Method for improving the airtightness of buildings using a biopolymer-based membrane

Abstract

The invention relates to a method for improving the airtightness of a building or a room in a building, involving applying a vapor barrier membrane to the inner face of the walls of the building or the room in a building, characterized in that the vapor barrier membrane is a humidity-regulating membrane having an active portion which comprises: - a first layer that has a thickness of 2 μm to 200 μm and consists of a biopolymer having a water vapor permeability coefficient P1 which increases with the average relative humidity and which, determined at 23°C and at an average relative humidity of 25.5%, is at least equal to 300 Barrers; and, on only one of the two faces of the first layer, preferably in contact therewith, - a second layer that has a thickness of 100 nm to 20 μm and consists of a synthetic organic polymer having a water vapor permeability coefficient P2, determined at 23°C and at an average relative humidity of 25.5%, of no more than 250 Barrers.

Description

[0001] Description

[0002] Title: Process for improving the airtightness of buildings using a biopolymer-based membrane

[0003] The present invention relates to a method for improving the airtightness of buildings or building parts using a vapor barrier membrane, comprising a hydrophilic biopolymer-based layer and an adjacent layer relatively more hydrophobic than the biopolymer-based layer.

[0004] Hygro-regulating or hygro-regulating vapour barrier membranes have been known for many years, the permeability of which to water vapour varies according to the humidity of the air. For the reasons explained for example in application WO96 / 33321, the aim is to obtain membranes which allow water vapour to pass easily when the relative humidity (RH) is high (70% to 100% RH) and which effectively block it at low relative humidity (50% RH and below).

[0005] Such membranes, when placed on the inner side of a thermal insulation material (side facing the inside of a building or room), prevent as much as possible during the cold and dry season water vapor from penetrating from inside the building into the space between the membrane and the wall and condensing on the latter (cold wall). Conversely, in the warm season, the high permeability of the membrane allows any moisture present in the structural elements of the building to escape into the interior of the building. This property is particularly important in the case of new constructions where, during installation, some elements may have a very high water content due to storage conditions, but also in the case of water infiltration into existing structures.In both cases, it is important to be able to allow the entire structure to dry effectively in summer, both towards the exterior and interior of the building. This need is crucial, especially if the elements making up the system are conducive to the proliferation of microorganisms.

[0006] Such vapor barrier membranes having differentiated behavior depending on the relative humidity conditions surrounding them are frequently referred to as "smart vapor retarder (SVR)". In the present application the adjectives "hygroregulator", "hygroregulating" and "smart" are used as synonyms when describing the variation of the water vapor permeability of the vapor barrier membranes.

[0007] It is common to express the water vapor permeability of a membrane in terms of the "equivalent air thickness" for water vapor diffusion (Sd). This thickness is expressed in meters and corresponds to the thickness of the air layer that would provide equivalent resistance to water vapor diffusion. Therefore, the greater the equivalent air thickness, the less permeable the membrane is to water vapor. The equivalent air thickness (Sd) can be determined in accordance with EN1931 and EN ISO12572.

[0008] A hygro-regulating vapor barrier membrane is generally considered to be all the more interesting and efficient the higher its equivalent air thickness is at low relative humidity and the lower it is at high relative humidity.

[0009] The hygro-regulating vapor barrier membranes available on the market and described in the state of the art are generally based on synthetic organic polymers manufactured from petroleum-based monomers.

[0010] The most frequently described and used polymers are polyamides, including polycaprolactam, polyvinyl alcohol (PVOH), copolymers of ethylene and vinyl acetate and / or vinyl alcohol (EVA and EVOH). The most hydrophilic polymers (PVOH, EVOH) can be combined, in multi-layer structures, with thin, more hydrophobic layers, particularly based on polyolefins, such as polyethylene, polypropylene and copolymers of ethylene and propylene.

[0011] Examples of documents describing such "smart" vapor barrier membranes include W02007 / 010388, W02006 / 034381, W02005 / 110892, US7008890, US 6808772 and US 6878455.

