A flexible polyurethane foam, process for preparing the same and use thereof

Abstract

The present invention relates to polyurethane foams having reduced flammability, smoke and toxicity, for use in railways.

Description

The present invention relates to polyurethane foams having reduced flammability, smoke and toxicity, for use in railways. BACKGROUND OF THE INVENTION Polyurethane (PU) foam obtained by reacting organic diisocyanates and / or polyisocyanate with compounds containing at least two reactive hydrogen atoms, for example polyoxyalkylenepolyamines and / or preferably organic polyhydroxyl compounds, in particular polyetherols having molecular weights of, for example, from 300 to 6000 g / mol, and, if desired, chain extenders and / or crosslinkers having molecular weights upto about 400 g / mol in the presence of catalysts, blowing agents, flame-retardants, auxiliaries, and / or additives is known and has been described many times. These PU foams find wide applications in areas, such as but not limited to, automotive seating / arm rests, foamed carpet backing and furniture. Railway applications, particularly for interior railway components, require a high standard for flame retardancy properties such as flame spread, heat release, and smoke generation upon burning. The European Union has approved the introduction of a new harmonized fire standard for railway applications, namely EN-45545, to replace all currently active different standards in each member state. This standard imposes stringent requirements on heat release, smoke density and toxicity and flame spread properties allowed for materials used in these applications. Smoke density (Ds-4) in EN-45545 is the smoke density after four minutes measured according to ISO 5659-2, and heat release in EN-45545 is the maximum average rate of heat emission (MARHE) measured according to ISO 5660-1 and flame spread in EN-45545 is the critical heat flux at extinguishment (CFE) measured according to ISO 5658-2. Hazard levels (HL1 to HL3) have been designated, reflecting the degree of probability of personal injury as the result of a fire. The levels are based on dwell time and are related to operation and design categories. HL1 is the lowest hazard level and is typically applicable to vehicles that run under relatively safe conditions (easy evacuation of the vehicle). HL3 is the highest hazard level and represents most dangerous operation / design categories (difficult and / or timeconsuming evacuation of the vehicle, e.g. in underground rail cars). For each application type, different test requirements for the hazard levels are defined. For DIN EN 45545-2 R21 applications, which include upholstery assembly for seat / mattresses, the requirements are very stringent. Particularly, for HL3 category, the MARHE of equal to or less than 50 kW / m2, determined according to ISO 5660-1, smoke optical density (Ds) of less than 200 m2 / m2, determined according to ISO 5659-2 and toxicity index (CITg) of less than 0.75, determined according to ISO 5659-2, is difficult to achieve. These standards are particularly required for overnight journey trains, i.e. for trains traveling longer distance. 2020342491   16 Mar 2026 In addition to the reduced flammability, smoke and toxicity requirements, it is also desired that the mechanical properties of the PU foam are not compromised. Incorporating suitable additives or flame-retardant packages during the foaming process, results in poor or degraded mechanical properties in the resulting PU foam. Despite this, there have been several attempts to pro- 5 vide PU foams that are suitable for railway applications. For instance, EP 3 101 045 A1 describes PU foams having reduced flammability, reduced smoke development and low smoke toxicity, for use in upholstery of seat, couchettes and berths in rail vehicles. The PU foam forming formulation here comprises a mixture of flame-retardants, which are mostly phosphate based. 10 Additionally, there are several state-of-the-art documents which also describe the PU foam formulation. However, they do not meet the EN-45545 requirements for railway applications. US 6,660,783 B2 describes one such PU foam, which is highly resilient and has acceptable mechanical properties. Another US 6,087,410 B1 describes a process for preparing PU foams, 15 wherein it is possible to mix additives such as flame-retardants in the foam forming formulation. Although, the PU foam formulations, wherein flame-retardants can be added during foaming, are known in the art, there is still not much described as to obtaining PU foams meeting the EN-45545 requirements for application in railways. In particular, PU foams meeting the require- 20 ments of EN-45545-2 for R21 applications are not known in the state of the art. Further, such formulations having acceptable mechanical properties is also not known in the art. It would, therefore, be advantageous to provide a PU foam which meets the EN-45545-2 requirements for railway applications and has reduced flammability, smoke and toxicity, without 25 compromising the mechanical properties. SUMMARY OF THE INVENTION Surprisingly, it has been found that the above-identified objects are met by the present invention 30 as described hereinbelow and as reflected in the claims. Accordingly, in one aspect, the presently claimed invention is directed to a polyurethane foam obtained by reacting a reactive composition comprising: (A) an isocyanate component, and 35        (B) an isocyanate reactive component comprising (a) at least one polyether polyol having an average functionality in between 1.9 to 5.0 and a OH value in between 10 mg KOH / g to 1000 mg KOH / g, (b) at least one surfactant, (c) at least one amine catalyst, and 40               (d) water, in the presence of (C) a flame-retardant mixture comprising (i) 70 wt.% to 99 wt.% of expandable graphite and (ii) 1 wt.% to 30 wt.% of ammonium polyphosphate, based on the total weight of the flame-retardant mixture, 22510156_1 (GHMatters) P117694.AU WO 2021 / 044002                          3                     PCT / EP2020 / 074798 wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:5 to 5:1. In another aspect, the presently claimed invention is directed to a process for preparing the above-mentioned polyurethane foam by reacting the reactive composition comprising the isocyanate component and the isocyanate component, in the presence of the flame-retardant mixture, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:5 to 5:1. In another aspect, the presently claimed invention is directed to a shaped article comprising the above-mentioned polyurethane foam. In yet another aspect, the presently claimed invention is directed to a process for preparing the above-mentioned shaped article. In still another aspect, the presently claimed invention is directed to a railway component comprising the above-mentioned polyurethane foam. DETAILED DESCRIPTION OF THE INVENTION Before the present compositions and formulations of the invention are described, it is to be understood that this invention is not limited to particular compositions and formulations described, since such compositions and formulation may, of course, vary. It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of', "consists" and "consists of". Furthermore, the terms "first", "second", "third" or "(a)", "(b)", "(c)", "(d)" etc. and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. In case the terms "first", "second", "third" or “(A)”, “(B)” and “(C)” or "(a)", "(b)", "(c)", "(d)", "i", "ii" etc. relate to steps of a method or use or assay there is no time or time interval coherence between the steps, that is, the steps may be carried out simultaneously or there may be time intervals of seconds, minutes, hours, days, weeks, months or even years between such steps, unless otherwise indicated in the application as set forth herein above or below. WO 2021 / 044002                          4                     PCT / EP2020 / 074798 In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some, but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination. Furthermore, the ranges defined throughout the specification include the end values as well, i.e. a range of 1 to 10 implies that both 1 and 10 are included in the range. For the avoidance of doubt, the applicant shall be entitled to any equivalents according to applicable law. Pll foam An aspect of the present invention is embodiment 1, directed to a Pll foam obtained by reacting a reactive composition comprising: (A) an isocyanate component, and (B) an isocyanate reactive component comprising (a) at least one polyether polyol having an average functionality in between 1.9 to 5.0 and a OH value in between 10 mg KOH / g to 1000 mg KOH / g, (b) at least one surfactant, (c) at least one amine catalyst, and (d) water, in the presence of (C) a flame-retardant mixture comprising (i) 70 wt.