An aqueous fire retardant composition

Abstract

The present invention relates to an aqueous fire retardant composition for treatment of a fiber-based substrate, the composition comprising: in the range of from 2 to 25 wt% of at least one first compound comprising an amine functional group and at least one additional functional group selected from an amine functional group, a hydroxyl functional group and / or a carboxyl functional group; in the range of from 0.5 to 25 wt% of at least one second compound comprising at least two carboxyl functional groups; in the range of from 0.1 to 15 wt% of a pH- adjusting agent; and at least 40 wt% water; wherein the functional groups in the at least one first compound and the at least one second compound can react in a condensation reaction in order to form a cross-linked material; and wherein the total nitrogen content in the composition is at least 1.5 wt%, based on the total weight of the composition.

Description

114212PC1AN AQUEOUS FIRE RETARDANT COMPOSITIONTechnical field

[0001] The present invention relates generally to an aqueous fire retardant composition and a method for treating a fiber-based substrate by contacting the substrate with said aqueous fire retardant composition so as to improve the fire retardant properties of said substrate.Background art

[0002] Wood and wood-based materials are widely used in various applications such as in buildings and for construction. Since wood is a renewable resource there is a desire to further increase the use of wood as a construction material. One common problem with using wood as a construction material is its inherent poor resistance to fire. Also with other fiber-based materials, such as paper, board and textiles, there are problems with poor fire resistance in many applications.

[0003] There are a number of fire retardants used for treating fiber-based materials in order to improve their resistance to fire. Traditionally, fire retardants commonly contain borate salts, or halogens such as bromine or chlorine. Many of those have been associated with various health threats and also have a negative impact on the environment if they leach out of treated products. Alternative fire retardants involve for example various hydroxide and phosphate salts. There are however often problems with ensuring that the salts are sufficiently bound to the treated material to prevent leakage. Leakage is in particular a problem for materials used outdoors, since such materials may be exposed to harsh weather conditions. The leaked salts may cause environmental harm, for example phosphate salts may contribute to eutrophication. Even though the salts used may not have a negative impact on the environment when leaking, the fire retardant properties are obviously impacted since less of the fire retardants remain in the treated product.

[0004] Nitrogen-containing compounds have also been used to improve fire retardant properties. In particular, melamine has been used in a number of114212PC2applications. There is however health implications associated with melamine, and when used as salts there may also be problems with leakage of the nitrogencontaining compounds e.g. when treated products are exposed to wet conditions.

[0005] WO2019214793 A1 describes an aqueous flame retardant and latent hardener composition comprising a blend of diammonium hydrogen phosphate and monoammonium dihydrogen phosphate. Due to potential environmental concerns there is a common interest in avoiding phosphate-based fire retardants. US2023072612 A describes a composition for imparting flame retardancy comprising an organic salt as a fire-retardant, a surfactant and a binder. The binder used is fossil-based, and thus the flame retardant composition is not biobased.

[0006] There is thus a need for an environmentally friendly fire retardant that is efficient in terms of improving the fire resistance of a fiber-based material. It is also important that the fire retardant does not leak from the treated material even when exposed to harsh conditions.

[0007] The fire retardant composition should further be aqueous in order to avoid solvents with a negative impact on health and / or the environment.Summary of invention

[0008] An object of the present invention is to provide an aqueous fire retardant that is not harmful to humans and / or the environment, but that is still efficient in improving the fire retardant properties of a fiber-based substrate.

[0009] A further object of the present invention is to provide an aqueous fire retardant that will remain in the treated substrate also when the substrate is exposed to wet and humid conditions. Thus, substrates treated with the fire retardant can be used outdoors with no significant risk of leakage from the substrates.114212PC3

[0010] A further object of the present invention is to provide a method for treating fiber-based substrates with an aqueous fire retardant composition so that the fire retardant properties of the substrate are improved.

[0011] According to a first aspect, the present invention relates to an aqueous fire retardant composition comprising, based on the total weight of the composition:- in the range of from 2 to 25 wt% of at least one first compound comprising an amine functional group and at least one additional functional group selected from an amine functional group, a hydroxyl functional group and / or a carboxyl functional group;- in the range of from 0.5 to 25 wt% of at least one second compound comprising at least two carboxyl functional groups;- in the range of from 0.1 to 15 wt% of a pH-adjusting agent;- at least 40 wt% water;wherein the functional groups in the at least one first compound and the at least one second compound can react in a condensation reaction in order to form a cross-linked material; and wherein the total nitrogen content in the composition is at least 1.5 wt%, based on the total weight of the composition.

[0012] It has surprisingly been found that a composition according to the first aspect of the present invention improves the fire resistant properties of a fiberbased substrate treated with the composition as compared to a non-treated substrate. The composition comprises at least 1.5 wt% nitrogen, which is known to have fire retardant properties. When thermally decomposed, the fire retardant composition can release incombustible nitrogen-containing gases such as ammonia, nitrogen and nitrogen oxides as well as water vapor. These gases will dilute the flammable gases generated by the fire, thus preventing spreading of the fire. In addition, the incombustible gases will dilute oxygen in the air, and will also react with the oxygen so that oxygen is consumed and not available to the fire. The formation of the incombustible nitrogen-containing gases also requires heat and will thus have a cooling effect on the fire.114212PC4

[0013] The first and second compounds as well as the pH-adjusting agent as used herein are all chemicals with no adverse health effects and with no negative impact on the environment, or alternatively used in such low concentrations that the amount present in the fire retardant composition is below the threshold of posing any risk. Preferably, the first and second compounds are biobased compounds.

[0014] The first compound and the second compound both comprises carboxyl, amine and / or hydroxyl functional groups that can react in condensation reactions to form covalent bonds between carboxyl functional groups on one molecule and amine or hydroxyl functional groups on another molecule. The condensation reaction is typically initiated by increasing the temperature in a curing step. After such a curing step, the composition will form a cross-linked material that will remain in the substrate it has been applied to also when the substrate is exposed to wet and humid conditions, such that are typically associated with outdoor use. There will thus be no significant leakage of the compounds in the composition once it has been cured. It is believed by the present inventors that in addition to condensation reactions between the compounds in the composition, there may also be reactions between the functional groups in the compounds in the composition and any functional groups present on the fibers in the fiber-based substrate the composition is applied to. Such reactions will contribute to strong attachment of the compounds in the composition to the substrate and thus help in preventing leakage of the compounds from the substrate. During the contacting step, the fire retardant composition will enter cavities and / or pores within the substrate and remain therein. Curing is thus not necessary to obtain fire retardant properties, but as explained above will prevent leakage in wet conditions.

[0015] The term “functional group” as used herein refers to particular groups of atoms within a molecule that primarily determine how the molecule will react. Functional groups of importance in the reactions of the present invention are amine functional groups (-NH2), hydroxyl functional groups (-OH), and carboxyl functional groups (-COOH). The phrase “compound comprising at least two functional groups” and similar as used herein, refers to a compound comprising at114212PC5least two functional groups per molecule. If the compound is a polymer, it comprises at least two functional groups per repeating unit.

[0016] The fire retardant composition comprises at least one first compound. The composition may thus comprise one first compound, or two or more first compounds different from each other. The first compound comprises an amine functional group. In addition, the first compound comprises at least one additional functional group selected from an amine functional group, a hydroxyl functional group and / or a carboxyl functional group. The first compound may comprise at least two additional functional groups, wherein at least one is an amine functional group. For example, the first compound may comprise at least two additional functional groups, wherein at least one is an amine functional group and at least one is a carboxyl functional group.

[0017] The amine functional groups are preferably primary amine functional groups since such groups have a higher reactivity than secondary and tertiary amines which in turn facilitates the condensation reaction with other functional groups.

[0018] The composition comprises in the range of from 2 to 25 wt%, or from 5 to 20 wt%, or from 10 to 15 wt%, based on the total weight of the composition, of the at least one first compound. If the composition comprises more than one first compound, the amount is the total amount of all the first compounds in the composition.

[0019] In some embodiments of the present invention, at least one of the at least one first compound is an amino acid. In such embodiments, if the composition comprises more than one first compound, at least one of those is an amino acid. Amino acids are advantageous to use in the fire retardant composition since amino acids are biomolecules and comprise at least two functional groups able to participate in a condensation reaction. Amino acids always comprise at least one amine functional group and at least one carboxyl functional group and will thus also contribute with nitrogen providing fire retardant properties. Thus, in114212PC6some embodiments, the at least one first compound is selected from one or more of arginine, lysine, glycine, glutamine, asparagine and histidine.