[0012] The research that led to the present invention aimed to replace the hygro-regulating vapor barrier membranes of the state of the art based on petro-sourced polymers, generally non-biodegradable, with hygro-regulating vapor barrier membranes based on bio-sourced and / or biodegradable polymers. These bio-sourced and / or biodegradable polymers will hereinafter be referred to as “biopolymers”. The biopolymers are preferably bio-sourced, i.e. based on materials of biological origin that are renewable in the short term. In a particularly preferred embodiment, the biopolymers used in the membranes of the present application are both bio-sourced and biodegradable.

[0013] Bio-sourced biopolymers include both natural organic polymers, present as such in biomass, organic polymers obtained by physical and / or chemical modification of these natural polymers, and synthetic organic polymers obtained by polymerization of bio-sourced ingredients.

[0014] Membranes based on such biopolymers, for example based on cellulose, chitosan or poly(3-hydroxybutyrate) (PHB) are known and have been used, replacing films based on petroleum-based synthetic polymers, particularly in the field of food packaging where membranes are generally required to have water vapor permeability relatively independent of humidity and temperature conditions. Furthermore, in the field of food packaging, the lifespan of packaging films is quite limited and generally ranges from a few days to a few weeks, at most a few months. In the field of vapor barrier membranes, on the contrary, a long lifespan of at least several years, or even several decades, is sought.

[0015] Biopolymer-based membranes are usually quite hydrophilic and have a high water vapor permeability. The equivalent air thickness of these membranes is generally less than 1 m and its absolute value varies only slightly with the relative humidity of the surrounding atmosphere. These membranes therefore remain extremely permeable to water vapor regardless of the surrounding conditions.

[0016] Without wishing to be bound by any theory, it is believed that the low variation in water vapor permeability of these fairly hydrophilic membranes can be attributed to the plasticizing effect of water, which "dissolves" in the membrane, even at low humidity. The higher the ambient humidity, the more the membrane material is plasticized by water and the easier it is for water molecules to diffuse within the membrane.

[0017] The main disadvantage of these biopolymer membranes, with a view to their possible use as hygroregulating vapor barriers, is therefore that their permeability to water vapor remains generally too high at low relative humidity for them to function satisfactorily during the cold and dry season. A membrane made solely of cellulose would therefore not form a sufficient barrier to water vapor coming from inside the building and would not effectively prevent water vapor from penetrating the space between the membrane and the wall and from condensing in the insulating material and on the internal face of the external wall.

[0018] In summary, hydrophilic biopolymer-based membranes used in the food packaging sector remain too permeable to water vapor in conditions of low relative humidity (cold season). They are therefore not "intelligent" enough to be able to function properly as vapor barriers in the field of thermal insulation of buildings, particularly in improving airtightness and managing water vapor flows in buildings.

[0019] The present invention is based on the surprising discovery that it is possible to very significantly increase the "intelligence" of biopolymer-based membranes and thus make them compatible with use as vapor barrier membranes in the building sector, by applying to only one of their two faces a very thin layer of hydrophobic polymer, which is very poorly permeable to water vapor.

[0020] This discovery was all the more surprising since the hydrophobic polymers deposited on both sides of the biopolymer membrane have a permeability to water vapor that is independent of the ambient relative humidity. In other words, membranes made solely of these hydrophobic polymers would have no hygroregulating properties. It was therefore impossible to predict that the deposition of these same hydrophobic polymers on one of the two sides of a membrane made of hydrophilic biopolymer(s) would dramatically increase the latter's intelligence by allowing it to be extremely low permeability to water vapor during the dry season and very permeable to water vapor during the wet season.

[0021] The Applicant recently filed an international application PCT / FR2022 / 050009 claiming a French priority of January 7, 2021 and not yet published at the time of filing of the present application. This application relates to a method for improving the airtightness of a building or a room in a building using a hygroregulating vapor barrier membrane comprising at least three layers, namely a middle layer consisting of a biopolymer having a relatively high water vapor permeability coefficient Pi and, on either side of the middle layer, two outer layers of an organic polymer having a water vapor permeability coefficient P2, lower than Pi.