% to 99 wt.% of expandable graphite and (ii) 1 wt.% to 30 wt.% of ammonium polyphosphate, based on the total weight of the flame-retardant mixture, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:5 to 5:1. In an embodiment, the Pll foam in the embodiment 1 is a flexible Pll foam. The flexible Pll foam has a density in between 50 kg / m3 to 120 kg / m3 determined according to DIN EN ISO 845. WO 2021 / 044002                          5                     PCT / EP2020 / 074798 In another embodiment, the isocyanate component (A) and the isocyanate reactive component (B) in the embodiment 1 is present in a mix ratio, (A):(B), in between 1.0:4.0 to 4.0:1.0. In another embodiment, the isocyanate component (A) and the isocyanate reactive component (B) in the embodiment 1 are present at an index in between 40 to 200. In another embodiment, the index is in between 40 to 180, or 40 to 160. In yet another embodiment, the index is in between 40 to 150, or 50 to 150, or 60 to 140. In still another embodiment, the index is in between 60 to 130, or 60 to 120, or 60 to 110, or 60 to 100, or 80 to 100. The isocyanate index describes the molar ratio of NCO groups to isocyanate reactive groups. An index of 100 relates to the ratio of 1:1. In the present context, the isocyanate component (A) can be referred as A-side component or iso-side, while the isocyanate reactive component can be referred as B-side component or resin-side. Isocyanate component (A) In one embodiment, the isocyanate component (A) in the embodiment 1 comprises an aromatic isocyanate or an aliphatic isocyanate. It is to be understood that the isocyanate includes both monomeric and polymeric forms of the aliphatic or aromatic isocyanate. By the term “polymeric”, it is referred to the polymeric grade of the aliphatic or aromatic isocyanate comprising, independently of each other, different oligomers and homologues. In an embodiment, the isocyanate has an NCO content in between 20 wt.% to 50 wt.%, or in between 20 wt.% to 40 wt.%, or in between 30 wt.% to 40 wt.%, or in between 30 wt.% to 35 wt.%. In one embodiment, the aliphatic isocyanate is selected from tetramethylene 1,4-diisocyanate, pentamethylene 1,5-diisocyanate, hexamethylene 1,6-diisocyanate, decamethylene diisocyanate, 1,12-dodecane diisocyanate, 2,2,4-trimethyl-hexamethylene diisocyanate, 2,4,4-trimethyl-hexamethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, cyclobutane-1,3-diiso-cyanate, 1,2-, 1,3- and 1,4-cyclohexane diisocyanates, 2,4- and 2,6-methylcyclohexane diisocyanate, 4,4'- and 2,4'-dicyclohexyldiisocyanates, 1,3,5-cyclohexane triisocyanates, isocy-anatomethylcyclohexane isocyanates, isocyanatoethylcyclohexane isocyanates, bis(isocy-anatomethyl)-cyclohexane diisocyanates, 4,4’-diisocyanatodicyclohexylmethane, pentamethylene 1,5-diisocyanate, isophorone diisocyanate and mixtures thereof. In one embodiment, the isocyanate component (A) in the embodiment 1 comprises an aromatic isocyanate. In another embodiment, the isocyanate component (A) in the embodiment 1 consists of the aromatic isocyanate only. Suitable aromatic isocyanate is selected from toluene diisocyanate; polymeric toluene diisocyanate, methylene diphenyl diisocyanate; polymeric methylene diphenyl diisocyanate; m-phe-nylene diisocyanate; 1,5-naphthalene diisocyanate; 4-chloro-1; 3-phenylene diisocyanate; 2,4,6- toluylene triisocyanate, 1,3-diisopropylphenylene-2,4-diisocyanate; 1-methyl-3,5-dieth-ylphenylene-2,4-diisocyanate; 1,3,5-triethylphenylene-2,4-diisocyanate; 1,3,5-triisoproply-phe-nylene-2,4-diisocyanate; 3,3'-diethyl-bisphenyl-4,4'-diisocyanate; 3,5,3',5'-tetraethyl-diphenylme-thane-4,4'-diisocyanate; 3,5,3',5'-tetraisopropyldiphenylmethane-4,4'-diisocyanate; 1 -ethyl-4-ethoxy-phenyl-2,5-diisocyanate; 1,3,5-triethyl benzene-2,4,6-triisocyanate; 1-ethyl-3,5-diisopro-pyl ben-zene-2,4,6-triisocyanate, tolidine diisocyanate, 1,3,5-triisopropyl benzene-2,4,6-triisocy-anate and mixtures thereof. In another embodiment, the aromatic isocyanate is selected from toluene diisocyanate; polymeric toluene diisocyanate, methylene diphenyl diisocyanate; polymeric methylene diphenyl diisocyanate; m-phenylene diisocyanate; 1,5-naphthalene diisocyanate; 4-chloro-1; 3-phenylene diisocyanate; 2,4,6-toluylene triisocyanate, 1,3-diisopropylphenylene-2,4-diisocyanate; 1-me-thyl-3,5-diethylphenylene-2,4-diisocyanate; 1,3,5-triethylphenylene-2,4-diisocyanate; 1,3,5-triisoproply-phenylene-2,4-diisocyanate; 3,3'-diethyl-bisphenyl-4,4'-diisocyanate; 3,5,3',5'-tetrae-thyl-diphenylmethane-4,4'-diisocyanate; 3,5,3',5'-tetraisopropyldiphenylmethane-4,4'-diisocya-nate and 1-ethyl-4-ethoxy-phenyl-2,5-diisocyanate. In yet other embodiment, the aromatic isocyanate is selected from toluene diisocyanate; polymeric toluene diisocyanate, methylene diphenyl diisocyanate; polymeric methylene diphenyl diisocyanate; m-phenylene diisocyanate; 1,5-naphthalene diisocyanate; 4-chloro-1; 3-phenylene diisocyanate and 2,4,6-toluylene triisocyanate. In still other embodiment, the aromatic isocyanate is selected from toluene diisocyanate; polymeric toluene diisocyanate, methylene diphenyl diisocyanate and / or polymeric methylene diphenyl diisocyanate; m-phenylene diisocyanate. In a further embodiment, the isocyanate comprises methylene diphenyl diisocyanate and / or polymeric methylene diphenyl diisocyanate. Methylene diphenyl diisocyanate is available in three different isomeric forms, namely 2,2'-meth-ylene diphenyl diisocyanate (2,2'-MDI), 2,4'-methylene diphenyl diisocyanate (2,4'-MDI) and 4,4'-methylene diphenyl diisocyanate (4,4'-MDI). Methylene diphenyl diisocyanate can be classified into monomeric methylene diphenyl diisocyanate and polymeric methylene di-phenyl diisocyanate referred to as technical methylene diphenyl diisocyanate. Polymeric methylene diphenyl diisocyanate includes oligomeric species and methylene diphenyl diisocyanate isomers. Thus, polymeric methylene diphenyl diisocyanate may contain a single methylene diphenyl diisocyanate isomer or isomer mixtures of two or three methylene diphenyl diisocyanate isomers, the balance being oligomeric species. Polymeric methylene diphenyl diisocyanate tends to have isocyanate functionalities of higher than 2.0. The isomeric ratio as well as the amount of oligomeric species can vary in wide ranges in these products. For instance, polymeric methylene diphenyl diisocyanate may typically contain 30 wt.-% to 80 wt.