WO2025181123A1

WO2025181123A1 - Pva based binder for stone wool applications

Info

Publication number: WO2025181123A1
Application number: PCT/EP2025/055134
Authority: WO
Inventors: Xiaomin Qian; Thomas Hjelmgaard; Claudia Margarete BAEKKEL; Kurt Van Durme
Original assignee: Rockwool AS
Current assignee: Rockwool AS
Priority date: 2024-03-01
Filing date: 2025-02-26
Publication date: 2025-09-04
Anticipated expiration: 2026-09-01

Abstract

The invention is directed to an aqueous binder composition comprising i) polyvinyl alcohol as a binder, ii) one or more polycarboxylic acids or anhydrides or salts thereof as a crosslinker, and iii) lignin, and to mineral fibre product, wherein the mineral fibres are bonded by the cured aqueous binder composition. The mineral fibre products are particularly suitable as plant growth substrates.

Description

PVA based binder for stone wool applications

Field of the invention

The invention relates to an aqueous binder composition based on polyvinyl alcohol, a method of producing a mineral fibre product with the aqueous binder composition, the mineral fibre product, preferably a plant growth substrate, and the use of the aqueous binder composition for the production of a mineral fibre product.

Background of the invention

Mineral wool products are generally components based on mineral fibres bonded together by a binder. Typical applications of mineral wool products are thermal or acoustic insulation or plant growth substrates.

A variety of binders exists for the manufacturing of mineral wool products. Examples for suitable binders are based on sodium silicates, polyesters, melamine urea formaldehyde, polyamines, furan-based resins, phenolic resins, formaldehyde- free binders such as carbohydrate-based or lignin-based binders.

Especially in connection with mineral wool-based plant growth substrates, there is a need for non-toxic, biodegradable products having an adequate wet strength to withstand the environment that the product is exposed to in use as well as adequate strength during handling in greenhouses. Among others, the need arises due to EU legislation requiring sustainable and biodegradable products.

The growth substrate products should be able to withstand daily use in a wet environment for a year (water-resistant), where the product maintains it shape, form and required properties as a growth substrate. After use (end -of-life), a need exists for the products to be recyclable and/or re-useable for example as compost, which requires the products to be biodegradable. In order to obtain such biodegradable products, there is also a need for a non-toxic, biodegradable binder, which can provide mineral wool growth substrate products with an adequate wet strength (water-resistance) when in use but being biodegradable and compostable for a sustainable end-of-life solution.

PVA is a water-soluble synthetic polymer from petroleum-based sources. It is one of the few synthetic polymers that is biodegradable. Polyvinyl alcohol (PVA) show a very good adhesion to mineral wool, but is not water-resistant. Multifunctional carboxylic acids have been shown to be good cross-linkers for PVA increasing the water resistance and wet strength. The crosslinking reaction is an esterification reaction.

The properties of PVA based binders also depend on the molecular weight of PVA. Thus, the use of low molecular weight PVA results in binders with low mechanical strength and water resistance, whereas higher molecular weight PVA yielded binders with sufficient mechanical strength and water resistance.

However, a drawback of binder based on high molecular weight PVA is a high viscosity, which significantly impairs handling. Viscosity is an important parameter of a binder. Generally, the viscosity of the binder should be as low as possible. For instance, high viscous binders impede spraying and clogging of the pipes/nozzles during production may occur.

As mentioned, PVA is a petroleum-based polymer. From an ecological point of view, at least partial replacement of petroleum-based resources with biobased, renewable materials is desirable to achieve more sustainable products. Summary of the invention

Accordingly, it was an object of the present invention to provide aqueous binder composition for mineral fibers, which provides sufficient mechanical strength and water resistance and is easy to handle by sufficiently low viscosity. Moreover, it should at least partially use renewable materials as starting materials.

The inventors found that this object could be solved when a binder based on PVA with a polycarboxylic compound as crosslinker is supplemented by lignin as a further component.

Accordingly, the invention is directed to an aqueous binder composition comprising i) polyvinyl alcohol as a binder, ii) one or more polycarboxylic acids or anhydrides or salts thereof as a crosslinker, and iii) lignin.

The invention further relates to a method of producing a mineral fibre product, which comprises the steps of contacting mineral fibres with an aqueous binder composition according to the invention.

The invention further relates to a mineral fibre product comprising mineral fibres bound by a binder resulting from the curing of an aqueous binder composition according to the invention.

The invention further relates to the use of an aqueous binder composition according to the invention for the production of a mineral fibre product, which is preferably a plant growth substrate.

The aqueous binder composition of the invention exhibits good mechanical strength and is sufficiently water resistant when cured. The viscosity of the inventive aqueous binder composition of the invention is low enough so that handling and application is easy. Since lignin is based on renewable materials, sustainability of the binder is enhanced. The aqueous binder composition of the invention is particular suitable for bonding mineral fibers. This is due to a good attachment of the binder to the mineral fibres. Accordingly, the inventive aqueous binder composition is particularly suitable for preparing mineral fiber products, in particular plant growth substrates.

Description of the preferred embodiments

The invention relates to an aqueous binder composition comprising i) polyvinyl alcohol as a binder, ii) one or more polycarboxylic acids or anhydrides or salts thereof as a crosslinker, and iii) lignin.

The inventive binder composition is aqueous. Accordingly, the binder composition includes water in which the components of the binder composition are dissolved or dispersed.

The aqueous binder composition is preferably free of formaldehyde.

Polyvinyl alcohol

The inventive aqueous binder composition comprises polyvinyl alcohol as a binder (component i)). The common abbreviation for polyvinyl alcohol also termed poly(vinyl alcohol) is PVA, which is not to be confused with PVAc which stands for poly(vinyl acetate).

PVA is a non-toxic, water-soluble, synthetic polymer from petroleum-based sources. The monomer of PVA, vinyl alcohol is very unstable, therefore PVA cannot be synthesized from the direct polymerization of vinyl alcohol. Instead, it is synthesized from the hydrolysis of poly (vinyl acetate) (PVAc). While PVAc is synthesized via the direct polymerization of the monomer vinyl acetate. The synthetic route determines the two most important parameters of PVA: the molecular weight (Mw) and hydrolysis degree. The hydrolysis degree may be 100% so that all acetate groups are hydrolyzed or less than 100% so that a part of the acetate groups are not hydrolyzed. A general reaction scheme for the preparation of PVA is given below:

Commercial PVA is usually characterized by means of indices: PVA X-Y. Common PVA on the market is e.g. PVA 4-88, PVA 4-98, PVA 10-98, PVA 20-98, PVA 56-98.

