WO2012098130A1

WO2012098130A1 - A tridimensional woven fabric, an integrated permeate channel membrane comprising said fabric and uses thereof

Info

Publication number: WO2012098130A1
Application number: PCT/EP2012/050662
Authority: WO
Inventors: Guy VAN DEN STORME; Manuel VAN DEN STORME; Walter Verhoeven; Wim Mues; Bart Cobben
Original assignee: Vds Weaving Nv
Priority date: 2011-01-17
Filing date: 2012-01-17
Publication date: 2012-07-26

Abstract

The invention relates to a tridimensional woven fabric wherein the material selection, construction and execution are such that a fabric is obtained with improved dimensional stability. This fabric is particularly suitable as a support material for use in membranes. The fabrics and membranes comprising said fabric find use in demanding technical applications such as water filtration in which the dimensional stability is primordial.

Description

A TRIDIMENSIONAL WOVEN FABRIC, AN INTEGRATED PERMEATE CHANNEL MEMBRANE COMPRISING SAID FABRIC AND USES THEREOF

FIELD OF THE INVENTION

The present invention relates to a tridimensional woven fabric and an integrated permeate channel membrane for water treatment, which comprises said tridimensional woven fabric as support. BACKGROUND OF THE INVENTION

Fabrics of all kinds have been used and tested as support structures in different application fields, such as carpets or liquid filtration. The support structure is used as a basis on which other layers are provided to obtain a layered structure.

In carpets, for instance, a layered structure with a support fabric provides resilience to the carpet. The fibers of the support structure fall open upon the application of weight on the surface of the layered structure. Similar compression performance is obtained in structures for car seats, as for instance provided in EP 0 505 788.

These layered structures however lack the high dimensional stability required for demanding applications such as liquid filtration. In this application, support structures between layers of functional membranes need to ensure that the membranes remain operational. A collapse of the structures is thereby highly undesirable. A further problem associated with existing tridimensional fabrics is that their life time is still limited. -Functional membranes deposited on existing fabric support structures have a high wear and tear.

Since many years, membrane systems have been used for various water treatments, such as filtration, purification and desalination. Membranes are typically made from polymeric materials, although ceramic and metal oxide membranes are also available. Membranes typically contain a permeate channel for the withdrawal of the treated water which is forced to pass through the membrane layer by applying a negative pressure inside the permeate channel with respect to the raw water outside the membrane or by applying a positive pressure on the raw water at the outside of the membrane with respect to the treated water inside the membrane. A membrane bioreactor (MBR) typically combines such a filtration with a (micro-)biological action for the reduction of the organic content of the raw water. The (micro-)biological action originates from the so-called activated sludge that is present on the surface of the membrane. Activated sludge results from the introduction of air or oxygen to the biomass of micro-ogranisms which develops on the surface of the membrane.

The MBR filtration performance inevitably decreases with filtration time as a result of fouling, which results from the deposition of components, such as the floe of dead microorganisms along with soluble and colloidal compounds, onto the membrane surface or into membrane pores. Fouling can be removed by backwashing, also called backflushing, i.e. by applying a positive pressure on the permeate channel with respect to the water outside the membrane, thereby producing a reversed water flow through the membrane layer and removing the deposited material from the outer surface of the membrane.

The membranes used in MBRs typically have a hollow fibre or flat sheet configuration. WO 2003/037489 discloses a filtration module comprising a plurality of "filter membrane pockets" which consist essentially of two parallel membrane layers of a flat and flexible material, which are separated by a flexible, liquid permeable core. The membrane pockets are fixed to a supporting frame which comprises at least one evacuation line for withdrawing the liquid that is sucked out via the filter membrane pockets.

WO 2006/056159 discloses a frameless membrane cartridge wherein membrane layers are coated on the outside faces of a reinforcing structure of at least two spaced apart drainage layers which are pressed together at the edges.

WO 2006/015461 discloses a flat "integrated permeate channel membrane" (hereinafter also referred to as IPC membrane) which comprises two membrane layers coated on opposite surfaces of a tridimensional fabric (3D fabric) that is used as support of the membrane layers. The 3D fabric consists of two parallel fabric layers which are spaced apart by loops of monofilament threads, thereby forming a permeate channel between the membrane layers. A further development thereof is disclosed in WO 2008/141935. The membrane layers are partially embedded into the fabric layers and into the connecting loops. As a result, such IPC membranes can withstand high positive internal pressure, enabling efficient backwashing and therefore long-term operation without the need for frequent removal and cleaning of the membranes. They can also be manufactured by relatively simple and low-cost methods.

A problem associated with the IPC membranes of the prior art however is that their life time is still limited due to leakage of the membrane layer, resulting from the occurrence of cracks and tears in the membrane during operation. In addition, the IPC membranes of the prior art are susceptible to collapsing of the integrated permeate channel during normal operation of the membrane, due to the negative pressure applied inside the permeate channel with respect to the raw water outside the membrane or the positive pressure applied on the raw water at the outside of the membrane with respect to the treated water inside the membrane.

It is an object of the present invention to provide an improved support structure. In particular, the support structure should provide a high dimensional stability and exhibit an improved life time. The support structure should exhibit high strenghts, even over a long period of time. It is the aim to provide a support structure suitable for use in the demanding field of liquid filtration.

It is a further object of the invention to provide a membrane comprising the support structure.

It is an object of the present invention to provide an IPC membrane suitable for water treatment such as filtration, purification and desalination.

It is also an object of the invention to provide uses for the improved fabric and membrane obtained therefrom, particularly in the field of liquid filtration.

As a result, the membrane has a longer lifetime during normal operation while maintaining a high permeability or flux and a high resistance to backflush pressure for cleaning the membrane.

SUMMARY OF THE INVENTION

This object is realised by a fabric having the features of claim 1. Preferred embodiments of the fabric of the present invention are defined in the dependent claims and the following description.

A fabric according to an embodiment of the invention has an improved tridimensional stability. The fabric displays higher strength and stiffness in all three dimensions. This is beneficial for use as a support structure in IPC membranes. The fabric is thereby providing higher resistance to tearing in both directions parallel to the integrated permeate channel and to compression in the direction perpendicular to the integrated permeate channel.

In addition, the surface smoothness of the woven fabric could be improved. This was beneficial to the lifespan of membranes deposited on the fabric.

The object of the invention is further realised by an IPC membrane having the features of claim 11. Preferred embodiments of the IPC membrane of the present invention are defined in the dependent claims and the following description.

The advantages of the present invention are realised by the use of an improved 3D fabric (1) as support for the membrane layers (21, 22). Although the applicants do not wish to be bound by any technical explanation of these effects, it seems that the advantages originate from the combined features that (i) the 3D fabric (1) is a woven fabric, i.e. that it comprises two fabric layers (11, 12) which are each woven fabric layers comprising a plurality of weft (111, 121) and warp (112, 113, 122, 123) threads and (ii) that said woven fabric layers (11, 12) are connected by spacer threads (131, 132) which are interlaced with weft threads (111, 121) of both said fabric layers (11, 12), thereby forming spacer threads (131, 132) which are woven into both said fabric layers (11, 12).

Further improvements of the stiffness and strength were obtained by using monofilament threads for the weft (111, 121) and warp (112, 113, 122, 123) threads of both fabric layers and/or for the spacer threads (131, 132) between said fabric layers (11, 12).

