Mineral porous article

Abstract

The present invention relates to a porous article comprising inorganic particles comprising from 3 to 35 wt.-%, based on the total amount of the porous article, inorganic fillers with anisotropic shape, at least one surfactant and a geopolymer obtained from polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from the inorganic binder comprising aluminosilicates in the presence of an activator comprising a water-soluble inorganic silicate, wherein the pores of the porous article having a mean pore size of not more than 2.0 mm; a process for producing said porous article; and the use of said porous article for building insulation.

Description

[0001] Mineral Porous Article

[0002] The present invention relates to a porous article comprising inorganic particles comprising from 3 to 35 wt.-%, based on the total amount of the porous article, inorganic fillers with anisotropic shape, at least one surfactant and a geopolymer obtained from polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from the inorganic binder comprising aluminosilicates in the presence of an activator comprising a water-soluble inorganic silicate, wherein the pores of the porous article having a mean pore size of not more than 2.0 mm; a process for producing said porous article; and the use of said porous article for building insulation.

[0003] Technical background

[0004] Thermal insulation market demand continues to grow, owing to the growing investments towards improving energy efficiency in buildings. To date, buildings account for approximately 40% of the global energy demands, with a corresponding estimated greenhouse gas emission value of 36%. This significant energy demand is due to the high heating and cooling energy requirements coming from buildings with inadequate thermal insulation systems. In order to reduce building energy demands, effective and sustainable thermal insulation is required, contributing to reduced energy use and CO2 emissions.

[0005] Today’s mostly used insulation materials are based on organic materials (polystyrene, polyurethane, cellulose) or inorganic materials (mineral wool, glass wool), which are either costly, flammable, toxic or difficult to recycle. The unsuitability of flammable insulation solutions is seen in fire tragedies. This has since led to growing legislature into the development and use of non-flammable solutions.

[0006] Generally, mineral or inorganic foams display significant advantages when used for insulation purposes. This material class is more lightweight than the bulk counterpart due to its porosity or empty spaces. These pores or empty spaces are due to the presence of air or other gases in the mineral matrix, and they may be in the form of bubbles. From 1 m3of a bulk material with a density of 2000 kg / m3it is possible to produce approximately 5 m3of a finished product if the porous body is composed by 20% of material and 80% of air (final density of approximately 400 kg / m3). Several inorganic solutions, such as porous cement or calcium silicate have been developed as sustainable alternatives. Despite having demonstrated interesting thermal and fire resistance properties, they present limited mechanical stability for thermal conductivities lower than 0.04 W / mK and they are typically associated with a substantial carbon footprint. In this context, US 2017 / 158568 A1 and WO 2017 / 093796 A1 in each case disclose a method for producing an ultra-light mineral foam (claimed 20 to 300 kg / m3, 0.030 - 0.150 W / (m. K)), wherein a slurry of Portland cement and an aqueous foam comprising water and a foaming agent are mixed. Thereby, a slurry of foamed cement is obtained, which is then subjected to casting and hardening upon cement hydration. In addition to cement foams, ceramic foams have been developed. EP 1 960 097 B1 discloses the manufacturing of porous ceramic articles, wherein said wet foams are prepared from a foamed suspension comprising colloidal particles. The surface of said particles has been modified by short chain surfactants and the hardening step was conducted upon sintering. Alternatively, aerogels tend to reach extremely low thermal conductivities, while being flame resistant. However, aerogels remain very expensive and cannot be produced at scale as a panels (at least 600x400 mm). Thus, they are blended in mortars (WO 2019 / 211421 A1 ) and are used in specific niche applications. As a result, there is a gap in the building insulation market that is not filled by currently available solutions.

[0007] The present invention provides a porous article comprising inorganic particles comprising inorganic fillers with anisotropic shape, at least one surfactant, a geopolymer derived from an inorganic binder comprising aluminosilicates and an activator comprising water-soluble metal hydroxide, which can be produced from inexpensive and ecologically friendly raw materials. The raw materials include inorganic particles with anisotropic shape and activators comprising water-soluble metal hydroxide such as water-soluble inorganic silicate. It has surprisingly been found that from a suspension of inorganic particles comprising inorganic fillers with anisotropic shape, at least one surfactant, an inorganic binder comprising aluminosilicates and an activator comprising water-soluble inorganic silicate stable foams can be obtained, which can be transformed into porous articles having a small pore size of not more than 2.0 mm, which show a superior balance of properties in regard of high porosity, good thermal insulation in form of low thermal conductivity (lower than 0.04 W / mK) and sufficient mechanical strength (compressive strength greater than 50 kPa) to be used as insulation board. Due to their composition the porous articles are non-flammable. The unique combination of ecologically friendly raw materials and smart processing imparts a very low ecological impact of the porous article.

[0008] The porous articles according to the present invention is therefore non-flammable lightweight, sustainable, thermal insulation, which shows a competitive mechanical strength. Summary of the invention

[0009] In a first aspect the present invention relates to a porous article comprising a) inorganic particles comprising from 3 to 35 wt.-%, preferably from 4 to 30 wt.-%, more preferably from 5 to 25 wt.-%, based on the total amount of the porous article, inorganic fillers with anisotropic shape, preferably clay or clay-based platelet particles; b) at least one surfactant; and c) a geopolymer obtained from polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from

[0010] • an inorganic binder comprising aluminosilicates, in the presence of

[0011] • an activator comprising a water-soluble inorganic silicate, wherein the pores of the porous article have a mean pore size of not more than 2.00 mm, such as in the range of from 0.01 to 2.00 mm, preferably from 0.02 to 1 .50 mm, more preferably from 0.05 to 1 .00 mm, still more preferably from 0.10 to 0.80 mm, measured by microscopy analysis.

[0012] In a second aspect the present invention relates to a process for producing the porous article as described above or below comprising the steps of

[0013] • providing a suspension comprising an aqueous liquid, preferably water, the inorganic particles comprising the inorganic fillers with anisotropic shape, preferably clay or clay-based platelet particles, and the inorganic binder, the at least one surfactant, the activator, and optionally additives, wherein the at least one surfactant at least partially hydrophobizes the surface of at least a part of the inorganic particles and a geopolymer is formed by polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from the inorganic binder in the presence of the activator;

[0014] • foaming the suspension comprising the inorganic particles, from which at least a part has an at least partially hydrophobized surface to obtain a foam;

[0015] • shape and expand the foam by casting or extruding or additive manufacturing, in particular 3D-printing, said foam to obtain a wet porous body,

[0016] • optionally setting or curing the wet porous body, and / or

[0017] • optionally drying or partially drying the wet porous body; and obtaining the porous article.

[0018] In a third aspect the present invention relates to the use of the porous article as described above or below for building insulation.

[0019] Definitions

[0020] Fillers having “anisotropic shape” means that the particle has a geometry with at least two axes with different length. Examples of anisotropic shape or geometry are platelets, oblate spheroids and rods. The shape anisotropy can be described by the aspect ratio. The aspect ratio is defined as the longer axes divided by the shorter axis. In case of an irregularly shaped particle, the axes are estimated from a fit of the particle shape.

[0021] Where the present description refers to “preferred” embodiments / features, combinations of these “preferred” embodiments / features are also deemed to be disclosed as long as the specific combination of the “preferred” embodiments / features is technically meaningful. Unless otherwise stated, the following definitions shall apply in this specification:

[0022] As used herein, the term "a", "an", "the" and similar terms used in the context of the present invention (especially in the context of the claims) are to be construed to cover both the singular and plural unless otherwise indicated herein or clearly contradicted by the context.

[0023] As used herein, the term “and / or” means that either all or only one of the elements of said group may be present. For example, “A and / or B” means “A, or only B”, or both “A and B”. In the case of “A”, the term also covers the possibility that B is absent, i.e. “A, but not B”.

[0024] As used herein, the terms "including", "containing" and "comprising" are used herein in their open-ended, non-limiting sense. It is understood that the various embodiments, preferences, and ranges may be combined at will. Thus, for instance a solution comprising a compound A may include other compounds besides A. However, the term “comprising” also covers, as a particular embodiment thereof, the more restrictive meanings of “consisting essentially of” and “consisting of, so that for instance a solution comprising A, B and optionally C” may also (essentially) consist of A and B, or (essentially) consist of A, B and C.

[0025] As used herein, the transitional phrase “consisting essentially of” (and grammatical variants) is to be interpreted as encompassing the recited materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention. Thus, the term “consisting essentially of” should not be interpreted as equivalent of “comprising”.

[0026] As used herein, the term “consisting of” means a closed list without any further compounds.

[0027] As used herein, the term "about" means that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the term "about” denoting a certain value is intended to denote a range within ± 5 % of the value. As one example, the phrase "about 100" denotes a range of 100 ± 5, i.e. the range from 95 to 105. Preferably, the range denoted by the term "about" denotes a range within ± 3 % of the value, more preferably ± 1 %. Generally, when the term "about" is used, it can be expected that similar results or effects according to the invention can be obtained within a range of ±5 % of the indicated value.

[0028] Brief description of the figures

[0029] Figure 1 shows a SEM micrograph of a porous article according to the present invention showing a smooth surface facing a mesopore.