-% of methylene diphenyl diisocyanate isomers, the balance being said oligomeric species. The methylene diphenyl diisocyanate isomers are often a mixture of 4,4'-methylene diphenyl diisocyanate, 2,4'-methylene diphenyl diisocyanate and very low levels of 2,2'-methylene di-phenyl diisocyanate. In another embodiment, reaction products of isocyanates with polyols and their mixtures with other diisocyanates and polyisocyanates can also be used. In still another embodiment, the isocyanate component (A) in the embodiment 1 is polymeric MDI, as described hereinabove. In an embodiment, the isocyanate component (A) in the embodiment 1 can further comprises ingredients which are non-reactive with isocyanate. Such ingredients include flame retardants, surfactants, catalysts, and other additives, as described herein. Isocyanate reactive component (B) In an embodiment, the isocyanate reactive component (B) in the embodiment 1 comprises: (a) at least one polyether polyol having an average functionality in between 1.9 to 5.0 and a OH value in between 10 mg KOH / g to 1000 mg KOH / g, (b) at least one surfactant, (c) at least one amine catalyst, and (d) water. In one embodiment, the polyether polyol in the embodiment 1 has the average functionality in between 1.9 to 5.0 and a OH value in between 10 mg KOH / g to 1000 mg KOH / g. In another embodiment, the average functionality is in between 1.9 to 4.0 and the OH value in between 10 to 500 mg KOH / g. The OH value is determined according to DIN 53240. Suitable polyether polyols are obtainable by known methods, for example by anionic polymerization with alkali metal hydroxides, e.g., sodium hydroxide or potassium hydroxide, or alkali metal alkoxides, e.g., sodium methoxide, sodium ethoxide, potassium ethoxide or potassium isopropoxide, as catalysts and by adding at least one amine-containing starter molecule, or by cationic polymerization with Lewis acids, such as antimony pentachloride, boron fluoride etherate and so on, or fuller’s earth, as catalysts from one or more alkylene oxides having 2 to 4 carbon atoms in the alkylene moiety. Starter molecules are generally selected such that their average functionality is in between 2.0 to 5.0. Optionally, a mixture of suitable starter molecules is used. Starter molecules for polyether polyols include amine containing and hydroxyl-containing starter molecules. Suitable amine containing starter molecules include, for example, aliphatic and aromatic diamines such as ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, phenylenediamines, toluenediamine, diaminodiphenylmethane and isomers thereof. Other suitable starter molecules further include alkanolamines, e.g. ethanolamine, N-methyleth-anolamine and N-ethylethanolamine, dialkanolamines, e.g., diethanolamine, N-methyldiethano-lamine and N-ethyldiethanolamine, and trialkanolamines, e.g., triethanolamine, and ammonia. In one embodiment, amine containing starter molecules are selected from ethylenediamine, phenylenediamines, toluenediamine and isomers thereof. Hydroxyl-containing starter molecules are selected from sugar alcohols, for e.g. glucose and pentaerythritol; polyhydric phenols, resols, e.g., oligomeric condensation products formed from phenol and formaldehyde, trimethylolpropane, glycerol, glycols such as ethylene glycol, propylene glycol and their condensation products such as polyethylene glycols and polypropylene glycols, e.g., diethylene glycol, triethylene glycol, dipropylene glycol, and water or a combination thereof. In one embodiment, the hydroxyl-containing starter molecule is glycerol. Suitable alkylene oxides having 2 to 4 carbon atoms are, for example, ethylene oxide, propylene oxide, tetrahydrofuran, 1,2-butylene oxide, 2,3-butylene oxide and styrene oxide. Alkylene oxides can be used singly, alternatingly in succession or as mixtures. In one embodiment, the alkylene oxides are propylene oxide and / or ethylene oxide. In other embodiment, the alkylene oxides are mixtures of ethylene oxide and propylene oxide that comprise more than 50 wt.-% of propylene oxide. The starter molecules, particularly the hydroxyl-containing starter molecules, undergo alkoxyla-tion reaction with the alkylene oxides to obtain the polyether polyols. Polyether polyols that contain a mixture of ethylene oxide-capped polypropylene oxides, as described herein, have been found to process well, especially with water as blowing agent. Good processing herein refers to the ability of the reactive composition to consistently produce good quality foam in an industrial setting. Good processing is indicated by consistently uniform cell structure, complete mold filling, consistently good surface appearance, consistent foam density and consistency in foam physical properties as the foam is produced over time. In one embodiment, the polyether polyol in the embodiment 1 is a first polyether polyol having a OH value of 35 mg KOH / g, prepared by an addition reaction of propylene oxide and ethylene oxide with glycerol as an initiator molecule, with terminal EO block and functionality of 3.0. In another embodiment, the polyether polyol in the embodiment 1 is a second polyether polyol having a OH value of 41 mg KOH / g, prepared by an addition reaction of propylene oxide and ethylene oxide with glycerol as an initiator molecule, with terminal PO block and functionality of 3.0. In yet another embodiment, the polyether polyol in the embodiment 1 is a mixture comprising the first polyether polyol and the second polyether polyol. In another embodiment, the polyether polyol in the embodiment 1 is present in an amount in between 70 wt.% to 98 wt.%, based on the total weight of the isocyanate reactive component. In one embodiment, a variety of surfactants known in the art can be used in the present invention. One type of surfactant is a silicone-based surfactant. Silicone-based surfactants for the present invention are selected from hydrolysable polyether-polysiloxane block copolymers, non- hydrolysable polyether-polysiloxane block copolymers, cyanoalkylpolysiloxanes, polyether siloxane, polydimethylsiloxane, and polyether-modified dimethylpolysiloxane. In one embodiment, the surfactant in the isocyanate reactive component in the embodiment 1 comprises a polyether polysiloxane and / or polyether siloxane. In another embodiment, the polyether polysiloxane is a polyether polysiloxane of general formula (I), Ri 12        ’ — Si--O--R4 - r3      - y (I) wherein, Ri, R2, R3 and R4 is, independent of each other, selected from alkyl, alkenyl, cycloalkyl, aryl, heteroaryl, alkylalkoxy, R9-C(=O)-, Rw-NH-C(=O)-, RnSi(Ri2)(Ris)-, Ri4-O-(-Ri5-O-)j-(CnH2n-)k-; Rg, R10, R11, R12, and R13 is, independent of each other, selected from alkyl, alkenyl, cycloalkyl, aryl, heteroaryl, alkylalkoxy; R14 and R15 is, independent of each other, selected from bivalent alkylene, cycloalkylene, alkenyl, aryl; n is an integer in between 1 to 10; j and k is, independent of each other, an integer in between 0 to 10; and x and y is, independent of each other, an integer in between 1 to 10000. The term “alkyl” herein refers to an acyclic saturated aliphatic group including linear or branched alkyl saturated hydrocarbon radical denoted by a general formula CPH2P+1 and wherein p denotes the number of carbon atoms such as 1,2,3,4 etc. In one embodiment, alkyl refers to an unsubstituted, linear or branched, C1-C30 alkyl group. The unsubstituted linear C1-C30 alkyl is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, noncosyl and triacontyl. In another embodiment, it is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and eicosyl. The term “alkenyl” refers to an unsubstituted, linear acyclic unsaturated aliphatic group including a linear alkenyl unsaturated hydrocarbon radical denoted by a general formula CPH2P-1 and wherein p denotes the number of carbon atoms such as 1, 2, 3, 4 etc. In one embodiment, alkenyl refers to an unsubstituted linear C2-C30 alkenyl selected from 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, 2-hexenyl, 1-heptenyl, 2-heptenyl, 1-octenyl, 2-oc-tenyl, 1-nonenyl, 2-nonenyl, 1-decenyl, 2-decenyl, 1-undecenyl, 2-undecenyl, 1-dodecenyl, 2-dodecenyl, 1-tridecenyl, 2-tridecenyl, 1-tetradecenyl, 2-tetradecenyl, 1-pentadecenyl, 2-penta-decenyl, 1-hexadecenyl, 2-hexadecenyl, 1-heptadecenyl, 2-heptadecenyl, 1-octadecenyl, 2-oc-tadecenyl, 1-nonadecenyl, 2-nonadecenyl, 1-eicosenyl, 2-eicosenyl, 2-henicosenyl, 2-do-cosenyl, 2-tricosenyl, 2-tetracosenyl, 2-pentacosenyl, 2-hexacosenyl, 2-octacoenyl, 2-non-acosenyl and 2-triacontenyl. In another embodiment, it is selected from 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, 2-hexenyl, 1-heptenyl, 2-heptenyl, 1-octenyl, 2-octenyl, 1-nonenyl, 2-non-enyl, 1-decenyl, 2-decenyl, 1-undecenyl, 2-undecenyl, 1-dodecenyl, 2-dodecenyl, 1-tridecenyl, 2-tridecenyl, 1-tetradecenyl, 2-tetradecenyl, 1-pentadecenyl, 2-pentadecenyl, 1-hexadecenyl, 2-hexadecenyl, 1-heptadecenyl, 2-heptadecenyl and 1-octadecenyl. In another embodiment, unsubstituted linear C2-C30 alkenyl selected from 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, 