WO2013007760A1 - Polycarbonate blends - Google Patents

Abstract

A blend comprising: (I) at least one poly(alkylene carbonate); (II) at least one polyolefin; (III) at least one compatibiliser which is polymeric and comprises at least ester or amide group.

Description

Polycarbonate blends

This invention relates to blends of poly(alkylene) carbonate (referred to as PAC herein) with polyolefins which are homogeneous despite the inherent incompatibility of these materials. In particular, blends of the invention have good dispersion and adhesion, superior processability in the form of reduced viscosities compared to pure matrix material and enhanced properties in the form of increased barrier towards oxygen compared with pure matrix material.

Until recently, polycarbonates have had limited commercial application. They have been used as sacrifice polymers in the electronics industry but in few other applications. Other applications of these polymers have been limited by, inter alia, their relative thermal instability.

The present inventors have realised that PACs are environmentally friendly and need to be considered for broader application. PACs can be made by the polymerisation of the greenhouse gas carbon dioxide and an epoxide monomer. The polycarbonate therefore uses carbon dioxide in its structure and provides therefore a sink for carbon dioxide. The present inventors have realised that if PACs can be incorporated into polyolefin blends and hence provide a substitute for a portion of polyolefin, a much more environmentally friendly polymer blend can replace a polymer based on a fossil fuel. As the oil price increases and fossil carbon sources become more expensive, there may also be an economic advantage to seeking alternative blend components. There are therefore significant environmental benefits and possible economic benefits to including PACs in polyolefins blends.

However, the inventors have gone much further and surprisingly found that poly(alkylene carbonates) can be blended with polyolefins (e.g. polyethylenes or polypropylenes) to give blends with improved properties relative to the base polyolefin alone. Not only can a more environmentally friendly material be formed, but also one which has the potential to outperform the pure polyolefin.

There are, however, several obstacles to achieving a successful blend of these materials. Polyolefins are highly non-polar structures while poly(alkylene carbonates) are polar. This makes blending to achieve a good mutual dispersion of the two phases a challenge. Moreover, polyolefins are semi crystalline and PACs are typically amorphous and this further increases the compatibility challenge.

A further significant hurdle to the use of these blends concerns extrusion temperatures. Extrusion can be carried out either to blend components or in article manufacture. Conventional PACs start to degrade at temperatures above 180°C and that is lower than conventional extrusion temperatures for polyolefins, especially for polypropylene. Polyolefins are normally processed at temperatures above this level. A polyolefin/PAC blend must therefore be processable at significantly milder conditions than are typical for pure polyolefins. If that can be achieved, however, considerable economic benefits flow in terms of energy consumption.

The present inventors have realised that a valuable polymer blend can be prepared by combining a polyolefin with a PAC in the presence of a compatibiliser. Moreover, the inventors have found that the compatibiliser should preferably be one based on acrylate polymers. Moreover, the inventors have found that valuable commercial products such as injection moulded articles can be prepared even though extrusion temperatures and article formation conditions are much lower than those conventionally used in the context of polyolefins.

It will be appreciated that bis phenol A type polycarbonates have been combined with polyolefins before. CA1262590 mentions a blend of LLDPE and aromatic polycarbonates for example. Such aromatic polycarbonates are becoming less commercial interesting however, as bisphenol A is a compound which is being restricted or banned. There are problems with leakage of bisphenol A in containing this substance and the use of phosgene in the production is also related to health and safety issues. Moreover, bispenol-A has inferior barrier properties. In countries such as the US, the use of bisphenol A in materials that may be used by the young has already been outlawed.

The present inventors sought to avoid these problem chemicals therefore. The combination of PACs and polyolefins is not new. In WO2011/005644 certain structurally precise PACs are combined with polyolefins to produce a blend with high processing temperature. The structure of the PAC encourages a higher decomposition temperature and hence higher processing temperatures can be used.

In the examples of WO2011/005664, the use of a maleic anhydride modified LLDPE or PP compatibiliser is mentioned in conjunction with polyethylene/PAC or polypropylene/PAC blends.

The present inventors have found that the combination of poly(alkylene carbonates) with polyolefins in the presence of a compatibiliser gives rise to materials which exhibit beneficial properties, in particular in terms of blend homogeneity, morphology, reduced viscosity and enhanced barrier properties.

These blends can be processed at low temperatures and still give rise to

advantageous articles of commerce. Moreover, highly beneficial properties, e.g. in terms of barrier properties can be achieved, for example using acrylate polymers as compatibiliser.

Thus, viewed from one aspect the invention provides a blend comprising:

(I) at least one poly(alkylene carbonate);

(II) at least one polyolefin;

(III) at least one compatibiliser which is polymeric and comprises at least one ester or amide group such as an ethylene alkyl (meth)acrylate (i.e. poly(ethylene co- alkyl (meth)acrylate). The Mw/Mn of the PAC is preferably at least 2, preferably at least 3. The Mw/Mn of the PAC may therefore be 2 to 30, e.g. 2 to 10 or 3 to 8.

Viewed from another aspect the invention provides an article, such as a film or moulded article comprising a blend as hereinbefore defined.

Viewed from another aspect the invention provides a blend as hereinbefore defined for use in the manufacture of an article such as a film or moulded article.

Viewed from another aspect the invention provides a process for extruding a blend comprising extruding said blend through a single or twin screw extruder, e.g. at a temperature of less than 190°C wherein said blend comprises

(I) at least one poly(alkylene carbonate);

(II) at least one polyolefin;

(III) at least one compatibiliser.

Viewed from another aspect the invention provides a process for the preparation of a moulded article comprising moulding a blend as hereinbefore described, e.g. at a temperature below the decomposition temperature of the PAC, e.g. at less than 190°C.

Viewed from another aspect the invention provides a process for the preparation of a film comprising blowing or casting a blend as hereinbefore defined, e.g. at a temperature below the decomposition temperature of the PAC, such as at less than 190°C.

