Field of the invention

The present invention is directed to a recyclable heat-resistant paper liner with high liquid resistance, water vapour, and oxygen barrier, for packaging of liquid food products. In particular, the present invention relates to a multi-layer metallized paper-based packaging material.

It is further directed to making a barrier layer on paper heat resistant, so that it can be integrated to processes involving thermal pressing for making three dimensional fiber based packaging items. Background of the invention

Plastic packaging is used frequently in the economy and in people's daily lives. It has multiple advantages, such as its flexibility and its light weight. Such a weight reduction contributes to fuel saving and C0 reduction during transport, for example. Its barrier properties help to reduce food waste due a positive effect on increasing shelf life. The barrier properties also help to secure food safety.

However, according to the European strategy for plastics in a circular economy, recently published by the European Commission, around 25.8 million tons of plastic waste are generated in Europe every year with less than 30% of such waste being collected for recycling and between 150 000 to 500 000 tons of plastic waste entering the oceans every year.

To ensure that plastic waste is reduced, significant efforts are made in the industry and in commerce. Several supermarkets replace plastic bags by paper- based bags, for example. However, replacing plastics with paper in food packaging is not an easy task. A change in packaging material must not compromise consumer safety. The packaging must serve to protect the food but must also be robust enough to be handled by machines during the production process and must allow that the food product is presented effectively. Hence, there is a need for paper-based materials with improved barrier properties. There is - in particular - a need for paper-based materials with improved barrier properties that do not include a plastic layer, to allow for easier sorting and separation of paper-based material during recycling. W02000076862A9 describes in this respect a laminate structure for packaging applications comprising a paper substrate; and at least one polymer/nanoclay composite layer having clay particles with a thickness ranging from 0.7 to 9 nanometres applied to said paper substrate. However, there is a need in the art to even further improve the barrier properties of a paper-based packaging material.

In particular, for packaging intended for food products, good barrier properties are essential for maintaining the safety and quality of packaged foods. Typically, such barrier properties shall include barrier against transfer of gases (typically 0 ₂ , C0 ₂ , and N ₂ ), against vapor (especially water vapor), against aroma transfers, and also against light, especially ultra-violet (UV) light. Suitable packaging materials should also preferably be liquid-tight, especially to prevent transfer of liquid water or oils.

One way to provide good barrier for paper-based packaging materials is the introduction of a metal layer. Indeed, currently metallized paper- materials are available on the market as alternatives to state-of-the-art multilayer packaging.

The introduction of a liquid barrier is often challenging for paper- based packaging materials. However in many food packaging applications, the introduction of a good liquid barrier is essential for packing moist food products.

In addition, for example for three-dimensional packaging components, the paper-based packaging material is often thermo-processed. For instance it can be heat-sealed during forming or closing of the packaging item, such that it is subject to temperatures that can be as high as 80°C or above, and simultaneously subject to high mechanical stress, for a few seconds, when pressed between hot sealing jaws. Such elevated temperatures and pressures can degrade or damage the integrity of the packaging material, create cracks or through-holes, melt or burn one or another constituent, such that the protective function of the package is lost. Such damage to the packaging integrity is unacceptable as it compromises th* ³ shelf life of the packaged good, and may even allow contamination of the latter by external germs.

More precisely, there is a risk that the portion of the material that comes in contact with the heated manufacturing tool, is damaged by melting, which is of course undesirable, especially when such layer brings barrier properties to the structure.

It is an object of the present invention to provide a packaging material that is fully recyclable in regular paper recycling stream, but at the same time demonstrates high liquid barrier, water vapor and oxygen barrier properties, while also being heat resistant so that it can be integrated to industrial processes involving thermal treatment, in particular during heat seal processes as described above.

More precisely, it is an object of the invention to provide the art with a recyclable barrier packaging material that can be thermo-processed until 180°C, in particular for thermoforming processes in manufacturing three-dimensional packaging objects, without being subject to melting of one or more of its constitutive layers by the heat conveyed by the thermo-processing tools, while at the same time being easy to recycle. It is a further object of the present invention to provide a packaging material suitable for making packages for dry or liquid food products.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field.

Summary of the invention The present inventors were surprised to find that, by applying to a paper-based and metallized packaging material, a high-density polyethylene copolymer dispersion coating on top of the metallized layer, it was possible to achieve the objective of the present invention.

