Flame-retardant thermoplastic polyurethane composition

Abstract

A thermoplastic polyurethane composition is disclosed, comprising 84 to 97 wt % of a thermoplastic polyurethane and 3 to 16 wt % of a flame retardant, based on the total weight of the thermoplastic polyurethane composition, the flame retardant comprising an ionic liquid and a phosphorus-containing ester. Articles produced from the thermoplastic polyurethane composition and uses thereof are also provided.

Description

[Technical Field]

[0001] The present disclosure relates to flame retardant thermoplastic polyurethane compositions, articles produced therefrom, and uses of the articles.

[0002] background Thermoplastic polyurethanes (TPUs) are suitable for many applications, for example, wire, cable, pipelines, etc. Because TPU itself is flammable, flame-retardant TPUs are highly desirable in scenarios such as aircraft, electric vehicles, appliances, buildings, and construction.

[0003] Conventional flame-retardant TPUs typically incorporate nitrogen- or phosphorus-based flame retardants, such as melamine cyanurate, ammonium polyphosphate, aluminum hypophosphite, and cresyl diphenyl phosphate. One challenge with these flame retardants is their insufficient flame retardancy. To achieve a UL 94 V0 rating, a flame retardant dosage of approximately 20-30 wt.% is required. Such high dosages affect the compatibility and mechanical strength of the TPU composition. Furthermore, high use of flame retardants also increases production costs.

[0004] Ionic liquids have been reported as flame retardants, but they also deteriorate the mechanical properties of the TPU matrix.

[0005] Chinese Patent No. 111909503 describes a thermoplastic polyurethane composition containing 3% by weight of tributylmethylammonium tributylphosphate. The tensile strength is reduced by 20% and 30% for polyether and polyester polyurethanes, respectively.

[0006] US Patent Application Publication No. 20150353832 simultaneously teaches the use of phosphinate ionic liquids as flame retardants and melt viscosity reducers for polymer processing.

[0007] Chinese Patent No. 105440652 discloses a flame-retardant thermoplastic polyurethane elastomer containing an intumescent flame retardant and an ionic liquid. The ionic liquid is preferably a dialkylimidazolium ionic liquid such as 1-ethyl-3-methylimidazolium hexafluorophosphate. The intumescent flame retardant may be aluminum hypophosphite, ammonium polyphosphate, or aluminum diethylphosphinate.

[0008] There remains a need for flame retardant thermoplastic polyurethane compositions that have low dosages of flame retardants and good mechanical strength.

[0009] overview An object of the present disclosure is to overcome the problems of the prior art described above and to provide a flame retardant thermoplastic polyurethane composition that requires low loading of flame retardant while maintaining physical properties such as tensile strength, abrasion loss, and elongation at break.

[0010] Surprisingly, it has been found that the above objectives can be achieved by a thermoplastic polyurethane composition comprising 84 to 97 wt. % of a thermoplastic polyurethane, and 3 to 16 wt. % of a flame retardant, based on the total weight of the thermoplastic polyurethane composition, wherein the flame retardant comprises an ionic liquid and a phosphorus-containing ester.

[0011] According to another aspect of the present disclosure, an article produced from the thermoplastic polyurethane composition is provided.

[0012] A further aspect of the present disclosure provides a use of the article.

[0013] Surprisingly, it has been found in the present application that by incorporating a phosphorus-containing ester and an ionic liquid into a thermoplastic polyurethane composition, the polyurethane composition exhibits good flame retardancy while at the same time exhibiting good mechanical properties.

[0014] Detailed Description Unless otherwise defined, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this disclosure belongs. As used herein, the following terms have the meanings set forth below unless otherwise specified.

[0015] As used herein, the articles "a" and "an" refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0016] Unless otherwise specified, all percentages (%) are "percent by weight."

[0017] Here, phosphorus-containing ester refers to a class of organophosphorus compounds including organophosphates, organophosphonates, or organophosphinates.