2-hexenyl, 1-heptenyl, 2-heptenyl, 1-octenyl, 2-octenyl, 1-nonenyl, 2-nonenyl, 1-decenyl, 2-de-cenyl, 1-undecenyl, 2-undecenyl, 1-dodecenyl, 2-dodecenyl, 1-tridecenyl, 2-tridecenyl, 1-tetradecenyl, 2-tetradecenyl, 1-pentadecenyl and 2-pentadecenyl. In yet another embodiment, unsubstituted linear C2-C30 alkenyl selected from 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, 2-hexenyl, 1-heptenyl and 2-heptenyl. The term “cycloalkyl” refers to an unsubstituted or branched C3-C10 cycloalkyl having a monocyclic or bicyclic 3 to 10 membered saturated cycloaliphatic radical. The unsubstituted or branched C3-C10 cycloalkyl is a monocyclic or bicyclic C3-C10 compound. The representative examples of unsubstituted or branched C3-C10 monocyclic and bicyclic cycloalkyl is selected from cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, bicyclo[2.2.1]heptyl and bicy-clo[3.1.1]heptyl. The C3-C10 monocyclic and bicyclic cycloalkyl can be further branched with one or more equal or different alkyl groups, as described hereinabove. The representative examples of branched C3-C10 monocyclic and bicyclic cycloalkyl include, but are not limited to, methyl cyclohexyl, dimethyl cyclohexyl, etc. The term “aryl” refers to a monocyclic, bicyclic or tricyclic hydrocarbon ring system having preferably 6 to 14 carbon atoms, wherein at least one carbocyclic ring is having a 4p+2K-electron system, wherein 'p' is the number of aromatic rings. An aryl moiety may be unsubstituted, monosubstituted or identically or differently polysubstituted. Examples of aryl moieties include, but are not limited to, phenyl, 1-naphthyl, 2-naphthyl or anthracenyl. The term “heteroaryl” refers to an aromatic monocyclic, bicyclic or a tricyclic hydrocarbon having 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 carbon atoms, or even 5, 6, 9 or 10 atoms, in which one to four carbon atoms are replaced by identical or different heteroatoms including oxygen, sulfur and nitrogen. Heteroaryl moieties may comprise 1, 2, 3, 4 or 5, or 1,2, or 3, heteroatoms independently selected from oxygen, sulfur and nitrogen. A heteroaryl moiety may be unsubstituted or monosubstituted or identically or differently polysubstituted. Representative examples of suitable heteroaryl moieties are selected from furyl, pyridyl, oxazolyl, thiazolyl, pyrazolyl, pyrimidi-nyl, pyrrolyl, isooxazolyl, triazolyl, tetrazolyl, pyridazinyl, isothiazolyl, benzothiazolyl, benzooxa-zolyl, benzimidazolyl, quinolinyl and isoquinolinyl. The term “alkylene” refers to acyclic saturated hydrocarbon chains, which combine different moieties. Representative examples of the alkylene groups are selected from -CH2-CH2-, -CH2-CH(CH3)-, -CH2-CH(CH2CH3)-, -CH2-CH(n-C3H7)-, -CH2-CH(n-C4H9)-, -CH2-CH(n-C5Hii)-, -CH2-CH(n-C6Hi3)-, -CH2-CH(n-C7Hi5)-, -CH2-CH(n-C8Hi7)-, -CH(CH3)-CH(CH3)-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)8-, -(CH2)io-, -C(CH3)2-, -CH2-C(CH3)2-CH2-, and -CH2-[C(CH3)2]2-CH2-. In one embodiment, C2-C10 alkylene is selected from one or more of -CH2-CH2-, CH2-CH(CH3)-, -CH2-CH(CH2CH3)-, -CH2-CH(n-C3H7)-, -CH2-CH(n-C4H9)-, -CH2-CH(n-C6Hi3)-, and -(CH2)4-. In one embodiment, the polyether polysiloxane of general formula (I) is a polyether polysiloxane of general formula (l)(a), (l)(a) wherein, Ri, R2, R3 and R4 is, independent of each other, selected from alkyl, alkenyl, Ri4-O-(-Ri5-O-)j-(CnH2n-)k-; Ri4 and R15 is, independent of each other, selected from bivalent alkylene, cycloalkylene, alkenyl, aryl; n is an integer in between 1 to 10; j and k is, independent of each other, an integer in between 0 to 10; and z is an integer in between 1 to 10000. In one embodiment, R2 and R3 is, independent of each other, an alkyl selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl. In another embodiment, it is selected from methyl, ethyl, propyl, butyl, pentyl and hexyl. In still another embodiment, R2 and R3 are identical and are selected from methyl, ethyl, propyl, butyl, pentyl and hexyl. In yet another embodiment, R2 and R3 comprise of methyl. In another embodiment, n is an integer between 1 to 8, or in between 1 to 6, or even in between 1 to 4 in the general formula (l)(a). In another embodiment, x and y are, independent of each other, an integer in between 1 to 10000, or in between 1 to 5000, or in between 1 to 1000, or in between 1 to 500, or in between 10 to 500, or even in between 10 to 250, or even still in between 10 to 100 in the general formula (l)(a). In the present context, the concatenations denoted by x and y are distributed to form a block polymeric structure or a random polymeric structure, as is understood by the person skilled in the art. In another embodiment, the non-ionic surfactant comprises a polyether siloxane represented by the general formula (II) r8 (II) wherein, Rs, Re, R7 and Rs is, independent of each other, selected from alkyl, alkenyl, cycloalkyl, aryl, heteroaryl, alkylalkoxy, R9-C(=O)-, Rw-NH-C(=O)-, RnSi(Ri2)(Ris)-, Ri4-O-(-Ri5-O-)j-(CnH2n-)k-; Rg, R10, R11, R12, and R13 is, independent of each other, selected from alkyl, alkenyl, cycloalkyl, aryl, heteroaryl, alkylalkoxy; R14 and R15 is, independent of each other, selected from bivalent alkylene, cycloalkylene, alkenyl, aryl; m is an integer in between 1 to 10; j and k is, independent of each other, an integer in between 0 to 10; and z is an integer in between 1 to 10000. In one embodiment, the polyether siloxane is represented by the general formula (I l)(a), Si--Cm H2mO--Si--O- r8 (H)(a) wherein, R5, Re, R7 and Rs is, independent of each other, selected from alkyl, alkenyl, Ri4-O-(-Ris-O-)j-(CnH2n-)k-; R14 and R15 is, independent of each other, selected from bivalent alkylene, cycloalkylene, alkenyl, aryl; m is an integer in between 1 to 10; j and k is, independent of each other, an integer in between 0 to 10; and z is an integer in between 1 to 10000. In one embodiment, the surfactant in the embodiment 1 is present in an amount in between 0.01 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component. In another embodiment, the amine catalyst in the embodiment 1 comprises a tertiary amine. Suitable catalysts can be selected from trimethylamine, triethylamine, triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylbenzylamine, N,N-dimethylethanola-mine, N,N,N',N'-tetramethyle-1,4-butanediamine, N,N-dimethylpiperazine, bis(dimethylami-noethyl)ether, bis(2-dimethylaminoethyl) ether, morpholine,4,4'-(oxydi-2,l-ethanediyl)bis, triethylenediamine, pentamethyl diethylene triamine, dimethyl cyclohexyl amine, N-acetyl N,N-dime-thyl amine, N-coco-morpholine, N,N-dimethyl aminomethyl N-methyl ethanol amine, N, N, N'-trimethyl-N'-hydroxyethyl bis(aminoethyl) ether, N,N-bis(3-dimethyl-aminopropyl)N-isopropano-lamine, (N,N-dimethyl) amino-ethoxy ethanol, N, N, N', N'-tetramethyl hexane diamine, l,8-di-azabicyclo-5,4,0-undecene-7, N,N-dimorpholinodiethyl ether, N-methyl imidazole, dimethylaminopropylamine, dimethylaminopropyl dipropanolamine, bis(dimethylaminopropyl)amino-2-pro-panol, tetramethylamino bis (propylamine), (dimethyl(aminoethoxyethyl))((dimethyl amine)ethyl)ether, tris(dimethylamino propyl) amine, dicyclohexyl methyl amine, bis(N,N-dime-thyl-3 -aminopropyl) amine, and 1,2-ethylene piperidine and methyl -hydroxyethyl piperazine, 1,4-diazabicyclo[2.2.2]octane-2-methanol, N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and mixture thereof. In another embodiment, the amine catalyst is selected from trimethylamine, triethylamine, triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylbenzylamine, N,N-di-methylethanolamine, N,N,N',N'-tetramethyle-1,4-butanediamine, N,N-dimethylpiperazine, bis(di-methylaminoethyl)ether, bis(2-dimethylaminoethyl) ether, morpholine,4,4'-(oxydi-2,l-ethanediyl)bis, triethylenediamine, pentamethyl diethylene triamine, dimethyl cyclohexyl amine, N-acetyl N,N-dimethyl amine, N-coco-morpholine, N,N-dimethyl aminomethyl N-methyl ethanol amine, N, N, N'-trimethyl-N'-hydroxyethyl bis(aminoethyl) ether, N,N-bis(3-dimethyl-aminopro-pyl)N-isopropanolamine, (N,N-dimethyl) amino-ethoxy ethanol, N, N, N', N'-tetramethyl hexane diamine, l,8-diazabicyclo-5,4,0-undecene-7, N,N-dimorpholinodiethyl