The object of the invention is further realised by the uses provided in claims 10 and 15 and a water filtration module as provided in claim 14.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 to 11 represent a schematic representation of a cross-section in the warp direction (i.e. perpedicullar to the weft direction) of specific examples of weave pattern of woven 3D fabrics of the present invention wherein the weft threads (111, 121) are represented by dots and the warp (112, 113, 122, 123) and spacer (131, 132) threads are represented by numbered lines and wherein a 1/2 V weave pattern is represented for the spacer threads in Figures 1 and 7, a 1/4 V weave pattern in Figures 2 and 8, a 3/6 W weave pattern in Figures 3 and 9, a 5/10 W weave pattern in Figure 4, a 3/8 W weave pattern in Figures 5 and 10, and a 5/12 W weave pattern in Figures 6 and 11. The weave pattern for the spacer threads are elucidated by a specific numbering for some weft threads, e.g. i[l], i[2], i[3], etc., as indicated at the foot of the figures. Figure 12 represents a cross section of an IPC membrane according to a specific embodiment of the present invention wherein a 3D fabric as represented in Figure 9 is used as support for the membrane layers.

Figures 13 to 23 represent a schematic representation of a cross-section in the warp direction (i.e. perpedicullar to the weft direction) of other specific examples of weave pattern of woven 3D fabrics which also belongs to the present invention wherein specific weave pattern are used. Figure 24 represents a schematic representation of a cross-section in the warp direction (i.e. perpedicullar to the weft direction) of a specific example of weave pattern of the woven 3D fabrics 3D-01 to 3D-15 which are defined in Table 1. DETAILED DESCRIPTION

Tridimensional woven fabric

The 3D fabric (1) comprises a first (11) and a second (12) fabric layer. Both these layers (11, 12) are woven layers comprising a plurality of weft (111, 121) and warp (112, 113, 122, 123) threads, which define the weft and warp direction of the woven fabric (1). In a preferred embodiment, the 3D fabric (1) has a flat and smooth surface without the presence of broken threads or parts of broken threads, so that no fragments protrude from the outer surface of the first or second fabric layer (11, 12). Such fragments are believed to increase the risk of crack formation during use of the membrane (2) and should be avoided as much as possible. A flat and smooth surface can be obtained by using monofilament threads for preferably all of the warp (112, 113, 122, 123) and weft (111, 121) threads of both fabric layers.

The fabric layers (11, 12) are mutually parallel layers which are separated from and connected to each other by spacer threads (131, 132) which are interlaced with weft threads (111, 121) of both fabric layers. These spacer threads (131, 132) are also referred in the field as pile warp threads but will be referred in the application as spacer threads. The spacer threads (131, 132) support a hollow structure (13), such as a channel, between the parallel fabric layers (11, 12) and thereby allow the formation of an integrated permeate channel (23), which is formed by applying a membrane layer (21, 22) on each of said fabric layers (11, 12). For better resistance against collapse of the integrated permeate channel (23), the spacer threads (131, 132) are preferably monofilament threads.

In a preferred embodiment, the spacer threads (131, 132) are woven in the fabric layers by a weave pattern which comprises (a) one or more interlacements between the spacer threads and the weft threads (111) of the first fabric layer, (b) a transition of the spacer threads from the first (11) to the second (12) fabric layer, (c) one or more interlacements between the spacer threads and the weft threads (121) of the second fabric layer and (d) a transition of the spacer threads from the second (12) to the first (11) fabric layer. Specific embodiments of such a weave pattern are shown in the Figures 1 to 11. Such weave patterns are known in the art of carpet making, e.g. as disclosed in EP-A 505 788, EP-A 628 649, EP-A 1 347 087, EP-A 1 122 347, EP-A 1 666 651 and US 6,182,708, US 6,923,219 and US 6,343,626. Other 3D fabrics which are also suitable for the present invention are represented in the Figures 13 to 24.

In the weave pattern of each of the two fabric layers of the 3D fabrics, schematically represented in Figures 1 to 11, only two warp threads (112, 113, and 122, 123) are indicated but it is an embodiment of the present invention that the weave pattern of each of these fabric layers may comprise more than two warp threads. The weft threads in these figures are numbered as indicated by i[l], i[2], i[3], etc. In the weave pattern of the 3D fabrics, schematically represented in Figures 1 to 6, only one spacer thread (131) is indicated. In the Figures 7 to 11, two spacer threads (131, 132) are indicated. It is also an embodiment of the present invention that one, two or more than two spacer threads may be used in the 3D fabric. In another embodiment, in the weave pattern of the 3D fabrics, schematically represented in Figures 1 to 11, each fabric layer comprises only one row of weft threads interlaced with warp threads but two or more rows of weft threads can also be used in each fabric layer, wherein weft threads of each of these rows are interlaced with one or more warp threads, as schematically represented in Figures 13, 14 and 23. In still another embodiment of the present invention, each of the two fabric layers may be composed of two or more woven sublayers, wherein each of these sublayers are connected to each other and optionally spaced from each other by spacer threads as defined above, as schematically represented in Figure 23. Examples of all types of weave patterns for 3D fabrics are schematically represented in the Figures 13 to 24.

In a preferred embodiment which provides higher resistance to compression, the number of interlacements between the spacer threads (131, 132) and the weft threads (111, 121) of each fabric layer is an odd number higher than one. More preferably said number is three, five, seven or nine. Such weave patterns may be referred to as a "W pattern" because the spacer thread follows a W-shaped path in each fabric layer, as schematically represented in Figures 3 to 6 and 9 to 11, whereas a weave pattern with only one interlacement between the spacer threads and the weft threads produces a "V" pattern, as schematically represented in Figures 1, 2, 7 and 8. In these figures, weft threads are numbered by i[l], i[2], i[3], etc. for explaining these weave pattern.

In a highly preferred embodiment, the weave pattern of the spacer threads (131, 132) comprises three or five or seven interlacements between the spacer threads and the the weft threads (111) of the first fabric layer (11), a transition of the spacer threads from the first (11) to the second (12) fabric layer, three or five or seven interlacements between the spacer threads and the weft threads (121) of the second fabric layer (12) and a transition of the spacer threads from the second (12) to the first (11) fabric layer, as schematically represented for 3/6W, 5/10W, 3/8W or 5/12W weave pattern in Figures 3 to 6 and 9 to 11.

In another preferred embodiment which provides higher resistance to compression, the transition of the spacer threads (131, 132) between both fabric layers is oriented substantially perpendicularly to each of the two mutually parallel fabric layers, meaning that the angle, formed between the fabric layer and the spacer thread between the two fabric layers, has an orientation which may deviate from 90° by less than 15°, preferably by less than 10°, more preferably by less than 5°, even more preferably by less than 2°, but most preferably has a value of 90°. Therefore, a 1/2 V weave pattern for the spacer threads is more preferred than a 1/4 V weave pattern.

A most preferrred embodiment of such a weave pattern is a so-called 3/6 W pattern, as schematically represented in Figures 3 and 9, which comprises three interlacements between the spacer thread (131, 132) and three consecutive weft threads (111) of the first fabric layer (11) as indicated in Figures 3 and 9 by the weft thread numbers i[l], i[2] and i[3], a transition to the second fabric layer (12) between weft thread numbers i[3] and i[4] as indicated in Figures 3 and 9, followed by three interlacements between the spacer threads and the three consecutive weft threads (121) of the second fabric layer as indicated in Figures 3 and 9 by the weft thread numbers i[4], i[5] and i[6].