[0030] Figure 2 shows a further SEM micrograph of a porous article according to the present invention at a higher enlargement showing the border between the platelet-like smooth surface of the inorganic fillers with anisotropic shape to the more three-dimensional structure of the geopolymer.

[0031] Detailed description of the invention

[0032] In a first aspect the present invention relates to a porous article comprising a) inorganic particles comprising from 3 to 35 wt.-%, preferably from 4 to 30 wt.-%, more preferably from 5 to 25 wt.-%, based on the total amount of the porous article, inorganic fillers with anisotropic shape, preferably clay or clay-based platelet particles; b) at least one surfactant; and c) a geopolymer obtained from polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from

[0033] • an inorganic binder comprising aluminosilicates, in the presence of

[0034] • an activator comprising a water-soluble inorganic silicate, wherein the pores of the porous article have a mean pore size of not more than 2.00 mm, such as in the range of from 0.01 to 2.00 mm, preferably from 0.02 to 1 .50 mm, more preferably from 0.05 to 1 .00 mm, still more preferably from 0.10 to 0.80 mm, measured by microscopy analysis.

[0035] The porous article comprises inorganic particles. Inorganic particles preferably comprise i. Inorganic fillers

[0036] II. Inorganic binders

[0037] The inorganic particles usually are not soluble in water and therefore form a slurry in water.

[0038] Preferably, the at least part of the inorganic particles, such as from 15 to 100 wt.-% based on the total weight of the inorganic particles, originate from sources of abundance, which make these inorganic particles comparatively cheap, easy to obtain and having a low environmental footprint. a) Inorganic fillers

[0039] The porous article comprises inorganic fillers.

[0040] The inorganic fillers can include any inorganic particles suitable for the production of porous articles, especially for building insulation.

[0041] The inorganic fillers usually are not soluble in water and therefore form a slurry in water. The inorganic fillers are distinguishable from the activator comprising a water-soluble inorganic silicate, which is soluble in water.

[0042] Further, the inorganic fillers are distinguishable from the inorganic binder, which is activated in the presence of the activator and forms a geopolymer. In contrast to that the inorganic fillers are not activated in the presence of the activator and therefore do not actively contribute to the polycondensation reaction to form a geopolymer.

[0043] The inorganic fillers preferably differ from the inorganic binder in a higher crystallinity. In the context of this invention, the inorganic fillers can get incorporated into the hardened matrix.

[0044] Preferably, the at least part of the inorganic fillers, such as from 15 to 100 wt%, preferably from 80 to 100 wt%, more preferably from 85 to 100 wt%, based on the total weight of the inorganic fillers, originate from sources of abundance, which make these inorganic particles comparatively cheap, easy to obtain and having a low environmental footprint.

[0045] In one embodiment the inorganic fillers consist of inorganic particles, which originate from sources of abundance.

[0046] Suitable sources of abundance for the inorganic fillers are

[0047] • naturally occurring fillers,

[0048] • inorganic waste particles and fibers,

[0049] • inorganic fillers and fibers obtained from industrial processes and recycling processes,

[0050] • and mixtures thereof.

[0051] Inorganic fillers originating from naturally occurring fillers, secondary raw materials in the form of inorganic waste particles and fibers, inorganic fillers and fibers obtained from industrial processes and recycling processes are materials with a low environmental impact.

[0052] Especially secondary raw materials in the form of inorganic waste particles and fibers and inorganic fillers and fibers obtained from industrial processes and recycling processes are usually used for landfill so that the use of such materials for the production of porous articles reduces their environmental impact and contributes to an up-cycling process in a waste-to-x approach.

[0053] Naturally occurring fillers, inorganic waste particles and fibers, inorganic fillers and fibers obtained from industrial processes and recycling processes do not contribute to the polycondensation process for forming the geopolymer. Naturally occurring fillers are preferably selected from mafic and ultramafic rocks and / or silica and / or phyllosilicates and their derivates, such as serpentine, clay and / or clay based materials, mica, feldspar, and / or perlite and / or calcium carbonate or sand, and combinations thereof, more preferably from serpentine, clay, mica, perlite, calcium carbonate and combinations thereof, still more preferably from clay, calcium carbonate, and mixtures thereof.

[0054] Clay based materials, i.e. clay minerals, are compounds, which mainly comprise silicon dioxide (SiC ), aluminium oxide (AI2O3). Possible traces of quartz (SiC ) and metal oxides such as aluminium oxide (AI2O3) and magnesium oxide (MgO) iron oxide (Fe20s) and alkali oxides such as potassium oxide (K2O) and sodium oxide (Na2O) can be present. Preferably, the clay mineral is selected from kaolin, montmorillonite-smectite, illite, chlorite, vermiculite, talc, pyrophyllite, halloysite, sepiolite, palygorskite and mixtures thereof.

[0055] Inorganic waste particles and fibers preferably originate from inorganic waste, such as glass and stone wool cutting processes, waste glass, ceramic waste and its dust, slags from sewage treatment and waste incineration, milled construction and demolition waste and mixtures thereof.

[0056] The inorganic waste particles and fibers comprise organic compounds in an amount of usually not more than 15 wt.-%, such as from 0 to 15 wt.-%, preferably 0.1 to 12.5 wt.- %, based on the total amount of the inorganic waste particles and fibers.

[0057] Inorganic fillers and fibers obtained from industrial processes and recycling processes are preferably selected from excavated materials, filter cakes from excavated materials and aggregate washing, inorganic particles and fibers obtained from mineral processing tailings, catalyst residues, calcium poor combustion residues without activable aluminosilicate sites, sludge from water treatments, particles and lightweight aggregate from mineral foams and mixtures thereof.

[0058] The inorganic fillers and fibers obtained from industrial processes and recycling processes comprise organic compounds in an amount of usually not more than 15 wt.- %, such as from 0 to 15 wt.-%, preferably 0.1 to 12.5 wt.-%, based on the total amount of the inorganic fillers obtained from industrial processes and recycling processes. The inorganic fillers can also be obtained by recycling final consolidated porous articles that have already been prepared previously, e.g. by the method according to the invention, wherein said final porous articles are crushed down so as to generate particles or the non-hardened porous article is dispersed in water, which particles are then re-used for a new preparation of porous articles according to the invention. In case of a final porous article, the binder phases, i.e. cement, geopolymers and the like, have been hardened during consolidation and will be used as inorganic filler. Since a fraction of the surfactants may volatize during the drying process or in general not being available as if freshly added, additional surfactant might be required to prepare stable foams from this recycled material.

[0059] It is mandatory that the inorganic fillers comprise inorganic fillers with anisotropic shape such as particles with a shape of platelets, oblate spheroids and / or rods.

[0060] Preferably inorganic fillers with anisotropic shape are particles with platelet structure, more preferably clay or clay-based platelet particles.

[0061] The aspect ratio of the anisotropic particles preferably ranges from 1 .1 to 500, preferred from 2 to 350 even more preferred from 2 to 300.

[0062] In case of rods, for safety reasons, the aspect ratio should be smaller than 3, i.e. from 1.1 to 3, if the axis-1 is greater than 5 pm and axis-2 smaller than 3 pm.

[0063] It has been found that the shape of the inorganic fillers with anisotropic shape provide several technical benefits:

[0064] In-situ (partially) hydrophobized inorganic fillers with anisotropic shape, such as clay particles, (by means of a surfactant, often electrostatically adsorbed on the solid surface of clay) adsorb at liquid-gas interfaces and stabilize bubbles upon Pickering mechanism upon foaming. Inorganic fillers with anisotropic shape, such as clay particles, are more effective bubble stabilizers compared to a spherical colloid since the platelet-like geometry leads to pinning phenomena at liquid interfaces. Thus, the energy penalty for desorption is higher compared to spherical particles. Additionally, liquid interfaces decorated with anisotropic particles gain interfacial yield stress. The resulting bubble has a finite rigidity or resistance to deformation leading to an increased bubble stability. Further, inorganic fillers with anisotropic shape, such as clay particles, can act as slurries rheology modifier. Clay has the capability to create a “house of cards” thus increases the slurry yield stress. The presence of water-soluble silicates strongly reduces this effect even making it vanishing to zero.

[0065] Still further, especially clay is a sustainable source of inorganic particle with anisotropic shape since it is an abundant, local, affordable raw material with negligible life cycle impacts.

[0066] Preferably, the inorganic fillers have an upper cut-off size of not more than 100 pm, more preferably not more than 75 pm, still more preferably not more than 63 pm in its largest dimension.

[0067] The lower limit of the cut-off size is usually 1 nm, preferably 100 nm, more preferably 200 nm in its largest dimension.

[0068] The upper cut-off size of the inorganic fillers with a larger upper cut-off size can be adjusted by sieving or ball milling techniques as commonly known in the present field of technology.

[0069] Clays are formed by anisotropic particles in the shape of platelets. In this case, the particle size refers to the largest dimension. Clay particles can exfoliate in basic conditions, e.g. in the presence of metal hydroxide and / or water-soluble inorganic silicate upon prolonged stirring or sonication increasing the shape anisotropy. If desired, the particle size can be adjusted by sieving or ball milling techniques as commonly known in the present field of technology.

[0070] The inorganic fillers are preferably untreated particles that can be used directly, wherein no purification process is required.