[0018] Organophosphates are a class of organophosphorus compounds with the general structure O=P(OH)2(OR), O=P(OH)(OR)2, O=P(OR)3, where R is an alkyl or aryl group, a central phosphate molecule with alkyl or aromatic substituents. Exemplary organophosphates include triethyl phosphate and triphenyl phosphate.

[0019] Organophosphonates are organophosphorus compounds containing a C-PO(OH)2, C-PO(OH)(OR) or C-PO(OR)2 group, where R is an alkyl or aryl group.

[0020] The organic phosphinate may be a phosphinate having the following group: [ka] is an organophosphorus compound containing In the formula, R is an alkyl group or an aryl group.

[0021] Unless otherwise specified, temperature refers to room temperature and pressure refers to ambient pressure.

[0022] Unless otherwise specified, the term ionic liquid refers to a salt with a melting point below 100°C.

[0023] According to the present disclosure, based on the total weight of the thermoplastic polyurethane composition: 84 to 97 weight percent thermoplastic polyurethane, and 3 to 16% by weight of flame retardant A thermoplastic polyurethane composition is provided, comprising: The flame retardant comprises an ionic liquid and a phosphorus-containing ester.

[0024] Preferably, a 2 mm thick sheet prepared from the thermoplastic polyurethane composition achieves a UL94 V0 rating according to the procedures of Underwriter's Laboratory Bulletin 94, entitled "Tests for Flammability of Plastic Materials, UL94."

[0025] [Flame retardant] The flame retardant according to the present disclosure comprises an ionic liquid and a phosphorus-containing ester. It has been discovered that the simultaneous use of an ionic liquid and a phosphorus-containing ester can enhance flame retardancy and thus reduce the total dosage of the flame retardant required. As a result of the reduced dosage of the flame retardant, the deterioration of the mechanical properties of the thermoplastic polyurethane composition can be mitigated.

[0026] Preferably, the ionic liquid is a phosphorus-based ionic liquid. More preferably, the ionic liquid has the formula: [ka] In the formula, M + represents a monovalent cation selected from the group consisting of ammonium, quaternary ammonium, imidazolium, guanidinium, pyridinium, pyridazinium, 1,2,4-triazolium, triazine, sulfonium, phosphazenium and phosphonium cations. +represents a phosphonium cation. More preferably, M + represents a quaternary alkylphosphonium or a quaternary arylphosphonium.

[0027] R1 and R2 are each independently selected from hydrogen, hydroxy, C1-C18 alkyl, aryl, C1-C18 alkoxyl, aryl, (C3-C10)heterocyclyl, (C3-C10)cycloalkyl, (C3-C10)heterocyclyl(C1-C8)alkyl, aryl(C1-C8)alkyl, heteroaryl and heteroaryl(C1-C8)alkyl groups (each unsubstituted or substituted with 1 or 2 halogen atoms), -NO2, -CF3, -OCF3, -OCH3, -CO2H, -NH2, -OH, -SH, -NHCH3, -N(CH3)2, -CN, -SCH3, -S03H, -CH=CH-CH2-CH=CH2, -P((C1-C5)alkyl)2, and -P(O)(OEt)2, or a mixture of substituents.

[0028] Preferably, the ionic liquid has a weight percentage of 0.2 to 2.8 wt %, preferably 0.3 to 1.5 wt %, more preferably 0.5 to 1.0 wt %, based on the total weight of the thermoplastic polyurethane composition.

[0029] The phosphorus-containing ester includes one or more organic phosphates, organic phosphonates, and organic phosphinates. Preferably, the phosphorus-containing ester includes one or more selected from trialkyl phosphates, triaryl phosphates, halogenated phosphates, and organic phosphonates. More preferably, the phosphorus-containing ester comprises one or more selected from resorcinol bis(diphenyl phosphate) (abbreviated as "RDP"), bisphenol A bis(diphenyl phosphate) (abbreviated as "BDP"), cresyl diphenyl phosphate (abbreviated as "CDP"), monomeric resorcinol dixylenyl phosphate, polymeric resorcinol dixylenyl phosphate, trixylenyl phosphate, triethyl phosphate (TEP), tricresyl phosphate, triphenyl phosphate, tris(1-chloro-2-propyl)phosphate (TCPP) and tris(2-chloroethyl)phosphate (TCEP), dimethyl methyl phosphonate (DMMP), and dimethyl propane phosphonate (DMPP).

