Recyclable polymer materials

Abstract

A recycled polyolefin film containing a block copolymer of formula (I) in which the polymer A comprises a chain of ethylenic or propylenic structures or an ethylene / propylene copolymer chain optionally interrupted by one or more structural units derived from higher 1-alkene comonomers such as hexene or octene and polymer B comprises a chain of structural units derived from two or more α,β – unsaturated polar monomers selected from unsaturated carboxylic acids, styrene, substituted styrene, unsaturated esters such as acrylate and methacrylate esters, vinyl esters, fumarate esters, itaconate esters, maleic anhydride, unsaturated acids such as acrylic acid and methacrylic acid and diene compounds and derivatives thereof and a process for making the film and a masterbatch for use therein.

Description

[0001] RECYCLABLE POLYMER MATERIALS

[0002] The present invention relates to improvements in or relating to recyclable plastic films and in particular to the recycle of films that are used in packaging. Further in particular the invention relates to improving the recyclability of films of polyolefins and more particularly the recyclability of polyolefine films that have been used for shrink wrapping or stretch wrapping. Polyolefine films are used for the packaging of a wide variety of articles ranging from small materials to larger materials such as in pallet wrapping or luggage handling as for example in airports where polyolefine, often polyethylene or polypropylene film or film from polymer blends is wrapped around a load of materials to prevent their movement during transportation. The films may be stretched around the articles where the film is known as stretch film or may be shrunk around the articles where it is known as shrink film. The shrinking is usually accomplished by the application of heat. This practice is extensively used for the wrapping of goods, which may be wrapping of boxes or materials to secure them on pallets.

[0003] There is a growing environmental need to reduce the use of plastic materials including polyolefine films since they are largely indestructible and depending on the nature of the particular plastic are difficult to recycle or at least require expensive recycling techniques. Additionally, there is growing legislation concerning single use materials and also about requirements for recycling.

[0004] An issue with the recycling of plastics and particularly plastic films that have been used for packaging is that labels or other paper based materials are often provided on the surface of the film perhaps to indicate the content of the package or maybe the destination of the package or both. The paper can contaminate the film when it is recycled and it is therefore often necessary to remove the paper before the film can be recycled which can be time consuming and / or expensive. Additionally, the total amount of the paper may not be removed thus resulting in contamination within the recycled material which can have a deleterious impact on the properties of articles made from the recycled material. The recycled polymer is usually converted into flakes or chips prior to reprocessing into articles such as by extrusion or moulding which may be injection moulding or blow moulding and residual paper particles in the recycled material can reduce mechanical properties such as the tensile properties tear strength or impact strength of articles particularly films made from recycled polyolefines particularly recycled pallet wrap.

[0005] The present invention is particularly useful in applications where a recycled polymer derived from a polyolefin film is used for the production of a new polyolefin film. We have found that if a certain block copolymer is included in a recycled polyolefin film it is not necessary to remove contaminants such as paper labels from the polyolefin film in order to obtain recycled films which retain the tensile properties of the original film prior to recycling. Additionally, we have found that if the block copolymer is provided in the film to be recycled satisfactory films can be obtained from recycled polymer if some paper contamination remains in the recycled polymer. We have found that if the film carrying the paper is comminuted so that the paper from the labels is reduced in size perhaps down to individual fibres and from 0.5 wt % to 2.0 wt % of the block copolymer is included in the comminuted material and the material is recycled the tensile properties of a film derived from the recycled material can be retained to an extent not attainable with film without the block copolymer as an additive of recyclable polyolefins.

[0006] Accordingly, the invention provides the use as an additive for recyclable polymers of a block copolymer of the following structure. polymer B

[0007] Formula I where R and R1may be the same or different and each independently represents an alkyl or aryl group, X may be hydrogen or a C1 to C20 alkyl group which may be branched or linear and wherein the aromatic ring substituent joined to Polymer B is positioned meta or para to the aromatic ring substituent joined to Polymer A, characterized in that: a) Polymer A is a polymer or copolymer of an olefine and b) Polymer B is a polymer of a polar monomer comprising one or more of a,p- unsaturated monomers selected from the group consisting of carboxylic acids, styrene, substituted styrene, acrylate, methacrylate, vinyl esters, fumarate esters and maleic anhydride and derivatives thereof, and diene compounds.