[0020] In some embodiments, the at least one first compound is not an amino acid, or not only an amino acid, but another compound comprising an amine group and at least one additional functional group selected from amine, hydroxyl and / or carboxyl groups. Examples of such compounds are guanidine carbonate, glucosamine and chitosan. In some embodiments, the composition comprises at least one first compound that is an amino acid and at least one additional first compound that is not an amino acid.

[0021] It is preferable that the first compound comprises more than one amine functional group since that will contribute to an increased nitrogen content of the composition which is advantageous when it comes to improving fire retardant properties. For example, the first compound may comprise two amine functional groups and one carboxyl functional group.

[0022] In some embodiments, at least one of the at least one first compound is selected from one or more of guanidine carbonate, glucosamine, chitosan, arginine, lysine, glycine, glutamine, asparagine and histidine, preferably arginine. In some embodiments, the first compound(s) are biobased, such that all first compounds in the composition are biobased. Biobased first compounds may be selected from glucosamine, chitosan, arginine, lysine, glycine, glutamine, asparagine and histidine.

[0023] Preferably, the composition comprises arginine. Arginine has a high nitrogen-content per molecule and has also several amine groups that can contribute to cross-linking. In some embodiments arginine is the only first compound. In other embodiments, the composition comprises arginine and at least one other first compound. For example, the composition may comprise arginine and one or more of guanidine carbonate, glucosamine, chitosan, lysine, glycine, glutamine, asparagine and histidine. In another example, the composition comprises arginine and at least one of glucosamine, guanidine carbonate and chitosan.114212PC7

[0024] The fire retardant composition comprises at least one second compound. The composition may thus comprise one second compound, or two or more second compounds different from each other. The second compound comprises at least two carboxyl functional groups. In addition to the at least two carboxyl functional groups, the second compound may comprise additional functional groups such as amine and hydroxyl functional groups.

[0025] In some embodiments the at least one second compound is a polycarboxylic acid, i.e. a carboxylic acid with two or more carboxyl functional groups. The at least one second compound may be selected from one or more of citric acid, salts of citric acid, itaconic acid, citraconic acid, butenedioic acid, ethylenediaminetetraacetic acid (EDTA), butanetetracarboxylic acid (BTCA), tartaric acid, succinic acid, maleic acid and mesaconic acid, preferably citric acid and / or salts of citric acid. Preferable salts of citric acid are monosodium citrate and trisodium citrate. Preferably, the second compound(s) are biobased.

[0026] The composition comprises in the range of from 0.5 to 25 wt%, or from 2 to 15 wt%, or from 4 to 10 wt%, based on the total weight of the composition, of the at least one second compound. If the composition comprises more than one second compound, the amount is the total amount of all the second compounds in the composition.

[0027] Preferably, the composition comprises citric acid. Citric acid comprises three carboxyl functional groups per molecule which enables bonding between one citric acid molecule with other molecules comprising amine or hydroxyl functional groups. Citric acid is therefore advantageous to use as the second compound in order to enable a high degree of cross-linking. In addition, citric acid is biobased. In some embodiments, the composition comprises citric acid and at least one salt of citric acid. For example, the composition may comprise citric acid and monosodium citrate and / or trisodium citrate.

[0028] The first compound(s) and second compound(s) are different from each other. Functional groups on the at least one first compound can react with functional groups on the at least one second compound in a condensation reaction114212PC8so as to form a cross-linked material. In the condensation reaction, covalent bonds are formed due to reactions between carboxyl groups with hydroxyl groups or amine groups. For example, one molecule of the second compound comprising two carboxyl groups can react with two molecules of the first compound, each molecule comprising an amine group. Other functional groups on the molecules of the first compound can also react with other molecules of the second compound. For efficient cross-linking to occur, it is advantageous for each of the at least one first and second compounds to comprise several functional groups, since that facilitates cross-linking and branching during the condensation reaction, which will in turn increase the molecular weight and water resistance of the formed polymer.

[0029] The fire retardant composition comprises at least 1.5 wt% nitrogen based on the total weight of the composition. One source of nitrogen is the amine group(s) in the at least one first compound. Other compounds in the composition may also contribute to the nitrogen content. In order to increase the nitrogen content, it may be advantageous to use a pH-adjusting agent comprising nitrogen. For the nitrogen to remain in the substrate also when the substrate is exposed to wet conditions, it is important that some of the nitrogen is present on a compound that contributes to the cross-linking reaction.

[0030] The nitrogen content is important for improving the fire retardant properties of a substrate treated with the composition. Specifically, it is not the nitrogen content in the composition but rather the amount of nitrogen that enters and is retained in the substrate that is important. Thus, the nitrogen content in the substrate may depend not only on the nitrogen content in the composition, but also for example on the method used for applying it to the substrate and the type of substrate. However, it has been found by the present inventors that it is easier to obtain a sufficient nitrogen content in the substrate if the nitrogen in the composition is at least 1.5 wt%.

[0031] Preferably the composition comprises at least 3.0 wt%, or at least 4.0 wt%, or at least 5.0 wt%, nitrogen based on the total weight of the composition.114212PC9Increasing the nitrogen content in the composition may facilitate obtaining a sufficient nitrogen content in the treated substrate.

[0032] The fire retardant composition further comprises a pH-adjusting agent. The pH-adjusting agent functions as a catalyst when the composition is heated, thus facilitating the condensation reaction between functional groups on the first and second compounds. The pH-adjusting agent is typically an acid.

[0033] The composition comprises in the range of from 0.1 to 15 wt%, based on the total weight of the composition, of the pH-adjusting agent. The amount depends on the type of pH-adjusting agent and the desired pH in the composition.

[0034] In one embodiment, the pH-adjusting agent comprises nitrogen and / or sulfur. Thus, the pH-adjusting agent may comprise nitrogen, sulfur or both nitrogen and sulfur. A pH-adjusting agent comprising nitrogen and / or sulfur will contribute to the fire retardant properties of the fire retarding composition which is advantageous. It is most preferred that the pH-adjusting agent comprises both nitrogen and sulfur.

[0035] In one embodiment, the pH-adjusting agent is an inorganic acid. In one embodiment, the pH-adjusting agent is selected from one or more of sulfamic acid, sulfuric acid, p-toluenesulfonic acid, and methanesulfonic acid.

[0036] Preferably, the pH-adjusting agent is sulfamic acid. Use of sulfamic acid is advantageous since it comprises both nitrogen and sulfur. Thus, in addition to its catalytic activity, sulfamic acid also contributes to improving fire retardant properties of a substrate treated with the composition.

[0037] Sulfur-containing compounds are known to have fire retardant properties by increasing the char formation and releasing non-flammable gases during combustion. The formed char will have a quenching effect on a propagating fire since it forms a sort of barrier on the burning substrate, and the non-flammable gases can dilute the fuel gases and oxygen thus inhibiting combustion.114212PC10

[0038] The composition preferably has a pH of less than 7. An acidic pH is advantageous for the condensation reaction to take place. In preferred embodiments, the pH of the composition is less than 5, or less than 3. An acidic pH is also advantageous in view of the solubility of the components in the composition. An acidic pH can be obtained by the second compound which is typically an acid, as well as by the pH-adjusting agent.

[0039] The composition is aqueous, meaning that it comprises water. The composition comprises at least 40 wt% water, based on the total weight of the composition. Preferably, the composition comprises at least 40 wt% water, at least 50 wt% water, at least 60 wt% water, or at least 70 wt% water. It should be noted that the composition is typically prepared as a concentrated composition which is diluted prior to use. However, also prior to dilution, the water content must be sufficient to fully dissolve the components of the composition. It is typically difficult to prepare a composition according to the first aspect with a water content lower than 40 wt%. If the composition is diluted too much, i.e. to a water content of 90 wt% or more, it may be difficult to obtain a sufficiently high content of the compounds in a substrate treated with the composition. The composition therefore preferably comprises less than 90 wt% water.

[0040] All weight ratios disclosed herein are given in wt% based on the total weight of the composition, i.e. including all the added compounds as well as water.