[0022] In continuing its research in this field, the Applicant recently discovered, with surprise, that it was not at all necessary to apply a thin hydrophobic layer on each of the two faces of the hydrophilic middle layer, but that it was sufficient to apply a thin hydrophobic layer on only one of the two faces of a hydrophilic biopolymer membrane to dramatically improve its hygroregulating power.

[0023] The present application thus relates to a method for improving the airtightness of a building or a room in a building comprising the application of a vapour barrier membrane to the internal face of the walls of said building or said room in a building, characterized in that the vapour barrier membrane is a hygroregulating membrane comprising an active part comprising

[0024] - a first layer with a thickness of between 2 pm and 200 pm, preferably between 4 pm and 100 pm, made of a biopolymer having a water vapour permeability coefficient Pi which increases with the average relative humidity and which, when determined at 23°C and at an average relative humidity of 25.5%, is at least equal to 300 Barrers, and, on only one of the two faces of the first layer, preferably in contact with it,

[0025] - a second layer with a thickness of between 100 nm and 20 pm, preferably between 200 nm and 2.5 pm, consisting of a synthetic organic polymer having a water vapor permeability coefficient P2, determined at 23°C and at an average relative humidity of 25.5%, at most equal to 250 Barrers, preferably between 0.05 and 100 Barrers, in particular between 1.0 and 20 Barrers. The application also relates to such a hygroregulating membrane with an active part comprising

[0026] - a first layer with a thickness of between 2 pm and 200 pm made of a biopolymer having a water vapour permeability coefficient Pi which increases with the average relative humidity and which, when determined at 23°C and at an average relative humidity of 25.5%, is at least equal to 300 Barrers, and, on only one of the two faces of the first layer, preferably in contact with it,

[0027] - a second layer with a thickness of between 100 nm and 20 pm, consisting of a synthetic organic polymer having a water vapor permeability coefficient P2, determined at 23°C and at an average relative humidity of 25.5%, at most equal to 250 Barrers, preferably between 0.05 and 100 Barrers, in particular between 1.0 and 20 Barrers. The active part of the membrane is preferably a two-layer structure consisting of the first layer of biopolymer and the second layer of synthetic organic polymer, these layers being as defined above.

[0028] The first layer of biopolymer and the second layer of synthetic organic polymer are, of course, continuous, non-perforated layers. They are therefore impermeable to fluids, whether liquid or gaseous.

[0029] The second layer made of a synthetic organic polymer advantageously has a thickness:

[0030] - greater than or equal to 0.8 pm, greater than or equal to 0.9 pm, greater than or equal to 1.0 pm, and / or

[0031] - less than or equal to 20 pm, less than or equal to 10 pm, less than or equal to 5 pm, less than or equal to 2.5 pm.

[0032] The permeability coefficients Pi and P2 are those of the polymers forming the first and second layers respectively. They correspond to the ratio of the mass flow of water vapor (Q) which crosses a zone (A) of a membrane of the polymer to be tested having a given thickness (E), under the effect of a difference in water vapor pressure (dP) existing on either side of the membrane.

[0033] P = (Q x E) / (A x dP) They are determined according to the experimental protocol described in detail below and are expressed in "Barrer", that is to say that the mass flux Q is expressed in cm 3(normal pressure and temperature) per second, the thickness E is expressed in cm, the area A of the zone crossed is expressed in cm 2 , and the water vapor pressure difference (dP) is expressed in cm Hg (see in particular SA Stern, Journal of Polymer Science: Part A-2, vol. 6 (1968), pages 1933-1934).

[0034] The membrane of the present invention therefore comprises a relatively thick layer based on a hydrophilic biopolymer (first layer), coated on only one of its two faces with a continuous layer of a hydrophobic polymer (second layer of synthetic organic polymer).

[0035] The second layer of synthetic organic polymer generally has a thickness less than that of the first layer of biopolymer. The ratio of the thickness of the first layer to the thickness of the second layer is advantageously between 1.5 / 1 and 1000 / 1, preferably between 2 / 1 and 500 / 1, in particular between 3 / 1 and 200 / 1.

[0036] The second layer of synthetic organic polymer is preferably in direct contact with the first layer of biopolymer, i.e. the interface between the layers is preferably free of adhesive.