X represents the viscosity (in mPas) of a 4 mass-% PVA solution in water at 20 °C usually determined according to DIN 53015:2019-06. It is proportional to the molecular weight (Mw) of the polymer. Therefore, X indicates the average molecular weight (Mw) of PVA. The larger X, the larger Mw is, and the more viscous is a PVA solution dissolved in water.

Y stands for the hydrolysis degree of PVA. Namely, the molar percentage of acetate group that has been hydrolyzed to become -OH group. It is determined by a saponification method according to DIN 53401: 1988. The larger Y, the greater is the number of -OH groups of PVA, and the more viscous is a PVA solution dissolved in water due to the hydrogen bonding between the -OH groups.

PVA is one of the few synthetic polymers that is known to be biodegradable, though reports indicates that the biodegradation of PVA is not as easy as for natural biopolymers. Hence, the biodegradation of PVA is comparatively slow.

The polyvinyl alcohol used in the inventive aqueous binder composition has preferably a hydrolysis degree of 80 to 100 mol-%, preferably 85 to 100 mol-%, more preferably 90 to 100 mol-%, in particular 95 to 100 mol-%. Particular good mechanical strengths could be achieved with PVA having a hydrolysis degree of 88% and 98%, respectively, wherein PVA with a hydrolysis degree of 98% exhibits still better mechanical strength.

The polyvinyl alcohol used in the inventive aqueous binder composition has preferably a weight average molecular weight of 10.000 to 200.000 g/mol, preferably 20.000 to 155.000 g/mol, more preferably 25.000 to 135.000 g/mol. The average molecular weight of PVA can be determined by gel permeation chromatography (GPC).

The polyvinyl alcohol used in the inventive aqueous binder composition preferably has a viscosity in the range of 2 to 40 mPa’s, preferably 4 to 20 mPa’s, as determined in a 4 mass-% solution of the PVA in water at 20 °C according to DIN 53015:2019-06.

Polvcarboxylic acids or anhydrides or salts thereof

The inventive aqueous binder composition comprises one or more polycarboxylic acids or anhydrides or salts thereof as a crosslinker (component ii)). Polycarboxylic acids refer to compound having two or more carboxylic acid groups. Suitable polycarboxylic acids may have e.g. two, three or four carboxylic acid groups, wherein dicarboxylic acids or anhydrides or salts thereof are preferred . The polycarboxylic acids may include further functional groups such as hydroxy groups or carbon-carbon double bonds.

While it is possible to use anhydrides or salts of a polycarboxylic acids, it is generally preferred to use the polycarboxylic acid as such or the anhydride thereof with preference for the polycarboxylic acid as such. This also applies to all of the preferred embodiments discussed below.

The polycarboxylic acid (PCA) serves as a crosslinker for PVA. The reaction mechanism is that the hydroxyl groups in PVA reacts with a carboxylic acid group of the PCA to generate an ester bond with water as the only by-product, as shown in the reaction scheme below (the PCA here is oxalic acid as an example):

This esterification reaction can be catalyzed by H ⁺ . Therefore, it is favorable that the aqueous binder composition is acidic (preferably pH < 4). Since the polycarboxylic acids are acidic by nature, a catalyst could serve to initialize the reaction, depending on the acidity and the reactivity of the PCA.

The one or more polycarboxylic acids or anhydrides or salts thereof are preferably one or more monomeric polycarboxylic acids or anhydrides or salts thereof.

The one or more polycarboxylic acids or anhydrides or salts thereof, in particular monomeric polycarboxylic acids or anhydrides or salts thereof are preferably dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids, more preferably dicarboxylic acids, or anhydrides or salts thereof or combinations thereof.

The one or more polycarboxylic acids or anhydrides or salts thereof are preferably selected from oxalic acid, itaconic acid, citric acid, tartaric acid, butanetetracarboxylic acid, terephthalic acid, or anhydrides or salts thereof, or a combination thereof, wherein oxalic acid, itaconic acid or itaconic anhydride are preferred. Further examples are sebacic acid and ethylenediaminetetraacetic acid (EDTA).

The most preferred polycarboxylic acid is itaconic acid or an anhydride or salt thereof, in particular itaconic acid. Itaconic acid has the following chemical formula

Lignin

The inventive aqueous binder composition comprises lignin (component iii)). Lignin such as lignosulfonate is a biobased, renewable material which exists in large quantities. Lignin such as lignosulfonate resembles PVA chemically as both possess a lot of -OH groups, which are the main reactive groups that contributes to the crosslinking of the binder. In this regard, the lignin also acts as binder component partially replacing PVA.

It has been found that lignin such as lignosulfonate exhibit a quite good adhesion to mechanical fibers, in particular stone wool, and good mechanical strength .

Lignin, cellulose and hemicellulose are the three main organic compounds in a plant cell wall. Lignin can be thought of as the glue that holds the cellulose fibres together. Lignin contains both hydrophilic and hydrophobic groups. It is the second most abundant natural polymer in the world, second only to cellulose, and is estimated to represent as much as 20-30% of the total carbon contained in the biomass, which is more than 1 billion tons globally.

Lignin is a complex, heterogenous material generally composed of up to three different phenyl propane monomers, depending on the source. Technical lignins available in the market can be divided in five groups depending on the process of manufacture. Kraft lignins are obtained from an extraction process (sulfur process) using sulfides. Lignosulfonates are obtained from an extraction process (sulfur process) using sulfites. Organosolv lignins are obtained from an extraction process (sulfur-free process) using solvent pulping. Soda lignins are obtained from an extraction process (sulfur-free process) using soda pulping. Biorefinery lignin is not obtained by an extraction process, but instead by the process origin, e.g. biorefining. Each group is different from each other and may be suitable for different applications. The lignin contained in the inventive aqueous binder composition may be selected from the group of Kraft lignins, soda lignins, lignosulfonates, organosolv lignins, lignins from biorefining processes of lignocellulosic feedstocks, or any mixture thereof. However, the lignin used is most preferably lignosulfonate. Lignosulfonates are also designated lignosulfonate lignins. The lignosulfonate may be e.g. ammoniumlignosulfonate, calciumlignosulfonate, magnesiumlignosulfonates or any combination thereof.

