2 w/v% to 50 w/v% successfully accelerates degradation in accordance with the invention, with the best results obtained above 1 w/v% concentration. However, it will be appreciated that the optimum concentration for a given scenario may depend, for example, on the total amount of solution able to be contacted with the surface, the method of application and the contact time between the solution and the surface (which might be reduced by run-off). Suitable concentrations of inorganic peroxo compounds in the solution may in some embodiments be from 0.2 w/v% to 50 w/v%, preferably 1 w/v% to 20 w/v%, such as from 2 w/v% to 10 w/v%.

[89] The inorganic peroxo compound may be applied to the surface of the polyolefin at any suitable loading to achieve an acceleration of degradation. The inventors have found that the application of inorganic peroxo compounds concentrations in the range of from 0.12 μιτιοΙ/οιτι² to 30.7 μιτιοΙ/οιτι² successfully accelerates degradation in accordance with the invention, with the best results obtained above about 0.6 μιτιοΙ/οιτι² concentration. Preferred loadings are from 0.12 μιτιοΙ/ατι² to 12 μιηοΙ/ατι², such as from 0.12 μιτιοΙ/οιτι² to 6 μιτιοΙ/οιτι². However, it will be appreciated that the optimum loading for a given scenario may depend on the nature of the inorganic peroxo compound, the amount and type of the transition metal prodegradant, the type of polyolefin, and other variables. Moreover, it may be unnecessary, and in many cases practically difficult or impossible, to apply a specific target loading of the inorganic peroxo compound to the surface of the polyolefin. In some embodiments, an over-riding consideration will be to ensure that the largest portion, and preferably all parts, of the surface receive an application of the peroxo compound, such that the degradation of the entire polyolefin composition is accelerated. To ensure this, it may be inevitable that at least some portions of the surface receive an unnecessarily high loading.

[90] The inorganic peroxo compound may be applied to the surface of the polyolefin by any suitable means. In preferred embodiments, a solution of the inorganic peroxo compound may be sprayed onto the surface. Alternatively it may be applied by a coating process or by immersing the polyolefin in the solution. In some embodiments, at least a portion of the surface receives an application of solution via flow of the solution under influence of gravity. For example, a mass of polyolefin, such as in an above-ground pile or below ground landfill, could be treated with a solution of the inorganic peroxo compound, the solution gradually percolating through the mass to cover a substantial portion of the polyolefin surface.

[91 ] The inventors have found that polyolefin degradation may be accelerated via a single application of inorganic peroxo compound to the surface of a polyolefin incorporating a transition metal prodegradant. In some embodiments, therefore, only a single application of inorganic peroxo compound is made. However, it is envisaged that multiple applications may be made to the surface, for example spaced apart by a period of time, to accelerate degradation of the polyolefin.

[92] The inorganic peroxo compound may optionally be applied to the surface of the polyolefin in combination with other additives. For example, a wetting agent (such as a surfactant) and/or a viscosifier may be included in a solution of the inorganic peroxo compound to improve the coverage and retention of the solution on the surface.

Post application steps

[93] The process of the invention may comprise heating the polyolefin during and/or after applying the inorganic peroxo compound to the surface of the polyolefin. Without wishing to be bound by any theory, it is believed that the mechanism of degradation accelerated by the invention is thermally mediated, such that the rate of accelerated degradation will be increased at higher temperatures. The polyolefin may be heated by any means. For example, in embodiments where the polyolefin is in the form of a film, the film may be bundled up after application of the inorganic peroxo compound and left exposed to the sun, optionally under a heat retentive cover, to increase the temperature of the polyolefin.

[94] The process of the invention may comprise contacting the polyolefin with water and/or water vapour after applying the inorganic peroxo compound to the surface of the polyolefin. Without wishing to be bound by any theory, it is believed that the mechanism of degradation accelerated by the invention may be increased at higher water partial pressures. Therefore, it may be beneficial to periodically wet the degrading polyolefin, or to ensure that high humidity at the decomposing polyolefin surface is maintained.