[0071] The total weight amount of inorganic fillers in the porous article is preferably in the range of from 3 to 50 wt.-%, more preferably from 5 to 40 wt.-%, still more preferably from 10 to 30 wt.-%, based on the total weight of the porous particle.

[0072] The amount of inorganic fillers with anisotropic shape, preferably clay or clay-based platelet particles, in the porous article is in the range of from 3 to 35 wt.-%, preferably from 4 to 30 wt.-%, more preferably from 5 to 25 wt.-%, based on the total amount of the porous article.

[0073] It is preferred that the amount of inorganic fillers with anisotropic shape in the total amount of inorganic fillers is in the range of from 20 to 100 wt.-%, preferably 25 to 100 wt.-%, more preferably 30 to 100 wt.-%, based on the total weight of the inorganic fillers present in the porous article. b) Surfactant

[0074] The porous article further comprises at least one, such as one to five, more preferably one or two, still more preferably one surfactant.

[0075] The at least one surfactant is preferably selected from surfactants being amphiphilic molecules comprising a hydrophobic group coupled to a hydrophilic group, wherein hydrophobic group comprises a backbone chain comprising at least 10 carbon atoms, preferably from 10 to 30 carbon atoms, more preferably from 10 to 26 carbon atoms. In an especially preferred embodiment the hydrophobic group comprises a backbone chain comprising from 12 to 26 carbon atoms.

[0076] By adding an amphiphilic surfactant to the suspension comprising the inorganic particles, depending on the type of surfactant, an initially hydrophobic or lyophobic particle surface can be rendered more hydrophilic or lyophilic, and an initially hydrophilic or lyophilic particle surface can be rendered more hydrophobic or lyophobic, respectively. The meaning of the terms “hydrophobic”, “lyophobic”, “hydrophilic” and “lyophilic” as used herein corresponds to the generally known meaning of these terms. For example, hydrophilic / lyophilic means readily dispersed by water / a solvent or readily absorbing water / a solvent, whereas hydrophobic / lyophobic means the opposite.

[0077] The use of surfactants having a backbone chain comprising at least 10 carbon atoms, not only yields foam stabilization through particles present at the gas-liquid interface, but the stability of the generated wet foam is also ensured by the formation of a particle percolating network formed around the air bubbles generated upon the foaming of the suspension. The percolating network can be seen as a gelation or strengthening structure, which increases the stability of the foam. The expression “percolating network” is well-known in the state of the art and can be referred to as a “percolating network of modified particles that form a gel with elastic modulus higher than the viscous modulus”. Generally, the percolation network is based on any kind of surface-active particles and active molecules. Active particles correspond to particles whose surface can be modified by the adsorption of molecules such as surfactants or which can adsorb at the gas-liquid interface without any surface modification. Active molecules are molecules such as surfactants that can adsorb at the surface of particles or at the gas-liquid interface.

[0078] It is preferred that the at least one surfactant has a molecular weight of at least 150 g / mol, such as from 250 to 1000 g / mol, more preferably from 300 to 900 g / mol, still more preferably from 350 to 750 g / mol, determinable by GPC measurement and / or mass spectroscopy

[0079] When using commercially available surfactants, their molecular weight is usually disclosed in the technical data sheet.

[0080] The at least one surfactant is preferably present in the porous article in an amount of 0.001 to 1 .0 wt.-%, preferably 0.01 to 0.8 wt.-%, more preferably 0.02 to 0.5 wt.-%, still more preferably from 0.03 to 0.4 wt.-%, based on the total weight of the porous article.

[0081] The at least one surfactant can be an anionic surfactant, a cationic surfactant or a zwitterionic surfactant.

[0082] It is preferred that the at least one surfactant is selected from anionic surfactants or cationic surfactants, preferably from cationic surfactants comprising ammonium, pyridinium, pyrrolidinium, piperidinium, imidazollium, morphollinium cations and / or amines.

[0083] Preferred cationic surfactants comprising ammonium cations are selected from didecyldimethylammonium bromide, didecyldimethylammonium chloride, dimethylditetradecylammonium bromide, benzyldimethylstearylammonium chloride monohydrate, trimethyltetradecylammonium bromide, methyl bis[ethyl (tallowate)] -2- hydroxyethyl ammonium methyl sulfate (commercially available as Stepantex® VK 90 from Stepan), decyltrimethylammonium bromide, benzyldodecyldimethylammonium bromide, 1 ,2-stearoyl-3-trimethylammonium-propane (chloride salt), benzyldimethylstearylammonium chloride, methylbenzethonium chloride, didodecyldimethylammonium bromide, dimethyldioctadecylammonium bromide, dimethyldihexadecylammonium bromide, dimethyldioctadecylammonium bromide, dimethyldioctadecylammonium chloride, cetyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, benzyldimethylstearylammonium chloride monohydrate, dodecylethyldimethylammonium bromide, domiphen bromide, n-alkyl dimethyl benzyl ammonium chloride, behentrimonium chloride and mixtures thereof.

[0084] Preferred cationic surfactants comprising pyridinium cations are selected from N- dodecylpyridinium chloride, 1 -dodecylpyridinium bromide, hexadecylpyridinium bromide, N-octylpyridinium chloride, 1 -cetylpyridinium chloride and mixtures thereof.

[0085] Preferred cationic surfactants comprising amines are selected from decylamine, laurylamine, tetradecylamine, hexadecylamine, octadecylamine and mixtures thereof.

[0086] Especially preferred are cationic surfactants selected from cetyltrimethylammoniumbromide, tetradecyltrimethylammoniumbromide, dodecyltrimethylammonium chloride, 1 -cetylpyridinium chloride, decylamine.

[0087] It is preferred that at least part of the inorganic particles and at least one surfactant are oppositely charged.

[0088] In the presence of clay or clay-based platelet particles at least part of the at least one surfactant is a cationic surfactant.

[0089] The weight ratio of inorganic fillers to at least one surfactant in the porous article is preferably in the range of from 25 : 1 to 1000 : 1 , more preferably from 35 : 1 to 750 : 1 , still more preferably from 40 : 1 to 500 : 1 .

[0090] The weight ratio of inorganic filler with anisotropic shape to at least one surfactant in the porous article is preferably in the range of from 25 : 1 to 900 : 1 , more preferably from 35 : 1 to 650 : 1 , still more preferably from 40 : 1 to 400 : 1 . c) Geopolymer

[0091] A geopolymer is an aluminosilicate polymer, which is usually formed by polycondensation of repeating units comprising silicate ions and aluminate ions from activated aluminosilicates.

[0092] In the present invention the sources for the geopolymer are an inorganic binder comprising aluminosilicates, which is activated by an activator comprising a water- soluble inorganic silicate. The activator preferably is a basic activator, which in solution increases the pH of the solution to more than 7, such as to a range of from 8 to 13.

[0093] In the basic surroundings of the solved activator the inorganic binder is preferably activated (i.e. partially dissolved) and the geopolymer is formed by polycondensation.

[0094] Typically, 10 to 100 wt.-%, preferably 20 to 95 wt.-%, more preferably 25 to 90 wt.-% of the inorganic binder present in the porous article are reacted to form a geopolymer.

[0095] Further, preferably 10 to 100 wt.-%, preferably 20 to 95 wt.-%, more preferably 25 to 90 wt.-% of the activator present in the porous article are reacted to form a geopolymer.

[0096] It is preferred that the geopolymer is present in the porous article in an amount of from 5 to 65 wt.-%, more preferably from 10 to 60 wt.-%, based on the total weight of the porous article.

[0097] • Inorganic binder

[0098] The inorganic binder can be natural or man-made. Inorganic binder comprises:

[0099] • aluminosilicate sources with latent hydraulic properties,

[0100] • hydraulic binders,

[0101] • non-hydraulic binders, or mixtures thereof.

[0102] One suitable group of inorganic binders are aluminosilicate sources with latent hydraulic properties also referred as latent hydraulic binder, also referred as pozzolans.

[0103] They are usually siliceous and / or aluminous materials (i.e. materials comprising SiO2 and / or AI2O3) that can display an amorphous part and / or an amorphous part based on aluminosilicates containing Al3+cations such that, in particulate form, react chemically with hydroxides comprising sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)2) in the presence of water at ordinary temperature to form compounds possessing cementitious properties.

[0104] Aluminosilicate sources with latent hydraulic properties, are preferably selected from calcined clay, such as metakaolin, fly ash, coal bottom ash, rice husk ash, palm oil ash, paper sludge ash and slags from metallurgic processes, expanded perlite, microsilica (silica fume), volcanic ash, pumice, diatomaceous earth, and mixtures thereof. Preferred examples of an aluminosilicate sources with latent hydraulic properties are calcined clay, like metakaolin, slags and ashes, like fly ash (F and / or C), and mixtures thereof, more preferably metakaolin and fly ash and mixtures thereof. Ashes and slags often refer also as secondary raw materials.

[0105] Fly ash is a heterogeneous material with silicon dioxide (SiC ), aluminium oxide (AI2O3), iron oxide (Fe20s) and calcium oxide (CaO) being the main chemical components. Certain grades of fly ash, such as class F or class C are pozzolanic. Fly ash is a lightweight residual from combustion processes and is captured by filtering equipment from flue gases. It is able to react and harden in an alkaline environment e.g.in presence of free lime in water or alkali-silicate solutions leading to geopolymer.