Other, more complex weave patterns suitable for the present invention are formed by combinations of at least two of the 3/6W, 5/10W, 3/8W, 5/12W, 1/2 V and 1/4 V patterns for the spacer threads. Also, the weave pattern does not need to be identical for all the spacer threads and a different weave pattern can be used for each spacer thread. Examples of such complex weave patterns are schematically represent in Figures 13 to 24.

The weave pattern used for the first and second fabric layer (11, 12) can be any weave pattern known in the art, e.g . a weave pattern as shown in Figure 9 or a twill weave pattern as shown in Figure 24. A twill weave pattern has the advantage of an improved flatness of the fabric layers and is a highly preferred weave pattern of the fabric layers.

In a preferred embodiment of the present invention, the 3D woven fabric (1) has a symmetric structure with respect to the hollow structure (13), meaning that the weave pattern and the number of threads are identical in both fabric layers (11, 12). More preferably, the symmetry extends also to the weave pattern of the spacer threads (131, 132), meaning that the weave pattern of one spacer thread (131) is mirrored by another spacer thread (132) at the opposite side of the hollow structure, so that both weave patterns are identical but in opposite phase, as shown in Figures 7 to 11 and 20 to 24. Highly symmetric 3D fabrics, wherein not only the number and the weave patterns of the threads are symmetric, but also the chemical composition, type, thickness, and strength of the threads are identical at both sides of the hollow structure (13), are most preferred.

The thickness of the 3D fabric (1), defined by the distance between the outer surfaces of the first and second fabric layers (11, 12), may range from 0.5 to 10 mm, more preferably from 1 to 5 mm, and most preferably from 1.5 to 3.5 mm.

In a preferred embodiment the surface smoothness of the fabric is improved. The surface roughness of the 3D fabric is defined by the maximum distance between the most outer points of the warp (112,113, 122, 123) threads and the most inner cross-section between the warp and weft ((112, 113) or (122, 123)) threads. A synonym for this distance is error.

In a preferred embodiment, the error in a fabric according to an embodiment of the invention is 0 to 0.5 mm, more preferably 0.01 to 0.2 mm, even more preferably 0.01 to 0.1 mm, most preferably at most 0.1 mm.

The improved smoothness of the fabric influences the effectiveness and strength of the other layers. It is particularly beneficial in a set-up where the support structure is coated with a membrane dope.

More preferably, the distance is constant over the 3D fabric.

In a preferred embodiment of a fabric according to the invention, the 3D fabric has a surface not exhibiting broken threads or parts of broken threads. The absence of surface debris our irregularities can be observed by light microscopy.

The weight of the 3D fabric (1) may range from 200 to 650 g/m², more preferably from 300 to 550 g/m², most preferably from 400 to 450 g/m².

The diameter of the warp (112, 113, 122, 123) and weft (111, 121) threads may range from 0.01 mm to 0.50 mm, preferably from 0.03 mm to 0.30 mm, more preferably from 0.06 mm to 0.20 mm and most preferably from 0.10 mm to 0.17 mm.

The diameter of the spacer threads (131, 132) have a diameter ranging between 0.01 mm and 0.80 mm, preferably between 0.03 mm and 0.50 mm, more preferably between 0.06 mm and 0.30 mm, most preferably between 0.10 mm and 0.20 mm.

In another preferred embodiment of the present invention, the 3D fabric (1) comprises monofilament warp threads (112, 113, 122, 123), monofilament weft threads (111, 121) and monofilament spacer threads (131, 132) each having substantially the same diameter, preferably in the range from 0.01 mm to 0.50 mm, preferably from 0.03 mm to 0.30 mm, more preferably from 0.06 mm to 0.20 mm, and most preferably from 0.13 to 0.18 mm.

Each of the weft and warp and spacer threads are preferably monofilament threads. These monofilament threads may be composed of only one thread but it also possible that more than one monofilament thread is used, e.g. the warp and the spacer thread may be composed of a pair of two monofilament threads to be used in the weaving process. Examples of 3D fabrics wherein such a pair of threads are used in the weave pattern are given in Figures 14 and 22, wherein the pair of threads is represented by double lines. Each thread of the pair of threads may have of the same type, thickness and composition but these two threads of the pair may be different such as another thickness, chemical composition, mechanical strength.

Each of the threads of the 3D fabric (1) may comprise one or more polymers selected from a polyester, a polyamide, a polyurethane, a poly(meth)acrylate, a polyolefine, a phenolic resin, a polysulfone, a polyether sulfone, a polyether ether ketone, polyether ketone polystyrene, poly para-phenylene sulfide, polytetrafluoroethylene, polyvinylchloride or copolymers thereof; more preferably a polyester, a polyamide, poly para-phenylene sulfide or polytetrafluoroethylene; most preferably a polyester or a polyamide. The polymer may be a homo-polymer, a co-polymer of at least 2 of these polymers or a mixture or blend of these homo- or co-polymers.

Each of the threads of the 3D fabric (1) may be a fibre selected from the list of a polyester fibre, a polyamide fibre, a polyacrylic fibre, an oxidized polyacrylic fibre, a polyurethane fibre, a polyolefine fibre, a high molecular weight polyethylene fibre, a para-aramid fibre, a meta-aramid fibre, a polybenzobisthiazole fibre, a polyetheretherketone fibre, a polyether ketone fibre, a poly para-phenylene sulfide fibre, a polytetrafluoroethylene fibre, a carbon fibre, a ceramic fibre, a boron fibre, a tungsten fibre, a copper fibre, a silver fibre, a basalt fibre, an alumina fibre, or a high modulus silicon carbide or silicon nitride fibre; more preferably a polyester fibre, a polyamide fibre, a polyolefine fibre, a high molecular weight polyethylene fibre, a para-aramid fibre, a meta-aramid fibre or a poly para-phenylene sulfide fibre; most preferably a polyester fibre or a polyamide fibre.

The woven fabric layers (11, 12) preferably have an open area formed by holes in their woven structure of at least 5%, thereby providing a high air and liquid permeability. In more preferred embodiments, the open area ranges from 10% to 95%, or from 20% to 80%, and even from 30% to 70%. The 3D fabric (1) may comprise holes in the woven structure of the fabric layers (11, 12), having a size in the range from 100 μιη to 1500 μιη, more preferably from 250 μιη to 1000 μιτι, most preferably from 300 μιη to 700 μιη. The presence of these holes enables a good penetration of the coated membrane layers (21, 22) into the fabric layers (11, 12), thereby producing a strong adhesion of the coated membrane layers on the supporting fabric layers, as schematically represented in Figure 12. The open area on both fabric layers preferably have the same value or approach to have the same value. In a preferred embodiment of the present invention, the difference in the value of the open area of both fabric layers may be at most 10 %, more preferably at most 5 %, most preferably at most 2 %.