[0037] In the less preferred case where the second layer is fixed to the first layer by means of an adhesive, the latter would preferably have a permeability coefficient P3 greater than Pi and P2. In other words, the adhesive should not oppose a resistance to the diffusion of water vapor greater than that of each of the layers constituting the membrane.

[0038] The layers defined above form the "active part" of the membranes of the present invention. This part is preferably a membrane obtained in a known manner by co-extrusion of thermoplastic polymers forming the different layers, by heat-bonding a film (second layer of synthetic organic polymer) on the biopolymer layer, or by depositing a coating on only one of the two faces of the first biopolymer layer.

[0039] Although the active part in principle has a mechanical strength allowing it to be used alone, i.e. without a support layer, it may be advantageous, in particular for active layers of low thickness (less than 50 μm), to reinforce it with a mechanical structure permeable to air and whose resistance to the diffusion of water vapor is therefore negligible compared to that of the active layer, impermeable to air.

[0040] In an advantageous embodiment, the vapor barrier membrane therefore further comprises an air-permeable reinforcing or protective layer, directly in contact with the active part, i.e. with one of the two layers constituting the active part. This support layer may be a grid, a perforated plate, an open-porosity foam or an air-permeable woven or non-woven textile. It is preferably an air-permeable textile, preferably a non-woven. Examples of particularly preferred support layers include non-woven fabrics made of polypropylene or polyester fibers or glass fibers. The support layer(s) are preferably fixed to the active membrane, or active layer, by bonding using a polyurethane adhesive.The present invention also encompasses membranes where a reinforcing structure, such as a grid or a non-woven fabric, is incorporated into the active portion of the membrane and more particularly into the first biopolymer layer or between the first biopolymer layer and the second synthetic organic polymer layer.

[0041] The water vapor permeability coefficient P2 of the organic polymer constituting the second, hydrophobic layer does not vary significantly with the average relative humidity. The ratio P2wet / P2dry is generally between 1.0 and 1.10, preferably between 1.0 and 1.05.

[0042] As explained in the introduction, the biopolymers forming the first layer are bio-sourced and / or biodegradable organic polymers. They are preferably bio-sourced.

[0043] Bio-sourced biopolymers are preferably chosen from the group consisting of

[0044] - osides,

[0045] - proteins and

[0046] - synthetic polymers obtained from bio-sourced monomers. Osides include heterosides whose hydrolysis produces oses and non-carbohydrate compounds and holosides which are polymers exclusively of oses.

[0047] Examples of osides that can be used to form the first biopolymer layer of the vapor barrier membrane of the present invention include those chosen from the group consisting of alginate, carrageenan, cellulose, in particular regenerated cellulose (cellulose hydrate), chitin, chitosan, pectin, dextrin, starch, curdlan, FucoPol, gellan gum, pullulan and xanthan.

[0048] Proteins are advantageously chosen from the group consisting of gluten, soy protein isolate, zein, whey protein, casein, collagen and gelatin.

[0049] Most of these bio-based polymers, extracted from biomass, have a high affinity for water and dissolve or swell in water to form hydrogels.

[0050] It may therefore be interesting, or even necessary, to modify them chemically in order to reduce their hydrophilic character, in particular to crosslink them in order to make them insoluble in water.

[0051] Examples of chemically modified bio-sourced biopolymers include cellulose esters, in particular cellulose acetate, cellulose ethers (in particular ethylcellulose, hydroxyethylcellulose), nitrocellulose, starch esters and ethers.

[0052] The third category of bio-sourced biopolymers is formed by polymers synthesized from bio-sourced monomers.

[0053] These polymers can be linear or branched, and therefore thermoplastic, or thermoset.

[0054] Examples of synthetic polymers obtained from bio-sourced monomers include those selected from the group consisting of polyhydroxyalkanoates (PHAs), in particular polyhydroxybutyrate (PHB) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactide-co-glycolide) (PLGA), polymers obtained by polymerization of lipid monomers, and thermoset polymers obtained by reaction of monosaccharides, disaccharides, oligosaccharides and / or alditols with a polycarboxylic acid and / or a polyaldehyde.