[0008] Wherein polymer A of the block copolymer comprises a chain of ethylenic or propylenic structural units, optionally copolymerised with higher 1 -alkene co-monomers, preferred chains are polyethylene or polypropylene or propylene / ethylene copolymer chains and polymer B of the block copolymer is derived from two or more a,p - unsaturated polar monomers selected from styrene, substituted styrene, unsaturated esters such as acrylate, methacrylate esters such as butyl acrylate, methyl(meth) acrylate, 2-ethyl hexyl methacrylate, glycidyl methacrylate, poly(ethylene glycol) methacrylate, butyl methacrylate, and hydroxyethyl acrylate and vinyl esters, fumarate esters, itaconate esters, maleic anhydride, unsaturated acids such as acrylic acid and methacrylic acid ionomers and diene compounds and derivatives thereof, polymer B may comprise a copolymer of such unsaturated monomers with an alkene such as a C2 to Cs, preferably a C2 to Ce alkene; styrene is considered to be a polar monomer as it has a dipole moment and can be polymerised with a free radical catalyst.

[0009] In one embodiment the invention provides a recycled polyolefin film containing from 0.5 to 2.0 wt % of a block copolymer as defined.

[0010] The preferred block copolymer used in this invention may be prepared by a) in a first step, polymerising alkenes such as ethylene, propylene or mixtures thereof and optionally one or more 1 -higher alkene co-monomers, to form polymer A, being a chain consisting of ethylenic, propylenic or ethylenic / propylenic structural units optionally bearing pendent alkyl groups originating from 1 -alkene comonomer(s), the polymerisation reaction being carried out in the presence of a compound of the formula wherein, in the course of the reaction, the compound (I) is terminally incorporated onto polymer A resulting in the formation of a terminally unsaturated intermediate of the formula (II): b) in an optional second step, recovering the intermediate (II) from the reaction mixture of the first step; and c) in a third step, reacting the intermediate (II) at its terminal double bond with one or more polar monomers (optionally copolymerized with a non-polar monomer) in a subsequent polymerisation reaction to form polymer B attached to intermediate (II). where R, R1 and X are as previously defined.

[0011] Optionally step a) may be performed under hydrogen pressure in order to control the characteristics of polymer A. Step a) employs a catalyst for the polymerisation of the monomer and also the reaction of the polymer with the compound of the formula (I). Any suitable olefine polymerisation catalyst may be used such as traditional Ziegler catalysts, metallocene catalysts being preferred although catalysts referred to in Angie-Chem. Int. Ed 2014 2-25 entitled Post Metallocenes in the Industrial Production of Polyolefins may be used.

[0012] In this specification, the word “terminal” when used in relation to a polymer chain (or block) simply refers to the end of the polymer chain (or block), and does not convey any additional mechanistic requirement that the chain (or block) end in question be the end at which the polymerisation reaction terminated. References to “terminally” shall be construed analogously.

[0013] Preferred block copolymer materials for use in this invention are those in which polymer A comprises a chain of ethylenic or propylenic structures or an ethylene / propylene copolymer chain optionally interrupted by one or more structural units derived from higher 1 -alkene comonomers such as hexene or octene and polymer B comprises a chain of structural units derived from two or more a,p - unsaturated polar monomers selected from unsaturated carboxylic acids, styrene, substituted styrene, unsaturated esters such as acrylate and methacrylate esters, vinyl esters, fumarate esters, itaconate esters, maleic anhydride, unsaturated acids such as acrylic acid and methacrylic acid and diene compounds and derivatives thereof, polymer B may be a copolymer of such monomers with an alkene such as a C2 to C8 alkene. In a preferred embodiment polymer B is a copolymer of at least three monomers with at least some of the monomers providing pendant polar groups on polymer B. Styrene is considered to be a polar monomer in that it can be polymerised by free radical catalysis and has a dipole moment.

[0014] Preferably, each R and R1group independently represents an alkyl group having from 1 to 4 carbon atoms. More preferably, R and R1are the same and most preferably are both methyl. Preferably, the aromatic ring substituent joined to polymer B is positioned meta to the aromatic ring substituent joined to polymer A.