[0106] Metakaolin is a type of calcined clay that is produced by firing kaolin clay to high temperatures (around 600-950°C), which causes it to undergo a transformation in its mineral structure and obtaining a partially amorphous state of the starting kaolin or kaolinic clay. Metakaolin is a pozzolanic material. Due to these amorphous components, it is able to react and harden in alkaline environment e.g.in presence of free lime in water or alkali-silicate solutions leading to geopolymer.

[0107] These inorganic binders are obtained from industrial processes, like pyrolysis, combustion, metallurgy processes, mining and froth frothation.

[0108] Another suitable group of inorganic binders are hydraulic binders which are processed inorganic particles, i.e. inorganic particles, which are especially prepared usually by using energy, such as GEM l-V, calciumsulfoaluminates (CSA), calciumaluminate cements (CAC), quicklime (CaO), gypsum, calcium sulfate, calcium aluminate, portlandite (Ca(OH)2), Mg(OH)2, MgO, and mixtures thereof. Preferred are calciumaluminate cements (CAC) and calciumsulfoaluminates (CSA) and mixtures thereof. Especially preferred are calciumaluminate cements (CAC).

[0109] Another suitable group of inorganic binders are non-hydraulic binder. An example of non-hydraulic binder is calcium sulfate hemi-hydrated.

[0110] Fly ash of type C and several possible other calcium-rich pozzolans (e.g. Ca-rich slags), are binders with both a hydraulic and latent-hydraulic characteristics. Depending on the extent of self-cementing properties, they can be treated as latent-hydraulic or hydraulic. For the sake of this invention, they are grouped as aluminosilicate sources with latent hydraulic properties.

[0111] The total amount of inorganic binder present in the porous article either in form of repeating units of the geopolymer or as unreacted residue is preferably in the range of from 10 to 70 wt.-%, more preferably from 15 to 65 wt.-%, still more preferably from 15 to 60 wt.-%, based on the total weight of the porous article.

[0112] The inorganic binder preferably comprises aluminosilicate sources with latent hydraulic properties, more preferably calcined clay, like metakaolin, slags and ashes, like fly ash (F and / or C), and mixtures thereof, more preferably metakaolin and fly ash and mixtures thereof.

[0113] In one preferred embodiment the inorganic binder is a mixture of metakaolin and fly ash. In said embodiment it is especially preferred that the amount of metakaolin present in the porous article either in form of geopolymer or as unreacted residue is preferably in the range of from 8 to 58 wt.-%, more preferably from 12 to 52 wt.-%, still more preferably from 10 to 45 wt.-%, based on the total weight of the porous article.

[0114] It is further preferred in said embodiment that the amount of fly ash present in the porous article either in form of geopolymer or as unreacted residue is in the range of from 2 to 25 wt.-%, more preferably from 3 to 20, still more preferably from 5 to 15 wt.- %, based on the total weight of the porous article.

[0115] In said embodiment the weight ratio of metakaolin to fly ash is preferably in the range of from 10.0 : 1 .0 to 1 .5 :1 .0, more preferably from 7.5 : 1 .0 to 2.0 : 1 .0, still more preferably from 5.0 to 1 .0 to 3.0 to 1 .0.

[0116] In another embodiment the inorganic binder is a mixture of fly ash and metakaolin.

[0117] In said embodiment it is especially preferred that the amount of fly ash present in the porous article either in form of geopolymer or as unreacted residue is preferably in the range of from 8 to 58 wt.-%, more preferably from 12 to 52 wt.-%, still more preferably from 10 to 45 wt.-%, based on the total weight of the porous article.

[0118] It is further preferred in said embodiment that the amount of metakaolin present in the porous article either in form of geopolymer or as unreacted residue is in the range of from 2 to 25 wt.-%, more preferably from 3 to 20, still more preferably from 5 to 15 wt.- %, based on the total weight of the porous article.

[0119] In said embodiment the weight ratio of fly ash to metakaolin is preferably in the range of from 10.0 : 1 .0 to 1 .5 :1 .0, more preferably from 7.5 : 1 .0 to 2.0 : 1 .0, still more preferably from 5.0 to 1 .0 to 3.0 to 1 .0.

[0120] In another embodiment the inorganic binder is a mixture of the aluminosilicate sources with latent hydraulic properties and hydraulic binder. Preferably, the hydraulic binder is a calcium aluminate cement.

[0121] In said embodiment the weight ratio of aluminosilicate sources with latent hydraulic properties to hydraulic binder is preferably in the range of from 99:1 to 1 :3, more preferably from 90:10 to 1 :2, still more preferably from 85:15 to 51 :49.

[0122] The amount of aluminosilicate sources with latent hydraulic properties present in the porous article either in form of geopolymer or as unreacted residue is preferably in the range of from 10 to 60 wt% to, more preferably from 15 to 49, even more preferably from 15 to 40 of the total weight of the porous article.

[0123] The amount of hydraulic binder present in the porous article either in form of geopolymer or as unreacted residue is preferably in the range of from 1 to 49 to, more preferably from 5 to 40, even more preferably from 10 to 35 of the total weight of the porous article. In a preferred embodiment, the aluminosilicate sources with latent hydraulic properties represent the majority of the overall amount of inorganic binder.

[0124] Inorganic binders can be in-situ (partially) hydrophobized by means of a surfactant, often electrostatically adsorbed on the solid surface. In this way, they can adsorb at liquid-gas interfaces and stabilize bubbles upon Pickering mechanism upon foaming.

[0125] For this specific purpose, also inorganic binders preferably have an upper cut-off size of not more than 100 pm, more preferably not more than 75 pm, still more preferably not more than 63 pm in its largest dimension.

[0126] The lower limit of the cut-off size is usually 1 nm, preferably 100 nm, more preferably 200 nm in its largest dimension. The upper cut-off size of the inorganic binders with the larger upper cut-off size can be adjusted by sieving or ball milling techniques as commonly known in the present field of technology.

[0127] For example, fly ash particles are generally spherical in shape and range in size from about 0.5 pm to about 15 pm.

[0128] It is preferred that at least 55 vol%, such as from 55 to 100 vol%, more preferably 60 to 100 vol% of the inorganic particles have an upper cut-off size of not more than 75 pm, preferably not more than 65 pm, more preferably not more than 60 pm in its largest dimension.

[0129] The lower limit of the cut-off size is usually 1 nm, preferably 100 nm, more preferably 200 nm in its largest dimension.

[0130] In one preferred embodiment the inorganic particles in the porous article is a mixture of clay, optionally unreacted inorganic binders, such as unreacted metakaolin and / or unreacted fly ash, and optionally inorganic fillers different from clay. d) Activator

[0131] The porous article further comprises an activator.

[0132] The activator necessarily comprises a water-soluble inorganic silicate.

[0133] Suitable water-soluble inorganic silicates are preferably selected from alkali silicates, preferably from sodium silicate, and / or potassium silicate and / or lithium silicate, and / or mixtures thereof, more preferably sodium silicate.

[0134] Another group of activators, which can be present in the porous article in addition to the water-soluble inorganic silicate are metal hydroxides, such as earth alkali hydroxides and alkali hydroxides and mixtures thereof, preferably alkali hydroxides selected from NaOH, KOH, LiOH, CsOH and mixtures thereof.

[0135] In one embodiment the activator consists of the water-soluble inorganic silicate.

[0136] The water-soluble silicate is preferably selected from alkali-metal silicates, preferably from sodium silicate and / or potassium silicate and / or lithium silicate, more preferably sodium silicate. The water soluble silicate can be a mixture of water-soluble silicates. Examples are mixtures of sodium silicate and potassium silicate; sodium silicate and lithium silicate; potassium silicate and lithium silicate; sodium silicate, potassium silicate and lithium silicate.

[0137] The amount of activator present in the porous article either in form of repeating units of the geopolymer or as unreacted residue is preferably in the range of from 10 to 50 wt.- %, more preferably 10 to 45 wt.-%, still more preferably 15 to 40 wt.-%, based on the total weight of the porous article.

[0138] The amount of water-soluble silicate present in the porous article either in form of repeating units of the geopolymer or as unreacted residue is preferably in the range of from 10 to 50 wt.-%, more preferably 10 to 45 wt.-%, still more preferably 15 to 40 wt.-%, based on the total weight of the porous article.

[0139] The weight ratio of inorganic binder and activator in the porous article is preferably in the range of from 0.55 : 1 .0 to 2.0 : 1 .0, more preferably from 0.6 : 1 .0 to 1 .7 : 1 .0, still more preferably from 0.7 : 1 .0 to 1 .5 : 1 .0.

[0140] The weight ratio of the particles with anisotropic shape and the water-soluble inorganic silicate in the porous article is in the range of from 1 .0 : 15.0 to 1 .0 : 0.3, preferably from 1 .0 : 9.0 to 1 .0 : 1 .5, more preferably from 1 .0 : 8.5 to 1 .0 : 2.0.

[0141] It has been found that the weight ratio of particles with anisotropic shape and water- soluble inorganic silicate in the porous article helps establishing a stable foam with high porosities and small mean pore size, which allows a good balance of properties in regard of mechanical properties and insulating properties.