Detailed Description of Invention The blends of the invention contain at least one poly(alkylene carbonate)

(PAC) (i.e. an aliphatic polycarbonate). The blends may contain a mixture of PACs but preferably only one poly(alkylene carbonate) is present in the blend of the invention. The term poly(alkylene carbonate) is used to indicate that the

polycarbonates of this invention are free of aromatic groups in the main backbone of the polymer. They can however, contain cyclic, non aromatic groups in the backbone. These cyclic groups can be saturated or unsaturated. The poly(alkylene carbonates) of the invention are not therefore based on bisphenol-A type products. The PACs are otherwise broadly defined.

The backbone of the PACs of the invention contains 0-C(=0)-0 linkages along with a non aromatic linker between those linkages.

The backbone of the polymer can however carry a wide variety of substituents (side chains) including aromatic side groups.

The PAC is preferably one formed from the catalytic copolymerisation of carbon dioxide with a cyclic ether. The term cyclic ether is used here to cover not only epoxides (3-membered cyclic ethers) but also larger cyclic ethers for example such as those based on 4-6 membered rings. Preferably, the cyclic ether is an alkylene based epoxide such as ethylene oxide, propylene oxide, cyclohexene oxide or blends thereof.

It will be appreciated that the length of the monomer unit in the PAC may vary depending on the nature of the cyclic ether employed. Alternatively, PACs can be formed during the ring opening polymerisation of a cyclic carbonate with a variety of catalysts as described in e.g. Suriano Polym. Chem., 2011, 2, 528-533; Endo et al. Journal of Polymer Science Part A: Polymer Chemistry 2002, 40(13), 2190-2198.

As long as the backbone of the PAC does not contain an aromatic group within the backbone then any method can be used to form the PACs of the invention.

It is most preferred however if the PACs are obtained through the

polymerisation of a cyclic ether with carbon dioxide and especially through the catalytic copolymerisation of carbon dioxide and an epoxide.

The PAC is preferably one formed from the polymerisation of carbon dioxide and an alkylene based epoxide. Again, the term alkylene is used here to exclude monomers in which an aromatic group forms part of the backbone of the monomer but may cover non aromatic cyclic monomers, monomers containing cyclic non aromatic groups or monomers containing aromatic side chains such as styrene oxide. Preferably, the epoxide of use in the invention is of formula (I)

wherein i to R₄ are each independently hydrogen; C_1-10 alkyl optionally interrupted by one or more heteroatoms selected from O or N; C_2-io-alkenyl optionally interrupted by one or more heteroatoms selected from O and N; C6-10- aryl or R₂ and R₃ taken together can form a non aromatic, cyclic group having 4 to 8 atoms in the ring, said ring optionally comprising one or more heteroatoms selected from O or N;

said non aromatic cyclic group or any of Ri to R₄ being optionally substituted by one or more C_1-6 alkyl groups, C_2-io-alkenyl groups, C6-10-aryl groups, -OCi-6 alkyl groups, halo or Ci-6-OH.

It is preferred if at least one, preferably at least two of Ri to R₄ are hydrogen. Ideally, the carbon atoms attached to the epoxide ring should also be bonded directly to a hydrogen atom. In a highly preferred embodiment, three of Ri to R₄ are hydrogen and the remaining one is methyl (thus forming propylene oxide) or all four of i to R4 are hydrogen (thus forming ethylene oxide).

When not hydrogen, it is preferred if substituents Ri to R4 are Ci_6-alkyl or C2-6-alkenyl groups. If an alkenyl group is present, the double bond should not conjugate the epoxide. Any alkenyl group should preferably contain at least 3 carbon atoms and the double bond should preferably be at least beta to the epoxide carbon. It is also preferred if the alkenyl group contains also a heteroatom like O, N, e. g. like in allyl glycidyl ether.

If R₂ and R3 are taken together, they preferably form a 5 or 6 membered ring with the carbon atoms to which they are attached, especially a carbocyclic ring. That ring can be saturated or monounsaturated, preferably saturated.

In formula (I), it is preferred if no heteroatoms other than the O of the epoxide are present.

A preferred monomer is therefore of formula (II)

where R₂- and R₃- are each independently hydrogen, phenyl, Cl-6-alkyl optionally substituted by chloro, C2-6 alkenyl or R₂- and R₃- taken together form a 5 or 6 saturated or monounsaturated carbocyclic ring.

Preferred epoxide monomers include limonene oxide, propylene oxide, styrene oxide, epichlorohydrin, ethylene oxide or cyclohexene oxide (i.e. the compound

In an ideal scenario, the PAC of the invention is one such as

where n is 0 to 4 and R is a side chain such as defined above for Ri to R4. In particular one of formula

It will be appreciated, however, that when the epoxide and the carbon dioxide are polymerised, the structure of the polymer which forms may not be a perfect ABABA type polymer as depicted here. The invention encompasses the polymer which forms when these two monomers are polymerised. The polymer may thus contain both ether linkages and carbonate linkages in the polymer chain, i.e. the polymer will include regular, alternating ABABA type chains or chain segments but may also include AAA blocks of monomer residues i.e. consecutive ether linkages. The percentage of carbonate linkages is, typically, dependent on the reaction conditions and the nature of the catalyst. It will be appreciated that, when an unsymmetrically substituted epoxide like e.g. propylene oxide is used, the regioregularity of the resulting poly(propylene carbonate) will be described by the

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conventional "head to tail" ratio. This can be determined by C NMR spectroscopy as described for instance in Lednor et al. J Chem. Soc. Chem. Comm. 1985, 598- 599.

Further, the polymer chains may also include blocks of e.g. epoxide monomer residues as is well known.

It is very common for ether linkages to be present in PACs. It is preferred if the content of polymer chains containing ether linkages is less than 15 wt%, preferably less than 10 wt%. The ether content can be determined by 13C or 1H

NMR e. g. as described in Luinstra, G. Polymer Reviews, 48: 192-219, 2008. The values observed for QPAC40 (used in the examples) lie between 4,8 to 7,5 wt%

(measured from NMR).

The poly(alkylene carbonate) may be produced by the polymerisation of two or more epoxides with C0_2. This may give rise to random or block terpolymers.