Lignosulfonates are generally obtained from sulfite pulping processes using sulfurous acid and/or a sulfite salt containing magnesium, calcium, sodium, or ammonium at varying pH levels. Currently, lignosulfonates account for 90 % of the total market of commercial lignin, and the total annual worldwide production of lignosulfonates is approximately 1.8 million tons.

The lignosulfonate process introduces a large amount of sulfonate groups, generally at least one for every four C9 units, making lignosulfonates soluble in water but also in acidic water solutions. Lignosulfonate has up to 8% sulfur as sulfonate, whereas Kraft lignin has 1-2% sulfur, mostly bonded to the lignin. The molecular weight of lignosulfonate is generally in the range of 15.000-50.000 g/mol. The high level of sulfonic groups in lignosulfonates makes lignosulfonates strongly charged at all pH levels in water. This abundance of ionisable functional groups can explain most of the differences compared to other technical lignins. Higher charge density allows easier water solubility and higher solid content in solution possible compared to Kraft lignin. For the same reason, lignosulfonates have lower solution viscosity compared to Kraft lignin at the same solid content which can facilitate handling and processing.

A commonly used schematic model structure of a lignosulfonate unit is shown below.

The lignin, in particular lignosulfonate, used may be oxidized lignin, in particular oxidized lignosulfonate. Such lignin, in particular lignosulfonate, may have a carboxylic acid group content of 0.03 to 1.4 mmol/g, preferably 0.05 to 0.6 mmol/g, in particular 0.1 to 0.4 mmol/g, based on the dry weight of the lignin or lignosulfonate, respectively.

For the purpose of the present invention, the term lignosulfonates encompass sulfonated Kraft lignins.

The content of lignin functional groups as given above can be determined by using ³¹P NMR as characterization method. Sample preparation for ³¹P NMR is performed by using 2-chloro-4,4,5,5-tetramethyl-l,3,2-dioxaphospholane (TMDP) as phosphitylation reagent and cholesterol as internal standard. Integration is according to the work of Granata and Argyropoulos (J. Agric. Food Chem. 43: 1538- 1544). Proportions and pH

In a preferred embodiment, the aqueous binder composition according to invention comprises, based on the total weight of the polyvinyl alcohol, the one or more polycarboxylic acids or anhydrides or salts thereof, and the lignin, i) 50 to 65 wt.-% of the polyvinyl alcohol, ii) 7 to 30 wt.-% of the one or more polycarboxylic acids or anhydrides or salts thereof, and iii) 15 to 40 wt.-% of the lignin, preferably lignosulfonate.

In a more preferred embodiment, the aqueous binder composition according to invention comprises, based on the total weight of the polyvinyl alcohol, the one or more polycarboxylic acids or anhydrides or salts thereof, and the lignin, i) 55 to 65 wt.-%, preferably 57 to 63 wt.-%, of the polyvinyl alcohol, ii) 7.5 to 20 wt.-%, preferably 8 to 15 wt.-%, of the one or more polycarboxylic acids or anhydrides or salts thereof, and iii) 20 to 35 wt.-%, preferably 25 to 35 wt.-%, of the lignin, preferably lignosulfonate.

It is particular preferred the aqueous binder composition according to invention comprises, based on the total weight of the polyvinyl alcohol, the one or more polycarboxylic acids or anhydrides or salts thereof, and the lignin, i) 58 to 62 wt.-%, preferably about 60 wt.-%, of the polyvinyl alcohol, ii) 8 to 12 wt.-%, preferably about 10 wt.-%, of the one or more polycarboxylic acids or anhydrides or salts thereof, and iii) 28 to 32 wt.-%, preferably about 30 wt.-%, of the lignin, preferably lignosulfonate.

In a preferred embodiment, the weight ratio of the polyvinyl alcohol to the one or more polycarboxylic acids or anhydrides or salts thereof in the aqueous binder composition is 10: 1 to 2: 1, preferably 8: 1 to 3: 1 or 8: 1 to 4: 1, in particular 7: 1 to 5: 1 such as about 6: 1.

The aqueous binder composition may contain only the three components discussed above, but it is also possible that one or more further additives are included. The total weight of the polyvinyl alcohol, the one or more polycarboxylic acids or anhydrides or salts thereof, and the lignin, preferably lignosulfonate, may be e.g. in the range of 70 to 100 wt.-%, preferably 80 to 100 wt.-%, preferably 90 to 100 wt.-%, based on the solids content of the aqueous binder composition. The aqueous binder composition of the invention is preferably acidic. The pH value of the aqueous binder composition is e.g. in the range of 0.5 to 3.0, preferably 1.0 to 2.5 or 1.5 to 2.5, more preferably the pH is about 2. The aqueous binder compositions are already acidic by virtue of the components included, e.g. a pH of about 3. If a lower pH is desired, an acid such as sulfuric acid may be added. If a higher pH is desired, a base such as NaOH may be added.

The solids content of the aqueous binder composition of the invention may be e.g. in the range of 5 to 50 wt.-%, preferably 15 to 35 wt.-%.

The solvent or dispersing agent is water. Optionally, one or more organic solvents such as alcohols may be included, but, if added, the amount is preferably less than 10 parts by mass, based on 100 parts of water.

Further additives

The aqueous binder composition of the invention may contain only components i), ii) and ii) discussed above with respect to the solids content, but it is also possible that the aqueous binder composition further comprises one or more additives.

The one or more additives may be selected from catalysts, silanes, reactive or nonreactive silicones, wetting agent, and combinations thereof.

As mentioned before, H⁺ can catalyze the curing reaction, which are present in the aqueous binder composition. Apart from H⁺, the aqueous binder composition may comprise an organic or inorganic catalyst that can provide extra H⁺, such as hydrochloric acid, sulfuric acid, and p-toluenesulfonic acid. The presence of such a catalyst can improve the curing properties of the binder compositions according to the present invention.

The one or more silanes may be organofunctional silanes. The silanes can serve as coupling agents. Examples of suitable organofunctional silanes are primary or secondary amino functionalized silanes, epoxy functionalized silanes, methacrylate functionalized silanes, alkyl and aryl functionalized silanes, urea funtionalised silanes or vinyl functionalized silanes. The one or more silicone resins may be one or more reactive or nonreactive silicones. The one or more silicone resins may be constituted of a main chain composed of organosiloxane residues, especially diphenylsiloxane residues, dialkylsiloxane residues, preferably dimethylsiloxane residues, which may bear at least one hydroxyl, carboxyl or anhydride, amine, epoxy or vinyl functional group capable of reacting with at least one of the constituents of the binder composition

Mineral fibers

The aqueous binder composition according to the invention is particularly suitable for mineral fibers as discussed below with respect to the inventive method and inventive mineral fibre products.