[0030] Preferably, the phosphorus-containing ester has a weight percentage of 1 to 18 wt %, more preferably 2 to 15 wt %, and even more preferably 3 to 10 wt %, based on the total weight of the thermoplastic polyurethane composition.

[0031] The weight ratio of the ionic liquid to the phosphorus-containing ester is preferably 1:100 to 1:0.7, more preferably 1:50 to 1:2, and even more preferably 1:20 to 1:5. At this preferred weight ratio, the overall dosage of the two flame retardants can be reduced while maintaining or even improving mechanical strength and other properties.

[0032] In addition to ionic liquids and phosphorus-containing esters, halogenated compounds, such as halogenated polyols, and solids such as diethylaluminum hypophosphite, aluminum hypophosphite, aluminum trihydroxide, ammonium polyphosphate (APP), red phosphorus, expandable graphite and melamine are suitable as auxiliary flame retardants.

[0033] The flame retardant may be added to the thermoplastic polyurethane during or after synthesis in liquid form, masterbatch pellets, or as a powder if a powdered flame retardant is used as a supplemental flame retardant, via an extruder, mixer, mill, or the like.

[0034] The ionic liquid and phosphorus-containing ester may be added to the thermoplastic polyurethane composition simultaneously or separately. The ionic liquid may be premixed with the phosphorus-containing ester to form a flame retardant mixture.

[0035] [Thermoplastic polyurethane] To prepare the thermoplastic polyurethane composition, a thermoplastic polyurethane is required, which may be pre-prepared in pellet form or synthesized in situ. For example, the polyurethane may be synthesized by reacting a polyol component with an isocyanate component. In various embodiments, the polyol component is polyether polyols, polyester polyols or mixtures thereof; and Contains one or more chain extenders.

[0036] The isocyanate component may comprise one or more selected from monomeric, oligomeric or polymeric isocyanates, prepolymers of isocyanates having active hydrogen-containing compounds end-capped with isocyanate groups, or polymerized alkyl or aryl isocyanates.

[0037] Preferably, the thermoplastic polyurethane has a weight average molecular weight in the range of 50,000 to 500,000 Da.

[0038] Preferably, the thermoplastic polyurethane composition has a hardness of from Shore 40A to Shore 80D, preferably from Shore 50A to Shore 98A, determined according to DIN ISO 48-4.

[0039] [Polyol component] The polyol component comprises a polyether polyol, a polyester polyol, or a mixture thereof and one or more chain extenders.

[0040] Polyether polyols and polyester polyols are collectively known as polyols. Polyols refer to polyhydroxy compounds. Preferably, polyhydroxy compounds having a functionality of 1.9 to 2.1 and a hydroxyl number of 30 to 200 mg KOH / g are examples of high molecular weight compounds having at least two reactive hydrogen atoms.

[0041] Suitable polyester polyols can be produced, for example, from organic dicarboxylic acids having 2 to 12 carbon atoms, preferably aliphatic dicarboxylic acids having 4 to 6 carbon atoms, and polyhydric alcohols having 2 to 12 carbon atoms, preferably 2 to 6 carbon atoms, preferably diols. Examples of dicarboxylic acids include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, and terephthalic acid. The dicarboxylic acids can be used individually or in mixtures. Instead of the free dicarboxylic acids, corresponding dicarboxylic acid derivatives, such as dicarboxylic acid mono- or diesters of alcohols having 1 to 4 carbon atoms, or dicarboxylic acid anhydrides, can be used. A dicarboxylic acid mixture of succinic acid, glutaric acid, and adipic acid in a ratio of 20-35:35-50:20-32 parts by weight is preferred, with adipic acid being particularly preferred. Examples of dihydric and polyhydric alcohols, especially diols, include ethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, glycerin, and trimethylolpropane. Preferred are glycol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or a mixture of at least two of these diols, especially ethanediol, 1,4-butanediol, and 1,6-hexanediol.