Block polymer structures of interest in the invention include those containing PPC,

PEC, PCHC, polyethylene oxide (PEO), polypropylene oxide (PPO) and so on.

Preferred options include PPC and PEC blocks; PPC and PCHC blocks; PPC and PPO blocks; and PEC-block-PEO etc.,

The poly(alkylene carbonate) may be produced by the polymerisation of two or more epoxides with C0₂ to give random polymer structure.

It is also within the scope of the invention for other monomers to be used in the manufacture of the PAC. For example, the use of lactone monomers is envisaged. Lactone monomers of interest include β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone. The use of lactones may typically result in the formation of block polymers.

Preferably however, the PAC is formed from the polymerisation of carbon dioxide and epoxide(s) of formula (I) only. In particular, the PAC is polypropylene carbonate (PPC), polyethylene carbonate (PEC) or polycyclohexene carbonate

(PCHC), most especially polypropylene carbonate.

Typically, the PAC of the invention contains more than 80wt % of the described polycarbonate units, even more preferred more than 90 wt% of such units.

As discussed below, a PAC may contain different end groups such as acetate, benzyl and so on which may contribute to the weight of the PAC as a whole.

Several catalyst systems are known that catalyze the copolymerisation reaction of epoxides and C0₂. The polymerisation can be catalysed by known catalysts, especially Zn based catalysts or Co based catalysts. The use of Zn catalysts are preferred. The use of heterogeneous Zn catalysts is preferred, such as catalyst based on zinc glutarate, e. g. as described in US4789727 and in Ree et al. J

Pol. Sci. Part A.: Polymer Chemistry Vol. 37, 1873-1876 (1999) or other Zn based catalysts e. g. as described in WO2009/130470. Cobalt based catalysts are typically cobalt salen catalysts as described in WO2010/028362 and in Cyriac et al.

Macromol. 2010, 7398-7801. Catalysts may need a cocatalyst as is well known in the art.

The PACs of the invention may be amorphous or crystalline. Typically they are amorphous. Preferably they will have a glass transition temperature (Tg) of at least 18°C, such as at least 20°C, preferably at least 22°C, such as at least 25°C.

The weight average molecular weight Mw of the PAC may be at least 25,000 g/mol, preferably at least 50,000 g/mol. The use of higher Mw PACs is preferred in this invention. It is envisaged that by using a higher Mw, this enhances

compatibility with the polyolefins which also typically are of high molecular weight for the embodiments described herein. Mw values of higher than 100,000 g/mol preferably at least 150,000 g/mol are also favoured. Mw and number average molecular weight, Mn can be measured by gel permeation chromatography.

The Mw/Mn of the PAC is preferably at least 2, preferably at least 3. The Mw/Mn of the PAC may therefore be 2 to 30, e.g. 2 to 10 or 3 to 8. Broader

Mw/Mn may conform better to the molecular weight distribution of the polyolefin with which the PAC is blended, hence improving compatibility and processability.

Alternatively viewed, the polydispersity index of the PAC is preferably at least 2, preferably at least 3. The PDI of the PAC may therefore be 2 to 30, e.g. 2 to 10 or 3 to 8.

The rheological properties of the PAC may also be important. Eta (0.05) values of at least 25,000 are preferred according to dynamic rheology

measurements..

The PACs of the invention are optionally end capped. Typically, at least one end group of a PAC is a reactive end group like an OH group. This allows a formed

PAC to be reacted with an end capping group. Such an end capping procedure can be carried out after the PAC is formed by reaction with a suitable end capping agent.

Suitable end capping agents include anhydrides, acid halides, isocyanates and other agents well known in the art.

It will be appreciated that the formation of the PAC may also give rise to a well known cyclic carbonate by product. For example, during the formation of polypropylene carbonate, propylene carbonate is formed as a by-product. That is the compound

It is common to try to remove this by-product from the poly(propylene carbonate) itself but the present inventors have realised that its action as a plasticiser can offer some beneficial properties in the blends of the invention, in particular in terms of processability. It may therefore be necessary to reduce the content of this by product but not necessarily remove it completely. Preferably, the amount of cyclic carbonate compound with Mw typically below 1000 g/mol in the PAC of the invention (i.e. relative to the weight of the PAC) is less than 10 wt%, preferably less than 7 wt%, e.g. 6 wt% or less. It is preferred however if there is at least 1 wt% of the cyclic carbonate compound in the PAC, e.g. at least 2 wt%. The cyclic carbonate compound is preferably propylene carbonate but obviously the nature of this side product depends on the nature of the epoxide monomers being used for the formation of the PAC. The amount of cyclic carbonate side product may be determined by 1H NMR.

Preferably the PAC's of the invention will have a glass transition

temperature (Tg) of at least 0°C, such as at least 20°C. It will be appreciated that the Tg will depend heavily on the nature of the PAC in question. The decomposition temperature of the PAC of the invention is preferably at least 170°C. It may however be lower than 270°C.

PACs of use in the invention can be purchased commercially, e.g. under the trade name QPAC (Empower Materials).

The density of the PAC may be at least 1.1 kg/m .

Compatibiliser The blend of the invention contains at least one compatibiliser. This component enables the formation of a homogeneous blend between the polar PAC and the non polar polyolefin. The nature of the compatibiliser can therefore vary widely as long as the material is capable of providing the desired homogeneous blend with desirable end properties.

Compatibilisers of interest are primarily based on ester, anhydride and amide compounds. Such compatibilisers are well known in the art and are commercially available from e.g. DuPont and others. Generally, compounds containing ester and/or amide groups which can function as compatibilisers are polymeric.

Preferably polyamides will comprise the amide linkage within the backbone of the polymer or grafted on the backbone thus constituting a side chain. Preferably, polyamides will contain the amide group in the backbone of a polymer. Polyester compatibilisers can comprise the ester group within the backbone or as a side chain.