[0142] The water-soluble inorganic silicate serves as dispersant for the inorganic filler with anisotropic shape which prevents agglomeration of the inorganic filler with anisotropic shape in suspension so that suspensions comprising particles with anisotropic shape and water-soluble inorganic silicate in the claimed weight ratio become fluid, showing a drop of yield stress and viscosity, also at low water content becoming easy to flow and pump. The yield stress can be less than 500 Pa. In the presence of an aluminosilicate source with latent hydraulic properties, such as metakaolin and / or fly ash, the activator can act as chemical activator to form a geopolymer, which is an alkaline polymer, i.e. gel with three-dimensional network of tetrahedral Si and Al sites. Geopolymerisation is a sol-gel-like process and includes dissolution, condensation and reorganization steps. Geopolymers primarily base on SiO2 and / or AI2O3, such as poly(sialate), poly(siloxo), poly(sialate-siloxo), or poly(sialate- disiloxo), which harden in alkaline aqueous environment. Sialate refers to silicon-oxo- aluminum. Geopolymers may contain compounds based on Fe20s, TiO2, CaO, MgO, NaO, or K2O. Strictly speaking, pure geopolymers generally have a low calcium content. In this invention, the term geopolymer comprises low and high calcium geopolymers. Geopolymers and zeolite have similar chemical compositions. Conversely to zeolites, geopolymers are amorphous in nature. Furthermore, examples of geopolymers comprise microsilica, metakaolin, aluminosilicates, fly ash, activated clay, pozzolans, or mixtures thereof. As a result, any traces of the heavy metals, which are present especially in inorganic particles originating from secondary raw materials, inorganic waste particles, inorganic particles obtained from recycling processes, are entrapped in these newly formed matrices, whereby a release of heavy metals in the environment can be minimized or even prevented. e) Additives

[0143] The porous articles can comprise further additives such as e.g. gas generating agent, a catalyst for the decomposition of the gas generating agents, rheology modifiers, fibers, water repellent agent, retarders, accelerators.

[0144] The amount of further additives in the porous article usually do not exceed 10 wt.-%, such as from 0.1 to 5 wt.-%, based on the total mass of the foaming formulation.

[0145] As gas generating agent aluminum powder / paste or hydrogen peroxide are conventionally used. Hydrogen peroxide is supplied as aqueous solutions. The wording “hydrogen peroxide” refers here the active component of the aqueous solution.

[0146] Suitable examples for the catalyst for the decomposition of the hydrogen peroxide as gas generating agent are iron oxides, iron hydroxides, iron(lll) oxide hydroxide (geothite), iron chlorides, copper (I) oxide, manganese(IV) oxide (Mn(IV)O2), titanium (IV) dioxide, iron (II) carbonate, potassium permanganate, potassium iodide, nickel (II) oxide.

[0147] Rheology modifiers can be used to adjust the viscosity of the slurry. This is especially useful when preparing the porous article by extrusion or 3D printing. Rheology modifiers then serve the purpose of improving the printability of the foam, wherein said printabilityimproving agent can be added to the optionally foamed suspension.

[0148] Suitable examples for rheology modifiers to increase the slurry viscosity are fumed silica, cellulose, salt insensitive superabsorbers such as poly(acrylamide-co-acrylic acid) or combinations thereof.

[0149] Suitable examples for rheology modifiers to decrease the slurry viscosity are sodiumhexametaphosphate, plasticizers and superplasticizers such as lignosulfonates, sulfonated synthetic polymers (naphthalene, or melamine, formaldehyde condensates), polycarboxylates-ether (PCE).

[0150] Fibers can be added for limiting cracks in the final porous article. Moreover, fibers also serve the purpose of increasing slurry viscosity and yield stress.

[0151] Suitable examples are glass fibers or cellulose fibers or cellulose microfibers or plastic fibers such as polypropylene, PAN and polyesters, or plant fibers, such as hemp fibers, or mineral fibers, such as stone wool fibers.

[0152] Retarders and accelerators can be used for adjusting the setting time of the foam during the preparation of the porous article.

[0153] Suitable examples for retarders are lignosulphonates, hydroxycarboxylic acid and their salts, phosphonates, saccharides, phosphates, borates and salts of lead, zinc, arsenic or antimony.

[0154] Suitable examples for accelerators are calcium chloride, potassium chloride, calciumaluminate, sodium aluminate, aluminum sulfate, aluminum hydroxide, aluminum nitrite, lithium carbonate, and combinations thereof.

[0155] Water repellent agents can be used for decreasing the water absorption of the porous article. - l -

[0156] Suitable examples for water repellent agents are silicon oils, siloxanes, organomodified siloxanes, silanes, emulsions of siloxanes, emulsions of silanes / siloxanes, siliconate and combination thereof.

[0157] The water repellent agents can be diluted in water, ethanol or other organic solvents.

[0158] The porous article preferably has a content of aqueous liquid, preferably of water, lower than 50 wt.-%, more preferably less than 40 wt.-%, such as from 0.01 to 15 wt.-%, based on the total weight of the porous article.

[0159] The porous article preferably is fully recyclable as discussed above, by grinding the porous article and using the particulate material as inorganic particles for the production a new cycle of porous article.

[0160] The porous article preferably shows a high porosity and small pore size, which allows for a superior balance of properties in regard of mechanical properties and insulation properties at low environmental impact.

[0161] The pores of the porous article have a mean pore size of not more than 2.00 mm, such as in the range of from 0.01 to 2.00 mm, preferably from 0.02 to 1 .50 mm, more preferably from 0.05 to 1 .00 mm, still more preferably from 0.10 to 0.80 mm, measured by microscopy analysis.

[0162] It is preferred that 1 to 75 vol.-%, preferably 3 to 70 vol.-%, more preferably 5 to 65 vol.- % of the pores of the porous article are capillary pores.

[0163] Capillary pores are pores having a mean pore size of from 10 nm to about 250 nm and are largely empty of water or can be dried.

[0164] In contrast to that gel pores are pores having a mean pore size of less than 10 nm and are usually filed with gel water.

[0165] The porous article preferably has one or more or all, preferably all of the following properties:

[0166] • a density in the range of from 10 to 350 kg / m3, preferably 25 to 250 kg / m3, more preferably 50 to 200 kg / m3; • a porosity of from 60.0 to 99.9.vol.-%, preferably from 65.0 to 99.5 vol.-%, more preferably from 70.0 to 99.0 vol.-%;

[0167] • a thermal conductivity of from 10 to 100 mW / mK, preferably from 20 to 75 mW / mK, more preferably from 26 to 50 mW / mK;

[0168] • a compressive strength of from 10 to 5000 kPa, preferably from 25 to 2500 kPa, more preferably from 40 to 1000 kPa;

[0169] • the pores in the porous article with a mean pore size of not more than 80 nm having a porosity of from 0.01 to 1 .00 cm3 / g, preferably from 0.05 to 0.85 cm3 / g, more preferably from 0.10 to 0.70 cm3 / g;

[0170] • the pores in the porous article with a mean pore size of not more than 80 nm having a BET surface area of from 2.5 to 65 m2 / g, preferably from 5.0 to 55 m2 / g, more preferably from 7.5 to 50 m2 / g;

[0171] • a global warming potential smaller than 3 kg CC>2-eq / kg, preferably smaller than 2 kg CC>2-eq / kg, even more preferably smaller than 1 kg CC>2-eq / kg;

[0172] • a non-renewable energy (NRE) smaller than 50 MJ oil-eq / kg, more preferably smaller than 20 MJ oil-eq / kg, even more preferably smaller than 15 MJ oil-eq / kg;

[0173] • a cumulative energy demand (CED) smaller than 50 MJ oil-eq / kg, more preferably smaller than 30 MJ oil-eq / kg, even more preferably smaller than 20 MJ oil-eq / kg.

[0174] In one specific embodiment the target properties of the porous article are:

[0175] • a density in the range of 60 to 90 kg / m3;

[0176] • a thermal conductivity of less than 40 mW / mK, such as 32 to less than 40 mW / mK; and

[0177] • a compressive strength of more than 40 kPa, such as more than 40 to 200 kPa

[0178] • a tensile strength of more than 7 kPa, such as more than 7 to 150 kPa

[0179] • a water absorption of less than 5 kg / m2, such as less than 5 to 0.1 kg / m2.

[0180] The porous article preferably does not include a detectable amount of crystalline metal carbonates, such as crystalline alkali-metal carbonates and / or crystalline earth alkali- metal carbonates, determined by SEM microscopy. Such crystalline metal carbonates are e.g. detectable by SEM microscopy in form of needles on a surface facing the mesopores and macro-pores. It is especially preferred that directly after preparation the porous article is free of crystalline metal carbonates, such as crystalline alkali-metal carbonates and / or crystalline earth alkali-metal carbonates, determined by SEM microscopy.

[0181] As a consequence the surface of the porous article facing the meso-pores and macropores is preferably quite smooth as can be seen from the SEM micrographs in Figures 1 and 2. In Figure 2 the border between the platelet-like smooth surface of the inorganic fillers with anisotropic shape and the more three-dimensional structure of the geopolymer is shown.