[95] The process of the invention may further comprise burying and/or bundling the polyolefin after applying the inorganic peroxo compound to the surface of the polyolefin. As described herein, burying and/or bundling may assist with heating and/or humidifying the polyolefin to enhance degradation thereof. Moreover, the burying and/or bundling after application of the inorganic peroxo compound may be necessary to reduce the space occupied by the polyolefin, for example where the polyolefin is an agricultural film at the end of its useful lifetime.

[96] The process of the invention may further comprise exposing the polyolefin to the sun after applying the inorganic peroxo compound, thereby accelerating the degradation by both photo-oxidative and chemically induced degradation mechanisms.

[97] The process may optionally also include irradiating the polyolefin surface with artificial radiation, such as UV C irradiation, as a complementary tool to initiate degradation. However, it is a potential advantage of the invention that operationally complex interventions such as irradiation, sonication etc are not required to significantly accelerate the polyolefin degradation, as a result of the synergistic interaction between the incorporated transition metal prodegradant and the applied inorganic peroxo compound. Accordingly, in some embodiments, the process excludes a step of irradiating or sonicating the polyolefin after application of the inorganic peroxo compound (other than via optional exposure to sunlight).

Agricultural applications

[98] As disclosed herein, the polyolefin for which accelerated degradation is required may be an agricultural film, such as a crop propagation film or mulch film. The agricultural film, comprising the transition metal prodegradant, may be installed on a field using conventional equipment and methods available to those skilled in the art. An alternative use of degradable agricultural films is as greenhouse covers.

[99] In an embodiment the polyolefin is a crop propagation film and is thus used to cover soil containing plant seeds or planted seedlings, thereby heating the soil and air, retaining moisture and/or protecting the germinating seeds or seedlings from frost. The crop propagation film may optionally be a clear film to allow transmission of sunlight to the plants. Crop propagation film is typically required to embrittle in use such that the plants can break through the film without intervention as they grow. The method of the invention may be employed prior to, during or after the use of the crop propagation film. For example, the inorganic peroxo compound may be sprayed onto film already laid on the field to initiate or accelerate polyolefin degradation, thereby facilitating plant breakthrough. Alternatively, the inorganic peroxo compound may be sprayed onto the film at the end of the cropping cycle, either while still on the field or after removing the film but prior to burial and/or bundling. If sprayed onto the film while on the field, a potential advantage of the invention is that the film may be allowed to degrade in situ without the need to remove and separately process or discard the used film.

[100] In an embodiment the polyolefin is a mulch film and is thus used to surround growing plants on top of the ground and thereby control soil temperature, water retention, weed growth, pest infestation and/or carbon dioxide retention. The mulch film may contain pigment, such as carbon black, to reduce light transmission and resultant weed growth, and to retain heat. The mulch film may be formulated to provide whitening during the use on the field. Generally, however, mulch film may be required to maintain a degree of structural integrity throughout the cropping cycle. Although it is not excluded that the method of the invention may be employed to provide useful functional degradation of mulch film during the cropping cycle, it is envisaged that the inorganic peroxo compound will be sprayed onto mulch film at the end of the cropping cycle, either while still on the field or after removing the film but prior to burial and/or bundling. If sprayed onto the film while on the field, a potential advantage of the invention is that the film may be allowed to degrade in situ without the need to remove and separately process or discard the used film. However, if a portion of the mulch film is buried on the field, it may be preferred to fully expose the mulch film before application of the inorganic peroxo compound.

[101 ] The inorganic peroxo compound may be applied to agricultural film comprising polyolefin by any suitable method. In a presently preferred embodiment, the agricultural film may be sprayed, for example with spraying equipment already available on farms, such as spraying equipment for irrigation or applications of fertiliser or pesticides.

[102] After application of the inorganic peroxo film, the agricultural film may be allowed to degrade, preferably to extinction, while optionally being heated, kept under wet or humidified conditions, buried and/or aggregated as bundles to minimise the footprint, as described herein.

EXAMPLES

[103] The present invention is described with reference to the following examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein.

Materials

[104] Linear low density polyethylene (LLDPE-1 ) resin with a density of 0.919 g.cm^"3 and a melt flow index of 0.90 g.10 mins^"1 , linear low density polyethylene (LLDPE-2) resin with a density of 0.920 g.cm^"3 and a melt flow index of 1 .0 g.10 mins^"1, and ultra-low density polyethylene (ULDPE) resin with a density of 0.905 g.cm^"3 and melt flow index of 0.80 g.l Omins^"1 were obtained from Dow Chemical Company and used to prepare films. Ecoflex F Blend C1200 polybutyrate resin (a random copolymer of adipic acid, 1 ,4-butanediol and dimethyl terephthalate) was obtained from BASF.

