SCAVENGER

Yves Roger WYSER

Maria Isabelle GIARDIELLO

Julien (NMN) BRAS

Field of the invention

The present invention relates generally to the field of packaging, in particular food packaging. One embodiment of the present invention relates to a cellulose-based multilayer packaging material comprising at least three cellulose- based layers, wherein the cellulose-based layers comprise a cardboard-based layer sandwiched between two barrier paper layers. The inventors have observed that such a cellulose-based multilayer packaging material has excellent long-term water vapor barrier properties. The packaging material may have a thickness in the range of about 200 to 1000 pm and a grammage in the range of about 200-800 g/m2. Background of the invention

Packaging of manufactured food products is a vital part of the food industry today as it ensures food safety, preserves food quality and plays an important role in production processes, in brand communication and in digitalization. Indeed, several studies show that for a large part of consumers the packaging of a product is one key aspect that drives the purchase decision.

Plastic packaging is used frequently in the economy and in people's daily lives. It has multiple advantages, such as its 3D shape flexibility, its light weight and its barrier properties. Such a weight reduction contributes to fuel saving and CO2 reduction during transport, for example. Its barrier properties help to reduce food waste due to 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.

One of the main problems associated with packaging in general is the generation of packaging waste. According to Eurostat in 2017, 172.6 kg of packaging waste was generated per inhabitant in the EU.

The industry addresses this issue by embracing the circular economy. In line with this, the European Commission has recently communicated a new Circular Economy Action Plan (COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT, THE COUNCIL, THE EUROPEAN ECONOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGIONSA new Circular Economy Action Plan For a cleaner and more competitive Europe, Brussels, 11.3.2020). Accordingly, the EU needs to accelerate the transition towards a regenerative growth model that gives back to the planet more than it takes, advance towards keeping its resource consumption within planetary boundaries, and therefore strive to reduce its consumption footprint and double its circular material use rate in the coming decade.

To ensure that plastic waste is reduced, significant efforts are made in the industry and in commerce. Replacing plastics with paper or fibre-based solutions in food packaging is one way forward, but not an easy task. A change in packaging material must not compromise consumer safety or product quality, nor generate food waste. 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.

One step towards meeting the challenges mentioned above is to use cellulose-based packaging material. One challenge with cellulose-based packaging material is that it often provides an insufficient moisture barrier for certain applications, for example in food packaging. This challenge is addressed in the art usually by using barrier papers, in other words paper-based packaging material comprising at least one barrier layer that provides the necessary barrier properties.

There is, however, still a need in the art for cellulose-based packaging materials that have even improved moisture barrier properties, for example effective moisture barrier properties in high moisture conditions and/or effective longterm moisture barrier properties. Rigid and barrier structures made with cardboard material are also expected.

US 2020/0189791 Al is a US patent application to ENVICAN GmbH which discloses a can containing a liquid and/or a gaseous medium which has positive pressure or develops such during transport or storage, wherein the cylindrical can shell of the can consists mainly of paper or cardboard material and is closed at the bottom with a bottom element and at the top with a cover element, wherein the can withstands an internal pressure of at least 5 bar, wherein the innermost layer of the can shell, consists of a straight-wound barrier layer having a longitudinally extending folded seam, wherein the barrier layer is a prefabricated laminate made of an inner diffusion-tight barrier film or an inner diffusion-tight barrier laminate and an outer kraft paper layer.

US 2014/0339230 Al is a US patent application to Guenter Keienburg that discloses a drinks container includes a lateral container surface defining an inner lateral surface and a height, a cover element which closes the lateral container surface, and a base element which closes the lateral container surface. The lateral container surface comprises the inner lateral surface comprising a barrier layer, an exterior side, at least one parallel-wound laminate comprising a cellulose-containing material, a multi-layered sheet material arranged in a region of the inner lateral surface, and a laminate overlapping region arranged on the exterior side. The laminate overlapping region comprises a first strip- like section extending over the height of the lateral container surface. A second section curves convexly outwardly in a circumferential direction. The second section symmetrically adjoins the first strip-like section. The at least one parallel-wound laminate comprises overlapping peripheral strips and is covered at least in the laminate overlapping region on at least one side with an adhesive sheet material.