Consequently, the objectives of the present invention are achieved by the subject matter of the independent claims. The dependent claims further develop the concept of the present invention.

Accordingly, the present invention provides a multi-layer metallized paper-based packaging material coated with a high-density polyethylene (HDPE) copolymer dispersion coating applied on top of the metallized coating layer.

The high-density polyethylene copolymer dispersion coating is applied in an amount of about 1-10 g/m2, and provides barrier properties against liquids when the contents to be package is liquid or a moist product.

The multi-layer metallized paper-based liner according to the invention, comprises in order, from its external side (i.e. the side in contact with the ambient atmosphere) to its inner side (i.e. the side in contact with the product to be packaged):

- a paper layer having a grammage comprised between 40 and 120 g/m ² ,

- a first layer of pre-metallization coating,

- a second layer of pre-metallization coating,

- a metallization layer having a thickness in the range of 20 to 500 nm, with an equivalent optical density in the range of 1 to 4,

- a heat-resistant high-density polyethylene (HDPE) post-metallization dispersion coating, wherein said HDPE dispersion coating is applied in an amount of 0.5-10 g/m ² . The present invention further relates to the use of the multi-layer metallized paper-based packaging material in accordance with the present invention to package liquid food products in three dimensional fiber-based packaging components manufactured by combining fiber based dry-moulded pulp and multi- layer metallized paper-based liner by thermal pressing (thermoforming).

The multi-layer metallized paper-based liner material according to the present invention can be recycled with other paper packaging materials in a regular paper recycling process, preferably in a process according to the according to PTS test method PTS-RH 021:2012 Category II. Such a possibility is due to the fact that, although it contains a certain amount of polymer (HDPE), this polymer is applied by a dispersion coating process.

Thanks to dispersion coating of the polymer layer, the overall thickness said polymer material in the structure is extremely reduced compared to the thickness of paper material, therefore the inventors have achieved a packaging multilayer structure with excellent barrier properties against oxygen and moisture transfer, as well as resistance to liquid contact, while achieving a total contents of cellulosic fibres which is very high in proportion of the total material weight. Furthermore, dispersion coating of polymer avoids high cohesion and high adhesion of the polymer and therefore solves the recyclability problem (solid particles of polymer dispersed in a water carrier medium instead of liquid polymer applied to substrate). The fact that the inventors succeeded in forming a multilayer structure completely deprived of polymer layers formed by extrusion (extrusion-lamination or extrusion coating), provides a multilayer structure with a ratio of cellulosic fibre to non-cellulosic material, which is extremely high in fibre contents, and wherein the polymer layers are easy to disintegrate in the repulping process of paper recycling streams, due to the relatively low cohesion strength of the polymer, and also the relatively low adhesion of the same polymer to the rest of the substrate (especially the cellulosic fibres). The resulting structure therefore demonstrates excellent repulping capabilities and hi^h fibre yield which allows it to be accepted in waste paper collection in most of the countries worldwide. The very low content of non-cellulosic polymer and metal materials vacuum deposited metal layer is easily disintegrated, dissolved and separated from the cellulose, unlike existing structures known from the art.

The present invention further provides a use of a multi-layer metallized paper-based packaging material in accordance with the present invention to package dry or liquid food and a food packaging comprising a multi-layer metallized paper-based packaging material in accordance with the present invention.

As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to". Brief description of the drawings

Additional features and advantages of the present invention are described in, and will be apparent from, the description of the presently preferred embodiments which are set out below with reference to the drawings in which: Figure 1 is a schematic representation of the heat resistant multi layer metallized paper structure according to the invention;

Figures 2 and 3 illustrate a pod or capsule for beverage preparation in a beverage machine, made out of the metallized paper which is integrated to fiber pulp; Figure 4 illustrates a bottle for containing edible liquids, made out of the metallized paper which is integrated to fiber pulp;

Figure 5 is a graphical representation of the extrapolated Cobb value over a period of 30 days for a material according to the invention. Detailed description of the invention

In the present specification, "optical density" (or "equivalent optical density") of a material is defined as amount of light being reflected from the material, using a reflection densitometer. Optical density is measured by any internationally recognized standard method (e.g. EN ISO 5-2:2009).

