This invention relates to polymeric materials and particularly, although not exclusively, relates to polyoxymethylene (POM) in which aldehyde may undesirably be associated, for example by virtue of being produced during manufacture of the polymeric material, during downstream meltprocessing of the polymeric materials and/or during use thereof.

Polyoxymethylene (POM) is also called acetal, polyacetal, or polyformaldehyde. It is a polymer with a linear ether structure (CH2O-)n along its backbone. This linearity leads to a high crystallization degree that can be up to 80%, and density of 1 .410-1 .420 g/cm3. In some cases, POM may be filled, for example with glass fibres or carbon fibres.

POM finds increasing use in numerous applications, including electrical and electronics, consumer products, automotive and industrial machinery, medical devices, building and construction.

POM may be sold as a copolymer or a homopolymer. Homopolymer POM has the structure

•••(CHa ■ O -

It consists essentially of the aforementioned repeat unit.

Copolymer POM includes the following repeat units:

It consists essentially of the aforementioned repeat units.

Both homo and copolymer POM use methanol as the major basic raw material. For POM homopolymers, formaldehyde is synthesized through air oxidation of methanol, followed by formation of acetal resins by using ionic initiators. Replacement of the hydroxyl groups on polymer chain ends by ester groups stabilizes the resins in POM homopolymers. POM copolymers in general are produced using trioxane as the raw material (also produced starting from methanol). Around 2-3 % epoxy-compounds are copolymerized with the trioxane to provide a stable POM copolymer. Chain end-capping may also be used. POM copolymer resin has greater stability but reduced crystallinity as a result of carbon-carbon bonded groups interspersed in its polymer chain. This polymer structure also imparts superior resistance to alkali, hot water, and other chemicals, as well as long life at elevated temperatures and more latitude in processing conditions. On the other hand, its tensile strength, rigidity, softening point and melting point are all lower than those found in the acetal homopolymer.

Polyoxymethylene (POM) is inherently unstable and prone to polymer degradation. POM degradation occurs via chain scission or end group decomposition. Common degradation products are formaldehyde, formic acid, cyclic acetals and oligomers. Melt processing of POM causes degradation of the polymer leading to the generation of formaldehyde. Formaldehyde emissions lead to challenges in workplace safety during polymer processing and restrict the use of the polymer in applications where air quality is critical such as automotive applications.

Formaldehyde generated by polymer degradation can oxidise to formic acid, contributing to the hydrolysis of the polymer chain. Aside from formaldehyde emissions, POM degradation leads to mold deposits, reduction in mechanical properties and discoloration.

POM resins may also be sensitive to acid hydrolysis by mineral acids. For example, low levels of chlorine in potable water can lead to environmental stress cracking. As such POM parts are stabilized to mitigate this degradation.

It is known to take steps to stabilise POM and reduce aldehyde emissions. For example, steps to effect stabilisation may be applied either during the final stages of POM production or during melt processing to form an article or masterbatch. Approaches to prevent POM degradation that have been developed include phenolic antioxidants to limit oxidative degradation, lubricants to reduce shear forces, acid scavengers to prevent formic acid hydrolysis, scavengers to react with free formaldehyde, use of end capping, light stabilisers and/or comonomers to improve stability.

In addition, to the problem of aldehyde generation as aforesaid, POM is susceptible to thermally induced oxidative decomposition. The relative thermo-oxidative stability of POM polymers may be assessed by measuring the Oxidative Induction Time (OIT). A relatively high OIT is preferred.

Although various kinds of stabilization packages are commercially used, it is challenging to both reduce aldehyde emissions in POM and improve its thermal stability as illustrated by an increased OIT.

It is an object of the present invention to address one or more of the above problems.

According to a first aspect of the invention, there is provided a method of decreasing aldehyde, for example formaldehyde, content in a polyoxymethylene (POM) polymer and/or increasing Oxidative Induction Time (OIT) and/or increasing thermal stability, the method comprising the step of contacting the POM polymer, or monomers, oligomers or pre-polymers involved in the preparation of said POM polymer, with an aldehyde scavenger selected from:

(i) a compound XX which includes at least three moieties of formula wherein each moiety (AA) includes an amine moiety (-NH2) bonded ortho or meta to the amide moiety (-CONH); wherein each R ¹ independently represents a substituent and m is an integer from 0 to 4; and wherein the three moieties (AA) are bonded, via their respective amide nitrogen atoms, to respective carbon atoms of a Main Fragment, wherein the Main Fragment includes carbon and hydrogen atoms only and is saturated; and

