Field of the invention

The invention relates to a multilayer substrate for cultivating plants. The multilayer substrate according to the invention is in particular suitable as a substrate for a vertical garden, a green wall, or a green facade.

Moreover, the invention relates to a system comprising a multilayer substrate for cultivating plants.

Background of the invention

Substrates, such as textile structures, for cultivating plants are known in the art.

Over the last couple of years there is an increasing demand for vertical gardens, green walls, and green facades. Vertical gardens, green walls and green facades are particularly important in areas with a limited soil surface, and can contribute extensively to create more green spaces in cities. Vertical gardens, green walls and green facades change the visual aspect of cities from gloomy and grey to lively and green (aesthetical characteristics). They also help to limit the heat-island effect by inhibiting the underlying construction from warming up (thermal characteristics) and have a positive influence on air quality, for example by reducing the amounts of fine dust in the air. Furthermore, they can absorb sound (acoustic characteristics).

Vertical gardens, green walls and green facades refer to both soil-based and non- soil-based systems (Living Wall systems). In soil-based systems plants are placed in natural open soil at the foot of the facade and can then, assisted or not, grow on the wall. Such systems are cheap but have the disadvantage that it takes a long time for a green wall or a green facade to be realised. On top of that, the choice of plants is limited. In non-soil-based systems the plants are not grown in natural open soil, but instead a system is attached to the wall in which the plants can be placed. Such systems can be composed of (pre-cultivated) panels, modules, bags, geotextile, etc. In the case of non-soil-based systems the plants can grow in organic material (for example pot soil or peat moss) or in an (inert) organic or synthetic substrate (for example a substrate consisting of rockwool or a textile substrate). In order to be able to use a large surface of substrate for cultivating plants in vertical applications, it is important for the substrate to have a sufficient mechanical strength and a sufficient water retention capacity, that allows the supply of sufficient amounts of water and air, and that permits to obtain a decent formation of roots.

Known substrates usually have a limited mechanical strength, a high weight, and a high price per square metre, and require a complex production. Known substrates that consist of rockwool present an insufficient mechanical strength and are, in most cases, not suitable for substrates having large surfaces for vertical gardens, green walls or green facades for the simple reason that they are not able to support their own weight.

Vertical systems require a complex and expensive irrigation system to guarantee that the substrate remains sufficiently moist over the complete surface.

US2014/0370238 (Vertical Ecosystem) describes a multilayer substrate for cultivating plants. The multilayer substrate has, however, a limited air permeability and a limited water retention capacity and plant roots can penetrate the substrate only in a limited way.

Therefore, there exists a need for enhanced substrates for cultivating plants.

Summary of the invention

It is an object of the invention to provide a multilayer substrate for cultivating plants.

It is another of the invention to provide a multilayer substrate for cultivating plants with a high water retention capacity, a sufficiently large air permeability, a sufficient penetrability for plant roots, and good mechanical characteristics.

Another object of the invention is to provide a multilayer substrate that can be used as substrate for a vertical garden, a green wall or a green facade.

It is also an object of the invention to provide a system comprising a multilayer substrate for cultivating plants.

A first aspect of the invention provides a multilayer substrate for cultivating plants. The multilayer substrate comprises a carrier and at least a first non-woven structure as well as a second non-woven structure. The first non-woven structure has a higher water retention capacity than the second non-woven structure.

The term "non- woven structure" refers to any type of non- woven structure that is known in the art. A non- woven structure or web is a textile material that is not woven or knitted. It can be produced by depositing fibres or filaments that are subsequently bonded together. The fibres can be oriented but need not necessarily be. The non- woven structure can be barely to very intensively bonded, can be supple or stiff, and can be compacted or not. The non- woven structures can for example be mechanically, chemically or thermally reinforced. A mechanical reinforcement comprises for example felting or needling. A chemical reinforcement comprises for example bonding by means of the use of binding or adhesive agents. A thermal reinforcement comprises for example melting or fusion.

A first group of multilayer substrates comprises multilayer substrates comprising a carrier and at least a first non- woven structure as well as a second non- woven structure, with the first non- woven structure (that is the non- woven structure with the highest water retention capacity) positioned closer to the carrier than the second non- woven structure (that is the non- woven structure with the lowest water retention capacity).