Mineral fibres are often denoted as mineral wool. In the context of the present invention, the terms mineral fibres such as stone fibres and mineral wool such as stone wool are used interchangeably with each other.

The mineral fibres employed are in particular man-made vitreous fibres (MMVF), examples of which are glass fibres, ceramic fibres, basalt fibres, slag fibres, and stone fibres. Preferred mineral fibers are glass fibres, slag fibres, and stone fibres.

In the most preferred embodiment, the mineral fibres are stone fibers or stone wool, respectively. The aqueous binder composition is particularly suitable for stone wool applications.

Method of producing a mineral fibre product

The invention further relates to a method of producing a mineral fibre product which comprises the steps of contacting mineral fibres with an aqueous binder composition according to the invention as described above, and curing the binder. All aspects and embodiments discussed above with respect to the aqueous binder composition according to the invention, in particular the aqueous binder composition and suitable mineral fibers mentioned above, equally apply to the inventive method so that reference is made thereto. As mentioned, the mineral fibres are preferably stone fibres or stone wool, respectively.

In order to contact the mineral fibres with the aqueous binder composition according to the invention, any conventional method may be used, preferably by spraying the aqueous binder composition onto the mineral fibres, preferably onto a cloud of air-laid mineral fibers.

The curing is effected by a chemical and/or physical reaction of the binder components by heating. The curing may substantially take place in a curing device such as a curing oven or by means of a hot air stream.

In the inventive method, the curing may be generally carried out at a temperature of 140 to 230°C. The curing is preferably carried out at temperatures of from 160 to 200 °C, preferably 170 to 190 °C, in particular 175 to 185 °C such as about 180 °C.

The curing time inter alia depends on the curing temperature. The curing time may be for instance in the range of 10 min to 180 minutes, preferably 20 minutes to 120 minutes hours, more preferably 30 minutes to 90 minutes such as about 60 minutes.

The aqueous binder composition is normally applied in such an amount that the binder content, i.e. the cured binder, in resulting mineral fibre product is in the range of e.g. 0.1 to 18%, preferably 0.2 to 8 % by weight, based on the total weight of the mineral fibre product.

Suitable fibre formation methods and subsequent production steps for manufacturing the mineral fibre product are those conventional in the art. Generally, the aqueous binder composition is sprayed immediately after fibrillation of the mineral melt on to the air-borne mineral fibres which are subsequently collected as a web, e.g. on a conveyor belt. The spray-coated mineral fibre web is generally cured in a curing oven or by means of a hot air stream. The hot air stream may be introduced into the mineral fibre web from below, or above or from alternating directions in distinctive zones in the length direction of the curing oven.

If desired, the mineral wool web may be subjected to a shaping process before or after curing. The bonded mineral fibre product emerging from the curing oven may be cut to a desired format e.g., in the form of a batt.

Mineral fibre product

The invention further relates to a mineral fibre product comprising mineral fibres, preferably stone fibres, bound by a binder resulting from the curing of an aqueous binder composition according to the invention as described above. The mineral fibre product of the invention is preferably obtainable by the inventive method described above.

All aspects and embodiments discussed above with respect to the aqueous binder composition and the method according to the invention, in particular with respect to the aqueous binder composition and suitable mineral fibers, equally apply to the inventive mineral fiber product so that reference is made thereto. As mentioned, the mineral fibres are preferably stone fibres or stone wool, respectively.

The mineral fiber product of the invention may be for instance a plant growth substrate, a thermal or acoustical insulation material, e.g. in form of pipe sections, a vibration damping, a construction material, a facade insulation, a reinforcing material for roofing or flooring applications, e.g. a roof board or a ceiling tile, or a filter stock.

The mineral fibre products of the invention may, for instance, have the form of woven and nonwoven fabrics, mats, batts, slabs, sheets, plates, strips, rolls, plugs, cubes, blocks, granulates and other shaped articles which find use, for example, as plant growth substrates, thermal or acoustical insulation materials, vibration damping, construction materials, facade insulation, reinforcing materials for roofing or flooring applications, as filter stock and other applications. In a particularly preferred embodiment, the mineral fibre product is a plant growth substrate, wherein the mineral fibers are preferably stone fibers or stone wool, respectively.

Plant growth substrates, in particular stone wool plant growth substrates, are used as growing media for plants, in particular in the horticultural field.

They generally represent soil-less and inert growing media. The plant growth substrates can be used e.g. in indoor, greenhouse and hydroponics cultivation.

The plant growth substrates, in particular stone wool plant growth substrates, can have any form and size depending on the desired application. They may have e.g. the shape of a plug, a cube, a block or a slab.

The binder content, i.e. the cured binder, of the mineral fibre product, in particular the plant growth substrate, preferably including stone fibers as mineral fibers, is e.g. in the range of e.g. 0.1 to 18%, preferably 0.2 to 8 % by weight, based on the total weight of the mineral fibre product.

In a preferred embodiment, the density of the mineral fibre product such as those described above may be in the range of 10-1200 kg/m³, such as 30-800 kg/m³, such as 40-600 kg/m³, such as 50-250 kg/m³, such as 60-200 kg/m³.

In a preferred embodiment, the mineral fibre product as described herein is an insulation material, such as a thermal or acoustical insulation material, in particular having a density of 10 to 200 kg/m³.

The mineral fibre products according to the present invention, in particular plant growth substrates or stone wool plant growth substrates, may for instance have a density within the range of from 60 to 140 kg/m³, preferably 70 to 100 kg/m³.

It is also possible to produce composite materials by combining the bonded mineral fibre product with suitable composite layers or laminate layers such as, e.g., metal, glass surfacing mats and other woven or non-woven materials. Use of aqueous binder composition

The invention also relates to the use of the aqueous binder composition according to invention as described above for the production of a mineral fibre product, preferably a stone wool product.

All aspects and embodiments discussed above with respect to the inventive aqueous binder composition, the inventive method, and the inventive mineral fibre product, in particular with respect to the aqueous binder composition, the mineral fibers, the mineral fibre product and the plant growth substrate, equally apply to the inventive use so that reference is made thereto.

In a particular preferred embodiment of the inventive use, the mineral fibre product is a plant growth substrate, a thermal or acoustical insulation material, a vibration damping, a construction material, a facade insulation, a reinforcing material for roofing or flooring applications, or a filter stock, wherein the mineral fibers are preferably stone wool.