[0041] In one embodiment, the composition comprises, based on the total weight of the composition, in the range of from 40 to 85 wt% water, in the range of from 2 to 25 wt% of the at least one first compound, in the range of from 0.5 to 25 wt% of the at least one second compound, and in the range of from 0.1 to 15 wt% of the pH-adjusting agent. Preferably, the composition comprises, based on the total weight of the composition, in the range of from 50 to 85 wt% water, in the range of from 5 to 20 wt% of the at least one first compound, in the range of from 5 to 15 wt% of the at least one second compound and in the range of from 0.1 to 15 wt% of the pH adjusting agent.114212PC11

[0042] In one embodiment, the composition comprises arginine, citric acid, and sulfamic acid. In such an embodiment, arginine is the first compound, citric acid is the second compound and sulfamic acid is the pH-adjusting agent. In a condensation reaction, bonds will for example form between carboxyl groups in the citric acid molecules and amine groups in the arginine molecules. In addition, bonds may form between hydroxyl groups in the citric acid molecules and carboxyl groups in the arginine molecules. There may also be bonds forming between carboxyl groups and amine groups in different arginine molecules. Sulfamic acid will catalyze the reaction and contributes to adjusting the pH of the composition such that an acidic pH is obtained.

[0043] In one embodiment, the composition comprises, based on the total weight of the composition, in the range of from 40 to 85 wt% water, in the range of from 2 to 25 wt% of arginine, in the range of from 0.5 to 25 wt% of citric acid, and in the range of from 0.1 to 15 wt% of sulfamic acid. Preferably the composition comprises, based on the total weight of the composition, in the range of from 50 to 85 wt% water, in the range of from 5 to 20 wt% of arginine, in the range of from 5 to 15 wt% of citric acid and in the range of from 4 to 10 wt% of sulfamic acid.

[0044] In one embodiment, the composition comprises at least two first compounds. In such embodiments, at least one of the first compounds may be an amino acid selected from one or more of arginine, lysine, glycine, glutamine, asparagine and histidine, and at least one of the first compounds may be selected from one or more of guanidine carbonate, glucosamine and chitosan. In one embodiment, the composition comprises, based on the total weight of the composition, in the range of from 40 to 85 wt% water, in the range of from 2 to 25 wt% of arginine and glucosamine, in the range of from 0.5 to 25 wt% of citric acid, and in the range of from 0.1 to 15 wt% of sulfamic acid. Preferably the composition comprises, based on the total weight of the composition, in the range of from 50 to 85 wt% water, in the range of from 5 to 20 wt% of arginine and glucosamine, in the range of from 5 to 15 wt% of citric acid and in the range of from 4 to 10 wt% of sulfamic acid.114212PC12

[0045] The composition may further comprise at least one third compound comprising at least two hydroxyl functional groups. The composition may thus comprise one third compound, or two or more third compounds different from each other. The hydroxyl functional groups can react with carboxyl functional groups present in the at least one first compound and / or the at least on second compound in a condensation reaction. Adding at least one third compound improves the cross-linking ability of the composition since more functional groups are available for reaction. In order to improve cross-linking further, it is preferred that the third compound comprises at least three hydroxyl functional groups, or at least four hydroxyl functional groups. In addition to hydroxyl functional groups, the third compound may comprise amine functional groups and / or carboxyl functional groups.

[0046] The third compound is different from the first compound and the second compound.

[0047] The composition may comprise in the range of from 0.5 to 15 wt%, or from 1 to 5 wt%, based on the total weight of the composition, of the at least one third compound. If the composition comprises more than one third compound, the amount is the total amount of all the third compounds in the composition.

[0048] In some embodiments, the third compound is selected from one or more of gluconate, sorbitol, glucose, glycerol, mannitol, maltitol, xylitol, mannose, fructose, sucrose, sucralose and sucrose esters.

[0049] In one embodiment, the composition comprises, based on the total weight of the composition, in the range of from 40 to 85 wt% water, in the range of from 2 to 25 wt% of the at least one first compound, in the range of from 0.5 to 25 wt% of the at least one second compound, in the range of from 0.5 to 15 wt% of the pH-adjusting agent, and in the range of from 0.5 to 15 wt% of the at least one third compound. Preferably the composition comprises, based on the total weight of the composition, in the range of from 50 to 85 wt% water, in the range of from 5 to 20 wt% of the at least one first compound, in the range of from 5 to 15 wt% of the at least one second compound, in the range of from 0.5 to 15 wt% of the pH114212PC13adjusting agent, and in the range of from 1 to 5 wt% of the at least one third compound.

[0050] In one embodiment, the composition comprises- arginine and optionally at least one of glucosamine and chitosan in a total amount of from 2 to 25 wt%;- citric acid in an amount of from 0.5 to 25 wt%;-sulfamic acid in an amount of from 0.1 to 15 wt%; and-optionally gluconate and / or glucose in a total amount of from 0.5 to 15 wt%.In such an embodiment, arginine, glucosamine and chitosan are all examples of first compounds, citric acid is the second compound and sulfamic acid is the pH-adjusting agent. Gluconate and glucose are examples of third compounds.

[0051] In all embodiments described above where the composition comprises citric acid, some of the citric acid may be replaced with one or more salts of citric acid, such as monosodium citrate and trisodium citrate. The defined amount of citric acid then refers to the total amount of citric acid and salts of citric acid present in the composition.

[0052] In one embodiment, the composition comprises at least one first compound comprising at least two amine functional groups, at least one second compound comprising at least two carboxyl groups, at least one third compound comprising at least three hydroxyl groups and at least one pH-adjusting agent.

[0053] As described above, the first, second and third compounds can react in a condensation reaction. In order to achieve an efficient cross-linking and a polymer with a high molecular weight it is advantageous that the number of carboxyl functional groups available to participate in the reaction is similar to the total number of hydroxyl functional groups and amine functional groups available to participate in the reaction. Only the functional groups on the first, second and third compounds are counted. The ratio of the total amount of carboxyl functional groups in the composition able to react in the condensation reaction to the total amount of amine functional groups and hydroxyl functional groups in the114212PC14composition able to react in the condensation reaction may be in the range of from 0.25:1 to 1.75:1, or from 0.5:1 to 1.5:1, preferably from 0.75:1 to 1.25:1, or from 0.9:1 to 1.1:1. In one embodiment, the ratio is around 1:1.

[0054] In one embodiment, the composition may comprise in the range of from 0.01 to 2 wt% of one or more additives selected from a wetting agent, a defoamer, a preservative, a dye, a pigment, a rheology modifier and a UV stabilizer.

[0055] A wetting agent may according to the present invention refer to any surfactant, thickener or stabilizer. A surfactant may be ionic or non-ionic. The surfactant may be chosen from the class of surfactants which are defined as nonionic emulsifiers having HLB values from 1 to 41 and that have wetting properties on the substrate used. Since only very small amounts of the wetting agent is added, it does not affect the reactivity of the compounds of the composition nor the condensation reaction to any significant extent. Examples of wetting agents include, but are not limited to, Lutensol TO5 from BASF, Lutensol TO7 from BASF, Brij S10 from CRODA and similar.

[0056] A defoamer may according to the present invention refer to a substance that provides less foaming during production and application of the composition. Examples of possible defoamers include, but are not limited to, EO / PO type defoamers, silicones, tri-butyl phosphate, alkylphthalates, emulsion type defoamers, fatty acid based defoamers and the like. In a preferred embodiment, CLiQSMART 1031 from CLiQ SwissTech AG is used.

[0057] A preservative may according to the present invention refer to a substance that prevents the composition from decomposition by preventing microbial growth or undesirable chemical changes. The preservative may be selected from one or more of a fungicide, a bactericide, a pharmaceutical preservative, a cosmetic preservative and a food preservative. The preservative is preferably biodegradable and / or renewable. Food preservatives, pharmaceutical preservatives and cosmetic preservatives are preferred since they are in general non-toxic. The food preservative can be selected from benzoic acid, sodium benzoate, hydroxybenzoate and derivates thereof, lactic acid, propionic acid and114212PC15sodium propionate, sulfur dioxide and sulfites, sorbic acid and sodium sorbate, potassium sorbate, ascorbic acid, sodium ascorbate, butylated hydroxytolouene, butylated hydoxyanisole, gallic acid and sodium gallate and tocopherols. A fungicide or bactericide such as 2-methyl-4-isothiazolin-3-one can either alone, or in combination with 1 ,2-benzisothiazolin-3-one be included in the compositions. Furthermore, a pharmaceutical preservative such as 2-bromo-2-nitro-1 ,3-propanediol can either alone or in combination with either one, or both of 1,2-benzisothiazolin-3-one and 2-methyl-4-isothiazolin-3-one be included in the compositions.