The packaging structures disclosed in the above prior art publications are not recyclable in the paper stream because they use a conventional laminated polymeric film, as well as a glued metallic foil, for the barrier layers. It was found that such laminated polymeric films are extremely difficult to recycle together with the paper components of the structure, due to the fact that laminated films have a high thickness, and also because they remain as polymeric films, if the whole packaging structure is recycled in a conventional paper-recycling process. This is highly undesirable because the paper slurry that is obtained from the recycling process, which is then subsequently transformed into a new paper material, is contaminated by bits and pieces of polymeric film. The same reasoning applies to metallic foils glued or otherwise attached to the rest of the packaging structure layers: metallic foils do not recycle together with paper and rather contaminate the paper recycling processes. Therefore, such paper-based structures made from lamination of polymer films and incorporating metallic foils cannot be recycled in a paper recycling process.

Consequently, there is a need in the art for a cellulose-based packaging material that is easy to recycle in a paper recycling process and that has improved moisture barrier properties compared to state-of-the-art barrier papers so that it can be used for demanding food applications.

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 objective of the present invention was to enrich or improve the state-of-the-art and in particular to provide a cellulose-based packaging material that is easy to recycle and that has excellent moisture barrier properties so that it can be used for food applications, in particular for food applications that require a good moisture barrier for extended time periods, or to at least provide a useful alternative to solutions existing in the art.

The inventors were surprised to see that the objective of the present invention could be achieved by the subject matter of the independent claims. The dependent claims further develop the idea of the present invention. Accordingly, the present invention provides a cellulose-based multilayer packaging material comprising at least three cellulose-based layers, wherein the cellulose-based layers comprise a cardboard-based layer sandwiched between two barrier paper layers. The cellulose-based multilayer packaging material may have a thickness in the range of about 150 to 1000 pm and/or a grammage in the range of about 150-800 g/m2.

According to the principle of the present invention, the barrier paper layers comprise a paper layer, a thin metallic layer which is a vacuum deposited layer, and at least one dispersion coating of a polymer. More precisely, according to the invention, the barrier paper layer is a multilayer which comprises a polymeric dispersion coated barrier layer having a thickness comprised between 1 and 10 pm, and at least one other layer of metal, preferably aluminium, that is deposited by vacuum deposition. The paper used for forming the multilayer barrier paper has a grammage comprised between 40g/m ² and 120 g/m ² .

In a preferred embodiment of the invention, the metallized barrier paper layer comprises:

- a paper layer,

- at least one pre-metallization polymeric dispersion coating applied from a water-based polymer dispersion onto said paper layer, and having a thickness comprised between 2 pm to 8 pm,

- at least one metallic layer of: aluminium, or aluminium oxide, or silicon oxide, said metallic layer being deposited onto said pre-metallization dispersion coating, said metallic layer having a thickness of between 20 nm and 500 nm,

- at least one layer of post-metallization polymeric dispersion coating applied from a water-based polymer dispersion on top of the vacuum deposited layer, and having a thickness comprised between 2 pm to 8 pm.

Said barrier metallized paper layer metallized structure has a preferred optical density of paper in range of 2-5, preferably in the range of 3.5-4.5. Further, it has a preferred water absorption Cobb measured at 60 min of 0 g/m2. Polymers used in the polymeric barrier dispersion coating of the barrier paper layer of the invention, are selected within the list of: ethylene acrylic and methacrylic acid copolymers, styrene acrylate, styrene-butadiene, propylene acrylic and methacrylic acid copolymers, polyesters, polyurethane, cellulose acetate, cellulose nitrate, polyamide, biodegradable polymers such as polylactic acid (PLA), polyhydroxyalcanoates (PHA), polyvinylalcohols (PVOH), or a combination thereof.

Due to dispersion coating, the overall thickness of polymer material in the structure is extremely reduced compared to the thickness of paper and paperboard (i.e. cardboard) material, therefore the inventors have achieved to overcome the technical limitations of the known multilayer barrier structures, and achieve a packaging multilayer structure with excellent barrier properties against oxygen and moisture transfer, as well as resistance to liquid contact from their inner or outer surfaces, while achieving a total contents of cellulosic fibres which is very high (above 80% typically). Furthermore, dispersion coating of polymer avoids high cohesion and high adhesion of the polymer molecules between themselves and with the substrate to which they are coated, which 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 repulping process 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 high fibre yield which allows it to be accepted in waste paper collection in the most of the countries. The very low content of non-cellulosic polymer, and of vacuum deposited metal, is easily disintegrated, dissolved and separated from the cellulose, unlike existing structures known from the art.