Examples

In the following examples, several binders, which fall under the definition of the present invention were prepared and compared to reference binders. The following properties were determined for the binders prepared.

Mechanical strength

The mechanical strength of a binder recipe is determined in the lab using a minibar method described below. The bars prepared are based on a waste product during mineral wool production, herein called "stone wool shots". The shots are small beads, typically in the size range of 300 - 700 micrometers, which are bonded with the binder to be tested . They have similar surface chemistry as the mineral wool fibres, therefore giving an indicative mechanical strength of a tested binder. The mechanical strength test of a binder includes 2 types of strengths: dry strength (unaged) and wet strength (water-bath aged). Since mineral fiber products used as plant growth substrates are always soaked in water during usage, the wet strength is very important for this application. Bar mechanical strength tests

The mechanical strength of the binders was tested in a bar test. For each binder, 16 bars were manufactured from a mixture of the binder and stone wool shots from the stone wool spinning production.

A sample of this binder solution having 20% dry solid matter (50 g) was mixed well with shots (330 g). The resulting mixture was then filled into four slots in a heat- resistant silicone form for making small bars (4x5 slots per form; slot top dimension: length = 5.6 cm, width = 2.5 cm; slot bottom dimension: length = 5.3 cm, width = 2.2 cm; slot height = 1.1 cm). The mixtures placed in the slots were then pressed with a suitably sized flat metal bar to generate even bar surfaces. 16 bars from each binder were made in this fashion. The resulting bars were then cured typically at 140 - 230 °C. The curing time was typically 10-180 min. After cooling to room temperature, the bars were carefully taken out of the containers. Four of the bars were aged in a water bath at 80 °C for 3 h.

After drying in a climate chamber with controlled humidity (50%) and temperature (22 °C) for 3 days, the aged bars as well as four unaged bars were broken in a 3 point bending test (test speed: 10.0 mm/min; rupture level: 50%; nominal strength: 30 N/mm²; support distance: 40 mm; max deflection 20 mm; nominal e- module 10000 N/mm²) on a Bent Tram machine to investigate their mechanical strengths. The bars were placed with the "top face" up (i.e. the face with the dimensions length = 5.6 cm, width = 2.5 cm) in the machine.

Water resistance test

The water resistance of a binder is also important as it endows a binder the wet strength. In other words, if a binder is not water resistant, it would not have wet strength. But even if a binder is water resistant, it does not mean it would have good wet strength because the mechanical strength is also dependent on the adhesion of a binder to mineral fibers such as stone wool. In our study, the water resistance of a binder is indicated by the water solubility in the water bath aging test, which is determined as the following: After the three-point bending test, the four unaged bars and the four water bath aged bars were weighed separately in a container (m_before). Then they were placed in an oven (585 °C) for 1 h to incinerate all the organic matter in the bars. After cooling down to room temperature, the remaining shots in the container were weighed again (m_after). Loss on ignition (LOI) is calculated as:

LOI (%) — (m before^_mafter)/m before* 100 %

In this way, both the LOI for unaged bars (LOIunaged) and water bath aged bars (LOIaged) could be determined. The water solubility of the binder is defined as "how much of the binder has been dissolved in the water bath aging", therefore it is calculated as:

Water solubility (%) ⁼ (LOI unaged ^— LOIaged)/LOIunaged * 100%

The higher the solubility, the lower the water resistance.

Viscosity test

The dynamic viscosity of the binders was measured using a Hydramotion Viscolite 700 viscometer. To ensure a fair comparison, all the samples were prepared at 10% solid content, and all the measurements were done at room temperature (23 °C).

Binder examples

The PVA-Polycaboxylic acid-based binders were prepared as the following: a certain weight of PVA was weighed and added to water. The mixture was then heated in a water bath at 80 °C to obtain a clear solution. The time it took to completely dissolve the PVA was dependent on the concentration, MW of PVA, and hydrolysis degree of PVA. In our case, it usually took 30 mins to 1 h. Afterwards, a certain amount of polycarboxylic acid was added and kept stirring for 5 more minutes to dissolve. Then 0.2% of amino silane was added to the solution. If necessary, additional water was added to adjust to the desired solid content. The solid contents were in the range of 10-30%.

The PVA-Polycaboxylic Acid-Lignin sulfonate-based binders were prepared as the following: a certain weight of PVA was weighed and added to water. The mixture was then heated in a water bath at 80 °C to obtain a clear solution. Afterwards, a certain amount of polycarboxylic acid and lignin sulfonate was added and kept stirring for 5 more minutes to dissolve. Then 0.2% of amino silane was added to the solution. Then the pH was adjusted to 2 using 10% H₂SO₄ solution. If necessary, additional water was added to adjust to the desired solid content. The solid contents were in the range of 10-30%.

A series of reference and inventive aqueous binder compositions are prepared and subjected to the bar test and water resistance as described below (PVA = polyvinyl alcohol, PCA = polycarboxylic acid, IA = itaconic acid, LS = lignosulfonate).

The following grades of PVA from Kuraray Europe GmbH are used (Mw = weight average molecular weight):

PVA 4-88 (Mw about 31.000 g/mol)

PVA 4-98 (Mw about 27.000 g/mol)

PVA 10-98 (Mw about 61.000 g/mol)

PVA 18-88 (Mw about 130.000 g/mol)

PVA 20-98 (Mw about 125.000 g/mol)

In general, the experimental results show that PVA/PCA/LS works as a binder with good mechanical strength, good water resistance, and low viscosity, in particular in comparison with PVA/PCA systems. As compared to PVA/PCA binders, the PVA/PCA/LS binder need a higher curing temperature (optimal curing temperature: 180°C compared to 140 °C) and lower reaction pH (optimal pH 2 compared to pH 3).

A further benefit of the PVA/PCA/LS binder as compared to the PVA/PCA binder is a significant higher flexibility regarding the type of PVA and/or PCA. Besides, since a much lower molecular weight PVA is applicable in the PVA/PCA/LS binder, the viscosity of the PVA/PCA/LS binder is also much lower than the PVA/PCA binder, which is a great benefit in production. Reference example 1

PVA (PVA 4-98, PVA 10-98 or PVA 20-98) without any crosslinker was used as a binder to see if it has good adhesion to stone wool. 15 g PVA was added to 60 g of water and heated at 80 °C for 1 h to obtain a clear solution with a solid content of 20%. Afterwards, 0.75 g silane (4% solution) was added to the solution to get the finished binder solution. 63 g binder was added to 460 g (aiming for 2.67% LOI) shots and mix well with a blender to ensure the homogenous distribution of the binder in the shots. 16 bars were prepared and cured at 140 °C for 1 h. The results are given in Fig. 1.