[0058] A dye and a pigment may according to the present invention refer to any dye and pigment used to induce different coloring than that of the original color of the substrate. A dye and pigment may be organic or inorganic.

[0059] A rheology modifier may according to the present invention refer to a substance that can change the rheology profile of the composition to fit a specific type of application method. Different types of rheology modifiers are for example fumed hydrophobic (Wacker HDK H30RM) and hydrophilic silica nanoparticles (Wacker HDK V15), both from Wacker Chemie AG, starches and its derivatives, or cellulose derivatives such as carboxymethyl cellulose.

[0060] A UV stabilizer may according to the present invention refer to any molecules that absorb / scatter UV radiation to reduce the UV degradation (photooxidation) of a substrate. The UV stabilizer may be organic or inorganic.

[0061] In a preferred embodiment, the aqueous fire retardant composition is not environmentally harmful or toxic. By a toxic composition is meant a composition being poisonous especially being capable of causing death or serious debilitation. By environmentally harmful composition is meant a composition being a threat to the surrounding natural environment or adversely affecting human health. Thus, the fire retardant composition can be used without posing a risk to humans neither during production of products treated with the composition, nor in the final products comprising the composition. It is submitted that the composition may comprise compounds that in a large enough concentration may be harmful to the114212PC16environment. However, when used in the present invention, such compounds are only used at concentrations well below the threshold for posing a risk. Thus, overall the composition is not environmentally harmful.

[0062] The aqueous fire retardant composition preferably does not comprise phosphorous. It is preferable to avoid using phosphorous for environmental reasons, where phosphates and similar compounds comprising phosphorous has a negative impact on the environment. In addition, the aqueous fire retardant composition preferably does not comprise boric acid. Boric acid can be harmful to humans since it can cause health problems, and it is therefore preferred to avoid its use.

[0063] The aqueous composition according to the present invention is a stable formulation, preferably with a shelf life of more than 1 month at room temperature or lower, or at temperatures ranging from 0 to 50°C.

[0064] According to a second aspect, the present invention relates to a method for treating a fiber-based substrate with a fire retardant composition so as to improve the fire retardant properties of the substate, the method comprising: a) providing a fiber-based substrate; b) providing an aqueous fire retardant composition according to the first aspect; and c) contacting the substrate with the composition.

[0065] The term “fiber-based substrate” as used herein refers to any kind of substrate that is largely composed of fibers. The fiber-based substrate can for example be wood or wood based materials, paper, paperboard, corrugated board, nonwovens and textiles. The fibers may be synthetic fibers such as PES, PET, PP and similar, or man-made biobased fibers such as viscose, lyocell, PLA and similar, and natural fibers such as wood fibers, hemp, flax, jute, cotton and linen. The fibers may comprise functional groups that can react with the functional groups in the compounds of the composition.

[0066] In preferred embodiments, the fibers comprise cellulose, such that the substrate is a cellulose-based substrate. For example, it may comprise at least 50114212PC17wt% cellulose. The cellulose-based substrate may comprise natural cellulose fibers or man-made cellulose fibers. Natural cellulose fibers are obtained from wood or other plants and maintain their natural structure. Depending on the method for preparing the cellulose fibers, lignin and hemicellulose may be present in the fibers together with cellulose. The cellulose based substrate may comprise cellulose fibers obtained from a pulping process, or may comprise wood fibers. Man-made cellulose fibers are prepared from dissolved cellulose which is regenerated and extruded to fibers. The cellulose may be chemically modified during the process.

[0067] In preferred embodiments, the fiber-based substrate is wood or a woodbased material. The term “wood-based material” as used herein refers to materials comprising wood, such as composite materials comprising wood chips or wood fibers as fillers. The wood or wood-based material can be any type of wood product, such as solid wood products and engineered wood such as plywood, medium density fiberboard, laminated veneer lumber, particle board, oriented strand board. Any type of wood may be used, such as spruce, pine, birch, oak, redwood or cedar.

[0068] Cellulose comprises a large number of hydroxyl functional groups on each molecule. The present inventors believe that those hydroxyl functional groups can participate in a condensation reaction with the compounds in the fire retardant composition according to the first aspect of the invention. Therefore, the compounds will after curing be strongly attached to the cellulose in the substrate, and the risk of leakage is further reduced.

[0069] In step c) of the method according to the second aspect, involves contacting the substrate with the aqueous fire retardant composition. The term “contacting” as used herein refers to exposing the substrate to the composition such that the composition can diffuse into the substrate. Contacting thus results in impregnation of the substrate with the composition. Any suitable contacting method can be used as long as a sufficient amount of composition diffuses into the substrate. If the amount is too small, fire retardant properties of the substrate may114212PC18not be obtained. As understood by a person skilled in the art, the method depends on the type of substrate used. After the contacting step, the substrate comprises the compounds of the composition.

[0070] Suitable contacting methods involve soaking, vacuum impregnation, pressure impregnation, vacuum-pressure impregnation, padding, foularding, dipping, spraying, brushing, coating, rolling and foam application. A person skilled in the art realizes that the methods must be adjusted such that they result in an impregnation of the composition into the substrate. In embodiments where the substrate is a paper or textile, soaking, spraying or brushing may be suitable contacting methods. In embodiments where the substrate is a wood-based substrate, vacuum-pressure impregnation, vacuum impregnation or pressure impregnation may be suitable in order to force the composition into the substrate. Heat may be applied during the contacting step, but due to the large amount of water present the condensation reaction will not take place, or not take place to an extent where sufficient cross-linking is obtained.

[0071] The method preferably comprises a step of drying the substrate after it has been contacted with the composition. Any suitable drying method can be used. The drying step may be carried out at room temperature or at a lower or elevated temperature. For example, drying may be carried out at temperatures in the range of from 15 to 80°C, or from 25 to 80°C. After drying, the substrate preferably has a moisture content of 20% or less. The temperature during drying is lower than the temperature during curing. Thus, the condensation reaction between the compounds in the composition does not take place during the drying step, or does not take place to a large extent during the drying step.

[0072] Drying can be carried out by using for example microwave drying, IR drying, induction heating, pulse drying, air drying, kiln-drying, dehumidification, vacuum-drying, solar kiln or similar. The drying can be carried out in the absence or presence of vacuum, inert atmosphere, steam or ambient atmosphere.

[0073] The method preferably comprises an additional step of curing the composition at one or more temperatures from 90°C or higher after the substrate114212PC19has been contacted with the composition. Curing is carried out such that the condensation reaction discussed above takes place. Thus, after curing the compounds in the composition are strongly attached to each other and leakage from the substrate is greatly reduced. At temperatures lower than 90°C, the condensation reaction is slow or not occurring at all.

[0074] Although curing is preferred in order to strongly attach the compounds in the composition to the substrate, it is not a necessary step. Depending on the substrate and its intended use, curing may or may not be needed. For substrates to be used outdoors curing is preferred to prevent leakage when the substate is exposed to wet conditions. However, for substrates only to be used indoors or where not exposed to wet conditions, curing is not needed. Fire retardant properties are obtained by the compounds, not by the curing process. Thus, for improving the fire retardant properties of the substrate, it is important that the compounds are present in the substrate, not that they are cross-linked. Crosslinking however ensures that the compounds remains within the substrate.

[0075] Curing can be carried out using any suitable equipment, for example any kind of oven or hot air oven, a vacuum dryer, an infrared (IR) dryer or a microwave oven. Curing can be carried out at ambient atmosphere or at an inert atmosphere, such as a nitrogen atmosphere. The pressure may be atmospheric pressure or reduced pressure, such as vacuum. The equipment used depends on the substrate. Temperatures used during curing depend on the method used for curing. Generally during curing, care must be taken so as not to damage the compounds in the composition. Therefore, prolonged exposure at temperatures higher than 170°C should be avoided. When using IR drying, higher temperatures than 170°C may be reached but only for short periods of time. Thus, even if some degradation occurs, the time period is too short to cause any significant damage. Curing may be carried out at one temperature or two or more temperatures.Curing may also involve increasing the temperature from one set value to another.