[0182] In specific environments small amounts of crystalline metal carbonates may form upon long-time exposure to air. These small amounts, usually obtained from the reaction of residual alkali metals and / or earth alkali metals with atmospheric carbon dioxide, usually do not exceed 1 wt.-% of the porous article.

[0183] The porous article preferably has a low amount of water soluble components, such as less than 10 wt.-%, preferably less than 5 wt.-%, more preferably less than 1 wt.-%, so that the tendency of efflorescence in the porous article is low.

[0184] The porous article is especially suitable as an insulation panel, acoustic insulation panel, fire resistance panel, semi-structural component or partitioning wall.

[0185] Process

[0186] In a second aspect the present invention relates to a process for producing the porous article as described above or below comprising the steps of

[0187] • providing a suspension comprising an aqueous liquid, preferably water, the inorganic particles comprising the inorganic fillers with anisotropic shape, preferably clay or clay-based platelet particles, and the inorganic binder, the at least one surfactant, the activator, and optionally additives, wherein the at least one surfactant at least partially hydrophobizes the surface of at least a part of the inorganic particles and a geopolymer is formed by polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from the inorganic binder in the presence of the activator;

[0188] • foaming the suspension comprising the inorganic particles, from which at least a part has an at least partially hydrophobized surface to obtain a foam;

[0189] • shape and expand the foam by casting or extruding or additive manufacturing, in particular 3D-printing, said foam to obtain a wet porous body,

[0190] • optionally setting or curing the wet porous body, and / or

[0191] • optionally drying or partially drying the wet porous body; and

[0192] • obtaining the porous article.

[0193] Thereby, it is preferred that all aspects of the porous article and its components as described above or below also apply to the process of the invention.

[0194] In one embodiment at least a part of the inorganic particles, preferably part of the inorganic fillers, optionally part of the inorganic binder, at least one surfactant and optionally additives are dry blended. The dry blend preferably makes up 0.1 to 10.0 wt.- %, preferably 0.1 to 5.0 wt.-% of the total weight of the suspension.

[0195] The inorganic particles, the at least one surfactant, the activator, and optionally the dry blend are mixed with an aqueous liquid, preferably water, to form a suspension.

[0196] Thereby, it is preferred that the at least one surfactant is at least one surfactant being amphiphilic molecules comprising a hydrophobic group coupled to a hydrophilic group, hydrophobic group comprises a backbone chain comprising at least 10 carbon atoms.

[0197] A critical issue is the stabilization of the air bubbles incorporated in the foamed suspension until the foam is set. Traditionally, surfactants such as lipids and proteins are used to slow down the coalescence of bubbles by adsorbing at the gas-liquid interface. However, these surfactant-stabilized methods prevent foam destabilization only for short time, i.e. minutes or hours, due to the low adsorption energy of the surfactants at the interface. Here, the stability of the foams results from two mechanism; the adsorption of the particles having the at least partially hydrophobized surface to the bubbles’ surface, i.e. adsorption of the surface-modified particles on the surface of the bubbles and stabilization due to the formation of a percolating network of particles throughout the aqueous liquid around the bubbles. Contrary to traditional surfactants, these particles are trapped at the surface of the air bubbles, thereby increasing the bubbles stability. The preferable use of surfactants having a backbone chain comprising at least 10 carbon atoms, herein called long-chain surfactants, can not only yield foam stabilization through particles present at the gas-liquid interface but can increase the hydrophobic interactions among at least partially hydrophobized particles. This can generate a percolating network. Generally, the percolation network is based on any kind of surfaceactive particles and active molecules. Active particles correspond to particles whose surface can be modified by the adsorption of molecules such as surfactants or which can adsorb at the gas-liquid interface without any surface modification. Active molecules are molecules such as surfactants that can adsorb at the surface of particles or at the gas-liquid interface. In addition to the percolating network triggered by hydrophobic interactions, the hardening of the foam matrix also lead to the formation of a second, stronger percolation network overtime. As a consequence, the stability of the generated wet foam is enhanced by at least a strong percolating network formed around the air bubbles generated upon the foaming of the suspension. The percolating network can be seen as a gelation or strengthening of the gas-liquid interface and of the surrounding aqueous medium, which in the present case increases the stability of the foam. The expression “percolating network” is well-known in the state of the art and can be referred to as a “percolating network of modified particles that form a gel with elastic modulus higher than the viscous modulus”. Hence, the gas-liquid interface is stabilized by a thus created composite-like material comprising the surface-modified particles that are interconnected with the network of modified particles.

[0198] Moreover, the amount of surfactant needed to stabilize the particles and the foams, respectively, is significantly smaller if long-chain surfactants are used instead of shortchain surfactants, i.e. surfactants having a backbone chain comprising less than 10 carbon atoms. In fact, it was found that about four times or even smaller concentrations of long-chain surfactants were needed in order to obtain a level of porosity comparable to the porosity obtained by using short-chain surfactants. The reduced amount of long- chain surfactants needed for obtaining a stable foam is due to the fact that long-chain surfactants are more effective in modifying the surface of the particles. In other words, one needs less surfactant to obtain the same degree of particle modification, i.e. particle hydrophobization, compared to a short -chain surfactant. Moreover, from a certain molecular weight of the surfactant, typically around 300 g / mol, the long-chain surfactant can also participate in building up the network by binding a few particles together, which additionally increases the stability of the foam. That is, additional stability is achieved by particles that interact with each other via the long-chain surfactants adsorbed on their surface.

[0199] The weight ratio of inorganic filler to surfactant in the suspension is preferably in the range of from of from 25 : 1 to 1000 : 1 , more preferably from 35 : 1 to 750 : 1 , still more preferably from 40 : 1 to 500 : 1 .

[0200] The weight ratio of inorganic filler with anisotropic shape to surfactant in the suspension is preferably in the range of from of from 25 : 1 to 900 : 1 , more preferably from 35 : 1 to 650 : 1 , still more preferably from 40 : 1 to 400 : 1 .

[0201] The weight ratio of inorganic particles to activator in the suspension is preferably in the range of from 1 .0 : 15.0 to 1 .0 : 0.3, more preferably from 1 .0 : 9 to 1 .0 : 1 .5, still more preferably from 1 .0 : 8.5 to 1 .0 : 2.

[0202] It is preferred that the amount of inorganic fillers with anisotropic shape, preferably particles with platelet structure, more preferably clay or clay-based platelet particles, in the suspension is in the range of from 1 .0 to 15.0 wt.-%, preferably from 2.5 to 12.5 wt.- %, more preferably from 3.0 to 10.0 wt.-%, based on the total weight of the suspension.

[0203] The total amount of inorganic fillers in the suspension is preferably in the range of from 1 .0 to 20.0 wt.-%, more preferably from 2.5 to 17.5 wt.-%, still more preferably from 3.0 to 15.0 wt.-%, based on the total weight of the suspension.

[0204] It is further preferred that the amount of inorganic binder in the suspension is in the range of from 15 to 35 wt.-%, preferably from 17 to 32 wt.-%, more preferably from 20 to 30 wt.-%, based on the total weight of the suspension.

[0205] The amount of activator in the suspension is preferably in the range of from 10 to 35 wt.- %, more preferably from 12 to 30 wt.-%, still more preferably from 15 to 25 wt.-%, based on the total weight of the suspension. The amount of water-soluble inorganic silicate in the suspension is preferably in the range of from 10 to 35 wt.-%, more preferably from 12 to 30 wt.-%, still more preferably from 15 to 25 wt.-%, based on the total weight of the suspension.

[0206] The amount of the at least one surfactant in the suspension is preferably in the range of from 0.0005 to 0.6 wt.-%, preferably 0.005 to 0.5 wt.-%, more preferably 0.01 to 0.3 wt.- %, still more preferably from 0.02 to 0.2 wt.-%, based on the total weight of the suspension.

[0207] The amount of aqueous liquid, preferably water, in the suspension is preferably in the range of from 25 to 55 wt.-%, more preferably from 27 to 50 wt.-%, still more preferably from 30 to 45 wt.-%, based on the total weight of the suspension.

[0208] The aqueous liquid preferably comprises water, more preferably is water.

[0209] The water can be untreated water, potable water, purified water, sea water, washing water from foaming production or distilled water.

[0210] In one embodiment all components are mixed with the aqueous liquid, preferably water, to form a single suspension.

[0211] All or part of the optional other components, like the additives, as discussed above for the porous article can be added to the suspension.

[0212] In another embodiment, two suspensions are formed.

[0213] In a first suspension, aqueous liquid, preferably water, is preferably mixed with the at least one surfactant and part of the inorganic particles, preferably at least the inorganic binder, to form a first suspension.

[0214] In the second suspension aqueous liquid, preferably water, is preferably mixed with the remaining part of the inorganic particles and the activator to form a second suspension. Then the first and second suspension are preferably mixed to obtain the final suspension.

[0215] All or part of the optional other components, like the additives, as discussed above for the porous article can be added either to the first or second suspension. The suspension is usually mixed at ambient temperature, i.e. of from 10 to 50°C, such as from 20 to 30°C.

[0216] The pH value of the suspension can be adjusted to about 3 to 14, preferably to about 8 to 14, prior to foaming the suspension or after foaming the suspension.