[105] A masterbatch containing 15 wt% manganese(ll) stearate in low density polyethylene (Mn-LDPE masterbatch) and a masterbatch containing 40 wt% carbon black in low density polyethylene (carbon black-LDPE masterbatch) were obtained from Integrated Packaging Group.

[106] Iron ( 111) stearate powder was obtained from SunAce, Melbourne, Australia. Brij S2 polyethylene glycol octadecyl ether (i.e. ethoxylated C18 octadecyl ether), with HLB of 5, was obtained from Croda.

[107] A LLDPE-based (90 wt%) polyethylene film containing manganese(ll) stearate (600 ppm manganese; 4 wt% of the Mn-LDPE masterbatch), 5 wt% low density polyethylene and 1 wt% polyisobutylene (molecular weight 2000 g.mol^"1) was manufactured by and obtained from Integrated Packaging Group in Victoria, Australia.

Example 1

[108] Polyethylene films incorporating manganese(ll) stearate were prepared by melt extruding a blend containing appropriate quantities of the Mn-LDPE masterbatch, the LLDPE-1 resin and the ULDPE resin. The amount of the Mn-LDPE masterbatch was varied to give manganese concentrations of between 1 and 300 ppm in the extrudate. The concentration of the ULDPE resin was kept constant at 20 wt%, with the balance of the extrudate being the LLDPE-1 resin. The pelletised extrudates were blown into films using an Axon BX25 single-screw extruder with a 70 mm-diameter blowing die operating at temperatures between 1 80 and 185°C.

[109] Identical samples of the resulting films were clamped into plastic slide holders and treated with either 10 w/v% ammonium persulfate solution (freshly prepared in 18 ΜΩ-quality ultrapure water) by spraying with a handheld pump spray pack at a dose rate of -0.3-0.4 imL per 25 cm², or a water-only spray at the same dose rate. The sample was kept horizontal to prevent any run-off after spraying.

[1 10] Directly following spraying, the samples were subjected to an accelerated laboratory test aging condition believed to directionally simulate dark thermo-oxidative degradation conditions as experienced, for example, when degrading film via soil burial or bundling. The samples were thus placed in the headspace of a sealed glass vessel, the base of which was filled with 20 mL of 18 ΜΩ-quality ultrapure water to provide 100% humidity during the aging. The samples were separated from the water using a steel mesh. The vessel was placed in a Contherm digital series fan-forced oven, thermostatted at 60°C. Samples were withdrawn periodically and evaluated for embrittlement by applying a small stress to the films and observing when multidirectional fracture occurs. Each experiment was performed in triplicate. The time period to reach embrittlement is shown in Table 1 .

Table 1. Effect of in-film manganese(ll) concentration on the time to embrittlement for thermally aged polyethylene films treated with 10 w/v% ammonium persulfate or water

[1 1 1 ] The embrittlement times demonstrate the synergistic effect of manganese(ll) stearate prodegradants incorporated in the film and ammonium persulfate solution applied to the surface of the film on the degradation of polyethylene film. Example 2

[1 12] Polyethylene films incorporating both manganese(ll) stearate and carbon black were prepared by melt extruding a blend containing appropriate quantities of the Mn-LDPE masterbatch, the carbon black-LDPE masterbatch, the LLDPE-1 resin and the ULDPE resin. The amount of the Mn-LDPE masterbatch was varied to give manganese concentrations of between 1 00 and 300 ppm in the extrudate. The concentrations of the ULDPE resin and the carbon black-LDPE masterbatch were kept constant at 20 and 15 wt%, respectively, with the balance of the extrudate being the LLDPE-1 resin. The pelletised extrudates were blown into films using an Axon BX25 single-screw extruder with a 70 mm-diameter blowing die operating at temperatures between 180-185°C.

[1 13] Identical samples of the resulting films were treated with 1 0 w/v% ammonium persulfate solution or water, heated in a glass vessel and tested for embrittlement following the procedure of Example 1 . The time period to reach embrittlement is shown in Table 2.