[0076] In some embodiments, curing is carried out at one or more temperatures in the range of from 90 to 170°C.114212PC20

[0077] The substrate may be dried to a moisture content of less than 25% prior to curing. Thus, drying and curing are to be seen as different steps in the method according to the present invention. The aim of the drying step is to remove water from the substrate and the aim of the curing step is to cross-link the compounds in the fire retardant composition. Drying and curing are carried out at different temperatures. Drying and curing may be carried out in direct sequence using the same equipment, or as discrete steps using different equipment. It is advantageous to carry out a drying step prior to curing instead of curing the wet substrate directly since water can hinder the formation of covalent bonds between the functional groups and also dissociate already formed bonds.

[0078] It may be advantageous that the substrate is dry when contacted with the fire retardant composition. That the substrate is dry means that it has a moisture content of 25% or less. It may be easier to force the composition into the substrate when the substrate is dry compared to if the substrate is already wet. Thus, the method may comprise a step of drying the substrate prior to contacting it with the composition. Drying can be carried out as outlined above. Drying before contacting is of particular importance when the substrate is wood or a wood-based substrate. Such substrates typically have a moisture content in the range of from 20 to 25 wt% before the contacting step.

[0079] The method according to the second aspect enables a process for improving the fire retardant properties of fiber-based substrates, wherein the method involves a composition that can be used in existing methods for impregnation of substrates. No special equipment is needed. The method can easily be used in industrial settings, for example in vacuum impregnation, pressure impregnation or vacuum pressure impregnation of wood. Drying and curing can also be carried out using standard equipment.

[0080] According to a third aspect, the present invention relates to a fiber-based substrate with improved fire retardant properties comprising a composition according to the first aspect. The substrate according to the third aspect may be obtained by the method according to the second aspect. The fire retardant114212PC21properties of a fiber-based substrate comprising a composition according to the first aspect are improved compared to a fiber-based substrate not comprising the composition according to the first aspect. A substrate according to the third aspect is suitable for use in applications where fire retardant properties are important. Such applications include wooden buildings and constructions, furniture, textiles and similar.Description of embodiments

[0081] In the following, a detailed description of the present invention is provided.

[0082] The composition according to the first aspect of the invention provides improved fire retardant properties to fiber-based substrates contacted with the composition. Fire retardant properties may be evaluated using various methods according to standards within the field, typically EN13823 and ISO 5660-1. The results from the methods are used to give the tested product a classification regarding fire behavior according to EN13501-1. The tested parameters measure for example the heat released during the test and generation of smoke. FIGRA refers to the fire growth rate and describes the rate of heat release of the tested material, and indicates how quickly a fire will propagate in the tested material. THR refers to the total heat release during the first 600 seconds of the test period, and indicates the impact the tested material will have on development of a fire.SMOGRA refers to the rate of smoke generation by the tested material, and gives an estimate on how quickly a room will be filled with smoke due to a fire in the tested material. TSP refers to the amount of smoke generated during the first 600 seconds of the test period, and indicates the impact the tested material will have on generation of smoke. Different values of the tests confer a certain fire classification to the tested products, with class A being the highest. Wood products is classified from B to F. The tested materials are typically also classified regarding smoke development (s1 , s2, s3) and the formation of burning droplets / particles (dO, d1 , d2). For these, s1 refers to a lower amount of smoke development than s2 / s3, and dO refers to a lower amount of burning droplets / particles than d 1 Zd2.114212PC22

[0083] As discussed above, the composition is not harmful to the environment and is not toxic. In addition, it is preferable that the compounds are easy to dissolve in water and also readily available at a low cost, to enable a cheap process. Suitable compounds are illustrated in the examples.

[0084] As also outlined above, the composition can be applied to fiber-based substrates by several different methods. A person skilled in the art is able to select an appropriate method depending on the substrate the composition is to be applied to. As also understood by a person skilled in the art, some methods are more suitable for large scale production than others.

[0085] In a preferred embodiment, a composition consisting of, based on the total weight of the composition, 73.03 wt% water, 10.0 wt% arginine, 0.99 wt% citric acid, 3.99 wt% monosodium citrate, 9.99 wt% sulfamic acid and 2.0 wt% glucosamine, is applied to wood by vacuum pressure impregnation.

[0086] The invention is further illustrated in the following examples, which do not limit the scope of the invention described in the claims.

[0087] The chemicals used in examples 1-10 are described in table 1.Table 1. Chemicals used for the present invention and their purity or quality grade Chemical Grade / purity / identificationCitric acid monohydrate Food gradeItaconic acid >99%, Reagent gradeCitric acid monosodium salt >99%, Anhydrous, Reagent gradeL-arginine Food gradeD-Glucosamine HCI Food gradeDAC: >90%, viscosity: 5-20 mPasChitosan(1% sol.)D-Glucose monohydrate Food gradeSodium gluconate >99%, Reagent gradeGlycine 98%, Reagent gradeSulfamic acid min 99,8%Sodium benzoate Reagent grade114212PC23

[0088] The equipment used in examples 1-10 is described below.

[0089] pH in formulations was measured with phenomenal pHIOOOH from VWR with Hamilton Polilyte Lab Temp BNC electrode (calibrated with buffers pH 4 and 7), or pH strips from Fisher scientific.

[0090] For hygroscopic tests, a climate chamber from Memmert was used.

[0091] Stirring of formulations was done with a magnet stirrer from IKA (Model: Color squid) or with an overhead stirrer from IKA (either Eurostar digital IKA- Werke or IKA RW28 basic) together with a propeller.

[0092] Homogenization of formulations was done using IKA T25 digital Ultra- Turrax.

[0093] Coating of nonwoven was performed with Wichelhaus WI-MU 505 A horizontal padder.

[0094] Viscosity of formulations was measured with Brookfield DV-II+ Pro LV Viscometer together with Rheocal software using spindle LV4 at 50, 10 and 6 rpm.

[0095] In-house flame test was performed with a gas burner (Cartridge Burner).

[0096] Curing of impregnated wood samples was done in an oven from Termaks or via IR by a 2000W IR lamp (Anslut Infrared Heater, 1 and 2 kW)) from Jula.

[0097] Weighing of materials was done with XT 220A Precisa swiss made balance.

[0098] Curing of impregnated filter paper and nonwoven material was performed in an oven (2 m long) from CAMPEN Machinery A / S.

[0099] All methods referred to in examples 1-10 are described below.

[0100] Method 0: General procedures of the preparation of a water-based fire-retardant formulation114212PC24Water was mixed with the other components in elective order of addition. Smaller batches (< 1 kg) were prepared via a magnet stirrer, and larger batches (>1 kg) was prepared with an overhead stirrer with propeller.

[0101] Method A: Impregnation with fire retardantFor spruce wood samples 50x30x5 mm: The test specimens were placed in the impregnation vessels and were Ballasted / fixed with a plastic net to prevent them from floating. A sufficient amount of fire retardant composition was added into the test vessel to cover the groups of test specimens and to ensure that the test specimens remained covered throughout the impregnation. The specimens were placed in such a way that allowed space in-between, so that the composition could penetrate from all sides. The impregnation time, since no vacuum or pressure was used, was 24 hours. The impregnations were performed at room temperature.

[0102] For ISO-5660 and EN 13823 samples: Pressure impregnation was performed at room temperature in a pressure impregnation tube. The pressure was 11 bar. Impregnation time was set between 0.5 h - 3 h depending on sample size, and desired uptake of liquid. Timing started when the pressure had reached 11 bar.

[0103] Method B: Curing of fire-retardant impregnated samples in oven: Samples were dried either in room temperature or in a climate chamber at 23°C and 50% relative humidity. The dried samples were placed in the hot-air oven at room temperature and thereafter the temperature was increased to 95°C for 10 min-30 min depending on sample size. Thereafter the temperature was increased to 120-170°C for 20 min-240 min, depending on chosen test parameters. The temperature was thereafter decreased to 100°C, and the samples were removed from the oven (and weighed when still being warm, to obtain dry weight).

[0104] Method C: Curing of fire-retardant impregnated samples by IR lamp The dried samples were placed on a 15-20 cm distance from the IR-lamp and irradiated for 2.5 min on each of the larger sides and 1 min on each of the edges / thin sides. The IR-lamp was set to 2 kW. The time started from the time of turning the lamp on.114212PC25

[0105] Method D: Accelerated ageing of samplesAccelerated ageing test are performed in order to simulate how the samples behave after being exposed to outdoor conditions. The samples were placed in the ageing vessels and were ballasted / fixed with plastic nets or weights, to prevent them from floating. A sufficient amount of water was added into the test vessels to cover the groups of samples and to ensure that the samples remained covered throughout the experiment.