In the present specification, "Bekk" smoothness of a material refers to the smoothness of a paper surface, evaluated by measuring the leakage of air applied at a specified pressure between a smooth glass surface and the surface of a paper sample. The time (in seconds) for a fixed volume of air to seep between these surfaces gives the "Bekk" smoothness value. Bekk smoothness is measured by any internationally recognized standard method (e.g. EN ISO 5627).

What is generally meant by "three-dimensional forming" is the application of a process to form a material into a three-dimensional item. Three- dimensional forming processes can comprise for instance deep-drawing, or thermoforming.

In the present application, a "deep-drawing" process is a process by which a material is formed into a shaped mould, by application of a deformation pressure inside said mould, such that the material takesthe shape of the mould. During forming in a deep-drawing process, the material can be either deformed and/or stretched.

In the present specification, a "thermoforming process" allows to form three-dimensional objects (such as bottles, trays, cups, bowls, coffee capsules or pods and the like), and requires the use of heat to form in a shaped mould, an initiall'/ flat material into a three-dimensional shape. This process requires the application of pressure in addition to heat, for several seconds, such that the object, once formed into a three-dimensional item, retains its final shape.

Thermo-processing of a material refers to the fact that heat is applied to a material in order to transform said material and allow to process it into a pre-determined item or to modify its mechanical properties. For instance, the material can be heated at least in some of its portions, in order to seal said material to another item, or to itself (e.g. to close a sachet made from said material). In another example, heat is applied to said material, e.g. to improve its mechanical resistance to mechanical stress.

The present invention relates to a heat resistant multi-layer metallized paper-based packaging material, referenced " HRBP " (which stands for "Heat Resistant Barrier Paper") in figure 1. Said heat resistant packaging material HRBP comprises from its outermost side to its innermost side (which innermost side is the side of said material to be in contact with the product to be packaged), the following layers:

- a paper layer 1 having a grammage comprised between 40 and 120 g/m ² ,

- a first layer of pre-metallization dispersion coating 2,

- a second layer of pre-metallization dispersion coating 3,

- a metallization layer 4 having a thickness in the range of 20 to 500 nm, with an equivalent optical density in the range of 1 to 4,

- a heat-resistant high-density polyethylene (HDPE) post-metallization dispersion coating 5, wherein said HDPE dispersion coating is applied in an amount of 0.5-10 g/m ² .

In a preferred embodiment of the invention, the packaging material described therein is used to package edible products. The edible product to H packaged may be a food or beverage product for human or animal consumption in liquid, pasty, gel, granulate, powder, or solid form.

The multi-layer metallized paper-based packaging material of the invention preferably has an overall thickness in the range of 30 to 150 pm, preferably 40 to 120 pm, or more preferably 50 to 100 pm.

For the purpose of the present invention, the term "paper-based" shall mean that the packaging material may comprise at least 50 weight-%, at least 60 weight-%, at least 70 weight-%, at least 80 weight-%, at least 90 weight-%, at least 95 weight-%, or at least 99 weight-% paper.

The multi-layer metallized paper-based packaging material is preferably a flexible material. For the purposes of the present invention, a packaging material shall be considered flexible if it is a material capable of bending without breaking. Further, for example, such a flexible material may be a material that can be bent without breaking by hand. Typically, a multi-layer flexible packaging material in accordance with the present invention has a basis weight (grammage) of 120 g/m ² or less.

An appropriate paper, especially in terms of thickness and mechanical and chemical stability, shall be selected based typically on the type of product to be packaged, the intended shelf life, and whether the paper material is to be used as primary packaging (i.e. in direct contact with the product), secondary or tertiary packaging. Typically, a thicker paper may be used for a tertiary packaging that for a primary packaging.

For some applications of the present invention it is preferred if the paper layer is non-porous. If the paper layer has a porous surface, an additional surfa^ ^p layer covering the porous paper surface may be added to make it impermeable to gas, especially to ambient air. If necessary, such an additional surface layer is selected within the list of: starch, pigment-starch, a pigment-latex, or a combination thereof. The ratio of pore volume to total volume of the paper material is called the porosity of the paper material. For the purpose of the present invention, a paper layer shall be considered as non-porous if a standard Gurley permeability test of the paper results in less than 20 ml/min (Tappi T547). This is achieved for a paper having typically a porosity of less than 40%, preferably less than 30%, more preferably less than 20%. Hence, in one embodiment of the present invention, the paper layer is a non-porous paper layer.