[0042] Polyester polyols can be produced by polycondensing organic polycarboxylic acids, such as aromatic or preferably aliphatic polycarboxylic acids and / or their derivatives, with polyhydric alcohols in the presence of a catalyst, or preferably an esterification catalyst, preferably in an inert gas atmosphere, such as nitrogen, carbon dioxide, helium, or argon, in the melt at temperatures of 150°C to 250°C, preferably 180°C to 220°C, optionally under reduced pressure, to the desired degree of polymerization, preferably less than 20, especially less than 15. In a preferred embodiment, the esterification mixture is subjected to polycondensation at the above-mentioned temperatures under normal pressure, then at a pressure of less than 500 mbar, preferably 50 to 150 mbar, to an acid value of less than 1 mg KOH / g. Examples of suitable esterification catalysts include iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium, and tin catalysts in the form of metals, metal oxides, or metal salts. However, polycondensates may also be formed in the liquid phase in the presence of diluents and / or synergists such as benzene, toluene, xylene, or chlorobenzene for azeotropic distillation of the condensation water.

[0043] To produce polyester polyols, organic polycarboxylic acids and / or derivatives thereof and polyhydric alcohols are polycondensed in a molar ratio of preferably 1:1-1.8, more preferably 1:1.05-1.2.

[0044] The resulting polyester polyol preferably has a functionality of 1.9 to 2.1 and a hydroxyl number of 30 to 200 mg KOH / g.

[0045] The polyhydroxy compound may be a polyether polyol obtained by a known method. For example, polyether polyols can be produced from one or more alkylene oxides having 2 to 4 carbon atoms in the alkylene radical by anionic polymerization using an alkali hydroxide such as sodium hydroxide or potassium hydroxide or an alkali alcoholate such as sodium methylate, sodium ethylate, potassium ethylate, or potassium isopropylate as a catalyst and adding at least one initiator molecule containing 2 to 8, preferably 3 to 8, reactive hydrogen atoms, or by cationic polymerization using a Lewis acid such as antimony pentachloride or boron trifluoride etherate, or bleaching earth as a catalyst.

[0046] Suitable cyclic ethers and alkylene oxides include, for example, tetrahydrofuran, 1,3-propylene oxide, 1,2- and 2,3-butylene oxide, styrene oxide, preferably ethylene oxide and 1,2-propylene oxide. The alkylene cyclic ethers and oxides may be used individually, alternately, one after the other, or as a mixture. Examples of suitable initiator molecules include water, organic dicarboxylic acids such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, optionally N-mono-, N,N- and N,N'-dialkyl-substituted diamines having 1 to 4 carbons in the alkyl radical, such as optionally mono- and dialkyl-substituted ethylenediamine, diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- and 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, phenylenediamine, 2,3-, 2,4- and 2,6-toluenediamine and 4,4'-, 2,4'- and 2,2'-diaminodiphenylmethane.

[0047] Suitable initiator molecules also include alkanolamines such as ethanolamine, diethanolamine, N-methyl- and N-ethylethanolamine, N-methyl- and N-ethyldiethanolamine, and triethanolamine plus ammonia.

[0048] Dihydric alcohols such as ethanediol, 1,2-propanediol and 1,3-propanediol, diethylene glycol, dipropylene glycol, 1,4-butanediol and 1,6-hexanediol are preferred.

[0049] The polyether polyol preferably has a functionality of 1.9 to 2.1 and a hydroxyl number of 30 to 200 mg KOH / g.

[0050] Like the polyester polyols, the polyether polyols can be used individually or in the form of mixtures. Furthermore, they can be mixed with the polyester polyols and polycarbonates and / or polycaprolactones.