A second group of multilayer substrates comprises multilayer substrates comprising a carrier and at least a first non-woven structure as well as a second non- woven structure, with the first non- woven structure (that is the non- woven structure with the highest water retention capacity) positioned further away from the carrier than the second non-woven structure (that is the non-woven structure with the lowest water retention capacity).

Because the first non-woven structure has a higher water retention capacity than the second non- woven structure, it is primarily the first non- woven structure that retains water and, hence, it is the first non-woven structure that is responsible for keeping the multilayer substrate moist. The first non-woven structure can be positioned closer to the carrier than the second non-woven structure. Such multilayer substrates have the advantage that the moisture is better shielded from possible evaporation. In other embodiments the first non-woven structure is positioned further away from the carrier than the second non-woven structure. Multilayer substrates in which the first non-woven structure is positioned further away from the carrier than the second non- woven structure have as an advantage that plants with a limited root structure or seeds that are deposited on the outer non-woven structure, for example by hydroseeding, can germinate or grow more easily.

The water retention capacity of the first non- woven structure is preferably 10% higher than the water retention capacity of the second non- woven structure. In certain preferential embodiments the water retention capacity of the first non-woven structure is 20% higher, 30% higher, 50% higher, or even 100% higher than the water retention capacity of the second non-woven structure.

The water retention capacity of a non-woven structure of a multilayer substrate according to the invention is for example determined after 30 hours under standard conditions, which means after 30 hours at a temperature of 22 °C, under an atmospheric pressure of 1 atm, and with an air humidity of 35%. The non-woven structure is thereby preferably positioned in a vertical orientation.

The first non-woven structure of a multilayer substrate according to the invention has preferably a water retention capacity after 30 hours under standard conditions that is higher than 50% of the initial water retention capacity of the first non-woven structure. The initial water retention capacity of a non- woven structure is determined by measuring the quantity of water that is taken up by immersing the non- woven structure for five minutes in a reservoir with tap water. To determine the initial water retention capacity, the difference between the weight of the non-woven structure before being immersed in a reservoir with tap water and the weight of the structure after having been immersed in a reservoir with tap water for five minutes is measured. After 30 hours under the above standard conditions the weight of the non-woven structure is determined again. The non- woven structure is preferably positioned in a vertical direction.

In certain preferential embodiments the water retention capacity of the first non- woven structure of the multilayer substrate after 30 hours under standard conditions corresponds to more than 60%, more than 70%, or more than 80% of the initial water retention capacity of the first non-woven structure.

The water retention capacity of the first non- woven structure after 30 hours under standard conditions is preferably 10% higher than the water retention capacity of the second non- woven structure after 30 hours under standard conditions. In certain preferential embodiments the water retention capacity of the first non-woven structure after 30 hours under standard conditions is 20% higher, 30% higher, 50%> higher, or even 100% higher than the water retention capacity of the second non- woven structure after 30 hours under standard conditions.

The characteristics of the first non-woven structure and of the second non-woven structure can further be selected in view of the application or use, for example in view of the kind of plants, the orientation of the multilayer substrate (for example horizontal or vertical), the climate, the irrigation system, etc. A choice can for example be made between a high or low air permeability, a high or low root penetrability, or a high or low mechanical strength.

The first non-woven structure and the second non-woven structure has preferably a density of between 100 and 1500 g/m ² , for example of between 300 and 1200 g/m ² , for example of 500 g/m ² , 600 g/m ² , 800 g/m ² , 1000 g/m ² or 1100 g/m ² . The density of the first non- woven structure and of the second non- woven structure can be identical or different. In a preferred embodiment both the first non- woven and the second non- woven structures have a density of 600 g/m ² .