[0055] Thermoset polymers obtained by reaction of monosaccharides, disaccharides, oligosaccharides and / or alditols with a polycarboxylic acid and / or a polyaldehyde are well known in the field of binders for mineral wools and are described in detail for example in international applications WO2009 / 080938, WO2010 / 029266, WO2013 / 014399,

[0056] WO201 3 / 021112 and WO2015 / 132518 in the name of the Applicant.

[0057] As explained in the introduction, it is also possible to use polymers of petrochemical origin to form the first biopolymer layer of the membranes of the present invention provided that they are biodegradable within the meaning of standard NF EN 13432.

[0058] The biodegradable biopolymers may advantageously be selected from the group consisting of homopolymeric aliphatic polyesters such as poly(caprolactone) (PCL) and poly(butylene succinate) (PBS), aliphatic copolyesters such as poly(butylene succinate-co-adipate), aromatic copolyesters such as poly(butylene adipate-co-terephthalate) (PBAT) and polyesteramides.

[0059] All biopolymers constituting the first biopolymer layer have a permeability coefficient Pi, determined at 23°C in dry conditions (approximately 25% average relative humidity), greater than or equal to 300 Barrers, preferably between 300 and 50,000 Barrers, in particular between 400 and 30,000 Barrers, and ideally between 500 and 20,000 Barrers.

[0060] This permeability coefficient is determined as follows:

[0061] Five samples of the same membrane thickness (E) are sealed using a jointing product above test cups containing a desiccant (CaCl2 powder imposing a relative humidity in the cup of approximately 1%). A template is placed on the surface of the films prior to the application of the jointing product, in order to create an exchange zone, free of any jointing product and of a defined area (A). Different jointing products can be used. The jointing product is, for example, a mixture of 60% microcrystalline wax and 40% refined crystalline paraffin. The cups thus produced are placed in a test chamber regulated in temperature (23 °C) and relative humidity (50%), also called a climatic chamber.

[0062] Due to the difference in partial vapor pressure (dP) prevailing inside the test cups and in the chamber, water vapor migrates through the exchange zone of the membranes. Periodic weighing of the cups is carried out in order to determine the water vapor transmission rates (Q) in steady state, then, by calculation, the water vapor permeability coefficient of the films considered, expressed in Barrer. The average of the permeabilities measured on the different assemblies is then calculated and corresponds to the aforementioned permeability coefficient Pi.

[0063] The first hydrophilic layer of the vapor barrier membrane of the present invention is covered on only one of its two faces with a continuous layer of an organic polymer that is more hydrophobic and less permeable to water vapor than the first biopolymer layer. The term "continuous" here means that the second layer completely covers said face of the first biopolymer layer so that this face is not in contact with the atmosphere. Of course, the other face of the first biopolymer layer, not covered by the second layer, is in contact with the surrounding atmosphere.

[0064] The permeability coefficient P2 of the second layer of synthetic organic polymer is at most equal to 250 Barrers, preferably between 0.05 and 100 Barrers, in particular between 1.0 and 20 Barrers. The permeability coefficient is determined in the same way as the coefficient Pi.

[0065] The organic polymer constituting the second layer is advantageously chosen from the group consisting of polypropylene, polyethylene, poly(ethylene-co-propylene), homopolymers and copolymers of vinyl monomers chosen from vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, tetrafluoroethylene and acrylonitrile.

[0066] A vapor barrier membrane with a first layer consisting of cellulose, in particular regenerated cellulose, and a second layer consisting of polyethylene, polypropylene, an ethylene-propylene copolymer or polyvinylidene chloride, preferably polyvinylidene chloride, is a particularly preferred embodiment of the vapor barrier membrane used in the method of the present invention.

[0067] The active part of the vapor barrier membrane used in the method of the present invention advantageously has a thickness of between 5.0 pm and 240 pm, preferably between 10 pm and 120 pm, in particular between 15 and 80 pm, these values ​​corresponding to the active part (bilayer) of the membrane but do not include a possible reinforcing and / or protective structure.