[0106] For accelerated ageing tests of ISO 5660 samples, plastic buckets of 3 liters were used as ageing vessels and placed inside a glass vacuum tube for the water impregnation part. No lid was used for the buckets in this case. The vacuum pump was then connected to the lid with a tube attached in a drilled hole in the lid. Vacuum was established corresponding to a pressure of 0.2-0.6 bar and maintained for 20 minutes before release. The pressure was controlled by attaching a manometer to the equipment.

[0107] The samples were kept in the vessels for 2 hours before emptying the water. Each vessel was directly refilled with an equal amount of fresh tap water as before. The samples thereafter remained immersed in water for 14 days, at room temperature, with nine changes of the water as follows:- The water was changed at the end of the first and second day of immersion. - The water was changed a further seven times in the remaining days, at intervals of not shorter than one day and not longer than three days.

[0108] Smaller 50x30x5mm impregnated spruce samples were not subjected to the vacuum treatment (the water impregnation part) and were thereby only subjected to the water immersion treatment for 14 days, as described above.

[0109] Method E: In-house flame test of wood (based on UL94):LIL94 was developed for plastic samples, and has been adapted as follows for the present test method. Spruce wood samples with dimension 50 mm x 30 mm x 5 mm were used for a direct flame contact method. The flame was in direct contact for 10 s at an angle of -45° with the wood sample. If the wood did not burn after removal of the flame, or stopped burning within one minute, the flame was applied114212PC26once again. The number of possible applications without the wood sample catching fire, or if the samples stopped burning within 1 minute, gave rise to a ranking number (flame score). The test was repeated seven times. If the wood sample burned for more than one minute at repetition number two, the ranking was 2. Likewise, if the wood sample burned for more than one minute at repetition number seven, the ranking was 7. If the wood sample did not burn for more than one minute on number seven, the ranking was 7++ and the test was stopped. The method was used for wood samples with and without accelerated ageing. For reference, untreated spruce wood samples received a ranking (flame score) of 1.

[0110] Generally, and based on internal experience, the result of the inhouse flame test could be correlated to a classification, according to total heat release, in the EN 13823 test, as defined in table 2 below.Table 2: correlation between in-house test and expected classificationUL 94 ranking Expected classification7++ B or C class6-7 C class2-5 C or D class<2 D class

[0111] Method F: ISO 5660-1:2015Indicative reaction to fire test according to ISO 5660-1 :2015. The method was carried out as indicated in the standard.

[0112] Method G: EN 13823:2020+A1 :2022Indicative reaction to fire test according to EN 13823:2020+A1 :2022. The method was carried out as indicated in the standard.

[0113] Method H: In-house Hygroscopic behavior based on EN 16755:2017 - Annex AFollowing the specific test option for end use product, but with modified sample size (22x100x120mm large samples).114212PC27

[0114] Method I: Preparation of formulationFor formulations comprising chitosan, the formulation was prepared by dissolving Chitosan using a part of the acidic components and thereafter mixing with the other components in elective order of addition. The formulation was prepared via overhead stirrer with propeller as well as homogenizing.

[0115] Method J: Impregnation of filter paper made of cellulose fibers The formulation was diluted to 14 wt% dry content before use. Impregnation was performed with a horizontal padder using a pressure of 0.1 MPa and speed 11.6 rpm. Drying was performed with an oven (2 m long) from CAMPEN Machinery A / S, where the nonwoven material was put on a conveyer belt with speed at 5m / min. The material was cured at 160 °C or at 180 °C until dry.

[0116] Method K: Impregnation of fiber insulation material made of a mix of polyester and cotton fibersThe samples were impregnated by submersion in the composition for 1 - 2 minutes, and thereafter being pressed between two plastic plates, by hand, to squeeze out abundant liquid.

[0117] Method L: Measurement of dry uptake of fire retardantThe weight of the absorbed fire retardant was estimated by measuring the weight of the dry sample before and after impregnation with the fire retardant. The weight increase was divided by the volume of the sample to obtain the dry uptake.

[0118] Formulation Type 1The recipe for the formulation used in experiments 1-3 and 6 is shown in Table 3. This formulation is named Type 1. The formulation was prepared according to Method 0.Table 3: The components of formulation Type 1Component Amount [weight%]Citric acid monohydrate 4.91L-Arginine 10.00Water 73.09D-Glucosamine HCI 2.00Sulfamic acid 10.00114212PC28

[0119] Experiment 1. Fire protection effect due to concentration of formulation Type 1To investigate the effect of changes in the amount / uptake of fire-retardant substances for the fire protection properties of impregnated spruce wood, formulations with varying concentrations of formulation Type 1 were used to impregnate spruce samples according to Method A. The impregnated samples were thereafter cured, at 170°C for 120 min, according to Method B. Dry uptake was measured according to method L. The samples were subsequently evaluated via an indicative reaction to fire with a test according to EN 13823:2020+A1:2022, Method G. During the test, a flame is placed in a corner of a wall built from the material to be tested and the material’s reaction to fire is tested.

[0120] Table 4 shows how different dilutions / concentrations affected the uptake of fire-retardant composition in the wood samples and how this in turn impacted the reaction to fire properties of the samples.Table 4. Results from experiment 1Formulation FIGRA FIGRA THR SMOGRA TSP Result Dry uptake Type 1 (0.4MJ) (0.2MJ) (600s) [m2 / s2] (600s) [kg / m3] Concentration [W / s] [W / s] [MJ] [m2][%]100 105.1 105.1 7.3 Threshold 34.7 B,s1,d0 53.08 not reached80 166.4 166.4 9.2 Threshold 39.1 C,s1,d0 39.39 not reached50 259.1 260.4 11.2 1.4 40.0 D,s1,d0 26.38

[0121] The data from Table 4 shows that with sufficiently high uptake / amount of fire-retardant, the result passed the requirements for B,s1,d0. The results decreased to Class C and D with decreasing uptake in the wood. The smoke development requirements in s1 were however reached for all three uptakes, meaning that all tested samples, regardless of uptake, showed good smoke inhibiting properties. The requirements for dO were reached for all three uptakes, meaning that there were no burning droplets in any of the tested samples, as is typical for wood.114212PC29

[0122] Experiment 2. The effect of accelerated ageing on fire protection propertiesTo investigate how accelerated ageing affect Total Heat Release (THR) and the Heat Release Rate (HRR), formulation Type 1 with a concentration of 100% was used to impregnate spruce samples. Impregnation was performed according to Method A (pressure impregnation). The impregnated samples were thereafter cured according to Method C, and subjected to accelerated ageing according to Method D. The samples were subsequently evaluated via indicative reaction to fire test according to ISO 5660-1 :2015, Method F. The heat release rate (HRR) and Total Heat Release (THR) results for samples before and after accelerated ageing are shown in Table 5.Table 5. Results from experiment 2.Sample Dry Accelerated Heat Total HeatName uptake ageing Release Release[kg / m3] Rate [MJ / m2][kW / m2] THRsoosHRR 30s aveSample 1 35.10 No 111.38 41.28Sample 2 38.99 No 114.42 42.38Sample 3 35.69 Yes 98.28 45.54Sample 4 34.78 Yes 109.70 47.33

[0123] To reach requirements for Class B products according to EN13501-1, after accelerated aging the samples must obtain a HRR 30 seconds average value of below 150 kW / m2, and the increase in the average THR 600s value must be less than 20% as compared to the value before accelerated ageing. The data from Table 5 shows that the samples all had a low HRR, and that the difference in average THR between the samples subjected to accelerated ageing and not was small.

[0124] Experiment 3. Fire protection effect due to concentration for formulation Type 1, after accelerated ageing.To investigate how changes in the amount / uptake of fire retardant substances affected the fire protection properties of impregnated spruce wood, formulations with varying concentrations of formulation Type 1 were used to impregnate114212PC305x30x50mm spruce samples according to Method A. The impregnated samples were thereafter cured, at 170°C for 240 min, according to Method B and subjected to accelerated ageing according to Method D. The samples were subsequently evaluated via the in-house flame test, Method E. Dry uptake was measured according to Method L.