Preferably, the paper layer has a low surface roughness. The inventors have found that a low surface roughness is beneficial for the purpose of the present invention. For example, the paper layer may have a Bendsten roughness of less than lOOml/min. The Bendsten roughness can be determined in accordance with ISO 8791-2:2013, herewith incorporated herein by reference.

Also preferably, the paper layer has a back side Bekk smoothness in the range of about 300-1000 seconds. Bekk smoothness is measured by air leak method. This method allows measuring time which is required to draw ambient air into a vacuum container at atmospheric pressure between a sample of paper and a glass plate. So Bekk smoothness corresponds to the time - in seconds - that expresses time interval needed to drop the vacuum from 50.7 kPa to 48.0 kPa. The higher the paper smoothness, the longer the time it takes for the air to permeate through the paper. Vacuum metallization process is a line of sight metal deposition process which means that metal layer can be uniformly deposited only on planar surfaces and not on surface contours. Therefore, the planarity of the paper surface is extremely critical for uniform deposition of metal on the paper surface. Bekk smoothness of paper in the range of 300 - 1000 seconds signifies that the pap^r features an adequate surface planarity, to allow uniform coating and vacuum metal deposition.

The inventors obtained very good results in terms of stability and maintenance of barrier properties with a multi-layer metallized paper-based packaging material, comprising two pre-metallization primer coating layers, each in an amount of about 1-10 g/m ² .

Preferably, the pre-metallization coating layers are applied, each, in an amount of 1 to 10 g/m2. Preferably, the first pre-metallization layer comprises an ethylene acrylic acid copolymer, which provides the moisture barrier, and the second pre-metallization layer comprises a polyurethane copolymer, or a polyvinyl alcohol (PVOH), which provides the oxygen barrier.

In the multi-layer metallized paper-based packaging material of the invention, the metallized layer has a thickness in the range of typically between 20 and 500 nm, preferably of 20 to 400 nm, or even more preferably of 20 to 300 nm; furthermore, it preferably has an equivalent optical density in the range of 1 - 4, more preferably of 1,2 - 3.9, most preferably of 1.4 - 3.8.

Preferably, the metallized layer is an aluminium layer. The metal layer may alternatively be a metalloid, and in that case, preferably an aluminium oxide ("AIOx", more precisely Al 0 ₃ ), or a silicon oxide (SiOx) layer.

Generally, in the present specification, by "metallized" (or "metallic") layer, it is meant a layer formed from a metal, and by extension a metalloid. Metalloids (like SiOx or AIOx mentioned above) are very close to metals but they differ by some properties to metals - and they are actually not considered as non-metallic elements. In the present specification, it is agreed that such words as "metallized", "pre-metallization", "post-metallization", refer to metallization as such, but also by extension, to metalloidization. The aluminium layer is applied to the packaging material by physical vapor deposition. For example, the aluminium layer may be applied by means of a vacuum deposition process. An example of a vacuum deposition process is described in Thin Solid Films, Volume 666, 30 November 2018, Pages 6-14. Vacuum deposition is an evaporative process in which aluminium from a solid phase is transferred to the vapor phase and back to the solid phase, gradually building up film thickness. Coatings produced by vacuum deposition have the advantage of good abrasion resistance, impact and temperature strength, as well as the capability to be deposited on complex surfaces. The range of optical density for the aluminium layer may be in the range of 1.4-3.8, which correlates with a thickness of 30-200 nanometres.

The thickness of the aluminium layer may be adjusted appropriately, for example, depending on the intended shelf life, the packaged product and the overall thickness of the packaging material.

Alternatively, the metal layer can be a vacuum deposition of silicon oxide (SiOx).

The paper-based barrier packaging material structure according to the invention requires packaging forming capabilities, to be able to be processed into a fully formed, filled, and closed package.

Such a material is typically designed for being formed into a package by using, in a preferred embodiment, a thermoforming process. Such a thermoforming process allows to form three-dimensional objects (such as bottles, trays, cups, bowls, coffee capsules or pods and the like), and requires the use of heat to form in a shaped mould, the - initially flat - material into a three-dimensional shape. This process requires the application of pressure in addition to heat, for several seconds.