The use of acrylate polymers is especially preferred. Maleic anhydride modified polypropylene, ethylene vinyl alcohol (EVOH), and POM

(polyoxymethylene copolymer) may also be used. The use of maleic anhydride modified polyolefins is not favoured due to the use of peroxides in the grafting process for the maleic anhydride onto the compatibiliser polymer backbone. In general the use of acrylates is preferred over the use of ester compounds in general which are preferred over the use of amides which are preferred over the use of anhydride modified polyolefins.

Suitable acrylates include those formed using alkyl (meth)acrylate monomers in which the alkyl group has 1 to 6 carbon atoms. Such a monomer is preferably used with non acrylate comonomers. Non acrylates comonomers are preferably alpha olefins or styrene.

However, the present inventors have found that the best results are obtained when the compatibiliser is at least one ethylene alkyl (meth)acrylate resin. The term (meth)acrylate is intended to cover both methacrylates and acrylates, i.e. compounds of formula CH₃-CH₂=CHCOO- or CH₂=CHCOO-. The (meth) designates therefore the optional presence of the methyl group forming the methacrylate. It is preferred, however, if the EAA of the invention is an acrylate. The term "alkyl" is used to designate a C_1-6 alkyl, preferably a C_1-4 alkyl. Preferably the EAA may be a poly ethylene methyl (meth)acrylate, ethylene ethyl (meth)acrylate or ethylene butyl (meth)acrylate resin, especially ethylene methyl acrylate, ethylene ethyl acrylate or ethylene butyl acrylate resin (EMA, EEA and EBA respectively). Whilst mixtures of these resins can be used, it is preferred if only one EAA is used. Most preferably this is EMA.

The amount of (meth)acrylate (relative to the amount of ethylene) in the EAA resin can vary over wide limits. It is preferred if there is an excess of ethylene present. Typical values range from 15 to 40 wt% of the acrylate, such as 15 to 35 wt% of the acrylate in the EAA polymer.

The density of the ethylene alkyl (meth)acrylate resin may be in the range of 935 to 960 kg/m³. Its MFR₂/190°C may range from 0.1 to 20 g/10 min.

These EAA polymers are commercially available materials and can be purchased from various suppliers, e.g. under the trade name Elvaloy™.

It will be appreciated that a mix of compatibilisers can be used.

It is particularly preferred if the MFR₂ of the compatibiliser is related to the MFR₂ of the blend as a whole. In particular, the ratio of the MFR₂ of the compatibiliser to the blend as a whole should be in the range 1 to 10, preferably 1 to 5, especially 1 to 3.

Viewed from another aspect the invention provides a blend comprising:

(I) at least one poly(alkylene carbonate);

(II) at least one polyolefin;

(III) at least one compatibiliser;

wherein the ratio of the MFR₂ of the compatibiliser to the blend as a whole is in the range 1 to 10, preferably 1 to 5, especially 1 to 3.

Polyolefin

The blend of the invention contains at least one polyolefin. The polyolefin is preferably a hydrocarbon based polyolefin. Preferably that polyolefin is a polyethylene or polypropylene, in particular a polyethylene or polypropylene which is a hydrocarbon. These can be homopolymers or copolymers with one or more comonomers. Such comonomers are preferably other C2-10 alpha olefins or are dienes. Preferred comonomers are ethylene, propylene, 1-butene, 1-hexene and 1- octene.

Preferably, the polyolefin is a low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE) or is a polypropylene. These are well known terms of this art. Suitable polypropylene polymers are homopolymers, random copolymers, block copolymers or heterophasic copolymers of propylene. All these polyolefins are commercially available from suppliers such as Exxon, Dow, Borealis, Basell and so on.

The polyolefin combined with which the PAC can be unimodal or multimodal, e.g. bimodal. Multimodal polymers have broad molecular weight distributions and possess two peaks in the GPC curve or at least broad overlapping peaks. Again, this is a well known term in this art. The Mw/Mn of the polyolefin may be 2 to 30. Unimodal polymers may have Mw/Mn ranges of 2 to 10.

Multimodal polyolefins may have Mw/Mn values of 5 to 30.

The density of any polyethylene with which the PAC is combined is preferably in the range 905 to 975 kg/m³, e.g. 905 to 935 kg/m³ or 940 to 975 kg/m³, i.e. an LDPE/LLDPE or HDPE respectively.

The MFR₂ values of the polyethylene are preferably in the range 0.1 to 20 g/lOmin. The use of commercially available moulding grades is preferred in the invention.

The MFP₂ of polypropylenes is preferably in the range 5 to 40 g/lOmin. Their densities are typically 900 to 915 kg/m

The polyolefin with which the PAC can be combined is preferably a polyethylene homopolymer or copolymer with butene or hexene. Alternatively, the polyolefin is a polypropylene homopolymer or polypropylene copolymer in particular a random heterophasic polypropylene. Alternatively, viewed the polyolefin is an LDPE, LLDPE or HDPE.

It will be appreciated that a mix of polyolefins can be used. Amounts of Components

As the PAC of the invention is an environmentally friendly material it is generally preferred to use as much of it as possible while retaining the properties of the blend. It is envisaged therefore that the amount of PAC may be up to 60 wt%, e.g. up to 50 wt% of the blend. Suitable ranges are 2 to 45 wt%, such as 5 to 40 wt%, preferably 6 to 35 wt%, such as 10 to 30 wt% of the blend. In some embodiments there should be a minimum of 5 wt% of PAC, such as at least 10 wt%, preferably at least 15 wt%, such as at least 20 wt% of the PAC in the blend.

The amount of compatibiliser is kept as low as possible to provide its desired effect. Amounts are preferably less than 20 wt%, e.g. 2 to 15 wt%, such as 3 to 12 wt%, more preferably 4 to 10 wt%. Typically there will be at least 1 wt% of the compatibiliser. In some embodiments there will be 15 wt% of less of it.

The remainder of the blend is preferably the polyolefin component although it will be appreciated that blends may contain small amounts of standard additives.