[0051] Suitable hydroxyl-containing polycarbonates include known types such as those obtained by reacting diols, such as 1,3-propanediol, 1,4-butanediol and / or 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol, with diaryl carbonates, such as diphenyl carbonate or phosgene.

[0052] [Chain extender] The thermoplastic polyurethane is prepared using a chain extender. Suitable chain extenders preferably include diols. Typical examples include aliphatic, cycloaliphatic, and / or araliphatic diols having 2 to 14, more preferably 4 to 10, carbon atoms, such as ethylene glycol, 1,3-propanediol, 1,10-decanediol, o-, m-, p-dihydroxycyclohexane, diethylene glycol, dipropylene glycol, preferably 1,4-butanediol, 1,6-hexanediol, and bis(2-hydroxyethyl)hydroquinone.

[0053] [Other additives and auxiliaries] Optionally, other additives and / or auxiliaries may be incorporated into the thermoplastic polyurethane composition. Examples include antioxidants, UV stabilizers, lubricants, matting agents, nucleating agents, plasticizers, catalysts, crosslinking agents, fillers, dyes, pigments, hydrolysis inhibitors, fungistatic agents, and bacteriostatic agents. The type and / or dosage of the additives and auxiliaries can be determined according to the specific application for which the thermoplastic polyurethane composition is used.

[0054] [Isocyanate component] The isocyanate component in the present disclosure includes one or more selected from the group consisting of aliphatic, alicyclic, araliphatic, and aromatic isocyanates. For example, the isocyanate component may be an alkylene diisocyanate having 4 to 12 carbon atoms in the alkylene radical, such as 1,12-dodecane diisocyanate, 2-ethyl-1,4-tetramethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, 1,4-tetramethylene diisocyanate, and preferably 1,6-hexamethylene diisocyanate; an alicyclic diisocyanate such as 1,3- and 1,4-cyclohexane diisocyanate and any mixture of these isomers; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate); 2, The organic diisocyanates and polyisocyanates may include 4- and 2,6-hexahydrotoluene diisocyanate and the corresponding isomer mixtures, 4,4',2,2'- and 2,4'-dicyclohexylmethane diisocyanate and the corresponding isomer mixtures, and preferably aromatic diisocyanates and polyisocyanates, such as 2,4- and 2,6-toluene diisocyanate and the corresponding isomer mixtures, 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate and the corresponding isomer mixtures, mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanate, and mixtures of polymeric MDI and toluene diisocyanate. The organic diisocyanates and polyisocyanates may be used individually or in the form of mixtures.

[0055] [Preparation] The preparation of thermoplastic polyurethanes has been described elsewhere, but basically involves the reaction of a polyol and a chain extender with an isocyanate, optionally in the presence of a catalyst.

[0056] The preparation of the thermoplastic polyurethanes can be carried out by known methods, either batchwise or continuously, for example using a reactive extruder or by the belt process, by the one-shot process or the prepolymer process, preferably by the one-shot process.

[0057] [process] The thermoplastic polyurethane compositions may be processed by conventional methods including injection molding, compression molding, extrusion, coextrusion, thermoforming casting, sintering, vacuum forming, extrusion, coextrusion, fused deposition modeling, fused filament fabrication, selective laser sintering, selective laser melting, powder bed fusion, sheet lamination, material extrusion, and the like.

[0058] The thermoplastic polyurethane composition may be in the form of a powder, flake, rod, sheet or block, or may be in the form of pellets or granules, for example, by strand cutting or underwater cutting.

[0059] [Application] A variety of articles can be produced from the thermoplastic polyurethane compositions according to the present disclosure, including artificial leather, films, sheets, molded articles, fibers, automotive trim, tubes, hoses, profiles, pipelines, cable connectors, traction cables, cable sheaths, wires, optical components, electronic components, electrical components, seals, nonwovens, belts, or damping elements, among others.

[0060] These articles may find use in electric vehicles or charging devices for electric vehicles, home appliances, home or office furniture, construction, optical devices, electronic devices, electrical devices, and the like. [Example]

[0061] (Measurement and Test Methods) The measurement and test methods are shown in Table 1.