The present invention further provides a method of manufacturing such a cellulose-based multilayer packaging material.

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".

The present inventors have shown that by introducing a cardboardbased layer in between two barrier paper layers it was possible to manufacture a cellulose-based multilayer packaging material that achieves the objective of the present invention.

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 shows an example of possible structure in accordance with the present disclosure;

Figure 2 shows a sample setup for a WVTR test;

Figure 3 shows the moisture pickup in the desiccant used during the water vapor transmission rate determination at 23 °C / 85 % relative humidity together with the theoretical moisture pickup without buffering effect, depicting the benefit of the present invention on delaying moisture pickup;

Figure 4 shows the evolution of WVTR over time. The increase of the value is linked to the scavenging/buffering effect of the paper board. Detailed description of the invention

Consequently, the present invention relates in part to a cellulose- based multilayer packaging material comprising at least three cellulose-based layers, wherein the cellulose-based layers comprise a cardboard-based layer sandwiched between two barrier paper layers.

The cellulose-based multilayer packaging material may have a thickness in the range of about 150 to 1000 pm.

The cellulose-based multilayer packaging material may further have a grammage in the range of about 150-800 g/m ² .

For example, the cellulose-based multilayer packaging material comprises at least three cellulose-based layers, wherein the cellulose-based layers comprise a cardboard-based layer sandwiched between two barrier paper layers, wherein the packaging material has a thickness in the range of about 150 to 1000 pm and a grammage in the range of about 150-800 g/m ² .

For the purpose of the present invention, a packaging shall be considered multilayer if it comprises at least three layers.

The cellulose-based multilayer packaging material may be a cellulose-based multilayer food packaging material. Accordingly, the packaging material of the present invention may have barrier properties that are sufficiently high so that the packaging can be used for packing food, for example sensitive food. The term "food" shall comprise for the purpose of the present invention petfood and/or food as defined by Codex Alimentarius. Codex Alimentarius defines the term "food" as any substance, whether processed, semi-processed or raw, which is intended for human consumption, and includes drink, chewing gum and any substance which has been used in the manufacture, preparation or treatment of "food" but does not include cosmetics or tobacco or substances used only as drugs.

A packaging material shall be considered as cellulose-based if it contains more than 50 weight-%, more than 60 weight-%, more than 70 weight-%, more than 80 weight-%, more than 90 weight-%, or more than more than 95 weight-% cellulose.

A cardboard-based layer shall be considered as cardboard-based if it contains more than 50 weight-%, more than 60 weight-%, more than 70 weight-%, more than 80 weight-%, more than 90 weight-%, or more than more than 95 weight-% cardboard. In one embodiment of the present invention the cardboard-based layer may consist of cardboard.

The cardboard-based layer may be any type of cardboard. For example, the cardboard be selected from the group consisting of fiberboard, paperboard, or mat board.

In the packaging material of the present invention one cardboardbased layer may be sandwiched between two barrier paper layers. In a further embodiment of the present invention two cardboard-based layers may be sandwiched between three barrier paper layers. Alternatively, three cardboard-based layers may be sandwiched between four barrier paper layers. For example, the multilayer packaging material of the present invention may comprise at least two barrier paper (BP) layers and at least one cardboard-based (CB) layer. Accordingly, the multilayer

- io - packaging material of the present invention may have the structure, BP/CB/BP, BP/CB/BP/CB/BP, or BP/CB/BP/CB/BP/CB/BP for example.

In the cellulose-based multilayer packaging material in accordance the present invention, the cellulose-based layers may be glued on top of each other, for example by means of a starch-based glue or a PVOH-based glue.

The inventors have obtained particular promising results with cardboard with a grammage in the range of about 100 - 500 g/m ² , in the range of about 200 - 400 g/m ² , or in the range of about 250 - 350 g/m ² .