[0217] Depending on the composition of the inorganic particles, a particular pH value will yield a better adsorption of the surfactant at the interface of the particles. For example, alumina (AI2O3) particles have a positive charge at a pH-value of 3-7. Under these conditions it is therefore preferred to use negatively charged surfactants since the adsorption of a negatively-charged surfactant on positively-charged particles is enhanced. Likewise, an improved interaction is obtained between e.g. clay and claybased platelet particles and a positively-charged surfactant. Or in other words, a good electrostatic adsorption of the surfactants to the particle surface is achieved if the surfactants and the particles have opposite charges. A preferred pH value is then a pH value at the pKa value, i.e. the logarithmic acid dissociation constant of the surfactant. The pH value can be adjusted by means of adding a basic or acidic compound or solution to the suspension. In doing so hydrochloric acid (HCI) and sodium hydroxide (NaOH) and or potassium hydroxide (KOH) are commonly used for adjusting the pH value.

[0218] In the suspension preferably geopolymers are formed from the inorganic binder, preferably selected from aluminosilicate sources with latent hydraulic properties, hydraulic binders and non-hydraulic binders and mixtures thereof, more preferably selected from metakaolin and / or fly ash, in the presence of the aqueous activator comprising the water-soluble inorganic silicate as chemical activator and optionally pH modifiers.

[0219] The suspension preferably has a yield stress of from 1 Pa to 1000 Pa, preferably from 10 to 200 Pa.

[0220] Further, the slurry preferably has a viscosity of from 1 to 5000 mPas, even more preferred 1000 to 4000 mPas. In a further process step, the suspension comprising the particles having the at least partially hydrophobized surface is foamed to obtain a foam.

[0221] The suspension comprising the particles having the at least partially hydrophobized surface is usually foamed by introducing and stabilizing gas bubbles in the suspension. The gas bubbles can be introduced by mechanical foaming, preferably by means of a mixer, and / or by in-situ foaming by adding a gas release agent, such as a gas generating agent, to the suspension.

[0222] Incorporation of gas into the suspension comprising the particles having the at least partially hydrophobized surface can be achieved in any convenient way such as by direct foaming, e.g. mechanical mixing, or by using gas generating agents, i.e. in-situ, wherein a gas such as oxygen (O2) is generated in a chemical reaction. For convenience and economy, it is preferred that the gas is air. Other gases such as nitrogen, oxygen, argon, hydrogen or carbon dioxide are however conceivable, too. For mechanical foaming it is possible to subject the suspension to a high-speed agitation while the suspension is exposed to the atmosphere or a selected gas in a confined chamber. The agitation can be carried out by a mixer and for a sufficient period of time, during which time bubbles of gas, preferably air, are introduced into the suspension until a desired expansion has been reached.

[0223] Other ways of mechanically introducing the gas into the suspension are for example by means of bubbling the gas through a filter into the suspension or by means of injecting pressurized gas through a nozzle into the suspension. Through the choice of the pore size of the filter or the diameter of the ejection nozzle it is possible to adjust the pore size of the foams and hence of the final porous article prepared from the foams. In another technique, a gas release agent, such as a gas generating agent, like hydrogen peroxide (H2O2) or aluminium powder can be added to the suspension, wherein the generated gas foams the suspension.

[0224] For inducing the gas generation additionally a catalyst for decomposing the gas release agent can be added to the suspension.

[0225] All or part of the optional other components, like the additives, as discussed above for the porous article can be added to the suspension upon introducing bubbles into the suspension.

[0226] It should be understood that the more gas is incorporated into the suspension or generated in the suspension the more porous the thus generated foam is, wherein the porosity levels reached are also dependent on the particle size, the particle type and the particle concentration.

[0227] It should furthermore be noted that the foams can be generated within a few minutes, wherein there is no need for any special treatment beyond the surface modification, i.e. the hydrophobization of the particles with the surfactant.

[0228] It is preferred that the foam comprises bubbles having a mean bubble size of from 0.001 to 2.5 mm, preferably from 0.05 to 2.0 mm, more preferably from 0.01 to 1 .5 mm, determined by microscopy analysis.

[0229] The foam preferably is a closed cell foam, meaning that the gas forms discrete pockets, each completely surrounded by the solid material. The foam can contain a part of open pores.

[0230] The foam preferably has a foam density of in the range of from 10 to 350 kg / m3, more preferably 25 to 250 kg / m3, still more preferably 50 to 200 kg / m3.

[0231] Further the foam preferably has a porosity of from 60.0 to 99.9.vol.-%, more preferably from 65.0 to 99.5 vol.-%, still more preferably from 70.0 to 99.0 vol.-%.

[0232] Beside the porosity generated by the bubbles, the confinement of solid particles and the products of the hardening process can generate a porosity within the foam struts. This left-over porosity dictated by the granular matter of the foam skeleton has a pore size smaller than the bubbles. Thus, foams generated by the process described above can display a hierarchical porosity.

[0233] The foam is then shaped and expanded by casting or extruding or additive manufacturing, in particular 3D-printing, said foam to obtain a wet porous body.

[0234] For casting, the wet porous body the foam is usually cast into a formwork and left at rest to complete the expansion.

[0235] When the foam is subjected to extrusion or additive manufacturing, it is discharged out of an orifice or nozzle. The nozzle size is preferentially ranging from 2 mm to 100 mm, even more preferably between 10 and 50 mm. The printing speed depends on the nozzle size and targeted filament cross-section. Suitable printing speed range from 1 cm / s to 20 cm / s, more preferred from 5 to 15 cm / s.

[0236] The foam is preferably expanded at a temperature of from 20 to 100°C, preferably from 25 to 97°C, more preferably from 30 to 95 °C.

[0237] The foam preferably remains stable for weeks. Thus, the wet porous body can be prepared at one production site and can be transported to a different production site for further producing the porous article.

[0238] After expanding the expanded foam is preferably left at rest to complete the expansion.

[0239] Then the expanded foam can be demoulded and cut.

[0240] Due to the presence of the activator comprising the water-soluble inorganic silicate in the foam it is not necessary to sinter the wet porous body at temperatures of about 800 to 1800°C to obtain the porous article.

[0241] Instead the wet porous body undergo self-hardening and optionally can be set or cured. Set or curing are steps of a self-hardening mechanism.

[0242] Curing can be conducted by subjecting the wet porous body to wet heat, e.g. by autoclaving or steaming.

[0243] Steaming conditions are usually at atmospheric pressure at temperatures of from 40 to 100°C, preferably from 45 to 100°C, more preferably from 50 to 100°C at relative humidity ranging from 70 to 100 RH%, preferably from 75 to 100 RH%, even more preferably between 80 and 100 %RH.

[0244] Autoclaving conditions are usually in saturated steam conditions (100 RH%) at elevated pressure and temperature.

[0245] The autoclaving pressure is usually in the range of from 1 bar(a) to 15 bar(a), preferably 1 bar(a) to 5 bar(a), more preferably 1 bar(a) to 2.5 bar(a).

[0246] The autoclaving temperature is usually in the range of from temperature of from 100 to 200 °C, preferably from 100 to 150 °C, more preferably from 100 to 125 °C.

[0247] Thereby, the temperature in the autoclave depends on the applied pressure in accordance with the vapour pressure curve of water: at 1 bar(a) the temperature is 99.6 °C; at 2.5 bar(a) the temperature is 127.4 °C; at 5 bar(a) the temperature is 151 .8 °C; at 10 bar(a) the temperature is 179.9 °C; at 15 bar(a) the temperature is 198.3 °C.

[0248] Curing does not include exposing the wet porous body to CO2 containing gas having a CO2 concentration of at least 4 vol%, which induces carbonation of alkali-metal ions, such as sodium ions, which are preferably present in the water-soluble inorganic silicate.

[0249] Further the wet porous body can be dried or partially dried.

[0250] These process steps usually are conducted at temperatures below 200°C, such as from 20 to 100°C, preferably from 25 to 97°C, more preferably from 30 to 95 °C at relative humidity ranging from 10 to 90 RH%, preferably from 20 to 70 RH%, even more preferably between 30 and 70 %RH.

[0251] The wet porous body can be dried under elevated temperatures and optionally increased pressure.

[0252] In another embodiment the wet porous body can be dried under environmental conditions, e.g. under room conditions.

[0253] When the wet porous body is cured, then the drying step is conducted after curing.

[0254] Use

[0255] In a third aspect the present invention relates to the use of the porous article as described above or below for building insulation.

[0256] Thereby, it is preferred that all aspects of the porous article, its components and the process for producing said porous article as described above or below also apply to the process of the invention.

[0257] Examples

[0258] A. Measurement methods

[0259] Porosity

[0260] Mesopores (pores having a mean pore size of 2 to 50 nm) are measured by scanning electron microscopy. Pores in the macro-range (pores having a mean pore size of more than 50 nm) are measured by light microscopy.

[0261] Nanopores (pores having a mean pore size of less than 2 nm) are characterized using Brunauer-Emmett-Teller (BET) method using a density functional theory (DFT) analysis based on a Non Local DFT (NLDFT) calculation model for nitrogen at 77 K on cylindrical pores in silica.