(ii) a cyanoacetamide, for example, of general formula wherein R ⁶⁰ and R ⁶¹ independently represent a hydrogen atom or an optionally-substituted, preferably unsubstituted, alkyl, cycloalkyl or aromatic group; and wherein R ⁶² and R ⁶³ independently represent a hydrogen atom or an optionally-substituted, preferably unsubstituted, alkyl, cycloalkyl or aromatic group; or R ⁶² and R ⁶³ together define an optionally-substituted alkenyl group. References herein to reducing aldehyde suitably primarily refer to formaldehyde which as described is a particular problem in the context of POM.

Said method preferably decreases aldehyde content in POM, when assessed according to VDA- 275. Said method suitably improves thermal stability of the POM and leads to an increased OIT which may be illustrated as described in Assessment 3.

Said POM suitably includes a -(CH2O)- repeat unit (referred to as “repeat unit X”). It may also include a -(CH2CH2O)- repeat unit (referred as “repeat unit Y”). Preferably, in said POM, the sum of the mole % of repeat units X and Y is at least 80 mole %, preferably at least 90 mole %, more preferably at least 95 mole %, especially about 100 mole %.

In said POM, suitably the wt% of the POM polymer made up of repeat units X and Y is at least 80 wt%, preferably at least 90 wt%, more preferably at least 95 wt% and, especially, at least 98 wt%.

Said POM may be a homopolymer POM which suitably consists essentially of repeat units X or may be a copolymer POM which may comprise or preferably consist essentially of repeat units X and Y.

In said compound XX, one or each R ¹ may be selected from a halogen atom, or an optionally- substituted hydrocarbon, alkoxy, amine, amide, phenol or carboxylic acid, group. An optionally- substituted hydrocarbon may be substituted by one or more halogen atoms or by alkoxy, amine, amide, phenol or carboxylic acid, groups. An optionally-substituted hydrocarbon is preferably un-substituted.

One or each R ¹ may be an optionally-substituted, preferably an unsubstituted, alkyl group, for example an optionally-substituted, preferably an unsubstituted, C1-20, for example C1-10, alkyl group. R ¹ may be arranged to improve the compatibility of compound XX in the polymeric material in which it may be incorporated, for example by virtue of R ¹ including relevant functional groups to improve compatibility.

One or each m may be 0 or 1 . Preferably, each m = 0. That is, other than the amine and amide moieties, each moiety (A) is unsubstituted.

Preferably, in compound XX, at least one moiety (AA) includes an amine moiety (-NH2) bonded ortho to the amide moiety (-CONH). Preferably in each moiety (AA) in compound XX, the amine moiety is bonded ortho to the amide moiety. Preferably, in this case, m=0. Preferably, said Main Fragment does not include any cyclic or aromatic moiety. Preferably said Main Fragment comprises a linear or branched chain.

Said Main Fragment may include 3 to 20 carbon atoms. Preferably, it includes 5 to 15 carbon atoms, more preferably 7 to 12 carbon atoms and, especially, 8 to 10 carbon atoms. When the number of carbon atoms is n, the number of hydrogen atoms may be equal to 2n-1 . Preferably, said Main Fragment includes 5 to 39 hydrogen atoms. Preferably, it includes 9 to 29 hydrogen atoms, more preferably 13 to 23 hydrogen atoms and, especially, 15 to 19 hydrogen atoms.

In a preferred embodiment, said Main Fragment is a C9H17 moiety.

Said Main Fragment may include a linear chain which includes 6 to 14 carbon atoms, preferably 6 to 10 carbon atoms. The linear chain may include a branch point to which a chain which includes 1 to 4 carbon atoms is attached.

Said Main Fragment may be of general formula

(CH ₂ ) _p CH(CH ₂ ) _r

(CH ₂ ) _q wherein p, q and r are integers, suitably in the range 1 to 10, preferably 1 to 5. Preferably, p is in the range 2 to 4, q is in the range 1 to 3 and r is in the range 2 to 6.

Preferably, the sum of integers p, q and r is at least 4, preferably at least 6, more preferably at least 7. Said sum may be less than 20, preferably less than 15, more preferably less than 10.