The barrier paper layer may be any barrier paper suitable for packaging the intended product. According to an essential principle of the invention, the barrier paper layer is a multilayer which comprises a polymeric dispersion coated barrier layer, and at least one other layer of metal, preferably aluminium, that is deposited by vacuum deposition. The paper used for forming the multilayer barrier paper has a grammage comprised between 40g/m ² and 120 g/m ² .

In a preferred embodiment of the invention, the metallized barrier paper layer comprises:

- a paper layer,

- at least one pre-metallization polymeric dispersion coating applied from a water-based polymer dispersion onto said paper layer, and having a thickness comprised between 2 pm to 8 pm,

- at least one metallic layer of: aluminium, or aluminium oxide, or silicon oxide, said metallic layer being deposited onto said pre-metallization dispersion coating, said metallic layer having a thickness of between 20 nm and 500 nm,

- at least one layer of post-metallization polymeric dispersion coating applied from a water-based polymer dispersion on top of the vacuum deposited layer, and having a thickness comprised between 2 pm to 8 pm. Said barrier metallized paper layer metallized structure has a preferred optical density of paper in range of 2-5, preferably in the range of 3.5-4.5. Further, it has a preferred water absorption Cobb measured at 60 min of 0 g/m2.

The inventors have obtained good results with barrier paper with a grammage in the range of 30-100 g/m ² , in the range of 50-90 g/m ² , or in the range of 60-85 g/m ² .

Polymers used in the polymeric barrier dispersion coating of the barrier paper layer of the invention, are selected within the list of: ethylene acrylic and methacrylic acid copolymers, styrene acrylate, styrene-butadiene, propylene acrylic and methacrylic acid copolymers, polyesters, polyurethane, cellulose acetate, cellulose nitrate, polyamide, biodegradable polymers such as polylactic acid (PLA), polyhydroxyalcanoates (PHA), polyvinylalcohols (PVOH), or a combination thereof.

The inventors have obtained excellent results with cellulose-based multilayer packaging material in accordance with present invention with the barrier layers of the barrier paper facing outside and the cardboard-based layer being sandwiched between the barrier papers so that the cardboard-based layer faces the side of the barrier paper facing away from the barrier layer.

Hence, in the cellulose-based multilayer packaging material in accordance with the present invention, the barrier layer (b) of at least one barrier paper (BP) layer may be facing the cardboard layer. Hence the structure of the cellulose-based multilayer packaging material in accordance with the present invention may be b-BP/CB/b-BP

The inventors were further surprised to see that they could also obtain excellent results with a cellulose-based multilayer packaging material in accordance with the present invention, wherein the barrier layers of the barrier paper layers are facing the cardboard layer. Hence the structure of the cellulose-based multilayer packaging material in accordance with the present invention may be BP-b/CB/b-BP

The inventors were even further surprised to see that they could also obtain excellent results with a cellulose-based multilayer packaging material in accordance with the present invention, wherein the barrier layers of the barrier paper layers are facing away from the cardboard layer.

Hence the structure of the cellulose-based multilayer packaging material in accordance with the present invention may be b-BP/CB/BP-b

Hence, alternative structures within the scope of the present invention include, for example the following: b-BP/CB/b-BP/CB/BP-b, b-BP/CB/b- BP/CB/b-BP, b-BP/CB/BP-b/CB/b-BP, BP-b/CB/b-BP/CB/b-BP

According to the principle of the invention, the multilayer packaging material in accordance with the present invention has particularly good gas barrier properties. For this, a metallized barrier paper is used. Accordingly, at least one of the barrier paper layers is a metallized barrier paper layer wherein the metal layer is an ultrathin layer of metal deposited by vacuum deposition. For example, the at least one metallized barrier paper layer may be an aluminized barrier paper layer.

In the cellulose-based multilayer packaging material of the present invention, the cellulose-based layers may be made from any cellulose-based material suitable for packaging materials for the intended purpose of the packaging. A person skilled in the art will be able to make an appropriate selection. Based on their work the inventors expect very good results with cellulose-based material selected from the group consisting of, mechanical pulp, recycled paper pulp, bagasse pulp, annual plant pulp, virgin cellulose pulp, refined cellulose pulp, or combinations thereof.