Table 2. Effect of in-film manganese(ll) concentration on the time to embrittlement for thermally aged carbon black-containing polyethylene films treated with 10 w/v% ammonium persulfate or water

[1 14] The embrittlement times demonstrate the synergistic effect of manganese(ll) stearate prodegradants incorporated in the film and ammonium persulfate solution applied to the surface of the film on the degradation of polyethylene film pigmented with carbon black (6 wt% carbon black). Example 3

[1 15] Polyethylene films incorporating iron(lll) stearate were prepared by melt extruding a blend containing appropriate quantities of iron(lll) stearate powder, the LLDPE-1 resin and the ULDPE resin. The amount of iron(lll) stearate was varied to give iron concentrations of between 1 and 300 ppm in the extrudate. The concentration of the ULDPE resin was kept constant at 20 wt%, with the balance of the extrudate being the LLDPE-1 resin. The pelletised extrudates were blown into films using an Axon BX25 single-screw extruder with a 70 mm-diameter blowing die operating at temperatures between 1 80 and 185°C.

[1 16] Identical samples of the resulting films were treated with 1 0 w/v% ammonium persulfate solution or water, heated in a glass vessel and tested for embrittlement following the procedure of Example 1 . The time period to reach embrittlement is shown in Table 3.

Table 3. Effect of in-film iron(lll) concentration on the time to embrittlement for thermally aged polyethylene films treated with 10 w/v% ammonium persulfate or water

Average (n=3) time to embrittlement (days)

Iron concentration

Post ammonium persulfate Post water

(ppm)

treatment (10 w/v%) treatment

300 35.3±1 .1 >106

200 41 .2±3.1 76.411 1 .4

100 44.5±2.7 >106

50 71 .5±2.4 >106

10 73.5±2.1 >106

1 77.5±4.9 >106

0 89.9±4.2 >106 [1 17] The embrittlement times demonstrate the synergistic effect of iron(lll) stearate prodegradants incorporated in the film and ammonium persulfate solution applied to the surface of the film on the degradation of polyethylene film.

Example 4

[1 18] Identical samples of the Integrated Packaging LLDPE-based polyethylene film containing manganese(ll) stearate (600 ppm manganese) were clamped into plastic slide holders and treated with either 0, 0.2, 0.5, 1 , 2, 5, 10, 20, 30, 40 or 50 w/v% ammonium persulfate solution (freshly prepared in 18 ΜΩ-quality ultrapure water) by spraying with a handheld pump spray pack at a dose rate of -0.3-0.4 imL per 25 cm².

[1 19] The samples were then heated in a glass vessel and tested for embrittlement following the procedure of Example 1 . The time period to reach embrittlement is shown in Table 4.

Table 4. Effect of ammonium persulfate concentration (0.2 - 50 w/v%) on the time to embrittlement for thermally aged polyethylene films that contain 600 ppm manganese from manganese(ll) stearate

Ammonium Approximate Approximate

Average (n=3) persulfate ammonium ammonium

time to

solution persulfate persulfate

embrittlement concentration surface loading surface loading

(days)

(w/v%) (mg.cm^"2) (μιτιοΙ/οιτι²)

0 0 0 104±4.0

0.2 0.028 0.12 13.3±2.2

0.5 0.070 0.31 9.3±1 .1

1 .0 0.14 0.61 5.3±0.8

10 1 .4 6.1 6.111 .5

20 2.8 12.3 5.511 .3

30 4.2 18.4 5.511 .3

40 5.6 24.5 5.511 .3

50 7.0 30.7 6.111 .3 [120] The embrittlement times demonstrate the effect of ammonium persulfate solution concentration / surface loading on the degradation of manganese(ll) stearate- containing polyethylene film.

Example 5

[121 ] Identical samples of the Integrated Packaging LLDPE-based polyethylene film containing manganese(ll) stearate (600 ppm manganese) were clamped into plastic slide holders and treated with 10 w/v% ammonium persulfate solution, or saturated% potassium persulfate solution (~5 w/v%), or 10 w/v% potassium peroxymonosulfate solution, or 10 w/v% sodium percarbonate solution, or 10 w/v% urea peroxide solution (all freshly prepared in 18 ΜΩ-quality ultrapure water) by spraying with a handheld pump spray pack at a dose rate of -0.3-0.4 imL per 25 cm², or a water-only spray at the same dose rate.