[0062] [Table 1]

[0063] (material) In the examples shown in Tables 2 and 3, the following materials were used:

[0064] Elastollan® 1190A, a polyether-based aromatic TPU from BASF Polyurethanes GmbH, tensile strength, 50 MPa; tear strength (angle), 89 kN / m; abrasion loss, 40 mm 3 .

[0065] CDP and RDP, manufactured by Zhejiang Wansheng Co., Ltd.

[0066] IL1, an ionic liquid based on a quaternary phosphonium cation and an organophosphate anion, was used as a flame retardant.

[0067] Butanediol from BASF used as a chain extender to synthesize the thermoplastic polyurethanes of the examples in Table 3.

[0068] Poly(tetrahydrofuran ether), functionality 2, hydroxyl value 112.2 mg KOH / g (BASF), used as polyol to synthesize the thermoplastic polyurethanes of the examples in Table 3.

[0069] Lupranate® MS, primarily 4,4′-MDI, from BASF, used as the isocyanate to synthesize the thermoplastic polyurethanes of the examples in Table 3.

[0070] Polystyrene-based matting agent.

[0071] Antioxidant Irganox® 1010, a sterically hindered phenol manufactured by BASF.

[0072] To prepare a flame-retardant thermoplastic polyurethane composition, two flame retardants were added to the thermoplastic polyurethane. The ionic liquid and phosphorus-containing ester were added separately and then uniformly dispersed. The mixture was heated at 80°C for several hours until the liquid was uniformly dissolved in the thermoplastic polyurethane matrix.

[0073] The resulting flame-retardant thermoplastic polyurethane compositions were molded into 2 mm thick test sheets by injection molding for mechanical performance and flame retardancy testing.

[0074] Table 2 shows examples with UL94 V0 level flame retardancy, and Table 3 shows examples with UL94 V2 level.

[0075] [Table 2]

[0076] Table 2 shows that compared with TPU compositions containing only phosphorus-containing esters as flame retardants, TPU compositions containing both ionic liquids and phosphorus-containing esters as co-flame retardants can achieve the same level of flame retardancy at much lower dosages. To achieve roughly the same level of flame retardancy, TPU compositions containing both ionic liquids and phosphorus-containing esters show improvements in mechanical performance, particularly tear strength and abrasion loss. Abrasion loss and tear strength are important for products such as cable sheaths, wires, hoses, pipelines, and belts. To achieve good mechanical performance, the weight percentage of the ionic liquid is preferably 0.2-2.8 wt%, 0.3-1.5 wt%, and more preferably 0.5-1.0 wt%, based on the total weight of the thermoplastic polyurethane composition. Compared with the original thermoplastic polyurethane Elastollan® 1190A, the flame-retardant thermoplastic polyurethane containing ionic liquids and phosphorus-containing esters exhibits less deterioration in tensile strength, tear strength, and abrasion loss.

[0077] [Table 3]

[0078] The TPUs in Table 3 were synthesized via an extruder. The isocyanate index, calculated as the ratio of the number of isocyanate groups in the polyisocyanate to the total number of hydroxyl groups in the chain extender and polyol, was approximately 1. Flame retardants, matting agents, and antioxidants were added to the thermoplastic polyurethanes during their synthesis.

[0079] Table 3 shows that TPU compositions containing both ionic liquids and phosphorus-containing esters as flame retardant co-agents can achieve the same level of flame retardancy at much lower dosages and in the presence of other additives. Thermoplastic polyurethane samples containing ionic liquids and phosphorus-containing esters outperform samples containing only phosphorus-containing esters as flame retardants in terms of mechanical strength, elongation at break, and abrasion loss.

Claims

1. 1. A thermoplastic polyurethane composition comprising, based on a total weight of the thermoplastic polyurethane composition: 84 to 97 weight percent thermoplastic polyurethane; 3 to 16 wt. % of a flame retardant; The flame retardant comprises an ionic liquid and a phosphorus-containing ester.