A high permeability is also obtained with embodiments wherein the hollow structure (13) between the inner surfaces of the first and the second fabric layer is sufficiently large. The volume of the hollow structure is defined by the distance between said inner surfaces which depends on the length of the spacer threads, and the frequency of transitions (number per cm) of the spacer threads (131, 132). Said transition frequency is mainly determined by the weave pattern of the spacer threads and by the density (number per cm) of the weft threads and of the warp threads. The number of weft threads preferably ranges from 5 to 40 per cm, more preferably from 10 to 30 per cm, most preferably from 15 to 25 per cm. The number of warp threads preferably ranges from 12 to 42 per cm, more preferably from 17 to 37 per cm, most preferably from 22 to 32 per cm. Suitable values of these parameters may be combined to obtain a sufficiently large volume of the hollow structure (13) in the 3D fabric. For example, a 3D fabric having a thickness in the range from 0.5 to 10 mm, may comprise from 5 to 40 weft threads per cm, wherein each spacer thread has a thickness in the range from 0.01 mm to 0.80 mm and may comprise from 12 to 42 warp threads per cm, wherein each warp thread has a thickness in the range from 0.01 mm to 0.80 mm. Another combination may have a thickness of the 3D fabric ranging from 1 to 5 mm and 10 to 30 weft threads per cm, wherein each spacer thread has a thickness in the range from 0.06 mm and 0.30 mm and 17 to 37 warp threads per cm, wherein each warp thread has a thickness in the range from 0.06 mm and 0.30 mm. Another combination may have a thickness of the 3D fabric ranging from 1.5 to 3.5 mm and 15 to 25 weft threads per cm, wherein each spacer thread has a thickness in the range from 0.10 mm to 0.20 mm and 22 to 32 warp threads per cm, wherein each warp thread has a thickness in the range from 0.10 mm and 0.20 mm.

The 3D fabrics (1) can be characterised by the mechanical parameters known in the literature, e.g. the tensile modules, ultimate strength, elongation at break and compressive stress. The definition of these parameters is described in e.g. Properties of Polymers, by D.W. Van Krevelen, second edition, Elsevier Scientific Publishing Company, Amsterdam, 1976, see especially chapter 13, and also Textbook of Polyler science, by F.W. Billmeyer, second edition, Wiley-Interscience, NY, 1971, see especially chapter 4, and also Standard Test Method for Tensile Properties of Thin Plastic Sheeting, as defined in ASTM D882-10.

Preferred 3D fabrics (1) have a high resistance against deformation upon an external load, expressed by the tensile modulus of the fabric which is at least 30 N/mm² when measured in the weft or the warp direction of the fabric; said value is more preferably at least 50 N/mm², and most preferably at least 80 N/mm². The ultimate strength has a value which is, in each direction, preferably at least 6 N/mm², more preferably at least 8 N/mm² and most preferably at least 10 N/mm².

Preferred 3D fabrics (1) have an isotropic dimensional stability, meaning that the tensile modulus has about the same value in both directions. In a preferred embodiment, the difference between the two values of the tensile modulus, wherein one value is measured in the warp direction and the other in the weft direction, is at most 25 %, more preferably at most 20 % and most preferably at most 15 %. Also the difference between the two values of the ultimate strength of the fabric, one measured in the warp and the other in the weft direction, is preferably at most 25 %, more preferably at most 20 %, most preferably at most 15 %. Also the difference of the values of the elongation at break is preferably less than 4%, more preferably less than 3%, and most preferably less than 2%.

A high resistance against compression of the 3D fabric (1) can be obtained by increasing the number of transitions of the spacer threads, determined by the weave pattern of the spacer threads and by the density (number per cm) of the weft threads, by increasing the thickness of the spacer threads, by decreasing angle of deviation from the perpendicular orientation of the spacer threads in the transition position between both fabric layers and by using stiff spacer threads. A high compressive stress of at least 8 N/cm², more preferably at least 10 N/cm² and most preferably at least 12 N/cm² can be obtained e.g. by using polyesters or polyamides as main or even sole component of the spacer threads, especially when these materials are combined with the preferred frequency of the transitions and preferred thickness of the spacer threads, mentioned above.

In a preferred embodiment, the 3D fabrics (1) used in the present invention are stabilised by heating at a temperature above 150°C. By this thermal relaxation process, the tensions or stresses, generated during the weaving processes and accumulated in the woven fabric, are reduced, thereby providing a flat non-curling 3D fabric. The temperature and heating time period for this thermal stabilisation process depend on the type of the threads, the weave pattern and the thickness of the threads used in the woven fabric. Preferably, the relaxation temperature is higher than 170°C, more preferably higher than 180°C, most preferably 190°C. The improved 3D stability of the fabric did not negatively impact the drapeability or flexibility of the membrane comprising the fabric. A membrane according to an embodiment of the invention can bend over a distance of 10 cm, in both the warp and weft direction, over an angle of 180 °C with itself. Increased pressure compensation is provided, which is for instance useful in filter applications. It also allows that the fabric can be folded onto rolls for transport and storage.

Specific examples of 3D fabrics (1) which are suitable for use in a membrane according to the present invention are summarised in Table 1.

Table 1

3D fabric Diameter (mm) and Number of ThickThermal

No. composition of threads weft ness stabili¬

Spacer Warp Warp Weft threads of fabric sation threads threads threads Threads (number (mm) (°C)

(131, (112, (122, (111, per cm)

132) 113) 123) 121)

3D-01 0.15/ 0.15/ 0.15/ 0.15/ 20 2.80 none

PET PET PET PET

3D-02 18 2.30 none

3D-03 15 2.00 none

3D-04 14 1.70 none

3D-05 20 2.80 170

3D-06 21 2.80 180

3D-07 22 2.80 190

3D-08 0.12/ 0.12/ 0.22/ 16 1.95 none

PET PET PET

3D-09 14 1.60 none

3D-10 0.15/ 20 2.95 none

PET

3D-11 0.12/ 20 1.80 none

PET

3D-12 25 2.00 none

3D-13 25 1.70 none

3D-14 0.15/ 0.15/ 0.15/ 20 3.00 none

PET PET PA

3D-15 20 1.80 none • PET represents a 100 % monofilament polyester fibre of poly(ethylene) terephthalate.

• PA represents a 100 % monofilament polyamide fibre, composed of a mixture of polyamide-6 and polyamide-6.6.

· 3D fabrics 3D-05, 3D-06 and 3D-07 are thermally stabilised by heating in a hot air oven at resp. 170°C, 180°C and 190°C at a speed of 7 m/minute.

• Measurements were carried out on the angle of a fabric layer and the spacer thread between the two fabric layers. The angles were measured by means of microscopy on a cross-section of the material. The angle between the spacers and the layers was 90 +/- 1°.

These examples are woven by a face-to-face weaving machine using a 3/6 W pattern for the spacer thread and a twill weave pattern for the first and second fabric layers, having 27 warp threads per cm, and a schematic representation of the weave pattern is given in Figure 24 wherein the warp threads (112, 113, 122, 123) in each fabric layer (11, 12) and the spacer threads (131, 132) are represented. The diameter and type of material of each thread are indicated in Table 1.

The membrane (2) comprises (i) a water-permeable tridimensional woven fabric (1) comprising a first and a second fabric layer (11, 12), as defined above, (ii) a polymeric membrane layer (21, 22) applied on each of said fabric layers (11, 12), wherein each membrane layer is at least partially embedded in the respective fabric layer, and (iii) a permeate channel (23) between said membrane layers (21, 22). A preferred embodiment of the membrane according to the present invention is schematically represented by Figure 12 wherein the 3D fabric of Figure 9 is used as support for the membrane layers. It is evident that any other 3D fabric described above can be used as support of the membranes of the present invention.