The first non- woven structure and the second non- woven structure have preferably a porosity that is higher than 50%, for example higher than 60%, higher than 70%, higher than 80%), or even higher than 90%>. The porosity of a non-woven structure corresponds to the fraction of the volume that is taken up by cavities or pores, in relation to the total volume of the non-woven structure. The porosity of the first non-woven structure and that of the second non- woven structure can be identical or different. In certain preferential embodiments the porosity of the non- woven structure that is positioned further away from the carrier is higher than the porosity of the non-woven structure that is positioned closer to the carrier. The porosity of the non- woven structure that is positioned closer to the carrier is for example at least 80%, while the porosity of the structure that is positioned further away from the carrier is for example at least 90%. In yet another example the porosity of the non-woven structure that is positioned closer to the carrier is for example 90%, whereas the porosity of the structure that is positioned further away from the carrier is for example higher than 92% or even higher than 95%. The thickness of the first non-woven structure and of the second non-woven structure varies for example between 1 mm and 100 mm, for example between 5 mm and 50 mm, and is for example 10 mm, 50 mm or 20 mm. The thickness of the first non- woven structure and of the second non-woven structure can be identical or different. In a preferred embodiment both the first and the second non-woven structures have a thickness of 6 mm.

The tensile strength of the first non- woven structure and of the second non- woven structure preferably varies more than 25 N/5 cm, and even better more than 250 N/5 cm. The tensile strength is determined according to normNF EN 29073-3. The tensile strength of the first non- woven structure and of the second non- woven structure can be identical or different. In a preferential embodiment the first non-woven structure and the second non-woven structure have the same tensile strength.

The first non-woven structure and the second non-woven structure can have the same air permeability or the first and the second non- woven structure can have a different air permeability. The air permeability of a non- woven structure is determined by directing a determined airflow through the non- woven structure, and by using a sensor to measure the amount of air that passes through the non-woven structure.

In certain preferential embodiments the non-woven structure that is positioned further away from the carrier has a higher air permeability than the non- woven structure that is positioned closer to the carrier.

The first non- woven structure and the second non- woven structure can have a root penetrability that is identical or different. In certain preferential embodiments the non- woven structure that is positioned further away from the carrier presents a higher root penetrability than the non- woven structure that is positioned closer to the carrier.

It is clear that both the air permeability and the root penetrability of the second non- woven structure can be higher than those of the first non- woven structure. In certain preferential embodiments the non-woven structure that is positioned further away from the carrier has a higher air permeability and of a higher root permeability than the non- woven structure that is positioned closer to the carrier.

It goes without saying that the multilayer substrate according to the invention may comprise more than two non- woven structures, for example three, four or five non- woven structures. If the multilayer substrate comprises more than two non-woven structures, it can be preferred that the non-woven structure that is positioned closer to the carrier has the highest water retention capacity. In alternative embodiments it can be preferred that the non- woven structure that is positioned further away from the carrier has the highest water retention capacity.

If the multilayer substrate comprises three non-woven structures, the non-woven structure that is positioned closest to the carrier can have a higher water retention capacity than the other two non-woven structures. The water retention capacity of the other two non-woven structures can be identical or different. In a preferred embodiment the water retaining capacity decreases when the non- woven structure is positioned further away from the carrier.

If the multilayer substrate comprises three non- woven structures, it is also possible that the non-woven structure that is positioned closest to the carrier has a lower water retention capacity than the other two non-woven structures. The water retention capacity of the other two non- woven structures can be identical or different. In a preferred embodiment the water retention capacity increases with the distance between the non- woven structure and the carrier.

Preferably, at least the first non- woven structure comprises a hydrophilic material. It is possible that both the first non-woven structure and the second one comprise a hydrophilic material. In that case, the first non-woven structure preferably comprises a larger quantity or a larger percentage (weight based) of hydrophilic material than the second non- woven structure.

Hydrophilic materials comprise for example hydrophilic polymers. Hydrophilic polymers preferably comprise one or more polar or charged functional groups. Examples of hydrophilic polymers comprise polysaccharides, for example alginates or carragenes, polymers based on polyacrylic acid as well as derivatives thereof, polymers based on polyvinylalcohol or derivates or copolymers of one or more of these polymers. The hydrophilic material can but need not necessarily be covalently bound.

In a first group of multilayer substrates according to the invention, at least the first non- woven structure comprises hydrophilic fibres. It is possible that both the first non- woven structure and the second non- woven structure comprise hydrophilic fibres. In that case, the first non-woven structure preferably comprises a larger percentage (weight based) of hydrophilic fibres than the second non- woven structure.