[0125] Table 6 shows how different dilutions / concentrations affected the uptake of fire retardant composition in the wood samples and how this in turn impacted the fire retardance of the samples after they had been subjected to accelerated ageing.Table 6. Results from experiment 3.FormulationNitrogenType 1 Drycontent in the Flame score afterConcentration uptakecomposition ageing([kg / m3][wt%][%]100 42.8 4.8 7++50 21.8 2.4 7++35 15.5 1.7 7++30 11.8 1.4 225 13.3 1.2 2

[0126] The data from Table 6 shows that the fire protection effect increased with increasing uptake of the fire retardant composition after accelerated ageing. Naturally, there is a minimum uptake needed to reach the top result of 7++. Wood is not a homogeneous material and every sample is different, the absorption of fire retardant will naturally differ between samples (even though aiming at similar values). Thereby, and since there is only a small difference in the concentrations, the sample treated with the 25% concentration obtained a slightly higher dry uptake than the sample treated with the 30% concentration. Both uptakes were however too low to yield a high flame score.

[0127] Experiment 4. The effect of curing temperature on fire protection after accelerated ageing.114212PC31To examine how different curing temperatures affect the water resistance of samples, 5x30x50 mm spruce samples impregnated with formulation Type 1 (which was diluted to a 50% concentration) were cured at 170°C, 140°C and 120°C respectively. The samples were impregnated according to Method A, and cured for 240 min according to Method B. They were thereafter subjected to accelerated ageing according to Method D, and evaluated via the in-house flame test, Method E. Table 7 shows the resulting flame scores for the samples cured at different temperatures.Table 7. Results from experiment 4.Formulation Temperature [°C] Flame scoretype 1 after ageingConcentration[%]50 170 7++50 140 7++50 120 2

[0128] The results presented in Table 7 show that curing for 4 h at 140°C was sufficient to yield good enough curing to obtain water resistance and a flame score of 7++ after accelerated ageing. However, treatment at 120°C for 240 min was not enough to induce the necessary level of curing. Here the time might need to be prolonged to reach the necessary level of water resistance.

[0129] Experiment 5. The effect of curing time on fire protection after accelerated ageing.To examine how different curing times affect the water resistance, 5x30x50 mm spruce samples impregnated with formulation Type 1 (which was diluted to 50% concentration) were cured at 170°C for 20 min and 140°C for 30 min, respectively. The samples were impregnated according to Method A, and cured according to Method B. They were thereafter subjected to accelerated ageing according to Method D, and evaluated via the in-house flame test, Method E. Table 8 shows the resulting flame scores for the samples. The flame scores after 240 min curing are added for comparison.114212PC32Table 8. Results from experiment 5.Formulation Temperature [°C] Curing time Flame score Type 1 [min] after ageing Concentration[%]50 170 240 7++50 170 20 7++50 140 240 7++50 140 30 1

[0130] The data from Table 8 shows that a curing time of 20 min at 170°C was enough to reach flame score of 7++ after accelerated ageing. But, when the temperature was set to 140°C, a longer time than 30 min was needed to obtain an adequate level of curing, and consequently water resistance during ageing, since the resulting flame score was 1.

[0131] Experiment 6. Comparing curing in hot-air oven to IR-curinqTo investigate if IR curing could be used as an effective curing method instead of oven curing, 5x30x50 mm spruce samples impregnated with formulation Type 1 were cured by either I R or in a hot-air oven and then subjected to a flame test. Impregnation was performed according to Method A. The impregnated samples were thereafter cured according to Method B or C, and subjected to accelerated ageing according to Method D. The samples were subsequently evaluated via the in-house flame test, Method E. Table 9 shows the resulting flame scores for the oven- and IR-cured samples.Table 9. Results from experiment 6.Curing of Flame score after formulation Dry Flame score after accelerated ageing,Type 1 uptake accelerated ageing, (IR-curing)[kg / m3] (curing in oven)Oven cured 46.4 7++IR-cured 40.3 7++

[0132] The data from Table 9 shows that both curing methods yielded good enough curing for the tests to result in flame scores of 7++, after the samples were114212PC33subjected to accelerated ageing. Both curing methods seem to be equally effective, and IR-curing is thus a viable option.

[0133] Experiment 7. Investigation of hygroscopic propertiesThe hygroscopic behavior of spruce wood impregnated with the Type 1 formulation is shown in Table 10 together with a comparison to untreated spruce. Formulation Type 1 was used to impregnate 22x100x120 mm spruce samples according to Method A. The impregnated samples were thereafter cured, at 170°C for 240 min, according to Method B. The samples were subsequently evaluated via Method H.Table 10. Results from experiment 7.Sample name Dry uptake Equilibrium Exudation of Visible salt at [kg / m3] Moisture content liquid surface [%] [Yes / No] [Yes / No] Formulation Type 86.70 19.43 No No 1 impregnatedspruceUntreated spruce - 18.46 No No

[0134] The data from Table 10 shows that an adequate equilibrium moisture content was reached for the impregnated sample, and that it was not much higher compared to untreated spruce. Also, no exudation of liquid was seen during the test and no salt residues were visible on the surface of the sample. The spruce wood samples treated with formulation Type 1 thereby show good hygroscopic properties even when the uptake of fire retardant was high compared to what is needed to reach class B in the EN 13823:2020+A1 :2022 test (see Experiment 1).

[0135] Experiment 8. Alternative raw materials and variations in concentrationsTo study the addition or substitution of components in the fire retardant formulation, formulation types 1-6 were prepared (see Table 11). Impregnation was performed according to Method A (with 5x30x50 mm spruce samples). The impregnated samples were thereafter cured according to Method C, and subjected to accelerated ageing according to Method D. The samples were subsequently114212PC34evaluated via the in-house flame test, Method E. The recipes for the formulations used in this experiment are shown in Table 11. The formulations were prepared according to Method 0.Table 11. Formulations used in experiment s.Formulation Formulation Formulation Formulation Formulation Formulation Component Type 1 Type 2 Type 3 Type 4 Type 5 Type 6[wt%] [wt%] [wt%] [wt%] [wt%] [wt%] Citric acid 2.455 4.50 0.99 4.97 monohydrate 4.91Citric acid 3.99monosodiumsaltItaconic acid 3.03L-Arginine 10.00 10.00 5.0 10.00 10.5 10.00 Glycine 7.0Water 73.09 74.97 76.545 73.50 72.57 73.03 D-Glucosamine 2.00 1.0HCI 2.00Chitosan 2.00Sodium 2,00gluconateD-Glucose 2.00 monohydrateSulfamic acid 10.00 10.00 8.00 10.00 9.90 10.00 Sodium 0.05benzoate

[0136] After being subjected to accelerated ageing the samples were evaluated via the in-house flame test (Method E). The results of the flame test are presented in Table 12 where the Type 1 formulation is used as reference.Table 12. Results from experiment 8.Formulation FlameDry Nitrogentype score afteruptake contentageing (IR- [kg / m3] [wt%]curing)Type 1 40.3 4.8 7++Type 2 44.9 4.8 7++Type 3 37.7 4.1 7++Type 4 40.9 4.8 7++Type 5 38.2 4.8 7++Type 6 33.4 4.7 7++114212PC35

[0137] All formulation types obtained 7++ results in the flame test. The data from Table 10 shows that it was possible to substitute citric acid with itaconic acid, another polycarboxylic acid used in formulation Type 2, without losing the fire retardance properties after accelerated ageing. The results for formulation Type 3 showed that addition of glycine, a molecule with one carboxylic acid- and one amine-group, also yielded a good flame score after accelerated ageing of the sample. The results for formulation Type 4-6 show that it was also possible to substitute glucosamine with chitosan, sodium gluconate or D-glucose monohydrate, that also are substances containing multiple reactive groups, acting as cross-linkers in the system. Furthermore, the results for formulation Type 5 show that it was possible to substitute a large part of the citric acid to the monosodium salt of citric acid (monosodium citrate), as long as the pH was kept below about 2.5.