The two membrane layers (21, 22) are linked at a multitude of points with each of said fabric layers (11, 12) to secure a strong adhesion on the fabric layers and this can be realised by coating a membrane dope, i.e. coating solution liquid, on each of said fabric layers (11, 12) whereby the membrane layers penetrate at least partially in the fabric layers, or by laminating coated membrane layers onto the fabric layers (11, 12) and securing the adhesion on the fabric layers by partially melting or dissolving the membrane layers or by using an adhesive.

In a preferred embodiment, the membrane layers (21, 22) are applied at both sides of the fabric layers (11, 12) by coating the membrane dope on the fabric layers by using a coating apparatus. Thereafter, the dope is made to coagulate by removing the solvent. Coagulation can be performed by a phase inversion process, in which the solvent of the membrane dope is extracted from the dope by a non- solvent of the membrane polymer. The phase inversion can be performed in an ambient comprising a vapour of said non-solvent or in liquid comprising said non- solvent (e.g. water) or a combination of both. Membrane formation may also be obtained by evaporation of the solvent (dry phase inversion) or by changing the temperature of the coated layer. Preferred coating and coagulation processes which can be used in the present invention are described in WO 2006/015461 Al, EP 1 992 400 Al and WO 2008/141935 Al.

The coating technique used for impregnating the two fabric layers with a coating solution or dope can be each type of coating techniques such as extrusion coating, slot coating, roller coating and bar coating. In a preferred embodiment, the two fabric layers (11, 12) are simultaneously double-sided coated by two coating systems mounted on each side of the 3D fabric. In a more preferred embodiment, the two fabric layers (11, 12) are simultaneously coated by a double-sided extrusion coating system or a double-sided slot coating system; a double-sided slot coating system as defined in WO 2008/141935 Al is most preferred. In order to obtain membrane layers which are linked at a multitude of points with each of the fabric layers, it is important that the woven structure of the two fabric layers exhibit an open area of at least 15 % and at most 95 %. The presence of these open area and holes in the fabric layers is important to obtain a good interpenetration with the coated membrane layers and a good adhesion of the coated membrane layer on the supporting fabric layers.

Each of the membrane layers (21, 22) can also be composed of two or more sublayers. These two or more sublayers can be coated simultaneously on each side of the fabric layer, or can be coated as separate layers consecutively on each other.

The membrane layer (2) comprises a membrane polymer selected from the group consisting of polysulphone (PS), polyvinyl chloride (PVC), polyacrylonitrile (PAN), polyester, polyethersulphone (PES), polyetherketone (PEK), polyetheretherketone (PEEK), polyvinylchloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyamide (PA), polyethylene (PE), polypropylene (PP), polyvinylpyrrolidone (PVP), crosslinked PVP, cellulosics including nitrates and esters thereof such as cellulose acetate (CA) and cellulose triacetate (CTA), polycarbonate block polymers, a rubber selected from the group consisting of silicone rubber, Polymethylpentene, Chloroprene, SBR, NBR, Urethane, Hypalon®, Neoprene, Nitrile, Buna, Urethane, Epichlorohydrin, Viton®, EPDM, Butyl, Natural Rubber (Latex), Acrylrubber, Fluoroelastomers and, Perfluoroelastomers, and mixtures/blends thereof. Further suitable membrane polymers include chlorinated polyvinyl chloride (CPVC), copolymers of acrylonitrile e.g. with vinyl chloride or ethyl acrylate, polyethylene succinate (PESU), polyurethanes (PU), polyimides (PI), polyetherimide (PEI) and cellulosics such as hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), and cellulose tricarbanilate (CTC) mixtures/blends thereof and their grafted derivatives (sulphonated, acrylated, aminated etc). The most common polymers in membrane synthesis are cellulose acetates, including nitrates and esters thereof, polysulfone (PS), polyether sulfone (PES), polyacrilonitrile (PAN), polyamide (PA), polyimide (PI), polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylchloride (PVC). The membrane layer may also comprise hydrophilic polymers such as polyvinyl pyrrolidone (PVP), crosslinked polyvinylpyrrolidone (PVPP), polyvinyl alcohol, polyvinyl acetate, methyl cellulose and polyethylene oxide. The membrane layer may also comprise hydrophilic inorganic materials such as Ti0₂, Hf0₂, Al₂0₃, Zr0₂, Zr₃(P0₄)4, Y₂0₃, Si0₂, perovskite oxide materials and SiC.

The membrane dope is a liquid polymeric solution or dispersion comprising a membrane polymer and preferably has a viscosity between 1000 and 100,000 at a shear of 10 s-1, with a viscosity in the range of 10,000 to 50,000 s-1. The membrane dope preferably comprises a membrane polymer, a hydrophilic polymer, optionally a hydrophilic filler such as a hydrophilic inorganic material, an aprotic solvent such as N-methyl-pyrrolidone (NMP), N-ethyl-pyrrolidone (NEP), N,N- dimethylformamide (DMF), formamide, dimethylsulphoxide (DMSO), N,N- dimethylacetamide (DMAC), tetrahydrofuran (THF), acetone, triethylphosphate and mixtures thereof, and a hydrophilizing and stabilizing agent such as glycerol and ethylene glycol.

Hydrophilizing and stabilizing agents such as glycerol and ethylene glycol can also be incorporated after the phase-inversion process is completed, but before drying. The hydrophilic filler influences the hydrophilicity of the membrane and its fouling behaviour. Often a variation in solvent mixture will give rise to different film morphologies and hence in membrane performance. Films formed by immersion of a polysulphone-NMP solution in water are porous. However, different membrane structures can be obtained upon immersion of a polysulphone-NMP-THF solution in water.

Each of the two membrane layers (21, 22) usually has an asymmetric pore size distribution, in which the smallest pores are present at the outside of the membrane layer. Large particles present in the waste water hence can not penetrate into the membrane layer. The membrane layers can be cleaned, e.g. by applying an air bubble flow and/or by applying a backflush. Otherwise, when the pore size on the waste water side is large, particles would penetrate into the membrane and obstruct the pores inside the membrane layer which are very difficult to clean. The pore size distribution is tailored during the coagulation step and the inner and outer surfaces at both sides of the IPC membrane should not be exposed to the coagulating agent to the same extent. An asymetric pore size distribution can be realised by coagulation in the vapour phase. It is also possible to obtain this asymmetric pore size distribution when the edges of the coated fabric layers are sealed prior to the coagulating step to prevent the coagulating agent penetrates into the permeate channel. In the art, this can be done in a separate step prior to coating the membrane or this can be done together with the coating step as disclosed in EP 1 992 400 Al and WO 2008/141935 Al .

The above method of making the IPC membranes (2) of the present invention typically provides membranes having a high quality, meaning that the membrane layers (21, 22) have a decreased number of defects or no defects at all such as pits, holes, protrudings, cracks or tears as a result that no leakage or only a reduced level of leakage is present in the membrane layers, making them suitable for a reliable filtration process.