[0015] Polymer A therefore is selected to be compatible with the olefine polymer or copolymer that is to be recycled. We prefer that when the block copolymer is to be used with a predominantly polypropylene based recycle polymer A is predominantly comprised of propylene although other comonomers can also be present. Similarly, when the block polymer is to be used with a predominantly polyethylene based recycle polymer A is preferably predominantly comprised of polyethylene although hereagain other comonomers can also be present.

[0016] In another preferred embodiment, polymer A in the block copolymer material used in this invention consists of a polypropylene chain.

[0017] In another preferred embodiment, polymer A in the block copolymer material used in this invention consists of an ethylene-propylene copolymer.

[0018] In another preferred embodiment, polymer A in the block copolymer material used in this invention consists of an ethylene 1 -hexene copolymer.

[0019] In another preferred embodiment, polymer A of the block copolymer material used in this invention consists of an ethylene 1 -octene copolymer.

[0020] If desired polymer A may after formation be provided with some polarity by the grafting of unsaturated monomers such as maleic anhydride onto polymer A.

[0021] When one or more higher 1 -alkene monomers are used in conjunction with ethylene or propylene to form polymer A preferably the total proportion of the higher 1 -alkene monomers is between 1 and 50 mol%, preferably between 2 and 40 mol%, the remainder of polymer A being derived from ethylene or propylene. When used the amount of the 1 -alkene monomer in polymer A preferably ranges from 2 to 15 mole %. A preferred 1 -alkene monomer is octene.

[0022] Polymer A of the block copolymer when used in this invention is preferably produced using a metallocene catalyst and suitable metallocene catalysts for the production of polymer A comprise a transition metal, particularly a metal from group IV of the periodic table such as Ti, Zr or Hf, with one or more ligands such as cyclopentadienyl (“Cp”), substituted cyclopentadienyl (including indenyl, fluorenyl and their derivatives), and bridged variants of the above. Additional ligands may be coordinated or bonded to the metal by heteroatoms such as N, O, S or P and may include bridges to Cp-type ligands as above.

[0023] Such catalysts are normally synthesised and stored as a metal dichloride / dialkyl (e.g. dibenzyl) or mono-alkyl-mono-chloride species (“pre-catalyst”). This is activated in solution by addition of a co-catalyst, generally a methylaluminoxane (MAO) or a polymethylaluminoxane (PMAO), but alternatively a non / weakly-coordinating anion may be used such as a combination of a boron containing species such as PhaC+ B(C6Fs)4- and a trialkylaluminium species such as i- (C4H9)3AI.

[0024] Examples of such catalysts include CP2MCI2, Cp*2MCh, EBIMCI2, Flu(Ph2Me)CpMCl2, and Cp(Me)4(Me2Si)NtBuMCl2, wherein M represents a transition metal. Preferred catalysts are catalysts in which M represents zirconium. An example catalyst is Cp2ZrCh together with a co-catalyst.

[0025] The polymer B of the block copolymer used in this invention is of one or more polar monomers and is preferably a copolymer of at least two polar monomers wherein at least one of the monomers ensures the dispersion or the solubility of the block copolymer in the recycled polymer. Polymer B preferably contains a monomer that aids the dispersion or solution of the block copolymer in the recycled polymer.

[0026] We prefer that at least one monomer of polymer B is an acrylate monomer as these have good reactivity with diisopropenyl benzene which is the preferred material for use in the block copolymer manufacture. In particular, we have found that using butyl acrylate together with acrylic acid is particularly useful.

[0027] The block copolymers used in this invention may contain other conventional additives such as stabilisers, antioxidants, viscosity modifiers, pigments, dyes, fillers and hardeners.

[0028] The preferred combination of polymer A and polymer B will depend upon the nature of the polymer being recycled. However, when polymer A is largely based on propylene we prefer that it has a number average molecular weight in the range of 1000 to 13000 preferably 3000 to 5000. Where polymer A is largely based on ethylene we prefer that it has a number average molecular weight in the range 1000 to 10,000 preferably 1000 to 2000. The preferred range for the number average molecular weight of polymer B is 500 to 5000. All molecular weights being measured by NMR. The block copolymer may be included in the virgin polyolefine polymer used to make the original article that is subsequently recycled. Alternatively, and preferably the block copolymer may be added to the polymer that is to be recycled for example during the recycling process.