[0138] Experiment 9. Other substratesFormulation Type 16 (see Table 13) was prepared according to Method I and filter paper (from Ahlstrdm Munksjb) was impregnated according to Method J. Dry uptake was measured according to Method L.Table 13. Formulation used in experiment 9.Component Amount [wt%]Citric acid monohydrate 4.50%L-Arginine 10.00%Water 73.50%Chitosan 2%Sulfamic acid 10%

[0139] The impregnated samples were evaluated via the in-house flame test, Method E, together with untreated reference samples. All trials were performed in duplicate. The untreated reference samples did not stop burning after removal of the external fire source and turned into ash powder in 28 seconds. The treated samples stopped burning between 0 and 4 seconds after the fire source was removed, and the flame did not spread across the samples. The structure of the treated samples was still intact, but they were severely charred. This shows that114212PC36the fire retardance properties of the filter papers were improved by the treatment with fire retardant composition.

[0140] In another experiment, samples with the dimension 25 x 50 x 50 mm were cut out from a fiber insulation mat made of recycled mix of polyester and cotton fibers. The samples were impregnated, with formulation Type 1, according to Method K. The samples were thereafter dried at 23°C / 50% RH before being evaluated via the in-house flame test, Method E. An untreated sample of the insultation mat was also evaluated as a reference.

[0141] Table 14 shows the resulting uptake of fire retardant and the flame scores obtained in the in-house flame test.Table 14. Results from experiment 9.Sample name Dry uptake [kg / m3] Flame score Formulation Type 1impregnated insulation 39.5 7++materialUntreated insulation- 1material

[0142] It can be seen, in Table 14, that the Type 1 impregnated sample obtains a high flame score while the untreated sample does not seem to have any fire retardant properties. The results show that the treatment also can be used to improve the fire retardance of other materials than wood.

[0143] Experiment 10. Fire protection effect due to dry uptake Formulation Type 17 (see Table 15) was used in experiment 10 and was prepared according to Method 0.Table 15. Formulation Type 17 used in experiment 10.Component Amount [wt%]Citric acid monohydrate 0.99Citric acid monosodium salt 4.66L-Arginine 10.00Water 72.26D-Glucoseamine HCI 2.00Sulfamic acid 9.99Sodium benzoate 0.1114212PC37

[0144] Spruce wood wall-specimens with different average uptakes of fire retardant substances were evaluated for fire protection properties. Samples with varying uptakes of fire retardant substances were sorted and selected after impregnation according to Method A. These samples were envisioned to be used for interior applications, and therefore not expected to be subjected to weathering, and were thereby not cured before testing. Dry uptake was measured according to method L. The samples were subsequently evaluated via an indicative reaction to fire with a test according to EN 13823:2020+A1:2022, Method G. During the test, a flame is placed in a corner of a wall built from the material to be tested and the material’s reaction to fire is tested. Table 16 shows how different uptakes of the fire retardant composition in the wood samples impacted the reaction to fire properties of the samples.Table 16. Formulation Type 17 used in experiment 10.Formulation FIGRA FIGRA THR SMOGRA TSP Result Dry uptake Type 17 (0.4MJ) (0.2MJ) (600s) [m2 / s2] (600s) [kg / m3] Relative uptake [W / s] [W / s] [MJ] [m2]levelLow 82.0 100.4 6.5 2.9 24.8 B,s1,d0 41.7High 92.5 109.4 6.7 4.4 30.4 B,s1,d0 45.8

[0145] The data from Table 16 shows that with sufficiently high uptake / amount of fire retardant, the results indicates that the wood samplespassed the requirements for B,s1,d0, even without curing of the components in the fire retardant composition. The requirements were reached with both high and low uptake, and no improvement was seen for specimen with the high uptake. The increase in uptake might be too small to yield any significant improvement. The small differences in the results could be due to natural variations in fire resistance within the wood itself and / or variations in the distribution of flame retardant in the samples. The smoke development requirements in s1 were reached for both114212PC38uptakes, meaning that the tested samples, regardless of uptake, showed good smoke inhibiting properties. The requirements for dO were also reached for both uptakes, meaning that there were no burning droplets in any of the tested samples, as is typical for wood.

Claims

114212PC39CLAIMS1. An aqueous fire retardant composition for treatment of a fiber-based substrate, the composition comprising, based on the total weight of the composition:- in the range of from 2 to 25 wt% of at least one first compound comprising an amine functional group and at least one additional functional group selected from an amine functional group, a hydroxyl functional group and / or a carboxyl functional group;- in the range of from 0.5 to 25 wt% of at least one second compound comprising at least two carboxyl functional groups;- in the range of from 0.1 to 15 wt% of a pH-adjusting agent; - at least 40 wt% water;wherein the functional groups in the at least one first compound and the at least one second compound can react in a condensation reaction in order to form a cross-linked material; and wherein the total nitrogen content in the composition is at least 1.5 wt%, based on the total weight of the composition.

2. The composition according to claim 1 , wherein at least one of the at least one first compound is an amino acid.

3. The composition according to any one of claims 1 or 2, wherein at least one of the at least one first compound is selected from one or more of guanidine carbonate, glucosamine, chitosan, arginine, lysine, glycine, glutamine, asparagine and histidine.

4. The composition according to any one of the preceding claims, wherein the at least one second compound is a poly-carboxylic acid.

5. The composition according to any one of the preceding claims, wherein the at least one second compound is selected from one or more of citric acid, salts of citric acid, itaconic acid, citraconic acid, butenedioic acid,114212PC40ethylenediaminetetraacetic acid (EDTA), butanetetracarboxylic acid (BTCA), tartaric acid, succinic acid, maleic acid and mesaconic acid.

6. The composition according to any one of the preceding claims, wherein the at least one pH-adjusting agent is an inorganic acid.

7. The composition according to any one of the preceding claims, wherein the at least one pH-adjusting agent comprises nitrogen and / or sulfur.

8. The composition according to any one of claims 6 or 7, wherein the at least one pH-adjusting agent is selected from one or more of sulfamic acid, sulfuric acid, p-toluenesulfonic acid and methanesulfonic acid.

9. The composition according to any one of the preceding claims, wherein the composition has a pH of less than 7.

10. The composition according to any one of the preceding claims, wherein the composition comprises at least one third compound comprising at least two hydroxyl functional groups, and wherein the functional groups in the at least one third compound can react with the functional groups in the at least one first compound and / or the at least one second compound in a condensation reaction.

11. The composition according to claim 10, wherein the at least one third compound is selected from one or more of gluconate, sorbitol, glucose, glycerol, mannitol, maltitol, xylitol, mannose, fructose, sucrose, sucralose and sucrose esters.

12. The composition according to anyone of claims 10 or 11 , wherein the composition comprises, based on the total weight of the composition, in the range of from 40 to 85 wt% water, in the range of from 2 to 25 wt% of the at least one first compound, in the range of from 0.5 to 25 wt% of the at least one second compound, in the range of from 0.1 to 15 wt% of the pH-adjusting agent, and in the range of from 0.5 to 15 wt% of the at least one third compound.

13. The composition according to any one of the preceding claims, wherein the ratio of the total amount of carboxyl functional groups in the composition able114212PC41to react in the condensation reaction and the total amount of amine functional groups and / or hydroxyl functional groups in the composition able to react in the condensation reaction is in the range of from 0.25:1 to 1.75:1.

14. The composition according to any one of claims 10 to 13, wherein the composition comprises citric acid, arginine, sulfamic acid and at least one of glucosamine, chitosan, sodium gluconate and glucose.

15. The composition according to any one of the preceding claims, wherein the composition further comprises in the range of from 0.01 to 2 wt% of one or more additives selected from a wetting agent, a defoamer, a preservative, a dye, a pigment, a rheology modifier and a UV stabilizer.

16. A method for treating a fiber-based substrate with a fire retardant composition so as to improve the fire retardant properties of the substrate, the method comprising:a) providing a fiber-based substrate;b) providing an aqueous fire retardant composition according to any one of claims 1-15; andc) contacting the substrate with the composition.

17. The method according to claim 16, wherein the step of contacting the substrate with the composition involves at least one of soaking, pressure impregnation, vacuum impregnation, vacuum-pressure impregnation, padding, foularding, dipping, spraying, brushing, coating, rolling and foam-application.

18. The method according to anyone of claims 16 or 17, wherein the method comprises a step of drying the substrate after it has been contacted with the composition.

19. The method according to anyone of claims 16-18, wherein the method comprises an additional step of curing the composition at one or more temperatures of at least 90°C after the substrate has been contacted with the composition.114212PC4220. The method according to claim 19, wherein the substrate is dried to a moisture content of less than 20% prior to the curing step.

21. A fiber-based substrate with improved fire retardant properties comprising a composition according to any one of claims 1-15.

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