ether, N-methyl imidazole, dimethylaminopropylamine, dimethylaminopropyl dipropanolamine, bis(dimethylaminopro-pyl)amino-2-propanol, tetramethylamino bis (propylamine), (dimethyl(aminoethoxyethyl))((dime-thyl amine)ethyl)ether and tris(dimethylamino propyl) amine. In yet another embodiment, the amine catalyst in the embodiment 1 is selected from trimethylamine, triethylamine, triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dime-thylbenzylamine, N,N-dimethylethanolamine, N,N,N',N'-tetramethyle-1,4-butanediamine, N,N-dimethylpiperazine, bis(dimethylaminoethyl)ether, bis(2-dimethylaminoethyl) ether, morpholine, 4,4'-(oxydi-2,l-ethanediyl)bis, triethylenediamine, pentamethyl diethylene triamine, dimethyl cyclohexyl amine, N-acetyl N,N-dimethyl amine, N-coco-morpholine, N, N, N', N'-tetramethyl hexane diamine, l,8-diazabicyclo-5,4,0-undecene-7, N,N-dimorpholinodiethyl ether, N-methyl imidazole, dimethylaminopropylamine, dimethylaminopropyl dipropanolamine, bis(dimethyla-minopropyl)amino-2-propanol, tetramethylamino bis (propylamine), (dimethyl(aminoethoxy-ethyl))((dimethyl amine)ethyl)ether and tris(dimethylamino propyl) amine. In still another embodiment, the amine catalyst in the embodiment 1 is triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylbenzylamine, N,N-dimethylethanola- WO 2021 / 044002                          -|4                     PCT / EP2020 / 074798 mine, N,N,N',N'-tetramethyle-1,4-butanediamine, morpholine,4,4'-(oxydi-2,l-ethanediyl)bis, triethylenediamine, pentamethyl diethylene triamine, l,8-diazabicyclo-5,4,0-undecene-7, N,N-di-morpholinodiethyl ether, N-methyl imidazole and dimethylaminopropylamine. In yet another embodiment, the amine catalyst in the embodiment 1 comprises triethylenediamine and / or dimethylaminopropylamine. In another embodiment, the amine catalyst in the embodiment 1 may be present together with suitable solvents. For instance, 1,4-butanediol and dipropylene glycol can be used as suitable solvents. In one embodiment, the amine catalyst in the embodiment 1 is present in an amount in between 0.01 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component. The isocyanate reactive component also comprises water, which performs the function of a blowing agent. In one embodiment, the water in the embodiment 1 is present in an amount in between 1.0 wt.% to 10.0 wt.%, based on the total weight of the isocyanate reactive component. In another embodiment, the isocyanate reactive component in the embodiment 1 further comprises at least one additive. Suitable additives are selected from blowing agents, cell openers, dyes, pigments, IR absorbing materials, stabilizers, plasticizers, antistats, fungistats, bacteriostats, hydrolysis controlling agents, curing agents, antioxidants, alkylene carbonates, carbonamides and pyrrolidones. The additives can be present in an amount in between 0.1 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component. Flame-retardant mixture In one embodiment, the flame-retardant mixture comprises (i) 70 wt.% to 99 wt.% of expandable graphite and (ii) 1 wt.% to 30 wt.% of ammonium polyphosphate, based on the total weight of the flame-retardant mixture. The flame-retardant mixture can be added directly to the isocyanate reactive component to obtain the reactive composition in the embodiment 1. Alternately, the flame-retardant mixture can be added as a separate component, similar to the isocyanate component and the isocyanate reactive component, to obtain the reactive composition in the embodiment 1. The weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:5 to 5:1. In one embodiment, the weight ratio is in between 1:3 to 3:1. In another embodiment, it is 1:2. In one embodiment, the expandable graphite in the flame-retardant mixture in the embodiment 1 is well known in the art. Examples include crystalline compounds that maintain a laminar structure of the carbon that has grown a graphite interlayer compound by treating natural flaky graphite, pyrolytic graphite, Kish graphite, or another such powder by concentrated sulphuric acid, nitric acid, or another such inorganic acid and concentrated nitric acid, perchloric acid, permanganate acid, bichromate, or another such strong oxidizing agent. Expandable graphite that has been neutralized by ammonia, an aliphatic lower amine, alkali metal compound, alkaline earth metal compound, or the like is preferably used. Examples of aliphatic lower amines include monomethyl amine, dimethyl amine, trimethyl amine, ethyl amine, and the like. Examples of alkali metal compounds and alkaline earth metal compounds include hydroxides, oxides, carbonates, sulfates, organic acid salts, and the like of potassium, sodium, calcium, barium, magnesium and the like. In another embodiment, the expandable graphite in the flame-retardant mixture in the embodiment 1 is formed of graphite, with H2SO4 or SO4, for example, having two free negative valences, which attach to two free positive valences of a hydrocarbon ring, incorporated between the planes of the graphite mesh. When the Pll foam is burned, this graphite expands to from 100 to 200 times its volume, giving off SO3 and / or SO2 and water. A loose, expanded mass that acts in an insulating manner thus forms. In addition to expandable graphite, the flame-retardant mixture in the embodiment 1 also comprises ammonium polyphosphate. Ammonium polyphosphate is known for its flame-retardant properties. Ammonium polyphosphate is an inorganic salt of polyphosphoric acid and ammonia. The chemical formula of ammonium polyphosphate is [NH4POs]n, with n being greater than 100. The chain length (n) of ammonium polyphosphate is both variable and can be branched, and can be greater than 100, preferably greater than 1000. In one embodiment, the ammonium polyphosphate may or may not be encapsulated. Suitable encapsulated ammonium polyphosphates are described in US Pat. nos. 4,347,334, 4,467,056, and 4,639,331, herein incorporated by reference. Such encapsulated ammonium polyphosphates contain a hardened water insoluble resin enveloping the individual ammonium polyphosphate particles. The resin may be a phenol-formaldehyde resin, an epoxy resin, surface reacted silane, a surface reacted melamine, or a melamine-formaldehyde resin. Other flame-retardants that may be optionally added as part of the flame-retardant mixture or directly to the isocyanate reactive component and / or the isocyanate component include phosphorus compounds selected from tris(2-chloroethyl)phosphate (TCEP), tris(2-chloropropyl)phos-phate (TCPP), tris(2,3-dibromopropyl)phosphate, tris(1,3-dichloropropyl)phosphate, tris(2-chloroisopropyl)phosphate, tricresylphosphate, tri(2,2-dichloroisopropyl)phosphate, diethyl-N,N-bis(2-hydryethyl)aminoethylphosphonate, tris(2,3-dibromopropyl)phosphate, tri(1,3-dichloropro-pyl)phosphate, diammonium phosphate, diethyl ethanephosphonate (DEEP), triethyl phosphate (TEP), dimethyl propanephosphonate (DMPP), diphenyl cresyl phosphate (DPK) and resorcinol-bis(diphenyl)phosphate (RDP). Such flame-retardants are typically present in an amount upto 15 wt.