Temperatures for thermoforming are typically within the range of 75°C to 200°C, generally within the range of 120°C to 180°C. At such temperatures a technical problem was found by the inventors that polymers used for thermoforming and/or sealing the package melt and that the integrity of the whole packaging material deteriorates, which is of course undesirable. At the same time, it is not possible to increase the thickness of the polymeric layer by using extrusion or lamination techniques, because it would render the whole material unsuitable for recycling in a paper recycling process, as explained above. The inventors have surprisingly found that an ultra-thin layer of HDPE dispersion coating allows at the same time, to meet:

- paper stream recyclability requirements, and

- heat resistance to the thermoforming processes used in manufacturing of packages, and in particular to ensure that the heated tool part of the thermoforming machine does not melt the polymer portion of the structure, which is in contact with said heated tool part.

The inventors were surprised to find that the application of an HDPE coating worked very well to introduce a performant liquid barrier to metallized barrier papers. In addition, the present inventors were surprised to find that such a high- density polyethylene copolymer dispersion coating applied on top of a metallized layer was found to be temperature resistant. For example, the high-density polyethylene copolymer dispersion coating applied on top of the metallized layer did not melt when brought into direct contact with sealing jaws under pressure and at 180°C for 5 seconds. This indicates that the multi-layer metallized paper-based packaging material of the present invention can very well be used for packaging applications that require e.g. a thermoforming step.

In a preferred embodiment, the high-density polyethylene copolymer dispersion coating is an acid-modified polyolefin dispersion coating. Very good results were obtained, when the inventors used CANVERA™1110 from the DOW Company, as high-density polyethylene copolymer (HDPE) dispersion coating, which is a preferred HDPE dispersion coating in the realisation of the present invention. The multi-layer metallized paper-based packaging material of the invention, does not comprise an extruded or laminated polyolefin layer, but instead an HDPE dispersion coating. The advantages of dispersion coating versus extruded or laminated layers as discussed above, relate essentially to the fact that an HDPE layer which is applied by a dispersion coating is recyclable in the paper stream with the rest of cellulosic material because the quantity of polymer is extremely low - while providing high barrier properties to the overall packaging material structure -, and the polymer molecules are also very easily dissociated in a recycling process, so they do not form solid residues in the recycling bath amongst cellulosic material.

The paper-based barrier heat resistant packaging material of the invention is recyclable with the paper and carton stream for example. This is due to the fact that the polymer and metal coating can be easily separated from pulp fibres in a recycling process adapted to recycle paper or other cellulosic material (e.g. paperboard). During recycling, the metallic layer is separated from the rest of the packaging material due to its very low thickness. The fact that the material of the present invention is deprived of an extruded or laminated polyolefin layer, such as a polyethylene (PE) or a polypropylene (PP) extruded or laminated film layer, improves the sortability of the packaging material of the present invention during recycling. Typically, aluminium is separated from the rest of the packaging material during recycling in a hydra-pulper. Hence, the entire multi-layer flexible packaging material in accordance with the present invention should be allowable to be recycled as paper and/or carton. One major advantage of the present invention is it that despite being deprived of an extruded or laminated polyolefin layer, such as a PE or a PP layer, excellent liquid and gas barrier properties are achieved with the combination of the ultra-thin metal layer which provides a barrier to gases, with the ultra-thin layer of HDPE dispersion coating which provides the barrier to liquids. The multi-layer metallized paper-based packaging material in accordance with the present invention may have a COBB value of not more than 10 g/m ² after 30 days, not more than 8 g/m ² after 30 days, or not more than 6 g/m ² after 30 days.

The multi-layer metallized paper-based packaging material in accordance with the present invention preferably achieves an oxygen transmission rate (OTR) of not more than 3 cm ³ /day/m ² at 23°C and 50% Relative Humidity (RH), more preferably of not more than 2.5 cm ³ /day/m ² at 23°C and 50% RH, and more preferably of not more than 2 cm ³ /day/m ² at 23°C and 50% RH.

The multi-layer metallized paper-based packaging material in accordance with the present invention may further have a water vapor transmission rate (WVTR) of not more than 1 g/d/m2 at 23°C/85%RH, not more than 0.9 g/d/m2 at 23°C/85%RH, or not more than 0.8 g/d/m2 at 23°C/85%RH.

Hence, in one embodiment of the present invention, the multi-layer metallized paper-based packaging material may have a COBB value of not more than 10 g/m2 after 30days, an oxygen transmission rate of not more than 3 cm3/d/m2 at 23°C/50%RH and a water vapor transmission rate of not more than 1 g/d/m2 at 23°C/85%RH.