In order to reduce the number of defects in the membrane layers (21, 22), it is particularly preferred that during the coating process and during the coagulation and washing steps no pinholes or pits are created in the coated membrane layers on the outer surfaces of both fabric layers. The inventors have surprisingly found a reduced number of pinholes when 3D fabrics are used with monofilament threads instead of multifilament threads. By the use of monofilament threads no broken threads or part of broken threads are protruding from the surface of the fabric layers (11, 12) to the outside, and therefore the coated membrane layer (21, 22) are not perforated by these broken threads and no pinholes are formed. In a preferred embodiment of the present invention, the warp and weft threads (111, 112, 113, 121, 122, 123) used in the fabric layers are monofilament threads. In another preferred embodiment of the present invention, the spacer threads (131, 132) are monofilament threads. In a more preferred embodiment, the warp and weft threads (111, 112, 113, 121, 122, 123)and the spacer threads (131, 132) are monofilament threads.

The IPC membranes (2) can be provided with a drainage pipe (not shown in the Figure 12) which is provided for extracting permeate from the permeate channel as defined in WO 2006/015461 Al, EP 1 992 400 Al and WO 2008/141935 Al.

The IPC membranes (2) can be sealed at their edge all around the border of the IPC membrane (not shown in the Figure 12) to prevent penetration of untreated water into the inside of the IPC membrane and contaminate the permeate water. A plurality of these IPC membranes (2) can be mounted in a module, mounted in a box-shaped housing which is open upwardly and downwardly. In such a module, each of the IPC membranes has an opening for discharge of the permeate and which are so arranged that the IPC membranes are vertical, mutually parallel and spaced apart from neighbouring IPC membranes. The intervening spaces between the individual IPC membranes form passages which are traversable by a fluid . Below this box with the IPC membranes, a housing may be arranged which includes a device providing air feed through which an upward flow is produced by means of which the liquid flows along the IPC membranes. This upward air flow parallel to the IPC membrane surfaces generates a cleaning stream to protect the membrane from clogging, i.e. deposit of debris on the membrane surface. During the treatment process and under the influence of the upward air flow, the coarse air bubbles give an excitation of the IPC membranes leading to a vibration which may induce the formation of cracks and tears in the membrane layers, resulting in the formation of leakages and a shortened life-time of the IPC membranes in the module.

Also, during the treatment process of raw water, the pressure applied on the inside of the IPC membranes is typically lower than outside the membrane so that permeate water is extracted through the membrane layer.

The IPC membranes (2) of the present invention exhibit an improved life-time during treatment process with a reduced level of leakages formed during the filtration and/or backflush process and with a high resistance against backflush pressure for cleaning the membrane. This effect is linked to the storage modulus of the IPC membranes as determined by a fatigue test with a Dynamic Mechanical Analysis measurement as described in the examples and as known in the literature, e.g. Properties of Polymers, by D.W. Van Krevelen, second edition, Elsevier Scientific Publishing Company, Amsterdam, 1976, see especially chapter 13, and also Textbook of Polymer science, by F.W. Billmeyer, second edition, Wiley- Interscience, NY, 1971, see especially chapter 4. Preferred membranes of the present invention are characterised by a storage modulus which at elongation of less than 0.25 % at an oscillation frequency of 20Hz, does not substantially decrease during at least 8000 minutes. A decrease of the storage modulus is an indication of the occurrence of initial damage of the IPC membrane layers (21, 22). In accordance with another preferred embodiment of the present invention, the IPC membranes of the present invention exhibit no decrease of the storage modulus and no damage in the IPC membrane layers (21, 22) at an elongation of less than 0.2 % at an oscillation frequency of 20Hz. The backflush pressure of the IPC membranes of the present invention is preferably more than 1 bar, more preferably more than 2 bar, most preferably more than 3 bar. After the formation of the membrane layers (21, 22), the IPC membranes are typically activated before they can be used for water treatment. In this activation step, water soluble compounds such as the hydrophilic polymer may be partially extracted from the membrane layer. Hereby, the pores in the membrane layers are opened and the permeability or flux of water increases to a high level. The inventors surprisingly found that, when the 3D fabrics (1) of the present invention are used as support for the IPC membranes, the speed of extraction and the level of extraction in the activation step are improved and result in a faster activation process and in a higher flux. In the activation step, ususally an aqueous solution of sodium hypochlorite is used for extracting the hydrophilic polymer such as polyvinylpyrrolidone.

The flux of the activated IPC membranes of the present invention is preferably more than 1500 l/h.m².bar, more preferably more than 2000 l/h.m².bar, most preferably more than 2500 l/h.m².bar.

The integrated permeate channel (IPC) (23) is formed by the hollow structure (13) present in the the 3D fabric (1) between the two fabric layers (11, 12) and needs to be large enough in order not to hinder the transport of the permeated water during the filtration and/or backflush process. The volume of the IPC is defined by the width of the hollow structure, which may be reduced by partial penetration of the coated membrane layer into the inside of the 3D fabric. This penetration may depend on several parameters such as viscosity of the dope, open area of the fabric layers and coating parameters, and is usually very small, compared with the total thickness of the 3D fabric. The volume of the IPC is also reduced by the number of transitions of spacer threads between the two layers and by the diameter of the spacer threads. The preferred number of transitions and the preferred diameter of the spacer threads are as defined above.

In a preferred embodiment of the present invention, the IPC membrane (2) has a symmetric configuration wherein a symmetric 3D fabric (1) as defined above is coated on both sides with the same dope compostion, forming membrane layers which have substantially the same properties such as thickness and pore distribution.

In addition to filtration, purification and desalination of water, the membranes (2) of the present invention can also be used for microfiltration, ultrafiltration, nanofiltration, reverse osmosis, membrane distillation, pervaporation, gas separation, immobilizing biological active species, such as enzyme membrane reactors or biofilm reactors, in membrane contractors, supported liquid membranes, perstraction, evaporation, oxygenation, liquid degassing, water degassing, aeratrion, humidification (vapour permeation), controlled release, in air conditioning, gas/air cleaning, etc.

EXAMPLES

INVENTION EXAMPLES 1 to 4 and COMPARATIVE EXAMPLE 1.

Specific examples of 3D fabrics which are suitable for use in a membrane according to the present invention were previously summarized in Table 1.

Preparation of the coating solution CS-1

The coating solution CS-1 was prepared by dissolving polyethersulfon (PES) and polyvinylpyrrolidone (PVP) in a mixture of N-ethylpyrrolidone (NEP) and glycerol in amounts as given in Table 2.

Table 2 :

(1) NEP is N-ethylpyrrolidone

(2) PES is RADEL A-100PNT, a polyethersulphon commercially available from SOLVAY Company.

(3) PVP is LUVITEC K90, a polyvinylpyrrolidone commercially available from BASF Company.

The dynamic viscosity of the coating solution CS-1, measured with a MCR

500 apparatus at a temperature of 20°C, was about 150000 at a shear rate of 10 s^"1 and about 500000 at a shear rate of 0.1 s^"1.

Comparative 3D-fabrics C3D-01 : a knitted 3D-fabric wherein the two fabric layers are knitted with multifilament polyester threads and are connected to each other by loops of monofilament polyester threads, commercially available from Muller.

C3D-02: a knitted 3D-fabric wherein the two fabric layers are knitted with monofilament polyester threads and are connected to each other by loops of monofilament polyester threads, commercially available from Muller.