The amount of polyolefin may therefore range from 40 to 95 wt% of the blend, such as 50 to 90 wt% of the blend. The use of at least 50 wt% of the polyolefin is preferred. Blending/Compounding

The components of the blend must be intimately mixed, i.e. blended. This can be achieved using any conventional mixing apparatus as is well known in the art. The blending process is preferably carried out in a known mixing apparatus such as a fluidised bed mixer, e.g. Forberg mixer. Depending on the amount of PAC present however, the blending technique can be altered.

It may be preferred to grind the PAC to a particular particle size before blending. It is also preferred if the PAC is free from surface water before blending.

In particular, where a blend contains less than 10 wt% of the PAC, it is preferred if the PAC is ground to a particle size of 0.5 to 2 mm or so before blending, e.g. about 1 mm. Where more than 10 wt% of the PAC is employed, it is preferred if a grinding step is avoided. It is preferred if the PAC employed before blending with the other components is dry, e.g. with a water content of less than 5000 ppm, preferably less than 2500 ppm. Drying can be achieved by any technique bearing in mind, of course, the degradation temperature of the PAC.

The PAC can then be blended with the polyolefin and compatibiliser. To ensure good mixing, it is preferred to employ a wetting agent at this stage. A small amount therefore (e.g. a few mis) of a liquid hydrocarbon, e.g. ClO-14 hydrocarbon can be employed here. Preferred diluents are oils or medium chain hydrocarbons such as isododecane.

The blend of the invention can incorporate standard polymer additives as is well known. Those are conveniently added before blending or before compounding. Those additives include antioxidants, fillers, UV stabilisers, pigments, dyes, antistatic agents, slip additives, processing aids, organic and inorganic nanoparticles, antiblocking additives and so on. There will typically be less than 1 wt% of the total blend of these.

After blending, the mixture can be compounded using an extruder, e.g. a single or twin screw extruder as is well known in the art. It will be appreciated that the temperature for the extrusion process must be kept below the degradation temperature of the PAC in question. Thus, the extrusion temperature might be two or more degrees below the decomposition temperature (TGA) of the PAC, e.g. 3 or more degrees lower, such as 5 or more degrees lower. For example, this may be less than 190°C, such as less than 180°C. Preferred temperatures are 150 to 160°C. It is a particular feature of the invention that extrusion can be successfully carried out at temperatures less than 190°C, such as 180°C or less or even 170°C or less.

Minimum temperatures may be 140°C. After extrusion, the product can be pelletised using known techniques.

It is worth noting that the blend of the invention is more easily compounded therefore than the polyolefin alone. The blends of the invention therefore require less energy to be converted into pellets than pure polyolefin blends. On an industrial scale a lowering of extrusion temperature can mean enormous economic savings. It was generally assumed in the art that extrusion at these lower temperatures would need lead to a useful compounded product. The present invention clearly shows otherwise.

It is also noted that other than the temperature, extrusion can be carried out under conditions standard for the extrusion of polyolefins. There is little adaption of commercial processes required therefore to introduce PAC to the manufacturing process.

Blend Properties The blend of the invention involves the intimate mixing of the components.

The components are blended together and the blend of the invention is thus very different from a two layer film for example, in which one layer contains a PAC and another polyolefin perhaps with an adhesive layer. That is not an intimate mixture and hence not a blend as required in the present invention. Once formed, it is essentially impossible to separate a blend back out into its constituent parts.

The blends of the invention are preferably homogeneous. The term homogeneous implies a good and even dispersion, on a macroscopic level, between the components of the blend. The components also adhere to each other to provide homogeneity. In the absence of the compatibiliser, we observe that adhesion between the components of the blend is absent.

It is believed that the blend of the invention provides a polymer composition with good morphology. This is especially true after compounding. Despite lower than normal compounding temperatures, homogeneous blends are still achieved. In the examples, we have shown through microscopy that the blends of the invention have excellent morphology especially with acrylate based compatibilisers.

It is particularly surprising that good homogeneity can be achieved even at low temperature compounding temperatures. As noted above, it is preferred if the compounding step (extrusion step) takes place at a temperature of less than 180°C to avoid degradation of the PAC. Even at this low temperature (for extrusion of polyethylene and polypropylene) excellent particle morphology is obtained.

It has also been found that the blend of the invention provides reduced viscosity for easier processability. The viscosity of the pure polypropylene in the examples, given as complex viscosity at 0,05 rad/s is 423,000 Pas. The viscosity of the corresponding blends should be lower that the viscosity of the polyolefin alone or indeed the blend of the polyolefin and the compatibiliser. It is also an advantage for the blends with respect to processability that the PAC has a relative broad Mw/Mn.

Polyolefin resins commonly used for standard moulding applications often have relatively high viscosities and use relatively high processing temperatures; about 200°C for polyethylene and above 200°C for polypropylene. Processing at lower temperatures is desirable from an energy saving point of view, but typically cannot be done due to the consequently poorer flowability of the polymer. Our blends offer a solution to this problem.

The most remarkable property of the blend of the invention relates to enhanced barrier properties, in particular lower oxygen transmission rate. Relative to articles that have been made with the polyolefin alone, the barrier properties of articles made with the blend of the invention can be an order of magnitude better.

It is also important to note that despite the presence of the PAC, the overall mechanical properties of the blend are not significantly affected so as to prevent commercial application. Thus, the impact strength of the blends of the invention are preferably within 30%, such as within 20%, or within 10% of the values of the polyolefin alone, for example. It is preferred if the impact strength of the blends of the invention is higher than the polyolefin alone. As shown in the examples, the tensile properties of the blends of the invention remain high.

The tensile strain at break properties of the blend are typically a lot better than the polyolefin alone, e.g. at least 20% greater. This forms a further aspect of the invention. Measured under the same conditions, it is preferred if the blend of the invention has a tensile strain at break value which is at least 10%, such as at least 20% higher than that of the equivalent polypropylene on its own. In some embodiments, the tensile strain at break may be 50% higher than that of the base polyolefin alone, may be up to twice the value of the base polymer alone.

The actual tensile strain at break values may be at least 100%, such as at least 150%), even 200%> or more. It must be remembered that mechanical properties are influenced by the amount of cyclo carbonate compound present (it acts as a plasticiser) .