[0068] The vapor barrier membrane is applied in the form of several strips (or lengths). These strips have a width greater than or equal to 0.5 m, preferably greater than or equal to 1 m. The length of the strips depends on the height of the walls to be insulated. The length is greater than 0.5 m, preferably greater than 1.0 m or greater than 2 m. The membrane strips located side by side overlap along their length. The overlap is at least 2 cm, preferably at least 5 cm, or even at least 8 cm or 10 cm.

[0069] Preferably, areas of overlap, opening or penetration are sealed. This can be done with tape or mastic.

[0070] Preferably, the wall or partition of the room or the wall of the building whose airtightness is to be improved is insulated, i.e. covered, with a thermal insulating material. The vapor barrier membrane is:

[0071] - fixed on the thermal insulating material or

[0072] - incorporated into the thermal insulating material.

[0073] In one embodiment of the method for improving the airtightness of a building or a room of a building,

[0074] - an insulating material is applied, preferably in the form of juxtaposed insulating elements, to the internal face of the walls of said building or said room of a building, then

[0075] - the vapor barrier membrane is applied to the internal face of the wall covered with thermal insulation material, i.e. on the internal face of the insulating material.

[0076] The inner face is the face facing the interior of a building or room

[0077] In this embodiment, the membrane is fixed to the insulating material comprising several insulating elements. The dimensions of the elements of the insulating material are different from those of the membrane. This is how the membrane improves the building's watertightness.

[0078] The vapor barrier membrane of the present invention is in an internal position relative to the thermal insulation material, preferably in direct contact with it. The fixing can be done by any suitable means which does not significantly affect the airtightness of the membrane. It can be done for example by gluing, stapling or by means of a mechanical fixing system using textile hooks and loops (in English hook and loop fastener) of the scratch / Velcro® type.

[0079] In another embodiment of the method of the present invention, the vapor barrier membrane is integrated into the insulation material and attached to the wall of the room or building at the same time as the latter. The membrane is then oriented parallel to the two main surfaces of the insulation material and is preferably located closer to the main surface facing the interior of the room or building than to the main surface facing the wall.

[0080] The thermal insulation material can be any insulating material that is permeable to water vapor and includes foams and fiber-based materials. It is preferably made of mineral fibers (mineral wool) or natural organic fibers (lignocellulosic fibers, cellulose wadding, animal wool), synthetic (polyester fibers) or artificial. It is preferably mineral wool.

[0081] Examples

[0082] A cellulose / PVDC bilayer membrane was produced by wet deposition of a PVDC latex (Diofan® B204, Solvay) onto a 23 μm cellulose film (NatureFlex® 23NP, UL Prospector). The deposition of this latex was carried out using a bar coater imposing a wet thickness of 4 μm. After drying, the thickness of the PVDC film is approximately 1.5 μm.

[0083] This cellulose / PVDC bilayer structure according to the invention was subjected to an evaluation of its permeability to water vapor in humid and dry conditions, in comparison with 3 membranes of the state of the art.

[0084] For this purpose, each membrane was positioned to close an aluminum cup using as a sealant molten paraffin wax (mixture of 60% microcrystalline wax and 40% refined crystalline paraffin) to ensure a seal. To measure the water vapor permeability in dry conditions, calcium chloride was introduced into the cup before sealing it with the membrane in order to impose a relative humidity of approximately 1% inside. The cup / membrane assembly was then introduced into a climatic chamber in which the relative humidity was set at 50% and the temperature at 23°C, so as to create a difference in water vapor pressure (dP) on either side of the membrane.By weighing the cups over time, the flow of water vapor (Q) passing through the zone (A) of the membrane of thickness (E) is determined and the permeability coefficient (expressed in Barrers) is calculated according to the formula.

[0085] P = (Q x E) / (A x dP)

[0086] The permeability coefficient Pi thus calculated corresponds to an average relative humidity of 25.5% ((1%+50%) / 2).

[0087] To measure water vapour permeability in humid conditions (90% average relative humidity), the procedure is similar, except that liquid water is introduced into the cup to set the relative humidity at 100%, and the relative humidity in the climatic chamber is set at 80%.

[0088] The equivalent air thickness (Sd) is also determined for each membrane in accordance with EN ISO12572.