[122] The samples were then heated in a glass vessel and tested for embrittlement following the procedure of Example 1 . The time period to reach embrittlement is shown in Table 5.

Table 5. Effect of different oxidants at concentrations of <10 w/v% on the time to embrittlement for thermally aged polyethylene films that contain 600 ppm manganese from manganese(ll) stearate

[123] The results demonstrate the effectiveness of a range of different inorganic peroxo oxidants for accelerating the degradation of manganese(ll) stearate-containing polyethylene film.

Example 6

[124] Polyethylene films incorporating both manganese(ll) stearate and carbon black were prepared by melt extruding a blend containing appropriate quantities of the Mn-LDPE masterbatch, the carbon black-LDPE masterbatch, the LLDPE-2 resin and the ULDPE resin, using the procedure described in Example 2. Films were prepared which either further included or lacked a Brij S2 non-ionic surfactant additive in the composition during melt processing of the composition.

[125] The resulting films were treated with 10 w/v% ammonium persulfate solution or water, heated in a glass vessel and tested for embrittlement following the procedure of Example 1 . The time period to reach embrittlement is shown in Table 6.

Table 6. Effect of in-film Brij S2 surfactant incorporation on the time to embrittlement for thermally aged polyethylene films incorporating both manganese (II) stearate and carbon black, and treated with 10 w/v% ammonium persulfate

[126] The embrittlement times demonstrate that incorporation of non-ionic surfactants may synergistically improve the degradability of polyolefin films containing transition metal prodegradants, when surface treated with ammonium persulfate solution. Example 7

[127] Polybutyrate films, either incorporating iron(lll) stearate or without a prodegradant, were prepared by melt extrusion. The polybutyrate base resin, including iron(lll) stearate powder if added, was pre-dried in a Yann Bang hopper dryer for 12 hours at 60^QC before melt processing and extrusion. The pelletised extrudates were blown into films using an Axon BX25 single-screw extruder with a 70 mm-diameter blowing die operating at 165°C.

[128] Identical samples of the resulting films were treated with 1 0 w/v% ammonium persulfate solution or water, heated in a glass vessel and tested for embrittlement following the procedure of Example 1 . The time period to reach embrittlement is shown in Table 7.

Table 7. Effect of ammonium persulfate treatment on the time to embrittlement for thermally aged Ecoflex-based films

[129] The embrittlement times demonstrate that ammonium persulfate, when applied to the surface of a polybutyrate film, is effective at accelerating the degradation of the polymer, whether compounded with iron (111) stearate or not. Ammonium persulfate may thus be effective for accelerating degradation of compositions comprising a polyolefin together with other polymeric materials, particularly polybutyrate, where at least the polyolefin comprises a transition metal prodegradant. Example 8

[130] Identical samples of the Integrated Packaging LLDPE-based polyethylene film containing manganese(ll) stearate (600 ppm manganese) were treated with either 50 w/v% ammonium persulfate solution (freshly prepared in 18 ΜΩ-quality ultrapure water) by spraying with a handheld pump spray pack at a dose rate of -0.3-0.4 imL per 25 cm², or a water-only spray at the same dose rate. Individual film samples were then folded to produce six-layered bundles, which were held closed at the ends using steel clips.

[131 ] The bundled samples were heated in a glass vessel and tested for embrittlement following the procedure of Example 1 . The time period to reach embrittlement is shown in Table 8.

Table 8. Effect of bundling on the time to embrittlement for thermally aged polyethylene films that contain 600 ppm manganese from manganese(ll) stearate

[132] The embrittlement times demonstrate that the inorganic peroxo oxidant, ammonium persulfate, is effective for accelerating the degradation of bundled manganese(ll) stearate-containing polyethylene film.

[133] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

Claims

1 . A process for accelerating degradation of a polyolefin, the process comprising:

incorporating a transition metal prodegradant in the polyolefin; and applying an inorganic peroxo compound to a surface of the polyolefin.

2. A process according to claim 1 , wherein the transition metal prodegradant is

incorporated in the polyolefin by melt processing.