In general therefore, PAC can be used to replace polyolefin content without a negative influence on mechanical properties. This means of course, that an environmentally friendly PAC can be employed instead of a fossil carbon source polyolefin.

In film technology, we have shown that the blends of the invention have improved surface tension - this can lead to improved printability in a film.

The blends of the invention also possess better welding properties. The presence of the PAC and the compatibiliser gives rise to a blend which is more easily welded to other substrates.

Applications The blends of the invention have a wide variety of applications but are of particular interest in moulding applications, e.g. in blow moulding, injection moulding or rotomoulding applications. Their use in films, especially blown films is also envisaged. As the articles made from the polymers of the invention possess good barrier properties, they may be of particular use with products that degrade in oxygen such as food and medical applications. The use of the blends of the invention in food and medical packaging is therefore envisaged.

As noted above, PAC have a low decomposition temperature which means that moulding/film blowing conditions have to reflect that. Moulding at high temperatures will simply destroy the PAC. It is therefore preferred if the forming of the blends into articles, e.g. moulding, casting or blowing of the blends also takes place at a comparatively low temperature, e.g. at a temperature two or more degrees below the decomposition temperature (TGA) of the PAC, e.g. 3 or more degrees lower, such as 5 or more degrees lower than TGA. For example, forming may take place at a temperature of 180°C or less, such as 179°C or less, preferably 170°C or less. Again, this is an unusually low temperature for moulding of a polyolefin and yet the results of the invention show that valuable products still form. Lower temperature moulding conditions again leads to a less energy intensive process and significant economic savings. This forms an important aspect of the invention.

Any film manufacturing process also needs to take place at low temperature.

The blends may be incorporated into multilayered systems, in particular where a barrier against oxygen is desired. Multilayered systems may include adhesive layers based on for example, EVOH or maleic anhydride grafted polyolefins. Such systems are well known in the art and can be made by coextrusion or lamination and so on. Such systems can be heat sealable and thermally formable. The blends can be used in the formation of films, sheets, moulded articles such as injection moulded articles. The blends can form one layer in a multilayer film or more than one layer of a multilayer film.

The blends can be extruded. The blends are of particular interest in food and non food packaging.

The invention will now be described with reference to the following non limiting examples and figures.

Figure 1 shows micrographs of the blends based on different compatibilisers. Figures 2 and 3 show micrographs of blends containing high amounts of

compatibilisers. Analytical Tests:

WVTR: Water vapour transmission rate was measured at 90 % relative humidity and 38 °C temperature according to the method ASTM E96. Charpy impact strength: charpy impact strength was determined according to ISO 179:2000 on V-notched samples at 23°C. The samples were produced by compression moulding (ISO 293-1986, 1872-2-1997, 1873-2-1997, 150°C, pressure intervals of 25-90-165-165-165 bar). Tensile properties: measured on compression moulded specimens (ISO 293-1986, 1872-2-1997, 1873-2-1997, 150°C, pressure intervals of 25-90-165-165-165 bar) according to IS0527-1/2. GPC (Molecular weight and molecular weight distribution., Mw and MWD): were measured by Gel Permeation Chromatography (GPC) according to the following method: the weight average molecular weight Mw and the molecular weight distribution (MWD = Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured by a method based on ISO 16014-1, Iso 16014-2 and ISO 16014-3. A Waters 150CV plus instrument, equipped with refractive index detector was used with columns 1 *PL Guard and 3*PL gel MIXED-B and tetrahydrofurane with BHT stabilization as solvent at 40°C and at a constant flow rate of 1 mL/min. 500μ1 of sample solution was injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with 15 narrow MWD polystyrene (PS) standards in the range of 1,0 kg/mol to 12 000 kg/mol. Mark Houwink constants: K=0,00014 and alpha=0,7. All samples were dissolved in THF at 40°C in 2-4h prior to sampling into the GPC instrument.

Rheology: Dynamic rheological measurements were carried out with a rheometer, namely Rheometrics RDA-II, on compression moulded samples under nitrogen atmosphere at 150°C using 25 mm diameter plates and plate and plate geometry with a 1,2mm gap. The oscillatory shear experiments were done within the linear viscosity range of strain at frequencies from 0,126 to 199 rad/s (ISO 6721-1). Five measurement points per decade were made. The complex viscosities at 0,05 rad/s, eta(0,05), are then extrapolated {also given above). MFR: The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the melt viscosity of the polymer. The MFR is determined at 230°C for PP and 190°C for polyethylene and the compatibiliser. The load under which the melt flow rate is determined is usually indicated as a subscript, for instance MFR₂ is measured under 2.16 kg load, MFR₅ is measured under 5 kg load or MFR₂i is measured under 21.6 kg load. PC content: Measured by FT-IR-ATR model calibrated from proton-NMR quantification of PC in PPC.

DSC (Tg): DSC was measured on a Netzsch 204-F1 instrument according to ISO 11357-2 for determination of glass transition temperature: 1. heating; -10 to

140°C, cooling; 140 to -10°CC, 2. heating; -10 to 140°C. Heating/cooling rate was 20°C/min. The evaluation of the glass transition temperature is performed at the second heating segment. The sample specimens are pellets. TGA: TGA was measured on a PerkinElmer TGA analyzer according to ISO 11358. the analyses were run up to 550°C in nitrogen with a heating rate of 20°C/min.

Barrier properties: AOIR has been measured according to procedure given in Larsen, H., Kohler, A., Magnus, E.M. 2000. Ambient oxygen ingress rate method - an alternative method to Ox-Tran for measuring oxygen transmission rate of whole packages. Packaging Technology and Science, Vol 13, pp 233-241.

Surface tension: Dyne level measurements have been done by surface tension testing ink.

Dart Drop: Film impact resistance is measured according to Dart Drop (g/50%). Dar Drop is measured using ISO 7765-1, method "A". A dart with a 38 mm diameter hemispherical head is dropped from a height of 0,66 m onto a film clamped over a hole. If the specimen fails, the weight of the dart is reduced and if it does not fail the weight is increased. At least 20 specimens are tested. The weight resulting in failure of 50% of the specimens is calculated.