2. 2. The thermoplastic polyurethane composition of claim 1, wherein the ionic liquid is a phosphorus-based ionic liquid.

3. The ionic liquid has the formula: 【Chemical 1】 M ＋ represents a monovalent cation selected from the group consisting of ammonium, quaternary ammonium, imidazolium, guanidinium, pyridinium, pyridazinium, 1,2,4-triazolium, triazine, sulfonium, phosphazenium, and phosphonium cations; R １ and R ２ are each independently hydrogen, hydroxyl, C1-C18 alkyl, aryl, C1-C18 alkoxyl, aryl, (C3-C10)heterocyclyl, (C3-C10)cycloalkyl, (C3-C10)heterocyclyl(C1-C8)alkyl, aryl(C1-C8)alkyl, heteroaryl and heteroaryl(C1-C8)alkyl groups (each unsubstituted or substituted with 1 or 2 halogen atoms), —NO ２ , -CF ３ , -OCF ３ , -OCH ３ , -CO ２ H, —NH ２ , -OH, -SH, -NHCH ３ , -N(CH ３ ) ２ , -CN, -SCH ３ , -SO ３ H, -CH=CH-CH-CH=CH ２ , —P((C1-C5) alkyl) ２ , and -P(O)(OEt) ２ or a mixture of said substituents.

4. M ＋ The thermoplastic polyurethane composition of claim 3 , wherein represents a phosphonium cation.

5. 2. The thermoplastic polyurethane composition of claim 1, wherein the ionic liquid has a weight percentage of 0.2 to 2.8 wt. %, preferably 0.3 to 1.5 wt. %, more preferably 0.5 to 1.0 wt. %, based on the total weight of the thermoplastic polyurethane composition.

6. 2. The thermoplastic polyurethane composition of claim 1, wherein the phosphorus-containing ester comprises one or more selected from resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), cresyl diphenyl phosphate, monomeric resorcinol dixylenyl phosphate, polymeric resorcinol dixylenyl phosphate, trixylenyl phosphate, triethyl phosphate, tricresyl phosphate, and triphenyl phosphate.

7. 2. The thermoplastic polyurethane composition of claim 1, wherein the phosphorus-containing ester has a weight percentage of 1 to 18 wt%, preferably 2 to 15 wt%, more preferably 3 to 10 wt%, based on the total weight of the thermoplastic polyurethane composition.

8. 2. The thermoplastic polyurethane composition of claim 1, wherein the ionic liquid and the phosphorus-containing ester are in a weight ratio of 1:100 to 1:0.7, preferably 1:50 to 1:2, and more preferably 1:20 to 1:

5.

9. 9. The thermoplastic polyurethane composition of claim 1, wherein the thermoplastic polyurethane has a weight average molecular weight in the range of 50,000 to 500,000 Da.

10. 9. The thermoplastic polyurethane composition according to any one of claims 1 to 8, wherein the thermoplastic polyurethane composition has a hardness, determined according to DIN ISO 48-4, of from Shore 40A to Shore 80D, preferably from Shore 50A to Shore 98A.

11. 9. The thermoplastic polyurethane composition of any one of claims 1 to 8, wherein a 2 mm thick sheet prepared from the thermoplastic polyurethane composition achieves a UL94 V0 rating according to the procedures of Underwriter's Laboratory Bulletin 94, entitled "Tests for Flammability of Plastic Materials, UL94."

12. 12. An article produced from the thermoplastic polyurethane composition of any one of claims 1 to 11.

13. 13. The article of claim 12, wherein the article is artificial leather, a film, a sheet, a molding, a fiber, an automotive trim, a tube, a hose, a profile, a pipeline, a cable connector, a tow cable, a cable sheath, a wire, an optical component, an electronic component, an electrical component, a seal, a nonwoven fabric, a belt, or a damping element.

14. 14. Use of the article of claim 12 or 13 in an electric vehicle or a charging device for an electric vehicle, a household appliance, a home or office furniture, a building, an optical device, an electronic device, or an electrical device.

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