Hydrophilic fibres are made up of or comprise a hydrophilic material, for example a hydrophilic polymer. Fibres that comprise a hydrophilic material are for example fibres (hydrophilic or non-hydrophilic fibres) that are covered with a hydrophilic coating.

The first non- woven structure preferably comprises fibres of which at least 5% on a weight basis are hydrophilic fibres. In certain embodiments the first non- woven structure comprises at least 10% on a weight basis of hydrophilic fibres, at least 20%> on a weight basis of hydrophilic fibres, at least 30%> on a weight basis of hydrophilic fibres, at least 40% on a weight basis of hydrophilic fibres, or at least 50% on a weight basis of hydrophilic fibres. In certain embodiments all fibres of the first non-woven structure comprise hydrophilic fibres.

In a second group of multilayer substrates according to the invention, at least the first non-woven structure comprises a hydrophilic material that is physically and/or chemically bound to the first non- woven structure, for example to the fibres of the non- woven structure. It is possible that both the first non- woven structure and the second non- woven structure comprise a hydrophilic material that is physically and/or chemically bound to the non-woven structure, for example to the fibres of the non-woven structure, i.e. of the first non- woven structure and/or of the second non- woven structure. In that case, the first non- woven structure preferably comprises a larger quantity of hydrophilic material that is physically and/or chemically bound to the non- woven structure than the second non- woven structure.

As carrier, any type of substrate that is suitable for carrying the first and second non- woven structures can be taken into consideration. The carrier can comprise a rigid or a flexible structure.

Examples of rigid structures comprise plates or grids made of metal or of a metal alloy, plates or grids made of a polymer, plates or grids made of gypsum or plaster, plates or grids made of wood, plates or grids made of compressed wood fibres (MDF), and plates or grids made of a composite material. The polymer preferably comprises polyvinylchloride (PVC), polyethylene (PE) or polypropylene (PP). A rigid structure can or cannot comprise a coating, for example a polymer coating. Examples of flexible structures comprise metal foils or films, polymer foils or films, and textile structures such as non-woven structures, woven structures, knitted structures, braided structures, or a combination thereof. A flexible structure can or cannot comprise a coating, for example a polymer coating. In a preferential embodiment, the carrier comprises a textile structure that comprises polyvinylchloride (PVC), polypropylene (PP) or polyethylene (PE), and possibly also a coating, for example a polymer coating.

It can desired that the carrier comprises a fire resistant material or that the carrier is provided with a fire resistant coating.

The carrier can be permeable to air and/or water, or can be impermeable to air and/or water.

Carriers that are permeable to air and/or water have the advantage that sufficient amounts of air can reach the roots of the plants, and as such are very suitable for plants that need a lot of space for the development of roots and/or that need a lot of air.

Carriers that are not permeable to air and/or water have the advantage that a limited amount of evaporation of water takes place, and as such are very suitable for plants that need large quantities of water.

The carriers have preferably a porosity considerably lower than the porosity of the first and second non-woven. The porosity of the carrier is preferably lower than 50 %, lower than 40 %, lower than 30 %, lower than 20 % or lower than 10 %.It is clear for a person skilled in the art that in some preferred embodiments the carrier has no porosity

(i.e. 0% porosity).

It can be interesting for the multilayer substrate according to the invention to comprise at least one reinforcing layer. This reinforcing layer or reinforcing layers may serve to strengthen the multilayer substrate, and preferably comprise(s) openings in which plants can be held. The reinforcing layer or reinforcing layers can comprise a rigid structure as well as a flexible structure.

It can be interesting for the multilayer substrate to comprise multiple reinforcing layers, such as two, three, four or five reinforcing layers. In case the multilayer substrate comprises multiple reinforcing layers, the reinforcing layer positioned closes to the carrier is referred to as the first reinforcing layer. A reinforcing layer is preferably positioned between two successive non-woven structures. In a preferred embodiment, the reinforcing layer is positioned between the first and the second non- woven structures.

A reinforcing layer may comprise a polymer or a polymer based layer. The polymer or polymer based layer preferably comprises openings in which plants can be held.