Tear resistance (determined as Elmendorf tear) [Nl): The tear strength of blown films is measured using the IS06383/2 method. The force required to propagate tearing across a film specimen is measured using a pendulum device. The pendulum swings under gravity through an arc, tearing the specimen from pre-cut slit. The specimen is fixed on one side by the pendulum and on the other side by a stationary clamp. The tear strength is the force required to tear the specimen.

Materials

Polypropylene carbonate (PPC) is used in the examples of the invention and is purchased under the trade name QPAC40: The main characteristics of the PPC are given in table 1.

Table 1: Main characteristics of the PPC

Unless otherwise given, the PPC used in the experiments described in this report is PPC(I). PPC purified in aqueous maleic acid:

150g of crude PPC(I) was cryomilled and transferred to a 41 reactor which contained 3000ml of an aqueous solution of maleic anhydride 1 wt/vol%. The reactor was locked, the mechanical stirring was adjusted to 400 r.p.m and the temperature was set to 60°C during 30 minutes and afterwards increased to 90°C during 3 hours. The aqueous solution was removed and replaced with fresh water; this operation was repeated two times in order to remove acid residues.

Agglomerates of -1.5 mm were obtained. These particles were dried during 48h at 35°C under N2 flushing. Polyolefin

The following polyethylenes/polypropylenes are used in the examples which follow: PE1 : Bimodal HDPE film grade, density 946 kg/m³ and MFR₅ = 0,2 g/lOmin. PE2: Bimodal HDPE blow moulding grade, density 958 kg/m and MFR₅ = 1,3 g/lOmin.

PE3: Bimodal LLDPE blown film grade, density 923 kg/m³ and MFR₅ = 2,0 g/lOmin.

PP1 : Random copolymer; MFR₂=13 g/lOmin, d=905 kg/m³ and T_m= 148°C. Compatibilizer

The following compatibilisers are used in the examples which follow:

Elvaloy AC 1330 (DuPont) is a copolymer of ethylene and methyl acrylate. The content of methyl acrylate is 30% by weight. The density is 0,95 g/cm and the melt flow rate (190°C/2,16kg) is 3 g/lOmin.

Orevac 18750 (Arklema) is a maleic anhydride modified PP resins with a melt index (230°C/2,16kg) of 35 g/lOmin. Hostaform C 27021 (Ticona) is a POM (polyoxymethylene copolymer) with density

1410 kg/m 3 and a given melt volume rate of 24 cm 3 /lOmin. General blend preparation and extrusion protocols The PAC was ground down to a particle size of 1 mm on a cryo mill for use in compositions where there is 10 wt% or less of the PAC. Where more than 10 wt% of PAC is present, no grinding step took place. The material was then dried in an oven under dry nitrogen flow at 35°C for minimum 24h to a level of 200-2000 ppm water content. This was quantified by Karl Fisher titration.

The PAC was then wet with a small amount of isododecane and mixed together with the polyolefin and the compatibiliser in a fluidized bed Forberg mixer. Standard additivation with antioxidant (1500ppm B215) and lubricant (500ppm Ca Stearate) was also done. It will be appreciated that any amount of additive present is counted in the examples as part of the polyolefin component. Thus where 85% polyolefin is present, that might represent 84.8 wt% of olefin and 0.2 wt% of the additive blend.

The resulting mixtures were then compounded on a twin screw extruder at set temperature 160°C. A Prisml6 extruder, with L/D25 and screw speed 500rpm, was used.

Injection Moulding protocol

Parameters and settings in IMfor 10 wt% PPC blends on Engel 600kN.

Temperature set IMfor 30% PPC blends on Netstal HP 1200-445. Set value f°CJ

Melt temperature 160

Nozzle 160

Metering section 160

Compression 160

Feed section 155

Example 1 - compatibiliser Different levels of compatibilizer Elvaloy AC 1330 were used in blends of 30wt% PPC(I) and balance PE2. The levels of compatibilizer selected were: lwt%, 2wt%, 5wt%, 10wt%, 20wt% and 30wt% of the total blend. From SEM evaluations it was concluded that 5wt% Elvaloy AC 1330 is a sufficient amount to achieve sufficient compatibilization for the blend of interest.

Example 2 - alternative compatibilisers

Blends of 85 wt% PPl, 10 wt% PPC(I) and 5 wt% compatibiliser were formed. The tested compatibilisers where Orevac 18750, Hostaform C 27021 and Elvaloy AC 1330.

The SEM pictures in figure 1 of PP/PPC blends compatibilized with both Orevac 18750 and Hostaform C 27021 show crater structures where the particles apparently have "fallen" out of the matrix. This is not observed for the PP/PPC blend compatibilized with Elvaloy AC 1330.

Example 3 - 10wt% Poly(propylene carbonate) blends

10wt% blends of PPC(I) or 10wt% of PPC(I) washed in aqueous maleic acid compatibilized with 5wt% Elvaloy AC 1330 and balance PPl were made following the protocols above. The injection moulding was carried out on an Engel 600kN (conditions above). Injection moulding machine and 1,2,3-plates and tensile bars were produced. The mechanical results on the injection moulded tensile bars are given in table 1.

Table 1: Mechanical results on injection moulded tensile bars.

Example 4

30wt% Poly(propylene carbonate) blends

A 30wt% blend of PPC(I), 5 wt% Elvaloy AC 1330 and balance PPl was made and injection moulded into square boxes {specification thickness bottom-side; 1,3-

1,2mm). The injection moulding was made on a Netstal HP 1200-445 with settings as above. Oxygen barrier properties of the square boxes have been measured and the results are given in table 2.

Table 2: Barrier properties of PPl + 30wt%PPC and reference.