[0089] The first membrane is a vapor barrier membrane according to the invention. It consists of a first cellulose layer with a thickness of 23.5 μm covered on one of its faces with a layer of polyvinylidene chloride (PVDC) with a thickness of 1.5 μm. The permeability coefficient Pi of the first cellulose layer is 5600 Barrers at a relative humidity of 25.5% (23 °C) and 34600 Barrers at a relative humidity of 90% (23 °C); the permeability coefficient P2 of the PVDC layer is 5 Barrers (23 °C). It does not vary as a function of the relative humidity.

[0090] For this two-layer membrane according to the invention, the equivalent air thickness is determined for the two possible orientations, namely a first orientation where the PVDC layer is facing and in contact with the dry atmosphere, and a second orientation where the PVDC layer is facing and in contact with the humid atmosphere.

[0091] The second membrane (comparative membrane) is the one used to manufacture the membrane according to the invention. It is made solely of cellulose which has the same permeability coefficient Pi as the first layer of the membrane according to the invention. Its thickness is 23.5 μm.

[0092] The third membrane (comparative membrane) is a membrane formed from a single active layer of polyamide 6 with a thickness of 40 µm fixed on a polypropylene non-woven fabric. It is available on the market under the name Vario KM Duplex® (Saint-Gobain Isover)

[0093] The fourth membrane (comparative membrane) is a three-layer membrane according to the state of the art, with an active part consisting of a middle layer of ethylene and vinyl alcohol copolymer (EVOH) sandwiched between two layers of polyamide 6, fixed on a polypropylene non-woven fabric. This membrane is available on the market under the name Vario Xtra® (Saint-Gobain Isover).

[0094] The technical characteristics of the four membranes (layer composition, thickness, equivalent air thickness in dry and humid conditions, orientation for the asymmetric membrane) are listed in Table 1 below.

[0095] [Table 1] The hygroregulatory behavior of the cellulose / PVDC bilayer membrane according to the invention is very interesting since a large difference in Sd is observed.

[0096] Compared to the performance of the Vario® KM Duplex membrane, we can see that the two-layer assembly considered here has much higher Sd values ​​in dry conditions and much lower values ​​in humid conditions (100-80% RH). Thus, the intelligent behavior of this two-layer film is much more pronounced than that of this commercial membrane.

[0097] The cellulose / PVDC two-layer membrane according to the invention has lower Sd values ​​in dry and wet conditions than the Vario® Xtra membrane. Thus, the membrane produced certainly blocks water vapor a little less in winter (low relative humidity) but allows more water vapor to circulate in summer (high relative humidity), which is particularly interesting for ensuring good drying in summer.

[0098] Furthermore, if we compare the active films of these three membranes we can note that the overall quantity of polymer used is lower in the case of the cellulose / PVDC membrane (24.5 pm compared to 40 pm of PA6 active film for the Vario® KM Duplex and 30 pm of PA6 / EVOH / PA6 for the Vario® Xtra). The environmental impact of this cellulose / PVDC membrane is thus better than that of the active films of current commercial membranes which, moreover, are made only of non-biodegradable organic polymers.

Claims

DEMANDS 1. A method for improving the airtightness of a building or a room in a building comprising the application of a vapor barrier membrane to the internal face of the walls of said building or room in a building, characterized in that the vapor barrier membrane is a hygro-regulating membrane with an active part comprising - a first layer with a thickness between 2 pm and 200 pm, preferably between 4 pm and 100 pm, made of a biopolymer having a water vapor permeability coefficient Pi which increases with average relative humidity and which, when determined at 23 °C and an average relative humidity of 25.5%, is at least equal to 300 Barrers, and, on only one of the two faces of the first layer, preferably in contact with it, - a second layer with a thickness between 100 nm and 20 pm, preferably between 200 nm and 2.5 pm, made of a synthetic organic polymer having a water vapor permeability coefficient P2, determined at 23 °C and at an average relative humidity of 25.5%, not more than 250 Barrers, preferably between 0.05 and 100 Barrers, in particular between 1.0 and 20 Barrers.

2. A method according to claim 1, characterized in that the active part of the membrane consists of the first layer in biopolymer and the second layer in synthetic organic polymer.