%, based on the total weight of the reactive composition. Process Another aspect of the present invention is embodiment 2, directed to a process for preparing the above-mentioned polyurethane foam by reacting the reactive composition comprising the isocyanate component and the isocyanate component, in presence of the flame-retardant mixture, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:5 to 5:1. In one embodiment, the isocyanate reactive component and the flame-retardant mixture is mixed, prior to reacting with the isocyanate component. Suitable techniques for preparing the Pll foam are well known to the person skilled in the art. One of the advantages of the present invention is that the reactive composition in the embodiment 1 can be obtained using any of the conventional techniques of foaming and allowed sufficient time for the composition to cure and form the Pll foam. In one embodiment, the process described in the embodiment 2 can be a slabstock process or a closed mold molding process. Slabstock foam is a large bun which is cut into the required shape and size for use. Closed mold molding process can be either so-called hot molding process or a cold molding process, wherein the foaming takes place in a closed mold. After the foam has cured, the mold is opened, and the foam is removed. An integral skin can be formed onto the surface of the foam in the mold. A film, fabric, leather or other coverstock can be inserted into the mold prior to introducing the reactive composition, to produce the Pll foam in the embodiment 2. In another embodiment, to produce the Pll foam in the embodiment 2, the reactive composition is first obtained by mixing the isocyanate component (A) and the isocyanate reactive component (B) in the embodiment 1. The B-side component is a premix comprising the appropriate amounts of the polyether polyol, surfactant, amine catalyst, water, flame-retardant mixture and optionally additives, as described herein. Depending on the composition of the B-side component, elevated temperatures, above 40°C, may be required to mix the components. Preferably, the B-side component is mixed together at a temperature less than 40°C. The B-side component is then mixed with the A-side component at suitable mix ratio. The resulting reactive composition is subjected to conditions sufficient to cure the reactive composition, thereby obtaining the Pll foam. The reactive composition is either introduced into a suitable mold, so that a foaming or curing reaction takes place within the mold to form the desired Pll foam. In another embodiment, the A-side component, pre-mixed with the flame-retardant mixture, and the B-side component can be mixed in a suitable mixing device and directly poured in a mold. For this purpose, nozzles may be used, with the mixing being carried out at high pressures, for instance more than 50 bars. Thereafter, the reactive composition can be poured in the mold and conditions sufficient for Pll foam provided. The Pll foam, as described herein, meets the EN-45545-2 standard. The EN-45545-2 standard specifies the requirements for fire behaviour during combustion of materials and products used in railway vehicles, for e.g. trains. According to this standard, it is necessary the heat development, oxygen consumption, smoke density and smoke toxicity not only of the Pll foam itself, but also of any material composition by testing. The term “any material composition” typically refers to a coating material, for e.g. fabric, natural leather, artificial leather, etc., polymer, plywood, wooden board, special textiles, etc. The Pll foam, as described herein, has a density in between 50 kg / m3 to 120 kg / m3 determined according to DIN EN ISO 845 and also meets the requirements as per EN-45545-2. That is, to say, that the Pll foam has a maximum average heat release (MARHE) of equal to or less than 50 kW / m2 determined according to ISO 5660-1 HL3, smoke optical density (Ds) of less than 200 m2 / m2 and toxicity index (CITg) of less than 0.75, both determined according to ISO 5659-2 HL3. Shaped article Another aspect of the present invention is embodiment 3, directed to a shaped article comprising the above-described Pll foam. The Pll foam can be molded into any desired shape and used for purposes requiring reduced flammability, smoke and toxicity as per EN-45545-2 standards, particularly meeting the requirements of R21 HL3 category. Process for preparing shaped article Another aspect of the present invention is embodiment 4, directed to a process for preparing above-described shaped article, said process comprising the step of molding the Pll foam in a mold. In one embodiment, the reactive composition can be directly subject to a suitable mold and provided with sufficient conditions to obtain the Pll foam having the desired shape. In one embodiment, the shaped article is a railway component. Railway component Another aspect of the present invention is embodiment 5, directed to a railway component comprising the Pll foam. In one embodiment, the railway component is a molded or extruded train seat component or a cladding. In another embodiment, the cladding in the embodiment 5 is an interior vertical surface selected from room dividers, flaps, boxes, hoods and louvres; an interior door or lining for internal and external doors; a window insulation; a kitchen interior surface; an interior horizontal surface selected from ceiling panelling, flaps, boxes, hoods and louvres; a luggage storage area selected from overhead and vertical luggage racks, luggage containers and compartments; a driver’s desk application selected from panelling and surfaces of driver’s desk; an interior surface of gangways selected from interior sides of gangway membranes (bellows) and interior linings; a window frame; an optionally folding table with downward facing surface; an interior or exterior surface of air ducts, or a device for passenger information. In particular, the railway component includes upholstery of seat, couchettes and berths in rail vehicles. The railway component meets the flammability requirements in accordance with DIN EN 45545-2 standards. The present invention is illustrated in more detail by the following embodiments and combinations of embodiments which result from the corresponding dependency references and links: I.A polyurethane foam obtained by reacting a reactive composition comprising: (A) an isocyanate component, and (B) an isocyanate reactive component comprising (a) at least one polyether polyol having an average functionality in between 1.9 to 5.0 and a OH value in between 10 mg KOH / g to 1000 mg KOH / g, (b) at least one surfactant, (c) at least one amine catalyst, and (d) water, in the presence of (C) a flame-retardant mixture comprising (i) 70 wt.% to 99 wt.% of expandable graphite and (ii) 1 wt.% to 30 wt.% of ammonium polyphosphate, based on the total weight of the flame-retardant mixture, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:5 to 5:1. 11.The polyurethane foam according to embodiment I, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:3 to 3:1. III.The polyurethane foam according to embodiment I or II, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is 1:2. IV.The polyurethane foam according to one or more of embodiments I to III, wherein the isocyanate component (A) and the isocyanate reactive component are present at an index in between 40 to 200. V.The polyurethane foam according to one or more of embodiments I to IV, wherein the isocyanate component (A) and the isocyanate reactive component are present at an index in between 60 to 100. VI.The polyurethane foam according to one or more of embodiments I to V, wherein the isocyanate component (A) and the isocyanate reactive component are present at an index in between 80 to 100. VII.The polyurethane foam according to one or more of embodiments I to VI, wherein the isocyanate component comprises an aromatic isocyanate or an aliphatic isocyanate. VIII.The polyurethane foam according to embodiment VII, wherein the aromatic isocyanate is selected from toluene diisocyanate; polymeric toluene diisocyanate, methylene diphenyl diisocyanate; polymeric methylene diphenyl diisocyanate; m-phenylene diisocyanate; 1,5-naphthalene diisocyanate; 4-chloro-1; 3-phenylene diisocyanate; 2,4,6-toluylene triisocyanate, 1,3-diisopropylphenylene-2,4-diisocyanate; 1-methyl-3,5-diethylphenylene-2,4-diiso-cyanate; 1,3,5-triethylphenylene-2,4-diisocyanate; 1,3,5-triisoproply-phenylene-2,4-diiso-cyanate; 3,3'-diethyl-bisphenyl-4,4'-diisocyanate; 3,5,3',5'-tetraethyl-diphenylmethane-4,4'-diisocyanate; 3,5,3',5'-tetraisopropyldiphenylmethane-4,4'-diisocyanate; 1-ethyl-4-ethoxy-phenyl-2,5-diisocyanate; 1,3,5-triethyl benzene-2,4,6-triisocyanate; 1 -ethyl-3,5-diisopropyl ben-zene-2,4,6-triisocyanate, tolidine diisocyanate, 1,3,5-triisopropyl benzene-2,4,6-triiso-cyanate and mixtures thereof. IX.The polyurethane foam according to embodiment VII or VIII, wherein the aromatic isocyanate comprises methylene diphenyl diisocyanate and / or polymeric methylene diphenyl diisocyanate. X.The polyurethane foam according to one or more of embodiments I to IX, wherein the at least one polyether polyol has an average functionality in between 1.9 to 4.0 and a OH value in between 10 to 500 mg KOH / g. XI.The polyurethane foam according to one or more of embodiments I to X, wherein the at least one polyether polyol is present in an amount in between 70 wt.