The average thickness of 20 boxes of the blend was 1,28mm with a variation from 1,327 (max.) to 1,208 (min), the thickest part in the bottom and the thinnest part on top. The average thickness of 20 boxes of PPl reference was 1,27mm with a variation from 1,395 (max.) to 1,175 (min). The thickness variation is slightly higher for the reference and the reference is also the specimen with the highest max thickness measured.

The oxygen barrier measurement showed a 9 fold increase in barrier property for the PP/PPC blend compared with the PP reference. Example 5 - Importance of compatibiliser

PPl + 40wt% PPC(II) + 5wt% compatibilizer (Elvaloy): The blend was

compounded on a Prisml6 twin screw extruder in the presence of isododecane as above but extruder at the lower temperature of 140°C.

PPl + 40wt% PPC(II) were added directly to the compounder and compounded on a Prisml6 twin screw extruder at 140°C, lkg/h and 500rpm.

2mm plates for microscopic investigations were made. Scanning electron

microscopy was measured on a Philips-XL-30 ESEM microscope with secondary electrons (SE) and back scattered electrons (BSE) detectors. Samples were prepared with high resolution sputter coater on a Polaron SC7640. From these pictures

(Figure 2) it is clearly concluded that the dispersion and adhesion of PPC in PP is improved by a compatibilizer and proper pre-mixing. Example 6 - Blown film

A blend of 5 wt% Elvaloy AC 1330, 10 wt% PPC(I) and balance PEl was made. A blend of 10 wt% Elvaloy AC 1330, 20 wt% PPC (I) and balance PEl was made. These blends were blown and compared to films made of PEl alone.

The blowing specifications were BUR 3: 1, screw speed 70rpm compared with 90rpm for reference and amperage varying from 2,3-3,9A. Amperage consumption being higher for the reference. Major observations were significant reduction in amperage use (41% for the 10% PPC(I) blend and 26% for the 20% PPC(I) blend.)

Measured film properties are given in table 3.

Table 3: Measured film properties ofPEl/PPC/Elv blends.

Note that the blends of the invention have improved surface tension - this can lead to improved printability.

Example 7 - Higher PPC content

A number of blend recipes were made and compounded on a Thermo Fisher Mini- Lab Compounder with conical twin-screw extruder. Set temperature was 150°C. Table 4 Polyethylene blends

Despite significant amounts of the PAC, these blends still presented as homogeneous materials after compounding. In Figure 3 the results for both 50wt% PPC(I) into PP1 and 30wt% PPC(I)into PE2 are shown.

Example 8

Poly(cyclohexene carbonate), PCHC, purchased from Empower Materials nder the trade name of QPACIOO was ground with liquid nitrogen and dried at 35°C for 24 h. 10wt% of the PCHC was then blended with 90wt% of a high density polyethylene, HDPE, purchased from Borealis under the trade name of FB1460. 5wt% Elvaloy AC 1330 was added as a compatibilizing agent and Irganox B 215 and calcium stearate was added as stabilizing agents.

The blend was compounded on a Prism24 twin screw extruder with L/D 30. The output rate was 5 kg/h and the screw speed was 250 rpm. Nitrogen flushing was applied, but no vacuum.The set temperature was 130°C and the logged process temperatures were 136-144-152-159°C.

The blends were extruded into film on a Collin small scale lab film line. The film blowing specifications are given in the table, together with film blowing specifications for pure FBI 460.

Claims

Claims

1. A blend comprising:

(I) at least one poly(alkylene carbonate);

(II) at least one polyolefin;

(III) at least one compatibiliser which is polymeric and comprises at least ester or amide group.

2. A blend as claimed in any preceding claim wherein said compatibilizer is an poly(ethylene co-alkyl acrylate).

3. A blend as claimed in any preceding claim wherein said compatibilizer is poly(ethylene co-methyl acrylate).

4. A blend as claimed in any preceding claim wherein said polyolefin is a polyethylene or a polypropylene.

5. A blend as claimed in any preceding claim wherein the Mw/Mn of the poly(alkylene carbonate) is 2 to 30.

6. A blend as claimed in any preceding claim wherein said poly(alkylene carbonate) comprises poly(propylene carbonate), poly(ethylene carbonate) or poly(cyclohexene carbonate).

7. A blend as claimed in any preceding claim wherein said compatibilizer forms less than 10 wt% of the blend.

8. A blend as claimed in any preceding claim wherein said poly(alkylene carbonate) forms up to 95 wt% of the blend.

9. A blend as claimed in any preceding claim wherein said poly(alkylene carbonate) forms up to 60 wt% of said blend, preferably up to 50 wt%, such as 10 to 30 wt%.

10. A blend as claimed in any preceding claim wherein the content of polyolefin in the blend is 40 to 95 wt%, preferably 50 to 90 wt%.

11. A blend as claimed where said blend has at least 20% improved oxygen barrier, preferably 50% improved (i.e. 20% reduced OTR/Oxygen Transmission Rate) compared with the pure polyolefin of the blend.

12. An article, such as a film or moulded article, comprising a blend as claimed in claim 1 to 11.

13. An article as claimed in claim 12 which is an extruded article, such as a film or moulded article.

14. A film comprising a blend as claimed in claim 9 or 10.

15. An article as claimed in claim 12 which is a moulded article such as an injection moulded article.

16. An article as claimed in claim 12 for use in food or non food packaging.

17. A process for extruding a blend comprising extruding said blend through a single or twin screw extruder at a temperature of less than the decomposition temperature of the poly(alkylene carbonate), e.g. less than 190°C, wherein said blend comprises

(I) at least one poly(alkylene carbonate);

(II) at least one polyolefin;

(III) at least one compatibilizer.

18. A process for the preparation of a moulded article comprising moulding a blend as claimed in claim 1 to 11 at a temperature of less than the decomposition temperature of the poly(alkylene carbonate), e.g. less than 190°C.

19. A process for the preparation of a film comprising blowing a blend as claimed in claim 1 to 11 at a temperature less than the decomposition temperature of the poly(alkylene carbonate), e.g. at less than 190°C.

20. A multilayered structure, e.g. multilayered film or moulded structure, comprising a blend as claimed in claim 1 to 11.