In compound XX, preferably the nitrogen atoms of the amide moieties (-CONH) are spaced apart by at least 2, preferably at least 4, carbon atoms; and suitably by no more than 10, for example no more than 7 carbon atoms.

Said compound XX may be of formula wherein p, q and r are as described above.

Said compound XX is preferably

In a preferred embodiment of said compound of formula XXV, R ⁶⁰ and R ⁶¹ independently represent a hydrogen atom or an unsubstituted alkyl or cycloalkyl group and R ⁶² independently represent a hydrogen atom or an unsubstituted alkyl or cycloalkyl group. In an especially preferred embodiment, R ⁶⁰ , R ⁶¹ , R ⁶² and R ⁶³ each represent hydrogen atoms.

A reference herein to “ppm” refers to “parts per million” by weight.

Said aldehyde scavenger may be part of a formulation which is contacted with the POM polymer. Said formulation may be a liquid or solid formulation. References to a state of a material herein (e.g. a liquid) refer to the state at standard temperature and pressure (STP).

Said formulation may include at least 50wt% of carrier, preferably at least 60wt%, more preferably at least 70wt%, especially at least 75wt%. Said formulation may include less than Said formulation may include 50-95wt% of a carrier, 5-50wt% of said aldehyde scavenger and 0-30wt% of other additives. Said other additives may be selected from colourants, antioxidants, thickeners, process stabilizers, acid scavengers, lubricants and UV additive.

Preferably, in said formulation, the sum of the wt% of carrier(s) and a said aldehyde scavenger is at least 80wt%, at least 90wt% or at least 95wt%.

Said formulation may be a solid masterbatch or a liquid formulation. When it is a solid masterbatch, it may comprise 60-95wt% of thermoplastic polymer, for example a polyoxymethylene (POM).

Said formulation may include 10-40wt% of said aldehyde scavenger and 60-90wt% of thermoplastic polymer, for example POM.

A solid masterbatch may include 0 to 10wt%, preferably 0.5 to 10wt%, of one or more antioxidants.

When said formulation is a liquid formulation, said formulation may comprise 50 to 90wt% (for example 50 to 80wt%) of liquid carrier and 10 to 50wt% (for example 20 to 50wt%) of said aldehyde scavenger. Said liquid carrier may be a liquid at STP. A carrier is suitably such that it has good solubility in the POM into which it is to be added. It may comprise an oil (e.g. vegetable or mineral oil) or a glycol.

It is found that anti-oxidant can act synergistically in the method and an anti-oxidant may be included in a said formulation, when used in the method; or may otherwise contact the POM.

The method may comprise contacting the POM with anti-oxidant. A ratio defined as the wt% of aldehyde scavenger divided by the wt% of anti-oxidant may be at least 1 .0, preferably at least 3.0. Said ratio may be less than 20.0, preferably less than 10.0.

When a formulation is used in the method and/or is contacted with POM in the method, said formulation may include 0 to 10wt% of one of more anti-oxidants. The sum of the wt% of antioxidants in the formulation may be in the range 0 to 10wt%, preferably in the range 0.5 to 10wt%, or 0.5 to 7.0wt%. Said formulation preferably includes at least 1 .0 wt% of an anti-oxidant.

Said formulation may optionally include a phosphorus-containing antioxidant (e.g., a phosphite- series compound such as triphenyl phosphite, a triphenyl phosphate-series compound such as tris(2,4-di-t-butylphenyl) phosphate, a diphosphonite-series compound, and a metal salt of hypophosphorous acid). Said anti-oxidant may (and preferably does) comprise a sterically-hindered phenol compound.

Said anti-oxidant may include a moiety: wherein R ⁵⁰ and R ⁵¹ independently include at least four atoms which are preferably selected from C, H, O and N atoms; and more preferably, are selected from C and H atoms. R ⁵⁰ and R ⁵¹ are preferably saturated. R ⁵⁰ may represent a tertiary alkyl moiety, for example a tertiary alkyl moiety which includes at least 4 carbon atoms. R ⁵⁰ preferably represents a t-butyl moiety. R ⁵¹ may represent a C1-4 alkyl moiety, especially a methyl group.

Said anti-oxidant may include at least two moieties XXX.

Said anti-oxidant may include one or more oxyalkylene moieties, for example oxyethylene moieties.

Said anti-oxidant may include one or more ester moieties.