PVA shows very good adhesion to stone wool and exhibits excellent unaged mechanical strength, regardless of its Mw. But due to its water solubility, it does not have any wet strength and dissolved in water 100% during water bath aging. Therefore, a crosslinker is needed to improve its water resistance and wet strength.

Reference example 2

To illustrate the feasibility of crosslinking PVA with a PCA, itaconic acid (IA) as PCA and PVA 20-98 were used as an example. IA was purchased from Sigma- Aldrich. Different amounts of IA were used to see how much of IA is needed to crosslink PVA 20-98 sufficiently. 15 g PVA 20-98 was added to 60 g water and heated at 80 °C for 1 h to obtain a clear solution with a solid content of 20%. To the solution, different amounts of IA (0% to 50% wt.% of PVA) were added and kept stirring for 5 mins until all the IA was dissolved . Afterwards, 0.75 g silane (4% solution) and different amount of water was added to the solution to get the finished binder solution with a solid content of 20%. 63 g binder was added to 460 g (aiming for 2.7% LOI) shots and mix well with a blender to ensure the homogenous distribution of the binder in the shots. 16 bars were prepared and cured at 140 °C for 1 h. The results are given in Fig 2 (0% means no IA added).

IA could potentially be used to crosslink PVA 20-98, with minimum 30% wt of IA to PVA (30 g IA to 100 g PVA). The optimal amount of IA is ca. 40% of PVA. The incorporation of the crosslinker lowers the unaged strength, but after crosslinking, PVA showed excellent water resistance and wet strength.

Reference example 3

A number of different types of PCA and other reagents were tested as cross-linkers that could also potentially react with the -OH groups of PVA. All crosslinkers were added as 40% wt. of PVA. The samples were prepared similarly to the above example except for changing the crosslinker. Curing was also conducted at 140 °C for 1 h. The results are given below in Fig. 3 (citric acid, tartaric acid, alginic acid, sebacic acid, oxalic acid, itaconic acid and itaconic anhydride were from Sigmal- Aldrich, PAE: polyamidoamine epichlorohydrin from Solenis; GPAM: glyoxalated polyacrylamide from Kemira, BTCA: 1,2,3,4-butanetetracarboxylic acid form Sigma-Aldrich, EDTA: ethylenediaminetetraacetic acid from Sigma-Aldrich).

It was found that only oxalic acid, itaconic acid, and itaconic anhydride could crosslink PVA 20-98 sufficiently to provide both good mechanical strength and water resistance. Oxalic acid showed comparable strength with IA, while itaconic anhydride showed relatively lower mechanical strength.

Reference example 4

The influence of the curing temperature on the mechanical strength and water resistance of cured binder was tested. The binder was prepared in the same manner as Reference example 2 with 40% IA to PVA 20-98. The bars were cured at 140, 180, 200, 200 °C for 1 h, respectively. The results are given below in Fig. 4.

Between 140 and 200 °C, there is no significant influence of curing temperature on the mechanical strength. Increasing the curing temperature to more than 200 °C leads to a decrease in mechanical strength. This is most likely a result of the thermal degradation of PVA at higher temperature, as seen in a lower LOI (loss on ignition) in the binder (See table below). It was found in the literature that PVA starts degrading at temperature above 180 °C.

Considering the energy cost and the potential of higher emission at higher temperature, and the stability issue of PVA at high temperature, 140 °C is the preferred curing temperature for the PVA/PCA binder, despite a lower water solubility at higher curing temperature.

Reference example 5

The influence of the pH value of the aqueous binder composition based on PVA/PCA on the mechanical strength and water resistance of cured binder was tested. 15 g PVA 20-98 was added to 60 g water and heated at 80 °C for 1 h to obtain a clear solution with a solid content of 20%. To the solution, 6 g IA (40 % of PVA) were added and kept stirring for 5 mins until all the IA was dissolved.

Afterwards, 0.75 g silane (4% solution) was added. The pH without adjustment was ca. 3. Then different amount of 10% H2SO4, 10% NaOH, or 10% ammonia was added to reach the desired pH. Afterwards, different amounts of water were was added to the solution to get the finished binder solution with a solid content of 20%. 63 g binder was added to 460 g (aiming for 2.7% LOI) shots and mix well with a blender to ensure the homogenous distribution of the binder in the shots. 16 bars were prepared and cured at 140 °C for 1 h. The results are given below in Fig. 5.

As mentioned, the esterification reaction can be catalyzed in acidic condition. Therefore, it is expected that the binder works best at acidic pH, which is consistent with the experimental result.

When the pH was increased to either 5 or 7 with addition of either NaOH or NH₃, the binder became weaker in unaged strength, but also no longer water-resistant. When decreasing the pH from 3 (when the pH is not adjusted, it is ca. 3) to 2, no significant influence was observed, indicating the reactivity of PVA and IA is good enough for this esterification to take place efficiently.

Reference example 6

The influence of the Mw and hydrolysis degree of PVA on the mechanical strength and water resistance of cured binder was tested. The samples were prepared similarly to the example 2 except for keeping the IA amount fixed at 40% of PVA and replace PVA 20-98 with different kinds of PVA. Curing was also conducted at 140 °C for 1 h. The results are given below in Fig. 6.

Both Mw and hydrolysis degree have a significant impact on the mechanical strength and water resistance of the binder. The higher Mw, and the higher the hydrolysis degree, the higher the mechanical strength and water resistance is. PVA 4-98 does not have water resistance at all, even though it has the merit of a much lower viscosity.

Reference example 7

As shown in the previous examples, the best results with respect to mechanical strength and water resistance were achieved with PVA 20-98. However, viscosity is an important parameter of a binder. Generally, the viscosity of a binder should be as low as possible, so it is easily sprayable and does not clog the pipes and nozzles during production.