[0262] The amount of capillary pores (pores having a mean pore size of 10 nm to 250 nm) is measured by taking a cured not dried foam, measuring its wet bulk density, from this piece taking a 50mm cube, subjecting it to 60°C and 30mbar vacuum for 1 day and measuring its dry bulk density. The density difference is divided by the density of water and the dry bulk density of foam and is reported as a porosity value in cm3 / g.

[0263] BET surface area

[0264] The BET surface area is determined by Brunauer-Emmett-Teller (BET) method using a density functional theory (DFT) analysis based on a Non Local DFT (NLDFT) calculation model for nitrogen at 77 K on cylindrical pores in silica.

[0265] Particle diameter

[0266] The term ‘upper cut-off size’ refers to the maximum particle diameter present in a particle size distribution, typically defined as the particle size below which at least 98% by volume of the particles lie, as determined by laser diffraction or sieving.

[0267] Density is measured by normalizing the dry mass of a 50x50x50 mm3cube (dried at in vacuum chamber) by its volume strength

[0268] Compressive strength is measured according to DIN EN 826. 50x50 mm cubes are compressed at 5 mm / min.

[0269] Thermal conductivity is measured according to DIN EN 12667. A 200x200x30 mm plate is measured at a mean temperature of 10°C with a temperature difference between hot and cold plate of 10°C. B. Preparation of porous articles

[0270] Example 1 :

[0271] An aqueous solution of sodium silicate (37 wt.-% of sodium silicate, R=1 .6) was mixed with clay (Sibelco, VM), metakaolin (metamax), fly ash (hydrolent), TTAB (Tetradecyltrimethylammonium bromide) and manganese(IV) oxide to provide a slurry.

[0272] An aqueous solution of hydrogen peroxide (35 wt.-% solution) was added to the slurry to provide a suspension having the composition depicted in the table below:

[0273] Table 1 : Composition of the suspension of example 1

[0274] A wet foam is generated upon in-situ foaming. The foaming slurry is cast in a formwork and left at rest to complete the expansion. The wet foam is kept in a water vapour saturated environment for 24 hours at a temperature of 50°C before being removed from the formwork.

[0275] The resulting foam displays a dry density of 100 kg / m3, a compressive strength at 7 day of 56 kPa, a thermal conductivity of 0.0448 W / m*K, a mean pore size of 1 .08 mm.

[0276] Example 2 (comparative):

[0277] To highlight the necessity of have shape anisotropic particles in combination with a surfactant oppositely charged to ensure foam stability, a comparative foam without any clay has been produced. An aqueous solution of sodium silicate (37 wt.-% of sodium silicate, R=1 .6) was mixed with metakaolin (metamax), fly ash (hydrolent), TTAB (Tetradecyltrimethylammonium bromide), manganese(IV) oxide to provide a slurry. An aqueous solution of hydrogen peroxide (35 wt.-% solution) was added to the slurry to provide a suspension having the composition depicted in the table below: Table 2: Composition of the suspension of example 2

[0278] A wet foam was generated upon in-situ foaming. The foaming slurry is cast in a formwork and left at rest to complete the expansion. The wet foam is kept in a water vapour saturated environment for 24 hours at a temperature of 50°C before being removed from the formwork.

[0279] The resulting foam displays a dry density of 953 kg / m3. This proves the lack of foam stability.

Claims

Claims1 . A porous article comprising a) inorganic particles comprising from 3 to 35 wt.-%, preferably from 4 to 30 wt.- %, more preferably from 5 to 25 wt.-%, based on the total amount of the porous article, inorganic fillers with anisotropic shape, preferably clay or claybased platelet particles; b) at least one surfactant; and c) a geopolymer obtained from polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from• an inorganic binder comprising aluminosilicates, in the presence of• an activator comprising a water-soluble inorganic silicate, wherein the pores of the porous article have a mean pore size of not more than 2.00 mm, such as in the range of from 0.01 to 2.00 mm, preferably from 0.02 to 1 .50 mm, more preferably from 0.05 to 1 .00 mm, still more preferably from 0.10 to 0.80 mm, measured by microscopy analysis.

2. The porous article according to claim 1 , wherein at least 55 vol% of the inorganic particles have an upper cut-off size of not more than 75 pm, preferably not more than 65 pm, more preferably not more than 60 pm in its largest dimension.

3. The porous article according to claim 1 or 2, wherein the inorganic particles comprise inorganic fillers, which are selected from naturally occurring fillers, inorganic waste particles and fibers, inorganic fillers and fibers industrial processes obtained from industrial processes and recycling processes and mixtures thereof.

4. The porous article according to any one of the preceding claims, wherein the inorganic particles are a mixture of clay, optionally unreacted inorganic binders, and optionally inorganic fillers different from clay.

5. The porous article according to any one of the preceding claims, wherein the at least one surfactant is present in the porous article in an amount of 0.001 to 1 .0 wt.-%, preferably 0.01 to 0.8 wt.-%, more preferably 0.02 to 0.5 wt.-%, still more preferably from 0.03 to 0.4 wt.-%, based on the total weight of the porous article.

6. The porous article according to any one of the preceding claims, wherein the at least one surfactant is selected from surfactants being amphiphilic molecules comprising a hydrophobic group coupled to a hydrophilic group, hydrophobic group comprises a backbone chain comprising at least 10 carbon atoms, preferably from 10 to 30 carbon atoms, more preferably from 12 to 26 carbon atoms.

7. The porous article according to any one of the preceding claims, wherein at least part of the inorganic particles and at least one surfactant are oppositely charged.

8. The porous article according to any one of the preceding claims, wherein the water- soluble inorganic silicates are selected from alkali-metal silicates, preferably from sodium silicate, potassium silicate, lithium silicate, and mixtures thereof, more preferably sodium silicate.

9. The porous article according to any one of the preceding claims, wherein the inorganic binder is selected from aluminosilicate sources with latent hydraulic properties, hydraulic binders and non-hydraulic binders and mixtures thereof, preferably aluminosilicate sources with latent hydraulic properties, hydraulic binders and mixtures thereof, more preferably the inorganic binder comprises metakaolin and / or fly ash.

10. The porous article according to any one of the preceding claims having one or more or all of the following features:• a density in the range of from 10 to 350 kg / m3, preferably 25 to 250 kg / m3, more preferably 40 to 200 kg / m3;• a porosity of from 60.0 to 99.9.vol.-%, preferably from 65.0 to 99.5 vol.-%, more preferably from 70.0 to 99.0 vol.-%;• a thermal conductivity of from 10 to 100 mW / mK, preferably from 20 to 75 mW / mK, more preferably from 26 to 50 mW / mK;• a compressive strength of from 10 to 5000 kPa, preferably from 25 to 2500 kPa, more preferably from 40 to 1000 kPa;• the pores in the porous article with a mean pore size of not more than 80 nm having a porosity of from 0.01 to 1 .00 cm3 / g, preferably from 0.05 to 0.85 cm3 / g, more preferably from 0.10 to 0.70 cm3 / g ;• the pores in the porous article with a mean pore size of not more than 80 nm having a BET surface area of from 2.5 to 65 m2 / g, preferably from 5.0 to 55 m2 / g, more preferably from 7.5 to 50 m2 / g;• a global warming potential smaller than 3 kg CC>2-eq / kg, preferably smaller than 2 kg CC>2-eq / kg, even more preferably smaller than 1 kg CC>2-eq / kg;• a non-renewable energy (NRE) smaller than 50 MJ oil-eq / kg, more preferably smaller than 20 MJ oil-eq / kg, even more preferably smaller than 15 MJ oil- eq / kg;• a cumulative energy demand (CED) smaller than 50 MJ oil-eq / kg, more preferably smaller than 30 MJ oil-eq / kg, even more preferably smaller than 20 MJ oil-eq / kg.11 . The porous article according to any one of the preceding claims being an insulation panel, acoustic insulation panel, fire resistance panel, semi-structural component or partitioning wall.

12. A process for producing the porous article according to any one of the preceding claims comprising the steps of• providing a suspension comprising an aqueous liquid, preferably water, the inorganic particles comprising the inorganic fillers with anisotropic shape, preferably clay or clay-based platelet particles, and the inorganic binder, the at least one surfactant, the activator, and optionally additives, wherein the at least one surfactant at least partially hydrophobizes the surface of at least a part of the inorganic particles and a geopolymer is formed by polycondensation of repeating units comprising silicate ions and aluminate ions, which are derived from the inorganic binder in the presence of the activator;• foaming the suspension comprising the inorganic particles, from which at least a part has an at least partially hydrophobized surface to obtain a foam;• shape and expand the foam by casting or extruding or additive manufacturing, in particular 3D-printing, said foam to obtain a wet porous body,• optionally setting or curing the wet porous body, and / or• optionally drying or partially drying the wet porous body; and• obtaining the porous article.

13. The process according to claim 12, wherein the foam is expanded at a temperature of from 20 to 100°C, preferably from 25 to 97°C, more preferably from 30 to 95 °C.

14. The process according to claims 12 or 13, wherein the foam comprises bubbles having a mean bubble size of from 0.001 to 2.5 mm, preferably from 0.05 to 2.0 mm, more preferably from 0.01 to 1 .5 mm.

15. Use of a porous article according to any of the preceding claims for building insulation.

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