Said anti-oxidant preferably includes C, H and O atoms only.

Said anti-oxidant may be of formula wherein L ⁵⁰ is a linking moiety which suitably includes said oxyalkylene moieties and one or more ester moieties. Said anti-oxidant may be as follows:

Said method preferably decreases aldehyde content in the POM polymer so the POM polymer includes 2 ppm or less of aldehyde when assessed according to VDA-275. It also suitably increases OIT.

According to a second aspect of the invention, there is provided the use of said Compound XX or said cyanoacetamide of the first aspect for decreasing aldehyde, for example formaldehyde, content in a polyoxymethylene (POM) polymer and/or for increasing Oxidative Induction Time (OIT) in POM and/or increasing thermal stability of POM.

According to a third aspect of the invention, there is provided a polyoxymethylene (POM) polymer, having a reduced level of aldehyde and/or increased Oxidative Induction Time (OIT) and/or increased thermal stability, said POM polymer incorporating an aldehyde scavenger according to the first aspect or a product of a reaction between an aldehyde scavenger according to the first aspect and aldehyde.

Said POM polymer preferably includes 2 ppm or less of aldehyde when assessed according to VDA-275. Said POM polymer suitably has an improved thermal stability and/or an increased OIT which may be illustrated as described in Assessment 3.

Said POM polymer preferably includes residual carrier as described according to the first aspect.

Said POM polymer preferably includes anti-oxidant as described according to the first aspect.

Said POM polymer may be in pellet form.

A formulation as described may be used in the manufacture of parts or in the manufacture of pellets, for example masterbatch pellets, which may be used in subsequent manufacture of parts. Thus, according to a fourth aspect of the invention, there is provided a method of making an article, for example a shaped article, or pellets from a polyoxymethylene (POM) polymer, the method comprising:

(a) selecting a formulation comprises a carrier and an aldehyde scavenger as described in the first aspect and/or second aspects;

(b) contacting the POM polymer with said formulation; and

(c) forming said POM polymer into an article, for example a shaped article or into pellets.

Said article or pellets preferably includes 2 ppm or less of aldehyde when assessed according to VDA-275. Said article or pellets polymer suitably have an improved thermal stability and/or an increased OIT which may be illustrated as described in Assessment 3.

Preferably, in step (c), the POM polymer is suitably melt-processed to define said article or pellets.

Said article or pellets may be defined by any process known in the art. For example, said process may comprise injection molding, blow molding, thermoforming or extrusion.

Said article or pellets may include one or more colourants and may include 5-500ppm of a colourant, for example when an article is made. The aforementioned ppm is suitably based on the amount of said POM polymer. A said colourant described herein may be a dye or pigment. When pellets are made, the pellets may include up to 60wt% of colourant, for example titanium dioxide. Such pellets may define a masterbatch which suitably includes 5 to 35 wt% fillers, for example colourants, suitably as described.

Preferably, in said shaped article, the sum of the wt% of one or more POM polymer(s), and the aldehyde scavenger is at least 90wt%, at least 95wt% or at least 98wt%.

According to a fifth aspect of the invention, there is provided an article or pellet having a reduced level of aldehyde and/or an improved thermal stability and/or an increased OIT, said article or pellet being made as described in the fourth aspect and/or comprising POM polymer and a said aldehyde scavenger as described.

Said article or pellet preferably includes 2 ppm or less of aldehyde when assessed according to VDA-275. Said article or pellet suitably has an improved thermal stability and/or an increased OIT which may be illustrated as described in Assessment 3.

Any aspect of any invention described herein may be combined with any other aspect of any invention described herein mutatis mutandis. Specific embodiments of the invention will now be described by way of example.

The following materials are referred to hereinafter:

2-cyanoacetamide - a commercially-available product obtained from Fisher Scientific;

Irganox 1010 - commercially-available pentaerythritol tetrakis(3,5-di-tert-butyl-4- hydroxyhydrocinnamate) obtained from Sigma Aldrich;

Carrier A - refers to Clearslip™ 2 available from ColorMatrix. Carrier A was selected to have good solubility in the POM co-polymer used.

Co-polymer POM - refers to Ultraform S2320 POM co-polymer obtained from BASF; lupital POM - refers to lupital™ F20-03 POM co-polymer.