% to 98 wt.%, based on the total weight of the isocyanate reactive component. XII.The polyurethane foam according to one or more of embodiments I to XI, wherein the at least one surfactant is selected from polyether polysiloxane and / or polyether siloxane. XI11.The polyurethane foam according to one or more of embodiments I to XII, wherein the at least one surfactant is present in an amount in between 0.01 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component. XIV.The polyurethane foam according to one or more of embodiments I to XIII, wherein the at least one surfactant is present in an amount in between 0.1 wt.% to 1.0 wt.%, based on the total weight of the isocyanate reactive component. XV.The polyurethane foam according to one or more of embodiments I to XIV, wherein the at least one amine catalyst comprises a tertiary amine. XVI.The polyurethane foam according to one or more of embodiments I to XV, wherein the at least one amine catalyst is selected from trimethylamine, triethylamine, triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylbenzylamine, N,N-di-methylethanolamine, N,N,N',N'-tetramethyle-1,4-butanediamine, N,N-dimethylpiperazine, bis(dimethylaminoethyl)ether, bis(2-dimethylaminoethyl) ether, morpholine,4,4'-(oxydi-2,l-ethanediyl)bis, triethylenediamine, pentamethyl diethylene triamine, dimethyl cyclohexyl amine, N-acetyl N,N-dimethyl amine, N-coco-morpholine, N,N-dimethyl aminomethyl N-methyl ethanol amine, N, N, N'-trimethyl-N'-hydroxyethyl bis(aminoethyl) ether, N,N-bis(3-dimethyl-aminopropyl)N-isopropanolamine, (N,N-dimethyl) amino-ethoxy ethanol, N, N, N', N'-tetramethyl hexane diamine, l,8-diazabicyclo-5,4,0-undecene-7, N,N-dimorpho-linodiethyl ether, N-methyl imidazole, dimethylaminopropylamine, dimethylaminopropyl dipropanolamine, bis(dimethylaminopropyl)amino-2-propanol, tetramethylamino bis (propylamine), (dimethyl(aminoethoxyethyl))((dimethyl amine)ethyl)ether, tris(dimethylamino propyl) amine, dicyclohexyl methyl amine, bis(N,N-dimethyl-3 -aminopropyl) amine, and 1,2-ethylene piperidine and methyl -hydroxyethyl piperazine, 1,4-diazabicyclo[2.2.2]octane-2-methanol, N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and mixture thereof. XVII.The polyurethane foam according to one or more of embodiments I to XVI, wherein the at least one amine catalyst comprises triethylenediamine and / or dimethylaminopropylamine. XVI11.The polyurethane foam according to one or more of embodiments I to XVII, wherein the at least one amine catalyst is present in an amount in between 0.01 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component. XlX.The polyurethane foam according to one or more of embodiments I to XVIII, wherein the at least one amine catalyst is present in an amount in between 0.01 wt.% to 2.0 wt.%, based on the total weight of the isocyanate reactive component. XX.The polyurethane foam according to one or more of embodiments I to XIX, wherein water is present in an amount in between 1.0 wt.% to 10.0 wt.%, based on the total weight of the isocyanate reactive component. XXI.The polyurethane foam according to one or more of embodiments I to XX, wherein water is present in an amount in between 1.0 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component. XXII.The polyurethane foam according to one or more of embodiments I to XXI, wherein the isocyanate reactive component further comprises at least one additive. XXIII.The polyurethane foam according to embodiment XXII, wherein the at least one additive is selected from blowing agents, cell openers, dyes, pigments, IR absorbing materials, stabilizers, plasticizers, antistats, fungistats, bacterio-stats, hydrolysis controlling agents, curing agents, antioxidants, alkylene carbonates, carbonamides and pyrrolidones. XXIV.The polyurethane foam according to embodiment XXII or XXIII, wherein the at least one additive is present in an amount in between 0.1 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component. WO 2021 / 044002                          21                     PCT / EP2020 / 074798 XXV.The polyurethane foam according to one or more of embodiments I to XXIV, wherein expandable graphite is present in an amount in between 75 wt.% to 85 wt.%, based on the total weight of the flame-retardant mixture. XXVI.The polyurethane foam according to one or more of embodiments I to XXV, wherein ammonium polyphosphate is present in an amount in between 5 wt.% to 15 wt.%, based on the total weight of the flame-retardant mixture. XXVII.The polyurethane foam according to one or more of embodiments I to XXVI, wherein the polyurethane foam has a density in between 50 kg / m3 to 120 kg / m3 determined according to DIN EN ISO 845, a maximum average heat release of equal to or less than 50 kW / m2 determined according to ISO 5660-1 HL3, smoke optical density of less than 200 m2 / m2 and toxicity index of less than 0.75, both determined according to ISO 5659-2 HL3. XXVI11.A process for preparing a polyurethane foam according to one or more of embodiments I to XXVII by reacting the reactive composition comprising the isocyanate component and the isocyanate component, in presence of the flame-retardant mixture, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 1:5 to 5:1. XXlX.The process according to embodiment XXVIII, wherein the isocyanate reactive component and the flame-retardant mixture is mixed, prior to reacting with the isocyanate component. XXX.A shaped article comprising the polyurethane foam according to one or more of embodiments I to XXVII or as obtained according to embodiment XXVIII or XXIX. XXXI.A process for preparing the shaped article according to embodiment XXX, said process comprising the step of molding the polyurethane foam in a mold. XXXII.A railway component comprising the polyurethane foam according to one or more of embodiments I to XXVII or as obtained according to embodiment XXVIII or XXIX. XXXI11.The railway component according to embodiment XXXII, wherein the railway component is a molded or extruded train seat component or a cladding. XXXIV.The railway component according to embodiment XXXII, wherein the cladding is an interior vertical surface selected from room dividers, flaps, boxes, hoods and louvres; an interior door or lining for internal and external doors; a window insulation; a kitchen interior surface; an interior horizontal surface selected from ceiling panelling, flaps, boxes, hoods and louvres; a luggage storage area selected from overhead and vertical luggage racks, luggage containers and compartments; a driver’s desk application selected from panelling and surfaces of driver’s desk; an interior surface of gangways selected from interior sides WO 2021 / 044002                          22                     PCT / EP2020 / 074798 of gangway membranes (bellows) and interior linings; a window frame; an optionally folding table with downward facing surface; an interior or exterior surface of air ducts, or a device for passenger information. 5 XXXV.The railway component according to one or more of embodiments XXXII to XXXIII, wherein the railway component meets the flammability requirements in accordance with DIN EN 45545-2. WO 2021 / 044002                          23                     PCT / EP2020 / 074798 EXAMPLES The presently claimed invention is illustrated by the non-restrictive examples which are as follows: Raw materials POLYOL (P) P1 Polyether polyol having a OH value of 35 mg KOH / g, prepared by an addition reaction of propylene oxide and ethylene oxide with glycerol as an initiator molecule, with terminal EO block and functionality of 3.0, obtained from BASF. P2 Polyether polyol having a OH value of 41 mg KOH / g, prepared by an addition reaction of propylene oxide and ethylene oxide with glycerol as an initiator molecule, with terminal PO block and functionality of 3.0, obtained from BASF. ISOCYANATE (ISO) ISO1 Blend of polymeric MDI and 4,4’-MDI having an NCO content in between 31 wt.