3. A process according to claim 1 or claim 2, further comprising producing and using an object comprising the polyolefin incorporating the transition metal

prodegradant, wherein the inorganic peroxo compound is applied to the surface during and/or after use of the object.

4. A process according to claim 3, wherein producing the object comprises at least one of film blowing, film casting, injection moulding, blow moulding, stretch blow moulding and rotational moulding.

5. A process according to claim 3 or claim 4, wherein the object is a film.

6. A process according to claim 5, wherein the film is used as an agricultural or a packaging film.

7. A process for accelerating degradation of a polyolefin incorporating a transition metal prodegradant, the process comprising:

applying an inorganic peroxo compound to a surface of the polyolefin.

8. A process according to claim 7, wherein the polyolefin is in the form of a film.

9. A process according to claim 8, wherein the film is an agricultural or packaging film.

10. A process according to claim 9, wherein the inorganic peroxo compound is applied to the surface during and/or after use of the film.

1 1 . A process according to any one of claims 1 to 10, wherein the inorganic peroxo compound is a persulfate salt or a peroxymonosulfate salt.

12. A process according to claim 1 1 , wherein the inorganic peroxo compound is

selected from the group consisting of ammonium persulfate, potassium persulfate, sodium persulfate, ammonium peroxymonosulfate, potassium peroxymonosulfate and sodium peroxymonosulfate.

13. A process according to any one of claims 1 to 10, wherein the inorganic peroxo compound is hydrogen peroxide or a hydrogen peroxide releasing agent such as sodium percarbonate, sodium perborate or urea peroxide.

14. A process according to any one of claims 1 to 13, wherein the inorganic peroxo compound is applied to the surface as an aqueous solution.

15. A process according to claim 14, wherein the inorganic peroxo compound is

present in the aqueous solution in an amount of from 0.2 w/v% to 50 w/v%.

16. A process according to claims 14 or claim 15, wherein the aqueous solution is applied to the surface by spraying, coating or immersion.

17. A process according to any one of claims 1 to 16, wherein the transition metal prodegradant is an organic salt of a transition metal selected from the group consisting of manganese, iron and cobalt.

18. A process according to claim 17, wherein the organic salt is a salt of a C₈-C₃6 fatty acid.

19. A process according to any one of claims 1 to 1 8, wherein the transition metal prodegradant is incorporated in the polyolefin in an amount of from 1 ppm to 1000 ppm of transition metal.

20. A process according to any one of claims 1 to 19, wherein the polyolefin further incorporates a non-ionic surfactant.

21 . A process according to any one of claims 1 to 20, wherein the polyolefin further incorporates a pigment.

22. A process according to any one of claims 1 to 21 , wherein the polyolefin is

blended with a further polymer and/or wherein the polyolefin and a further polymer are both components of an object, wherein degradation of the further polymer is also accelerated by application of the inorganic peroxo compound.

23. A process according to claim 22, wherein the further polymer is a polyester.

24. A process according to any one of claims 1 to 23, wherein the polyolefin is

selected from the group consisting of polyethylene, polypropylene and blends and copolymers thereof.

25. A process according to claim 24, wherein the polyolefin is polyethylene.

26. A process according to any one of claims 1 to 25, further comprising heating the polyolefin during and/or after applying the inorganic peroxo compound to the surface of the polyolefin.

27. A process according to any one of claims 1 to 26, further comprising contacting the polyolefin with water and/or water vapour after applying the inorganic peroxo compound to the surface of the polyolefin.

28. A process according to any one of claims 1 to 27, further comprising burying

and/or bundling the polyolefin after applying the inorganic peroxo compound to the surface of the polyolefin.

29. A system for accelerating degradation of a polyolefin, the system comprising:

a polyolefin incorporating a transition metal prodegradant;

an inorganic peroxo compound; and an applicator configured to apply the inorganic peroxo compound to a surface of the polyolefin.

30. A system according to claim 29, wherein the polyolefin is in the form of a film.

31 . A system according to claim 29 or claim 30, wherein the inorganic peroxo

compound is present in an aqueous solution.

32. A system according to claim 31 , wherein the applicator comprises a sprayer for spraying the aqueous solution onto the surface.