In one embodiment of the present invention, all cellulose-based layers are made from the same cellulose-based material. This has the advantage that the resulting packaging material will be very homogeneous.

In another embodiment of the present invention, the barrier paper layers are made from one cellulose-based material and the cardboard-based layer is made from a different cellulose-based material. This has the advantage that the cellulose-based material of the barrier paper layers can be selected to provide good barrier properties, while the cellulose-based material of the cardboard-based layer can be selected to provide good water vapour absorption properties. Accordingly, the at least one cardboard-based layer can function as moisture storage buffer, scavenging all moisture that is able to pass one barrier paper layer during a certain period of time.

Consequently, in the cellulose-based multilayer packaging material in accordance with the present invention, at least one of the cellulose-based layers may be made at least in part from a cellulose-based material selected from the group consisting of, mechanical pulp, recycled paper pulp, bagasse pulp, annual plant pulp, virgin cellulose pulp, refined cellulose pulp, or combinations thereof.

One advantage of the packaging material of the present invention is that it allows to provide very strong moisture barriers for extended periods of time. The inventors were able to produce prototypes providing a water vapour transmission rate (WVTR) of less than 0.05 g/m ² /day for at least 60 days and of less than 0.1 g/m ² /day as stable value. Hence, in one embodiment of the present invention, in the cellulose- based multilayer packaging material in accordance with the present invention the packaging material may have a water vapour transmission rate (WVTR) at 23°C/85% RH of less than 0.2 g/m ² /day, of less than 0.15 g/m ² /day, or of less than 0.1 g/m ² /day for at least 120 days. In the same or an alternative embodiment of the present invention, in the cellulose-based multilayer packaging material in accordance with the present invention the packaging material may have a water vapour transmission rate (WVTR) at 23°C/85% RH of less than 0.5 g/m ² /day, of less than 0.4 g/m ² /day, or of less than 0.3 g/m ² /day as a stable value.

As discussed above, the excellent moisture barrier properties of the packaging material of the present invention allow that the packaging material of the present invention can be used to package wet or moist products and/or can be used to protect products from high moisture environments. Accordingly, the cellulose- based multilayer packaging material in accordance with the present invention may be for use as a food packaging material, as a pet food packaging material, or as a packaging material for nutritional supplements or pharmaceutical products.

The cellulose-based multilayer packaging material in accordance with the present invention may be selected from the group consisting of primary packaging, secondary packaging and tertiary packaging. A primary packaging for a food product may be a packaging for a food product that is in direct contact with the actual food product. A secondary packaging for a food product may be a packaging for a food product that helps secure one or more food products contained in a primary packaging. A secondary packaging is typically used when multiple food products are provided to consumers in a single container. A tertiary packaging for a food product may be a packaging for a food product that helps secure one or more food products contained in a primary packaging and/or in a primary and secondary packaging during transport. In one embodiment of the present invention, the cellulose-based multilayer packaging material is biodegradable and/or compostable. Biodegradable materials can be decomposed by the action of living organisms, usually microbes, into water, carbon dioxide, and biomass. According to the European Commission, for example, biodegradability is the capability of being degraded by biological activity, Pure Applied Chemistry 84 (2), pp. 377-410. The capability of the compostable material to be converted into CO2 under the action of micro-organisms can be measured with a laboratory standard test method: the EN 14046 (also published as ISO 14855: biodegradability under controlled composting conditions). In order to show complete biodegradability, a biodegradation level of at least 90% must be reached in less than 6 months.

The present invention further relates to a method of manufacturing a cellulose-based multilayer packaging material in accordance with one of the preceding claims comprising the steps of providing a cardboard-based layer, distributing a glue on one side of the cardboard-based layer, applying a barrier paper layer on top of the glue on the cardboard-based layer by means of roller coating, distributing glue on the other side of the cardboard-based layer, and applying another barrier paper layer on top of the glue on the cardboardbased layer by means of roller coating yielding the cellulose-based multilayer packaging material.