In a preferred embodiment the polymer or polymer based layer comprises a polymer grid or mesh, for example positioned between the first and the second non- woven structures.

In a preferential embodiment the multilayer substrate comprises a carrier, a first non- woven structure that is positioned on top of the carrier, a first reinforcing layer such as a polymer based layer, positioned on top of the first non-woven structure, a second non-woven structure that is positioned on top of the first reinforcing layer, and a reinforcing layer such as polymer based layer, positioned on top of the second non- woven structure.

The non- woven structure that is situated closest to the carrier can present a higher water retention capacity than the non- woven structure that is positioned furthest from the carrier. In alternative embodiments, the non-woven structure that is positioned furthest away from the carrier has a higher water retention capacity than the non- woven structure that is situated closest to the carrier.

It can be interesting that the multilayer substrate comprises particles that are preferably integrated into the multilayer substrate. Such particles for example comprise seeds, nutrients, porous and/or water absorbing particles such as lava, perlite, and/or pumice. The particles can but need not be enclosed, for example by a capsule. The latter can be interesting when the particles contain nutrients, in order to guarantee that these nutrients are only slowly released over the course of time. The particles can for example be integrated into the first non-woven structure, into the second non-woven structure, or both into the first and into the second non-woven structure. Preferably, the particles are integrated into the non-woven structure during the production process of the non-woven structure. It is also possible to integrate the particles into the multilayer substrate by positioning them between two successive layers, for example between two non-woven structures, between a non- woven structure and a reinforcing layer, or between the carrier and a non-woven structure. Preferably, the carrier does not comprise particles such as seeds, nutrients, porous and/or water absorbing particles such as lava, perlite, and/or pumice.

It can be interesting that the water retention capacity of at least one non- woven structure of the multilayer substrate increases gradually over the width or over the height of the multilayer substrate. That way, the water retention capacity of the multilayer substrate increases gradually over the width or over the height of the multilayer substrate.

The water retention capacity of the multilayer substrate can gradually vary because the water retention capacity of one of multiple layers of the multilayer substrate varies gradually. In a first example, the water retention capacity of the first non- woven structure gradually increases over the width or over the height of the multilayer substrate, whereas in a second example the water retention capacity of the second non- woven structure gradually increases over the width or over the height of the multilayer substrate, and in a third example the water retaining capacity of the first non- woven structure and that of the second non- woven structure increase gradually over the width or over the height of the substrate, be that in to the same or to a different extent.

The water retention capacity can for example increase gradually over the width or over the height of a non-woven structure because the quantity of hydrophilic material, such as the percentage (weight based) of hydrophilic fibres of a non-woven structure increases gradually over the width or over the height of the non-woven structure.

When, during use, the multilayer substrate is positioned vertically, the zone with the highest water retention capacity is preferably situated at the top.

It can be interesting to provide the multilayer substrate with one or more additional layers, such as a thermally insulating layer, a light reflecting layer and/or an air permeable layer. Such additional layers can be positioned at any position of the multilayer substrate. Such additional layer can for example be positioned in contact with the carrier, in between two non-woven structures, in between a non-woven structure and a reinforcing layer, or such additional layer can be positioned on the external surface of the multilayer substrate.

Moreover, it can be interesting to add one or more additives to one or more layers of the multilayer substrate, such as fungicides or growth hormones. Such additives can for example be added to or be integrated into the first non-woven structure or into the second non- woven structure.

The different layers of a multilayer substrate according to the invention can be connected to one another using any technique known in the art. Examples of such techniques comprise stitching, gluing, melting and fusing. It can be desired to mutually connect two successive layers, or it can be desired to mutually connect all the structures of a multilayer substrate according to the invention.

The multilayer substrate can be partially or completely based on biodegradable material and/or can be completely or partially biocompostable. The fibres of the first non- woven structure and/or of the second non- woven structure of the multilayer substrate according to the invention may consist of a biomaterial, for example a biodegradable material or a biocompostable material or may partially comprises a biomaterial as for example a biodegradable material or a biocompostable material. The multilayer substrate is preferably recyclable.