3. A method according to claim 1 or 2, characterized in that the water vapor permeability coefficient P2 of the synthetic organic polymer constituting the second layer does not vary significantly with the average relative humidity.

4. A process according to any one of claims 1-3, characterized in that the biopolymer is a bio-based biopolymer selected from the group consisting of glycosides, proteins and synthetic polymers obtained from bio-based monomers.

5. A method according to claim 4, characterized in that the glycosides are selected from the group consisting of alginate, carrageenan, cellulose, and particular regenerated cellulose, chitin, chitosan, pectin, dextrin, starch, curdlane, FucoPol, gellan gum, pullulan and xanthan gum.

6. A method according to claim 4, characterized in that the proteins are selected from the group consisting of gluten, soy protein isolate, zein, whey proteins, casein, collagen and gelatin.

7. A process according to claim 5 or 6, characterized in that the glycosides and proteins are chemically modified.

8. A process according to claim 4, characterized in that the synthetic polymers obtained from bio-based monomers are selected from the group consisting of polyhydroxyalkanoates (PHA), poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactide-co-glycolide) (PLGA), polymers obtained by polymerization of lipid monomers, thermoset polymers obtained by reaction of monosaccharides, disaccharides, oligosaccharides and / or alditols with a polycarboxylic acid and / or a polyaldehyde.

9. A process according to any one of claims 1-3, characterized in that the biopolymers are biodegradable polymers selected from the group consisting of aliphatic polyesters, aliphatic copolyesters, aromatic copolyesters and polyesteramides.

10. A process according to claim 9, characterized in that the biodegradable biopolymers are selected from the group consisting of poly(caprolactone) (PCL), poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) and poly(butylene adipate-co-terephthalate) (PBAT).

11. A method according to any one of the preceding claims, characterized in that the synthetic organic polymer constituting the second layer has a thickness between 0.9 pm and 20 pm.

12. A method according to any one of the preceding claims, characterized in that the synthetic organic polymer constituting the second layer is selected from the group consisting of polypropylene, polyethylene, poly(ethylene-co-propylene), homopolymers and copolymers of vinyl monomers selected from vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, tetrafluoroethylene and acrylonitrile.

13. A method according to any one of claims 1-5, characterized in that the first layer is made of cellulose and the second layer is made of polyethylene, polypropylene, an ethylene-propylene copolymer or poly(vinylidene chloride), preferably poly(vinylidene chloride).

14. A method according to any one of the preceding claims, characterized in that the active part of the membrane has a thickness between 5.0 pm and 240 pm, preferably between 10 pm and 120 pm.

15. A method according to any one of the preceding claims, characterized in that the vapor barrier membrane further comprises a reinforcing or protective layer which is in contact with the first or second layer of the active part of the membrane.

16. A method according to any one of the preceding claims, characterized in that the vapor barrier membrane is applied to the wall in the form of several strips having a width greater than or equal to 0.5 m and a length greater than 0.5 m.

17. Method according to the preceding claim, characterized in that the membrane strips located side by side overlap along their length with an overlap of at least 2 cm.

18. A method according to any one of the preceding claims, characterized in that: - a thermal insulating material, preferably in the form of juxtaposed insulating elements, is applied to the inner face of the walls of said building or of said room of a building, then - the vapor barrier membrane is applied to the inner face of the wall covered with the thermal insulation material.

19. Method according to claim 18, characterized in that the thermal insulating material is made of mineral or organic, natural, synthetic or artificial fibers.

20. Hygroregulating membrane with an active part comprising - a first layer with a thickness between 2 µm and 200 µm made of a biopolymer having a water vapor permeability coefficient Pi that increases with average relative humidity and which, when it determined at 23 °C and at an average relative humidity of 25.5%, is at least equal to 300 Barrers, and, on one of the two faces of the first layer, preferably in contact with it, - a second layer of a thickness between 100 nm and 20 pm, preferably between 0.9 pm and 20 pm, made of a synthetic organic polymer having a water vapor permeability coefficient P2, determined at 23 °C and at an average relative humidity of 25.5%, at most equal to 250 Barrers, preferably between 0.05 and 100 Barrers, in particular between 1.0 and 20 Barrers.

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