% to 33 wt.%, obtained from BASF. SURFACTANT (S) S1 Non-hydrolysable silicone-based surfactant, obtained from Evonik CATALYST (CAT) CAT Triethylenediamine and Dimethylaminopropylamine, obtained from Sigma Aldrich FLAME-RETARDANT (FR) FR1 Expandable graphite, obtained from Asbury carbons FR2 Ammonium polyphosphate, obtained from Sigma Aldrich FR3 Tris(2-chloropropyl)phosphate (TCPP), obtained from Sigma Aldrich FR4 Resorcinol-bis(diphenyl)phosphate (RDP), obtained from Sigma Aldrich Standard method DIN 53240 OH value ISO 5660-1 Maximum average rate of heat emission (MARHE) DIN EN ISO 845 Density ISO 5659-2 Smoke optical density ISO 5659-2 Toxicity index 10 General synthesis of reactive composition for producing PU foam The aforementioned raw materials were added in the amounts mentioned in Table 1 in both the A-side and B-side components (all in wt.%). Both the A-side and B-side components, along with the flame-retardant mixture were then added to a mixing cup and subjected to a mixing at rpm of 1500 to obtain a desired index. The temperature of A-side and B-side components was main-15 tained between 20±2°C and the mixing ratio (Resin-side : Iso-side) was kept at 100:30-35. The PU foams thus obtained was tested for the properties, which are reported in Tables 1 and 2 below. Table 1: Inventive Pll foams Ingredient IE 1 IE 2 Iso-side (wt.%) ISO1 77.38 100 FR4 22.63 — Resin-side (wt.%) P1 93.23 84.75 P2 2.50 2.27 S1 0.30 0.27 CAT 1.27 1.15 Water 2.70 2.45 FR3 — 9.11 FR mixture (wt.%) FR1 80 80 FR2 20 20 Pll foam Index 100 100 Density, kg / m3 95 95 Table 2: Properties of IE 1 determined in accordance with respective standard methods Properties Value Standard method Density, kg / m3 95 DIN EN ISO 845 Compression set (50%, 70°C, 22h), % < 10 DIN EN ISO 1856 Tensile strength, kPa > 60 DIN EN ISO 1798 Elongation at break, % >45 DIN EN ISO 1798 Compression load deflection, kPa 9 DIN EN ISO 3386 Resilience, % > 35 ISO 8307 Dynamic fatigue test - loss in thickness, % <5 DIN EN ISO 3385 Dynamic fatigue test - loss in force deflection, % < 10 DIN EN ISO 3385 Fire property HL 1~3 DIN EN 45545-2, R21 5 The inventive Pll foam was tested for MARHE, smoke optical density and toxicity index according to respective standard methods. The results have been summarized in Table 3 below. 2020342491   16 Mar 2026 Table 3: DIN EN 45545-2 test results for inventive PU foams IE 1 & IE 2 IE 1 MARHE 37 kW / m2 Classification according to DIN EN 45545-2:2016-02, set of requirements R21, with respect to test method ISO 5660-1, at 25 kW / m2 HL3 Smoke optical density, m2 / m2 54.79 Mean value of specific optical density after 4 minutes, Ds(4) 48 Cumulative value of specific optical densities in the first 4 minutes of the test, VOF4 110 Mean value of maximum specific optical density, Ds(max) 64 Conventional index of toxicity, CITg 0.10 Classification according to DIN EN 45545-2:2016-02, set of requirements R21, with respect to test method ISO 5659-2, at 25 kW / m2, with pilot flame HL3 IE 2 MARHE 42 kW / m2 Classification according to DIN EN 45545-2:2016-02, set of requirements R21, with respect to test method ISO 5660-1, at 25 kW / m2 HL3 Smoke optical density, m2 / m2 81.36 Mean value of specific optical density after 4 minutes, Ds(4) 32 Cumulative value of specific optical densities in the first 4 minutes of the test, VOF4 73 Mean value of maximum specific optical density, Ds(max) 50 Conventional index of toxicity, CITg 0.11 Classification according to DIN EN 45545-2:2016-02, set of requirements R21, with respect to test method ISO 5659-2, at 25 kW / m2, with pilot flame HL3 As evident above, the PU foam meets the requirements of DIN EN 45545-2. More importantly, the inventive PU foams IE 1 and IE 2 have MARHE values < 50 kW / m2, smoke optical density 5   (Ds) < 200 m2 / m2, and toxicity index (CITg) < 0.75. Thus, the inventive PU foams can be used for making railway components. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge 10 in the art, in Australia or any other country. 22510156_1 (GHMatters) P117694.AU

Claims

1. A polyurethane foam obtained by reacting a reactive composition comprising:(A) an isocyanate component, and(B) an isocyanate reactive component comprising5               (a) at least one polyether polyol having an average functionality in between 1.9 to5.0 and a OH value in between 10 mg KOH / g to 1000 mg KOH / g,(b) at least one surfactant,(c) at least one amine catalyst, and(d) water,10 in the presence of(C) a flame-retardant mixture comprising (i) 70 wt.% to 99 wt.% of expandable graphite and (ii) 1 wt.% to 30 wt.% of ammonium polyphosphate, based on the total weight of the flame-retardant mixture,wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive 15 component is in between 1:5 to 5:1,wherein the expandable graphite is present in an amount between 75 wt.% to 85 wt.%, based on the total weight of the flame-retardant mixture, and wherein ammonium polyphosphate is present in an amount between 5 wt.% to 15 wt.%, based on the total weight of the flame-retardant mixture.

202. The polyurethane foam according to claim 1, wherein the weight ratio between the flameretardant mixture and the isocyanate reactive component is 1:2.

3. The polyurethane foam according to claim 1 or 2, wherein the isocyanate component25 comprises methylene diphenyl diisocyanate and / or polymeric methylene diphenyl diisocyanate.

4. The polyurethane foam according to one or more of claims 1 to 3, wherein the at least one polyether polyol is present in an amount in between 70 wt.% to 98 wt.%, based on the to-30 tal weight of the isocyanate reactive component.

5. The polyurethane foam according to one or more of claims 1 to 4, wherein the at least one surfactant is present in an amount in between 0.01 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component.

356. The polyurethane foam according to one or more of claims 1 to 5, wherein the at least one amine catalyst is present in an amount in between 0.01 wt.% to 5.0 wt.%, based on the total weight of the isocyanate reactive component.40 7. The polyurethane foam according to one or more of claims 1 to 6, wherein the isocyanate reactive component further comprises at least one additive.2020342491   17 Jun 20268. A process for preparing a polyurethane foam according to one or more of claims 1 to 7 by reacting the reactive composition comprising the isocyanate component and the isocyanate component, in presence of the flame-retardant mixture, wherein the weight ratio between the flame-retardant mixture and the isocyanate reactive component is in between 5           1:5 to 5:1.

9. A shaped article comprising the polyurethane foam according to one or more of claims 1 to 7 or as obtained according to claim 8.10 10. A process for preparing the shaped article according to claim 9, said process comprising the step of molding the polyurethane foam in a mold.

11. A railway component comprising the polyurethane foam according to one or more of claims 1 to 7 or as obtained according to the process of claim 8.1512. The railway component according to claim 11, wherein the railway component is a molded or extruded train seat component or a cladding.

13. The railway component according to claim 12, wherein the cladding is an interior vertical 20 surface selected from room dividers, flaps, boxes, hoods and louvres; an interior door or lining for internal and external doors; a window insulation; a kitchen interior surface; an interior horizontal surface selected from ceiling panelling, flaps, boxes, hoods and louvres; a luggage storage area selected from overhead and vertical luggage racks, luggage containers and compartments; a driver’s desk application selected from panelling and sur-25 faces of driver’s desk; an interior surface of gangways selected from interior sides of gangway membranes (bellows) and interior linings; a window frame; an optionally folding table with downward facing surface; an interior or exterior surface of air ducts, or a device for passenger information.