The multilayer substrate preferably comprises openings or carriers in the form of pouches (pockets) in which plants can be held. The pouches (pockets) are preferably added during the production process of the multilayer substrate.

Furthermore, it can be interesting to add a mixture of seeds, water and/or other components to the multilayer substrate or to one or more layers of the multilayer substrate (hydroseeding). The mixture of seeds can for example be added to one or more non- woven structures.

According to a second aspect of the invention a system for cultivating plants is provided. The system comprises a multilayer substrate for cultivating plants as described above. Moreover, the system comprises a housing around the multilayer substrate, as well as an irrigation system suitable to add moisture to the multilayer substrate at predetermined moments in time.

The housing comprises for example a metal, a polymer or a composite material. A system according to the invention can be installed or mounted horizontally, vertically, diagonally or in any other orientation. In case the multilayer substrate is flexible, the multilayer substrate can also be installed or mounted in a non-plain form, for example in an undulated pattern.

In a third aspect, the invention relates to the use of a multilayer substrate as described above, as a vertical wall, a green wall or a green facade, for example for aesthetical or architectural applications as well as for functional applications, for example for creating specific thermal or acoustic characteristics.

Short description of the figures

The invention will hereafter be described, referring to the annexed figures in which:

Figure 1 is a schematic view of a first embodiment of a multilayer substrate according to the invention;

Figure 2 is a schematic illustration of a second embodiment of a multilayer substrate according to the invention.

Description of the embodiments

The figures are merely meant to be schematic and as such are not supposed to limit the scope of the invention. The dimensions and relative dimensions of the different elements in the figures do not correspond to their real dimensions and relative dimensions. The sizes of certain elements in the figures can be exaggerated and are not necessarily to scale.

Figure 1 shows a representation of a first embodiment of a multilayer substrate 1 according to the invention. The multilayer substrate 1 comprises a carrier 2 and two non- woven structures 3, 4.

The carrier 2 comprises for example a coated textile (PVC/PES) with a weight of 1400 g/m ² .

The non- woven structure 3, that is the non- woven structure that is positioned closest to the carrier 2, comprises for example a polyester non-woven structure with a weight of 600 g/m ² , a thickness of 6 mm, and a water retention capacity after 30 hours under standard conditions that corresponds to at least 50% of the initial water retention capacity of this non- woven structure 3. The water retention capacity of the non- woven structure 3, that is the non-woven structure that is positioned closest to the carrier 2, corresponds, after 30 hours under standard conditions, to at least 70% or at least 80% of the initial water retention capacity of this non- woven structure 3.

The non-woven structure 4, that is the non-woven structure that is positioned furthest away from the carrier, comprises for example a polyester non-woven structure with a weight of 600 g/m ² , a thickness of 6 mm, and a water retention capacity after 30 hours under standard conditions that corresponds to at least 35% of the initial water retention capacity of this non-woven structure.

The non- woven structure 3 and the non- woven structure 4 are in direct contact with each other.

In an alternative embodiment, the non-woven structure, that is the non-woven structure that is positioned closest to the carrier, comprises for example a polyester non- woven structure with a weight of 600 g/m ² , a thickness of 6 mm, and a water retention capacity after 30 hours under standard conditions that corresponds to at least 35% of the initial water retention capacity of this non- woven structure 3, as well as the non- woven structure 4, that is the non-woven structure that is positioned furthest away from the carrier, for example a polyester non-woven structure with a weight of 600 g/m ² , a thickness of 6 mm, and a water retention capacity after 30 hours under standard conditions that corresponds to at least 50% and preferably to at least 70% or 80% of the initial water retention capacity of this non-woven structure.

Figure 2 shows a representation of a second embodiment of a multilayer substrate 1 according to the invention. The multilayer substrate 1 corresponds to the multilayer substrate of figure 1, but also comprises, in addition to a carrier and two non- woven structures 3, 4, a reinforcing layer 5. The reinforcing layer 5 comprises for example a PVC-coated mesh structure in which openings can be found, for example openings with a size of 10 x 10 mm. The reinforcing layer 5 is for example positioned in between the two non-woven structures, which means in between the non-woven structure 3 and the non- woven structure 4.