[0029] The material to be recycled is generally collected and when it is a mixture of materials it may be separated into the materials that are to be recycled. The material to be recycled is then comminuted into flakes or pellets which can then be used in the processing of the recycled polymer, typically by extrusion or blow or injection mould where it is melted and shaped perhaps in a mould. The block copolymer may be added to the recyclable polymer as it is being comminuted and / or pelletised or it may be introduced into the extruder or moulding device together with the recyclable material. In this instance the block copolymer may be added to the polymer to be recycled during the comminution step of the process or it may be added with the comminuted material in the moulding apparatus such as an extruder or an injection moulding machine. We have found that use of the block copolymer improves the mechanical properties of recycled material particularly recycled polyolefin film containing up to 5 wt % of contaminants such as paper. Other contaminants can include polymer films that are used in laminar structures such as multilayer films of two or more of polyolefines, polyamides, ethylene vinyl alcohols as well as tie layers.

[0030] The block copolymer may be introduced into the polymer as a single polymeric additive or it may be introduced as a masterbatch in a polymer comprising a polymer miscible with the polymer to be recycled which depending on the nature of the polymers may help the dispersion of the block copolymer within the recyclable material. The masterbatch preferably contains one or more antioxidant and may also contain acid scavengers.

[0031] A preferred masterbatch comprises i. 10 to 50 wt % of the diblock copolymer ii. Up to 5 wt % of an antioxidant, preferably 0.1 to 5 wt %, more preferably 2 to 5 wt % iii. Up to 5 wt % of an acid scavenger, preferably 0.1 to 5 wt %, more preferably from 2 to 5 wt % iv. 50 to 90 wt % of a polyolefin resin.

[0032] The polyolefin resin is preferably an ethylene and / or propylene base resin such as high density polyethylene, low density polyethylene or linear low density polyethylene and various polypropylenes. The polyolefin resin should be selected to be compatible with the polymer that is to be recycled. Examples of antioxidants that may be used are Irganox 1076 and Irgafos 168, which may be used together. An acid scavenger such as a carboxylic acid, for example stearic acid may be also be included.

[0033] This invention is illustrated by the following Examples in which a single layer pallet wrap film derived from a blend of polypropylene and polyethylene containing about 4 wt % of paper from labels that had been applied to the pallet wrap film was recycled.

[0034] The original film was pelletised and then recycled into film by extrusion from a slot die at a temperature of about 280°C and a speed of rotation of the extraction screw of about 50 RPM. In comparative runs recycled film was produced containing no block copolymer and recycled films containing from 0.5% to 1 .5% by weight of a block copolymer as used in this invention in which polymer A was a polyethylene polymer and polymer B was a copolymer of methyl acrylate and maleic anhydride.

[0035] In Example 1 film was produced from recycled pallet wrap film having labels attached thereto obtained from Ergis by melt mixing the diblock copolymer with the recycled pellets in a twin screw extruder the diblock copolymer was added as a single additive. The recycled pellets had been washed to remove about 50 to 70 wt % of the paper contamination and they contained up to 3 wt % of paper. The pellets produced containing the block copolymer were then cast into film using a cast film extruder. In Example 2 the diblock copolymer was added as a 50 wt % masterbatch of the diblock copolymer in a cast film extruder without premixing in a twin screw extruder.

[0036] The tensile properties of the films were determined on dumbbell shaped pieces of the films in an Instron Tensile tester in which the samples were pulled until they broke when subject to a test speed of 200 mm per minute.

[0037] The results were as follows. MD is Machine Direction; TD is Transverse Direction

[0038] Example 1 Example 2

[0039] Example 3

[0040] The tear strength of the films of Examples 1 and 2 were also measured in an Elmendorf tear tester with the following results in Newtons

[0041] The tests were repeated with the following results

[0042] Example 4

[0043] Example 5

[0044] Example 6

[0045] The tear strength of the films of Examples 4 and 5 were also measured in an Elmendorf tear tester with the following results in Newtons