Assessment 1 - General procedure for determining formaldehyde content of plaques

The formaldehyde content of samples is determined on injection moulded plaques (40 x 100 x 3 mm (W x L X D)). The level of formaldehyde is determined using a Markes Micro- Chamber/Thermal Extractor™ (p-CTE™). The device is a versatile and compact unit with up to four small cylindrical chambers that enables the sampling of chemicals released from products or materials. Released volatile and semi-volatile organic compounds (VOCs and SVOCs) are collected in cartridges containing 2,4-dinitrophenylhydrazine for analysis by HPLC in accordance with ISO 16000-3. Formaldehyde reductions are calculated on the basis of percentage reduction seen in the formaldehyde levels of a part with additives, compared to a reference part that did not contain the additive. The assessment described has been shown to be comparable to VDA- 275 which is an automotive standard formaldehyde test.

Assessment 2 - Procedure for

Plaques (sizes 95 x 165 x 3 mm (W x L X D))_made in a manner similar to that described below and relevant controls were made and optical properties (i.e. L*, a* and b*) were assessed using a Minolta CM-3700d spectrophotometer in transmission mode fitted with a D65/1 O ⁰ light source.

Assessment 3 -Oxidative induction time testing

Oxidation induction time (OIT) tests were conducted using a heat-flux differential scanning calorimetry (DSC) to analyse the thermal stability of POM samples. Samples of about 5-6mg were heated from room temperature to 230°C under a flow of nitrogen gas (50ml/min) and held for 5minutes. The gas flow was switched to oxygen (50ml/min) and held constant to investigate the induction time. The peak maximum and not the onset temperature of the OIT response will be taken as the OIT results as observation shows that it is difficult to determine a well-defined onset temperature, as discussed in V. Archodoulaki, S. Lliftl and S. Seidler, "Oxidation induction time studies on the thermal degradation behaviour of polyoxymethylene", Polymer Testing, vol. 25, no. 1 , pp. 83-90, 2006.

Example 1 - Preparation of acetaldehyde scavenger N,N'-(2-(4-(2- aminobenzamido)butyl)pentane-1 ,5-diyl)bis(2-aminobenzamide) (referred to as Compound X)

Compound X has the following structure. 2H-benzo[d][1 ,3]oxazine-2,4(1 H)-dione (98.84 g, 3.5 Eq, 605.9 mmol) was dissolved in dimethylformamide (500 ml) at room temperature. To the reaction mixture was drop-wise added a solution of 4-(aminomethyl)octane-1 ,8-diamine (30.00 g, 1 Eq, 173.1 mmol) in dimethylformamide (250 ml). The reaction mixture was stirred at room temperature overnight until full conversion was evidenced by LC-MS. The dimethylformamide was removed under reduced pressure yielding a dark brown oil. To this was added water (1 I), ammonium hydroxide (25%, 50 ml) and the product extracted with dichloromethane. The dichloromethane was removed under reduced pressure and the product recrystallized in a mixture of methanol and acetonitrile. The solids were collected by filtration and dried to yield N,N'-(2-(4-(2- aminobenzamido)butyl)pentane-1 ,5-diyl)bis(2-aminobenzamide) (51.0 g, 55.5% yield). The structure of the compound was confirmed by NMR and LC-MS and the melting point was 160 °C.

Example 2 - General procedure for preparing solid formulations

Solid Masterbatch formulations were prepared by the blending of the required amounts of base polymer, formaldehyde reducing agent and optional antioxidant stabilizer in a twin screw extruder. Pellets were cut using a strand cutter. The materials were prepared using a Labtech LTE444-16 twin-screw extruder using the following conditions

Example 3 - General procedure for preparing liquid formulations Liquid formulations were prepared by combining the liquid Carrier A and optional dispersant (Solplus K240 (Poly(12-hydroxystearic acid)-polyethyleneimine copolymer; CAS number 124578-12-7) in a liquid mixing vessel. To this was added the aldehyde scavenging agent and optional antioxidant. The formulation may be milled to yield desirable particle sizes. Rheology modifiers may be optionally added. The formulation was mixed under vacuum to remove any residual air.