In this regard, the very high viscosity of PVA 20-98 in the PVA/PCA binder (5 times of PVA 4-98) is a potential issue (see table below). At 10% solid content and room temperature, which resembles the condition in a production line, the binder prepared with PVA 20-98 (108.6 mPa’s) had a much higher viscosity than PVA 4- 98 (14.4 mPa’s), while our standard reference phenol-urea-formaldehyde (PUF) binder had a viscosity of only 2.2 mPa’s. Therefore, trials were made to achieve a suitable aqueous binder composition based on PVA 4-98 by varying various parameters, but without success. The reason behind this phenomenon is not yet clear. The results of these trials are given below in Fig. 7a-d. a) PVA 4-98 with different crosslinkers (40% w.t. of PVA), Curing condition: 140 °C, 1 h (the results are shown in Fig. 7a). b) PVA 4-98 with IA (40%) at different curing time. Curing condition: 140 °C, 1/2/3/4 h (the results are shown in Fig. 7b). c) PVA 4-98 with IA (40%) at different curing temperatures. Curing condition: 140/180/200/220 °C, 1 h (the results are shown in Fig. 7c). d) PVA 4-98 with IA (40%) at different reaction pH. Curing condition: 140 °C, 1 h (the results are shown in Fig. 7d).

The conclusion is that almost all the PVA/PCA binder based on PVA 4-98 showed no water resistance, indicating not sufficient crosslinking and therefore no aged strength. The only exception is when the binder is cured at high temperature (200 °C and above). But at such a high temperature, due to the thermal decomposition of PVA, the binder showed clearly lower unaged strength and is therefore not feasible.

Example 1

Aqueous binder compositions were prepared which include PVA 4-98, itaconic acid (IA), and lignin sulfonate (LS) in various weight ratios. As an example, 12 g PVA 4-98 was added to 50 g water and heated at 80 °C for 30 min to obtain a clear solution. To this solution, 2 g itaconic acid was added, followed by 6 g lignin sulfonate (supplied from LignoTech Florida). In this case, the weight ratio between the 3 components were PVA:IA:LS=6: 1:3. The mixture was kept stirring for another 5 mins until a homogeneous solution was obtained. Afterwards, 1 g amino silane (4% solution) was added to the solution. The pH of the solution was 2.95. Then the pH of the solution was adjusted to 2 by adding 10% H₂SO₄ solution dropwise. Additional water could be added to adjust to the desired solid content if necessary. After stirring for 5 more mins, the homogeneous binder solution with a pH of 2.01 was obtained. 32.6 g of the binder solution was added to 345 g of stone shots and mixed well. 12 mini bars were made, and the bars were cured at 180 °C for 1 h. Other weight ratios were prepared in the similar way. The results of mechanical strength and water resistance of the bars are given below in Fig. 8.

As can be seen, PVA 4-98, IA and LS can form a binder with very good mechanical strength and water resistance at certain weight ratios. A higher ratio of PVA or LS in the binder giver higher unaged strength, while the amount of IA contributes to the water resistance. The performance of this binder system is a delicate balance between these 3 components.

The optimal weight ratio between these three components is PVA:IA: LS = 60: 10:30. The following experiments were all done at this ratio, unless specified.

Example 2

Aqueous binder compositions are prepared in accordance with Example 1, except that the type of polycarboxylic acid (PCA) was varied (weight ratio of PVA: PCA: LS = 60: 10:30). The curing was done under the same condition as Example 1. The results of mechanical strength and water resistance are given below in Fig. 9 (BTCA: l,2,3,4-butanetetracarboxylic acid, EDTA: ethylenediaminetetraacetic acid).

As can be seen, itaconic acid can be replaced with other polycarboxylic acids in this PVA/PCA/LS binder system, though with differences in strength and water solubility.

This PVA/PCA/LS binder is much more flexible than the PVA/PCA system, as many of the PCA that did not work in the PVA/PCA system works in this binder system.

Example 3

Aqueous binder compositions are prepared in accordance with Example 1, except that lignosulfonate was replaced by tannic acid (weight ratio of PVA:IA:tannic acid = 60: 10:30). The curing was done under the same condition as Example 1. Tannic acid resembles lignin structurally but much smaller in molecular weight. Therefore, it was of interest to see if it behaved in a similar way as lignin sulfonate. The results of mechanical strength and water resistance in comparison with the use of lignosulfonate are given below in Fig. 10.

As can be seen, the replacement of lignin sulfonate with tannin results in lower strength and lower water resistance.

Aqueous binder compositions are prepared in accordance with Example 1, except that pH values were varied (weight ratio of PVA:IA: LS = 60: 10:30). The pH of the aqueous binder composition was set to pH 2, 3 and 4, respectively. The pH of the reaction mixture was ca. 3 without any adjustment. pH 2 was reached by adding 10% H2SO4 solution, and pH 4 was reached by adding 0.5 M NaOH solution. The curing was done under the same condition as Example 1. The results of mechanical strength and water resistance are given below in Fig. 11.

Similar to the PVA/PCA binder, a low pH is also favored for the PVA/PCA/LS binder, optimal pH is ca. 2. This means it needs a lower pH than the PVA/PCA binder (pH 3). We assume that this is due to the reactivity difference between the -OH group in PVA and in LS. The -OH groups in PVA are alkyl while PVA in LS are aromatic. Aromatic -OH has a lower reactivity, therefore needing a more acidic condition to catalyze this reaction. This reactivity difference is also observed in terms of curing temperature (cf. Examples 5 and 6).

When the reaction pH was not adjusted (ca .3) or even further increased to pH 4, the unaged strength dropped significantly. The binder also lost the water resistance, hence no wet strength.

Example 5

Aqueous binder compositions are prepared in accordance with Example 1, except that the type of PVA was varied (weight ratio of PVA:IA: LS = 60: 10:30). The curing was done under the same condition as Example 1. The results of mechanical strength and water resistance are given below in Fig. 12. As can be seen, the weight average molecular weight (Mw) of PVA did not show a significant influence on the mechanical strength of the binder, whether it was PVA 4-98, PVA 10-98, or PVA 20-98, while for PVA 20-98 based binder, it has a better water resistance. However, due to the drastically lower viscosity, PVA 4-98 is the preferred choice in the PVA/IA/LS binder system. The viscosity of the different binders are shown in the table below.

The hydrolysis degree, on the other hand, showed a significant impact on the mechanical strength and water resistance of the binder. When PVA 4-98 was replaced by PVA 4-88, the mechanical strength dropped, especially for the wet strength, as supported by the higher water solubility.

Example 6

Aqueous binder compositions are prepared in accordance with Example 1. In this trial, curing temperature and curing time, respectively, were varied. The results of mechanical strength and water resistance are given below in Fig. 13a and 13b. a) Curing time was fixed at 1 h while varying the curing temperature (results shown in Fig. 13a). b) Curing temperature was fixed at 180°C while varying the curing time (results shown in Fig. 13b).