Claims

CLAIMS1 . The use as an additive for recyclable polymers of a block copolymer of the following structure.where R and R1may be the same or different and each independently represents an alkyl or aryl group, X may be hydrogen or a C1 to C20 alkyl group which may be branched or linear and wherein the aromatic ring substituent joined to Polymer B is positioned meta or para to the aromatic ring substituent joined to Polymer A, characterized in that: i) polymer A of the block copolymer comprises a chain of ethylenic or propylenic structural units, optionally copolymerised with higher 1 -alkene co-monomers, preferred chains are polyethylene or polypropylene or propylene / ethylene copolymer chains and ii) polymer B of the block copolymer is derived from two or more a,p - unsaturated polar monomers selected from styrene, substituted styrene, unsaturated esters such as acrylate, methacrylate esters such as butyl acrylate, methyl(meth) acrylate, 2-ethyl hexyl methacrylate, glycidyl methacrylate, poly(ethylene glycol) methacrylate, butyl methacrylate, and hydroxyethyl acrylate and vinyl esters, fumarate esters, itaconate esters, maleic anhydride, unsaturated acids such as acrylic acid and methacrylic acid ionomers and diene compounds and derivatives thereof, polymer B may comprise a copolymer of such unsaturated monomers with an alkene such as a C2 to Cs, preferably a C2 to Ce alkene styrene is considered to be a polar monomer as it has a dipole moment and can be polymerised with a free radical catalyst.

2. A recycled polyolefin containing from 0.1 to 5 wt % preferably from 0.5 to 2.0 wt % of a block copolymer as defined in Claim 1.

3. A recycled polyolefin film according to Claim 2 comprising a film in which the polymer A comprises a chain of ethylenic or propylenic structures or an ethylene / propylenecopolymer chain optionally interrupted by one or more structural units derived from higher 1 -alkene comonomers such as hexene or octene and polymer B comprises a chain of structural units derived from two or more a,p - unsaturated polar monomers selected from unsaturated carboxylic acids, styrene, substituted styrene, unsaturated esters such as acrylate and methacrylate esters, vinyl esters, fumarate esters, itaconate esters, maleic anhydride, unsaturated acids such as acrylic acid and methacrylic acid and diene compounds and derivatives thereof.

4. A recycled polyolefin film according to Claim 2 or Claim 3 containing up to 5 wt % of contaminants.

5. A recycled polyolefin film according to Claim 4 in which the contaminant comprises paper.

6. A recycled polyolefin film according to Claim 4 in which the contaminant comprises a multilayer film.

7. A recycled polyolefin film according to any of the preceding claims where in the polyolefin comprises an ethylene or propylene containing polymer or is a copolymer of ethylene and propylene.

8. A recycled polyolefin film according to Claim 6 in which the multilayer film comprises a polyolefin layer, a polyamide layer, vinyl alcohol copolymer layer.

9. A process for recycling a polyolefine polymer wherein a block copolymer as defined in Claim 1 is included in a virgin polyolefine polymer used to make the original article that is subsequently recycled.

10. A process for recycling a polyolefine polymer wherein a block copolymer as defined in Claim 1 is added to the polymer that is to be recycled.11 . A process according to Claim 10 in which the polymer to be recycled contains up to 5 wt % contaminants.

12. A process according to Claim 11 in which the contaminant comprises paper.

13. A process for the production of a recycled film according to any of Claims 2 to 7 wherein the material to be recycled is comminuted into flakes or pellets which are recycled typically by extrusion or blow or injection moulding and the block copolymer is added to therecyclable polymer as it is being comminuted and / or pelletised or as it is introduced into the extruder or moulding device.

14. A process according to Claim 12 wherein the block copolymer is introduced into the polymer as a single polymeric additive.

15. A process according to Claim 12 where the block copolymer is introduced into the polymer as a masterbatch in a polymer comprising a polymer miscible with the polymer to be recycled.

16. A process according to Claim 15 wherein the masterbatch contains from 15 to 50 wt % of the diblock copolymer of Claim 1.

17. A masterbatch comprising a polymer containing 15 to 50 wt % of a diblock copolymer of Claim 1.

18. A masterbatch according to Claims 11 or 17 wherein the polymer comprises a polyolefin.

19. A masterbatch according to Claims 17 or Claim 18 containing an antioxidant.

20. A masterbatch according to any of Claims 17 to 19 containing an acid scavenger.

21. A masterbatch according to any of Claims 17 to 20 comprising from 10 to 50 wt % of a diblock copolymer according to Claim 1 , up to 5 wt % of an antioxidant, up to 5 wt% of an acid scavenger and from 50 to 90 wt % of a polyolefin resin.

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