Notably, the glue may be applied sequentially first to one and then to the other side of the cardboard layer, or simultaneously to both sides of the cardboard-based layer. Similarly, the barrier paper layers may be applied sequentially first to one and then to the other side of the cardboard-based layer or simultaneously to both sides of the cardboard-based layer. The method of the present invention may further comprise a drying step to dry the cellulose-based multilayer packaging material. The drying step can be carried out by air drying, heat drying or a combination of both, for example.

Those skilled in the art will understand that they can freely combine all features of the present invention disclosed herein. In particular, features described for the product of the present invention may be combined with the method 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.

Examples:

The following tests have been performed.

Materials:

Barrier paper: The barrier paper used for this study is a 81 g/m ² paper coated with a PVdC (polyvinylidene chloride) suspension coating providing a barrier. The paperboard used for this study is a 340 g/m ² , 3-layered sandwich of bleached chemi-thermomechanical pulp, coated on both sides with bleached chemical pulp.

The glue used to prepare the multilayer materials was a starch-based glue. The glue was prepared according to the supplier's recommendation, i.e. one volume of glue powder to 9 volumes of water. The mix was thoroughly mixed and used immediately.

Multilayer preparation

A thin layer of glue was applied on one side of an A4 sheet of paperboard. A sheet of same size of the barrier paper (barrier layer facing the outside of the structure) was placed on the glued size taking care to avoid air bubbles. The sample was then passed three times in a laboratory laminator with a roller spacing adequately set for the sample. The same procedure was then applied on the other side of the paper board.

To avoid excessive curling, the bi-layer material was not allowed to dry between the two deposition processes.

Once both layers were applied, the multilayer was left to dry for at least 72 hours at room temperature (approximately 23 °C and 30 % Relative humidity). Figure 1 schematizes the obtained structure.

Methods

All samples were conditioned at 23 °C and 50 % relative humidity prior to any testing.

WVTR measurement

The water vapor transmission rate was determined gravimetrically by applying ISO 2528 (2017). Samples were sealed at room temperature on dishes containing silica gel (Silica gel with indicator (orange gel, Supelco, Darmstadt, Germany) using a mix of wax (60 % w/w, Sasolwax 7835, Sasol Wax GmbH, Hamburg, Germany) and paraffin (40% w/w, Parrafin Wax, Sigma Aldrich, Darmstadt, Germany). The exposed surface area was 50 cm2. Figure 2 depicts a scheme of the setup.

A sample prepared identically but containing no silica gel was used as blank, to compensate for moisture uptake by the sample itself and buoyancy effects linked to atmospheric pressure changes.

The samples were stored in climatic cabinets set at 23 °C and 85 % relative humidity.

The samples were weighed to a 1 mg precision (Precision scale, PG 2035, Mettler Toledo, Greifensee Switzerland) at regular intervals for 146 days. The weighing intervals were 1-4 days during the first 2 weeks and up to 10 days for the rest of the test duration. The samples were taken out of the climatic cabinet approximately 15 minutes before weighing and were reintroduced directly after.

The water vapor transmission rate (WVTR, g/m ² /day) was determined by the slope of the weight uptake versus time curve, corrected for weight changes in the blank specimen, divided by the exposed surface area of paper. In the case of the multilayer material, the value was determined at different periods of time to demonstrate evolution of the value.

Results:

The water vapor transmission rates (WVTR) of the barrier paper was determined as being equal to 0.16 g/m ² /day at 23 °C and 85 % relative humidity.

The WVTR of the paperboard was determined to be higher than 1000 g/m ² /day in the same conditions.

Figure 3 shows the moisture uptake measured on the multilayer samples (average of

4 specimens) corrected with the moisture uptake of the blank specimen. It also shows the theoretical moisture uptake calculated from the value given above. These results clearly shows the buffering/scavenging effect of the paper board.

While hardly no moisture uptake is observed in the first weeks of the test, it then slowly accelerates until reaching a slope similar to that of the theoretical moisture uptake.

This is further observable in Figure 4 where the calculated WVTR of this multilayer cellulosic structure reaches a stable and extremely low value (0.08 g/m ² /day at 23 °C and 85 % relative humidity) after approximately 120 days. The shift in moisture uptake curves suggests that, with this specific multilayer material, a specific moisture content is reached approximately 50 days later than predicted without considering the buffer effect.

The shelf life of a food product packed using such a structure could therefore be increased by approximately 1.5 months.