Curing temperature has a significant influence on the mechanical strength and water resistance on the binders. When the curing temperature was 140 °C, the cured binder dissolved in water completely, indicating an insufficient degree of crosslinking. When the curing temperature was 220 °C, the wet strength dropped dramatically. This may be due to thermal decomposition of PVA at high temperatures (Table 2), similar to what was observed in the PVA/PCA binder. A curing temperature of 180 °C is an appropriate curing temperature for the PVA/IA/LS system.

With respect to the curing time, a curing time of 1 h at 180 °C is sufficient.

Prolonging the curing time led to a lower water solubility, but also led to a lower mechanical strength. Longer curing time has a similar effect as increasing the curing temperature, as suggested by the LOI of the unaged bars (Table 3)

Table 2: LOI of the unaged bars with different curing temperatures

Table 3: LOI of the unaged bars with different curing time

Example 7

Aqueous binder compositions are prepared in accordance with Example 1, except that the type of PVA was replaced by PVA 10-98 and PVA 20-98, respectively (PVA/IA/LS = 60:30: 10). In this trial, the curing temperature was varied. The results of mechanical strength and water resistance are given below: a) PVA10-98/IA/LS: the results are shown in Fig. 14a below b) PVA20-98/IA/LS: the results are shown in Fig. 14b below Similar trend as in Example 6 was observed for both PVA 10-98 and PVA 20-98. Namely, curing temperature of 140 °C and 220 °C provided systems with deteriorated results. It is clear that after the incorporation of LS into the binder, the binder needs a higher curing temperature as compared to PVA/PCA binder system. It is assumed that this is also caused by the reactivity difference between -OH groups in PVA and in LS.

Example 8

The biodegradability of PVA/PCA and PVA/PCA/IA was also studied. a) PVA 20-98+40% oxalic acid: the results are shown in Fig. 15a below. b) PVA 20-98+40% itaconic acid: the results are shown in Fig. 15b below. c) PVA 4-98+10% itaconic acid+30% LS: the results are shown in Fig. 15c below.

PVA/PCA showed better biodegradability than PVA/PCA/LS binder. This is not surprising since lignosulfonate is not biodegradable. All 3 binders did not meet the 90% degradation requirement, therefore cannot be certified as"biodegradable". The PVA/PCA binders are partially biodegradable.

Claims

1. An aqueous binder composition comprising i) polyvinyl alcohol as a binder, ii) one or more polycarboxylic acids or anhydrides or salts thereof as a crosslinker, and iii) lignin.

2. The aqueous binder composition according to claim 1, wherein the polyvinyl alcohol has a hydrolysis degree of 80 to 100 mol-%, preferably 85 to 100 mol-%, more preferably 90 to 100 mol-%, in particular 95 to 100 mol-%.

3. The aqueous binder composition according to any one of the preceding claims, wherein the polyvinyl alcohol has a weight average molecular weight of 10.000 to 200.000 g/mol, preferably 20.000 to 155.000 g/mol, more preferably 25.000 to 135.000 g/mol.

4. The aqueous binder composition according to any one of the preceding claims, wherein the one or more polycarboxylic acids or anhydrides or salts thereof are one or more monomeric polycarboxylic acids or anhydrides or salts thereof, and/or the one or more polycarboxylic acids or anhydrides or salts thereof are one or more dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids or anhydrides or salts thereof.

5. The aqueous binder composition according to any one of the preceding claims, wherein the one or more polycarboxylic acids or anhydrides or salts thereof are selected from oxalic acid, itaconic acid, citric acid, tartaric acid, butanetetracarboxylic acid, terephthalic acid or anhydrides or salts thereof, or a combination thereof, preferably oxalic acid, itaconic acid or itaconic anhydride, wherein itaconic acid is most preferred.

6. The aqueous binder composition according to any one of the preceding claims, wherein the lignin is lignosulfonate.

7. The aqueous binder composition according to any one of the preceding claims, comprising, based on the total weight of the polyvinyl alcohol, the one or more polycarboxylic acids or anhydrides or salts thereof, and the lignin, i) 50 to 65 wt.-% of the polyvinyl alcohol, ii) 7 to 30 wt.-% of the one or more polycarboxylic acids or anhydrides or salts thereof, and iii) 15 to 40 wt.-% of the lignin.

8. The aqueous binder composition according to any one of the preceding claims, comprising, based on the total weight of the polyvinyl alcohol, the one or more polycarboxylic acids or anhydrides or salts thereof, and the lignin, i) 55 to 65 wt.-%, preferably 57 to 63 wt.-%, of the polyvinyl alcohol, ii) 7.5 to 20 wt.-%, preferably 8 to 15 wt.-%, of the one or more polycarboxylic acids or anhydrides or salts thereof, and iii) 20 to 35 wt.-%, preferably 25 to 35 wt.-%, of the lignin.

9. The aqueous binder composition according to any one of the preceding claims, wherein the weight ratio of the polyvinyl alcohol to the one or more polycarboxylic acids or anhydrides or salts thereof is 10: 1 to 2: 1, preferably 8: 1 to 3: 1 or 8: 1 to 4: 1.

10. The aqueous binder composition according to any one of the preceding claims, wherein the pH value of the aqueous binder composition is in the range of 0.5 to 3.0, preferably 1.0 to 2.5.

11. The aqueous binder composition according to any one of the preceding claims, which is an aqueous binder composition for mineral fibers.

12. A method of producing a mineral fibre product which comprises the steps of contacting mineral fibres with an aqueous binder composition according to any one of the claims 1 to 11 and curing the binder.

13. The method of producing a mineral fibre product according to claim 12, wherein the curing is carried out at temperatures of from 160 to 200 °C, preferably 170 to 190°C.

14. A mineral fibre product comprising mineral fibres, preferably stone fibres, bound by a binder resulting from the curing of an aqueous binder composition according to any one of claims 1 to 11, preferably obtainable by a method according to claim 12 or claim 13.

15. The mineral fibre product according to claim 14, which is a plant growth substrate, a thermal or acoustical insulation material, a vibration damping, a construction material, a facade insulation, a reinforcing material for roofing or flooring applications, or a filter stock.

16. Use of an aqueous binder composition according to any of the claims 1 to 11 for the production of a mineral fibre product, which is preferably a plant growth substrate, a thermal or acoustical insulation material, a vibration damping, a construction material, a facade insulation, a reinforcing material for roofing or flooring applications, or a filter stock.