C3D-03: a knitted 3D-fabric wherein the two fabric layers are knitted with monofilament polyester threads and supported by additional supporting threads, and wherein the two fabric layers are connected to each other by loops of monofilament polyester threads, commercially available from Muller.

Preparation of IPC membranes 3D fabrics of the present invention as defined in Table 1 and comparative

3D-fabric materials such as the knitted 3D-fabrics defined above were simultaneously double-sided coated as described in WO 2008/141935 Al with the coating solution CS-1 at a temperature of 70°C by means of a double-sided slot coating apparatus. Immediately after coating, the fabric with the wet coating layers was passed through water-vapour having a relative humidity of about 100% during about 5 seconds and, subsequently, the material with the vapour induced pores in the coating layer was further put into a water tank having a temperature of 45°C. After about 5 minutes, the membrane material was further rinsed with water.

Table 3 summarises the composition of the IPC membranes of Invention Examples 1 to 4 and Comparative Example 1.

Table 3 :

Activation of IPC membranes

The IPC membranes were activated by washing with an aqueous solution of sodium hypochlorite in a concentration of 2 g/l and at a temperature of about 55°C. In this activation step, the polyvinylpyrrolidone present in the coated membrane layer was partially extracted from the membrane layers. The flux increase resulting from this washing process and the results are summarised in Table 4.

For measuring the flux of the membrane, the IPC membrane was split into two separated membrane layers by cutting the threads which connect the two fabric layers of the 3D-fabric. A tube, having a diameter of 45 mm, was positioned onto the outside surface of one of these split membrane layers. The tube was filled with water and a pressure of 1 bar was applied on the water tube. The flux was measured at each washing time as specified in Table 4. The flux is defined as the amount of water (in liter) permeated through an area of 1 m² of the membrane layer during 1 hour at a pressure of 1 bar.

Table 4:

The improved permeability of the IPC membranes is demonstrated by the Examples of Table 4. The flux of the membrane of the Comparative Example 1 increases gradually and after a washing time of about 1 hour a value of about 1350 l/h.m².bar is obtained. The flux of the membranes of the Invention Examples 1 and 4 increases also gradually, but, surprisingly, a much higher value of more than 3000 l/h.m².bar is achieved after about the same time period. The more efficient washing process demonstrates the high liquid permeability of the woven 3D-fabrics of the present invention.

After the washing step, the membranes were further treated with glycerol to stabilise the hydrophilic property of the membranes and with a biocide to protect the membrane. Finally, after these treatments, the membrane was dried. Pore diameter and backflush pressure

The IPC membranes of Invention Examples 1 to 4 and Comparative Example 1 are further characterised by the pore diameter and the backflush pressure as summarised in Table 5.

The measurement of the pore diameter of the membranes was carried out before the activation step and drying the membrane. The pore size was measured at the outside surface of the membrane by scanning electronic microscopy (SEM). By this SEM technique, an average pore size was determined which is comprised between the two values as indicated in Table 5, e.g. 0.20-0.30 μιη means that the average pore size has a value ranging between 0.20 μιη and 0.30 μιη.

The backflush pressure was measured by means of a Back-flush meter of Millipore. The IPC membrane was split into two separated membrane layers by cutting the threads which connect the two fabric layers of the 3D-fabric. A tube, having a diameter of 45 mm, was positioned on the inside surface of one of these splitted membrane layers. The tube was filled with water. The water pressure applied on the tube was measured by a manometer. The water pressure was increased until the membrane bursted. The pressure required to break the membrane defines the backflush pressure of the membrane.

Table 5 :

DMA fatigue test The IPC membranes of Invention Example 1 and Comparative Example 1 were further characterised by a fatigue test with Dynamic Mechanical Analysis, hereinafter also referred to as DMA. The DMA fatigue test was carried out by the use of a TA-Instruments DMA 2980 apparatus with a film tension geometry. An IPC membrane sample of 40 mm x 6.5 mm was clamped in the film tension geometry with a total sample length between fixed and movable clamp of approximately 20 mm. The actual sample length was accurately measured by the instrument and was used to calculate the amplitude necessary for an elongation of 0.5 %. The sample was stretched at this amplitude at an oscillation frequency of 20 Hz. The experiments were repeated with an elongation of 0.2 %. The storage modulus was measured as function of the time. The occurrence of initial damage was detected by the time required for poducing a decrease of the storage modulus. This time was measured in the warp direction, hereinafter also referred to as "Warp-D", and weft direction, hereinafter also referred to as "Weft-D", of the supporting 3D-fabric of the IPC membrane and both results are summarised in Table 6.

Table 6:

The DMA fatigue measurements demonstrate that the membrane of the present invention exhibits an increased resistance against occurrence of damages such as tears or cracks. This resistance, measured at an elongation of 0.5 %, is about 4 to 6 times higher than the IPC membrane of Comparative Example 1 and is approximately the same in both directions while the resistance of the membrane of Comparative Example 1 is about 2 times higher in the warp direction than in the weft direction. At an elongation of 0.2 %, no damage and no decrease of the storage modulus was observed for the Invention Example 1 during at least 8000 minutes, compared with the Comparative Example 1 which show a decrease of the storage modulus and damages after about 45 minutes. This improved dynamic stability demonstrates the improved quality of the IPC membranes of the present invention which exhibit a decreased number of defects in the membrane layers resulting in a longer life-time of the membrane.

INVENTION EXAMPLES 5 to 7 and COMPARATIVE EXAMPLES 2 and 3.

The preparation steps of the IPC membranes of Invention Examples 5 to 7 and Comparative Examples 2 and 3, as summarised in Table 7, was carried out in the same way as described above for Invention Example 1. Table 7 :

The pore diameter, flux and backflush pressure were measured for the IPC membranes of Invention Examples 5 to 7 as described above and the results are summarised in Table 8.

Table 8 :

The IPC membranes of the Invention Examples 1 to 4 have a pore size in the range of 0.20 to 0.30 μιη and are capable to resist to high backflush pressures of at least 5 bar.

Tensile stress-strain properties and compressive stress of 3D-woven fabrics

The strength properties of 3D-woven fabrics 3D-05, 3D-06, 3D-07 which are used in Invention Examples 5 to 7 and of knitted 3D-fabrics C3D-02 and C3D-03 which are used in Comparative Examples 2 and 3, were determined from the tensile stress-strain curve in tension of these 3D-fabrics, measured in accordance with ASTM D882-10. An Instron 4469 with a load cell of 500N was used with 3D-fabric strips of 25 mm x 70 mm at a temperature of 22°C (+/- 1°C) and a relative humidity of 50% (+/- 2%), specific gauge length of 70 mm, grip distance of 30 mm, sample rate of 0.015 pts/s, crosshead speed of 10.0 mm/minute and with the tensil program. From these stress-strain curves in tension, various mechanical properties can be determined such as the tensile modulus of elasticity, also known as Young's modulus, the Yield strength, the Ultimate strength and the Elongation at break.

The compressive stress of the 3D-fabrics was also measured by the use of a Instron 4469 wherein a load cell of 5000N was used to compress the 3D-fabrics with a compression rate of 20 mm/minute to a compression amplitude of 1 mm. The results obtained in warp and weft direction are summarised in Table 9.