Due to the excellent heat resistance of the HDPE dispersion coating, the multi-layer metallized paper-based packaging material may be used for processes that involve thermo-processing. Hence, the subject matter of the present invention also relates to the use of a multi-layer metallized paper-based packaging material in accordance with one of the preceding claims for applications that involve thermo processing, for example thermoforming of air-laid dry fiber pulp for making three dimensional shapes. Such thermo-processing may be carried out at temperatures in the range of 75-180°C, of 100-180°C, or of 150-180°C, for example.

The excellent barrier properties allow it that the multi-layer metallized paper-based packaging material in accordance with the present invention may be used to package food, in particular moist food.

The subject matter of the present invention also extends to a food packaging made out of multi-layer metallized paper-based packaging material of the invention, by thermo-processing such as thermoforming.

Figures 2 illustrates a pod or capsule shell 6 for beverage preparation in e.g. a beverage preparation machine which is made of fiber pulp moulded or otherwise formed in the desired cup shape. The paper-based metallized barrier material of the present invention is then applied and joined by deep-drawing onto the fiber-pulp, made out of the metallized paper which is integrated to the fiber pulp shell in order to provide a finished paper-based capsule 7, as illustrated in figure 3, that is barrier to liquids, has excellent barrier properties to moisture and oxygen transmission, and furthermore is recyclable in the paper recycling processes and facilities. During the deep drawing process, the heated tool of the packaging making machine is in direct contact with the HDPE dispersion coating layer of the multi-layer material.

Alternatively, the paper-based barrier heat resistant material according to the invention can be formed into a three-dimensional complex object such as a bottle illustrated in figure 4. Such a bottle is suitable for containing edible liquids, and is manufactured, for instance by thermoforming two semi-cylindrical shells made out of the metallized paper which is then integrated to fiber pulp to form an entire bottle. As illustrated in the enlarged cross-section part of figure 4, the thickness of the resulting bottle comprises one layer of fiber pulp 9 and one layer of the barrier paper-based material HRBP of the invention. In order to provide resistance of th* ³ bottle to the liquid contained therein, the paper-based material of the invention is located on the innermost side of the bottle thickness, such that the packaged liquid is in contact with the HDPE dispersion coating layer 5 of said material HRBP.

Example

A paper-based barrier packaging material was formed according to the above principles of the invention. In this example, the material comprises from its outer to its inner side:

- a paper layer 1 having a grammage of 62 g/m ² ,

- a first layer of pre-metallization coating 2 being an ethylene acrylic acid copolymer, having a thickness of 4 g/m ² ,

- a second layer of pre-metallization coating 3 being a polyurethane-based coating having a thickness of 1.5 g/m ² ,

- a vacuum deposited layer of aluminium oxide 4 having a thickness in the range of 50 nm, with an equivalent optical density of 3.5,

- a CANVERA™1110 (from the DOW Company) heat-resistant high density polyethylene (HDPE) post-metallization dispersion sealing coating 5, wherein said HDPE dispersion coating was applied in an amount of 5 g/m ² .

The above material was produced as a flat blank sheet, which was then subject to a conventional heat sealing process by pressing said edges one against the other between a pair of sealing jaws. The sealing jaws temperature was set at 180°C, and a sealing pressure of 900 N was applied to said material during 5 seconds.

None of the material layers, and especially the HDPE sealing layer presented cracks, through-holes, or any other damage that would comprise the integrity of the material structure or its barrier capabilities against liquids or gas transmission. A series of tests, especially for paper characterization, barrier and heat-resistance tests were performed, providing the results as follows.

The COBB value measured by a standard text process according to the International Standard ISO 5637 revealed the following values:

These values were then extrapolated to provide COBB values for the same material over a period of 30 days, as shown in figure 5.

The barrier to water vapour and oxygen, of the material were then assessed, and provided the following results:

Those skilled in the art will understand that they can freely combine all features of the present invention disclosed herein. In particular, features described forthe products of the present invention may be combined with the use of the present invention and vice versa. Further, features described for different embodiments of the present invention may be combined.

Although the invention has been described by way of example, it should be appreciated that variations and modifications may be made without departing from the scope of the invention as defined in the claims.

Furthermore, where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred in this specification. Further advantages and features of the present invention are apparent from the figures and non-limiting examples.