Example 4 - Oxidative induction time (PIT) testing of 2-cvanoacetamide and Compound X formulations and comparison to prior art formaldehyde scavengers for POM Technologies identified in the prior art were extruded in lupital POM and compared to use of 4- cyanoacetamide and Compound X in terms of formaldehyde emissions and OIT. In each case, anti-oxidant (Irganox 1010) was fixed at 0.3%. Results are provided in the table below. The results show that respective uses of Compound X and 2-cyanoacetamide both result in very low formaldehyde emissions in POM coupled with high OIT. It should be noted that cyanoacetamide offers high levels of formaldehyde reduction with only 50% of the addition level compared to other scavengers. In addition, it is known that OIT corelates with the concentration of anti-oxidant present in the POM polymer. A synergistic benefit was observed with combinations of Compound X or cyanoacetamide together with anti-oxidant.

It is concluded from the above that both Compound X and cyanoacetamide provide improvements and/or are advantageous compared to the prior art referenced.

Example 5 -Preparation of solid and liquid formulations comprising Compound X

Following the procedures described in Examples 2 and 3, solid and liquid formulations comprising Compound X were prepared having the compositions detailed in the table below.

In the following, the aldehyde scavenger (AS) component was Compound X, the anti-oxidant was Irganox 1010, the liquid carrier for Formulation No. VIII was Carrier A and the solid carrier for Formulation No. VII was Co-polymer POM.

Examples 6 and 7 - Assessment of solid and liquid formulations comprising Compound X

Solid and liquid formulations VII and VIII were added to Ultraform S2320 POM co-polymer and plaques produced by injection moulding at the let-down-ratios (LDRs) as described in the table below. The formaldehyde emissions were assessed as described in Assessment 1 and the L*, a* (D65), b* (D65) were assessed as described in Assessment 2.

The control refers to CoPolymer POM with no additives.

Both the solid masterbatch and the liquid formulation provided a significant formaldehyde reduction coupled with reduced discoloration with a low addition level. In addition, no discernible differences in oxidation induction time between formulation options were observed - both had an advantageous effect on OIT as described in Example 4.

Example 8 -Preparation of solid and liquid formulations comprising 2-cvanoacetamide

Following the procedures described in Examples 2 and 3, solid and liquid formulations comprising cyanoacetamide were prepared having the compositions detailed in the table below. In the following, the aldehyde scavenger (AS) component was 2-cyanoacetamide, the antioxidant was Irganox 1010, the liquid carrier for Formulation No. X was Carrier A and the solid carrier for Formulation No. IX was Co-polymer POM.

Examples 9 and 10 - Assessment of solid and liquid formulations comprising 2- cyanoacetamide

Solid and liquid formulations IX and X were added to Ultraform S2320 POM co-polymer and plaques produced by injection moulding at the let-down-ratios (LDRs) as described in the table below. The formaldehyde emissions were assessed as described in Assessment 1 and the L*, a* (D65), b* (D65) were assessed as described in Assessment 2.

The control refers to CoPolymer POM with no additives.

Both the solid masterbatch and the liquid formulation provided a significant formaldehyde reduction coupled with reduced discoloration with a low addition level. In addition, no discernible differences in oxidation induction time between formulation options were observed - both had an advantageous effect on OIT as described in Example 4.

Examples 11 to 15 - Use of Compound X as aldehyde scavenger and synergistic impact of formulation components on formaldehyde emissions

Following the procedure generally described for examples 6 and 7, individual components or mixtures of components included in the liquid formulations described were dosed into copolymer POM at the levels indicated and then assessed to determine the individual and/or collective effect on formaldehyde emissions and optical properties. Details of components and mixtures assessed and results are provided in the table below.

Where a carrier and an anti-oxidant were used, the components were Carrier A and Irganox 1010 respectively.

Examples 16 to 20 - Use of cvanoacetamide as aldehyde scavenger and synergistic impact of formulation components on formaldehyde emissions

Following the procedure generally described for examples 6 and 7, individual components or mixtures of components included in the liquid formulations described were dosed into copolymer POM at the levels indicated and then assessed to determine the individual and/or collective effect on formaldehyde emissions and optical properties. Details of components and mixtures assessed and results are provided in the table below.

Where a carrier and an anti-oxidant were used, the components were Carrier A and Irganox 1010 respectively.

For POM formulations, a wide range of materials may be incorporated into the formulations, including stabilisers such as hindered amine light stabilizers (HALS); acid scavengers eg calcium stearate, hydrotalcite; lubricants: eg waxes; BaSO4, TiOa, carbon black, pigments, aromatic polyamide, silicon powder, polytetrafluoroethylene and UV stabilisers.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.