Table 9 :

Table 9 demonstrates that the 3D-woven fabrics of the present invention exhibit a high value for the tensile modulus of about 100 N/mm² which reflect the improved stiffness and strength of these 3D fabrics, compared with the knitted 3D- fabrics of the Comparative Examples 2 and 3 which have a much Iower value (about 15 N/mm²) for the modulus.

This is also demonstrated by the high value of the ultimate strength for the 3D fabrics of the present invention, compared with the much Iower values for the knitted 3D-fabrics of the comparative examples. The high modulus of the 3D fabrics of the present invention is within a range of about 10 a 15 % the same in the warp direction (Warp-D) and weft direction (Weft-D) which demonstrate the isotropic behaviour and the dimentionally stability of the 3D fabrics, compared with the knitted 3D-fabrics of the Comparative Examples 2 and 3 which are anisotropic characterised by a modulus of 15 N/mm² to 1 N/mm² and 16 N/mm² to 6 N/mm² in both directions.

This high isotropic behaviour of the 3D fabrics of the present invention is further also demonstrated by the small difference between the value for the ultimate strength, while a much larger difference is obtained for the 3D-fabrics of the comparative examples.

The high isotropic behaviour of the 3D fabrics of the present invention is further also demonstrated by the small difference between the value for the elongation at break in each direction (about 1 or 2 %), while a much larger difference (4 % and even 55 %) is obtained for the knitted 3D-fabrics of the comparative examples.

The 3D fabrics of the present invention exhibit a high value for the compressive stress of about 12 to 16 N/cm² which demonstrate the improved resistance against compression of these 3D fabrics, compared with the knitted 3D- fabrics of the Comparative Examples 2 and 3 which have a much lower value (5 N/cm²) for the modulus.

Dimensional stability of 3D-woven fabrics

The dimensional stability of 3D-woven fabric 3D-01 which is used in Example 1 was determined using the following dimensional stability test.

Samples with a size of 250 x 450 mm were placed in a water bath during 20 days in standard environmental conditions of 20 °C (+/- 1 °C) and 50 %RH (+/- 2 %). These samples were then taken out of the bath and dried in an environmental chamber at 20 °C (+/- 0.5 °C) and 65 %RH (+/- 2%). The samples were measured after taking them out of the water bath and after the drying step.

From these measurements the dimensional stability in an aqueous environment and the regeneration ability can be determined. The results obtained in warp and weft direction are summarised in Table 10. Table 10:

Type 3D-01 3D-01

3D-fabric No. Initial dimension Warp-D 250 250

(mm) Weft-D 450 450

Dimension after water Warp-D 250.4 249.8

bath Weft-D 450.3 450.3 (mm)

Dimension after drying Warp-D 250 249.6

(mm) Weft-D 449.9 449.7

Table 10 demonstrates that the 3D-woven fabrics according to an embodiment of the present invention exhibit a high dimensional stability in an aqueous environment and after drying of the fabric.

The dimensions of the fabric change only by less than 0.2% in both warp

(Warp-D) and weft (Weft-D) direction after 20 days in an aqueous bath. This demonstrates the isotropic behaviour necessary for the use as a structural support.

The dimensions of the fabric change only by less than 0.2% in both warp (Warp-D) and weft (Weft-D) direction compared to the initial value after drying the fabrics in an environmental chamber which demonstrates the isotropic behaviour necessary for the reuse of the fabric.

Claims

1. A tridimensional woven fabric (1) comprising a first (11) and a second (12) fabric layer, which are mutually parallel layers separated from and connected to each other by spacer threads (131, 132), wherein both said fabric layers

(11, 12) are woven fabric layers comprising a plurality of weft (111, 121) and warp (112, 113, 122, 123) threads and wherein said spacer threads (131, 132) are interlaced with weft threads (111, 121) of both said fabric layers, characterised in that said warp threads (112, 113, 122, 123), said weft threads (111, 121) and said spacer threads (131, 132) are monofilament threads, wherein said warp (112, 113, 122, 123), weft (111, 121) and spacer (131, 132) threads comprise a polyester or a polyamide or copolymers thereof and the angle formed between the fabric layer and the spacer thread between the two fabric layers has an orientation which deviates from 90° by less than 15°.

2. Fabric (1) according to claim 1, wherein said angle deviates from 90° by less than 5°; preferably less than 2°.

3. Fabric (1) according to claim 1 or 2, wherein the surface roughness of the 3D fabric defined by the maximum distance between the most outer points of the warp (112,113, 122, 123) threads and the most inner cross-section between the warp and weft ((112,113) or (122, 123)) threads is 0 to 0.5 mm.

4. Fabric (1) according to claim 3, wherein said surface roughness is 0.01 to 0.2 mm.

5. Fabric (1) according to any of the preceding claims, wherein said spacer threads (131, 132) are woven into both said fabric layers (11, 12) by a weave pattern comprising (a) one or more interlacements between the spacer threads and the weft threads of said first fabric layer, (b) a transition of the spacer threads from said first (11) to said second (12) fabric layer, (c) one or more interlacements between said spacer threads and the weft threads of the second fabric layer and (d) a transition of the spacer threads from the second

(12) to the first (11) fabric layer.

6. Fabric (1) according to claim 5, wherein the number of interlacements between the spacer threads and the weft threads of the first fabric layer and the number of interlacements between the spacer threads and the weft threads of the second fabric layer are independently an odd number higher than one.

7. Fabric (1) according to claim 6, wherein the number of interlacements between the spacer threads and the weft threads of the first fabric layer and the number of interlacements between the spacer threads and the weft threads of the second fabric layer are independently selected from three, five, seven and nine.

8. Fabric (1) according to claim 7, wherein the weave pattern of the spacer threads (131, 132) is a 3/6 W pattern.

9. Fabric (1) according to any of the preceding claims, wherein the number of weft threads ranges from 5 to 40 per cm and the number of warp threads ranges from 12 to 42 per cm.

10. Use of a tridimensional woven fabric (1) according to any of the preceding claims as a support structure in a multilayer structure, preferably said structure is a membrane (2) for liquid or air filtration.

11. A membrane (2) for water treatment comprising :

- a water-permeable tridimensional fabric (1) according to any of claims 1 to 10;

- a polymeric membrane layer (21, 22) applied on each of said fabric layers (11, 12), wherein each membrane layer (21, 22) is at least partially embedded in the respective fabric layer (11, 12); and

- a permeate channel (23) between said membrane layers (21, 22);

characterised in that said tridimensional fabric (1) is a woven fabric wherein both said fabric layers (11, 12) are woven fabric layers comprising a plurality of weft (111, 121) and warp (112, 113, 122, 123) threads and wherein said spacer threads (131, 132) are interlaced with weft threads (111, 121) of both said fabric layers (11, 12).

12. Membrane according to claim 11, wherein the tridimensional woven fabric (1) has a structure which is symmetric with respect to the permeate channel (23).

13. Membrane according to claim 11 or 12, wherein said membrane (2) comprises two membrane layers coated on opposite surfaces of said tridimensional woven fabric (1).

14. A water filter module comprising a plurality of membranes (2) as defined in any of the preceding claims.

15. Use of a membrane (2) according to any of the preceding claims for the

treatment of water, in particular for filtration and/or purification of domestic or industrial wastewater or for desalination of seawater or brackish water.